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Full text of "Practical Electronics 1968 May"



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CTRONIC PERCUSSION 
EFFECTS 




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Qhtr 

HIS ISSUE 



FOR SMALL CRA 




{flcgd Trade Mark} 



SOLDERING EQUIPMENT 

for ike 

DISCRIMINATING 
ENTHUSIAST 




ILLUSTRATED: 

L64 -k" BIT INSTRUMENT IN 
L700 PROTECTIVE SHIELD 



APPLY DIRECT TO: 
SALES & SERVICE DEPT. 
ADCOLA PRODUCTS LTD. 
ADCOLA HOUSE 
GAUDEN ROAD 
LONDON, S.W.4 
TELEPHONE 01-622 0291 





ABOUT BOOKS BY 0. A. BRIGGS IN 

HIGH FIDELITY MAGAZINE 

U.S.A. JANUARY 1968 

Is there any reason why audio books can't be written in high style? 
G. A. Briggs has been doing it ever since High Fidelity first emerged 
from the exclusive domain of engineers and began to be cultivated 
by the cultivated. Consider his temerity in opening a chapter on 
distortion in his classic Sound Reproduction with a quotation from 
Milton: ". . . dire was the noise of conflict". Or recall his wit in 
replying to a letter from a man who asked why "the body missing" 
from the sound when he put a back on his home-made speaker 
enclosure, and why the speaker sounded better when he took the 
back off again. Briggs wrote ". . . when you leave off the back . . . 
you obtain . . . reflection from the wall . . , use the system which 
sounds best, even if contrary to every textbook. In any case, as the 
body has disappeared, there would not be much point in screwing 
[down the lid of the coffin," 

Nojjpdy else writes them with quite that flair. 

The BRIGGS books listed below are still 
obtainable. 



AERIAL HANDBOOK (second edition) 

176 pages, 144 illustrations 

Price (semi -stiff cover) 15/- (16/- post free) \%X 
(cloth bound) 22/6 (24/- post free) 

CABINET HANDBOOK 

I 12 pages, 90 illustrations 
Price 7/6 (8/6 post free) 

AUDIO BIOGRAPHIES 

344 pages, 64 contributions from pioneers 
and leaders in Audio. Cloth bound 
Price 25/- (26/6 post free) 

MUSICAL INSTRUMENTS AND 
AUDIO 

240 pages, 212 illustrations. Cloth bound 
Price 32/6 (34/- post free) 

LOUDSPEAKERS 

Fifth edition — 336 pages, 230 illustrations. 

Cloth bound 

Price 25/- (26/6 post free) 

A TO Z IN AUDIO 

224 pages, 160 illustrations. Cloth bound 
Price 15/6 (17/- post free) 

MORE ABOUT LOUDSPEAKERS 

136 pages, 1 12 illustrations 
Price 8/6 (9/6 post free) 








PIANOS, PIANISTS AND SONICS 

190 pages, 102 illustrations. Cloth bound 
Price 18/6 (20/- post free) 



# 



AUDIO AND ACOUSTICS 

168 pages, 140 illustrations 
Price 12/6 (13/6 post free) 





ABOUT YOUR HEARING 

132 pages, 1 12 illustrations 

Price (semi-stiff cover) 15/6 (16/6 post free) 

Cloth bound 22/6 (24/- post free) 



Sold by Radio Dealers and Book Shops or in cose of difficulty direct 
from the Publishers 

RANK WHARFEDALE LTD. 
IDLE, BRADFORD, YORKS. Tel.: Bradford 6I25S2 



Build Your Own Heathkit Electronics 

A kit for every interest — Home Workshop — Hi-Fi — Radio — Test — Amateur 



Latest STEREO TAPE RECORDER, STR-1 

Fully portable — own speakers 
Kit £45. IB. 

FOR THIS SPECIFICATION 

i track stereo or mono record and 
playback at 7±,3f and Hips. Sound- 
on-soiind and sound-with-sound 
capabilities. Stereo record, stereo 
playback, mono record and playback 
on either channel, 18 transistor circuit for cool, instant and depend- 
able operation. Moving coil record level indicator, Digital counter 
with thumb-wheel zero reset. Stereo microphone and auxiliary inputs 
and controls, speaker/headphone and external amplifier outputs . . . 
front panel mounted for easy access. Push-button controls for 
operational modes. Built-in stereo power amplifier giving 4 W rms per 
channel. Two high efficiency 8" n 5" speakers. Operates on 230V 
a.c. supply. 
Versatile recording facilities. So easy to build — so easy to use. 





Latest STEREO AMPLIFIER, TSA-12 

12 x 12 watts output 
Kit £30. 10.0 less cabin* 

Cabinet £2. 5, extra 

FOR THIS SPECIFICATION 

17 transistors, 6 diode circuit. -JildB, 16 to 50,000c/s at 12W 
per channel into 8 ohms. Output suitable for 8 or 15 ohm 
loudspeakers. 3 stereo inputs for Gram, Radio and Aux. 
Modern low silhouette styling- Attractive aluminium, golden 
anodtsed front panel. Handsome assembled and finished 
walnut veneered cabinet available. Matches Heathkit models 
TFM-1 and AFM-2 transistor tuners. 

Full range power . . . over extremely wide frequency range. 
Special transformerless output circuitry. Adequately heat- 
sinked power transistors for cool operation — long life, 6 position 
source switch. 



High-performance CAR RADIO, CR-1 




Superb long and medium wave 
entertainment wherever you drive. 
Complete your motoring pleasure 
with this compact outstanding unit. 



8 Latest semiconductors (6 transistors, 2 diodes). For 12V positive or 12V 
negative earth systems. Powerful output (4W). Praassembled and aligned 
tuning unit. Push-button tone and wave change controls. Positive manual 
tuning. Easy circuit board assembly. Instant operation, no warm-up time. 
Tastefully styled to harmonise with any car colour scheme. High quality 
output stage will operate two loudspeakers if desired. Can be built for a 
total price. 

KIT (less speaker) £12. 17. Oincl. P.T. 
6" x 4" Loudspeaker £1. 4. 5 extra. 



Latest Portable Stereo Record Player, SRP-1 

Automatic playing of 16, 33, 45 
and 78 rpm records. All transis- 
tor — cool instant operation. Dual 
LP/78 stylus. Plays mono or 
stereo records. Suitcase port- 
ability. Detachable speaker en- 
closure for best stereo effect. 
Two Sin x Sin special loud- 
speakers. For 22Q-250V a.c. 
mains operation. Overall cabi- 
net size 15* x 31 : 10±in. 

Compact, economical stereo and mono record playing for the whole 
Family — plays anything from the Beatles to Bartok. All solid-state 
circuitry gives room filling volume. 

KIT £27.15.0 incl. P.T. 





SSU-1 




A wide range of 
SPEAKER SYSTEMS 

HI-FI SPEAKER SYSTEM. Model 

SSU-1. Ducted-port bass reflex cabi- 
net "in the white". Two speakers. 
Vertical horizontal models with legs, Kit 
£12. 12. without legs, Kit £11. 17. 6 incl. 
P.T. 



The BERKELEY SUM-LINE 

SPEAKER SYSTEM, fully finished 
walnut veneered cabinet for faster con- 
struction. Special 12* bass unit and 4" 

frequency unit, Range 30- 
Size 26" x 17" only 7j" deep. 

attractive styling. Excellent 



mid/high 
17,000c/s, 
Modern 
value. 
Kit £19. 10. 0. 



Berkeley 



SEE HEATHKIT MODELS AT: 
GLOUCESTER 

Factory and Showroom, Bristol Road, 

LONDON 

233 Tottenham Court Road, W.1. 

BIRMINGHAM 

17-18 St. Martin's House, Bull Ring. 

Demonstrations by arrangement. 

Deferred terms available over £10 (U.K. only). 

Prices quoted are Mail Order prices. 



Send 
for 

Latest 
FREE 

Catalogue 

36 pages, 
many 
models 
in Colour 



Transistor Portables 

UXR-1, now available in Modern 
coloured cases or leather. 

6 transistor, 1 diode circuit. 7 x 4in. 
speaker. LW and MW coverage. 
Case: brown leather, or colours 
navy blue, coral pink, lime green. 
Please state 2nd choice. 

Kit £11. 19. 0, Colour 

Kit £12. 18. 0. Leather 



UXR-2, choice of black or brown 
real leather cases. 

7 transistor, 3 diode circuit. Battery 
saving circuitry. LW and MW 
coverage. Pushbutton wave change. 
Slide rule tuning. 

Kit £14. 18. 0. leather 'UXR^^*"""MIBi^ 

j HEATHKIT 

P lease add rest all enquiries to 

I DAYSTROM LTD., Dept. P.E5, GLOUCESTER 
' rn Please send me FREE CATALOGUE 

j I Full details of mod el (s) 

' NAME - - 

| 

1 ADDRESS - 

.L__ 




313 



GOODMANS 



t_j*»U3Beyt¥_ 






HIGH FIDELITY 
MANUAL 

A Guide to full 
listening enjoyment 

The Manual is much more than a cata- 
logue ol Goodmans High Fidelity Loud- 
speakers—it contains informative articles, 
including advice on stereo, special begin- 
ners page, aid full cabinet drawings. 
You'll find it interesting as well as 
informative. 

The Perfect Combination 

MAXAMP30 
TRANSISTORISED STEREOPHONIC HIGH FIDELITY AMP- 
LIFIER 15 + 15 watts ■ Silicon solid state ■ Integrated pre-ampltfier 
Negligible distortion • £49,10.0. 

STEREOMAX 
MATCHING AM/FM STEREOPHONIC FM TUNER 
Transistorised • Outstanding specification - Stereo de-coder (optional) 
£60.0.0. + £11.18.3. P.T. inc. Surcharge. 

Both MAX AMP 30 and STEREOMAX have polished wood cases 
flOi" x 5%" x ?i" deep) in Teak or Walnut to order 

Full specifications of the Maxamp 30 and Stereomax are given in 
the High Fidelity Manual — send the coupon for your FREE copy — 
or pay an early visit to your Goodmans dealer. 



r-z^z 



Please send Hi-Fi Manual together with name and address 
ol my nearest Goodmans dealer. 



P.E.3 



GOODMANS LOUDSPEAKERS LTD 

AXIOM WORKS • WEMBLEY • MIDDLESEX. Tel: 01-902 1200 



AUDIO 
TRANSDUCER 



A new concept 
in sound 
reproduction 





The '309' Audio Transducer repre- 
sents a breakthrough in sound repro- 
duction without the use of hard to 
place loudspeakers. It has been 
designed to reproduce sound by 
utilising the vibrant qualities of 
wooden, plastic, glass, metal and 
similar surfaces. It has an exception- 
ally good frequency response and 
provides excellent quality music and 
speech, A versatile unit, fully water- 
proof and suitable for many indoor 
and outdoor uses. Impedance 8-15 
ohms. Power Handling 10 watts. 



TGNS. P, & P. 4/6 

Complete with simple instructions 
Available from most dealers or direct from the Sole U.K. Distributors 

ELECTRO-APPARATUS (LONDON) LTD. 

BENTFIELD END, STANSTED, ESSEX Tel: Stansted 3437 



MARTIN IS HIGH-FIDELITY 

■«. PREFERRED FOR RELIABILITY, 
QUALITY, ADD-ON-ABILITY AND 
ECONOMY 




You can do so much with MARTIN 
kits. The system, of using pro-fabri- 
cated transistorised, units which can 
be interlinked in a variety of ways 
enables you to assemble the com- 
bination of your choice and then 
extend it unit by unit until you 
possess a full stereo gramophone 
and radio assembly. When new units 
are produced, they can be added to 
existing equipment very easily with 
the advantage that you can continue 
to use equipment you already have, 



so that your installation is always 
up to date. Most important of ail 
is the power and quality which 
MARTIN Audiokits give you. Their 
sturdy construction assures com- 
pactness without sacrifice to quality 
or efficiency. They offer excellent 
value, are very easily installed and 
will give years of unfailing service. 
That is why people prefer MARTIN 
— it's simple to instal, good to 
listen to, and looks completely 
professional. 



STEREO CONTROL 
ASSEMBLY 



ONLy FROM MARTIN 



MARTIN AUDIOKITS are available for 
Mono, and can be doubled up for 
stereo, or as complete stereo units. 3 
ohm and 15 ohm systems are available. 
There is a special pre-amp for low out- 
put pick-ups and escutcheon panels to 
suit the arrangement you choose. The 
tuner is styled to match. 

Start by sending for leaflets at once 



AMPLIFIER SYSTEMS • TUNERS • RECORDERS 

UNITS INCLUDE: 

■ 5-stage input selector 

■ Pre-amp tone controls 

■ 10 watt amp. (3 ohms) 

■ 10 watt amp. (15 ohms) 

■ Mains power supply 
I F.M. Tuner 



Trade enquiries invited 



MARTIN ELECTRONICS LTD. ^LtSSST^SSSfWi 



MARTIN ELECTRONICS 

154 High Street, Brentford, Middlesex 

Please send RecordakitF.M. TunerlAudiokit 
Hi-Fi Leaflets. (Strike out items not wanted) 



Name .... 
Address 



■••■■■•■•■■■■■■•■•■■■••(■•••••■••> 



P.E.S/68 ■ 
••■■■■ ■■■•■«•*■■! 



314 



BUILD YOURSELF A QUALITY TRANSISTOR 
RADIO— FULL AFTER SALES SERVICE! 



THE MAGNIFICENT 

ROAMER 



SEVEN WAVEBAND PORTABLE AND CAR 
RADIO WITH A SUPER SPECIFICATION 

• 7 FULLY TUNABLE WAVE BANDS— MW1, MW2, LW, SW1, 
SW2, SW3 and Trawler Band. 

• Extra Medium waveband pro- 
vides easier tuning of Radio 
Luxembourg, etc. 

• Built in ferrite rod aerial for 
Medium and Long Waves. 

• 5 Section 22 in. chrome plated 
telescopic aerial for Short Waves 
— can be angled and rotated for 
peak S.W. listening. 

• Socket for Car Aerial. 

• Powerful push-pull output. 

7 transistors and two diodes 
including Philco Micro-Alloy 
R.F. Transistors. 

make 7 x4 in. P.M. 



• Famous 
speaker. 



• Air spaced ganged tuning con- 
denser. 

• Separate on/off switch, volume 
control, wave change switches 
and tuning control. 

• Attractive case with hand and 
shoulder straps. Size 9 x7 x4 in. 
approx. 

• First grade components. 

• Easy to follow instructions and 
diagrams make the Roamer- 7 a 
pleasure to build with guaran- 
teed results. 

Total building costs 

£5.19.6 p * p 




Parts price list 
easy build plans 3/ 
(FREE with parts) 




Total building costs 

42/6 %%"• 



Attractive «iso with red speaker grille. SlzaSj :, 
il x llin. J'uliy tunable. 7 staj;K»— 8 transistors 
atid 2 dioiles— fflrrite rod aerinl. tuning condenser, 
volume control, fine tone roper dynamit: Sin. 
speaker, all Ural grade components. Easy build 
plans anil parts price list 1/6 (FBEE with parts). 



Total building costs 

39/6 \% p - 



MEDIUM WAVE, LONG WAVE 
AND TRAWLER BAND PORTABLE 

Attractive black and gold ease. Size fi} x 1| x 
Hi in. Fully tunable over both Medium and Lour 
Waves with extended M.W. baud for easier tuning 
nf Luxembourg 1 , etc, .Ml first grade components, 
7 stages — & transistors and 2 diodes— super- 
sensitive ferrite rod aerial, fine tone 3tn. moving 
coil speaker, etc. Easy build plans and parte 
price List, 3/5 (FREE with parts). 




NEW MELODY MAKER SIX 



3 WAVEBAND PORTABLE 



8 stages — 6 transistors and 2 diodes 



Covers Medium and Long Waves and EXTRA M.W. BAND FOR EASIER TUNING OF 
LUXEMBOURG, ete. Top quality 3 in. Loudspeaker Tor quality output. Two RF 
stages for extra boost. High "Q" 6in, Ferrite Rod Aerial. Approx. 350 milliwatts push-pull out- 
put. Handsome pocket size case with gilt fittings. Size 6i :•; 3 J ;< liin. 



This amazing receiver 
may be built for only 



69/6 



P. &.P. 3,6 



Parts Price List and easy build plans 2f m 
(Free with parts}. 




Total building costs 

79/6 -■£-■ 



Attractive ease with gilt fittings. Size 7= K oi >: 
I Jin. World wide reception. Tunable on Medium 
and Long Waves, twn Short Waves. Trawler 
Baud plus an extra M.W. band for cagier tuning 
of Luxembourg* etc. .Sensitive ferrite rod aenal 
and tek'H'ftplc aerial for S3WN*t WiwCS, AM 
lop grade c<niii]K>iicuis» 8 StUfW- «J trwwtetott 
and 2 diodes int-Sin Eiili^ Philoct Mhin-Alfoy K.F. 
TranatatorS, etc (carry ins strop I/O evtr:i). Ensy 
build plana ami porta price Ret 8/- (PttBE with 
parts) . 



Total building costs 

69/6 p & p 



THREE WAVEBAND PORTABLE 
WITH 3in. SPEAKER 

Attractive ease size 7 £ ■< 5 \ N IJin, with gilt 
fittings. The ideal radio for home, car or outdoors. 
Covers Medium and Long Waves and Trawler 
Ha mi. Special circuit incorporating '2 K,F. stages, 
puBh-pull output, ferrite rod aerial, 7 transistors 
and 4 2 dlodi-i» liin. apeaker (will drive larger 
speaker) anil nil first grade components. Price 
list 2h (FKEE with parts). 



RADIO EXCHANGE Ltd 



Callers side entrance Barratt's Shoe Shop. Open 9-5 p.m. Saturday 9-12.10 p.m. 



61a HIGH STREET, BEDFORD 
Telephone: Bedfo rd 52367 



315 




LINO-AIR 



(MINUSX) 

ALPHABETICALLY... 
we can list the names 

GEOGRAPHICALLY... 
we can list the countries 

All over the world students know that 
CREI HOME STUDY COURSES are sup- 
plying the answer to their need for 
advanced Technical Education in the field 
of Electronic Engineering Technology. 

CREI PROGRAMMES ARE AVAILABLE IN: 

Electronic Engineering Technology 

Industrial Electronics for Automation 

Computer Systems Technology 

Nuclear Engineering 

Mathematics for Electronic Engineers 

Television Engineering 

Radar & Servo Engineering 

Citv & Guilds of London Institute : 

Subject 49 and Advanced Studies 

Subject No. 300 

Write for free brochures to: 

C.R.E.I. (London) (Dept. P.E.8 ) 

WALPOLE HOUSE,173/176SLOANEST. T LONDON S.W.1 

Telephone : Belgravia 8662 



INTERNATIONAL DIVISION OF CAPITOL RADIO ENGINEERING INSTITUTE WASHINGTON D.C 

i ' — " - " — —[ 

PFease send me (for my information and entirely without obligation) full details j 

of the educational programmes offered by your institute [_ 

Send details of the City 6* Guilds Programme \~_ 

I 

Name I 



Address 



Electronics Experience 



- I 

I 

C.R.E.I. { LONDON) (DEPT. P.E.8), WALPOtE HOUSE, 173-176 SLMKE STREET, S.W.1 I 



COMM 



SiflWW^ 



WE HAVE A COMPLETE RAHOE 0T KEW 
AltD OLD TTPKS OF VALVSS. TRANSIS- 

T0B8 AJTD DIODES, FULL LISTS AVAIL- 
ABLE OH AFEL1CATI0K. 

V60201P 8/- 

V6030 10/- 

BFYOO 8/8 

BFY61 7/- 

BFY62 6/- 

BYZ12 10/- 

BYZ13 10/- 

BCY33 7 6 

BCY34 8/6 

BCY10 7/8 

BCY38 9/6 

BCY39 12/6 

BCY12 7/6 

AC107 14/6 

AC127 »/- 

ACY17 8/8 

ACY1D 6/6 

AOY20 s/s 

ACY21 e/- 

ACY22 4/6 

AF102 18/- 

AF114 71- 

AF11S 6/6 

AF110 7/- 

AF117 6/- 

AF118 17/6 

AF124 10/- 

AF125 10/- 

AF126 10/- 

AF127 fl/6 

AF139 10/- 

AFimj its 

AFZ11 17/- 

AFZ12 12 6 

A8Y20 8/8 

HAT 100 7/8 

HAT101 S/6 
MAT1BO 7/9 

MAT! 21 8'S 



P.P. and insurance 2;- 




EZ80 


6/6 


EZ81 


8/8 


PCC84 


8/6 


PCL8B 


11/8 


PCL82 10/B 


PCL88U/6 


KT66 


w/e 


KT88 


W/6 


DY8S 


9/6 


EBC33 


96 


DK96 


fl'S 


DAF96 7/9 


DL9S 


86 


DF96 


>/- 


PY81 


7/6 


FL81 


8/6 


PY83 


10/B 


PL36 


16/8 


OAB 


4/6 


OA3 


87- 


OA71 


3/6 


OA81 


m 


OA96 


1,'tl 


OA200 


3/3 


OA202 


4/3 


GA203 


*l- 


OA12C 


7 8 


OA9 


4/8 


OAJO 


3/- 


OA47 


»i- 


OA70 


2/- 


OA7U 


2/6 


IN91 


>/- 


IN253 


71- 


1N234 


4f- 


IN255 


6/8 


INB37 


6/6 


IN 647 


W- 


1N237 


6/6 


IN2374 16/- 


IN2379 26/- 


1X38 


3/6 


INTJ5S 


3/6 


GEX44 8/8 


CEX5 


1 it/- 


FGT Power 


Mount 


i/9 


Klta 



OTOR 



Made by CJrouiptun Parkinson- Single phase 
i h.p. Motor. 230/25OV; &0 cycles, I-3A, 
1,424 r.p.m. Continuous rating. rtpiudle 
l|in. x Sin. ilin. Overall size leas spindle 
approx. 8 :■: Oin. Perfect condition. A 
bargain lor the workbench. ONLY 79/6, 
Carriage 20/- li h,p. Motor also available 
B9/8, Carriage 20/-). 




SELECTOR DRIVE 

Numerous 
applies* 

tlOQB. 

Electro 
I'laguet 
and brass 
tooth 
wheel.* A 
switch 
wafer and 
contacts 
ace 
coupled 
* ^^ totals 

iiud arranged to be on lor 10 pulses and off 
for IS. An Auxiliary contact is normally 
on but ofl 1 in every 26. Complete with 
suppressor, resistors, plus series contact 
for continuous operation. Ideal window 
displays, twitching lamps, models, etc. 
12V or 24V d.c. Brand new and boxed 
18/8. P. & P. 2/ti. 



SYNCHRONOUS CLOCK 
MOTORS 



Geared for 40 
revolutions per 
hour. 230V W 
cycle. With 
mounting 
flanges. 3 lie 
appro*. 11 in. 
deep -■- 21 m. 
dia. ONLY 
22/6. P. & P. 
2/6. 



DELAY ACTION TIME 





SWITCH 



Ideal for model 

makers, record 

players, tape 

decks, etc. 



8.3 d,c. Motor. 
10,900 r.pjn, at 
230mA, ljln X 
lin dia. Shalt illl 
long x 3J84in dia. 
6/6. P. & P. 2/6. 

9V d.c. Grim deck 
replacement motor. 
2in X. liin dia. 
Shalt lin Jong x 
3/32in. 17/6. T. * P- 



Made by 

Smithi. A.i_, 
operation 200/ 
250V. Double 
pole, will give 
time delays 
from 0-10 

minutes. Size 
2iln. dia. x 
2 flu. long inc. 
Jin. x 3/1 6 in 
dia. spindle. 
BARGAIN riUCE 17/6. P. * P. 2/«. 



UNREPEATABLE BARGAIN? 



FANE 122/17 
12in 2a WATT 
HEAVY DUTY 
HI - FI 
LOUD 
SPEAK- 
ERS. 
With high 
efficiency 
Anti- 
strop Ic 

Kerrite magnet. 17.000 gauss. Imp. 
3-5 ohms. Brand new and guaranteed. 
List Price £12.' USD AIK TRICE 
18.19.8. P. * P. 7/6, 




E.KJ. COMBWATIOTf 
LOUD SFEAKBRS 

13} x 8 lin. Elliptical 
with 3 lin dia. Tweeter. 
Imp. 8 ohms. Power 
handling 10 watte. Brand 
new and guaranteed. List 
price £8,6.0. LIND 
AIR PRICE 99/6, P. & 
P. 7/6. {AIM available 
without tweeter 60/6 
P. A P. 7/61. 





b'anc 302 3in TWEETERS. 
Imp. 3-5 ohms. 17,000 
gauss. 12 watt. Brand 
New and guaranteed. List 
Price £3.15.0. LIND-AIR 
PRICE 58/6, P. A P. 3/8. 



$€£ LIND-AIR 0PP0$/rZ 



LINO-AIR 

(OPTRONICS) LTD. 




25 & 53 TOTTENHAM COURT ROAD, LONDON, W.1. ret. 01.590 4534,7679 

Open 9-6 p.m. Monday to Saturday inclusive. Open Thursday until 7 p.m. 



ALL POST 
ORDERS TO 
Dept. P.E. 568 
25 Tottenham 

Court Road 
London, W.1 




1-3 WATT AMPLIFIER 



An Ideal baits foe building your own port- 
able record player. Just add speaker and 
turntable, and you will have an above* 
average mode) far a. mere fraction of the 
cost. 2-3 -watt printed circuit wltb 
control panel on flying toad. OK/ OFF, 
TONE CONTROL AND VOLUME, 
colourful escutcheon. Brimar valves: 
EZ80, ECL82 and composite Installation 
booklet. Price £4 C ft ft * P- 3/6. 



MAGNAVOX-COLLARO 14] TAPE 
DECK! 



The very latest 3-speed model— 1|, 3j, 7i i.p.B. 
available with either 2 track or 4 track head. 
Features Include: Pause control; digital counter; 
fast forward and rewind; new 4-pole, fully 
screened induction motor; Interlocking keya. Size 
of top plate 131 x 11 x Biio deep below unit 
plate. For 200/260V a.c. mains, DO c/s operation. 
New, unused and fully guaranteed. 

VSt £10.10.0 *g? £13,19.6 

Carriage and Packing 12/(5 extra. 



FOB USE WITH ABOVE DECKS 
2 track model 114.18 6; 1 track model 116.19.8. Carriage and Packing 12/3 . 



MULTIMiTEHJ 



9 in 1 ELECTRONIC KIT 




MODEL TTC.10O1. 
20.000 O.P.V. with 
overload protection; 
d.C. volts, S, 29. 12fi, 
000, 3,500V; a.c. 
volts, 10. 50 
100 V; d.c. 
260mA to 
With prods 
Carry hist case 
ONLY 85J-. 
P. ft F. 3/fl. 



250, 

mA 
50A. 
and 




MODEL TTC. 
1030. 50,000 
OJ.V.; d.C 
vol l =. 0-3, 12, 
SO, 120, 300, 
800, 1,200 V; 
a.c. volte, 6, 30. 
130. 000, 

1,200V; d.o. 
mA 0-03-300. 
with prod* 

and carrying 
case ONLY 
(11.19.0, P. A 
P. B/-. 




Build nine different projects from one 
basic kit — simple Instructions, do tech- 
nical knowledge required for you to build 
a Police Siren, Metronome, Morse Code 
amplifier, Electronic Massager, W/T 
Transmitter, Radio, Telephone, One- 
translator Radio Two-transistor Radio, 
Electronic Music Kit. Completely safe- 
operated on 9V PF3 battery. Hours of 
fun for boys and dads of all ages. Complete 
with all parts and simple step by step 
instructions. ONLY 69/8. P. & P. 5/-. 



■'■" li ll'll l tiHiH-1 







Input 0-200, 220, 


240V 


Output 110 V 




50W 11.7. 8 


1.000W (8.8.0 


75W (1,17.0 


l.oOOW (15,15.0 


100W £2.5.0 


2.000W 118.10.0 


160W (8.16.0 


3.000W (25, 10.0 


2001V fS.5.0 


4.000W (34.18.0 


3O0W 84.8.0 


0-S0V, 1A 80/- 


400W (4.19.8 


0-80V. }A 17/8 


500W (5.0.8 


0-SOV, 2A 87/6 


600W 88.8,8 


0-30V, 3A 4*/- 


Fost extra. 







Input 2QO-25QV 60c/a. 
24V 3AU.U.8 24V 8 A (6.5. 
24V A (3,15.0 24V 12A (4,15,0 
Post extra. 

Mains and Output Transformer lists avail- 
able on request. 

GOODMANS SPEAKER BARGAINS! 
Sin 3 ohms, 18/8; Bin. 3 ohm, £9/6.' Sin. 
3 ohm, S2/B; 10ln 5 ohm, 88/-; 10 x Gin. 
3 ohm, 38/8; Tweeter, 18/8. P. & P. 3/0 
per Speaker. 



9€£0PP0SIT€ 



Vantemv Table Top V Aerial BBC/IT V, 

26/8. 

Crest* Room Aerial Band I.'ll/Ill. Cream 

or Black, 88/§. 

Yeemstler Table Top VHF/UHF Tunable 

Aerial. Chrome or Orey, 76/6. 

YAM all Channel Table Top Aerial BBC1,,' 

2/ITV/VHF. 66/-. 

HL623 Loft Aerial HILO V + 5 tor vertical 

Band I/UJ. With mounting ami and 

bracket, 58/-, 

Hew Major 10 element BBC2 Aerial for loft 

or outdoor fixing. With roller bracket for 

up to 2in dia. mast, 45,18. 

HI, Hunter 13 element BBC2 Aerial as 

above, 67/-. 

El, Explorer IS element BBC2 Aerial as 

above, 68/-, 

Lolt Six. 6 element BBC2 Aerial for loft or 

outdoor fixing. With arm and bracket, 

87/6. 

J-Beam 4 element outdoor Baud 11 

VHF/FM Stereo Aerial. With mast, 87'-. 

Please add 4/- postage. 



STEREO HEADPHONES 



STEREO HEADPHONES 

Enjoy Stereo Bound 
as you have never 
heard It before. 
MODEL TTC. 

ami as illustrated 
soft padded ear- 
phones. Adjustable 
headband. Impe- 
dance 8 ohms per 
phone. Frequency 
range 25- 1 3. 000c/ s. 
With 5ft lead. Price 
88/6. P. A P. 4/0. 
Other similar types 
available. AKAI AS ESS, S ohms, (6,8.0: 
CORAL E 102, 10 ohms. (5.18.6: EAGLE 
SB1, 10 ohms, 78/6. T.T.C. Stethoscope, 
8 ohms, 48/6, P. ft P. 4/6 each. 




TEAK FINISH 

PLINTHS with perapex 
cover 61 gns. (for LAB80 
B f gns.). P. & P. 12/6 
Agents for Tborens, Dual, 
old ring, etc. 



GARRARD DECKS 



3000 wi th Sonotone 9TA HC Ste reo Cartrld ge . . (8.19.6 
3000 with Sonotone 9TAHC Diamond Stereo 

Cartridge 48.18.6 

ATSO MKI less cartridge (10.19.6 

ATSOMKTI less cartridge (If. 19. 6 

AT 60 MKII with Decca Dcr.im Stereo Cartridge (17.14.0 

SP. 25 MRU less cartridge (10.19.8 

3P. -25 MKII with Decca Derani stereo Cartridge (16.14,0 

AP.75 less cartridge (22, 11 .6 

LAB.30 HKH less cartridge (£4.18.6 

All plus P. 4 P. 12/fi 
Mono Cartridge 17/ G extra. 
Stereo Cartridge 22/S extra. 




SAVE £2,2.0 



Transistor FM tuner. Frequency range 88- 

I08Mc/b. Sire 8 x 4 x 2iln. Beady built lor 

use with most amplifiers, flv battery operation. 

CompIete;wlth instructions. LIST PRICE 9 gns. SWttolM adaptor for Stereo Radio 

L1ND AIR PRICE 7 gJlS. F. ft P. 4/-. Reception (6,18.6 extra. 



8ARGAIINLOFFER! FANTAVOX CASSETTE TAPE PLAYER 




Specially designed to replay the well known and 
popular Mnslcasseltea— prerecorded tape cassette 
offering a wide choice of all types of music from pop 
to classical. Vp to 40 minutes of quality repro- 
duction through built-in speaker. Simple off/play 
and volume controls. Fully transistorised operating 
on six peniight batteries. Modern compact styling 
with earpiece socket and wrist strap. Size Si x 
41 x 2in. 

LTND AIR PRICE. £9.19.6. *"* -**» ** 



I us. 5/-. 




COMPLETE HI-FI STEREO SYSTEM 



ALL TRANSISTOR B 
WATTS FEE CHANNEL 
STEREO HI-FI SYSTEM 
OFFERING A PERFOR- 
MANCE EQUAL TO IF 
NOT BETTER THAN 
SIMILAR SYSTEMS 

COSTING UP TO 

DOUBLE THE PRICE. 
-Modem styling plus ad- 
vanced circuitry using 
latest silicon transistors 
throughout. 

The famous GARRARD 3000 Record Changer fitted lightweight tubular arm with SONO- 
TONE 9TAHC STEREO/MONO DL4M0ND CARTRIDGE will play all (lies of records. 
(4 speeds "8, 45. 33 1/3, 16 2/3 r.p.m.l. Will play up to 9 records automatically, also pro- 
vision for manual play. Amplifiers and controls are mounted below record player and Incor- 
porate Bass, Treble, Volume and Balance controls and On/Off, Cram/Radio, Mono^Stereo 
slide switches, TWO IDENTICAL LOUDSPEAKER SYSTEMS each Incorporating 
separate bass speakers and high frequency units with crossover network provide full 
frequencj- reproduction and are complete with 10ft leads and plugs for connection la 
amplifier. Will fit easily on to bookshelves, room dividers or existing furniture. BRIEF 
SPEC. Player/ Amplifier unit. Teak finish, size 18i x 14 K Slln 200/050V a.c. operation. 
Inputs for Radio Tuner/Tape Recorder also outputs for Tape Recorder. Loudspeaker 
Systems, Teak finish, size (each)l 3 x 7 x Sin. Supplied complete wltb Instruction booklet. 
ready to plug in and plav. SEND YOUR ORDER NOW OR CALL AND HEAR THIS 
MARVELLOUS HI-FI STEREO SYSTEM (Teak finish). Only 68 CM. plus 20/- Carriage 
and Insurance. (Rosewood 3 gns. extra.) (Clear Ferepex Cover 3 gns. extra.) 



LINEAR AMPLIFIERS 



Latest i.e. mini Models offering highest duality 
at moftest wnt. ... 

LT68. All Transistor 12 watts Stereo. Inputs for 
Tuner, Oram, Mike, Separate Bans, Treble, 
Balance and Volume Controls (16.11,0. Carr. 7/0. 
Teak case (3.10.0 extra. 

PTA 16 (as lllus.l. All Transistor, 10 watts Mono. 
Inputs for Tuner, Oram, Mike, (lullar, Bass. Treble 
and two volume controls, (15.15.0. Carr. 7(6. Teak 
case (8.10,0 extra. LT46, 2 Valve 6 watte Mono. 
Inputs for Tuner, Gram, Bass, Treble and volume 
over Uf~ extra. FuUdetallesent on request. 




controls, (4.18.8. Carr, 7/6. Metal 



317 





20 WATT 

SOLDERING 
INSTRUMENT 

CONTROLLED TEMPERATURE 

Design holds max, temp, of 380°C. 
within close limits. 

• EASY BIT REPLACEMENT 

Simple, fast replacement of low-cost 
copper bits. Non-wearing PERMATIP 
bits cut servicing costs. 

# BEAUTIFULLY COMPACT 

Length 7{*. Weight 1± 02. 
Max. handle dia. 0.715" 

# UNEQUALLED PERFORMANCE 

Ideal for fast production soldering 
on the majority of modern electronic 
equipment. 

• ALL VOLTAGES 



The LITESOLD range includes six other 
models (10, 18, 25, 30, 35 and 55 watts), and 
many accessories. Please ask for colour 
catalogue L'37. 



LIGHT SOLDERING 
DEVELOPMENTS LTD. 

28 Sydenham Road, Croydon, CR9 2LL 

Tel. 01-688 8589 & 4559 



W" 1 



FANTASTIC BARGAINS 

SONOTONE 
SOLENT 
2 SPEAKER 
HI-FI 

SYSTEMS 

# LIST £18 EACH 

SPECIAL 
OFFER 

II gns. 

# Impedance 8 ohm. Power input up to 12 watts. 
Suitable for valve or transistor amplifiers. 

Frequency response 40c/s to 20 k/cs. 
Scandinavian style cabinet. 

# Small attractive size 14 x 9 x 8 J. 

# On permanent demonstration. 

# Reviewed by Hi-Fi News, The Gramophone, etc. 

Send large s.a.e. for FREE Leaflets and Test Reports available 
from our Showrooms. 




J. J. FRANCIS LTD. 

123 ALEXANDRA ROAD 
tONDON, N.8 BOW 1662 



LEE ELECTRONICS 

400 EDGWARE ROAD 
PADDINGTON 5521 



BUILD YOUR CIRCUITS 
on 

VEROBOARD 

— the Universal Wiring Board — 

obtainable from your local Retailer 

Trade enquiries to : 

NORMAN ROSE (ELECTRICAL) LTD. 

8 St. Chad's Place, Gray's Inn Road, London, W C.I 

Technical enquiries to: 

VERO ELECTRONICS LTD. 

Industrial Estate, Chandler's Ford, Hants 




All items previously ad- 
vertised available, alto see 
item* advertised in Prac- 
tical Wireless. Huge Hi- 
Fi and Components stock* 
at all branches. 



ECHNICAL 
TRADING 



* PORTSMOUTH 

(Tel. 22034) 
150-352 Fratton Road 

* SOUTHAMPTON 

(Tef. 2S8SI) 
n East Street 
■*• BRIGHTON (Tel. 23975) 
6 Queen's Road 
all mail order Brighton 



FANTASTICALLY POPULAR 



TAPE 



We offer yon fntly to utilised polyester/mylar 
and P.V.C. tapes ol identical (.ntiity bi-fl, wide 
range recording characteristics si ton grade 
tapes. Quality oontrol msnufactnre. They 
are truly worth s lew more coppers than 
acetate, snb-staodard, jointed or cheap imports 
TBY OKK AHD PROVE IT YOUKSELF. 

Ems Am 

3 in. 2251 '.. 2,9 

tin. 450ft, SB 

Sin. 900ft. 10/6 

5ita. 1,200ft. 18/- 

7in. j ,800ft. 18/8 

Triple Play 

tin. 900ft. 18/- 

5in. 1,800ft. 26;- 

5Jin. 2,400ft. 84/- 

7in. 3,600ft, 44/- 

Qnitdniple Pier 

3in. 600ft. 8/8 

Ptitttiget 1/- reW, 

Post Free lets 5",. on three reels. 

Quantity and Trade en fairies incited. 

NOTE. Large tape *f«*» at alt branrhti. 





Standard Play 


am. 


150ft. 


M 


4in. 


300it. 


*t* 


Sic. 


600ft, 


7/8 


Si in 


900ft. 


10/8 


Tin. 


1. 20Oft. 
Double Play 


12.6 


3in. 


300ft. 


*l- 


4m. 


600ft. 


tll- 


4in, 


l,200tt. 


187- 


4f:i 


1 ,800ft. 


19/8 


At, 


2,400ft. 


27/- 



318 




PRINTED 
CIRCUITS 

Five assorted 

printed circuit 

boards with 

transistors, diodes, 
resistors, conden- 
sers, etc, Guaran- 
teed minimum 
20 transistor?. 
Ideal for experi- 
menters. 5 boards 
lot lit— ?■ * P- 
2/-. 




F.M. WIRELESS 

MICROPHONES 

94-104Mc/s. Transistor- 
ised. Operates from 9 V 
battery. Complete with 
additional secret tie-clip 
rnlcrophone.Ltst £12.10.0 
ONLY «/15,'0. P. ft T. 
216. 

These cannot be operated 
In U.K. 



MODEL TE.80 
20,000 O.F.V. 

MULTIMETER 

0/10/50/ 100/ 500/ 
1,000V B.C. 0/5/20/ 

oo/aeo/ 600/ i.ooov. 

d.c. 0-50^ A 6/50/ 
000mA. O,'6,'60K/ 
60OK/6M{l.M/17/'8. 
P. ft P. 3/-. 





HEW MODEL EM 

30,000 o.p.v, With 
over Ion. d protection, 
mirror scale 0-5/ 1/2 -5/ 
10/25 / 100 / 250 /6O0 / 
1,000 V d.c. 
0/2'5 / 10 / 25/100/250/ 
500/1.000V a.c. 
0/50jiA/fl7 60 /500 mA 
12A d.c. 

o/eokh/sMn/eoMQ. 

f8;17.r6. Post Paid. 



MODEL Z0M TRANSISTOR CHECKER 

It has the tallest capacity lor 

checking on A, B and Ico. 

Equally adaptable 

checking d iodes, etc. Spec. 

A:0-7-0-9B67. D: 6-200. 

Ico: 0-60 mtcroamps 

0-5mA. Resistance lor 

diode 200(1 -1MB. 

Supplied complete with 

Instructions, battery and 

leada.iS.M.S.P.ftP.2/6. 



■lor 




VARIABLE VOLTAGE 
TRANSFORMERS 

Brand New— fully Shrouded. Input 230V 
60/60c/s. Output 0-260 V. 

1A W.10.0 

2-BA £8.15,0 

5A 19,16.0 

HA 114.10.0 

10A £18.10.0 

ISA 121.0.0 

20 A 187.0.0 

Post extra. 

SILICON RECTIFIERS 

800V P.I.V. 200mA 2/0 

200V p.I.V. 6A 5/f 

400V P.I.V. 3A 7/8 

I.OOOV P.I.V. 5A 7/8 

400V P.I. V. 8A 676 

400VP.I.V.8A 7/8 

I.OOOV P.I.V. 860mA 8/8 

800V P.I.V. 600mA 6/8 

800V P.I.V. 6A 7/8 

400V P.I.V. 600mA 3/8 

70V P.I.V. 1A 8/8 

160V P.I.V. 186mA 1/- 

150V P.I.V. 25A U/8 

700V P.I.V. 100A 49/S 

400V P.I.V. 3A (S.C.R.) 7/8 

100V P.I.V. 6A (S.C.B.) 18/8 

200V p.I.V. BA (S.C.B.) 15 6 

400V P.I.V. 5A IS.C.R.) 17/0 

Discounts for quantities. Post extra. 





■k TRANSISTORISED FM TUB HE * 
6 TRANSISTOR 
HIGH QUA- 
LITY TUNER, 
SIZE ONLY 6tn 
X 4in X 2)in. 
8 I.F. stages. 
Double tuned 
dl scrim Id* tor. 
Ample output to 
feed most amp liners. Operates on V 
battery. Coverage 88-108Me/«. Ready 
built ready for use. Fantastic value for 
money, SOW «/7/6. P. 4 P. 2/6. 
STEREO MULTIPLEX ADAPTORS S gni. 



AV0METERS 

Supplied in ex- 
cellent condition 
fully tested and 
checked. Com- 
plete with prod*, 
leads and Instruc- 
tion!. 

Model 47A 

HUM 

Model 8 118. 
Model 9 £20. P. ft P, 7/6 each. 

TE22 SINE SQUARE WAVE 
AUDIO GENERATORS 

Sine : 20c/s to 
200 kc/s on 4 
bands. Square: 
20c/a to 30ke/B. 
Output Imped- 
ance 5,000 ohms, 
200/250V a.c. 
Supplied brand 
new and guaran- 
teed with Instruc- 
tion manual and leads, £15. Carr. 7/6. 

TE-20RF SIGNAL GENERATOR 

Accurate wide 
range signal gen- 
erator covering 
120kc,s — 260 
Mc/s on 6 bands. 
Directly cali- 
brated. Variable 
R.F. attenuator. 
Operation 200/ 

240V a.c. Brand new with Instructions. 

fl£/10/0. P. ft P. 7/6. S.A.E. for details. 

LAFAYETTE TE-46 RESISTANCE 
CAPACITY ANALYSER 

2pf - 2,000 
mid 2- ohms 
200 megohms. 
Also cheeks im- 
pedance turns 
ratio, insulation . 
200/260 V a.c. 
Brand Hew 515. 
Carr. 7/6. 






ARM 00 COMBINED AF-RF 
SIGNAL GENERATOR 

AF. 8 IKE WAVE 

20-200,000 c/s. 
Square wave 20- 
30,000 c /,. O/p. 
HIGH IMP. 21V 
P/P 600 O 38V 

p/p. 

TF. lOOke/s-300 

Mc/B. 

Variable R.F. attenuation iul/ext. modu- 
lation. Incorporates dual purpose meter to 
monitor AF. output and % mod. on R.F. 
220/240V a.c. £27/10/0. Carr. 7/8. 

TE-65 VALVE VOLTMETER 

High quality Instru- 
ment with 28 ranges. 
D.c. volts 1-5-1.500V 
A.c. volts 1S-1.500V 
Resistance up to 1,000 
MB. 

220/240V a.c. opera- 
tion. 

Complete with probe 
and instructions. 118. 
P. ft P. 6/-. 
Additional ProWes 
available: R.F. 35- 
H.V. 42/8. 





I catalogue 

1 Electronic 
i components 

\ Equipment 




t,f,)j\ 87/8 

lOOuA 35/- 

200)uA 82/8 

600/itA 27/6 

50-0-BO^A 85/- 



10mA . 
20mA . 
.Win A . 
1 00m A . 
160mA . , 



CATALOGUE 



ir ELECTRONIC COMPONENTS 

* TEST EQUIPMENT 

* COMMUNICATIONS 
EQUIPMENT 

* HI-FI EQUIPMENT 

We are proud to introduce our first 
comprehensive catalogue ol Electronic 
Components and Equipment. Oyer 160 
pages fully illustrated, lifting thousands ot 
items, many at bargain prices. Free discount 
coupons with every catalogue. Everyone in 
electronics should have a copy. 

CLEAR PLASTIC PANEL METERS 

First grade quality Moving Coll panel meters available 
cx-Btock. 8.A.E. for Illustrated leaflet. Discount for 
quantity. Available as folio ws: Type MR 38 P, 1 21/32ln 
square front * . 

25/- 
26/- 
25/- 
26/- 
25/- 
257- 
26/- 
26/- 
, 86/- 
85/- 
1mA 
29/8 



ioo-o-ioojua sue 

500-0-500 nA 25/- 
1-0-lmA . . 25/- 

1mA 85/- 

2mA £57- 

25/- 



eooiiiA . 
aooinA 

flOOmA 
750mA 
1A d.c. 



26/- 
85/- 
25/- 
86/- 
25/ 



26/- 
26/- 

. 26/- 
. 25/- 
. 25/- 

2A d.c 257- 

5A d.c 28/- 

3V d.c 25/- 

10V d.c. . . 26/- 
2flV d.c. , . 25/- 
30V d.c. . . . 26/- 



100V d.c. 
150V d.c. 
300V d.c. 
500V d.c. 
750V d.c. 
16V a.c. 
50V a.c. 
150V n.c. 
300V a.c. 
500 V a.c. 
Meter 



POST EXTRA. Larger sizes available — send for lists. 




ADMIRALTY B.40 RECEIVERS 

Just released by the Ministry, High quality 10 valve receiver, 
manufactured by Murphy. Coverage in 5 bands fj50kc/B-3GMc/s. 
I.F. 500kc/s. Incorporates 2 R.P. and 3 l.F. stages, bandpass 
filter, noise limiter, crystal controlled B.F.O., calibrator, I.F. 
output, etc. Built-in speaker, output for phones. Operation 
150/230V a.c. Size 191m X 13£lo X 16in. Weight 114 lb. 
Offered In good working condition, 222.10.0. Carr. 30/-. With 
circuit diagrams. Also available B.41 L.F. version of above, 
16kc,'s-7O0kc/s. 217.10.0, cirr, 30/-. 

U N R-30. 4-BAIMD 

COMMUNICATION 

RECEIVER 

Covering 560 Kc/a — 30 Mc/s. Incorporates 
variable BFO for CW/SSB reception. Built- 
in speaker and phone Jack. Metal cabinet. 
Operation 220/240 v. A.C. Supplied brand 
new, guaranteed with A ,*i ia n 
Instructions. tll.W.V Carr. 7/6 

HEW LAFAYETTE MODEL HA -700 AM CW 
88B AMATEUR 0OMMUFICATIOK RECEIVER 
8 Valves, 5 bands Incorporating 2 MECHANI- 
CAL FILTERS for exceptional selectivity and 
sensitivity. Frequency coverage on 6 bands 
160-400 kc/s 650-1 ,600kc/s, 1-6-4-OMc/e, 
4-B-14-5Mc/s 10-6-30Mc/s. Circuit incorpor- 
ates R.F. stage, aerial trimmer, noise limiter. 
B.F.O. product detector, electrical baudspread, 
H meter, slide rule rlial. Output for phones, low 
to 2k O or speaker 4 or 80- Operation 
220/240V a.c. Size 7jln X 15fn * lOin. 
Supplied brand new and guaranteed with hand- 
book 36 0H8. Carr. 10/-. S.A.E. for leaflet. 




R.C.A. AR88 SPEAKERS 

Sin, 3 ohm speakers In metal case. 
Black unickle fin lab to match our 
88 Receivcra, Available Brand 
New and Boxed with leads. 
59/8. Carr. 7/6. 



LAFAYETTE U-224T TRANSISTOR STEREO AMPLIFIER 

19 transistors, 8 diodes, ]HK munis 
power, 30W at 8(1 . Response 
30-20,000 ± 2dB at 1W. Distortion 
1% or less. Inputs 3MV and 
250MV. Output 3-1611. Separate 
L. and R. volume controls. Treble 
and bass control. Stereo phone Jack. 
Brushed aluminium, gold anodlsed 
extruded front panel with compli- 
mentary metal case. Size 10 tin X 
3&x7fttn. Operation 115,230V 
a.c. £25, Carr. 7/8. 





SINCLAIR EQUIPMENT 

Z.12 12 watt amplifier, 89,6, PZ4 
Power Supply Unit, 99/6. Stereo £5 
Preamp.. 29.19.6. 0.14 Speakers, 
18.19.6. Mieromatie Radio Kit, 49/8. 
Hull!. 59 6, Micro PM Hadiij Kit. 
15.19.5. 

ALL POST PAID 



SPECIAL OFFER 



2 Z12 Amps., PZ4 Power 
Supply. Bterao 26 Pre- 
amplifier, 122. 




I (RADIO) LIMITED 

2 Phone: GERRARD 8204/9155 

__T Cables: SMITHEX LESQUARE 

3-34 LISLE STREET, LONDON, W.C.2 



319 




POCKET MULTI-METER 

Size 31x2ix l£in. Meter siJ.e 2J :-: ljin. Sensitivity 
1000 O.P.V. on boih A.C. and D.C. volts. 0-15, 
0-150, 0-1000, D.C. current 0-1 50mA. Resistance 
0-100kfi. Complete with test prods, battery and full 
instructions, 42/6. P. & P. 3/6. FREE GIFT for 
limited period only. 30 watt Electric Soldering Iron 
value 15/- to every purchaser of the Pocket Multi- Meter. 



3 to 4 WATT AMPLIFIER 

3-4 watt Amplifier built and 
tested. Chassis size 7 X li X I in. 
Separate bass, treble and volume 
control. Double wound mains 
transformer, metal rectifier and 
output transformer for 3 ohms 
speaker. Valves ECC8I and 6v6. 
£2.5.0 plus 5/6 P. & P, 



BSR TAPE DECKS 

200/250 v. A.C. mains. Type TD2 
Tape speed H twin track. Type 
TD10 2-track, 3 speed, plus rev. 
counter. Type TD10 4-track, 3 
speed, plus rev. counter. 

Due to 33j"„ Purchase tax wlitch is rvnw 
applicable on these Items, prices will he 
announced as soon as available. 




Special offer ELEGANT SEVEN 

SPECIAL OFFER. Power supply kit to 
purchasers of 'Elegant Seven' parts, incorporating 
mains transformer, rectifier and smoothing con- 
denser, A.C, mains 200/250 volts. Output 9v. 100 
inA. 9/6 extra. 

Buy yourself an easy to build 7 transistor radio and 
save at least £1 0.0.0. Now you can build this superb 
7 transistor supernal radio for under £4.10.0. No - ONLY 

one else can offer such a fantastic radio with so +/\ a ft 
many de luxe star features. B*w • W • 9 

it De luxe wooden cabinet site 12i" x «T x 3±". fl^7.6Post&Pa<:king 
ie Horizontal easy to read tuning scale printed grey with black letters, 
size 11;" x 2". it High 'Q' ferrile rod aerial. it IF neuttalisation on 
each separate stage. it D.C. coupled push pull output stage with 
separate A.C negative feedback, if Room filling output 350mW. 
■+■ Ready etched and drilled printed circuit board back printed for 
foolproof construction, it Fully comprehensive instructions and point to 
point wiring diagrams, ic Car aerial socket, it Fully tunable over medium 
and longwave, 168-535 metres and 1250-2000 metres. -A* All components. 
ferrile rod and tuning assembly mount on printed board, it 5' P.M. 
Speaker, it Parts list and circuit diagram 2, 6, tree with parts. 




(music power). 



X101 10 WATTS (RMS) SOLID-STATE HI-FI 
AMP. WITH INTEGRAL PRE-AMP 

Its great versatility ranges from: a simple 
intercom, to a modern HI-FI STEREO 
AMPLIFIER (two are required for Stereo). 
The XtOI is a brilliant new addition to our 
highly successful range of products. Its 
professional performance and advanced 
solid-state circuitry techniques ensures 
reliability, combined with high fidelity 
reproduction, at an unbeatable price of 
49/6 + 2/6 P. & P. 

SPECIFICATIONS: R.M.S. Power Output. 

I0W (SINE WAVE). Sensitivity: for rated output ImV into 3k£2 
load. Frequency Response: minus 3dB points are 20Hz and 40kHz. 
Total Distortion: at I kHz; for rated output I -5%; for 5W output 
0'35%. Output Impedance : 3 ohms (3-15 ohms may be used). Supply 
Voltage : 24V d.c. at 800mA (6-24V may be used) ; output at 
I4V d.c. supply with 3 ohms speaker 7W. Size; 2|in 3in •,: 1 -ft in. 
The fully comprehensive instruction manual does not only show the 
basics, such as circuit diagram and connections, but also gives practical 
easy-to-understand detailed information about the X101. Standard 
equalisation networks are given for most types of conventional 
inputs. They include; Tape head, Mag. P.U., Xtal. P.U., Tuner, Mie, etc. 

CONTROL ASSEMBLY. (including resistors and capacitors) : 

I. Volume, price 5/-; 2. Treble, price 5/- ; 3. Comprehensive 
bass and treble, price 10/-. 

POWER SUPPLIES FOR THE X101 : P10I/M (for Mono) 35/- 
P. & P. 2/6. P10I/S (for Stereo) 42/6 P. & P. 2/6. 

PRIGI/M : A High Quality, Monoral P re-amp and Control Unit, 
particularly suitable for use with the XI01 if a ready-built, 
comprehensive, multi-input system is desired. 

CONTROLS; Selector Switch, Tape Speed Equalisation Switch (3j and 
?i I.P.S.), Volume. Treble, Buss, three position scratch filter and 
three position rumble filter, 

SPECIFICATION : Sensitivities for 200m V output at \kHz, Tape Head : 
3mV(at3JI.P.S.). Mag. P. U.: 2m V. Cc r, P. U. : 80mV. Radio: lOOmV, 
Aux. : lOOmV. Tape/Rec. Output; lOOmV. Equalisation for each input 
is correct to within = 2dB (RIAA) from 20Hz to 20kHz. Tone Control 
Range: Bass: ± I3dB at 60Hz; Treble: l4dB at l5kH?. Total 
Distortion: (for 200mV output) < 0-02";. Signal Noise: > — 60dB. 
Supply Voltage: 24V, d.c. 59/6 plus 2/6 P. & P. A STEREO 
VERSION (PR101/S) WILL BE ANNOUNCED SHORTLY. 

THE CLASSIC: High Quality Solid-State Amplifier (Mono). 
SPECIFICATION: Switched inputs for: Tape head. Mag. P.U.. Cer. 
P.O.. Radio and Aux. Mains Input 220-250V, a.c, 50Hz. The Classic 
is the combination of the above described items (X10I.P10I/M and 
PR 101 /M) on one common chassis. Its performance and space age 
styling makes if the ideal choice for the value-conscious Hi-Fi enthusiast . 

8 gnS. P. & P. FREE. 



STAR SR 150 COMMUNICATION RECEIVER 



Frequency range: 535 kc/s-30 Mc'/s. 
four wavebands, four valve plus 
metal rectifier superhet circuit. In- 
corporates B.F.O. bsndspread 
tuning, "S" meter, external telescopic 
aerial— ferrite aerial, built-in 4" 
speaker, easy-to-read dial. For240v. 
A.C. operation. Complete, brand 
new, with full instruction manual. 
£17.17.0. P. &P. 10/-. 




600 mi Hi- watt solid state 

7. transistor plus diode 

and thermistor 




NEW! DORSET 

Transistor Portable Radio 

plus Baby Alarm Facilities 
Special offer— Power Supply Kit to 
purchasersof Dorset Portable Radioparts, 
incorporating mains transformer, rectifier 
and smoothing condenser, A.C. mains, 
200/250V., output 9v., 100mA. 9/6 extra. 

Completely modulised high quality port- 
able radio featuring complementary 
N.P.N, and P.N.P, output stage. 

The comprehensive easy-to-follow drawings supplied make this 
the easiest-ever transistor radio set of parts, with the following 
features: 

• Simple connections to only 6 
tags on the R.F./I.F. module, 
3 I,F, stages, osc. coil and 3 
transistors which with their 
associated components are 
completely wired. 

# Only 4 connections on the A.F. 
module to complete the 4 tran- 
sistor 600 milli-watt solid state 
amplifier. 

# Pre-aligned R.F./I.F. module 
built and tested. 

9 A.F. module built and tested. 

# Fully tunable over M.W. and 
L.W. bands. M.W. 540-1640 
Kc/s (557-183 metres). L.W. 
150-275 Kc/s (2000-1 100 
metres). 

• Intermediate Frequency 470 
Kc/s. 

• Sensitivity, M.W. at 1 Mc/s 10 
microvolts plus or minus 3db. 
L.W. at 200 Kc/s 40 microvolts 
plus or minus 4db. 



• High Q internal ferrite rod 
aerial on both wavebands. 

9 Class "B" modulised output' 
stage with thermistor controlled 
heat stabilization. Class "B" 
output stage ensures long 
battery life. Current drain is 
proportional to the output level. 
Total current drain of the 
receiver under no signal con- 
ditions is 10- 1 2mA. At reason- 
able listening level 20-30mA. 

# Extension sockets for car aerial 
input, tape recorder output 
(independent of vol. control) 
and Ext. Speaker. 

% All components(except speaker) 
mount on the printed circuit 
board. Easy to follow instruc- 
tions. Size of cabinet 12" long, 
8* high and 3" deep. 

Finger tip controls. 

Circuit and parts list 2/6, free with 

parts. 

PRICE: £5*5*0 plus 7/6 P. ft P. 




FIRST QUALITY P.V.C. TAPE 



$f 


Std. 850ft. 


. 9/- 5' L.P. 850ft. . . 10/6 


:■■ 


Std. 1200ft. . 


11/6 3" T.P. 600ft. .. 10/6 


r 


L.P. 240ft. . 


41- 5" T.P, 1800ft. . . 25/6 


w 


L.P. 1200ft. . 


. 11/6 51" T.P. 2400ft. .. 32/6 


V 


L.P. 1800ft. . 


. 18/6 7" T.P. 3600ft. . . 42/6 


5f 


D.P.I 800ft. . 


. 18/6 4" T.P. 900ft. . . 15/- 




P. & P. on 


each If 6, 4 or .more post free 



600m W SOLID STATE 
4-TRANSIST0R AMPLIFIER 

Speaker output impedance 12 ohms. 
90 c/s and 12 Kc/s. Price 19/6 plus 1/- 
13/6 plus 2/- P. & P. 



Features NPN and PNP 
Complementary Sym- 
metrical Output Stage. 
Size: .24" x l" x J* 
Frequency response 3db points 
P. & P. 7"x4" speaker to suit. 



2i WATT ALL TRANSISTOR AMPLIFIER 

AC mains 240v, Size 7" x 4±" x 1 J". Frequency response 100 c/s — 10 
Kc/s. Semiconductors, two OC 75's, two AC 128's and two stabilisers 
AA129. Tone and volume controls on flying leads. £2.10.0. P. & P. 
3/6. Suitable 8* > 5" 10,000 line high flux speaker 18/6. P. & P. 2/-. 



Available within 4 weeks. 



8-WATT 4^ALVE PUSH-PULL AMPLIFIER & Metal RECTIFIER 

Size 9" x 6" x 1 i". A.C. Mains, 200-250 v. 4 
valves. For use with Std. or L.P. records, 
musical instruments. All makes of pick-ups 
and mikes. Output 8 watts at 5 per cent of 
total distortion. Separate bass and treble 
lift control. Two inputs, with controls for 
gram, and mike. Output transformer tapped 

for 3 and 15 ohm speech coils. Built and tested. £4.4.0. P. & P. 11 /-. 

8* x 5" Speaker to suit. Price 14/6 plus 1/6 P. & P. Crystal Mike to 

suit 12/6 plus 1/6 P. & P. 




-1-9-9-** 



RADIO AND T.V. COMPONENTS (ACTON) LTD. 

21 D HIGH STREET, ACTON, LONDON, W.3 

Shop hours 9 a.m. lo 6 p.m. Early closing Wednesday 

Goods not despatched outside U.K. 

Alt enquiries stomped addressed envelope. Terms C. W.O. 

Alio at 323 EDGWARE ROAD, LONDON, W.J. 

PERSONAL SHOPPERS ONLY. Early closing Thursday, 

All orders by post must be sent to our Acton address. 



320 



rfg=^ Now available 



Mmiard 1 1968 Data Book 



^S 



1 36 pages of data, including for the first time, colour-coded 
sections for quick reference — covering comparables and equivalents 
and all current Mullard semiconductors, valves, tubes and compon- 
ents for Radio, TV, Audio and HiFi applications. 

PRICE 3j6 from your local TV retailer OR direct from Milliard — cash 

with order, plus 9d for pr and p. 

Mullard Limited, Distributor Sales Division, 
Mullard House, Torrington Place, London, W.C.1 . 



Mullard 




TRANSISTOR 
STEREO 8 + 8 




A really (lrat-claai Hi-Fi Stereo Amplifier KM. Uses 14 transl stars giving 
8 -watts push-pull output per channel, (IB W mono}. Integrated pre-amp 
with Bass, Treble and Volume controls. Suitable lor use with Ceramic or 
Crystal cartridges. Output stage lor any speakers from 3 to 16 ohm?. 

Compact design, all parts supplied including drilled metal 

work, Clr-Klt board, attractive front panel, knobs, wire, 
, a solder, nuts, bolts — nn extras to buy. Simple step by step 

instructions enable any constructor to build an amplifier to 

be proud of. 



Brief Specification: From response = 3 db 20-20,000 c,s. 
Bass boost appro*, to +18 db. Treble cut approx, to 
— IB db. Negative feedback IS db over main amp. 
Power requirements 2a V at 0'fl amp. 



PRICES 

Amplifier Kit 
Built and Tested 
Power Pack Kii 
Built and Tested 
Cabinet (as illui.j 



£9.10.0 

£12.10.0 

£2.10.0 

£3.0.0 

£2.10.0 



& P. 4,6 
, & P. 4, 8 
. 4 P. 4,'- 

& P. 4> 

, ft p. s, e 



(Special offer — £14.10.0. Post 1'ree if all above kits 
ordered at same time or can be supplk'.l buiit and tested 
tor £18.0,0 Post Free), 

Circuit diagram, construction details and parts list (free 
with kit) 1/6 (S.A.E. > 





STEREO AMPLIFIER 
Incorporating 3 ECLSos and 1 EZ60. heavy duty, 
double wound mains transformer. Output 4 watts 
per channel. Full tone an d voj ume controls. Alisolutely 

complete. 

ONLY 

£5.9.6 

P.1P.5/- 
luper De- 
nse version 
with ECLS6 
valves, sep. 
bast, treble anil balance con- 
trols. Full feedback. 8 gnt, 
P. A P. 8,'-. 

HIGH GAIN 4 TRANSISTOR 
PRIN TED C IRCOIT 
AMPLIFIES KIT 

Type TA1 

• Peak out- 
put In excess 
of 11 watts. 

• All stan- 
dard British 
components. 

• Built on 
printed circuit panel size 6 

• Generous size Driver and Output Transformers. 

• Output transformer tapped for 3 ohm and 15 ohtn 
speakers. • Transistors- (GET 114 or HI Mullard 
OCB1D and matched pair of OCB1 o/p). • 9 volt 
operation. • Everything supplied, wire, battery clips, 
solder, etc. 9) Comprehensive easy to follow instructions 
and circuit diagram 2/8 (Free with Kit). All parts snl.l 
separately. SPECIAL PRICE 45/-. P. & P. 3j: Also 
ready built and tested, 52/6. 1'. ft P. 3,'-. 

FM.'AM TUNER HEAD 
Beautifully designed and pre- 
cision engineered by Dormer 
and Wadsworth Ltd. Sup- 
plied ready fitted with twin 
-0003 tuning condenser for 
AM connection. Prealigneil 
FM section covers 86-102Mc/s. 
I.F. output 10-7 Mc/s. Com- 
plete with ECC8S <6L12) valve 
and full circuit diagram of 
tuner head. Another special bulk purchase enable* us 
to offer these at 87/6 each. P. & P. 3/-. Order quickly 1 
HATCHED PAIR AM/FM I.P.'s. Comprising 1st I.F. and 
2nd I.F. discriminator, (465 Kc/s/10-7 Mc/s). Hize 
lln.xljin. :-2Jin. M. Will match above tuner head. 
11/- pair. P. & P. 2A . 

GORLER P.M. TOTTER BEAD. H5-KJ0 Mc.s 10 7 Mc/s. 
I.F., 15/-, Plus 2/6 P, * P. <ECC85 valves, 8/6 extra. 1 
S.T.C. SILICON AVALANCHE HALF-WAVE RECTI- 
PDXRS. Type BAS. 508 AF. 6 amps. 560 P.I.V. lin. long 
X iin. dia. approx. List 50/-. OUR PRICE B/6. P. Free. 
SPECIAL OFFER ! PLESSET TYPE 29 TWDI TUKBIG 
GANG, 400 pt + 146 pf. Fitted with trimmers and 8:1 
Integral slow motion. Suitable for nominal 470 kc's. I.F 

Size approx. 2"x l'Xl}'. ONLY 8/8. 1". & P. 2/6. 

PEW OHLY : SIEMENS MINIATURE RELAYS. D.P.C.O. 

Gold plated contacts. Size approx, Ij* X i" XI i". 8». 

at 30 niA. ONLY 15/-. P. fc P. 1/B. 

NEON A.C. MAINS INDICATOR. For panel mounting, cut 

out size 1 1 X I X lin. deep inc. terminal. White case with 

lens giving brighter light. For mains 200/250v. 2/8 each. 

P. g P. 6d. (6 or more post free). 

VIBRATORS. Large selection of 2, 4. 6, 12, 24 and 

32 Volt. Non-sync. 8/8; Sync. 10/-, P. A P. 1/6 per 

■vibrator. S.A.E. with all enquiries. 





3-VALVE AUDIO AMPLIFIER MODEL HA34 

Designed for HI-FI reproduc- 
tion of records. A.C. Mains 
■iperation. Ready built nn 
plated heavy gauge metal 
chassis, size 7;tn. w. -. 4in. 
d. x 4Jin. h. Incorporatcs 
EOC83, EL84. EZ80 valves. 
Heavy duty, double wound 
mains transformer and output 
transformer matched for 
3 ohm speaker, separate Ban, Treble and volume controls. 
Xegatlve feedback line. Output 4J watt*. Kront panel 
can be detached and leads extended for remote mounting 
of controls. Complete with knobs, valves, etc.. wired and 
tested for oidv £4,5.0. P. It P. 6/-. 

HEL " FODR ■ AMPLIFIER KIT.' Simitar In appearance 
to HA34 above but employs entlrelv different an- 1 ad-" 
vaoced drcuitry. Com plete set of parts, etc, 79/6. P.* P. 9/- 

16,14 WAH Hf-h 

AMPLIFIER SIT 
A Btyllshly finished 
monaural amplifier 
with an output of 
14 watts from 2 
ELS4a in push-pull. 
Super reproduction 
of both music and 
speech, with neg- 
ligible hum. Sep- 
arate inputs for 
mike and grain 
allow records and 
announcements d 
follow each nthcr. l'"«iJI^ phr-mli-'! sovilcrtl 'w.uwt output 
transformer to malLih 3-lifl speaker and 2 Independent 
volume controls, ami separate bass and treble controls arc 
provided giving good lift and cut. Valve llnn-up 2 ELMs. 
KCC83, EK«i|. and EZH0 rectifier. Simple instruction 
booklet 8,6. i t'n-c with parts.) All parti sold separately. 
ONLY 17.9.8. I'. .V 1'. 8/8. Also available ready built 
aad tested iiimjil,!,' with' std. input sockets, £9.5.0. 

MAINS TRANSFORMER, l-'nr iian-i-'.:i yen:-, supplies. 
Pri. 200/24(lv. Bus. 9-<t.'.i at 300 niA. 11/-. P. <t P.2/B. 
Pri. UO0/240V. Sec. 12-U-I2 at I amp. 14/6. P. & P. 8/6. 
MAINS TRANSFORMER. I'm- transistor power supplies. 
Tapped pri 200-230V. Bee 40-0-40 at 1 amp (with 
electrostatic screen) and S-3v, at -C amp fur dial Inmpsctc. 
Drop thro* mounting, tftnek sine IJIn, Sfta. Ulin. 
£7/8. P. & P. 4/6. 

MATCHED PAIR OF Bl WATT TRANSISTOR DRIVER 
AND OUTPUT TRANSFORMERS. Stack size 1 ' U ■ 

- in. 'Output trans, tapped for 3 ohm and 15 ohm out- 
put. 10/- pair plus 2/- P, U I*. 

PARMEKO 7-10 wait OUTPUT TRANSFORMERS In 
match pair of ECL «2's in push-pull. Sec Lapped 3-7u. 

- - and is.ihm. Stack tin: Sl'xl'XS* approx, osi.v 




12 ■ 



r. & 



•A ■. 



7-10 watt OUTPUT TRANSFORMERS to match pair of 
ECL Hfi's In push-pull lo 3 nhm output. OSLV 11'- 

p. & i: 2/6. 

10-12 wait OUTPUT TRANSFORMERS. Mm llln. tat 
I'lamp rilting. For Iwo EL84 - s in push-pull. Slate 3 oi 
iaohtn iinpL-danw. 18,8. P. * P. 2/6. 

ACOS HIGH IMPEDANCE CRYSTAL STICK MIKES 
Listed at 42.-. Our price, 21.-. 1: & P. 1 H. 
ACOS CRYSTAL MDXES. High im p. For desk or ha ml usf 
High sensitivity, 18,8. P. * P. 
1/0. 

SPECIAL OFFER: MOVING 
COIL MIRE. Fmed on/ofl 
switch tor remote control. High 
Huallty. High or Low impe- 
dance. (State Imp. rend.) 
BARGAIN PRICK 30/-. 
P. A T. 3/6. 



LATEST COLLARO MAGNAVOX 363 STEREO 
TAPE DECK. Three speeds, 4 track, iakes up to 7in, 
spools. BD2.10.0. Pius 7/B t'arr. & ins. (Tapes extra), 
B.S.E. TD.2. 4 track Stereo Tape Deck. Dgns. Carr. 7. 6. 
aUALITY PORTABLE TAPE RECORDER CASE. Brand 
new. Beautifully made. Only 49/6. P. i P. 8/6- Deal 
Purpose Bulk Tape Eraser and Tape Head Demaanetiaer 
35.'-. P. Is P. 3/-. 

4-SPEED RECORD PLAYER BARGAINS 

Mains models. Ail brand new in maker's original 
packing . 

LATEST B.S.R. MODELS 

TB 12 Single Player with mono Cart £3.8.8 

GD7 Sinele Player with mono Cart. £4.18.8 

OA85 Changer with mono Cart 16.7.6 

All plus Carriage and Packing 6 6. 
Sea below lor suitable stereo cartridge ! 
LATEST OARRARD MODELS 
ALL types available 1000, SP25. 3000, AT60, etc. 

Sena S.A.E. for latest Bargain Prices I 

BRAND HEW CARTRIDGE BARGAINS : LATEST B.S.R. 

X3M MONO COMPATIBLE CARTRIDGE 
With (turnover sapphire styli suitable for playing 78, EP, 
LP and Stereo records with mono equipment. 

ONLY 22/8. P. & P. 1/6. 
SON0TONE 9TAHC Compatible Stereo Cartridge with 
diamond stylus 50/- or with sapphire stylus 40/-. 

1*. & P. 1,'ti each. 

QUALITY RECORD PLAYER AMPLIFIER 
A top-quality record player amplifier employing hcavy 
iluty double wound mains transformer, ECCS3. ELo4, 
K2y0 valves. Separate Bass, Treble and Volume 
contrt.de. Complete with output transformer matched 
fnr 3 nhui speaker. Size Tin. w. :< 3in. d. X fiin. h. 
Kendy built ami tested, PRICE 75,'-. P. & P. 0/-. 
ALSO AVAILABLE mounted rm board with output 
transformer and speaker ready to fit into cabinet below. 
PRICE 97/6. V. ,t P. 7,'ij. 

DE LUXE QUALITY PORTABLE R/P CABINET 
Uncut motor Ward size 14} in. :.; 12in. clearanee 2in. 
below, oiin. above. Will take above amplifier and any 
B.S.R. or GARKARD Autochanger or Single Player Cnif 
(except AT60 and SP2a). Size ISin. :•: I Sin. < Sin. 
PRICE £3,9.6. P. li P, 9/fi. 

VYNAIR AND REXINE SPEAKER AND CABINET 
FABRICS iipp. 54in, wide. Usuidly 85/- yd,, our price 
13/6 per vd. length., P. & P. 2/6. (miu, 1yd.). S.A.E £or 

samples. 

BRAND NEW 3 OHM LOUDSPEAKERS 
Sin.. 14/-; 6. '.In. ,18/6; 8Iti.,27/-; 7in. x 4in. 18/6; lOin. 
i 6in., 27/6. 

E.M.l. Sin. : oin, with high fluK magnet JS1,'-, 
E.M.I. 131ln. . Sin. with high flus ceramic magnet, 42/-. 
{15 ohm, 48/-). P. & P. 5in. 2.'-, eiSn. i Bin. 2/6, lOin. * 
121n. 3-6 per s peaker. 

BRAND NEW. 12in. tow. H/D Speakers, 3 or 13 ohfll. 
Current production by well-known British maker. Offered 
below list price at 89/6. P. & P. 5/-. Cultar mode's: 
25w. 15.5.0; 35w. £S.8.0. 

E.M.I. 3! in. HEAVY DUTY TWEETERS. Powerful 
ceramic magnet. Available in 3, 3 or 15 ohms. 15/-. 



P. AM'. 



2'B. 



ISin. "RA" 
peak output. 



31j.i. 12 8; 



TWT5 CONE LOUDSPEAKER. 10 watts 
3 i t 15 ohm. 36/-. P. & P. 3/6. 
35 OHM SPEAKERS 



41s. 21 -. P. Jc P. 2/- per speaker. 



HARYERSON SURPLUS CO. LTD. 

170 HIGH ST., MERT0N, S.W.I 9 01-540 3985 

Open all day Saturday Early closing Wed., I p.m. 

A few minute* from South Wimbledon Tube Station , tP/eose write clear if) 

OVERSEAS P. A P. CHARGED EXTRA. S.A.E. with all enquiriai 

32t 



OUTSTANDING HIGH FIDELITY 
DESIGNS FROM SINCLAIR 



The 

world's 

smallest 

radio 





SINCLAIR MICROMATIC 

The ultimate in personal listening, the Micro- 
matic is as easy to have with you as your wrist- 
watch. It has enormous power and range, and 
the magnetic earpiece now supplied assures 
marvellous quality. Hear how Radio 1 and other 
stations simply pour in. Build it yourself or buy 
your Micromatic ready bulit. This is the set you 
will never be without once you hear it for yourself. 



• H' I &■ » r 

Q Tunci over medium 
waveband 

# Slow motion tuning 
control 

£ Aluminium front 
panel and dial 

9 H agnatic tar piece 



Complete kit including 



innfucliom 



49/6 



Read/ built with 
magnetic eorp/ece 



59/6 



tAoUory Mercury Ce" 
RM.67S (2 needed) 
each 1/9 



SINCLAIR 

Q.I4 

LOUDSPEAKER 



BRILLIANTLY EFFICIENT 
. . . especially in stereo 

When Sinclair Radionics decided to design and manufacture a new loud- 
speaker, it was required from the start that its performance should be worthy of 
today's best high fidelity standards and be so reasonably priced thatthe greatest 
numbers could afford it. By using ultra-low resonant materials to form its 
acoustically contoured housing, outstandingly brilliant performance resulted. 
Furthermore, the unusual form of the Q.14 meant It could be used as a free- 
standing shelf speaker, as a wall-corner sound radiator or flush mounted 
singly or in multiple units on a flat surface such as a wall. The correctness of 
the design of the Q.14 has amply proven itself since within a few months of its 
introduction, It is already amongst the four most demanded loudspeakers 
irrespective of price. Independent laboratory tests have already shown thatthe 
0,14 has amazingly good performance characteristics. As a judge of good 
sound yourself, your ear will confirm this instantly. At its price, there is nothing 
to stop you changing to Sinclair at once. 



• Size 9 V i n x 9|in x 4|in 
deep plus detachable base 

• IS ohms impedance 

• Up to 14 watts loading 

• Smooth response between 
60 and 16,000 Hz 

• British manufacture 



The Q.14 is finished in matt black with solid 
aluminium bar embellishment on the front. 
Supplied in strong fitted carton and sent 
post free under money back guarantee if 
you are not satisfied. 



IDEAL WITH Z.12 HI-FI SYSTEMS 




SINCLAIR RADIONICS 
Cambridge 



► 

LTD., 22 Newmarket Road, 
Phone OCA-3 52996 



322 




SINCLAIR 



UNCHALLENGED LEADER IN ITS FIELD 



COMBINED 12 WATT HI-FI AMP AND PRE-AMP 



No constructor's transistor amplifier has ever achieved such success 
as the Sinclair Z. 12. it favours the user in so many ways— with fantastic 
power-to-size ratio, with far greater adaptability, with freedom to 
operate it from batteries or mains power supply unit (the new PZ.4 is 
ideal for this) with the opportunity to obtain superb stereo reproduction 
for very little outlay. Countless thousands of Z,12s are in use through- 
out the world— in hi-fi installations, electronic guitars and organs, P.A. 
installations, intercom systems, etc. This true 12 watt amplifier is 
supplied ready built, tested and guaranteed together with the Z.12 
manual which details control circuits enabling you to match the Z.12 
to your precise requirements. For complete listening satisfaction, use 
your Z.12 system with Q.14 loudspeakers. It assures superb quafity 
with substantial saving in outlay. 




• 3" x fi' x U" 

• Class B Ultralinear output 

• 15-50,OOOHz ± 1dB 

• Suitable for 3, 5, 8 or 151* 
speakers. Two 3-ohm speakers 
may be used in parallel. 

• Input— 2mV into 2k t' 

• Output— 12 watt, R.M.S. 
continuous sine wave 
(24W peak) 



YOUR SINCLAIR 
GUARANTEE 

Should you not be completely 
satisfied with your purchase when 
you receive it from us, your money 
will be refunded in full at once and 
without question. FULL SERVICE 
FACILITIES AVAILABLE TO 
ALL SINCLAIR CUSTOMERS. 



"/ made this (Z.12} stereo record player 
for my work as hospital chaplain and it 
has been a great success." 

K.S.B. Basingstoke 

"The Z.12 and Q.14 live up to your 
high standard. I could spend pages 
praising these products." 

I.A.W. Hereford. 



Ready built, 
tested and 
guaranteed. 



89/6 



For use with two Z. I2's or any good hi-fi stereo 
system. Frequency response 25 Hi to 30kHzJ- IdB 
connected co two Z.I2's. Sensitivity Mie.2mVinto 
50k Q ; P.U. -ImV into 50k R : Radio — 20m V into 
4.7k n. Equalisation correct to within :: IdB on 
RIAA curve (rem 50 to 20,0O0Hi. With brushed 
and polished aluminium front panel with solid 
aluminium knobs to match. Size 6)inX2JinX 2lin 
plus knobs. 



BUILT 
TESTED 
AND 
GUARAN- 
TEED 

£9.19.6 



SINCLAIR PZ. 4 

STABILISED POWER SUPPLY UNIT 




A heavy duty a.c, mains 
power supply unit deliver- 
ing 18V d.c. at 1-5A. De- 
signed specially for Z.12 
assemblies. 
Ready built 
and tested. 



99/6 



WE PAY POSTAGE ON EVERYTHING YOU ORDER 



To: SINCLAIR RADIONICS LTD., 22 NEWMARKET ROAD, CAMBRIDGE 



Please send POST FREE 



For which I enclose cashicheque/money order 



I tor which I enclose cast, 



I 



NAME. 



ADDRESS. 



PE,5 



323 



DONT MISS THIS 



Lasky's Birthday Draw f " EASI-TUNE '* AM/FM MAJOR 



The to! lowing 85 number* bare been drawn lor prim in our 3Stb Birtbdij Dnw. 
PImm refer to Pige 12 at our Catalogue tor oolaili ol entry il jonr number (on tbe 
iron! psge ol roar Catalogue) It among thoM lilted here : 

GMT17 



000013 


001415 


002313 


012603 


024444 


028688 


oooose 


001510 


002414 


012777 


024818 


028875 


mat 


001582 


O0S47S 


013828 


024850 


028800 


0OG89S 


001711 


003080 


013750 


028516 


028989 


000827 


001777 


003183 


015000 


027000 


030138 


OOO0S9 


001800 


004000- 


oieooi 


027008 


030744 


000874 


001800 


005016 


018020 


028010 


030S44 


001054 


ooien 


005IS1 


020003 


028456 


030882 


001274 


001922 


005815 


021414 


028480 


031010 


001288 


O01B81 


008788 


021444 


028030 


032013 


001282 


002101 


003900 


021500 


028131 


033417 


001333 


002230 


011717 


023486 


029444 


034111 



038000 

037017 
636111 
038212 
039414 
039S85 
043472 
048792 
047111 
037388 
048001 

The Brit 10 correct entries to be opened will receive tb Laiky'j Gift Voucher i, 
tbe next 25 will receive f 1 raucheri end tbe next 50 will receive 10/8 vouchers. 

Note; Humbert of Lotly't Radio itaff n„it rektirti ate rxprei*lv excluded from 
entry in Ihit compel l< ion. 

HA VE YOU GOT YOUR LASKY'S CA TAL0GUE 

CDCC Second Great He print lime How Reedy . 

■ Jut lend tout name, iddrets end 1- for post only. 





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SCOOP Price £7.19.6 imw 



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Branches 

207 EDGWARE R0A0, LONDON, W.2 Tel: 01 723 3271 

Open ail day Saturday, early closing 1 p.rrt, Thursday 

33 TOTTENHAM CT RD„ LONDON, W.I Tel.: 01-636 2605 

Open all day, 3 a.m. — 6 p.m. Monday to Sattmfey 

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Open all day Thursday, early closing 1 p m Saturdav 



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LASKY'S PRICE 23 Gns. f^fhk 



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High Fidelity Audio Centres 

42 TOTTENHAM CT. RD., LONDON, W.I 

Open all day Thursday, early closing 1 p.m S; 

118 EDGWARE ROAD. LONDON, W.2 

Open oil day Saturday. □ ipm, Tl\ 



Tel.: 01-580 2573 



Tel.: 01-723 9789 



ALL MAIL ORDERS AND CORRESPONDENCE TO: 3-15 CAVELL ST., TOWER HAMLETS, LONDON, E.I Tel.: 01-790 4821 



324 



VOL. 4 No. 5 
May 1968 



PRACTICAL 

ELECTRONICS 



LABOUR OF LOVE 



Te trouble with certain amateurs" we heard a well 
known professional recently complain, "is that 
they make things far too good". This was a mild 
protest at the fastidious concern for detail and elabora- 
tion indulged in by some spare time constructors. 

In expressing this opinion, this critic certainly revealed 
his awareness of amateurs, and indirectly paid tribute 
to the high standard of craftsmanship often found 
amongst the non-professionals. This is certainly 
gratifying. In all walks of life too much distinction is 
maintained between the amateur and the professional. 
In general parlance the term professional, when applied 
to person or product, suggests superiority. Quite 
commonly it is assumed -that the amateur represents 
merely the second best. 

The activities and achievements of individuals in 
fields outside their normal vocation are often belittled 
without just cause. Resentment of outsiders poaching 
upon their exclusive preserves, plus a feeling of in- 
security or even of inferiority (unadmitted, of course) 
may be contributory factors for the patronising manner 
adopted by some professionals towards their amateur 
brethren. 

So far as our own particular field of interest is con- 
cerned, we have occasionally encountered such attitudes 
from individuals professionally engaged in the 
electronics industry. Happily such cases are the rare 
exception. Many of our most esteemed friends and 
associates are in the industry. Professionals they may 
be, but also real amateurs at heart. For what does the 
word really mean but a lover, or devotee. Genuine 
interest and high proficiency in a subject (whatever it may 
be) should not be automatically nor exclusively equated 
with professionalism. Let's face it, there are good 
and bad workers on both sides of the fence ! 

Now to answer the above quoted criticism levelled 
at some amateurs. A project undertaken for enjoyment 
in one's own time is bound to reflect this in countless 
little ways. The finalised piece of home-made equip- 
ment will carry some marks of the builder's own 
personality, and not an inspector's rubber stamp applied 
at the end of a production line. The amateur has no 
time sheet to fill in, and if the fancy leads him to a little 
extravagance — it is his own pocket he dips into. Fussy 
concern for detail is no cause for condemnation, but 
rather for envy. Many a professional must, on occa- 
sion, wished he could have spent more time or used more 
material on a given project. But in the commercial 
world things are necessarily rather different. Ay, 
there's the rub t 

F. E. Bennett — Editor 



THIS MONTH 



CONSTRUCTIONAL PROIECTS 



BOAT INTRUDER ALARM 
TRANSISTOR CURVE TRACER 
ELECTRONIC CYMBALS 
P.E. ANALOGUE COMPUTER 

FLUORESCENT 

CAMPING LIGHT 



SPECIAL SERIES 



NUCLEONICS FOR THE 
EXPERIMENTER— 7 

TRANSISTOR AMPLIFIER 
DESIGN— 4 



GENERAL FEATURES 



DENTOPHONICS 



BEGINNERS 



SEMICONDUCTOR BASICS 6 
MULTIVIBRATOR 



NEWS AND COMMENT 



326 
333 
342 

360 

375 



352 
347 

372 



356 

358 



EDITORIAL 


325 


AUDIO FAIR PREVIEW 


330 


BOOK REVIEWS 


346 


BETTER SOUND 


351 


READOUT 


376 



Our June issue wilt be published on 
Friday t May 17 



All correspondence Intended for the Editor should be addressed to: The Editor, PRACTICAL ELECTRONICS, George Newnes Ltd., Tower 
House, Southampton Street, London, W.C.2. Advertisement Offices: PRACTICAL ELECTRONICS, George Newnes Ltd., 15/17 Long Acre, 
London, W.C.2. Phone: 01-836 4363. Telegrams: Newnes London. Subscription Rates including postage for one year, to any part of 
the world, 36s. © George Newnes Ltd., 1 968. Copyright in all drawings, photographs and articles published In PRACTICAL ELECTRONICS 
is specially reserved throughout the countries signatory to the Berne Convention and the U.S.A. Reproductions or imitations of any of 
these are therefore expressly forbidden. 



INTRUDER 





FOR SMALL 
CRAFT 




-pHis article describes the construction of a simple low 
cost alarm that will prove effective as a deterrent 
to vandals or marauders visiting your yacht or motor- 
boat. 

Although primarily designed to prevent unlawful 
entrance through boat doors and hatches, it may also be 
employed as a burglar alarm for cars or as a domestic 
sentinel. Current consumption on standby is exceed- 
ingly low, in the order of microamps and the choice of a 
silicon transistor in the first stage insures against 
fortuitous switching of the relay through thermal 
influences. 

CIRCUIT DESCRIPTION 

The circuit diagram for the alarm system is given in 
Fig. 1. In essence the circuit consists of an npn 
emitter follower TR1, the load of which is a 500 ohm 
600 type relay RLA, followed by an astable pulse 
generator (TR2, TR3) switching an alarm at a selected 
frequency. 

In the standby condition the transistor TR1 is held 
off by the loop of closed microswitches which are fitted 
to hatches and doors. It was found in practice that the 
relay would not trip even for a loop resistance of 
50 kilohms, so it can be seen that high contact resistance, 
effected by alternative choice of contact plate switching 
through poor connection, should not reduce the 
efficiency of this alarm. 

ACTIVATION OF ALARM 

If the loop line is broken through forced entrance, 
the small quiescent current through Rl is diverted to the 
base of TR1 which switches on, so energising relay RLA. 
The normally open contacts RLA1 close. This has the 
initial effect of providing a latching potential to the 
relay by way of R2 thus ensuring that any attempt to 
cut off the alarm by closing doors or hatches and so 
completing the loop is frustrated since the relay 
armature is held in effect by its own contacts. 

Any attempts by the marauder to rip out the loop 
wires are equally ineffectual with this latching action. 

ASTABLE MULTIVIBRATOR 

The closed relay contact RLA1 also completes the 
circuit for the complementary astable multivibrator 
circuit composed of TR2 and TR3. Most readers are 

326 



probably familiar with the conventional multivibrator, 
easily recognised by its crossed pair of feedback 
capacitors. The circuit employed in this boat alarm 
produces a similar output pulse, but it is very different 
in its operation. 

In the standby condition the electrolytic capacitors 
C 1 and C2 are discharged, but with the closing of RLAI , 
CI charges through the point contact diode Dl and RLB 
coil with a time constant appropriate to this series train. 
Simultaneously C2 charges by way of RLB coil, VR1, 
and R3 — with a relatively larger time constant. 

Since the charging of C2 is exponential from zero, a 
negative potential will appear at the base of the npn 
silicon transistor TR2, proportional to the values of R3 
and the frequency control potentiometer VR1. This 
negative bias holds off TR2 and consequently TR3, 
since no collector current is being passed to the base of 
this transistor. With the charging of C2 the negative- 
hold-off bias is removed and TR2 is switched into con- 
duction with consequent bottoming of TR3. 

This means that most of the supply volts now 
appears across RLB so closing the normally open 
contacts of RLB1. At this point the diode Dl is 
reverse biased and does not allow the rapid discharge of 
CI through TR3. This capacitor now acts as a 
temporary supply to maintain the complementary pair 
in conduction. With the discharge of CI and C2 by 
way of the base-emitter junction of TR2, Dl, and VR1, 
the circuit reverts to its original state, with relay 
contacts opening prior to the next cycle of charging 
events. 

MARK-SPACE RATIO 

Whilst the consumption of the operating unit is a 
nominal 20mA, the current taken by the alarm audio 
transducer will be very much greater. A degree of 
power conservation can be achieved by adjusting VR1 
for the smallest mark-to-space ratio. 

This setting will of course, be a compromise between 
an urgent alarm repetition rate, if this is required, and 
the available capacity of the batteries employed. 

If a bank of high power zinc-carbon dry cells, such 
as Ever Ready HPl's are used with a car horn, the 
mark-space potentiometer setting should be at its 
lowest — although it must be stated that these cells 
would be more suited to a large underdome bell as 
an alarm. 






COMPONENTS . . 

Resistors 

Rl 1 00k a 
R2 33011 
R3 270kQ 
All 10%, | watt carbon 

Capacitors 

CI I00 M F elect. 15V 
C2 8 M F elect. 15V 

Potentiometer 

VRI 10k ft horizontal preset 

Transistors 

TRI 2N2926 (Yellow) 
TR2 2N2926 (Yellow) 
TR3 OC7I 



Diodes 

Dl, D2 



OA8I (2 off) 




Switches 

51 Bulgin s.p.s.t. key operated rotary snap 

switch (Home Radio) 

52 Push-to-break-single pole miniature push 

button switch (Radios pares) 
SW-SZ Alarm switches — miniature button 
lever type (Bulgin) (Quantity 
required) 



Relays 

RLA 



RLB 



9V 500 Q coil, I make light duty contacts 

600 Type (Keyswitch) 
9V 500 Q coil, I make heavy duty contacts 

600 Type (Keyswitch) 



Fig. I . Circuit diagram of the boot alarm 

Connectors 

PL I, SKI 8-way standard multi-pole connector 
(plug, socket, cover shell and retainer, 
Radios pares) 

Miscellaneous 

BY I 12V battery (see text) 
XI Car horn (see text) 

Diecast Box (S.T.C.) 8Jin x Sfin x 2^ in (Elec- 
tron iques) 
Miniature p.v.c. wire 7/40 (Radiospares) 



} 

§ 

5 

) 

j 

I 

I 




17 18 19 20 l\ 22 23 24^25j,26 
RLA coil 



28 29 30 



Fig. 2. The Veroboard 
sub-assembly 



fa) top view, showing 
arrangement of com- 
ponents 



R ~ 

J c 
I c 
H C 

G "5 
F C 
E C 

c 

C C 

B G 


■ ooooooooeo»oo oOoooo»oo • o i of < 


>1~5" 
^o 
jj^o 

3 Jo 


looooooooeeooo ooooo(o)o»o«#o o(< 


Boooeooooooooo eooo eooeeooo oft 


ijoooooooooooooooooooooooooo(< 




■ o oooooooooeoo oooo • o|oro o eTr^^^nl 




Bo ooo ooo o • o o • o ooo o oto)o o o • o • • m 



(b) underside view, 
showing breaks in con- 
ductor strips, and 
soldered connections 



1 2 3 4 5 6 7 8 9 10 fl 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 



^* slfi *V^33^* %x '* 



^V, 




MOTE Retoy Srodwt 
ucurcd to box with 
3-4BA fixings \ 




Irtiu lotion 

bushes 



Fig. 4. Interior view of the main unit.* Relays and circuit 
board have been moved from their normal positions to 
clarify the wiring details 

Obviously secondary type batteries, i.e. lead acid or 
nickel cadmium will provide a much larger capacity, 
and may be preferred. Of the latter kind, the DEAC 
5M6 is suitable (two will be required). 

VETO SWITCH 

The key operated rotary snap switch SI is in shunt 
with the alarm loop and is intended to be installed 
outside the cabin or other protected enclosure. When 

51 is closed the alarm is inoperative and hatches and 
doors can be opened with impunity. 

When the cabin is vacated and the door locked prior 
to departing from the vessel, the keyswitch is turned and 
the key pocketed, leaving the system set up. It follows 
of course, that the siting of this switch should be such as 
to make.it as inconspicuous as possible. 

RESET SWITCH 

If an intruder does set off the alarm the deactivation 
procedure on return would be to close the veto switch SI 
with the key, and then press the push-to-break switch 

52 which will de-energise relay RL1, so breaking the 
alarm contacts RLAI. Releasing this switch 
immediately sets the system to standby again. 

CONSTRUCTIONAL DETAILS 

A suitable housing for the electronic assembly is an 
S.T.C. diecast box slotted to take the Veroboard sub- 
assembly (see diagrams and photograph). 

Since this box is made of an aluminium alloy it is 
essential to paint this with a waterproof metal primer 
(as used on boats) to prevent corrosion. This should 
be done after the unit is sealed so that the paint applied 
forms a barrier to corrosive influences. Technical data 
sheets on the choice of primers and paints applicable 
may be obtained by writing for relevant data sheets to 
British Paints Ltd., Little Ship Division, Northumber- 
land House, 303-306 High Holborn, London, W.C.I. 




Fig. 5. Relay mounting bracket 

In the relay sub-assembly, drilling of all holes in the 
mounting bracket should be done using the template 
shown as a guide. Since the circuit consists entirely 
of switching elements there is nothing particularly 
critical in the construction. 

The unit should be given a functional check prior to 
boxing and particular care should be taken in making 
the breaks in the copper strip of the Veroboard at the 
extremes of the board, as one is sometimes inclined to do 
this extremely fast with a spot fact cutter and leave 
pieces of swarf to short adjacent strips. 

LOOP CIRCUIT SWITCHES 

It is recommended that linear action micros witches 
be used in the loop circuit as "break-in" detectors. 
Either the button or lever type microswitches may be 
used as both types can be suitably recessed for doors and 
hatches. 

Perhaps a more economic system would be the 
employment of stainless steel shims arranged to operate 
as contact plates. Wiring to these plates would be by 
way of eyelet tags, the assembly being both electrically 
and mechanically joined by brads driven through eyelet 
tags and shims to the wood backing. As this was not 
tried in the prototype system it can only be a suggested 
possible alternative. 

Connection to all microswitch detectors should be by 
miniature p.v.c. 7/40 wire. Although not as incon- 
spicuous as thin enamelled wire, there is less likelihood 
of abrasion producing false alarms through short 
circuits if the loop wires are spliced in the run. 

Since any attempt to cut wires will trigger the alarm, 
concealment of these wires by channelling is not really 
important. Any burglar who is au fait with alarm 
systems would be deterred if he was made aware of some 
protective guard against his intended pillaging; after all, 
many motorists display stickers on their windows to the 
effect that X's proprietary alarm system is installed 
— which is a daunting first line deterrent. 

ACOUSTIC TRANSDUCER 

The audible alarm device suggested is a v.h.f. car 
horn. However, since the contacts of relay RLB are 
heavy duty, other types of alarm may be fitted, such as a 
strident bell— this applies particularly if the system is 
adopted for home or business protection. 

For the larger vessel with its own power supplies, 
existing hooters, marine horns, or loud hailers can be 
connected in the external switch circuit. 

If the system is used for car protection, horn and 
headlights can be arranged in series with the RLB 
contacts. This will necessitate the use of an extra pair of 
contacts at the multi-pole connector PL1, SKI for load 
sharing, as these contacts are only rated at 5 amps. -^ 



329 




\ — MHf — ^ 

J U I 




Baker "Major" loudspeaker 



Garrard SL9S auto 
transcription turntable 



By M. A. Colwell 



Now that stereophonic broadcasts are in full swing 
in the U.K. (albeit of insufficient quantity and in 
a limited number of areas) the manufacturers are 
jumping on what is now an established bandwagon. 
The trend to what is termed the "tuner amplifier" is 
spreading to include stereo. 

The problem re-emerges: What is the best unit to 
buy? This is one question constantly being asked, and 
it is almost impossible to answer in a few words, 
because of the many and varied aspects which anyone 
would look into— not least of these being the capital 
cost. 

Probably the best approach is to take advantage of 
free entrance facilities offered to that popular event, 
the Audio Festival and Fair (April 18 to 2 1 ). This year 
the Hotel Russell, Russell Square, London. W.C.I, 
will open its back doors once again to the hoards of 
enthusiasts who diligently sort their way through the 
hotel rooms looking (or should I say listening) for the 
ultimate in sound reproduction. 

Among a plethora of equipment, no doubt, the regular 
visitor will find his pet subjects and the newcomer will 
be baffled by what may appear to htm to be the old 
game of hunt the thimble. How best can we help 
him? First of all, decide before you go whether your 
visit will be confined to certain types of equipment or a 
general survey of the whole scene. Stamina could be 
sucked dry if you attempt to take in every single item 
and demonstration, so that by the time you reach the 
fourth floor you will be glad to go down again. 

If you are set on a particular branch of the audio 
scene, get a catalogue— it will save quite a bit of shoe 



leather. Browse through and make jottings of special 
interests. See the equipment on the ground floor 
booths; then after further jottings find your way to the 
demonstration rooms of your choice. The catalogue 
will help here again to locate these although, with a 
little common sense and observation of the direction 
arrows at strategic points, you should have no difficulty. 
Now for the gear! The following is a preview of some 
of the equipment to be seen. It is interesting to note, 
during the current national prestige boosting campaign, 
that imported products are generally more expensive 
than the "home grown" varieties. 

TUNER AMPLIFIERS 

The "tuner amplifier" mentioned earlier is a term 
applied in recent years to equipment combining radio 
tuning and amplification. The addition of a loud- 
speaker {or in the case of stereo, two loudspeakers) is 
usually left to the choice of the user, since there is a 
wide variety of types at different prices according to 
one's requirements. 

Typical examples are shown by the Sansui range. 
The one illustrated here is the Model 2000 stereo 
tuner amplifier which overcomes input matching 
problems by using a field effect transistor at the front 
end of the amplifier. Jnputs are provided for tape head, 
pick-up, or tuner (internal) for mono or stereo listening. 

Later this year the Sansui Model 3000A will be 
available and offers a higher power output than the 
current Model 3000. This is also in stereo. The 
importers are Technical Ceramics Limited. 



HOH^HHHBiHI 




Sansui Model 2000 stereo 
tuner amplifier 



• 



\ 



^ 



330 



Arena stereo tuner amplifier type TISOOF with two HT2t speaker units 



Arena of Denmark will be introducing their new stereo 
tuner amplifier type TISOOF through Highgate 
Acoustics. Modular construction has been used and ii 
offers an output power of 6 watts per channel for input 
sensitivities of 10// V for a.m. and 1/*V for f.m. The 
picture shows the unit with two matching speakers 
typeHT21. 

In addition to their current range of tuner amplifiers, 
the Trio Corporation of Japan are presenting a new 
solid state amplifier, the TK.150E stereo, through their 
agents B. H. Morris & Co. (Radio) Ltd., a subsidiary 
of Lasky's Radio. The price compares modestly with 
the Supreme I— a 64W per channel stereo amplifier, 
employing separate bass, mid- and high-range amplifiers. 
expected to retail at £280. 

Armstrong will be showing their Series 400 and 
Series 27 equipment which includes amplifiers, tuners, 
and stereo decoders. 

When selecting f.m. tuners, look for a.f.c. This 
overcomes many drifting and fading problems often 
caused by intervening obstructions between trans- 
mitter and receiver, or varying atmospheric conditions. 

Provisional information obtained from Rogers 
Developments (Electronics) Ltd., reveals a new f.m. 
tuner using an f.e.t, front end enabling it to handle 
large signals without cross modulation, while at the 
same time being suitable for areas of low signal strength. 
A.F.C. is incorporated in this model. A multiplex 
stereo decoder is available as an optional extra. This 
"Ravensbourne 2" tuner has been designed to match 
the "Ravensbourne" stereo amplifier. 

SPEAKER UNITS 

Many people have different ideas on what is the best 
speaker. It is largely a matter of personal choice since 
almost all manufacturers claim the best from their 
units. Look for a specification with a high flux 
density magnet and strong rigid frame if going for a 
moving coil type. Of course, it must have an impe- 
dance to match the amplifier. Excellent results are 
obtained with the established Quad electrostatic unit. 

Well known names such as Wharf edale, Whiteley, 
Celestion, Goodmans, and so on, will no doubt attract 



Shure M7SE-95G "Goord-o-Motie" 
cartridge with suspension system 




the usual audiences for comparative listening. Of 
course, they all use different records, pick-ups, and 
amplifiers, which may give slightly differing results. 
So it is difficult to make direct comparisons, especially 
when the rooms are packed with steaming bodies 
under the floodlights. Perhaps you may be athletic 
enough to dash from one room to another before the 
memory of what was heard first has faded. 

In between the aural bliss of Satchmo and the "1812", 
take a look at the Titan Minor loudspeaker by Audio & 
Design. This uses a titanium cone on beryllium 
copper suspension. It is claimed to reproduce bass 
more efficiently than conventional types for its size. It 
is available housed in a cabinet I7iin x llin x 8{in. 
Power handling capacitv is 15 watts from 40Hz to 
22kHz. 4dB. 

DISC EQUIPMENT 

Ancillary equipment can be added ai various stages 
as funds permit, but it is always worth making notes at 
the Fair for future reference. 

Pick-ups have seen some design changes in recent 
years and it will be interesting to see what is new. 
Tracking weight is frequenth a subject of much 
confusion. Let it not be assumed automatically that 
the lighter the stylus pressure, the better the performance. 
Similarly with record wear, much depends on the 
design of the pick-up arm and, even more, on the 
true running of both turntable and disc. 

Where these factors are near perfect, then one can 
entertain the i ounce pressure, otherwise there is the 
risk of groove jumping on less accurate turntables and 
discs. Pick-up arms should be very free moving both 
horizontally and vertically. 

Of unusual design, the Shure M75E-95G "Gard-a- 
Matic" Hi-Track cartridge, is designed specifically for 
the new Garrard SL95 transcription turntable* (see 
later). The performance is equivalent to that of the 
M75E but with a retractile safety suspension system, 
claimed to provide scratch- proof, bounce-proof opera- 
tion where floor vibration is a problem. Shure also 

Rogers "Ravensbourne 2" f.m. tuner 




331 



announce new models in the "economy" range of 
cartridges. The M3IE and M32E have elliptical tipped 
stylii for tracking at l-2gm and 2^-5gm respectively. 

Audio & Design are introducing a stereo "induced 
field" cartridge with an output of 0-9m V per cm/sec. 
It uses an elliptical tipped stylus and is intended for 
feeding into high impedance inputs. 

Cosmocord have developed another version of the 
stereo compatible cartridge announced last year. The 
Acos GP91SC incorporates a mono crystal for mono or 
stereo records. The stylus is suspended on a flexible 
plastics arm so that it will track stereo grooves, while 
reproducing a mono signal. It is available in three 
versions with outputs of 200, 350, or 640mV at 1 '2crn/sec. 

The Goldring Model GL75 transcription unit, with 
"free field' 1 stereo magnetic cartridge, maintains the 
tradition of their using variable speed motor units. The 
new pick-up arm has a sliding counter balance to cali- 
brate stylus pressure, and can be raised or lowered 
hydraulically on to the disc by operating a simple lever. 

Garrard equipment at a more modest price include the 
AP75 single record player, Models SL95 and SL75 
auto transcription turntables and the Model 3500 auto 
turntable, with a low mass pick-up arm, and cue and 
pause control. 

The Model SL95 features "gimbal-type" pick-up arm 
pivots; the arm has afromosa wood set into aluminium 
for low frequency resonance damping. The record 
platform can be pushed down out of the way for single 
play operation. 

Following some suggestions made to B.S.R. they 
have now superseded the UA70 with a new Model 
UA75, which uses a heavy cast alloy machined turn- 
table. 

TAPE RECORDERS 

Probably the most interesting news in the tape 
recording field is from Ferrograph. After 18 years of 
pounding on their "Tape Deck" (which was originally 
registered as a trade mark), with very little alteration 
to the basic design, they have decided to up-date the 
appearance and construction to the sleek squarish 
model basic to the new Series 7. 

The electronics are similarly up-dated to all. solid 
state silicon devices, including f.e.t. input stages. The 
machine can be used horizontally or vertically with easy 



Ferrograph Series 7 stereo recorder 



Goldring GL7S transcription unit with 
tever operated pick-up arm 




access to the electronic units. A time switch is in- 
corporated for preset starting without the need for it 
to be previously powered. Several other features are to 
be found, based on principles in its forerunners. Pre- 
record facilities for multi-play echo will be found on 
stereo models, which are supplied with either half- 
or quarter-track heads. 

For another example of a professional studio tape 
recorder, look out for the BTR4 by E.M.I. Its 
complementary portable recorder the L4, with film 
sync facilities is popular for field work among profes- 
sionals and amateurs. 

The latest Brenell deck, Mark 5 Series 3, will be on 
show; features of this model include a self-compensating 
braking system, and space for accommodating up to 
four heads for mono or stereo. 

ACCESSORIES 

Microphones for mono or stereo will be in abundance, 
including the MD409, and MD415 by Sennheiser 
(through Audio Engineering), specially designed for 
"pop" group vocalists. Both have an ti -feed back 
properties and the bass response is tailored for close 
microphone technique. 

The same Company is also demonstrating a new pair 
of stereo headphones, HD414, for those audiophiles 
who want personal listening while the wife watches the 
television. 

The well known range of Shure microphones is to be 
supplemented by the Unidyne IV series. Models 548 
(mono) and 548s (stereo). These are designed for 
professional applications and are fitted with Cannon 
type connectors. 

Finally, a word of advice. Don't arrive at the doors 
without a ticket or you may not get in. Tickets can be 
obtained free of charge through your local hi fi dealer 
or from the organisers of the Audio Festival and Fair, 
42 Manchester Street, London, W.l. (include a stamped 
addressed envelope). ^X> 




332 




rE most useful test for a transistor is to plot its com- 
plete range of input/output characteristics. Not 
only will this show up the transistor limitations but a 
great deal of useful information can be derived from a 
study of the curves. 

These characteristics can be produced by making 
measurements point-by-point using meters to indicate 
the value of currents flowing. However, this "static" 
method is subject to a number of serious limitations, 
the most important of which is the overheating and 
possible destruction of the transistor when measure- 
ments are attempted at the higher current end of its 
characteristics. 

A much better method is to allow the transistor to 
reach its high current values for only a very short 
period of time. This is called the "dynamic" method 
and to use it a cathode-ray oscilloscope must be used 
to display the transistor characteristics. 

This article describes a unit which may be connected 
to almost any conventional oscilloscope in order to 
display the transistor characteristics. Single curves 
can be shown and arrangements are included to permit 
"families" of ten or more curves to be displayed. 

METHOD OF TESTING 

The basic technique is shown in Fig. 1 . Half sine 
waves of voltage are applied to the collector of the 
transistor from a mains transformer via a load resis- 
tance Rl and rectifier Dl. A constant bias current is 
fed to the transistor input through switch SI, either to 
the base or the emitter depending upon whether 
common-base or common-emitter curves are required. 

A voltage proportional to the collector current (7c) is 
developed across the load resistance Rl and applied to 
the Y-plates of the oscilloscope. The collector voltage 
Vch applied to the X-plates, 

Thus as the voltage Vc varies from zero to the peak 

of the half sine wave, so the current /c changes due to 

t- le non-linear characteristics of the transistor The 

fcLVc transistor characteristic is plotted on th£ c.r.o. 

eeri. . ■■ 



Since the transistor is put through this cycle of applied 
collector voltage change at a rate of 50 times per second 
(actually 100 times if the reverse change of Vc is also 
used as in Fig. 1) then a clear trace of this characteristic 
is maintained on the face of the tube. This curve is, 
of course, applicable to the particular bias current 
chosen which depends on Vn and the value of bias 
resistor R<q, To plot a series of such curves it is only 
necessary to change the value of Ru in steps, allowing 
one complete curve to be traced for each fixed value 
of R\>. 

With the simple arrangement of Fig. I it is possible to 
plot hjVc curves for common-emitter or common-base 
configurations by suitable settings of SI . Both pup and 
iipn transistors can be tested by choosing the correct 
polarity of half-sine wave obtained by the appropriate 
setting of a reversing switch S2, connected to the 
rectifier D I . 

In order to convert this circuit into a practical arrange- 
ment it is necessary to add a means of changing the 



VoltQgtwovtfbtm 
-*■ 



Tramistor 



°sL«i 



|§P switch rtvtraw 
NPN wvtform pokwity 




value of Rb between each curve traced in order that 
multiple curves can be displayed. It will also be neces- 
sary to include a cathode follower (or emitter follower) 
between the X output of the circuit and the oscilloscope 
in order to avoid loading the high impedance collector 
circuit. This is particularly important when common 
base curves are to be displayed. Several different 
collector voltage and current ranges will be required to 
accommodate all the transistors that are likely to be 
tested. 

PLOTTING FAMILIES OF CURVES 

A convenient number of curves to produce a useful 
"family" is about ten. These curves will be traced 
one by one and in order to see them all together on the 
oscilloscope screen it will be necessary to repeat them 
fairly regularly (or alternatively a cathode-ray tube 
could be used having a very long persistance phosphor 
screen). What is required is a rapid single-pole ten- 
way switch stepping on automatically and continuously 
to repeat its sequence of ten positions. A Post Office 
type uniselector switch meets this specification admir- 
ably. For those not familiar with this device a brief 
description will not be out of place. Refer to Fig. 2. 

The uniselector switch is operated by applying a pulse 
through the coil which pulls down an armature carrying 
a claw to engage on the ratchet wheel, This wheel is 
attached to the wiper arms of the switch; the fixed 
contacts are arranged in a semi-circle around the switch 
arm. Thus each applied pulse rotates the switch arm 
by one position and engages with the next fixed contact. 

Many versions of the uniselector are available and 
can generally be adapted for our purpose. A number 
of parallel banks of switch contacts are usually found 
and three will be required for the Curve Tracer. A 
standard type of driving coil is one requiring 50 volts 
to initiate a switch operation. Other types may be 
found and the driving voltage can be changed or coil 
rewound to accommodate a different design. The one 
used in the prototype had a 75 ohm coil. 

FINAL CIRCUIT 

The complete circuit is shown in Fig. 3. A stabilised 
power supply is included which uses two 150V refer- 
ence tubes VI and V2. This supplies the constant 
voltage source for the base current determining net- 
work, and also voltage supplies for the cathode fol- 
lower V3 driving the X-plates of the oscilloscope. 

A five-pole, two-way switch S8 enables either a single 
curve to be traced or a family of characteristics dis- 
played. (S is for a single sweep display; A is for 
auto-repetition.) It is convenient to commence our 
description of the curve tracer by considering switch 
S8 to be in the "single" position. 

The appropriate polarity of base current is selected 
by switch S5 (generally negative for pnp and positive for 
nptt transistors, although a reverse characteristic may 
be required sometimes). 

The reference voltage is applied to a potentiometer 
network S6 which allows a selection of input currents 
covering the range 10mA, 5mA, 2mA, 1mA, 500/* A, and 
200/xA, depending on the switch position. Fine 
control of input current for a single trace is provided by 
potentiometer VR2, which can be calibrated 0-1, 0-2, 
and 0-5 if desired, to correspond with the choice of 
range available. 

A meter is also included in the circuit to measure the 
exact value of current supplied to the base. This has 
current shunt resistors, wound to give full-scale 
deflection of 10, 1, and 0-lmA. The current passing 




Fig. 2. Side view of uniselector; the armature is at top 
left above the coif 

through the meter is direct current; a full-wave bridge 
rectifier has been included in the circuit. This is to 
avoid changing connections to the meter when the 
polarity of the input voltage is reversed by S8. If 
desired this bridge can be omitted and its place taken by 
a reversing switch similar to that shown for S2. 

The configuration of the transistor undergoing test is 
selected by means of S4. This permits the current set 
bv VR2 to be applied to the base or emitter depending 
upon whether it is desired to display the grounded 
emitter or grounded base characteristic. 

The collector voltage is a rectified sine wave supplied 
via D3 from the 50V secondary of a mains transformer. 
The maximum amplitude of this sweep voltage is con- 
trolled by the setting of potentiometer VR1. The 
polarity of the sweep voltage is selected by S2 to suit 
either pnp or npa transistors. 

The sweep voltage is also applied via the cathode 
follower V3 to the X-plate of the oscilloscope tube. A 
preset adjustment VR3 is provided in V3 cathode 
circuit to give zero adjustment. 

The current axis voltage, representing the change in 
collector voltage as the transistor collector potential is 
swept through its range of values, is taken from across 
a resistor, selected by S3, and fed to the Y-axis ter- 
minal of the oscilloscope tube. 

Six current ranges are provided for maximum 
currents of approximately 5mA, 25mA, 500/* A, 
250/tA, 100/M, and I0/*A, depending on the position of 
S3. Resistor R7 is included to complete the circuit and 
prevent a surge in current which would otherwise occur 
each time S3 was moved to a new position. 

When switch S8 is moved to the "auto" position, the 
uniselector is brought into action. Instead of the 
value of the input current being set by the position of 
VR2, a set of resistors, R26 to R34, are sequentially 
brought into circuit as the uniselector is stepped round 
to each of its contact positions in turn. 

A separate curve is displayed during the lime that 
the uniselector is stationary and a particular resistance 



334 




PR ACTICAL! /^ "V 



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VALVE EXPERIMENTS 
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SIMPLE TRANSMITTER 



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SERVICING PROCEDURES 



This new style course will enable anyone to really understand electronics by a modern, practical and visual method — 
no maths, and a minimum of theory — no previous knowledge 'required. It will also enable anyone to understand how 
to test, service and maintain all types of Electronic equipment, Radio and TV receivers, etc. 



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335 



I'MlMiUmU^^iiM.Hi.M'li-H 




PORTABLE TYPE 
£9. 5. 0. 



INPUT 230 240v. A.C. 50 60 
OUTPUT VARIABLE 0-260v. 
BRAND NEW 

Keenest prices in the country. 
All Types (and Spares) from 
J to SO amp. from stock. 

SHROUDED TYPE 

I amp, £5. 10. 0. 2.5 amps, 

£6. 15. 0. 4 amps, £9. 0. 0. 

S amps, £9. 15. 0. 8 amps, 

£14. 10. 0. 10 amps, £18. 10. 0. 
12 amps. £21. 0. 0. 15 amps, 

£25. 0. 0. 20 amps, £37. 0. 0. 
37.5 amps, £72, 0. 0. 50 amps, 
£92. 0. 0. 

OPEN TYPE (Panel Mounting) 
' F amp, £3. 10. 0. I amp, £5. 10. 0. 
1\ amps, £6, 12. 6. 
PORTABLE TYPE 
1.5 amp. portable fitted rnetiil case, 
voltmeter. lamp, switch, etc. £9.5.0. 
Similar to above 2,5 amp. £1 1 .7.6. 



100 WATT POWER RHEOSTATS (NEW) /ggt, 

AVAILABLE IN THE FOLLOWING VALUES !$vlS>» 

I ohm, 10 a.; 5 ohm, 4.7 a.; 10 ohm, 3 a.; *\„fe^J.' 

25 ohm, 2 a. ; 50 ohm, 1 .4 a.; 100 ohm, I a.; " \jm)f.' 

150 ohm, .7 a,; 500 ohm, .45 a.: 1,000 ohm, 

280 mA; 1,500 ohm, 230 mA: 2,500 ohm, .2 a. Diameter 

S^in. Shaft length s'"-. <•'»• A:i'". All at 27'6 each. 

P. & P. 1/6. 

50 WATT. 1/5/10/25/50; 1 00; 250 ,'500, 1 .000, 1,500.2,500 

ohm, 21/-. P. & P. 1/6. 

25 WATT. 1 0/ 25/50 / 1 00 ,250. 500 . 1 .000 1 , 500 : 2 , 500 

ohm, 14/6- P. & P. 1/6. _ 

VENNER ELECTRIC TIME SWITCH 

200-250 v. A.C. 20 amp. contacts twice on, 
twice off, at any manually pre-set time. 
Spring'reserve (in case of power cut) fully 
tested £3/9/6. P. & P. 4/6. Or complete 
in weatherproof metal case (illustrated) 
£3/19/6, plus 4/6 P. & P. Can be supplied 
with solar dial, on at dusk off at dawn. 
Prices as above. 

mm AIR BLOWER 

Highly efficient blower unit fitted with , 
totally enclosed 200/250 v. A.C. 50 cycles. V 
.'„ h.p. motor producing 2.&00 r.p.m. 
Outlet 21 I)., used, but in first class con- 
dition and tested . Pric e £3/15 .'-- P - & P . 7 6 

230250V. A.C, SOLENOID 

Heavy duty type, approx. 3 lbs. pull. Price: I 

17/6 plus 2'6 P. & P. ^>k> 

12 24V, D.C. SOLENOID 

Appro x. 8 o z. push. Price fl,6 plus i 6 P. & P . 

" PRECISION INTERVAL TIMER 

From 0-30 seconds (repetitive). Jewelled 
balanced movement. Lever re-set. 
Operates 230V. A.C. 5 amp. c o Micro- 
switch. New . Price 17,6 p l us 2.6 P . & P. 

CONDENSER 4.000 mfd isv. 10.6 plus 1 6 p. & p 

cTnstXnt^oijageTraIwformer" r-^ 

Input 185 250 v. A.C. Output 230 v A.C. 
Capacity 250 watt. Attractive metal case. 
Fitted red signal lamp. Rubber feet. 
Weight 17 lb. Price £1 I / 10/0. P. & P. 15/ . '=^7^ 

PHOTO" ULTIPLIER. Type CV337" This super- 
sedes type 93 1 A. Complete with special P.T.F.E. base 
and divider network. 57/6 incl. P. & P. 





RADIO 
ALTIMETER 




This precision instrument, built 
to highest Ministry specification, is based on a 24 v. D.C. 
LOW INERTIA Integrating Motor. The Motor, fitted 
with gold brushes and drawing only 800 microamp at 
24 v. D.C., drives two precision pots with platinum 
wipers through close tolerance gear-trains, including 
miniature slipping clutch, combined with two sub- 
miniature pots for calibrating the electrical bridge 
circuit. The 3 in. calibrated dial, with a number 
aperture indicating one rev. per revolution of pointer 
with maximum of 5 revs, gives an effective scale length 
of approx. 30 in. Offered at fraction of Manufacturer's 
price. 32/6. P. & P. 6/-. 



LIGHT SENSITIVE SWITCH 



f 




Kit of parts, including ORPI2 Cad- 
mium Sulphide Photocell, Relay. 
Transistor and Circuit, etc., 6-12 
volt D.C. op. price 25 - plus 2/6 
P. & P. ORP 12 including circuit, 
10/6 each, plus I/- P. & P. 
A.C. MAINS MODEL Incorporates 
Mains Transformer, Reetifier and special 
relay with 3, 5 amp mains c/o contacts. 
Price inc. circuit 47,6 plus 2/6 P. & P. 

LIGHT SOURCE AND PHOTO 
CELL MOUNTING! 

Precision engineered 

light source with focusible-l 

lens assembly and ventilated 

lamp housing, to take M8C bulb. Separate 

photo cell mounting assembly for ORP. 12 

or similar celt. Both units are single hole 

fixing. Price per pair £2.15.0. P. & P. 3/6. 

RESETTABLE HIGH SPEED 

COUNTER. 4 figure, 1,000 ohm coil, 
36 48 v. D.C. operation. £3/10/-. P. & 

P. 1/6. 3 figure, 24 v. D.C. £1/12/6. 
P, & P, 1/6. 

DRY READ SWITCHES. New 

special offer of Dry React Switches half 

amp. Contact. Size li x i. 4 for 10/- 

Fom P.. id. 

MINIATURE UNISETEaoVswiTCH 

3 banks of I I positions plus 
homing bank. 40 ohm coil, 
24-36 v. D.C. operation. 
Testcd.22 6jjIus2/6P. & P. 

COMPACT HEAVY DUTY 6v. D.C. RELAY 
2 change over, 30 ohm coil. 7,6 each. 
P. & P. I 6. 3 (or 20/-. Post paid. 

"nIcKEL™ "cADmTum"" BATTERY 

Sintered Cadmium Type 1-2 v, 7AH. 
Size: height 3'. in., width 11 I ,1, in. 
Weight: approx. 13 oz. Ex-R.A.F. 

Tested. 12/6. P. & P. 2/6. 

I/MP MULTI 
RANGE METERS 

New Model U50D Muki tester, 
207000 OPV, mirror scaled with overload 
protection. Ranges • d.c. volts: lOOmV, 
0-5 v. 5 v., 250 v., 1,000 v.; a.c. volts: 
2-5 v., 10 v., 50 v., 250 v., 1,000 v.: D.C. 
current: 5 /-A, OS MA, 5 MA, SOMA. 
250 MA, Complete with battery and test 
probe. £7/5/0 post paid. Three other 
models available from stock. Descriptive 
leaflet on request. 

THYRISTOR 400 piv, 5 amp,, 14 6 ™" 
THYRISTOR 400 piv, 8 amp.. 28,6 

~ 220~ 40 ~ A.C FANTlN IT™ 

2,300 r.p.m. 6" blade size. ^^«fc. v> <r 
Smooth powerful motor. |" 
All metal construction. 
Continuously rated. 
Individually tested. 
Offered ac fraction of I 
maker's price. £2.15,0, 

— — '■J' — 

SANGAMO WESTON 

Dual range voltmeter. 5 
and 100 v. D.C. FSD I m/a. 
In carrying case with test 
prods and leads, 32/6, P. & 

P. 3/6. 

A.C. CONTACTOR 

2 make 2 break (or, 2 
c/o.). 15 amp. contacts. 
230/240V. A.C. operation. 
Brand new. Price 22/6 plus 
1 ,6 P. & P. 

20 Amp LEVER MICRO 

Brand new lever operated 
Micro Switch. 20 amp A.C. 
c/o contacts. Price 4/6 each 
plus 16 P. & P. 5 for £ 
Post Paid. 





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SHOWROOM NOW OPEN CLOSED SATURDAY 

336 



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With particular reference to the 
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There are 157 diagrams and photographs and 
83 illustrations in colour. 

by G, N. Patchett 
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MOOERN TAPE RECORDING AND 
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INSTRUMENT CASES AND CHASSIS 
27 sizes and styles 

OLSON ELECTRONICS Ltd. 
Factory No. 8 5-7 LONG STREET 
London, E.2 .Telephone 1 -739 2343 



CIRCUIT DIAGRAM 



Q 



200V 



IA 



ikfi 



■M50V 




ToC.R.O. ToC.S.0 
Common Y-Plott 
Tsrminol 



Fig. 3. The complete circuit of the curve tracer for connection to a d.c. oscilloscope 



337 



VEIP HAD JUST CL-KHfNT 



is in the circuit. The uniselector is automatically 
stepped on to the next position and a second curve is 
displayed. The process then repeats and the whole 
cycle repeats every 200ms. This is sufficiently rapid 
to give the illusion of a stationary set of curves being 
displayed on the screen simultaneously. 

The uniselector is energised from the 40V secondary 
winding of a mains transformer T3 via rectifier D4. 



• • • 



The primary of this transformer is connected to the 
mains supply via one of the arms of the switch S8a. 
A time-constant (C5, R8) is included in the primary 
circuit in order to phase the application of an operating 
pulse to the uniselector to correspond to the half cycle 
when the collector sweep is inoperative. 

COMPONENTS 

It is appropriate to mention some of the components 
used in the instrument. The majority of them are 
easily obtained, but it may be necessary to select values 
of some resistors by measurement of a batch of the 
nearest preferred nominal types. Others will need to 
be made up by combinations of suitable values, these 
being indicated in the components list and in Table 1. 

Resistors R35 and R36 are made from resistance wire 
(eureka or nichrome) to give the required values to 
indicate 10mA and 1mA f.s.d. on the meter. The 
thinner the wire used, the shorter its length need be. 
It can be wound on any insulating former to hand. If 
the wire obtained is not insulated make sure that 
adjacent turns do not touch; it is probably a good idea 
to deposit molten wax on the finished article to keep 
the wire firmly in place. 

As an example, 38 s.w.g. eureka wire has a resistance 
of 23-8 ohms per yard or I -5 inches measures one ohm. 



Resistors 

Rl l-5k<) 



R2 
R3 
R4 
R5 
R6 
R7 
R8 
R9 

*RI0 
Rll 

>RI2 



l-Skli 

IkO 

27k ii 

68011 

I2k£15% 

22kti IW 

lOkfi 

5kn 

Ikii 

500 Q 



RI3 

RI4 

RI5 

*RI6 

RI7 

*RI8 

*RI9 

*R20 

*R2l 

*R22 

R23 

R24 



loon 
ion 

ISkQ 

30kQ 

IBkO 

5-4kn 

6kD 

9-6k« 

3kQ 

l2-2kQ 

1-Bkfl 

l-2kfi 



*R25 

*R26 

*R27 

R28 

R29 

R30 

R3I 

*R32 

*R33 

*R34 



13-8ki2 

1 35k Q 

60kil 

33ki> 

27k Q. 

ISkii 

IOkO 

6-4kn 

3-8kQ 

l-6k£l 



R35, 36 {see text) 



1A chassis or panel mounting fuseholder 



All 10%, £ watt except R7, R8, R35 and R36 
Resistors marked with an asterisk are not standard 
preferred values and should be selected from nearest 
preferred values, or made up from combination of 
two resistors to give each required value. See 
Table 1 

Potentiometers 

VRI 50kO linear carbon 
VR2 lOkH linear wirewound 
VR3 5000 linear wirewound 

Capacitors 

CI 16,/F elect. 450V C3 

C2 IVr elect. 450V C4 



I00 M F elect. 450V 
100/iF elect. 450V 



Transformers 

Tl Mains transformer (Parmeko type P2752) 

Pri.: +10, 0, 200, 220, 240V; 

Sec. 1 : 200-0-200V 75mA; Sec. 2: 6-3V IA; 

Sec. 3:6-3V2A; Sec. 4: 6-3V I A 

(Sec. 3 and sec. 4 are not used in this circuit) 
T2 Mains transformer (Douglas type MT I02AT) 

Pri.:0, 210, 240V 

Sec: 0, 19, 25, 33, 40, 50V 0-5A (Sec. 0-50V used for T2) 
T3 Same as T2 but Sec. 0--40V used 

Valves 

VI Gas filled stabiliser type 1 50C2 V3 6LI8 triode 
V2 Same as VI 



Diodes 

Dl BYZI2orSJ403 

D2 BYZI2orSJ403 

D3 G/3M 

D4 GEX54I 

D5-8 Meter bridge rectifier 1 0mA 

Meter 

Ml 0- 1 QOfiA moving coil 

Fuse 

FSI 

Switches 

51 Double- pole, on /off, toggle 

52 Double-pole, changeover, toggle 

53 2-pole, 6-way wafer (only I pole is used) 

54 Double-pole, changeover, toggle 

55 Single-pole, changeover, toggle 

56 2-pole, 6-way wafer (only I pole is used) 

57 Single-pole, 12-way wafer {only 3 ways are used) 

or 4-pole, 3-way (only I pole is used) 
SB 6- pole, 2- way (only 5 poles are used) 

Uniselector switch 

US I 3 or 4 banks, each 25 ways, coil resistance 75 Q 
Terminals 

X I , X2, X3 Screw terminals (3 off) 

Plug and socket 

PL I Mains plug, chassis mounting, type P73 

Miscellaneous 

Chassis lOin x 7in x 2in or made from aluminium 

sheet I4in x Min 18 s.w.g. 
Plywood or aluminium sheet for case I2in x Bin x 

Sin internal dimensions 
Clamps and insulation for C3 and C4 (2 off) 
Valveholders, B7G (2 off); B8A (I off) 
Tags boards, double, IB-way, 12-way, and 7- way 
Tag strip, single, 5-way 
Brackets for 1 8-way tag board 
Pillars, 2 Jin long, for 12-way tag board 
Grommets; 3-way terminal block 
Seven knobs, nuts and bolts, wire 



338 




Table 1: 


NON-STANDARD RESISTOR 




COMBINATIONS 




Required 


Resistor 


value Combination 


RIO 


SkO I0k£l - lOkii in parallel 


RI2 


SOOfl IkD - IkOin parallel 


RI6 


30k£> ISkfi I5kn in series 


RI8 


5-4ki> 2-7kii 2-7kH in series 


RI9 


6k Q I2kfl ■ 12k P. in parallel 


R20 


9-6k£2 6-8kO ; 27k fl in series 


R2I 


3kii 1-SkQ- l-5kft in series 


R22 


l2-2ki> I2k0 nominal selected by 




measurement 


R25 


13-8k<> 56k Q 1 8kQ in parallel 


R26 


I35k0. 560kH ISOkO in parallel 


R27 


60kU l20kQ r I20kil in parallel 


R32 


6-4ki» 33kO 8-2kfi in parallel 


R33 


3-8kO 8-2kiJ 6-8kil in parallel 


R34 


l-6kil 5-6kii 2-2k Q in parallel 



n 

5ec50V 



Fig, 4. Front pane! and chassis assembled. Hole sizes and 
positions will depend on the components actually obtained, 
but the wiring diagrams in Figs, S, 6, and 7 appear half scale 
and give a reasonable guide to positions 



I s r ff P* ■% 

i I I I 

,r]jr! Tr 



I I 



\*\W 



R. 
i|4m(3! [IZ"iHI ilOi i9i 

Hv : VV L r J v 



Ik. U_ ^tm ••• nil 



NASA 



w fill 

1241 fcs 

I, J L,J 



., 



J 



4N 



i i 

fR 1 '"(I" 1 

L,J i-,J 

I 



r — ^ 

|R :R 

ia! Izo! 



rii rii O 



jRiiR 
|f9i H8 r 

l,J LJ 

I 



i 

Si 



13) 




R6 US(e T2 V3 USla ,TZ T3 TE 1 -%^' FS1 

sec p,n6 ' y ' pii 

Priftwiw Moins 
Plug 



COMMON 



Fig. 5. Wiring the components on the front panel. The component group board Is tilted up to show connections, but 
is in fact fitted to brockets on the front panel. This drawing appears approximately half scale 



339 



NOTE 



Compontnt ftoord nounted 
on Pillars abovt C3andC4 



® 



To VW 



ToStc 



ToSW (GoSf (O) To 05 
Wiper v |-^ ^—^ 



for/'/l"/^/'//'/!/! /'/'/-//J /?/7/7/? /- 7/7 ~'/7/, 



Hipir 
taqs 



,. 




»SZb 

, Wip*r 



\ USI shown in schtmatk 
form to clarify wiring 

Fig. 6. Top side wiring of the chassis. Each dash on the uniselector represents an outlet tag; the wiper is at the right 
hand end and coil connections underneath (not visible here). The uniselector is mounted on pillars above the chassis. 
C3 and C4 are underneath the group board. This drawing appears half scale 



i£3^ 



jBSfc 




D2 C2 B3 m CI Rl H6 

Fig. T. Underside wiring of the chassis. The group board is tilted to show the component wiring clearly 
340 



Do not allow the wire to become stretched or the 
resistance will increase per unit length. The values of 
resistance needed for R35 and R36 will depend on the 
d.c. resistance of the meter coil. These can be cal- 
culated from the formula: 



Rs = 



Ru x /m 
Is — hi 



where R$ is the shunt resistance required, 
jRji is the meter resistance, 
/s is the current scale required, 
/m is the nominal current rating of the meter (in 
this case 100/<A). 

When making the calculation, resistances are in 
ohms and currents in amperes, so allowance must be 
made for the multiple and sub-multiple signs. 

Capacitors CI and C2 are tubular types and usually 
insulated. In any case the can of C2 must not be 
connected to chassis. C3 and C4 are the kind that have 
to be mounted vertically on the chassis, but here again 
the can of C4 must not be connected to chassis. It 
can be wrapped with plastics insulating tape. 

The transformers have been selected as being readily 
available types. TI has three 6-3 V windings but only 
one is used for V3 heater. If desired, one of the other 
6-3 V windings can be used to supply a panel bulb, 
although this is not shown. 

The diodes originally used were A El types SJ403 but 
it may be easier to obtain the Mullard BYZI2, which 
has a substantially higher current rating. 

The wafer switches are pre-assembled types that can 
be bought for a reasonable sum, but S8 may have to be a 
slightly more expensive "Yaxley" or "Maka-s witch" 
type. 

The uniselector switch is obtainable at many surplus 
stores. At least three banks are required and a 75 fi 
coil. Check the action of this component before 
buying to make sure that the wipers ride smoothly 
through the arc of contacts. This can be done by 
pressing the armature several times. No parts should 
be damaged otherwise operation may be intermittent. 
The uniselector has 25 ways; two series of 1 1 contacts 
on each bank are paralleled. 

FRONT PANEL 

Front panel mounting position is given in Fig. 4 with 
the wiring below it (Fig. 5). The wiring to S8 has been 
abbreviated in the interests of clarity, but it should not 
be difficult to ascertain the appropriate tags if wiring to 
them is followed in alphabetical sequence, from a pre- 
determined starting pole, in counter-clockwise fashion. 

The "common" terminal on the front panel must 
make either direct connection to the panel (if metallic), 
or wired to a chassis connection. 

Resistors for connection to S3 and S6 are mounted 
on an 1 8-way group tag board, which is fitted to the 
top of the front panel by right-angle brackets. If the 
resistors are uppermost, minor alterations to their 
values can be achieved in situ while the instrument is 
operating. 

CHASSIS CONSTRUCTION 

Drilling details of the chassis are not given because 
some adjustment may be necessary according to the 
components acquired. However, the top and under- 
side wiring diagrams of the prototype (Figs. 6 and 7) are 
drawn to scale to give reasonable indication of the 
positions of the components. 

Transformer Tl is mounted so that the turret tags 
project through the chassis for connection underneath. 




Photograph of a family of IciYc curves displayed on an 

oscilloscope 

If there are "screen" tags on the transformers these must 
be connected to chassis. 

The main power supply components are mounted 
on a group tag board under the chassis, while C3 and C4 
are fitted (as mentioned previously) to clamps on the 
chassis. It may prove to be helpful to make the holes 
for these large enough so that they can project through 
to about one inch below the chassis top. 

A 12-way group board is mounted on pillars above 
these two capacitors to take the resistors for USlb. 
Here again, easy access is achieved for alteration of 
component values. 

Finally, before going on to the operation, a word of 
warning: if it is necessary to make alterations while the 
instrument is switched on, be careful where you put 
your fingers and soldering iron. Components on the 
front panel, as well as T2 and T3 carry exposed live 
mains. 

OPERATION 

The curve tracer must be used in conjunction with a 
directly coupled (d.c.) oscilloscope. The time base 
must be capable of being switched out of circuit and a 
d.c. amplifier substituted in its place. Not all oscillo- 
scopes have this facility and it may be necessary to add 
an amplifier to the design of the unit. It need only 
have a modest gain of about a hundred times and quite 
a small bandwidth and could derive its power from the 
supply incorporated within the unit. 

The type of display obtained is shown in the photo- 
graph. The illuminated graticule shown in the photo- 
graph was made from £in perspex placed immediately 
in front of the oscilloscope screen. Edge lighting 
through one edge of the perspex by means of a low 
power bulb will light up the scribed scale lines. This 
graticule was found useful in calibrating the curves 
displayed on the screen. 

The photograph shows the /c/ Vc characteristic of a 
low gain pnp transistor having increasing values of 
reverse. base bias. The ninth and tenth bias values 
bring the transistor into its cut-off region and conse- 
quently only a single straight line is traced for both 
steps. -fa 



341 




So 



eyj ^/wm^ 





THERE ARE two kinds of electronic music effects circuit : 
one can be considered as self-contained and self- 
generating; the other is dependent on a sound source from 
a musical instrument. 

Sounds made by real cymbals or drums can be modified 
electronically to produce unusual effects. This is where 
the Drummer's Whoosh Unit comes in; this will be based 
on a modified version of the purely Electronic Cymbals 
described in the present article. 



The electronic cymbals unit uses the white noise 
generator (described in January) and a power 
supply (described in December) with a new filter circuit. 
The circuits of the white noise generator and power 
supply are reprinted in Fig. 1 so that the whole extent 
of the circuit involved is realised from the outset. 

The power supply is not shown in the photographs as 
it was external to unit, but there is plenty of room to 
incorporate it in the box if required. Alternatively, 
the performer may prefer to use dry batteries, so making 
the unit entirely self-contained and portable. 

If required to be housed in the same box as the 
Drummers Whoosh amplifier, this can still be done, 
but we would recommend the constructor to exercise 
some patience until next month's article appears. The 
same box can house one white noise generator and 
filter for both purposes, with modifications to suit the 
Drummer's Whoosh. 

With all these circuits it is necessary to add a power 
amplifier and, since there is a wide variety of commercial 
types available, the user should select one that will suit 
the environment in which he is performing. Tone 
controls are a desirable facility as will be seen later. 



SWITCHED FILTER 

One white noise generator will provide sufficient- 
output to operate a set of cymbal effects circuits of 
different pitches and qualities, giving a set of transis- 
torised "cymbals" of relatively small size, and at 
reasonable cost. The cymbals effect circuit is enclosed 
in the dotted line box in Fig. la. 

The 100 kilohm potentiometer VR1 controls the 
level of the white noise signal fed to the filter circuit. 
The white noise is filtered and deliberately "coloured" 
by transformer Tl and capacitor C5, then passes by 
way of C6 to the base of TR1. This transistor is 
normally biased into non-conduction by a negative 
supply applied through RIO. A 15V or 3V battery 
will usually suffice here, and serves to prevent a hissing 
noise between strokes. 



342 





10uF Xi* ME4I03 





CYM6ALS FILTER 
ATTACK* DEC* 



r«t 



C5 




O-OCHuF 
V 



To^HS^ 



Ti 



Fig. la. Complete circuit of the 
cymbals effect unit 



*LJ 



O-Iuf 



ISI50 



15150^ 

i 1 * 



S2o 




Si/ 

«^<- Br 



.08 _LC9 <^R9 , 
JW S50-0f_>K> 
PF ~jjF ^ 



^ W ?Efftct? 
jo output 

I" 



TR2 

C4Z4or 

ME4103 



RIO 

VW — E^ 



Puli« input _ WMA 



POWER SUPPtY UNIT 




Fig. lb. Modified 
power unit to 
supply negative 
bias 



In order to simulate a cymbal stroke, a positive pulse 
must be applied to the circuit via C7, and must be of 
sufficient magnitude to overcome the negative bias with 
ease, and cause TR1 to conduct. To obtain a realistic 
result, this calls for a pulse of at least 6 volts, and indeed 
any voltage up to about 50 volts may be used. 

A simple way to test the circuit would be to connect a 
! megohm resistor from C7 to the negative supply 
(common) line, and a Morse key or a push button 
switch from this input to the 18V to 24V positive supply 
line. A quick jab on the push button will charge up 
C8 via diode pump D2 and D3. C8 will then discharge 
by way of R8, R9, and TR1 . 

R8 and C9 act as a filter to reduce "thump" effects. 
As long as C8 holds sufficient charge, the potential 
maintained at the base of TR2 will cause TR2 to 
conduct, and to amplify the signal fed to its base via 
C6. As C8 discharges, the output from TRl will die 
away. This output is fed through a further filter-circuit 
(T2 and CIO) to the effects output jack JK2. 

It is worth mentioning that a l^V or a 3V battery 
connected between chassis and the negative bias line 
in this circuit will suffer negligible drain, and can be 
wired in permanently without any need for an on/off 
switch. A new leakproof battery would be likely to 
last for a number of years (well beyond normal shelf 
life), until corrosion sets in. 



WwloRH 



■_ Better results may be obtained from the circuit by 
using an adjustable negative bias. The power supply 
circuit in Fig. lb incorporates a negative bias supply 
suitable for the purpose. Bias adjustment may be 
used to control the decay time of the cymbal stroke. 

ASSEMBLY AND TESTING 

Prepare the printed circuit board according to the 
design shown (Fig. 2) and assemble parts on it as shown 
in Fig. 3. Fig. 2 shows the hole-spacing to suit a 
TOS transistor encapsulation, and this spacing will suit 
type C424. If type ME4103 is used, the hole spacing 
may be made closer to suit the TO 1 8 leadout arrange- 
ment of this transistor. 

When assembly of the components on the cymbal- 
effects circuit-board is complete, wire it up to a 
white noise generator, d.c. power supply of 18V to 24V 
and an audio amplifier or mixer unit. Temporarily 
connect the positive supply line to the junction of 
D2and D3. Switch on and adjust VRl and the controls 
on the amplifier so that the sound of the white noise 
generator comes from the loudspeaker as a loud hiss. 

Disconnect the positive line from D2 and D3. The 
sound should die away fairly rapidly. With some 
transistors, the sound will fade to a very low level 
without the need for a negative bias supply; others may 
need the application of a negative base bias via RIO, 



343 




Fig. 2. Printed circuit pattern 
for cymbals filter (full size) 



TO S2a 



Fig. 3. Layout of components on the printed circuit board 







PULSE INPUT 
TO JK1 & S1 



*"■! ' TO JK1 



-vtBIAS FROM VR1 WIPER © = TURRETUG 



COMPONENTS 



* • • • 



Resistors 

R7 1M£) R9 lOMil 

R8 IMQ RIO 10MQ 

All 10%, £ watt carbon 

Potentiometer 

VRI lOOkO log, carbon 



Capacitors 

C5 0-00 1 M F 



C6 
C7 
C8 
C9 



OI^F 

0-I^F 
0-0 1 M F 



CIO 00033/iF 



All low voltage 
> polyester or 
paper 



CYMBALS FILTER 

Transformers 

Tl, 2 Transistor transformers type 
LT44 (2 off) 



Transistor and Diodes 

TR2 ME4I03 or 

C424 (S.G.S. Fairchild) 
D2andD3 IS 1 30 (2 off) 



Jacks {with Plugs) 

JK I , JK2 Standard ±in jack sockets 
(2 off) 



Switches 

SJ Single pole push on, release off 

push button 
S2 Double pole on/off toggle switch 
(S2a in low voltage line: 
S2b mains input to power 
unit if used) 



Miscellaneous 
Printed circuit board 
Single core screened cable 
Chassis I2in x 4in X 2yin 
Knob 

Component layout shown in Figs. 2 and 3 




344 



COMPONENTS 



POWER SUPPLY UNIT 

Resistors 

Rll 47fl RI3 I-8Q 

RI2 47 £2 RI4 I Mil IO%iW 

All 5% 3W,-wirewound except RI4 

Potentiometer 
VR2 2Mfi linear carbon 

Capacitors 

CM 1,000/tF elect. 2SV 

CI2 I.OOO^F elect. 25V 

CI3 l t 0O0ftF elect. 25V 

CI4 I ><.F polyester 160V 

CIS 5<VF elect. 25V 

CI6 I pF polyester 160V 

CI7 0-l^iF polyester 160V 

Transformer 

T3 Mains transformer, charger 
type. Pri. 240V mains; sec. 0-I7V I A 



Transistors 

TR3 XCI4I 



TR4 AC 1 76 



Diodes 

D4 to DtO DDG00 (Lucas) (7 off) or IS 130 

Switch 

S2b (see under Cymbals Filter) 

Miscellaneous 

FSI Fuse 0-5A with holder 
LP) Neon panel indicator with resistor 
Printed circuit board 6in x 2£in 
Heat sink for XCI4I 
Knob 
Component layout given in December 1967 issue 



in order to achieve a quiet background in between 
strokes, and a HV battery is usually quite sufficient. 

If the positive line is quickly touched on to the junc- 
tion of D2 and D3 a few times in succession, a sound 
similar to a cymbal stroke may be heard, but may not 
be very realistic at this stage, as adjustment of VR1 
and the tone controls of your amplifier will have a 
considerable effect on the output qualities. 

VR1 must not be set too high, or the effect will result 
in a continuous roaring or crackling sound. This is 
because the white noise is fed to the base of TR 1 at a 
high level to overcome the negative bias. Turn down 
VR1 to a level somewhat below that at which the roar 
occurs. If, now, the cymbal strokes tend to have a 
somewhat crackly ending, VR1 must be set to an even 
lower level to give a smooth finish to each stroke. 

VARIATIONS 

The circuit is not by any means restricted to the 
component values given. By changing the values of 
C5 and C10 the cymbals pitch may be altered; the use 
of different transformers will give yet further ranges 
of effects. A choke or other inductor could be used in 
place of T2, and the output taken from the collector of. 
TR1 by way of an 01/fF capacitor. 

Changing the values of C7, C9, and R9 will affect 
the "attack" and "decay" characteristics of the circuit, 



WHITE NOISE GENERATOR 

Resistors 

Rl 4-7kS2 R4 2-7kii 

R2 4-7kO R5 I5kil 

R3 39kft R6 Ikfi 

All 10%, i watt carbon 

Capacitors 

CI 25,iF elect. 25V 
C2 10/iF elect. 25V 
C3 lOO^Felect, 12V 
C4 10^F elect. 25V 

Transistor and Diode 

TRI C424 (S.G.S. Fairchild) or ME40I3 
D! Point contact diode, any noisy 
type, such as sold for crystal 

receivers 

Miscellaneous 

Printed circuit board 2in ■ 2in 

(Bonanza Board) 
Connecting pins and wire 
Component layout given in January 1967 issue 

Components for cymbals fitter given an 
previous page 




although the combine ji value of R8 and R9 should 
not be reduced to a poi|t which would result in excessive 
collector-dissipation iif TRI (rated about 200mW in 
free air). 

METHODS OF OPERATION 

For manual operation, the simplest method is to 
connect a 1 megohm resistor (R7) from C7 to the 
negative (common) supply wire, and apply pulses to this 
input from the 18V to 24V positive supply point by 
use of a Morse key or a push button switch. The 
final circuit shown in Fig. 1 performs the same function. 

The circuit may also be operated electronically by 
connecting C7 directly to an electronic switching 
circuit (via JKl) such as a slow running multivibrator 
(for automatic "repeat" effects); a ring counter (for 
rhythm effects) or an electronic keying circuit. In all 
these circuits the pulse may be supplied from the 
collector of the switching transistor concerned. If 
using the multivibrator described in the article on a 
Simple Rhythmic Control Unit (February issue) JKl 
would be connected to the collector of either TRI or 
TR2 in that circuit. 

The "Cymbals" circuit may be used very successfully 
with an electronic rhythm machine or a rhythm genera- 
tor. An adaptation of the circuit may be used for 
beat group sound effects; this will be described next 
month in the Drummer's Whoosh Unit. 



345 





S7ira 



BEGINNER'S GUIDE TO ELECTRICITY 

By Clement Brown 

Published by George Newnes Limited 

185 pages, 7£in. X Sin. Price 15s 

Anyone starling a career or hobby in electronics 
mighi be put off by the title of this book when 
looking for an elementary guide. In order to under- 
stand and appreciate the technicalities of even the most 
simple of electronic circuits, one should have, or be able 
to grasp, the fundamentals of basic electricity. Jt 
comes at a time when more and more schools and 
training colleges are giving courses in the subject, and 
is therefore suitable for almost any beginner from 
14 to 40 years of age. 

It is written in an intelligently straightforward style 
that will complement course lectures and lab. experi- 
ments. Of necessity it is not by any means exhaustive 
but will certainly cover in adequate terms the theory to 
be found in advanced level G.C.E. and O.N.C. courses. 
Electronics is not strictly introduced until Chapter 7, 
and even then in only basic form. 

Technical terms tend to baffle many beginners, but 
here they will find explanations easily understood, and 
related to everyday electrical appliances and electronic 
circuits. Valve and transistor theory is included. The 
relationship between theory and domestic and industrial 
applications provides a suitable balance to a book that 
could otherwise have been rather dry reading. 

The final chapter gives some guidance for those 
wishing to make a career in this fascinating activity. 

M.A.C. 



ABC's OF TRANSISTORS 

By George B. Mann 
1 12 pages. Price 20s 

F.E.T. CIRCUITS 

By Rufus P. Turner 
160 pages. Price 25s 

ABC's OF VACUUM TUBES 

By Donald A. Smith 
128 pages. Price 20s 

BRIDGES AND OTHER NULL DEVICES 

By Rufus P. Turner 

143 pages. Price 26s 

Published by W. Foulsham & Co. Ltd. 

All 8|in x Si in 

Another four titles 
Foulsham Sams 
expanding technology. 



in the impressive catalogue of 
educational primers in an 
All four of the books present 
their subjects with a minimum of mathematics apart 
from the last title which sets out the necessary bridge 
equations happily, without qualification. Treatment of 
tjie subject matter is succinct and well illustrated and all 



four volumes are recommended as beginning texts for 
those anxious to be taught the rudiments of electronics. 

ABC's of Transistors deals simply with the basic 
physical and electronic features of these devices and 
analyses their action in oscillators and amplifiers. 
Practical servicing and testing procedure of these 
circuits are also discussed. 

F.E.T. Circuits is an excellent book for those readers 
who like their electronics practical. From a brief 
introductory chapter on structure and performance you 
are launched into the whole gamut of circuit applica- 
tions of this versatile high impedance device: trans- 
mitters, receivers, test gear, control circuit, each one in 
effect a potted constructional project as all component 
and performance details are given. 

ABC's of Vacuum Tubes. Dealing in the main with 
the construction and action, both dynamic and passive, 
of valves from the diode to the multigrid family. 
Biasing and classes of operation are covered and the 
final two chapters deal with miscellaneous and special 
purpose valves. Altogether a painless introduction to 
valve technology. 

Bridges and Other Null Devices. Measurement is 
fundamental to all sciences. In electronics the bridge 
type circuit predominates in this application and this 
book sets out to explore its various forms for specific 
measurement purposes. From basic bridge circuit 
theory the reader is introduced to most of the equipment 
found in a test gear laboratory. Although the illustra- 
tions are of American equipment, the principles and 
measurement capabilities are universal. 

G.G. 



COLD CATHODE TUBES 

By J. B. Dance, M.Sc. 
Published by lliffe Books Ltd. 
125 pages, 8fin x 5£in. Price 35s 

In a world largely dominated by the semiconductor, 
glass enveloped devices are becoming increasingly 
rare. But one group of tubes seems to have gained a 
new lease of life due, indeed, to the general expansion of 
electronic techniques brought about by solid state 
devices. For visual displays of data, or indication of 
the operational condition of circuitry, there is no real 
substitute for the cold cathode tube. This can be a 
simple neon lamp (which may double as a voltage 
regular), or a rather more complex numerical or 
character indicator tube. The orange-red glow of neon 
is the outward manifestation of electronic sophistry, as 
we well know. 

But the cold cathode tube family includes the well 
known CM. tube for nuclear radiation detection, 
stepping tubes for counting circuits, and other 
important specialised types, besides. 

The electronics enthusiast who is "genned up" on 
solid state may be lacking in knowledge about cold 
cathode tubes. He can now find the basic facts of gas 
discharges and straightforward descriptions of those 
tubes he is most likely to encounter in modern electronic 
apparatus in this book. Some experiments with neon 
diodes and trigger tubes are described and there are 
many practical circuits which show typical applications 
of the various devices. A good practical introduction 
to the subject, with a minimum of maths. 

D.D.R. 



346 



Transistor Amplifier 



SUC1H 



NEGATIVE 
FEEDBACK 



By A.Foord 



Hi 



'-.--.'-■ :J "' -•',;"-' ■ 



■V',-:- 



Negative feedback occurs when a proportion of 
the output voltage of an amplifier is fed back to 
the input in such a way as to reduce the overall gain, 
so that the gain with feedback is less than the gain 
without feedback. Feedback can be used to: 

(1) Give a predictable mid-band gain, the greater 
the amount of feedback the less sensitive the 
amplifier is to changes of transistor character- 
istics. 

(2) Increase bandwidth or to give a shaped fre- 
quency response curve which depends almost 
solely on the passive components forming the 
feedback network, and does not depend on an 
accurate knowledge of transistor parameters 
(which may vary between one specimen and the 
next of the same type). 

(3) Increase or decrease input or output impedances; 
by using different feedback arrangements it is 
possible to obtain input or output impedances 
higher (or lower) than those normally associated 
with transistor stages. In particular it is possible 
to arrange for a high input impedance and a 
low output impedance, so that amplifier stages 
can be cascaded without interaction. 

(4) Reduce the distortion which normally occurs in 
the final stages of an amplifier, where current 
and voltage swings are highest. 



BASIC PRINCIPLE 

Any study of negative feedback begins with a func- 
tional block diagram, Fig. 4.1. 

The circuit has two signal paths: the forward path, 
which is usually an amplifier and contains all the 
active devices, is marked with its voltage gain A ; the 
feedback path B which has a gain less than unity. 
The bar above the symbol A indicates that there is a 
phase reversal in the amplifier, while B represents the 
fraction of the output voltage fed back to the input. 



The phase reversal to obtain negative feedback 
occurs in the amplifier; the arrows in the block diagram 
reassure us that the feedback is in fact negative. In a 
simple case this is obvious, but for more complicated 
arrangements a check will ensure that we do not 
accidentally use positive rather than negative feedback. 

Take a simple example, Fig. 4.2. Without feedback 
we require an input of OTV to the amplifier for an 
output of — 10V. If negative feedback is added 
making B equal to 01 times, 0-1V is still required at 
the input of the amplifier itself to obtain an output of 
-10V. 

The input to the addition point needs to be 1*1 V, so 
that when the — 1 *0V is added to the input we are left 
with 0-1V to give an output of I0V. The overall gain 
with feedback is now 



G' = 



-10 
11 



9-1 limes 



The negative feedback has reduced the gain from its 
open loop value of 100 times to a closed loop gain of 
91 times, therefore the closed loop gain is approxi- 
mately XjB times (1/5 = 10). 

A more detailed examination will show that the 
gain with feedback is approximately \jB provided the 
closed loop gain is much less than the open loop gain, 
Fig. 4.3. 

Starting at the input to the amplifier (call this V) 
then the output of the amplifier is A V, the voltage fed 
back is A VB, and the input k V + A VB. Then the 
overall gain with feedback is given by 



C 



Vo 

Vi 



AV 



-1 



AVB 



1 4- AB 1 r _ 
A + B ' 



If B is much greater than If A (i.e. A is much greater 
than \jB) then G = l/B. 



«*>+ 



r fb 




*-<?■ 



Fig. 4.1. Functional dia- 
gram of an amplifier with 
negative feedback path 



fig. 4.2. A simple example 
of negative feedback 



3VB 

V x *V + AVa*V{\+AB) 

Fig. 4.3. Voltage relation- 
ships between the amplifier 
and the feedback circuit 



347 



1111 ." 




^ 



A 



FREQUENCY 



FREQUENCY 



Vv- 



/^ 




SATISFACTORY 



UNSATISFACTORY 



Fig. 4.4. Gam and phase 
characteristics which would 
cause instability 



Fig. 4.5. instability shown 
by "ringing" cycles 



Fig. 4.6, The practical 
example of a high gain 
amplifier with feedback re- 
sistor and "anti -ringing" 
capacitor C 



Therefore, the ideal gain with feedback (C) is equal 
to 1/B, if the gain without feedback (A) is much 
greater than 1/5. 

To confirm this, compare the results using the 
accurate formula and the approximate formula; drop 
the minus phase sign since we are interested in magni- 
tudes rather than the phase reversal we know occurs in 
the amplifier. 



Actual closed loop gain 



Ideal closed loop gain 



C ■> 



1 -f AB 



r l 
G =_ 



Calculation will show that, if the required gain with 
feedback is one tenth of the gain without feedback, 
then we do not need to use the accurate formula, since 
errors in assuming G equal to 1 IB are small enough to 
be discounted. 



STABILITY 

Having assumed that the design of the amplifier is 
such that the feedback will always tend to reduce the 
gain, but unfortunately this will not always be so, any 
practical amplifier will contain reactive elements which 
will introduce a phase shift in the signal as it passes 
through the amplifier (quite apart from the 180 degree 
mid-band phase shift required to obtain mid-band 
negative feedback). The gain and phase characteristics 
of the amplifier might appear as Fig. 4.4. 

Above a certain frequency f, gain falls and an extra 
phase lag is introduced. If we applied 100 per cent 
negative feedback to an amplifier with this character- 
istic, to give an overall gain of unity, the amplifier would 
oscillate. 

While there is still greater than unity voltage gain 
around the loop, there is an extra 1 80 degrees of phase 
shift to cause the feedback (which was negative below 
/) to become positive at /'. The system would there- 
fore oscillate at the frequency f. 

Designing for stability is complicated when a con- 
siderable amount of feedback is applied, instability 
in a feedback amplifier is shown by a peak in the 
frequency response curve and ringing on a square 
wave signal (see Fig. 4.5). 

Feedback over one or two stages is normally safe, 
although later on, when considering the use of 100 per 
cent feedback to raise input impedance, a non-mathe- 



matical approach will be applied to the stability 
problem. For most purposes, it is in order to see that 
the frequency response curve does not have a peak of 
more than a couple of decibels in it, and that the square 
wave response is satisfactory, i.e. free from ringing 
effects. 

The photographs show results obtained with a high 
gain amplifier, this had a gain of 1,000 times (60dB) 
without feedback, and a gain of 10 times (20dB) with 
feedback (see Fig. 4.6). 

Photo A shows the leading edge of the I kHz square 
wave input ; photo B shows the ringing on the output 
waveform without the capacitor C, and this was con- 
sidered unsatisfactory. The capacitor was adjusted in 
value to obtain the acceptable response of photo C. 
Since for clarity the photographs only show the leading 
edge of the square wave, the time scale was extended to 
show the leading edge more clearly. The capacitor 
was increased to reduce the bandwidth to 20kHz 
which increased the rise time to that shown in photo D. 

Feedback around one stage only is called local feed- 
back, and since only the common emitter stage pro- 
vides a phase reversal of its output signal with respect 
to its input, it follows that local feedback can only 
be applied around the common emitter stage. 

There are two basic ways of applying feedback to 
the common emitter stage; one arrangement is con- 
sidered next, and the other is dealt with later, in the 
section on virtual earth amplifiers. 

SERIES LOCAL FEEDBACK 

Referring to Fig. 4.7, the resistor Rv. in series with 
the emitter accounts for the applied feedback, this 
resistor enables a feedback voltage Vt proportional to 
load current, to be fed back in series with the input 
voltage V\. The base-emitter voltage of the transistor 
is reduced by the feedback so that Kn E is less than V\. 

If Rf. is small and of the same order of value as the 
internal emitter impedance rn (say 100 ohms or so), 
then the amount of feedback is small. Distortion is 
slightly reduced and bandwidth is increased very 
slightly, at the expense of a small decrease in gain. 
If Re is large then the gain is given by 

G - n ~ m 

The input impedance is given by 
Zi = htcRiz 



348 




INCREASING * E 




FREQUENCY Hz 



Fig. 4.t. Strict local Fig. 4.8. The effect of Rf 
feedback by the unby- on gain and frequency 
passed emitter resistor response 




Fig, 4.9. Emitter follower output to prevent undue 
loading on the amplifier stage 



In practice for a single stage amplifier biased in the 
normal way with a divider chain on the base, this 
increase In input impedance is masked to some extent 
by the shunting effect of the chain. The effect of Re 
on gain and frequency response is as shown in Fig. 4.8. 

To avoid loading J?l and to maintain a high gain 
without feedback, the output can be taken via an 
emitter follower, a practical circuit is shown in Fig. 4.9. 

Since the transistor is used in common emitter we 
must work out approximately the bandwidth we would 
expect. For TR 1 the collector current is of the order of 
0-5mA. Suppose the transistor current gain is typically 
50 at 0'5mA. The 3dB down point in common emitter 
is given by 

1,000 



J Ate 



50 



/ = 20kHz. 

One would expect the response to roll off somewhere 
at this frequency, the exact point depending on Are and 
ft for the particular specimen of transistor. Since 
TR2 acts as an emitter follower the overall frequency 
response is limited by TR1 since an emitter follower 
has a 'frequency response far better than that of a 
common emitter stage. 




Photo A. Leading edge of the I kHz square wave 



Photo C. Ringing is brought down to an acceptable level 
by selection of a parallel capacitor across the feedback 
resistor 




Photo 8. Ringing caused by non-selective feedback 



Photo D. 
rise time 



Larger value of capacitance increases the 



349 



The results without feedback (C2 connected) and 
with feedback are: 



Gain without feedback 
Bandwidth 
Input impedance 
Output impedance 
Maximum output 



310 times 50dB 

30kHz 

IkO 

300 Q 

1-5V r.m.s. no load 

500mV r.m.s. into lkH 



The frequency response was measured under no load 
conditions at lOOmV r.m.s. Up to 50kHz or so, the 
amplifier will provide 500mV r.m.s. into 1 kilohm, but 
above this frequency the emitter follower current gain 
starts to drop and the waveform distorts, so that 
500mV would only be obtained without distortion into 
a load greater than 1 kilohm. 

The gain without feedback appears high until we 
remember that the collector load is 27 kilohms rather 
than the 1 kilohm or so we would expect for another 
common emitter stage and a high gain transistor is 
being used. 



Gain with feedback — = 10 times = 20dB 

Bandwidth 
Input impedance 
Output impedance 
Maximum output 



27 
2-7" 
68kHz 
7k a 
300fi 

500mV r.m.s. into 
(up to 50kHz) 



IkO 



The actual measured gain was 19*5dB, which is 
probably an error in measurement or tolerances on the 
collector and emitter resistors. Since the open loop 
gain is 30 times the closed loop gain, one might expect 
the gain of 20dB to be independent of variations in 
characteristics between one OC75 and the next, 
although the bandwidth might alter slightly. 

Although the gain has been reduced by a factor of 
30 times, bandwidth has only increased twice. Series 
local feedback is often used inside another overall 
feedback loop, where a predictable stage gain is 
required rather than an unpredictable (though higher) 
gain. 

With an input impedance of 7 kilohms and an output 
impedance of 300 ohms, these amplifiers can be cascaded 




GAIHdB 
A1 AZ 40 

A1 OR A2 20 



12<ffi/0CTAVE 



6dB/0CTAVE 



& 



"\ 



FHE0UEMCY 



M 



Fig. 4.(0. Combining 
two identical amplifiers 



Fig, 4.11. The response of 
each amplifier is added 
to give overall response 



^***y R R R **\^ R 

- GAiM>YWYSAAfWS- t c *$ > ~t' w t~ 

T T T T J -L 



Fig, 4.12. Equivalent cir- 
cuit of a transistor looks 
like that of a transmission 
line at high frequencies 



Fig. 4.13. A single CR 
conversion of Fig. 4.12 



without interaction. Bandwidth is also extended at 
the low frequency end, but since this is within our 
control (coupling and decoupling capacitors) the main 
benefit of this type of negative feedback is the pre- 
dictability of mid-band gain rather than the small 
extension of bandwidth. 

TRANSFER FUNCTIONS 

The amplifier can be represented as a block, so that 
two amplifiers in series could be represented by adding 
the two separate gains in decibels (see Fig. 4.10). 



A, 


■= 10 times 


20dB 


A, A., 


= 100 times 


A ? 


-= 10 times ■ 


20dB 




= 40dB 



Working on the frequency response curve and adding 
decibels this would result in the response shown in 
Fig. 4.11. 

















20 
IS 
10 






At 






























































AZ 
























































1 



-3 

3 
3. 

m_ 


i SLOPE 6d»/ OCTAVE 




































IZOaa/DECADEJ « 






































35 

30 
l 25 
\ 20 

to 






>* 
















AWROXIMAI 


E CUR 


VE 




















!■"! 


B 


»■ 


"* m 


^-^S^ 
































"^J 


^ 






























i 


h-^ 


























ACCURATE CURVE — 




>s 
























_ 






$! 


s 






0-1 1 t lOf 


























Kg 
res 
ret 


FREQ 

. 4.14. Appro xi'm 
pome, then der 
ponse (solid line) 


UEHCT 

oting t 
iving t 


he freqt 
he ace 


iency 

urate F 


t 2 5 10 20 50 U 

FREQUENCY (kHz) 
fg. 4. 1 5. Summing the response of two amplifiers in cascade 


n 



350 



Where each amplifier was 3dB down (at /), the 
response is now 6dB down (for two identical amplifiers), 
and the new 3dB down point is lower down at/i, as one 
would expect. The slope of the curve for a single 
amplifier is approximately 6dB per octave, and for 
two amplifiers in series this will be 12dB per octave. 

In the equivalent circuit of a transistor (Fig. 4.12) it 
appears as a transmission line for high frequencies, but 
as a first approximation it can be considered as a 
single CR network, Fig. 4.13. 

Taking the CR network or single time constant on 
its own, at low frequencies C has a high impedance 
and Vq = V. At a frequency when C has a reactive 
impedance equal to R, V Q is 3dB down with respect to 
V, and continues to fall at 6dB per octave (20dB per 
decade) with increasing frequency, as in Fig. 4.14. 

The solid line curve is the accurate frequency res- 
ponse, while the dotted line is the straight line approxi- 
mation. The point / where the impedance of the 
capacitor is equal to the resistor is called the "turnover" 
or break point. The maximum error between the 
accurate and straight line approximation is 3dB which 
occurs at the break point. In practice the approximate 
curve is drawn; /is 3dB down, 0-5/ and 2 /are ldB 
below the approximate curve; the accurate curve is 
drawn from this information. 

For two amplifiers in cascade the procedure just 
outlined is shown in Fig. 4.15. The bandwidth of the 
two amplifiers in series is almost identical, but the 
ultimate slope is now 12dB per octave rather than the 
6dB per octave for a single common emitter stage. 

RELATION OF RISE TIME AND 
BANDWIDTH 

A square wave can be considered as the sum of a 
number of harmonically related sine waves; these 
include a fundamental sine wave at the basic repetition 
frequency and frequencies of three, five, seven times, 
and so on (odd harmonics of the basic frequency). 

If a square wave of 1kHz is fed into an amplifier with 
a sharp cut off at l-5kHz all the harmonics are filtered 
out, leaving only the 1kHz fundamental, Fig. 4.16. 

If the response of the amplifier is extended to 20kHz 
the output would consist of the fundamental and 
harmonics up to 19kHz. Harmonics at 21kHz, 



I\I - 




INPUT OUTWIT 


Fig. 4.1 6. * A square wave signal can be filtered to 
give the fundamental frequency only 


_TLP- 




INPUT r OUTPUT » 
1kHz 1kHz 


Fig. 4.17. Increase in the rise time of the square 
wave by loss of harmonics 



23kHz upwards would be attenuated according to the 
roll-off of the amplifier response curve. The square 
wave would hardly be degraded at all, since the ampli- 
tudes of these harmonics (relative to the fundamental) 
are small. The loss in harmonics increases the rise 
time of the square wave, Fig. 4.17. 

To determine the bandwidth of an amplifier we would 
feed in a square wave with a rise time better than we 
would expect the amplifier to handle, and measure the 
degradation on the output. 

Suppose our square wave had a rise time of 5/ts and 
after passing through the amplifier this was degraded 
to 25/fs, then our amplifier has a rise time of \/(25 3 - 5 2 ) 
or 24-5/ts and its bandwidth is given by: 



/- 



0-35 



_0-35 

rise time 24-5 



x 10« = 143kHz 



This method is only an approximate means of deter- 
mining bandwidth, it would tell us if our amplifier had 
a bandwidth of 20kHz- or 10kHz, but we could not rely 
on discriminating between bandwidths of 20kHz and 
17kHz. 

However the edges of the square wave do represent 
the type of signals present in a transient, Which simple 
sinewave testing cannot do, so that we can see immedi- 
ately any instability or excessive overshoot or ringing 
in the amplifier. The disadvantages are that we do 
need a square wave of good rise time, and an oscillo- 
scope capable of showing it. 

Next month: Negative feedback applied to prac- 
tical circuits. 



BETTER SOUND 

The BBC announces that four programmes in a new 
series "Better Sound" will be broadcast on Fridays 
at 7.00-7.30 p.m. in Study Session, Radio 3 from May 3 
to 24. Listeners will be invited to send questions of general 
interest, or requests for more information on particular 
topics covered in the series and these will be dealt with in 
two extra programmes which will follow the repeat of the 
series later in the year. 

The series will be repeated on Radio 4 on Saturday 
mornings at 11. 00-1 1 .30 a.m. from August 17 to September 
14. There will be no programme on August 31 (Bank 
Holiday weekend), but there will be two additional pro- 
grammes on Saturdays, September 21 and 28. 

Each programme will focus attention on one area of this 
wide field. A number of topics (e.g. microphones, loud- 
speakers, stereo) will therefore be treated in more than one 
programme. Advice on particular makes cannot be given 
and the construction and repair of equipment will not be 
dealt with. 

Programme 1 : Transmission and reception of radio, 
including stereophonic broadcasting. Explanation of 
AM and FM, etc. 

Programme 2: The nature of sound, and room 
acoustics, with demonstrations of the effect of different 
placings of microphones and loudspeakers. 

Programme 3: The reproduction of music in mono 
and stereo; hi fi equipment. 

Programme 4 : Tape-recording for the amateur. 
The diagrams in the Study Notes (BBC Publications, 
2/6 plus 5d postage) will be helpful in following the broad- 
casts and the explanations in the text of the basic principles 
of the transmission, recording and reproduction of sound 
in mono and stereo will be useful for reference, particularly 
for the less knowledgeable listener. 



351 



1?^^. 



«f 



ERIMENTER 



*£ 



• By M.L. Michaelis M.A 



/^RADIOACTIVITY MEASUREMENT; STRACE RADIATION METER 



Previous articles in this series have discussed nuclear 
radiation, atomic structure, and the practical 
applications of nucleonic measurements; measuring 
methods and various kinds of detectors have been 
considered in a general Way. A distinction lias been 
made between activity measurements and energy 
measurements, and electronic methods for sorting 
electrical pulses sfrom a spectroscopic, i.e. energy- 
distinguishing, nuclear radiation detector explained. 

Mow theiPoint is reached where wc have sequences of 
pulses, ready for activity determination, i.e. for counting 
the numbers arriving per unit time, corresponding to the 
numbers of radioactive atoms disintegrating per unit time! 
This counting process is the function of the actual radiation 
meter unit in any nucleonic equipment. This month, we 
will discuss the basic requirements and electronic circuit 
techniques which are involved. It is quite immaterial 
whether the pulses originate from a non-spectroscopic 
detector like a G.M. counter, or from a spectroscopic 
detector such as a scintillation detector with kick-sorter 
amplifier. 

In the former case, the mean pulse frequencies may 
correspond to the gross activity of a mixture of different 



kinds of radioactive atoms, whereas in the latter case, the 
activity of a particular species of radioactive atoms can be 
observed selectively, to the exclusion of others which may 
be; present at the same time in the radioactive sample. 
However, the principles of making activity measurements, 
and the structure of the radiation meter used for the 
purpose, are the same in both cases. 



ACTIVITY AND DETECTION EFFICIENCY 

The activity of a radioactive sample is the number of 
atoms disintegrating in it in unit time, irrespective of the 
type of disintegration or the energy of the emitted nuclear 
radiation. We have already seen {in Part 3) that the unit 
of activity is the curie (Ci), corresponding to 2*2 x 18 12 
distintegraiing atoms per minute. This is the activity of 
I gram of pure radium, by definition. Convenient prac- 
tical units for amateur measurements are the pko-curie 
(pCi), corresponding to 2-2 disintegrating atoms per 
minute in the given sample, and the nano-curie (nCi). 
corresponding to 2,200 distintegraiing atoms per minute 
in the given sample. 

ft is customary to take one minute as the time unit for 
radiation meters, so that their essential function is to 
determine the pulse counts per minute. The abbreviation 
c.pm. is conventionally used for "counts per minute" 



STRACE 

RADIATION 

METER 



352 




It is not possible to calibrate a radiation meter directly 
in pCi or nCi, but only in c.p.m. This is because the 
ratio of c.p.m. to pCi depends on the numerical detection 
efficiency of the radiation detector employed. The ratio 
is 2-2 only if every disintegrating atom in the radioactive 
sample produces an electrical response pulse in the de- 
tector. This is rarely the case in practice; a greater or 
smaller proportion of the radiations will miss the detector, 
so that the ratio c.p.m. /pCi is practically always con- 
siderably less than 22. Of course, it is the aim of any 
detector and sample arrangement to achieve as high a 
numerical detection efficiency as possible. This is also 
referred to as the geometry factor. 

TWO EXAMPLES 

Two examples will make this point clear. 

In the first case, consider a radioactive sample lying on 
a large flat radiation detector, i.e. G.M. counter. The 
nuclear radiations may be emitted in any direction by 
chance. Thus, on the average one half of them will fly 
upwards or obliquely upwards, and miss the detector. 
The other half will travel downwards or obliquely down- 
wards, and enter the detector to produce a pulse. The 
ratio c.p.m. /pCi would be M in this case. 

In the second case, consider the sodium iodide crystal 
of our scintillation detector {see Part 5), with the radio- 
active sample placed at the bottom of the axial sample 
well. Nuclear radiation emitted in almost any direction 
will then strike the crystal, so that we would expect very 
nearly the ideal value of 2-2 for the ratio c.p.m. /pCi. 

In practice, we actually find values considerably smaller 
than 1*1 and 2*2 for the respective cases, because two 
further factors reduce the detection efficiency. Firstly, 
some quanta of radiation may be absorbed within the 
sample, or other insensitive material, before reaching the 
sensitive detector region. Secondly, some quanta may 
pass straight through the detector without getting absorbed 
to produce a pulse. Thus the ratio c.p.m./pCi is only 
about 0-1 for a liquid sample in the Mullard MX124/01 
G.M. counter tube specified for our equipment (see 
Part 4). The scintillation detector possesses a considerably 
greater detection efficiency, under some conditions 
approaching closely to the ideal value of 2-2 for the ratio 
C.p.m./pCi. 

RADIOACTIVE DECAY 

Since the activity of a given radioactive sample is a 
statement of the number of atoms disintegrating per unit 
time in that sample, this activity must necessarily diminish 
with the progress of time, because the number of atoms 
left over is continuously decreasing. For any given 
species of radioactive atoms, the activity is strictly pro- 
portional to the number of atoms of that species which 
are present in the sample, i.e. the rate of decay is directly 
proportional to the amount present. 

This is the basic characteristic of any exponential 
process (the rate of fall of the voltage across a capacitor 
discharging through a resistor is always proportional to 
the actual voltage left across the capacitor at the instant 
considered, or the rate of growth of a sum of money on 
compound interest is at all times proportional to the 
accumulated capital). Thus the activity of a simple 
radioactive sample decreases exponentially with time. 
This is a very important principle, known as the radio- 
active decay law. 

Different species of radioactive atoms decay at different 
rates, which are specifically characteristic of the respective 
species, just as different capacitor/resistor combinations 
discharge at different rates according to the produce of 
capacitance and resistance (time constant) of the circuit. 

DECAY HALF-LIFE 

For radioactive samples, we specify a decay half-life. 
This is the time taken for one half of a large initial number 
of atoms to disintegrate. If we wait a further equal period 
of time, one half of the remainder will have disintegrated, 
i.e. the number of atoms still left over is halved during 
each successive half-life period. The process theoretically 
never goes to completion. The smaller the number left 
over becomes, the greater the random departures from 




One of the rotemeter 

modules of the 

STRACE Radiation Meter 



smooth exponential decay. Ultimately, when only one 
atom is left over, it is inherently impossible to predict how 
long it wilt continue to remain intact. 

A similar indeterminacy prevails already at the outset, 
when we had a very large number of atoms. If we were 
to single out any particular atom for close observation, 
there is no way of predicting, in which successive half-life 
period it will meet its fate. This is subject to pure chance. 
Thus whilst we can be pretty sure that almost exactly one 
half of a large number of atoms will disintegrate in a 
half-life period, we are unable to determine in advance 
which particular atoms will belong to the decaying half. 

STATISTICAL FLUCTUATIONS 

The inherent unpredictability of the lifetime of any 
single radioactive atom introduces random fluctuations in 
the predictable mean behaviour of a large number of 
similar atoms. If the smooth exponential decay law 
would ideally demand that n atoms should disintegrate in 
a given sample within a certain time of observation, then 
the actual number of atoms observed to decay within that 
time will in all probability differ from n. It may be 
smaller or larger. If we repeat the experiment numerous 
times under identical conditions, the average of all observa- 
tions will approach ever more closely to n. Regarding the 
discrepancies of individual results, we will find that these 
average to ± \'n. This is called the mean uncertainty of 
the count n. 

As far as practical measurements are concerned, this 
means that if we want our activity reading to be reliable 
to within 1 part in n, we must count at least « a pulses 
before we stop the counter and divide by the total time 
taken. Otherwise random fluctuations will exceed our 
tolerance limit and the readings are meaningless to the 
envisaged accuracy. 

It is common practice to specify four accuracy classes, 
namely 1, 5, 10, and 20 per cent. These correspond to 
desired reliabilities of 1 part in 100, 20, 10 and 5, so that 
we must respectively count at least 10,000, 400, 100 or 
25 pulses. 

Note carefully that it is solely the total pulse count which 
determines the statistical accuracy, quite irrespective of the 
time taken for clocking-up this count. The radiation 
meter must simply be left running until the required 
number of pulses have arrived, and if this takes a very 
long time in the case of low activities, the circuits must be 
designed with adequate long-term stability. 

RADIATION METER TIMING 

The relationships explained in the previous section 
dominate the design of practical radiation meters. In the 
case of digital counting, there are few basic problems as 
far as long-term stability is concerned. Professional 
equipment often adopts count timing here. In other 

353 




PULSE INPUTS FROM BftOIATtON DETECTORS 

Fig, 7.1, STRACE RADIATION METER: Circuit diagram of the ratemeter module 



words, the time taken to achieve a predetermined count 
is measured. Suppose we desire a statistical accuracy of 
1 per cent. The clock will then be zeroed and the counter 
set to 10,000. The clock is then set running forwards 
and the counter backwards. When the counter reaches 
zero, it stops the clock automatically. 

In the case of analogue counting, more special con- 
siderations are required. We remember that analogue 
counting establishes the activity reading as the voltage 
developed across a capacitor. Each pulse pumps a 
definite small electric charge into the capacitor, whilst the 
capacitor at the same time discharges through a precision 
resistor. The resulting voltage across the capacitor is 
directly proportional to the rate of arrival of the pulses. 
This voltage will fluctuate in a random manner, due to the 
random fluctuations of the pulse rate. The meter reading 
thus fluctuates over a certain range of the scale, instead 
of being steady. 

RATEMETER TIME-CONSTANT 

Consider the lowest range of the ratemeter in our 
STRACE equipment, which is 100 c.p.m. for full-scale 
deflection. The design figure is the 5 per cent statistical 
accuracy class, which calls for 400 pulses in the "counting 
time". These take four minutes to arrive at 100 c.p.m., 
so that the product of the integrating capacitor value 
(pF) and its discharge resistor (megohms) should be 240 
seconds. 

If the value of the capacitor is kept constant, but the 
value of the discharge resistor halved, then a given pulse 
rate will produce only half as great a meter deflection. 
The full-scale deflection c.p.m. value is thus doubled. But 
the statistical accuracy is unchanged, because although the 
time constant has been halved, the rate of arrival of the 
pulses for full-scale deflection has been doubled, so that 
the same number of pulses arrive within the time-constant 
period. 

In general, this leads to a simple rule. The various 
desired c.p.m. ranges are obtained by switching corre- 
sponding different discharge resistors across the same 
integrating capacitor, whereby the same statistical accuracy 



is then obtained on all ranges. This is most fortunate, 
since only one capacitor is thus required. The capacitor 
must be of immaculate quality, above all, it must have 
very low leakage and excellent long-term capacitance 
stability, so that it is rather expensive. Precision resistors 
are much cheaper, and only these are required in quantity 
according to the desired number of ranges. 

STRACE RATEMETER MODULE 

Fig. 7.1 shows the complete circuit of the ratemeter 
module for the STRACE radiation meter unit.* 

The components within the broken-line rectangle are 
accommodated on a 4in x 6in printed circuit board. 
Layout is in no way critical. 

Almost any silicon npn transistors are suitable for 
TR2, 7, 8, 9, and almost any silicon pnp types for TRI, 3, 
4, 5, provided collector voltage ratings are at least 12V 
working in all cases. TR6 may be any small germanium 
pnp audio power transistor, e.g. OC72 is also suitable. 
The small diodes may be any silicon type with small self- 
capacitance and at least 100V p.i.v. rating, D7 is a 5V 
miniature Zener diode, D8 is a 500mW dissipation (at 
least) 12V power Zener diode. Resistors should be 
±10 per cent, except those connected to S2B, which must 
be ±5 per cent, or better still ± I per cent. The specified 
prototype semiconductors are all S.T.C./Intermetal types, 
but in no way imperative. 

TRI is a polarity inverter for those radiation detector 
types feeding negative pulses to PLI. DI suppresses 
positive pulses or components while D2 prevents overload 
of TRI on excessive negative pulse amplitudes at PLI. 
TR2 is the main pulse amplifier stage. It is fed at the 
base with the positive output pulses from TRI collector, 
as well as with the inputs of positive-pulse radiation de- 
tectors connected to PL2 and/or PL3. D9 is included 
here to prevent short-out of PL3 input by the low- 
impedance output stage of a detector connected to 
PL2, thus it is not necessary to disconnect the cables of 
switched off detectors. 

• (Ref to Fig. 2.1 for block diagram of STRACE Radiation Meter Unit.) 



354 



THRESHOLD LEVELS 

VR1 is the collector load of the main pulse amplifier. 
It is preset to give the response threshold levels marked 
against PH to PL3. D4 suppresses negative pulses or 
components at TR2 base, and D3 prevents overload of 
TR2 if excessive positive pulse amplitudes are applied to 
PL2 or PL3. The diodes Dl to D4 associated with TR1 
and TR2 thus make the circuit very tolerant of large 
differences in input pulse amplitudes. The performance 
is still perfect even if the pulses fed to PL] , PL2 or PL3 
are ten times larger than the specified threshold values. 
Gain controls are thus not necessary on the front panel. 

PULSE EXPANDER 

TR3 is a driver emitter follower, to feed the pulse ex- 
pander from the necessary low source impedance. The 
pulse expander TR4/TR5 is a transistorised equivalent of 
the valve-operated pulse expanders already introduced 
last month in the gamma ray spectrometer kick-sorter 
amplifier. 

TR4 normally rests cut-off, and TR5 conducting. 
When a trigger pulse arrives via C4, the roles of the two 
transistors change over for a time determined by C9 or CIO 
in conjunction with R19. Thereafter, the transistors 
revert to the resting state of their own accord. The 
duration of conduction of TR4 in response to each trigger 
pulse from TR3 is independent of the form or duration of 
that trigger pulse, being determined solelv bv C9, CIO 
and R19. 

PUMP INTEGRATOR 

During each conduction pulse of TR4, a definite quantity 
of positive charge is pumped via D6 and R20 into the 
integrating capacitor C14. S2B switches the appropriate 
discharge resistor across CI 4, to establish the different 
c.p.m. ranges as discussed previously. The other wafer, 
S2A* of the range switch selects C9 or CIO for determining 
the pump pulse duration. On the lowest range (f.s.d. 
100 c.p.m.), C9 is in circuit and gives a long pump pulse, 
whereas the short pump pulse with CIO is used for all 
other ranges. 

The value of the integrating capacitor CI4 is 40>F, and 
the net value of the discharge resistance (R32, VR4 and 
the input impedance of the read-off voltmeter TR7, 8, 9) 
is 4 megohms for both range 1 and range 2. Due to the 
different pump pulse duration, range 1 is 100 c.p.m. and 
range 2 is 250 c.p.m. for full-scale deflection, so that the 
statistical accuracy is in fact somewhat poorer than 5 per 
cent on range 1 but somewhat better than 5 per cent on 
range 2 and all other ranges. This is a compromise made 
to avoid unduly high values for CI 4, or unmanageably 
high circuit resistances. 

READ-OFF VOLTMETER 

The read-off voltmeter for the integrator capacitor C14 
comprises the remainder of the circuit on the right of 
Fig. 7.1. The design figure is for a ImA fsd meter and/or 
chart recorder connected to the output. 

TR7, 8, 9 are cascaded current amplifiers to reduce the 
current drain on the integrator capacitor CI 4 for the 
voltage read-off process. VR3 sets a d.c. bias voltage 
in series with C14 on ranges I and 2, to overcome the 
silicon threshold of TR7, 8, 9. TR6 is in parallel with 
VR3 and possesses a compensating temperature co- 
efficient to cancel thermal drift of the threshold level of 
TR7, 8, 9. TR6 must be positioned close to TR7, 8, 9 
to sense the same temperature as the latter components. 

VR6 and VR7 fulfil the same function as VR3 for the 
other ranges. VR5 sets the meter sensitivity for all 
ranges. D8 stabilises the supply voltage for all stages. 
D7 limits the maximum voltage developed across CI 4, to 
prevent damage to the meter Ml or TR7, 8, 9 if the range 
switch is set to a range too low in relation to the input 
pulse rate. 



Next month: The remaining circuitry for the STRACE 
radiation meter; this includes the pip generator, audio 
amplifier, and power unit. 



next month ! 



Build this 
Radio-controlled 




A pleasure to construct and a joy to run, this 34in 
kit-built diesel-powered high speed craft carries a 
multi-channel control system which will make it the 
king-pin of any water on which it is sailed. Incor- 
porates proportional rudder and progressive throttle 
control for good manoeuvrability, with simultaneous 
or one-at-a-time operation of these systems. Full 
how-to-build instructions, with details of transmitter 
and receiver (including control gear). Begins in next 
month's issue. Don't miss it ! 



Other Constructional Projects include : 



DRUMMER'S WHOOSH UNIT 
CAMERA TRIGGER 



PRACTICAL 



ELECTRONICS 



$55 



SEMICONDUCTOR 



ofltoiui 



This serrt 
used mej 





6-OTHER SEMICONDUCTORS 



By 6. |. KING 



>iso far dealt with the more commonly 
Ira of the semiconductor family, and in 
this concluding article the aim is to consider briefly 
some of the more recent developments using semi- 
conductor materials. 

TUNNEL DIODE 

The tunnel diode action differs considerably from 
the conventional diode. The main difference concerns 
the reverse current characteristic which reveals that the 
diode is highly conductive for all values of reverse 
voltage (see Fig. 6.1 ); the forward current changes with 
increasing forward voltage. 

Initially, the forward current increases with forward 
voltage in the normal way up to current f P due to 
forward voltage V v . As the voltage is further increased 
the current starts to fall, and subsequently falls into a 
deep valley before it starts rising again to follow the 
normal diode forward characteristic. This is called a 
negative resistance characteristic because it is opposite 
to ordinary resistive current flow. 



NORMAL 
FORWARD 

CHARACTERISTIC 




HICH 
CONDUCTIVITY' 



[REVERSE 

i CURRENT 



Fig. 6.1. Characteristics of tunnel diode. Note the negative 
resistance zone and that high conductivity occurs in the 
reverse direction 




QUARTZ TUNNEL 
CRYSTAL DIODE 



Fig. 6.2. 

diode 



Simple crystal -controlled oscillator using tunnel 



The depletion layer (potential barrier or "space 
charge" region) is much narrower than in conventional 
junction diodes due to a very high concentration of 
/?- and n-type impurities in the basic crystal. Hence, 
electrical charges are encouraged to traverse the 
junction by an action called tunnelling. 

In most applications the tunnel diode is biased so 
that the operating point is established in the negative 
resistance region, and it is suitable for use as an ampli- 
fier, detector, oscillator, high-speed switch and rectifier. 
This latter aspect may seem strange in view of the high 
reverse conductivity. 

Conventional rectifiers are arranged for substantial 
current flow in the forward direction, but extremely 
small in the reverse direction. Tunnel rectifiers, on 
the other hand, are arranged for substantial reverse 
current flow at very low voltages and much smaller 
forward current due to the negative resistance effect. 
This means that tunnel diodes can provide efficient 
rectification at much smaller signal voltages than con- 
ventional rectifiers, but note the reversed polarity 
requirements (for which reason they are sometimes 
called "back diodes"). 

Their amplifying attributes are particularly valuable 
at microwave frequencies (above 300MHz) due to 
low noise operation and low current demands. 

Stabilisation assumes great importance when the 
device is arranged as an amplifier, for it has a great 
tendency to oscillate more freely than to amplify 
without oscillating. This results from the wideband 
negative resistance characteristic which, when the 
amplifier is really well designed, can yield gain over a 
bandwidth in excess of an octave without variable 
tuning. 

There is no trouble at all in getting a tunnel diode to 
oscillate, even with only a fraction of a volt bias. 
A basic oscillator circuit using a quartz crystal as con- 
trol is given in Fig. 6.2. This yields a high range of 
harmonics because as the diode oscillates it swings 
continuously from the low voltage state, through the 
unstable negative resistance region to the high voltage 
state. 

INTEGRATED SCREEN TRANSISTORS 

Early transistors were troubled with a high output/ 
input feedback capacitance which called for neu- 
tralising techniques in high gain amplifying applica- 
tions to prevent the amplifier from changing into an 
oscillator. 

In ordinary transistors the unwanted feedback 
capacitance stems from the comparatively large bonding 
areas required for the emitter and base leadouts. The 



+ 35V 



4Tkfl 



SATE Ifl GATE ID 

^^ISOURCE ^-^SOURCE 



(a) n-cbannei type (b) p-ehannel type 



OUTPUT 



INPUT 



50pFS <IOkfl 



CATHODE 


N 








6ATE 




1 



ANODE 



Fig. 6.3. F.E.T. symbols 



Fig. 6.4 F.E.T. audio amplifier circuit 



Fig. 6.5. Make-up of silicon 
controlled rectifier (see text) 



effect of this causes a portion of the output signal to 
get back to the input of the transistor in phase with the 
real input signal, thereby creating conditions for 
positive feedback. Even though oscillation may not 
actually occur the effect can distort the response 
characteristics of the amplifier. 

The "integrated screen" is a section of diffused semi- 
conductor beneath the base bonding area. Feedback 
capacitance is considerably reduced making them 
suitable for intermediate-frequency amplifiers in par- 
ticular, Their use ensures that the response character- 
istics retain a close tolerance even when the equipment 
is mass produced. 

FIELD EFFECT TRANSISTORS 

The field effect transistor differs from the type of 
transistor that we have looked at so far, in that it is a 
voltage amplifier (as is the thermionic valve) rather 
than a current amplifier. It has a very high input 
impedance (millions rather than thousands of ohms) 
stemming from reverse biasing of the input junction 
required for normal operation. It will be recalled 
that the ordinary transistor is biased on the emitter/base 
junction for forward conduction, and it is this which 
endows it with the relatively low input impedance. 

Basically, the f.e.t. consists of a slice of high resistance 
semiconductor sandwiched between two wafers of low 
resistance semiconductor having either p- or //-type 
characteristics. One end of the high resistance slice is 
called the source and the other end the drain. The 
two wafers are connected together to form what is 
called the gate. 

The f.e.t. also differs from the ordinary transistor in 
that its action is governed only by one type of current 
carrier — either the electron or the hole — and for this 
reason it is sometimes termed "unipolar". Its symbol, 
too, is different, as shown in Fig. 6.3, where (a) is an 
n-channel type and (b) a /(-channel type, the carriers 
being electrons and holes respectively. 



Sectional view through a typical Texas f.e.t. 




Fig. 6.4 shows basic f.e.t. amplifier stage, using an 
n-channel device. While the drain polarity is positive 
on the //-channel type, it is negative on a /^-channel 
device, and the latter often incorporates a resistive 
potential divider across the supply, with the junction 
connected to the gate. 

THYRISTOR 

The thyristor (or silicon controlled rectifier) is a 
junction diode with four semiconductor layers in npnp 
formation, as shown in Fig. 6.5. The end /7-type is 
called the "anode" and the end /j-type the "cathode". 
The sandwiched p-type is the "gate" or triggering 
electrode. 

Owing to the four-layer make-up, current will not 
flow from cathode to anode (or vice versa) under 
ordinary conditions. However, when a pulse is 
applied to the gate, current is allowed to flow in the 
forward direction from anode to cathode. 

When the polarity of the applied source is reversed 
the thyristor, like an ordinary diode, only passes a 
small leakage current. Unlike an ordinary diode, it 
will not pass forward current again when the polarity 
changes back, that is. not until it is once more gated 
or triggered. 

The gating pulse controls the instant during a 
forward input pulse at which diode conduction starts. 
Once triggered, conduction is maintained as long as 
the supply polarity is correct and until the forward 
current falls below a small holding value, fn this way, 
the thyristor is considered as the semiconductor version 
of the thyratron trigger valve. 

STRAIN GAUGE PRINCIPLE 

Finally, a word or two about the semiconductor 
strain gauge principle. While the inherent resistivity 
of a piece of semiconductor like silicon depends on the 
various factors that we have already discussed, like the 
addition of impurities, heat and light, it also depends 
on mechanical strain. That is, by twisting, bending, 
or straining a small chip of semiconductor the crystal 
lattice is "distorted" and a change in resistivity occurs. 
This is the basic strain gauge principle, currently 
employed in various commercial and domestic devices. 

A very interesting and fairly recent application of 
the principle is adopted in the strain gauge pick-up 
cartridge. The well-known crystal cartridge employs 
the strain gauge principle, but more recently has been 
replaced by the ceramic type. Very recent strain 
gauge pick-ups use a very small chip of silicon, less 
than 001 in long and less than 0000! in in cross section. 





[MoMfi Owl ItetPMi QtDtp 



AN ELECTRONIC SWITCH 




Last month's beginners project explored the light 
dependent resistor (I.d.r.) and its use as a "light- 
operated switch". This month's project demonstrates 
another "electronic" switch, namely the multivibrator. 

The multivibrator is basically a two transistor circuit 
in which one transistor is switched on and the other off, 
i.e. the circuit 'has two distinct "states", and may. be 
regarded as an electronic two-pole on/off switch, 
sometimes referred to as a "Flip-Flop". 

To demonstrate the action of the multivibrator, two 
lamps have been inserted in the circuit and these flash 
on and off as first one transistor is switched on and then 
the other. 

CIRCUIT 

The circuit diagram (Fig. 1) has numbered circles, 
which represent the terminal strip connections; these 
are also indicated on the wiring diagram in Fig. 2. 

The two transistors TR1 and TR2 employed in this 
circuit are inexpensive npn types 2N2926 readily 
available from most components shops, and advertised 
elsewhere in the magazine. 

The collector of TR1 is capacitively coupled to the 
base of TR2 by CI, and the collector of TR2 is coupled 
to the base of TR1 by C2. These capacitors are 
electrolytic types and the polarities must be adhered to, 
see Figs. 1 and 2, 

The cross-coupling of the multivibrator circuit 
produces what, in effect, is an oscillator, due to the 
feedback action of the capacitors. Oscillation is 
started by the unbalance in each half of the circuit due 
to component tolerances. The output waveform at the 
collector of each transistor is almost square. 

THE OPERATION 

When power is first applied to the circuit from the 
battery the unbalance between each half of the circuit 




RY1. 
9V. 



Mm oritur 
^ronvstor c . e «|kclor 

°°* b-tMM 



2H2«6 



pushes one transistor towards current cut-off and the 
other towards full conduction. 

Let us assume at the start that TR1 and LP1 is 
switched on and TR2 is off; the voltage at TR1 collector 
charges CI because the collector end of CI is less 
negative than the base of TR2. At the same time, the 
base of TR2 becomes negative bringing it into con- 
duction from its off state and switches LP2 on. 

The capacitor CI discharges through VR1 and C2 
starts charging, making the base of TR1 go negative. 

The result is alternative conduction through TR1 
and TR2. 

The flow of current in the base of the transistors 
causes a larger flow of current in the collectors and it is 
this larger current which drives the lamps. 

The timing of the switch-over is determined by the 
values of the capacitors, the amount of charge on them, 
and the value of resistors Rl, R2, and VR1, through 
which the charge leaks away. 

SWITCHING TIME ADJUSTMENT 

By adjusting the setting of the potentiometer VR1, 
the value of the resistance affecting the discharge of each 
capacitor can be altered to change the switching time, 
so that one bulb will be on for a different period of 
time compared with the other. In fact, as one bulb 
comes on for a longer time, the other does so for a 
shorter time.* This is called altering the mark-to-space 
ratio of the generated waveform. 




Fig. I . Circuit diagram of the multivibrator. The numbered 
circles represent the terminal strip connections 



Fig. 2 Constructional and wiring details. Note the transistor 
and capacitor connections 



Low consumption 6V lamps are used with a current 
rating of 0-06A (60mA), but lamps rated at 01 A 
(100mA) will work just as well. Higher ratings should 
not to be used unless the transistors are changed for 
higher current types. 

USING PNP TRANSISTORS 

If the reader wishes to use pnp transistors the 
capacitor polarities must be changed round, i.e. the 
positive ends are connected to the bases of the transis- 
tors. Also, the battery connections will have to be 
reversed, i.e. negative terminal connected to the lamps, 

CONSTRUCTION 

Commence the construction by cutting a softwood 
baseboard Sin x 5in x |in. The next stage is to wire 
the 12-way terminal strip before mounting this in 
position on the baseboard. A plastics sleeved link 
wire should be inserted between terminals 1 and 12. 
The two resistors Rl and R2 should be positioned 
between terminals 3 and 6; 8 and 10. 

The outer leads of the subminiature potentiometer 
VRI should be carefully bent so that they can be 
inserted in terminals 6, 7, and 8, see Fig. 2. The 
electrolytic capacitors CI and C2 are positioned in 
terminals 2 and 10, 3 and 11. It is important that CI 
and C2 are wired to the correct terminals; reference 
should be made to Fig. 2. 

Finally, before mounting the terminal strip on the 
baseboard, the transistors should be mounted on the 
strip, see Fig, 2. Particular care should be taken to 
ensure that the transistor leads are wired to the correct 
terminals, as they can be damaged if wired incorrectly. 

FINAL ASSEMBLY 

The terminal strip and m.e.s. bulb holders can now be 
screwed to the baseboard, see wiring diagram for 
relative positions. The terminal strip should be 
checked against the wiring diagram and screwed to the 
baseboard with two |in No. 4 countersunk woodscrews. 
The m.e.s. bulb holders are screwed to the baseboard 
with four iin No. 4 countersunk wood screws. 



COMPONENTS 



Resistors 

Rl 2-2kQ R2 2-2kO 
10%, £ watt carbon 

Potentiometer 

VRI lOkO linear subminiature preset 

Capacitors 

CI, 2 50/xF electrolytic, 12V (2 off) 

Transistors 

TRI.2 2N2926(2off) 

Lamps 

LP I, 2 6 V 0-06A (60mA) (2 off) 

Miscellaneous 

BY I 9 V type PP9 battery 

One 12-way plastics terminal block 

Two m.e.s. bulb holders, batten mounting 

Wooden baseboard Sin x Sin X ^in 

Two miniature crocodile clips or battery connectors 

Six fin No. 4 countersunk wood screws 

Plastic covered, single core copper wire 

Total cost £1 approx. 



A lead from terminal 1 1 is taken to LP2 bulb holder. 
Two leads are taken from the other connecting screw 
and wired to terminal 8 and LP I bulb holder, see 
Fig. 2. The other connecting screw of LP1 should be 
wired to terminal 2. 

Finally, the battery leads should be wired in circuit. 
The negative lead is taken from terminal 1 and clipped 
on the battery negative connector by a miniature 
crocodile clip. The battery positive lead is taken from 
terminal connecting both lamps together. 

The crocodile clip acts as a simple switch if removed 
when not used. All the wiring should be given a final 
check before making the final battery connection. 
The multivibrator lamps will start flashing or switching 
on and off as soon as the supply is connected. 

All components wired to 
the terminal strip. Note 
the link wire 




Fixing a connecting lead to one of the m.e.s. bulb holders 
The completed multivibrator 1 




The detailed explanation concerning the operation of 
UNIT "A" is continued in this month's article, 
with further practical examples. 

We resume by considering the use of the operational 
amplifier as an integrator. 

An operational amplifier will be handling time as well 
as voltage when acting as an integrator, so some means 
must be found of inserting intervals of time onto the 
computer. One method is to employ external oscil- 
lators to provide known functions of time in terms of 
frequency. An input to an integrator might consist 
of a steady d.c. voltage which is switched on for a time t 
(step function or square wave), or alternatively, a sinu- 
soidal voltage of frequency /and period 1//. 

If a graph is drawn of the resulting integrator output 
function, and this is the form that answers to problems 
involving change or motion will usually take, the X axis 
of the graph will be calibrated in intervals of time, with 
voltage on the Y axis. It follows that an oscilloscope, 
which also uses time on the X axis and voltage on the 
Y axis, can provide a convenient form of output dis- 
play, especially when an integrator is operating at high 
speed. 

The operational amplifier is converted to an inte- 
grator when a capacitor Cr is inserted, in place of a 
resistor, in the feedback path; see Fig. 5.1, When an 
input voltage —E- in is applied to the integrator by 
means of a simple switch S for a time f, the output £ 
will take the form of an increasing ramp voltage pro- 
portional to t with slope 

~F t J— 

-KinCf 

Note that the operational amplifier will continue to 
invert an input voltage even when used as an integrator. 



THE INTEGRATOR IN EQUATION 
SOLVING 

The electronic analogue computer does provide a 
powerful technique for obtaining rapid solutions to 
problems involving calculus, which cannot be equalled 
either by numerical methods or by a digital computer. 

If differentiation and integration are regarded as 
straightforward mathematical operations, it will be 
found that the terms of, say, a second order differential 
equation can be manipulated on the computer in much 
the same way as the terms of a "steady state" algebraic 
equation. 

For example, whsn an equation term y is differen- 
tiated against time its derivative dyjdt is obtained, and 
a second differentiation yields the second derivative 
d 2 yjdt 2 . The reverse process is where integration of the 
second derivative d 2 v/df 2 produces the first derivative 
dyldt, and another integration gives y as the result. 

Fig. 5.2 shows how a simple integrator can handle 
equation terms. Combined operations are made 
possible by cascading integrators, while using coefficient 
potentiometers and computing component ratios for 
summation, multiplication, and division (Fig. 4.1). 

The process of differentiation, although feasible if 
care is taken, is generally avoided on analogue com- 
puters because it gives rise to unstable operational 
amplifier configurations, but this imposes only a slight 
limitation since integration can be employed— in the 
majority of cases — in place of differentiation. 

INTEGRATOR ACCURACY 

The transfer accuracy of an operational amplifier, 
when it is used as an integrator, will be theoretically 
limited by its finite value of open- loop gain. However, 




©©^[Ptyjir 




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per 100. 

TRANSISTOR BABO AIH SALE I 

OC44, 0C4S, OC81D now only 

OC71, OC72 equivalent 

ASY22 Switching Transistors 



All Tested. 1/6 each or £6.0.0 



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BSY28 >\P.N. Silicon Planar, Epitaxial, 300inW. 300Mc/s . . ..tit each! 

BSY60 N.F.N. SUiean Planar, EpitAslal, 800m W. 10OMc,b .. .. 8/fl each! 

AFZ12 F.N.P. Germanium Alloy Mil. low noise V.H.F. ainiillnirr i . 2.6 each! 

Complete sets of transistors for radio: 

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GET120, 2 watt*. Heat sink: Inclui led .. 8/6 each! 

Transistor Driver Transformers 8/6 each! 

Transistor Output Transformers (nil bible for our kits above I . . . . 8/6 each! 

0C28 Equivalent til- each! 

BYZ13, S amp rretJtters 8/6 each: 

Light Benaltlvltv transistors similar to OCP71 ■ ■ V- each! 

UNMAKKED, UNTESTED TKANHIKTORS TO CLEAR . . . . 7/6 for 60 ! 

Silicon diodes. Make excellent detectors. Also suitable for kcvln^ elect runic organs, 

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ELECTROLYTIC COHDEHSERS! PAHTASTIC BELECTI0K 
20+4 



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O-SSftF 



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m 

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iooaoo, 6ov 

160J3B0, 300V 
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32 + 32 



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40 + 40 + 20 
.. 8/8 

.. */- | 

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nt ■ 

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270 volte 

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460 volts 

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1! 4 volt 

volt 

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All at IS/- per 100. 3/- per dozen 



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0-0022/iF 400 volts 4d 0-I6uF 160 v 

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7d 
18 



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9d e»ch. __ 

COMNECTIHG WIRE. THIS. F.V.C. n_0_ATE_T 

10yd. 1,'-; 100yd, 7,8; oOOvd, _.,'- (post 4,'fiK 1,000yd. 40,'- (post 6;-). 



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DY87 

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EY51 

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RECORD PLAYER CARTRIDGES 

Souotone Mono, 10/-: Acos GP67/29 .Mono, IB,'- i Acos GP9 1/35C Htereo coinpiitiblc, 

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Signal Injector Kit— 10/-. Signal Tracer Kit— 10/-. ' 



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Cutter and 5 Boards 21 in 

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3!ln 



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lin, 9/9. Cutter only, 7/8. Pin Insert Tool. 9 8. Terminal 



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Please Include suitable amount to co>er postage. Stamped addressed -_ > _ U p t must 
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For cnstoiners in the Illrmlnghain area goods may be obtevin&L from Rock Exchange?, 
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MIHIMTJM ORDER 10/- 




Through this ICS 
3- way Training Method: 



H 




MASTER THE THEORETICAL SIDE 
From basic principles to advanced applications, 
you'll learn the theory of electronic engineering, 
quickly and easily through ICS. That's because 
each course is set out in easy-to-understand terms. 

MASTER THE PRACTICAL SIDE 
ICS show you how to develop your practical 
abilities in electronic engineering— alongside your 
theoretical studies. It's the only sure way to 
success. All training manuals are packed with 
easy-to-follow illustrations. 

MASTER THE MATHEMATICAL SIDE 
To many this aspect is a bitter problem. Even 
more so because no electronic engineer is complete 
without- a sound working knowledge of maths. 
But new ICS teaching makes mathematics easier 
to learn. 

Wide range of courses available include: 

Radio/TV Engineering and Servicing, Closed Circuit TV, Electronics, 
Electronic Maintenance, Servo mechanisms, Computer Engineering, 
Numerical Control Electronics, etc. 

EXPERT COACHING FOR: 

INSTITUTION OF ELECTRONIC AND RADIO ENGINEERS 

CITY AND GUILDS TELECOMMUNICATION TECHNICIANS 

CITY AND GUILDS ELECTRONIC SERVICING 

R.T.E.B. RADIO/TV SERVICING CERTIFICATE 

RADIO AMATEURS' EXAMINATION 

P.M.G. CERTIFICATES IN RADIOTELEGRAPHY 

Build your own radio, tranttttor portable, and profeulonal-type test 
instruments with an ICS Practical Radio and Electronic* Course. Every- 
thing simply explained and easy to handle. All components and tools 
supplied. For details past coupon below. 

Member of the Association of British Correspondence Colleges 



FOR FREE HANDBOOK POST THIS COUPON TODAY 

I.C.S., Octet. 151, INTERTEXT HOUSE. 
PARKGATE ROAD, LONDON, S.W.11 



NAME 



ADDRESS 



OCCUPATION AGE.. 



■ _/«» 



INTERNATIONAL CORRESPONDENCE SCHOOLS 



361 




PRINTED CIRCUIT KIT 

BUILD 40 INTERESTING PROJECTS on m PRINTED CIRCUIT 
CHASSIS with PARTS and TRANSISTORS from your SPARES BOX 

CONTENTS: (I) 2 Copper Laminate Boards 4±- x 2i". (2) I Board for Match- 
box Radio. (3) 1 Board for Wristwatch Radio, etc, (4) Resist. (5) Resist 
Solvent. <6) Etchant. (7) Cleanser/ Degreaser. (B) 16-page Booklet Printed 
Circuit! far Amateur;. (9) 2 Miniature Radio Diatj SW/MW/LW. Also free 
with each kit. (10) Essential Design Data, Circuits, Chassis Plans, etc. For 

40 TRANSISTORISED PROJECTS 

A very comprehensive selection of circuits to suit everyone's requirements 
and constructional ability. Many recently developed very efficient designs 
published for the first time, including 10 new circuits, 

EXPERIMENTER'S 

PRINTED CIRCUIT KIT 

8/6 

Postage & Pack. 1/6 (UK) 

Commonwealth: 

SURFACE MAIL 2/- 

AIR MAIL B/- 

Australia, New Zealand, 

South Africa, Canada 

(I) Crystal Set with biased Detector. (2) Crystal Set with voliage-quadrupler 
detector. (3) Crystal Set with Dynamic Loudspeaker. (4) Crystal Tuner with 
Audio Amplifier. (SJ Carrier Power Conversion Receiver. (6) Split-Load 
Neutralised Double Reflex. (7) Matchbox or Photocell Radio. (8) "TRI- 
FLEXON" Triple Reflex with self-adjusting regeneration (Patent Pending). 
N§ Solar Battery Loudspeaker Radio. The smallest 3 designs yet offered to 
the Home Constructor anywhere in the World. 3 5ubminiature Radio Receivers 
based on the "Triflexon" circuit. Let us know if you know of a smaller 
design published anywhere. (10) Postage Stamp Radio. Size only 1-62* X '95* 
x -25-. (II) Wristwatch Radio 115* x -80' x -55*. (12) Ring Radio -70* x 
'70" X '55*. (13) Bacteria-powered Radio. Runs on sugar or bread. (14) Radio 
Control Tone Receiver, ( IS) Transistor P/P Amplifier. (I6> Intercom. (17) 
I -valve Amplifier, (IB) Reliable Burglar Alarm. (19) Light-Seeking Animal, 
Guided Missile. (20) Perpetual Motion Machine. <2I> Metal Detector. (22) 
Transistor Tester. (23) Human Body Radiation Detector. (24) Man/Woman 
Discriminator. (25) Signal Injector. (26) Pocket Transceiver (Licence required). 
(27) Constant Volume Intercom. (2B) Remote Control of Models by Induction. 
(29) Inductive-Loop Transmitter. (30) Pocket Triple Reflex Radio. (31) Wrist- 
watch Transmitter/Wire-less Microphone. (32) Wire-less Door Bell. (33) 
Ultrasonic Switch/Alarm. (14) Stereo Preamplifier. (35) Quality Stereo Push- 
Pull Amplifier. (36) Light-Beam Telephone "Photophone". (37) Light-Beam 
Transmitter. (38) Silent TV Sound Adaptor. (39) Ultrasonic Transmitter, 
(40>Thyristor Drill Speed Controller, 

PHOTOELECTRIC KIT 

CONTENTS: 2 P.C. Chassis Boards. Chemicals, Etching Manual, Cadmium 
Sulphide Photocell, Latching Relay, 2 Transistors, Condenser, Resistors, 
Gain Control, Terminal Block, Elegant Case, Screws, etc. In fact everything 
you need to build a Steady-Light Photo-Switch/Counter/Burglar Alarm, etc. 
(Project No, 1 ) which can be modified for modulated-!! ght operation. 

PHOTOELECTRIC KIT 

39/6 

Postage & Pack. 2/6 (UK) 

Commonwealth; 

SURFACE MAIL 3/6 

AIR MAIL £1.0.0 

Australia, New Zealand, 
S. Africa, Canada & U.S.A. 
Alto Essential Data Circuits 

and Plans for Building 

12 PHOTOELECTRIC PROIECTS. (I) Steady-Light Photo-Switch/Alarm. (2) 
Modulated-Light Alarm. (3) Long-Range Stray-light Alarm. (4) Relay-Less 
Alarm. (5) Warbling-Tone Alarm. (6) Closed-Loop Alarm. (7) Projector Lamp 
Stabiliser. (8) Electronic Projector Modulator. (9) Mains Power Supply. 
(10) Car Parking Lamp Switch. (II) Automatic Headlamp Dipper. (12) Super- 
Sensitive Alarm. 

INVISIBLE BEAM OPTICAL KIT 

Everything needed (except plywood) for building: I, Invisible-Brain Projector 
and I Photocell Receiver (as illustrated). Suitable for -ill Photoelectric Burglar 

Alarm*,, Counters, Door Openers, etc. 

CONTENTS: 2 lenses, 2 mirrors, 1 45*degree wooden blocks, Infra-red filter, 
projector lamp holder, building plans, performance data, etc Price 19/6* 
Pottage and Pack 1/6 (UK). Commonwealth; Surface Mail 2{-; Air Mail 8/-. 

JUNIOR PHOTOELECTRIC KIT 

Versatile Invisible-beam, Relay-less, Steady-light Photo-Switch. Burglar 
Alarm, Door Opener, Counter, etc., for the Experimenter. 

CONTENTS: Infra-Red Sensitive Phototransistor, 3 Transistors, Chassis, 
Plastic Case, Resistors, Screws, etc., Full Size Plans, Instructions, Data 
Sheet "10 Advanced Photoelectric Designs". 
Price 1 9; 6. Postage and pack. 1/6 (UK). 

SUBMINIATURE SOLAR BATTERY. 10/6. Post and pack. I/-, 
Output in Bright Sunlight: 7 v./2S0 microamps. 

Build that Sun Powered Wristwatch Radio for your Holiday and amaze 
your friends. Plans supplied free with each battery. 

YORK ELECTRICS, 333 York Road, London, S.W.11 

Send a S.A.E. for futi dettfjJx, a brief description and Photographs of all Kits and 
alt 52 Radio, Electronic end Photoelectric Projects Assembled* 




SILICON RADIATION DETECTOR 

The NUTRONICS semiconductor radiation 
detector ND7 is a compact, low cost, versatile 
radiation detector with a window area of 
7mm2 and Alpha energy resolution of 50-100 
Kev, FWHM, which has been expressly 
designed for use in educational establishments 
and by amateur experimenters. 

The NUTRONICS semiconductor radiation 
detector ND7 detects Alphas, Beta, Gamma 
Radiation, Fission Fragments, X-rays and 

Protons. 

Send for technical data sheet, 

SOLID STATE NUTRONICS LTD. t.i. 

SA Voltaire Road, London, S.W.4 01-874 8608 




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362 



TABLE 5.1 


c f 


Rin 




t 


IjttF 


tOOkfi 

i ok a 




2-8sec 
800ms 


O-I^F 


lOOkQ 

ioka 




280ms 
80ms 


0-0 VF 


lookn 




28ms 


Maximum value of 


t for an error 


of 


% 











the situation is much more complicated than with, for 
example, a summing amplifier (Fig. 3.8) since the 
amplifier error can no longer be defined in terms of the 
simple relationship between closed-loop and open-loop 
gains. 

As a guiding principle, integrating amplifiers may 
have very large values of closed-loop gain provided 
that the time t of an input function remains small. 
Closed-loop integrator gains of 1,000 or more are not 
uncommon in transistor computers, since low voltages 
and low impedances discourage the use of computing 
resistors of more than 100 kilohm, and capacitors of 
more than 1/*F are too bulky. Table 5.1 is calculated 
for UNIT "A" amplifiers, and sets out the maximum 
allowable interval / for selected values of Ct and Ri n , 
where the amplifier transfer error must not exceed 
one per cent. 

Errors due to unwanted drift voltages also become 
significant when t is long and Ct is small. The greatest 
care must be exercised when zero-setting integrators to 
eliminate offset voltages, for good accuracy at long 
time intervals. Also, the computer should not be 
subjected to fluctuations of ambient temperature when 
computations cover several hours of integrator use. 

COMPUTING CAPACITORS 

The computing capacitors used for PEAC will 
normally He within the range 001-1/tF, and the three 
values most commonly employed are 0-01/iF, 01/fF, 
and 1/fF. Polystyrene is the preferred capacitor 
dielectric, for high insulation resistance, but polyester 
makes an acceptable second best. Mica, paper, and 
ceramic capacitors should be avoided. 

Small value polystyrene capacitors of ±1 per cent 
and ±2 per cent tolerance are easily obtained, but 
0-1 fi¥ and I/*F precision components are rare and 
expensive. To get around this difficulty, the bridge 
circuit of Fig. 5.3 was devised to allow computing 
capacitors to be made up from specially selected low 
cost ±20 per cent capacitors. 

The circuit of Fig. 5.3 can be constructed in bread- 
board form on Verobojird or s.r.b.p., with miniature 
sockets to take C x and Rl. If an audio signal gener- 
ator is not available to supply the bridge with about 
10V r.m.s. at 1kHz, a signal could be obtained from a 
transistor multivibrator powered by the 25V computer 
power supply. Headphones serve to detect the null 
point when the bridge is in balance, and should have 
an impedance of about 2 kilohms. 

The method of making up a computing capacitor of, 
say, 1/iF is as follows. A capacitor panel of plain or 
perforated s.r.b.p. is fitted with small turret tags as in 
Fig. 5.4. A ±20 per cent capacitor of about 0*68^F is 
wired into position on the capacitor panel before it is 
plugged into the bridge C x sockets, and a 1 kilohm 





f •"*"* In a. V V0LT5/SEC 



Fig. S.I. The operational amplifier as an integrator 



BASIC OPERATIONS IN CIRCUIT FORM 



fl in 
yo Wr 



AY 



-4^> I o 

^ -a/Cd/ 



RtG 



fW 



fi 




INTEGRATION 



SYMBOL 



yo— a 




-oyv it 



*{r>* 



Fig, S.2. The handling of equation terms by a simple 
integrator 

■ nlft"! 
10V RMS. 



Q-ljiF 10Mi±1% 
IjtF lkfi + 1% 



I 



111! 



ci 

t0,000pF 



100kfl 
i O O n 



HIGH I 



TTT 



* 1000 XR1 



n 




Fig. 5.3. Bridge circuit used for making up computing 
capacitors 



TURRET TAGS 




20 S.W.G. TINNED 
COPPER WIRE 



Fig. 5.4. Computing capacitor plug-in panel 



363 



resistor is inserted for Rl. Assorted polystyrene or 
good quality polyester capacitors of lower value are 
then temporarily connected across the capacitor panel 
to increase Cx by small increments, while listening on 
the headphones for a drop in the level of the 1kHz 
tone as Cx approaches 1/*F. 

A typical computing capacitor might finally consist of 
a parallel combination of the following values, 0*68/tF, 
0-22/iF, 002/xF, and 0005/tF. 

If the required value of C x is exceeded, the note in 
the headphones will increase in volume when the null 
point is passed. Allow capacitors to cool off after 
soldering, and before making a measurement, as heat 
can cause a temporary or permanent change in capaci- 
tance. With the Fig, 5,3 bridge circuit it is possible 
to detect increments of less than OOl/^F in a nominal 
1/aF capacitor. 

DIFFERENTIAL ANALYSIS WITH 
UNIT "A" 

A second order linear differential equation with 
constant coefficients has become firmly established as 
the "classic" introduction to differential analysis on 
the analogue computer. 

The equation describes an oscillatory system with 
variable damping which can be used to simulate 
indirectly many physical systems, such as the spring 
pendulum, a tuned LC circuit, or a servomechanism. 
Also, the equation is easy to set up on the computer, 
and does not necessarily demand the use of integrator 
mode switching. 

In general form the equation is, 



aS + 6^ + cv=/(/) 



df s 



dt 



(Eq. 5.1) 



where a, b, and c are the constant coefficients, y is 
unknown, and /(/) represents some function of time. 
Equation 5.1 can be rewritten to suit a particular 
system by substituting appropriate terms. 

Spring pendulum 

m d? + /t d7 + ^ =/( ' ) 

(Eq. 5.2) 

where m is the mass of a weight suspended on a spring 
of constant k, which is damped by friction fi. The 
weight is displaced by an amount v when subjected to a 
force dependent on/(/). 

Tuned LC circuit 

j €® 

** dr* 



*§ +*<>-/« 



(Eq. 5.3) 



where L is an inductance tuned by a capacitance C, and 
damped by a series resistance R. Q is the charge in 
coulombs on C at any instant of time. The current 
flowing in the tuned circuit is given by dQIdt, and /(f) 
represents an input function. 



Ser vomechanism 



d 2 o , ,„ dd a . 



w 2 0i (Eq. 5.4) 



where o is the angular displacement of the output 
shaft, £ the damping factor, m the angular velocity, and 
0i the angular displacement of the input shaft. 

The obvious similarity between the above equations is 
emphasised when, in Fig. 5.5, it is seen that they all have 
virtually the same problem layout on the computer. 



Furthermore, as the computer will allow operation at 
almost any fraction or multiple of real time, a spring 
pendulum and a tuned LC circuit can be simulated 
simultaneously, and interesting electro-mechanical 
parallels can be seen to exist between the properties of 
inductance and mass, resistance and friction, and capa- 
citance and elasticity. 

The only real difference between the analogous 
behaviour of a weight on a spring, a servo shaft, and a 
tuned LC circuit is that the LC combination will nor- 
mally resonate at a much higher frequency. 

PROBLEM EXAMPLE 3. 
TUNED CIRCUIT ANALYSIS 

UNIT "A" will simulate any series tuned circuit by 
solving Equation 5.2, and will give answers in the form 
of a.c. meter readings or oscillograms. Tuned circuits 
resonating in the MHz region are catered for by slowing 
down the problem to some convenient decadal fraction 
of real time, so that a simulated circuit on the computer 
which is, for example, resonating at 300Hz, will serve 
as a model for a real circuit resonating at 30 MHz, with 
suitable rescaling of L, C, and t. 

To initially determine the relative values of L, C, R, 
voltage V, and current /, without too much paperwork, 
it is helpful to start with a representative tuned circuit 
which allows computer operation in real time, at 
frequencies convenient for display by an a.c. voltmeter 
or an oscilloscope. 50Hz is a good frequency to 
employ as a datum because it can be readily obtained 
from the mains supply, and rounded values of L = 1 H 
and C = 10/fF will also offer resonance at 50Hz. 

Taking the circuit of Fig. 5.6a as a starting point, 
from the knowledge that a series tuned circuit will 
exhibit an impedance equal to R at resonance, the 
r.m.s. current flow at 50Hz will be Ei[R, or 20mA when 
E\ - 2V r.m.s. and R = 100 ohms. 

It is necessary to rearrange the basic equation. 
Equation 5.2, for the computer by dividing through by 
L, and solving for the second derivative. 

Substituting known values from Fig. 5.6a, 
d z e 100R dQ I 



Q + 



dt 2 ' 1H dr 1H x 10- 5 C~ ' 1H 

(Eq. 5.6) 

f{t) in the present case represents a sine wave input of 
2V r.m.s. In other circumstances the input function 
could be a square wave of amplitude E\ n and period 2/. 

Equation 5.6 is solved on the computer by successive 
integration. Looking at the symbolised diagram of 
Fig. 5.6b, it can be seen that there are two closed-loops, 
one linking the output of OA1 viaCPl to OAl/Input 1, 
and the other passing through OA1, OA2, and OA3, 
v4a CP2, and thence back to OAl/Input 3. The 
coefficient of CP1 will be multiplied by the gain factor 
associated with OAl/Input 1. CP2 coefficient is 
multiplied by the product of gains OAl/Input 3, OA2, 
and OA3, i.e. 1,000 x 100 x 1 = 100,000. 

d 2 Q/dt 2 , obtained from the sum of the voltages 
present at the inputs of OA1, is initially assumed to be 
present. After one integration OA1 provides an 
output dQIdt, and from this all the terms on the right 
hand side of Equation 5.6 are assembled. So, dQjdt is 
multiplied by R/L = 100, using CP1 set for a coefficient 
of 0*1, and is taken back to OAl/Input 1 where it is then 
added to f(t)/L = 2V r.m.s. 



364 



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366 



Moving in the other direction on the symbolised 
diagram of Fig. 5.6b, dQjdt is integrated by OA2 to 
obtain +Q. Inverting amplifier OA3 changes the 
sign of Q before passing it on for multiplication by 
1/LC = 100,000 (CP2 coefficient of I). - (]/LC)Q is 
then added, at OA1 /Input 3, to 

L d/ + L 

and the sum of all OA1 input voltages yields the re- 
quired d 2 Q/df 2 . Because there are two closed-loops 
in the computer set-up the equation will be self- 
enforcing. 

Routine. Switch on UNIT "A" power supply and 
allow a warm-up time of at least 1 5 minutes. Ensure 
that the three operational amplifiers are disconnected 
from their summer networks, and have no feedback 
components. Apply 10V d.c. voltmeter leads to 
OA1/SK13 and an earth socket, and zero-set OA1 for 



an output voltage of less than ± 1 V from the back of the 
UNIT "A" box, by means of VR1 (Fig. 3.7). Repeat 
for OA2 and OA3. 

Set up the problem according to the patching circuit 
of Fig. 5.6b, but omit the feedback capacitors and the 
patching link between OA3/SK13 and CP2/SK1. 
Set CP1 dial to approximately "1". Connect the volt- 
meter to miniature socket OA1/SK6 (Fig, 2.9) and 
zero-set OA1 again, but this time using the front 
panel control VR15. 

Next, zero-set OA2 using VR16, and OA3 using 
VR17. Insert 0-I/tF computing capacitors into OA1/ 
SK11 and SK12, and OA2/SK1I and SK12, and make 
good the link between OA3 output and CP2. Set CP2 
for a dial reading of "10". Apply the voltmeter to 
OA2/SK.7 and zero-set the complete assembly of 
amplifiers by adjustment of VR15(OAI) only. 

The problem layout will now be ready for dynamic 
checks and should not need to be re-zeroed for several 
hours if UNIT "A" is being operated in stable ambient 
temperature conditions. 



_A iy 

a it 



rOH 



77* a it a r o 






o 



COMPUTER LAYOUT FOR S0LUTI0H OF SECOND ORDER EQUATION 




dH m it *> i» 



'\Jjl_TI\w: — 1\-, 



a 



LAYOUT TO SIMULATE THE MOTION OF A SPRING PENDULUM 




R iO 
L it 



to 

M 1 



O 1 



-m° 



4Q 

it ' 



rg _ « do i a . *£} 

it 1 L it ~LC V L 



CURRENT 7- 



~^ — l>i 



o 



LC 



CHAffeE | 
I o V>-| 



LAYOUT TO SIMULATE A TUNED CIRCUIT 






it 2 dSp i _^ I 



~P^> * dr IX ^ *** r^y*'' 



<yL 



LAYOUT TO SIMULATE OVERSHOOT IN A SERVO SYSTEM 




Fig. 5 .5. A second order differential equation applied to physical systems 



367 



TABLE 5.2 

SHOWING HOW COMPUTER OPERATING FREQUENCIES ARE 
RELATED TO CP2 SETTING AND AMPLIFIER CLOSED-LOOP GAINS 



Resonant 

Frequency 
f 



Typical 

Values 

L C 



CP2 J_ Amplifier Gains 

Coefficient LC OAI OA2 OA3 

Input 3 



005Hz 


I.000H 


I0,Q00 M F 


1 


0-1 


to 


10 


0-1 


0-5Hz 


I00H 


I.OOO^F 


10 


10 


10 


10 


01 


5Hz 


I0H 


I00^F 


001 


I0 3 


1,000 


100 


10 


to 

50Hz 


IH 


I0^F 


10 


I0 5 


1,000 


100 


1-0 


500Hz 


IQOmH 


I^F 


10 


io r 


1.000 


'.ooo 


10 


IkHz 


lOOmH 


0-VF 


to 


5x io* 


1,000 


1.000 


50 



]. — 

£in 

2VER.S. 

SOHr 

i nji 



HJ 



C-tOjjF 



1H 

fouoir^ 



*-100fl 

— w» — 



/-20 mA 



TUNEO 
CIRCUIT 
RESONATES 
AT50H* 



REPRESENTATIVE TUNED CIRCUIT USED FOR SETTING UP 
THE PROBLEM LAYOUT IN "REAL TIME" 



fin 



INPUT 1 

rm N 

L INPUT 2 



SYMBOLIZED DIAGRAM 



INPUT 
2V UU 
50 Hi 




1 0A3 



Or! 



DYNAMIC CHECK VOLTAGES, 

AND POT SETTINGS SHOWN THUS 



2V 
r.m.i. 



-0 




f 



[CPI 



INPUT1 



INPUT 
FUNCTION I INPUT 



INPUT 2 lOOkOl f\ 

. ifcJDJ IT T */\i. A W^ 



PUT 3 Wkll 



C, O-liiF 

HI- 



2^-= 100,000 



Fig. 5.6. Programme layouts 
for tuned circuit analysis 



1 r 



100kQ 



C f 0-1uf 

-II- 

T> 



I SUMMER 2 AND 



i r 
i 

i 

T 

i 
I 



ttkO. 






~l 



1> 



i SUMMER 3 AND 



w^l«l«!!)_of:*MM_. I Lit.* M - p -i I l*!*!!!? I 

r 
I 
1- 



LP/i. l 



SIMPLIFIED PATCHING CIRCUIT 



368 



MINIATURE WAFER SWITCHES 

■I pole, 2 iray— 3 pole, 3 way — 4 pole, 
3 way — 2 pole, 4 way — 3 pole, 4 way 
—2 pole, 6 way— 1 pole, 12 way. All 
at 3/6 each, 86/- dozen, yonr aseort- 
m eat. 




WATERPROOF HEATING ELEMENT 



26 yards length TOW. 
temperature control. 



Sell-regulating 
18/- peat free. 



SPECIAL BARGAINS 

SO ohm 50 Witt Wire Wound Pot-meters, 8/6 each. 
1 Meg Miniature. Pot-meter Morganite standard. 
£ in spindle 1/-. each; 9/* per dozen. 
1 Meg Mini* tore, fat -meter Morgan ite preset 
screwdriver control. W each; 8/- per dozen. 
Fre-Set iOOK by Welwyn with intrienl bokellte 
knob, 1/- each; 9/- per dozen. 
100K Pot-Meter. Miniature type with double pole 
switch and standard iln spindle, by Morgan I tc. 
B/- each; 18/- per dozen. 

B Unite tstst Oltn. Enclosed, normally closed 
circuit, wlllopen should blanket overheat, 4/6 each. 
Thermal Belay. Can be used to delay the supply 
ot ET while heaters warm up, or will enable 
16A loads to be controlled by miniature switches 
or relays. Regular list price over £2, price 7/9 
each. 

Siemens High Speed Relay. Twin 1 ,000 ohm colls. 
Platinum points changeover contacts— E.v 
equipment S/6 each. 

Toggle Switch Bargain. 10. v asov normal one 
hole fitting BjB each; or 30/- per doz. 
Electric Look. 24V coil, but rewindable to other 
coltages, 4/fl each. 

Com we ssi on Trfnunert. Twin lOOpF, 1/- each; 
9/- per dozen. 

Precision Wheatitone Bridge. Opportunity to 
build cheaply. 100K wire wound pot. 15W rating, 
only 6,'-. 

Sheet FtJtolfn. Ideal lor transistor projects. 12 
panels each Sin :■, Sin, 5, -. 

3in PM Loudspeaker. 3 ohm, IB, ■8; SO ohm, 18/ B. 
Transistor Ferrlte Slab Aerial with medium and 
long wave coils, 7/6 each. 

Slide Switch, Sub miniature double pole change- 
over, Bl- each ; 18/- per dozen. 
Vacuum Cleaner Flax. Xon-klnkabk ribbed rubber, 
most pliable but very tough. 24/36 Cores. Nor- 
mally, 1/9 per yard, offered nt £3 per 100 yard 
coll, post and Insurance 8/6. 
Sub-Miniature Silicon Diodes. General purpose 
type with gold-plated lends, 1/- each or 7/0 per 
dozen. 

Menage Tapes. 225It Tape on Sin spools, nor- 
mally 4/6 each, we offer 4 tapes for li'8. 
White Circular Flex. Ideal (or lighting drops, 
twin made by BICC. Usually 8*1 yd, 100 yd coil 
lor 30/-, plus 61- postage. 

Edgewise Control, Morganitc, as fitted many 
transistor radios, 2K or 6K with switch, 8/8 each 
or 34/- per dozen. 

1ST Inverter, Full transistorised for operating a 
20- watt fluorescent tube, size a In long . \\ v. Ij. 
£3.10.0. Poet and insurance 3/-. 
Silicon Boctifler. Equiv. BY 100 750mA 400V 
10 for 20/-. 

Miniature Pickup for Tin records made by Cosmo- 
code, cryBtnl cartridge with sapphire stylus only 
S/8 or 30/- dozen. 

Telescopic Aerial for radio or transmitter, chrome 
plated; 6 section extends from 7 J in to 47in, 
7/8 each, £4 per dozen. 

Midget Beou for mains indicators, etc., 1/3 each 
or 12/- dozen. 

Midget Belay twin 2oO ohm colls, size appro*. 
l|in X liu X Iln. 4 pairs changeover contacts 
7/8 each. 

P.O. Type Belay. Twin 200 ohm coils, size approx. 
Sin x 2ln ;< Lin. 4 pairs changeover contacts. 
8/B each. 

Printed Circuit Board, Edge Connector, solder 
terminations, 32 contacts, standard spacing for 
veroboard, etc. Sin long but ensllv cut. 7/8 each, 
80/- doz. 

1,000 W Fire Spiral, replacement for most fires. 1/3 
each, 12/- doz. 

I PP3 EH mini tor, Play your pocket radio 
I from the mains! Save £§. Complete 
omponent kit comprises 4 rectifiers— 
[ mains dropper resistances, smoothing 
[condenser and Instructions. Only 6 6 
(plus 1/- post. 

PHOTO-ELECTRIC KIT 

All parts to make light operated switch/burglar 
a tarm/counte r, etc. Kit comprises printed ci rcul t , 
Laminated Boards and chemicals, Latching relay. 
Infra-red sensitive Photocell and Hood, 2 Tran- 
sistors, cond., Terminal Block, Plastic case, 
Kssential data, circuits and P.C. chassis plans of 
10 photo-electric device Including auto, car 
parking light, modulated light alarm. Simple 
invisible ray switch — counter— stray light alarm— 
warbling tone electronic alarm— projector lamp 
stabiliser, etc., etc. Only J8/6, plus 2/- post and 
insurance. 




Be first this year 
SEED AND 
PLANT RAISING 

Soil heating wire and trans- 
former. Suitable for standard 
size garden frame. IB/8, 
plus 3/8 post and ins. 



XONTROl 

DRILL 
SPEEDS 




DRILL CONTROLLER 

Electronically changes speed 
rom approximately 10 revs, to 
tsocimum. Full power at 
all speeds by fingertip control. 
Kit Includes all parts, case, 
everything and full Instruc- 
tions 10/8, plus 2/6 post 
and insurance. Or available 
made up 32/8, plus 2/0 post and insurance 

SUPERTONE G.C.V. 

Saras »ou work— 
It's partly bail! 

Like Its predecessors this latest Companion 
has full ft performance— such aa only a 
good wooden cabinet anil billux speaker can 
give, and due to its being partly built you will , 
have It going in an evening. Sett Lhea* 
features. 

• 7 Transistors, superhcl circuit. 

• Two-tone Cabinet, size 1 1 ■;< 6 / 3in. 

• All circuit requirements — Push-pull out- 
put — A.Y.C. and feed back, etc. 

Printed circuit board all wired only con- 
nections, e.g., to Volume control" W.C", 
Switch ami Tuning Condenser, 

• Pre-allgned IF stages complete with full trust r*e lions. Pi let nnh- £4.9.8 plus 
6/0 post ami insurance. 

RADIO STETHOSCOPE 

Easiest wiy to lault find - traces signal {rom aerial to 
speaker— when signal stops you've found the fault. Use 
it on Radio, T.V., amplifier, anything • complete kit com- 
prises two special transistors and all parts including probe 
tube and crystal enrpWc 298— twin stctiwet III if (mil ot 
earpiece 7/6 extra 
post and Ins. 2/9. 





THIS MONTH'S SNIP" 
MICRO-SONIC 



7 transistor Key chain Radio in verv 
pretty case, size 2 J in :< 2Jin ;: liin " 
complete with soft leather zipped bag. 
Specification: Circuit— 7 transistor 
superhcterotlvuc ; Frequency range — 
1530 to l.OOOkc/s; Sensitivity— omV.'di: 
Intermediate f re que ney — 465ki '.» . n i 
453kc/s; Power output — 40oilV; 
Antenna— ferrite rod; Loudspeaker— 
Permanent magnet type. In transit 
from the East these sets suffered slight 
corrosion as the batteries were left in 
them but when this corrosion is cleared 
away they should work perfectly- 
offered without guarantee except ih:<i 
they are new, 18/0 plus 2/0 post and 
insurance, less batteries. 





BATTERY OPERATED TAPE 
DECK 

With Capstan control. This unit is extretnely 
well made ami measures appro*. 6 :< 8 x 2ln 
deep. Has three piano key type controls lor 
Kecord, Playback and Rewind. Motor Is 
a special heavy duty t ype Intended tor 
operation off 4/5 volts, .Supplied complete 
with 2 spools ready to install. Record, 
Replay head Is the sensitive M4 tvpe intended 
for use with transistor, amplifier, PrJrv 
*4.'16,'-. Post and insurance 4/0. 



RECORD PLAYER SNIP 



The "Princess" 4 speed auto 
mntlc record changer and player 
engineered with the utmost pre- 
cision for beauty, long life and 
trouble free service. Will take 
up to ten records which may be 
mixed— Tin. lOin or 121n.'Patent 
stylus brush cleans stylus after 
each playing and at shut off, the 
pick-up locks itseK Into Its recess 
— a most useful feature with port- 
able equipment — other features 
include pick-up height adjust- 
ment and sfylus pressure adjust- 
ment. This truly Is n tine instru- 
ment which you can purchase 
this month at only (5.19,6, complete with 
Post and insurance 7/0 extra. 




art ridge and ready to pin 



CASSETTE LOADED DICTATING MACHINE 

Batter)' operated and tilth all accessories. 
Really fantastic offer, a British mad.' 
£31 outfit tor only 18/19/6, brilliant Iv 
designed for speeil and efficiency- - 
cassette takes normal spools, drops In 
and out for easy loading— all normal 
functions — accessories include Btetho- 
scopie ear-piece— cry >ti J microphone 
has on/off switch — telephone pick-up- 
take reference pad — DON'T MISS 
THIS UNREPEATABLE OFFER- 
SEND TO-DAY. #,8/19/6, plus 7/0 post 
and insurance. Footswltch 18/8 extra. 
Spare Cassettes at 7/6 each, three for £1. 




SEHSITIVE 
HAND MICROPHONE 

Dynamic type. Low Impedance, moving 
ion, fitted In mutually neat plastic head 
with ant i -microphonic coupling to 
handle. Extra small size'Wt very sen- 
sitive. 15;'- each. 

B7GJ ValTS Holders with bottom screen— 
p.t.f.e. insulation finest for HP and 
VHF, 1/- each : 10/- doz. 
Fractional H.P. Motor. 240V o0c/«— 
open construction Ideal for ventilation 
fan — Mower heater, etc. 
Clock Motor. 230V GOc'ft synchronous— self 
starling, 6/6. 

Pentode Output Transformer— standard siie, 
40-1 , ex equipment but O.K., 4/3 each; 48 '- doz., 
post paid. 

Jfeon Main* Tester, 1.3 each ; 12/- doz. 
MAINS TRANSFORMER. Upright mounting with 
primary tapped 200, 220, 240V H.T. secondary is 
250-0-26W at 100mA and it has two L.T. secon- 
daries of 6-3V 1JA — unused (removed from 
equipment), IS/- plus 3/fl poet and insurance. 



FLUORESCENT CONTROL KITS 

Each kit comprises seven Items — Choke, 2 tube 
ends, starter, starter holder and 2 tube clips. 
with wiring instructions. Suitable lor normal 
fluorescent tubes or the new "Orolux" tubes for 
fish tanks and Indoor plants. Chokes are super- 
silent, mostly resin Ailed. Kit A.— 15-20W. 19/6. 
Kit B-30-40W., 17/8. Kit C— SOW., 17/6. 
Kit I>— 126W., B2/-. Kit E— 6oW„ 19/6. Kit 
MF1 is lor Sin., Oin. and 12in. miniature tubes 
19/8. Postage on Kits A ami B 4/6 for one or two 
kits then 4/6 lor each two kits ordered. Kit* C 
D and K 4/6 on first kit then 3/0 for each kit 
ordered. Kit MF1 3/6 on first kit then 3/6 on 
each two kits ordered. 




MAINS TRANSISTOR POWER PACK 

Designed ttf operate transistor sets and amplifiers. 
Adjustable output 6V, »V, 12V for up to 000mA 
(class B working). Takes the place of any ot 
the following batteries: PP1, FP3, PP4, PP6., 
FP7, PPit, and others. Kit comprises; mains 
transformer rectifier, smoothing and load resistor, 
condensers and Instructions. Real snip at only 
16/6, plus 3/0 postage. 

MAINS MOTOR 
Precision made — ns used 
in record decks and tape 
recorders — ideal also for 
extractor fan blower 
heater, etc. New and 
perfect. Snip at 9/6. 
Postage 3/- ior first 
one then 1/- for each 
■-^Ii one ordered. 12 
and over post 
free, 

RELAY SWITCHES. Tbese enable micro switches, 
delicate thermostats or other low current devices 
to control up to 30A. Ideal to switch thermal 
storage heaters — motors, etc., made by the 
famous AEI group these arc listed at £25 each — 
you can buy if you hurry at a very keen price of 
39/6 each and we will include diagrams and data. 
Moulded on panel size appro*. 6 x 7 ;■; 2ln deep 

THERMOSTATS 

Type "A" I5A for controlling room heaters, 
greenhouse, airing cupboard. Has spindle for 
pointer knob. Quickly adjustable from 30-80°F. 
fl/6 plus 1/- poet. Suitable box for wall mounting 
5/- P. A P. I/-. 

Type "B" ISA. This Is a I7ln long rod type 

made by the famous Sunvle Co. Spindle adjusts 

this from 30-050° F. Internal screw- 

§ alters the setting so this could be 
adjustable over SO' to I.fKKPF. Suitable 
** *•»> ■ " ' ■■ ! tor con- 

trolling 
furnace, 
oven kiln, immersion heater or to make 
flame-start or Arc alarm, B/6 plus 2/6 
post and Insurance. 
Type "D", We call this the Ice-stat as it cuts in 
and out at around freezing point. 2/3 amps. Has 
many uses, one of which would be to keep the loft 
pipes (rom freezing, if a length of our blanket wire 
(IB yds. 10/-) is wound round the pipes. 7/t. 
P. A P. 1/1. 

Type "E". This is standard refrigerator thermo- 
stat. Spindle adjustments cover normal refrigera- 
tor temperatures. 7/6 plus 1/- post. 
Type "F". Glass encased for controlling the temp, 
of liquid— particularly those in glass tanks, vats 
or sinks— thermostat Is held (half submerged) by 
rubber sucker or wire clip— ideal for nsh tanks- 
developers and chemical baths of all types. 
Adjustable over range 60'F to 150F. Price 18/- 
plui 2/- post and insurance. 



Where postage is not definitely stated as an 
extra then orders over tt are post free. Below 
*3 add 2/9. Semiconductors add 1/- post. 
Over 11 post free. S.A.E, with enquiries please. 



ELECTRONICS (CROYDON) LIMITED 

(Depl P.E.) 102/3 TAM WORTH RD M CROYDON, SURREY iOpp. W. Croydon Stn.) 

alto at 26o LONDON ROOT, CROYDON, SURREY S.A.E, with enquiries please 



369 



TWO-YEAR GUARANTEE 

EX-RENTAL TELEVISIONS 

FREE ILLUSTRATED 
LIST OF TELEVISIONS 

it*— it*— ir— w* 




WIDE RANGE OF MO DECS 

SIZES AND PRICES 

DEMONSTRATIONS DAILY 



1 7in.— £11.10.0 

3 Star Guarantee 

-A- Tube •Valves 

• Component* Carr. 30/- 

TRANSISTOR CHASSIS 
5-/6 

6 TVantistors, LW/MW, Tele- 
seopic Aerial, Brand New. 
Famous British Manufacturer, 
(LESS SPEAKERS) P. & P. 4/6. 

SINGLE PLAYER 

CABIN ET5 1 9.6, P, & P. 7/6. 

TRANSISTOR CASES 19/6. 
Cloth covered, many colours, 
5iie9±-X6i'x3r. P. & P. 3/6. 
Similar cases in plastic 7/6. 



£19 
STEREOGRAM CABINET 

An iltEint 8l»r«o-ram Cabinet 

in modern Veneered Mahogany 

and cloth covered Front Panel 

BLACK LEATHERETTE SIDE PANELS 

Dimension' : 52* x I7|" x 1 2* 

Speaker positions for Twin 

10" x 5" Speakers 




OTHER MODELS— SEND FOR LIST 



RADIOGRAM CABINETS 
ONLY £5.19.6 




An attractive discreetly 
designed space saving 
cabinet in natural grained 
polyestered sapele. Press- 
drop flap for autochanger 
and record storage com- 
partment. 10* X 5* speaker 
position. Complete with 
legs. Dim.29i*Hxl4±*D 
x 29* W. Carr. Ins. 25/-. 



DUKE & CO. (LONDON) LTD. 

631/3 Romford Road, Manor Park, E.13 

Phone 01 -478 6001-2-3 Stamp for Free List. 



TWO SCOOPS FROM "KINGS' 



CONTINUOUS LOOP 

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105/107 DAWES ROAD, FULHAM, S.W.6 

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25/- 




mnmiR 




PROGRAMMED 

BASIC 



COURSE OF INSTRUCTION 
ELECTRICITY (5 vols.) 
ELECTRONICS (6 vols.) 



You'll find it easy to learn with this out- 
standingly successful NEW PICTORIAL 
METHOD — the essential facts are explained 
in the simplest language, one at a time, and 
each is illustrated by an accurate, cartoon- 
type drawing. The books are based on 
the latest research into simplified learning 



techniques. This has proved that the 
PICTORIAL APPROACH to learning is 
the quickest and soundest way of gaining 
mastery over these subjects. Each Volume 
has a unique PROGRAMMED supplement 
for you to test and check your knowledge. 



The series will be of 

exceptional value in 

training mechanics and 

technicians in Electricity, 

Radio and Electronics. 

WHAT READERS SAY 

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explain in simple language what other books make hard 
gmng of." C. B., Hartlepools. 

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370 




Step input. Tuned circuit under- 
damped when R is decreased 



Fig. S.T. Response of a simulated tuned circuit 



Current flow in under-damped 
tuned circuit, in response to a 
step function 



Apply a 2V r.m.s, 50Hz signal to OA1 /Input 2, and 
monitor by means of a reliable 10V a.c. meter of not 
less than 1 kilohm/volt sensitivity. The input function 
should preferably come from a low impedance source 
to avoid serious loading errors when the voltmeter is 
removed. Next, connect the a.c. voltmeter to the out- 
put, of OA1 and adjust CP1 so that OA1 input and 
output voltages are exactly equal. CP1 could alterna- 
tively be set by the reference voltage and d.c. voltmeter 
method mentioned earlier, for a coefficient of 0*1. If 
the CP2 setting is altered it will be discovered that the 
simulated circuit goes off resonance, and can be tuned 
by CP2 between approximately 5Hz and 50Hz. 

UNIT "A" will now be ready for analysis of the 
Fig. 5.6a tuned circuit, and will also cover a useful 
range of other values for L, C, and R in real time. 

When handling sinusoidal or step functions, an 
amplifier will still have a maximum output voltage 
swing of ± 10V, but this will be the peak voltage value. 
To check for overloading with an ax. meter, ensure 
that amplifier output voltages do not exceed 707V 
r.m.s. for a sine wave function, and 5V mean for an 
equal mark-space square wave. 

RESCALING PROBLEM EXAMPLE 3, 

To rescale the problem for larger or smaller values 
of L and C, beyond the coverage of CP2, and by 
abandoning real time operation, note that a tenfold 
increase in tuned circuit frequency corresponds to a 
hundredfold increase in 1/LC. For most applications, 
where the series resistance R will lie between zero and 
just beyond critical damping (R > 2\/[X7C]), the scaling 
of RfL can stay as it is for all reasonable values of 
L and C, but should anyway only be changed by adjust- 
ment of the gain factor at OAI /Input 1 . Similarly, the 
/(T)/£ gain of 100 at OAI /Input 2 can remain fixed. 



It is not necessary to use inconveniently large or 
small input functions when rescaling for new voltages 
and currents. 2V r.m.s. could equally well represent an 
input function of, say, 02V r.m.s., and from Ohm's 
Law the current / will automatically become 2mA, 
instead of the former 20mA, even though it is still 
represented by 2 computer volts. 

If it is desired to extend the computer operating time, 
by adjustment of integrator and inverting amplifier 
closed- loop gains, refer to Table 5.2, while remembering 
that integrator closed-loop gains are calculated on the 
basis of 1/RmCi where i? is in ohms and C is in farads. 

For reasons of reduced accuracy, it is not advisable 
to use computer operating frequencies above 1kHz or 
below 005Hz in connection with Problem Example 3. 
It should be mentioned that although frequencies in the 
region of 005Hz are too low for display on an a.c. 
coupled oscilloscope, the behaviour of a system can be 
demonstrated in slow motion by the oscillating move- 
ment of a d.c. voltmeter pointer (centre-zero). 

Some typical oscillograms are given in Fig. 5.7 to 
show the response of a simulated tuned circuit. If the 
computer oscilloscope is provided with a good graticule, 
and has a linear response, amplitude and time measure- 
ments which are accurate to within approximately 
5 per cent may be obtained straight from the trace. 

The behaviour of a real tuned circuit can be evaluated 
by comparison with a simulated circuit. A tracing is 
made of the real circuit oscilloscope display, and is then 
superimposed on the readout given by the simulated 
circuit. The computer is adjusted so that time scales 
are related by a known factor, and tracing and readout 
display are identical, then quantitative measurements 
are taken from the computer voltages and dial settings. 
Next month: The construction and operation 
of UNIT "B" 



371 



DENTOPHONICS 

BY F.R.BERTRAND, BOS. 



The term Dentophonics has been applied to the tech- 
nique of broadcasting speech from the mouth by the 
use of electronics. 

Dentophonics works on the same principle as a throat 
microphone, where a transducer picks up the sonic energy 
transmitted through the tissues as a person speaks. 
This is quite distinct to normal microphone techniques 
which rely upon air pressure waves. 

Dentophonics (DP) is easily demonstrated by the follow- 
ing experiment. Plug a sonic probe into the input socket 
of an audio amplifier. Press the sonic probe against a 
subject's tooth as that subject is speaking, and the voice 
of the subject will be clearly heard through the loudspeaker. 

TISSUE TRANSMISSION 

A sonic probe with a broad surface will pick up sound 
from various parts of the head, including the forehead, 
temple, cheekbone, and the cheeks themselves. To 
obtain good speech reproduction from the cheeks, the 
sonic probe has only to be gently pressed against a cheek. 
This shows quite clearly that sound is transmitted through 
both hard and soft tissues of the body, and it would 
therefore be better to drop the term "bone conduction" 
and use the term "tissue transmission". 

The extent of the tissue transmission of sound is shown 
by the following experiment. 

A sonic probe was held firmly in a subject's extended 
right hand. This sonic probe was connected to the 
output of an audio amplifier, and a signal generator was 
connected to the input socket of the same amplifier. 
The same subject held another sonic probe in his extended 
left hand and this second sonic probe was connected to 
the input of another amplifier, a loudspeaker being con- 
nected to the amplifier output. The subject holding the 
probes was in one room, and the loudspeaker was in 
another room. When a signal of 1,000Hz was transmitted 
through the sonic probe in the subject's right hand, this 
signal was picked up by the sonic probe in the subject's 
left hand, and was clearly heard by an observer in the 
room with the loudspeaker. 

BUILT-IN ELECTRONICS 

Whilst speech may be picked up by a transducer from 
various sites of the head, the mouth offers the most 
interesting possibilities, in that there would appear to be 
no reason why miniaturised electronic equipment should 
not be built-in, at this present time. Already in various 
experiments to obtain information on the occlusion of 
the teeth, up to six radio transmitters have been "built 
into" the mouth. 

Any miniaturised electronic equipment designed for 
placing in the mouth could be incorporated into bridges 
or dentures. The miniaturised equipment could be 
designed to be removable, and capable of being switched 
on or off. 

A dentophonic appliance will have the advantages over 
a throat microphone, of being less bulky, and also of 
giving better and clearer speech reproduction. A DP 
probe will pick up speech from an artificial tooth provided 
the artificial tooth is firmly fitted. 

The great advantage of dentophonics is the elimination 
of background noise. Transducers used for DP are 
designed to pick up the transmission of sound in solids, 
and should not pick up airborne sound. This means 
that the speech of a subject in a high level of background 
noise could be heard quite clearly without any inter- 
ference by the background noise. 



Another advantage of DP is that there will be no need 
for the so called "microphone technique" that the public 
speaker or performer has to learn. 

One objection to DP is that the noise of the teeth 
occluding will be picked up; but this objection would 
only be valid where a subject has nervous clenching 
habits, as normally the teeth mainly occlude during 
mastication, the position of rest being with the teeth 
slightly apart. 

POSSIBLE APPLICATIONS 

The applications of DP will be many and varied, but 
this technique could certainly be used by the following 
persons: outside television and radio commentators, 
motor racing drivers, aviators and astronauts, public 
speakers, theatrical performers, and deep sea divers. 

Where background noise is such that a subject's hearing 
may be damaged, the ears could be protected by muffling, 
and communication established by using the DP technique. 

DP could be used for teaching deaf children to speak, 
The DP probe would pick up the sound of the deaf child's 
own voice, and even if the child had no hearing whatso- 
ever, the child would be able to compare the movement 
his or her voice produced with the movement that the 
teacher's voice produced. 

THROUGH SOLID MASS 

Another interesting experiment can be described. 

Two audio amplifiers were used, one had a microphone 
and a probe connected to it; the other had a DP probe 
and a loudspeaker connected to it. A subject spoke into 
the microphone, and as he was speaking the probe was 
pressed against the wooden casing of the first amplifier, 
and the second probe was pressed against the other end 
of the wooden casing of the same amplifier. The subject's 
voice was clearly heard over the loudspeaker. Thus, 
audio sound had been transmitted through a solid and 
picked up at the other end. 

Perhaps this technique could be applied as a means of 
communicating with people who become entrapped in 
certain tragedies such as occur in mines or at sea. 

Finally, it is apparent that dentophonics in conjunction 
with the audiodental technique opens up a new, relatively 
untried, but highly promising field of communications. 



For Future Reference 



An index for volume three (January 1967 
# to December 1967) is now available price 

Is 6d inclusive of postage. 

Easi-binders are available price 14s 6d 
9 inclusive of postage. State whether "Vol. 

I ", "Vol. 2", "Vol. 3" or-'Vol. 4" is required. 

Orders for Binders and Indexes should be 
addressed to the Binding Department. 

Orders for copies of the Index only should be 
addressed to the Post Sales Department, George 
Newnes Ltd., Tower House, Southampton 
Street, London, W.C.2. 



372 



DE LUXE PLAYERS 

4-Speed Mono Players 2-tone 
CaMnets 17xl5-x 8tfn. High 
flui loudspeakers and High 
Quality Amplifier* ready 
built. Quality output. Volume 
and Ban controls 
Special instructions 
enable assembly in 
30 minutes, Only 5 
wlrei to iota. 
12 months' 
guarantee. 

ASSEMBLE 
YOURSELF > 

Port 5/8 per item. 
PORTABLE CABINET 
Ai ill nitrated. To St 
standard player £Q If, 
or au to change r. •"/w 
BOS AMPLIFIER 3 
WATT. £^z'- made and 
tested with V L8B triode 
pentode valve CO if. 

ind loudspeaker •'T/O 
SDT GLE PLAY S RS M NO 
Starr (6 volt; £8.18.6 

EMI Junior £3.10 ts 

Garrard SRF32 18.19.6 
Gorrard SPSS £13.19.8 
Philips AG1016 Jll.lfl.8 
Garrard A70 £14.19.8 
Garrard LAB 30 £84.19.8 
Garrard 401 £89.19 6 




SUPERIOR AMPLIFIER. 
Ready made and tested. 
Better sound! Isolated AC 
Mains Transformer 3 watt 
output. ECL82 triode 
pentode valve. Volume 
and tone controls with 
knobs, quality QQ .' Z 
Londspeaker, *" ; ° 

A UTOCH ANGERS MONO 
BSR Snpersiini £7.19.8 
Garrard 1000 £8,19.6 

BSR Transcription UA.70 

Stereo/Mono £18.19.6 
Garrard Stereo Mono 

Model 3000 £18.19.6 
Garrard AT60 £14.19 6 



All fitted LP/7S Stylii and PSek-up complete 
GARRARD TEAKWOOD BASE WB.l Ready tf ' 
cut lor mounting 1000, 8000. 3000. SP85, AT80 • J ' " 
GARRARD PERSPEX COVER SPC1 lor WB1. 65- . 
TRANSCRIPTION TONE ARM with template Qf\T 
two plug-in shells. Counterbalanced. OUR PRIDE '«.' " 
Decoa Dersm Stereo Diamond Cartridge £4 10 eitra 
Eade Stereo Movim; Coil Diamond £0-13,000 c.p. s 55 5 



Q MAX CHASSIS CUTTERS 

Complete: a die, a pnneh, an Allen screw and key 
J)0, 14/B Jin. 15/9 liin. 18,'- liin. 80,8 a&in. 37 '9 
iln. 14/9 lin. 18/- liin. 18/8 IJin. 22/6 2'Tii 44/3 
*' n ' lQ'6 lAin. IB/- 1 lin. 80/- Sin. 34/3 lin. sq 31/6 



PICK-UP ARM Complete with ACOS LF-78 Turnover 

£!2;'K, a ., 8 Il!!i£ S/ - f AC0S OP67 ' 1S '-- BS -»- TC8 85/-. 
SPEAKER FRET Tyg&n various colours, 52in, wide, from 
10/- It.; 26in. wide from 5/- It. SAMPLES S A E 
EXPANDED METAL Gold or Silver 18 x 18 la B ; - 



49/6 
99/6 



FULL WAVE BRIDGE CHARGER RECTIFIERS ■ 

8 or 18 T. outputs, 11 amp.. 8/8: 8 a. 11/3; 4 a.. 17.6. 
CHARGER TRANSFORMERS. P.&P.5/-. Input 800 850 
lor 8 or 12 y„ 1> amai,, 17/6: 2 amps,, 21,'- ; 4 amps.', 30' 

MOVING COIL MULTIMETER TK 85. 
0-l,000v. A.C./D.C, ohms to 100k. etc., 
SUPERIOR MOVING COIL MULTIMETER 
0-2,500*. D.C. 80,000 ohms per volt. 0-l.OOOv, A.C 
Ohms to B meg. 60 Mlcroamas. (Full list Meters S.A.E. ' 

NEW MULLARD TRANSISTORS 
OC71 6/-; OC78 6/-; OC81D 6'-; 0C81 6/-; AF115 8/-- 
AFU4 8/8; 0044 6/-; 0045 6/-; OC171 6.'-; OC170 6/- 
AF117 6/-. OC26 12/S: ADI40 15,-: OC35 15'- Holders 1,- 
REFAHCO TRANSISTOR TRANSFORMERS 

TT45. Push F ul 1 Driver 9 ; 1CT «/- 

TT40, Push Pull Output CT 8:1 6- 

TT49, Interstate, etc. 4.5:1 .„...„. 5. 

TT6B, Output 3 ohmi8Q:l , .,,. si. 

TRA1TSI8TOR MAINS ELIMINATORS. FAMOUS "POWER 
MITE", 9 VOLT. SAME SIZE AS FF9 BATTERY. Ar I 
FULLY SMOOTHED. 150mA, FULL WAVE CIRCUIT,^'" 

9 VOLT. 500mA POWER PACK. Size S:< 3! \ Bin, . .496 
DrTTO TRANSFORMER ONLY. SJgeE^:-: l:Vliin....lO:6 

WEYRAD PS0 — TRANSISTOR COILS 

RA2W 8 in. Ferrite Aerial Spare Cores 6d. 

with car aerial coil 12/6 Driver Trans, LFDT4 9'6 

O10. P50/1AC 5/4 Printed Circuit. PCAI. ...9/6 

I.F,pfiO/8CC 470 kc/s ... 5/7 I.B. Tuning Gang 10/8 

3rd I.F, P50/3CC 8/- Weyrad Booklet g/. 

Telescopic Chrome Aerials 8in. extends to 23j n . 5/- 



Volume Controls 

LOUS SPINDLES. MIDGET 
SIZE 5 K. ohms to 8 He;:. 
LOG or LOT. L/S 3/-. D.P. 67- 
STEREO LIS 10/6, D.P. 14/6. 
5 g. 8, P. Edge Type 5/-, 



80 ohm Coax 8d. yd, 

SEMI -AIR SPACED 
40yd. 20/-; 60yd. 30-. 



FRINGE LOW LOSS I 
Ideal BBS lines ■ 



A 



COAXIAL PLUG 1/3, PANEL SOCKETS'1/3. LINE SOCK- 
ETS 8/-. OUTLET BOXES, SURFACE OR FLUSH 4/6. 
BALANCED TWIN FEEDERS 1,'- yd., 80 or 300 ohms. 
CAB AERIAL PLUGS 1/6. SOCKETS 1/3; LINE SOCKETS 2 - 

SELMER 

TRANSISTOR 
AMPLIFIER 

QHE WATT 
POWER OUTPUT 

Portable Cabinet aije 12 X 4 
X 8in. fitted 7 X 4ta. Speaker, 
Volume Control, Standard 
Jack Socket. Uses PP9 Bat- 
tery. Will increase to tome and perlormauce 
ol Tranalator Radios, Record Players, Tape Recorders, etc. 
Ideal tor Guitar practice. OUR lO/i POST 




NOTICE 

ALL THESE PRICES FIXED TO JUNE 1st, 1968 



THE E.A.R. RECORD PLAYER CABINET 

Strongly built wooden cabinet covered in Blue and Orey 
leatherette size 15 X 17x8 in. Motorboard 14}xl2t in. 
ready cut out lor B.3.R. Monarch UA 12/14/15/18/85 decki. 
Gilt fittings, strong carrying handle. Amplifier space site 14 
X7x3in.il completely en do sed. The baffle board FQ if. 
is cot out lora Bi in, dia. speaker. P. St P. 5/8. PRICE 3 ~/ *» 



NEW TUBULAR ELECTROLYTICS , | 



2/350 v 
4/850 T 

8/450 t, 
16/450 » 
38/450 v, 
25/25 v. 
50/50 v. 



100/25 v. 
260/85 v. . 
500/25 1. . 
B-^ 8/450 t. 
8^16/460 v. 



CAN TYPES 
8/600 v 9S 

i8'600 t ie/8 

16-18,500 ». 7/6 
33^38/850 r. 3/8 
50-50/350 r. 71- 
60 + 100/350 y. 11/6 
100^200/275 v.12/6 



9 16 + 18/450 v, 4/3 

- 32->- 32/350 T. 4/6 
SUB-MIN. ELECTEOLYTICS, 1,8.4,5.8,16,85,80,50,100, 
850 mid. 15v, 2/-; 500, 1000 mtd. 12v. 3'B 8000 mid. 85v. 9/8. 
CERAMIC, 500 v, 1 pF. to 0.01 mid.. 8d. Discs 1/-. 

PAPER TUBULARS 
350v.-0.1 9d„ 0.5 2'6; 1 mid. 3/-: 2 mfd. 150T, 8'-, 
500v. -0.0O1 to 0.05 8d: 0.1 1/-; 0.85 1/8; 0.5 3/-. 
l.OOOv.-O.OOi, 0.0083,0.0047. 0.01,0.08, 1/8; 0.047,0.1 2/6. 
E.H.T. CONDENSERS. O.OOlmld.. 7kV., 6'6; 20kV., 10/8. 
SILVER MICA. Close tolerance (plus or minus i pF.l, 5 to 
47 pF.. 1/-: ditto 1°; 50 to 800 pF„ 1/-; 1,000 to 5,000 pF.. 2/-. 
TWIN GANG. "0-0" 208 pF. -■■ 176 pF,, 10/8; 385 pF„ minia- 
ture 10/-: 500 pF. standard with trimmers, 9/6; SOOpF. 
midget less trimmers, 7/6; 500 pF. Blow motion, standard »/-; 
small 3-cang 500 pF. 1B/B. Single "0" 385 pF. 7/8. Twin 10/-, 
SHORT WAVE. Single 10 pF., 25 pF., 50 pF„ 75 pF., 
100 pF., 180 pF., 5 6 each. Can be ganged. Couplers 9d. each. 
TUNING. Solid dielectric. lOOpF., 300pF.,500pF.. 5/- each. 
TRIMMERS, Compression ceramic 30. 50, 70 pF., 9d.; 
100 pF„ 150 pF., 1,3; 250 pF„ 1,6; 600 pF., 750 pF„ 1/9 . 

250 v. RECTIFIERS. Selenium 1 wave 100mA 5,'-: BY10O 10 -. 
CONTACT COOLED i wave 60mA 7/6 ; B5mA 9/8. 
Full wave 75mA 10*. ; 150mA. 19/6 j T.V. rests, Irom 10,'-. 



'S0N0C0L0R' CINE RECORDING TAPE 

5* reel. B00' LP with strobe markings also cine light de- 
flector-mirror lor synchronisation. Suitable 1 J 1 
all tape recorders and cine projectors. List 28.- 11; - each 

NEW B.A.S.F. LIBRARY BOXED TAPE 

Tin. L.P. i, 800 ft. 45 -; 7 in. D.P. 2.400 ft. 70 - 
60 min. Cassette C60 (For Philips, etc.) 17/6 

Spare Spools 2/6. Tape Splicer 5/-. Leader Tape 4/6. 
REUTER Tape Heads lor Collaro models 8 track 81/- pair. 



MAINS TRANSFORMERS 



Post 

/- each 

850-0-350 80 mA, 6.3 v, 3.5 a. 8.3 v. 1 a, or 5 T. 2 a. 80/- 
350-0-350 80 mA. 6.3 v. 3.5 a. 8.3 v. 1 a, or 5 v. 8 a. 35'- 
MT. 5I0'3OO-O-30O v. 120 mA.. 6,3 v. 4 a, 6.3 v, 2 a. 457- 

MINIATORE £00 v. 20 mA., II.3t.1i 12/8 

MIDGET 820 v. 45 mA., 6.3 T. 8 a. 17/6 

HEATER TRANS. 6.3 v. U a., 8/6; 6.3 v. 4 a 12/6 

Ditto tapped sec. 1.4 v., 2, 3, 4, 5, 8.3 v. I! amp. . . 18/6 
GENERAL PURPOSE LOW VOLTAGE, Outputs 3, 4, 5, 

6, 8, 9, 10, 12, 15, 18. 84 and 30 v. at 2 a 30/- 

1 amp., 8, 8, 10. 12, 16, 18, 20. 24, 30, 36, 40, 49, BO, 35/- 
AUTO TRANSFORMERS 0-115-230 v. Inpnt Output, 
80w. 18 6: 150W.30/.; 500w. 926; lOOOw. 175'-. 



CRYSTAL MIKE INSERTS 

l: :: tin. 68; ACOS 1} - iin. 8.6, BM3, 1' dia. 9/6 
MOVmo COIL MIKE with Remote Control Switch 19/8 
ALL PURPOSE HEADPHONES 

H.R. HEADPHONES 2000 ohms 19/6 

H.R. HEADPHONES 2000 ohms Super Quality 36/' 

LOW RESISTANCE HEADPHONES 3-5 ohms 35/> 



1968 
ORAM 
CHASSIS 




Post 5/- 

Tbree Waveba nds : F i v e V a 1 v es : EC H S 1 . EF88 . 

Long., Med., Short. Gram. EBC81, EL84, EZ80, 

12-month guarantee. A.C. 200-250 v. Ferrite Aerial 
5 waits 3 ohm. Chassis 13 tin. :■ Tin. X Sin. dial size 
18in y 4in, Two pilot Lamps. Fonr Knobs. /If) 10 
Aligned calibrated. Chassis isolated Irom mains •" ■ V. I T 
DE LUXE STEREO GRAM CHASSIS V.H.F., MW, SW 
19-50m, SW 60-lS0m. Magio eye, push buttons,/ 10 10 
8 valve plus rect. Size 15' at "'." 1 6' high fc I F. I F 



VEROBOARD 0.15 MATRIX 
8/ :■" 5iu. 3/8d. 8! X 3Jin. 5/8d. 32 x 3;in. 3,'Bd. 
EDGE CONNECTORS 16 way 4/-: 24 war 6/-. 
PINS 38 per packet 3/4d. FACE CUTTERS 7/6. 
S.R.B.P. Board 015 MATRIX 8: in, wide 6d. per lin; 3 iin. 
wide 8d. per lin; 5in. wide 1'- per lin. (up to lTin. 
BLANK ALUMINIUM CHASSIS. 18 t.w.g. 2! in. aides, 
7x4in.. 5'6; 9x Tin.. 6/8: llx3in. 6/6; llx7in. 7/8; 
13 x Bin. 9 6; 14*1110. 12/8; 15 <14ia.. 15/-. 
ALUMINIUM PANELS 18 s.w.e. 18xl2in. 8/6; 14 - Bin. 
5/8; 12 x Bin. 4/8; 10>i 7in. 3/6; SxBin. 2/6; 6>:4itt. 1/6. 

THE INSTANT 

BULK TAPE 

ERASER AND 

RECORDING HEA 

DEMAGNETISE 



800/250 t. A.C 
Leaflet S. A.E, 




CANCELLED EXPORT 
SHIPMENT 

15 BAKER 
WOOFERS 

80-10,000 eps. Bass 
Resonance 18-25 eps. 
Massive Ceramic 
Feirobar Magnet. 
Flu density 15,000 
lines. Rated 20 watts. 
15 ohms. Overall depth 
only 61in. Weight 15 lbs 




OUR C11 1Q C Carriage, packing 

PRICE *l lil «7iO and insnranee 10/6, 
"BONDACOUST " Cabinet Wadding 18in. wide 2/6 loot, 

BAKER GROUP SPEAKERS— ^J 

'Group 25' 'Group 35' 'Group 50' 

Jf»-.5gns. ^w a :Hgns. ^; I8gns. 



E.M.I. CONE TWEETERS 3J.in. Bfluare. 3-80kc/i. lOw. 17/8. 
Smtlity Horn Tweeters 8-18kc/s. lOw. £9/6. Crossover 18/6- 
LOUDSPEAKERS P.M. 3 OHMS. 2iin„ 3in.. 4in.. 5in.. 
7in. X 4in„ 15/6 each; Sin. 22/6; 6 J in. 18/6; lOio. 80/-; 
18in. double cone 3 or 15 ohm 35.-; 10 X Bin. 30/-; 8 X Sin. 21/.; 
E.H.I. Doable Cone 13J x Sin., 3 Of 15 ohm models, 45/-. 
SPECIAL OFFER! 8 ohm. 21io„ 5in,; SO ohm. 2iin.. 2jia. 
I C if. 25 ohm. 6in., 6x4in.; 35 ohm. 3in.,5in., 7 x din. 
1 J /° EACH TYPE. 16ohm.3in„7 ^5in.,10 X BJin. 
JACK SOCKETS Std. open-circuit 8/6. closed circuit 4/6. 
Chrome Lead Socket 7/8. DIN 3-pin 1/3, 5-pin 1'6; Lead 3/6, 
Phono Plugs 1/-, Socket 1/-. JACK PLUGSStd. Chrome 8/-; 
2.6mm.; 8.5mm. 1/8; DIN 3-pin 3/6: 5-pin 5/-. 
WAVE-CHANGE SWITCHES WITH LOHG SPINDLES. 

3 p. 2- way, or 8 p. 6-way, or 3 p. 4-way 4/6 each. 
1 p. 18-way, or 4 p. 8-way, or 4 p. 3-way, 4/8 each. 
Wavechmnge " MAKTTS " 1 p. 18-way, 8 p. 6-way, 3 p. 4-way, 

4 p. 3-way, 6 p. 2-way, Prices inclnde click spindles, adjustable 
stops, spaces, ete„ 1 water, 10/6; 8 water, 15/-; 3 water, 18/8. 
TOPPLE SWITCHES, sp. 2/6; sp. dt. 8/6; dp. 3/6: dp. dt. 4/6, 



ALL EAGLE PRODU CTS 

79/6 



EAGLE AM TUNER. Medium Wave. 
Transitto rSuperhei. Ferriteaerial.e tc. 

EAGLE DE LUXE TAPE SPLICER Cuts, trims, I fit, 
joins tor e diting and repaira. With 3 bla des. I */v 

EAGLE 4 CHANNEL TRANSISTOR MIXER. Add 
musical highlights and sound effects to recordings. Will 
mix Microphone, records, tape and tuner with 

separate controls into single output. 

EAOLE DVSAMIC MICROPHONE. Impe- /£ IZ #, 
dance 600 ohm/50K. 70-12,000 ops. Universal ***• I Q.U 
mounting , stick, hand or stand. Prolesgiona l qaality, 

Siz Transistor. Ready 
Calibrated slide dial £Q Inn 



EAGLE FM TUNER 88-108 Mc 
built. Printed Circuit, 
toning. Size 6" x 4' 



EAGLE 3 WATT AMPLIFIER. 4 Transistor Z Q If. 
Push-pull Ready built, with volume control OF/ a 

40- PAGE EAGLE CATALOGUE St- Post Free 



■k RADIO BOOKS -k (Postage 3d.) 

High Fidelity 6 peaker Enclos ore a a nd Plant 5/- 

Traosistor Snperhet Commercial Receivers 7/6 

Mullard Audio Amplifier Manual 8/6 

Radio Valve Guide, Books 1, 2, 3, or G each 5/- 

Practical Radio Inside Out.. 4/6 

Transistor Audio Amplifier Manual Book 1, 3/6 ; Book 2, 6/- 

Shortwave Transistor Receivers 5/- 

Traniistor Communication Set! 6/- 

International Radio Stations List 2/0 

Modern Transistor Circuits for Beginners 7/6 

Sub-Miniature Transistor Receivers 57- 

Wirele is World Radio Valve Data 9/S 

At a glance valve equivalents... 6/» 

Tarvel. Transistors. Diodes equivalents manual ,10/6 



Worth Doable! PRICE 

RETURN OF POST DESPATCH Minimum P«t and Packing ehorgeTi/6, 

RADIO COMPONENT SPECIALISTS 



RESISTORS. Prelerred values, 10 ohms to 10 meg. 
i w., i w., 1 w., 20% 3d.; li w. 8d,; 2 w. 1/-; * w, 10% Id. 
HIGH STABILITY. I w. 1% 10 ohms to 10 meg., 2/-. 
Ditto 5%. Prelerred values 10 ohms to 22 meg,,8d. 
5 watt -) 0.5 to 8.2 ohm 8 w, f 1/6 

10 watt > WLRE-WOUND RESISTORS < 1/B 

15 watt J 10 ohms to 6.800 obras L 2 - 

10K, 15K, 80K, 85K, 68K, 10W. «/- 
WIRE-WODND 3-WATT WIRE-WOUKD 4-WATT 
POTS. T.V. Type. Valnes STANDARD SIZE POTS. 
10 ohms to 30 K., 3/3, LONG SPINDLE VALUES 
Carbon 30 K, to 8 meg., 3/-. ■ 60 OHMS to 100 K„ 7/8, 

VALVE HOLDERS. MOULDED Sd; CERAMIC 1'- EACH. 

SCREEB1WO CAW3 1.'-; VALVE BASE PLUGS T 8i3. 

SANGAMO 3 inch SCALE METERS 45/- e a. 

Virions calibrations and movements. 100 Microsmp; 
1 MilUamp 50-0-50 Microamps, etc.,, S.A.E. lor Hit. 

BRAND NEW QUALITY 
EXTENSION LOUDSPEAKER 

Black plastic cabinet, 20ft. lead and 
adaptors. For any radio, intercom, tape 
recorder, etc. 3 to 15 ohm. POST JQ / 



Size: 




i' I Si' i 3' 
C.O.D. Sj. extrc. Full List //-. CALLERS WELCOME 

337 WHITEH0RSE ROAD, WEST CROYDON 



Written guarantee with every purchase. (Export; Sencf remittance and extra postage, no C.O.D.) Buses 133, 68 pass door.S.R. Sin. Seihurst. Til. 01-6384-18(5 



373 



4 STATION INTERCOM 




SoItc your communica- 
tion problems with tais 
*-SUrton Trumitor Intercom system (1 matter ami 
8 Sabii, in de-luxe pl.ieitc cabinets [or desk at wall 
mounting. Call/talk/lletcn Irom Muter tn Suit ami 
Sub! to Hsiter, Meal lj- suitable (or Business, Sur- 
gery, Schools, Hospital, Office and Home. Operates 
on one 9V battery. On/oft switch. Volume control. 
Complete with 3 connecting wires curb fiOIt. ami 
other accessories. P. & F. 7/G, 
WIRELESS INTERCOM 
Ho batteries — no wi«r. Just plug in tlw maius lur 
instant two-way, loud and clear 
On.'ofl switch and volume control. 
T. & r. 7/0 extra, 

If! 




Same a« 4-Station Intercom lor two-way instant 
communication. Ideal as Bahy Alarm asd. Uoor 
Phone. Complete with 06ft, connecting wire. Battery 
2(8. P. & P. 3/6. - 

map 

59/6 

'Why not boost 
business effi- 
cieucy with this incredible De-Luxe Telephone Ampli- 
fler. Take down long telephone messages or converse 
without holding the handset. A uselul office aid. On/ 
oft switch. Volume control. Battery 2/0 extra. P. & P. 
2/6. Full price refunded it not satisfied In 7 days. 
WEST LOrTDOH DIRECT SUPPLIES (P/E5) 
169 KEHSraGTOrf HIGH STREET, LONDOJT. W.S 




CRESCENT RADIO LTD. 

(electronic component specialists) 

For all regular components try 

40 Mayes Road, Wood Green, N.22 

For surplus components 

and equipment try 

1 1 Mayes Road, Wood Green, N.22 

BARGAIN BOARD NO. I 

7in x Sin board with the following compo- 
nent) attached: 

2 GET872A transistors 
2 Mullard OA 10 diodes 
2 Mullard OA5 diodes 
(2 Midget iW Resistors various values 
8 Midget Capacitors various values 
Including postage in Great Britain 4/- each 

BARGAIN BOARD NO. 2 
Siin -, 4in printed board with the following 
long lead components: 20 diodes, including 
Mullard OA73 and OA86; 12 5% jW resistors. 
Including postage in G.B. 3 - each 

TRANSISTORS AND DIODES 

2/6 each 
5/6 each 
5/- each 
5/- each 
2/6 each 
3/6 each 
4/- the pair 
1/6 each 
2/6 each 



AAI20 

BYI05 

ACI67 

ACI6S 

2N397 

2NI308 

Matched 2G37BB and 2G339B 

2G339A 

2G40I 

SPECIAL LINES 
Power transistor heat sinks 7tn X 2lr> I/- each 
Double transistor copper cooling clips 9d each 
2jin transistor speaker, B0 ohms 5/6 each 
Double pole rotary ON/OFF mains switch 
2/- each 
On one bracket 2-500WQ pre set pots plus 

! D.P, rocker mains switch, 1/9 
250k(l pre set pot linear I/- each 
Midget Skll pot with D.P. switch 2/6 each 
PRINTED CIRCUIT BOARD 

9±in .-: Bin 2/6 each 

Bin x Sin I /I I each 

I2in v. 3in 1/3 each 

A. M. RADIO TUNER 
2 valve Medium and Long Wave tuner with 
power supply, will give good reception through 
any amplifier. Price on this item includes 
Postage and Packing, tA. 0. 0. 
PLEASE INCLUDE POSTAGE WITH 



NEW RANGE BBC 2 AERIALS 

AU U.H.F. aerials now fitted with tilting bracket 
and 4 element grid reflectors, 

JjOtt Mounting Arrays, 7 element, $71*. 
11 element, 45/-. 14 element, S2/6. 13 element, 
«/-. Wall Mounting; with Cranked Arm, 

7 element, «0/-. 11 element, 87/-. 14 element, 
75/-. 18 element, 83/6. Mast Mounting with 
2ln. clamp. 7 element, 42/8; 11 element, 55/-; 
14 element, 62/-; 18 element, 70/-. Chimney 
Mounting- Arrays, Complete, 7 element, 
72/6; 11 element, 80,'-; 14 element, B7/6;18 element, 
«/-. Complete assembly Instructions with every 
unit. :Low Loss Cable, 1/8 yd. U.H.F. Pre- 
amps from 75/-. State clearly channel number 
required on all orders. 

BBC • ITV AERIALS 

BBC CBaad 1). Telescopic 

loft, 3*/-. External S/D, »/-. 

"H", £2.15.0. 

ITV (Band 3). 3 element loft 

array, 30/-. 5 element, 410/-. 

7 element, 50/-, Wall mounting, 

3 element, 47/6. 5 element. 52/6. 

Combined BBC/ITV. Loft 

1+3, 49/-; 1 + 5, 50/-; 1+7, 

60/-: Wall mounting 1+3, 57/6; 

1+5, 67/6; Cnlmney 1+3. 67/6; 

1+5,75/-. 

VHF transistor pre-amps, 

75/-. 

COMBINED BBC1— ITV— BBC2 AERIALS 

1+3+9. 70/. 1+5+9, 8*-/. 1+5 + 14, It/-. 
1+7+14, 100/-. Loft mounting only. Special 
leaflet available. 

F.M. (Band 2>. Loft S/D, IS/-, "H", 32/6, 3 
element, 55/-. External units available. Co-ax. 
cable, 8d. yd. Co-ax. plugs, 1/4. Outlet boxes, 5/-. 
Dlplexer Crossover Boxes, 13/6. C.W.O. or CO.D. 
P. & P. 5/-. Send 6d. stamps for Illustrated lists. 

CALLERS WELCOME 

OPEN ALL DAY SATURDAY 

K.V.A. ELECTRONICS (Dept. P.E.) 

27 Central Parade, New Addinaton 

Surrey— CRO-O J B 

LODGE HILL 2266 



J 



p\-'*i3^' 



HOME RADIO (MITCHAM) LTD. Dept. PE, 187 London Road, Mitcham, Surrey, CR4 2YQ Phone 01-648 3262 

CAPACITORS, Hon Electrolytic 




CAPACITORS, El 


(ctrolytic 




Lilt No. 


Opacity 


Voltage 


Price 


1SGI 


1.500mF 


50V 


6/- 


IBG2 


SDOmF 


25V 


4/- 


IBG3 


500mF 


12V 


V- 


IBG4 


lOOmF 


50V 


2/6 


IBGS 


32m F 


45QV 


4/6 


IBG6 


32mF 


350V 


% 


IBG7 


BmF 


500V 


m 



Liit No. 


Capacity 


Voltage 


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Capacitor Pack containing Silver Mica, Moulded Mica and paper condensers. Silver Mica 
values 15,25,65,71,80, 160,200.240,330,470, 1,000, 1,500, 1,670,4,000 (the470pFare 
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Price 3/6 

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Lilt No. Capacity Gangs Notes 
IBGIS lOpF 



Air Tune 
lacks on 



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F.M.) 



3/6 



46 



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IBG23 50 + 50x50 1- 
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CAR SUPPRESSORS 

I BG26A Car Plug Suppressor* 4 for 4/6 



Every year we acquire a number of exceptional bargains which 
we offer first of all to the purchasers of our Catalogue, in the 
form of a special bargain list. To give you a taste of these 
tempting bargains we reproduce a part of the list here. 
The rest of the list consists of many other most interesting bargain 
items — Diodes, Neon Lamps, Switches, Transformers, Valves, 
etc. We can supply the complete list for a shilling, but better 
still, why not buy our 1968 Catalogue and get the list free. The 
Home Radio Catalogue is acknowledged as one of the finest 
electronic components catalogue available today — its 256 pages 
list over 7,000 items, more than 1,300 of them illustrated. And 
with the catalogue, in addition to the bargain list, you get five 
vouchers, each worth a shilling when used as directed, a voucher 
worth another five shillings if used to purchase a Weller Soldering 
Iron, an order form and an addressed envelope. All this for 9/6! 
(7/6 plus 2/- P. & P.). Why wait? 



Send your cheque or P. O. with 
this coupon today! 



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374 




MODIFICATION FOR PRE- HEATING 
THE LAMP ELECTRODES 



We have been advised by a well known lamp manu- 
facturer that the 6W 9in lamp employed in the 
Fluorescent Camping Light (March 1968) is designed to be 
used only in circuits which arrange to pre-heat the lamp 
electrodes either before, or simultaneously with, the 
application of a pulse or steady state voltage across the 
lamp in order to start it. 

It is explained that the practice of cold starting, as in our 
published design, can result in very heavy lamp end 
blackening, and a very short lamp life. 

We are therefore publishing an alternative circuit by 
R. B. Hayle which incorporates a pre-heat facility. 

In the modified circuit Fig. 1 the "low" output switch 
position is omitted, and a three- pole switch is used in place 
of the two-pole switch specified in the original circuit. This 
enables the electrodes to be energised via R4, which should 
be selected so that, with a 12V supply battery, the pre- 
heating current is not less than 160mA. 

Under these conditions, switch SI should be held in 
position 2 (pre-heat) for at least one second before going 
over to position 3. Capacitor C2 is permanently connected 
to CI, Rl, R2, and Tl. The switch is now used entirely 
for preheating and running. The amount of rewiring in- 
volved is not great, and readers will be able to convert their 
Camping Lights with little difficulty. 

A modified wiring diagram 
of SI is shown here in Fig. 2, 
Similarly modified versions 
of the main unit wiring are 
shown in Fig, 3. 

The pot-core assembly LAS 
can be obtained from retail 
outlets of Milliard com- 
ponents including Henry's 
Radio Ltd. whose address is 
on the back cover. 

The author does not advise 
the circuit to be converted 
for a 6 volt battery supply. 
The saturation voltage across 
the transistor becomes a sig- 
nificant factor and leads to 
reduced efficiency. A 6V 
version would have lead to 
undesirable circuit complica- 
tions. 

Fig. 3. Top and underside 
views of the electronics in- 
cluding the modified wiring 
details 




Switdi pottUom 1-OFF 

2-PftEHEAT MQ-J50ml" 
_. , 3-START 440mA 

Fig. *. Modified circuit diagram. An extra resistor R4 Is 
needed 




r«d orwn LMd5 „((„ 

TogA TogF onn ToflE 

Fig. 2. New wiring details of SI. Resistor R4 is 4 7 LI 3W 

wirewound 




375 



nA 



A SELECTION FROM OUR POSTBAG 




Traffic delay 



Sir — I am interested in the mechanical 
delay system employed in car rever- 
beration units that I have seen and 
heard on recent visits to the U.S. 

Radiomobile have done some 
research but have since dropped the 
idea as they feel there is insufficient 
interest over here (or so they say). 

One problem appears to be the 
harder springing of U.K. vehicles 
than that found on U.S. cars, however, 
1 hear there is even one delay system 
now that allows the car to be driven 
off the curb without vibration to the 
unit. 

I am told that the spring (or 
whatever) assembly should be 
mounted along the car axis and not 
across it. 

I am not deterred by hard springing 
and am keen to build one and use it in 
conjunction with my car radio, and 
do not see the electronics posing too 
much of a problem. 

I am advised that a 2 watt output 
from the echo amplifier would be 
sufficient against the 8 watt output 
of my radio. Control of echo is 
normally done from a potentiometer 
mounted under the dashboard. 

A speaker mounted on the back 
shelf (if possible) alongside the main 
speaker makes the sound appear to 
be 100ft behind you. A marvellous 
sensation for relaxing in heavy 
traffic. 

In conclusion, I should appreciate 
any information you or any readers 
could give me as to the best drive, 
pick-up units (to avoid microphony) 
and the best suspension to avoid 
rattle. 

M. C. Bell, 
Henley-on-Thames. 
Any suggestions ? 



Cranky? 



Sir— Whilst this magazine publishes 
many interesting and useful projects 
it sometimes contains circuits which 
are complicated when compared with 
the function they are intended to 
perform. I feel that there is a real 
danger of using electronics simply for 
the sake of using them. This could 
easily detract from the useful purpose 
of the magazine and the good 
standing of electronic experimenters. 
Any person using a complicated 
circuit to perform a simple function 
must be regarded as a "crank". For 
Impact Counter (March 1968) with 
a transducer, Schmitt trigger, twenty 



resistors, eleven capacitors, seven 
transistors, five diodes, etcetera, why 
not connect the electro-mechanical 
counter to a pair of contacts and a 
battery? The contacts may wear 
but the saving on the other compon- 
ents would more than pay for them. 
As for the steam presence alarm, same 
issue, dare I suggest a whistling 
kettle? 

F. Crimmins, 
Folkestone, Kent. 

IMPACT COUNTER. To answer this 
criticism, it is necessary to explain the 
particular problem this device was 
designed to cope with, 

The originat purpose of the impact 
counter was to count small neon lamps, 
which weigh J$oz. The contacts must 
not close more than once per neon, and 
must always close whether the neon wire 
leads are upwards or downwards. It is 
not possible to use anything but a very 
open funnel as the neons tend to bridge. 
The closure time must be long enough for 
the counter to operate properly, therefore 
the monostable pulse is adjusted so that 
it allows the neon to bounce inside the 
pulse length. 

For industrial use reliability and ease 
of replacement are important. This 
circuit divides readily into four parts 
which can be tested independently. 
STEAM PRESENCE ALARM. You can 
certainty suggest a whistling kettle, but 
it would be no use to a deaf person, or if 
you are out in the garden. The simple 
sensor can be used with an electronic 
relay to operate an audible alarm, or even 
to switch off the stove if you wish. 

May we suggest these are two good 
examples of electronics being used 
practically? 



What's in the box? 

Sir — I was very interested by C. F. 
Weir's article in the February issue 
of P.E. on Cine and Tape Sync. His 
suggestion at the end for an all-elect- 
ronic version prompted some thinking 
on my part because I possess a similar 
cine system to that of Mr Weir, but 
in 8mm. 

It occurred to me that a 1 6 frame/sec 
projection has each frame flashed 
three times on the screen to avoid 
flicker, this being done by a rotating 
disc with three sectors in the optical 
projection system. Thus the screen 
picture flashes 48 times per second. 

If the projection rate is increased 
to 16i frames/sec, then the picture 



flashes become 50 per sec. This 
could be synchronised with a 50Hz 
signal from the second track of a 
tape recorder, if the flashes are 
detected by a light sensitive resistor. 
At this point I am stumped, because 
the next step is to convert any error 
in the two frequencies into a signal 
which will fire an s.c.r. in the power 
leads to the projector. The problem 
is set in the following diagram. 

Could any readers possibly suggest 
a circuit for the black box? 

The tape recorder need not be a 
full stereo type, but it should be four 
track with leads to the head winding 
which is not actually playing the 
sound track. This is the case with 
many Philips/Cossor/Stella machines 
which are mono with a stereo outlet 
socket. If the model is transistorised, 
then the same socket could provide 
power for the "black box", since a 
few milliamps at about — 20V are 
available. Two-track machines could 
have a third head mounted to scan 
the lower track, which should be pre- 
recorded, when the upper track is 
recorded with 50Hz from a step-down 
mains transformer. 

It is important to note that the 
s.c.r. will only control an a.c./d.c. 
type motor, and the control should 
never feed a transformer which is used 
to power a low voltage projector bulb. 
D. Watts, 
Lincoln. 




Series of talks 

Sir — Your Sussex readers may be 
interested in the following announce- 
ment, which will shortly be locally 
advertised : 

"A series of six talks and de- 
monstrations on High Fidelity, 
Stereo and Sound production will 
be given weekly at the Portland 
Further Education Centre, 1 1 Port- 
land Road, Hove, on Wednesdays, 
commencing 24th April, 1968. 
Evenings from 7.0-9.0 p.m. 

Further details may be obtained 
from the Principal for Further 
Education at 62 St Leonards 
Gardens, Hove, Sussex." 



376 






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SERVICE SHEETS 



SERVICE SHEETS, ltntlio, TV, 5000 models. 
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RADIO TELEVISION, over 8,000 Models. 
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advantage. 

Pay according to age, e.g. at 19— £828, 
at 2 5 -£1,076. 

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salary range £1,159-£1,°41. There are a 
few posts carrying higher salaries. 
Annual Leave allowance of 3 weeks 
3 days, rising to 4 weeks 2 days. Normal 
Civil Service sick leave regulations apply. 
Application forms available from: 

Recruitment Officer (RT/54) 

Government Communications Headquarters 

Oakley 

Priors Road 

CHELTENHAM, Cloi. 




SITUATIONS VACANT (continued) 
RADIO & TELEVISION SERVICING 
RADAR THEORY & MAINTENANCE 

Vacancies regularly exist in industry for men with good knowledge 
of Radio TV and Radar, Our one-year day courses provide 
effective training. Shorter day courses available for men with 
experience. Write for details to: — 

The Secretary, London Electronics College, 20 Penywern 
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YOU NO MAM, age about 17, required for 
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378 



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TRONICS with the world's luraest home study 
organisation. I.E.R.E.; City t fe Guilds; 
R.T.E.B., etc. Also practical courses with 
equipment. Xo books to buv. Write for 
FREE Prospectus to K.'S { Dept. 577), Tntertext 
House, London, SW11. 



FREE TO AMBITIOUS ENGINEERS! 182 

page Guide to B.Sc. (Ens.). A.M.I.E.R.E., 
A.M.S.E., A.M.T.M.I., City ,t Guilds, A.I.O.H., 
A.R.I.C.S., G.C.B., etr., on "Satisfaction or 
Refund" terms. Thousands of passes — over 
800 Home Study Courses in all branches of 
Engineering Building, Radio. Electronics, etc. 
Write: B.I.E.T. (Dept. 125K), Aldermaston, 
Cnurt, Aldermaston, Berks. 



SET INTO ELECTRONICS — big opportunities 
for trained men. Learn the practical way with 
low-cost Postal Training, complete with equip- 
ment. A.M.I.E.R.E., R.T.E.B., City & Guilds, 
Radio, T/V, Telecoms,, ete. For FREE 100- 
page book, write Bept. 858K, CHAMBERS 
COLLEGE, 148 Holborn, London, E.C.I. 



HI-FI EQUIPMENT 



EXT ENS (ON SPEAKERS in mahogany, hand 
veneered and polished complete with 7x4 
speaker. Retail price 46/- carr. paid. Trade 
enquiries invited. P. F. & A. R. HEI.ME, 
Dept. PE, Butcher Pasture, SiimmeTb ridge, 
Harrogate, Yorks, 



BRIMHAM 

—A NAME WORTH HEARING! 

FULL DETAILS OF: 

BRIMHAM SPEAKER 
SYSTEMS 

LOUDSPEAKER CABINETS 
EOR D.I.Y. 

FROM 

P. F. & A. R. HELME 

(Oept. P.E.) 

BUTCHER PASTURE, SUMMERBRIDGE 

HARRUUATE, YORKS. 



CITY AND COUNTY OF BRISTOL 

BRISTOL TECHNICAL COLLEGE 

Principal: E. Poole, B.Sc.(Eng.), C.Eng., M.LMech.E., M.I.Prod.E. 

CAREERS IN RADIO AND RADAR 



Licensed Aircraft Radio 
Engineers 

2-year full-time course for 
A.R.M.E. Licences, categories A 
and B, and six months courses 
for Radar Rating in association 
with the above. 



Marine Radio Officers 

2-year full-time course for young 
men aged 16, upwards, leading 
to First and Second Class P.M.G, 
Certificates and B.O.T. Radar 
Maintenance Certificate. 

Conversion Course (Second 
Class to First Class). 

R.T. Courses (for Full or 
Restricted Licence). 

Marine Electronic Maintenance 
Engineers Course (for qualified 
Marine Radio Officers). 

Training given on the latest types of Marine and Aircraft 
Equipment in newly equipped Laboratories at 

THE SCHOOL OF MARINE RADIO AND RADAR 

Senior Lecturer-'tn-Charge: F. E. Barltrop 
For details, write to: — 

The Registrar, BRISTOL TECHNICAL COLLEGE 

ASHLEY DOWN, BRISTOL 7 



379 



ELECTRICAL 




Brum) new luJIy I Transistorised and luUy portable 
Comnitialo!vti"n» Betel ver. Sjiecitieatituis: 4, complete 
r3D(!i.'8 530 K i-H to 30 Mrs, cotcriag nil miialciir hands, 
shipping ami trawler bamis. and bn>»ik-ai>l buhl, A 
blahlv t-IDi-iciit dsdbte tuneil snperhct, comprliluu H/l' 
aeriut tunlDB Motion, A.V.C. and built in R.f-'.O. tot 
C.W. nr 8MB reception. Ideal fur fixed or mobile 
reception. With upcnker ami headphone milpvit. 
Hainrncr rttibhial fibitst steel raise of plrusliisr modern 
design. Sine appnij,. !« 7 tiin. HritMj inamiiwtiirc. 
Due to huge purchase «t ran oiler ihese excellent 
receivers at less then hall their normal (price . Complete 
with handbook llfl/lO/O, eaftlsge and insurance 17/ii. 
Hcadphoiiei" il required 13 - art**, 1>-V- S/*, FRKE. 
FRKE. Kirrt on I era received up to tour teen day* niter 
publication dale at this advertisement will receive free 
a wonderful battery eliminator enabling yon U> rim 
this receiver and moat transistor radios dine I from the 
■Nktttja, 



HEAT 






mm 
comoLUw* 




LATEST KletSUXKUAJUJ liMAMHKUi MM, l.LT 
YOrit KLKCTRIUTV BILLS BY WALf. FISHER- 
TIP CONTROL OF ALL ELKl'TKICAL 
ACTLIASCBH YV TO 3,000 WATTS, HEAT. Vary 
the heat of vour KLBCTBIC KIBES, and save elcc- 
Irlcitv. Ideul lor ELECTB1C BLASKKTS. house- 
hold "IRONS, nitunicr vour ELECT R If KETTLE. 
Excellent lor St 'N -RAY LAMPS. LIGHT. I'lmtrnl 
tho lirlitbluis- of ;ill household LAMl'S, from a (thai 
to lull lirlf.hlac M . Ideal fur SPOT LAMPS. ARC 
LAMPS, etc. refill for FLOODLIGHTS. SPEED. 
Controls the toeed of ANY KLKCTKIC DRILL. Mr any 
application. Snner Mr LATHES, t.HIXDEUS, 
FOOI> MIXERS. \ At Ut'M L'LEASEKs. WASlilNO 
M.1CHISES. SPIN DRIERS. HEDliE t'lTTEHS. 
WILL CONTROL ALL UNIVERSAL MOTORS t'P 
TO 2 H.P. These units must not fie contused with 
ordinary rahttflntSM and rheostats that wuete pmrtr. 
Contained In ■ atfonff metal case, In Mack or grey, siie 
now il 5' 21 inches, SIMPLE TO I'SK. No 
epcelalistd knowledge requited A uniftne elect ionic 
achievement, coBtnitm 7 transistors and lhyrlstors 
and niiuiv micro miniature electron le components, 
COMPLETELY SAFE ANO A [' PROVED. Brand 
netr and rcadv t.i use improved de-luxe model. Price 
M 10, i arrhigc and insurance 10, -. C.O.0. 11 required. 
Discount itlvcli In Schools, Universities and Research 
EataMMmirntc, Free demonstration at our prcmlws. 
Dent. F.E.U 



MISCELLANEOUS 

(continued) 



MzamsMHMm 

24 C A WOODS YARD, MILL STREET 
LEEDS ■ TEL. LEEDS 25593 



Cillers weleome 



MISCELLANEOUS 



CALL OR SEND for list from the most Interest- 
inti sliti|> iit LiitUMishire. KJpftrical Mech- 
anic-ill and Electronic Goods. JtOGKKS. :ii 
Xelsou Sirt-it, Smithport. 



"PRACTICAL ELECTRONICS" Rhythmic 
Effects Unit, Itnpact Counter. Fluorescent 
Camping Light. Giissandavibe. Spring Line 
Reverberation Unit. I.e. Tape Recorder. 
UombotrOB. Analogue Computer, Photo- 
graphic Exposure Meter. Water Level Alarm. 
i>'u/,/. Hox. Yodeller Door Monitor. Marmonit! 
Distortion Meter. IX. Oram Amplifier. 
Thyristor l'ower Controller. Trttnsbtor 
Millivolt meter. Screen wiper Delay Unit. 
Investigator Oscilloscope. C.R.O. Trace 
lii pi idler. Light Operated Stopwatch. 
Proximity Detector. Photoflash Slave Unit. 
Integrated Stereo Amplifier, and all construc- 
tional projects going hack to Issue 1. -Send 
s.a.e. for vour choice of itemised price lists. 
AJAX ELECTRONICS, 18a llumhold Road, 
Fuiham, London, S.W.6. 



1 GANG SOOpF TUNING CAPACITORS 

New and boxed 7 6 post paid 
BIG BARGAIN PARCEL 

Capacitors, resistors some high stab, rectifiers, 
potentiometers, diodes, transistors, connecting 
wire, ere, only 10- post paid. 

S.A.E. for (ill J of other bargains 

SALOP ELECTRONICS 

9a GreyTriars Road, Colehim, Shrewsbury, Salop 



BOOKS AND PUBLICATIONS 



SURPLUS HANDBOOKS 

19 set Circuit, and Notes 5/6 P.P. fid 

1 155 set Circuit and Notes .... 5/6 P.P. 6d 
H.R.O. Technical Instructions . . 4/6 P.P. fid 

38 set Technical Instructions 4/6 P.P. fid 

46 set Working Instructions. . , , 4/6 P.P. fid 
88 set Technical Instructions . .. - 6,'- P.P. fid 

BC. 221 Circuit and Notes 4/6 P.P. fid 

Wavemeter Class DTech, Inscr 4/* P.P. fid 

18 set Circuit and Notes 4/6 P.P. 6d 

BC. 1 000 (31 set) Circuit & Notes 4/6 P.P. fid 
CR.I00 B.28 Circuit and Notes 9/6 P.P. 9d 

R.I07 Circuit and Notes 6/- P.P. fid 

A.R.88D. Instruction Manual 16/- P.P. 1/6 

62 set Circuit and Notes 5/6 P.P fid 

52 set Sender& Receiver Circuits 7/6. post free 
Circuit Diagrams 4/- each post free. 
R.lllfi/A, R.I224/A, R.I3SS. R.F. 24, 25, & 26, 
A, 1134, T.I 154, CR.300. BC.342. BC.3I2. 
BC.348.J.E.M.P. BC.624. 22 set. 
Resistor colour code indicator, %l- P.P. fid. 
S.A.E. with ail enquiries please. 
Postage rates apply to U.K. only. 
Mail order only to j 

instructional Handbook Supplies 

Dept. P.E., Talbot House, 28 Talbot Gardens 
Leeds 8 



RECEIVERS AND COMPONENTS 



BARGAIN PARCELS of new surplus Elec- 
tronic Components, 2/6, 6/-, TO/-, post free. 
DOLPHIX ELECTRO NMCS, n Pooles Way, 
Briar Close, Durntwood, nr. Lichfield. 



COMPUTER PANELS 

Eight assorted printed 
circuit panels with tran- 
sistors, diodes, resistors, 
capacitors, etc. Guaran- 
teed minimum . 30 
transistors. Ideal for 
Experimenters. 8 boards 
10/-. POST FREE. 
Trade ond Bulfc enquiries 

welcome. 
I SO0 + 2000 MFD Electro- 
lytes 25 volt DC wke, 
3/- each. 9d. P. & P. 

KEYTR0NICS, 52 Earls Court Road, 
London, W.8, Mail order only 




RECEIVERS AND COMPONENTS 

(continued) 

REPANCO Transistor Coils and Transformer. 
for tlie Constructor. Send stamp for lists 
RADIO EXPERIMENTAL PRODUCTS 
LTD., !W Much Park Street, Coventry. 



MICROMINIATURE MICROPHONES 

Sensitive dynamic type. Will pick- 
up rustle of newspaper from 30 feet. 
Size 9 mm. X 9 mm. X 3S mm. 
Impedance I Kfl. 

ONLY SB/ft 
Post frtt — CvV.O. 

MICRO DATA SYSTEMS 
30 BAKER ST., LONDON, W.I 




DUXF0RD ELECTRONICS (PE) 

DUX FORD, CAMBS. 

C.W.O, P. & P. I/-. Minimum order value 5/-. 
(Trade inquiries invited) 

CAPACITORS (Tubular, Axial Lead*): 
Electrolytic (Mullard): -10% to +50%. 
4V: BuF, 32pF, 64uf, ITSuF, 2SQnf. 400uF. 
S-4V: 6-4nF, 2SfiF. SO^F, IOOmF, 200; t F, 320^F. 
10V: 4*tF, IfifiF, 32/iF, 64uF, I25uF. 200liF. 
16V: 2 5/iF. lOjiF, 20(tF, 40nF, BOuF, llS^tF. 
25V: |-6 M F. 6-4^F, 13-5^F, 2S/iF, SOuF, BOjiF. 
40 V: IjjF, 4uF, 8uF, I6^F. 32>jF. 50uF. 
♦4V; 0-64mF. 2-SmF, SkF. lOuF, 20fiF, 31mF. 
All values 1 .3 each. 
Polyester (Mullard): -10%. 

160V: 001 uF. OOISijF, 0022uF, 6d. 0033(uF, 
0047fiF, 76. 0068aiF, OluF. 8d. OlS^F. tOd, 
0-22aF, ltd. 0-33^F, 1/2. 47^F, 1/5, 0-6BuF, 
2/1. I jjF, 1,6. 

400V: 0001 uF, OOOISjuF, 0-0022/iF. 00O33mF, 
00O47(iF. 00068/iF, OOlfiF, 6d. 0015/iF, 0022^F. 
7d, 0033fiF, 8d. 0047mF, 068fjF, 9d. 0'lnF, 
lOd. ISuF, 1/1. 0-22mF. I/S. 33»iF, 2/1. 
0-47nF, 2/6. 

Polystyrene: =5%. 160V: 5pF, lOpF, !5pF. 
I2pF. 33pF. 47pF. S6pF, 6BpF, lOOpF, !50pF, 2I0pF, 
330pF, 470pF. 680pF, 820pF, 5d. I ,O00pF, I .SOOpF, 
2,200pF. 6d. 3,300pF, 4.700pF, 5.600pF, 7d. 
ID.OOOpF, Bd. IS.OOOpF, 22,0OOpF, 9d, 
POTENTIOMETERS (Carbon): Long life, low 
noise. iW at 70°C. -20%£iM, !■ 30% > JrM. 
Body dia., Jin. Spindle, lin x iin. 2;- each. 
Linear : 100, 250, 500 ohms, etc., per decade to 
I0M. Logarithm. c; 5k, I0k, 25k, etc.. per decade 
to 5M. 

SKELETON PRE-SET POTENTIOMETERS 
(Carbon): Linear: 100, 250. 500 ohms, etc., per 
decade to 5M. 

Miniature: Q-3W at 70°C. 4:20% ^iM, ±30% 
> ±M. Horizontal (0-7in x 0-4in P. CM.) or Ver- 
tical (0-4in x 0-2in P. C.M.I mounting, I/- each, 
Submin. 0IW ar 70°C. ±20% SIM, -J: 30°/ ? > 
IM. Horizontal (0-4in X 0-2tn P. CM.) or Vertical 
(0-2in x lin P.C.M.) mounting, lOd. each. 
RESISTORS (Carbon fltm): Hiah nihility, very 
low noise. jW it 70*C. Body 4 in x iin. Value* in 
each decade: 10, 1 1, 12, 13, IS, 16. I B, 20. 22. 24, 27, 
30. 33, 36, 39, 43, 47. 51. 56. 62. 68, l.S. 82. SI from 
4 70 to IM. =5%, 2d each. 1-2M. I-5M. I -8M. 
2-2M, 2-7M. 3-3M, 3-9M. 4-7M, 5 6M, 6-BM, 8-2M, 
I0M. i 10%, Id. each. 

SEMI-CONDUCTORS (All new): OA5. OABI, 
1/6. OC44. OC45, 1/9. OC7I, OC72, OC73, 
OC6I, OC81D, OCS2D, OCI70, OCI71, 2/1. 
OCI40, AFM5, AFII6, AFH7, 3/-. 
SILICON RECTIFIERS: 5A at 70°C. 400 
P.I.V,, 3/-. 800 P.I.V., 3/3. 1,250 P.I.V., 1/9. 
1,500 P.I.V.,4/-. 

SEND S.A.E. FOR JANUARY I96B 
CATALOGUE 









OC22 B/- OC84 


4,6 


AFZI2 


5 6 


BYZI0 


»/6 


NKT674 


6/- 


RECORDS 


OC23 B/- 
OC24 B/- 


0070 
OCI7I 


4/- 
4 - 


BCY33 

BCY34 


5/6 

5/6 


8YZI1 
BYZI2 


8 - 
6/6 


NKT677 
NKT7I1 


6/- 
5/6 


,_ 






OC25 6/6 


OC202 


6 6 


BCY3B 


5/6 


BYZI3 


5/6 


NKT734 


5/6 


Tnr 




OC26 6/6 


OA8I 


1 6 


BCY39 


5/9 


GET 1 02 


41- 


NKLT736 


6/6 








OC28 6/6 


OAIB2 


»- 


BCY70 


6/6 


GET103 


41- 


NKT773 


5/* 


7- r>/p 


2,400' 


ia.» 


OC35 6/6 


OA200 


2/- 


BCY7J 


10/6 


NKT74I 


6/6 


NKT78I 


6/- 


7- UP 


1,800' 


12.'- 


OC36 6/6 


OA202 


S- 


BCY71 


6/6 


NKT242 


6/- 


2N696 


5/- 


7" STD 


1,200' 


V- 


OC44 1/- 


AC 107 


61- 


BFYI8 


5/- 


NKT244 


5/6 


2N697 


5/- 


5j- D/P 


1,800' 
1,200' 




OC4S 2/6 


AC 126 


4/- 


BFYI9 


5/6 


NKT245 


5/6 


2N706 


4/6 


8/9 


OC46 1/- 


ACI27 


41- 


BFY50 


5/6 


NKT26I 


4/6 


2N706A 


4/6 




OC70 1/- 


ACYI7 


41- 


BFY5I 


5/6 


NKT262 


4/6 




5/- 
5/- 


sr STD 


900' 


6/1 


OC7I 2/6 


ACT IB 


41- 


BFY52 


5/6 


NKT264 


4/6 


2N2220 


5'' D/P 


1,200' 


10/6 


OC72 2/6 


ACYI9 


41- 


BSY20 


5/6 


NKT27I 


4/6 




900' 


91- 


OC74 4/- 


ACY20 


5/6 


BSY26 


4/6 


N KT603 


6/6 




5/- 


5" STD 


600' 


5/- 
1/9 


OC7S 2/6 

OC7B 2/- 


ACY2I 
ACY22 


5/6 

4/- 


BSY27 
BSY28 


4/6 
4'6 


NKT6I3 


6/6 


2N2222 


51- 














OC7BD 1/- 


AD 1 40 


8'- 


BSY29 


4 m 


VEROBOAF 


: 3*- X 2*' 


1/6; 


3" UP 


225' 


2/9 


OC8I 3/- 


AD 149 


«/- 


BSY38 


4/6 


3J- X 2i~ 


4/3; cu 


teer, ♦/-. 




3' STD 


ISO' 


Hf- 


OC8ID 1/- 


AFII4 


4/- 


BSY39 


4/6 


DEE GEE 














OCB2D 3/- 


AFII6 


41- 


BSY9SA 


4/6 


16/- each. 
SPEAKEI 
25/6j 12'. 
RESISTC 








Spool*: 


81 -. 5/6 


7", 


OCB2 31- 


AFI 17 


41- 


BY 100 


4,6 


«; 3 t 

19/6; 7" 
KStiH 


ihm, 5', 14/6; 8* 
X4", 16/6; 3', 9/6. 

.-.tt. 8d; •.■ watt, 6d, 


2/3; 5!", 1'-; 3 , *M 
3', 9d. 


Send S.A.E. for eompl 


ete list. P. & P. 


1 - 


A. MARSHALL & SON ( London ) LTD. 


reels 2/9 


otherwise 


4/6. 


28 Cricklewood B 


roadway, N.VV.2 


ELECTRO LYTI 


:S: I5v 1 MFD up 


Tel- 01-452 0161:2. 


Dept. P.E 


.19 


to 100 MFD. 1/6 e 


ach. 





380 



RECEIVERS AND COMPONENTS (continued) 



MULLARD 



AC 1 07 
AC 127 
AC 128 
AC 176 
AD MO 
AD 1 49 
ADI6I 
AD 1 62 
ACYI7 
ACY20 
ACY2I 
ACY22 
AFZII 
AFZI2 
AFI 02 
AFI 14 
AFII5 
AFII6 
AFII7 
AFI IB 
AFI86 
AF239 
ASY26 
ASY2S 
ASY29 
AS 22 1 
BAII5 
BCJ07 
BCI08 
BC109 
BCYIO 
BCY12 
BCY30 
BCY3I 
BCY32 
BCY33 
BCY34 
BCY3B 
BCY39 
BCY40 
BCY7I 
BCZII 



14/6 

6/- 
41- 
6/- 
12/8 
11/- 
7/6 
7/6 
3/- 
3/6 
4/- 
2/6 
10/- 
11/9 
18/- 
4/9 
4/9 
419 
4/9 
91- 
11/- 
12/- 
S/- 
3/- 
6/6 
4/- 
2/6 

ffi 

4/3 
4/3 
20/- 
«/- 
7/- 
9/- 
8/- 
6/- 
■/- 
19/- 
10/- 
16/- 
13/- 
10/- 



BFY50 


*/- 


BFY5I 


s/- 


BFYS2 


6/- 


BSX79 


3/- 


BTY79-4O0R 


24/6 


BTYB7-I50R 


23/- 


BTY91-I50R 


33/- 


BSX36-IOO 


3/- 


BTYB7-5Q0R 


47/- 


BYZIO 


M/- 


BYZI2 


7/6 


BYZI3 


51- 


BZY93 C24 


12/- 


BY1QO 


5/- 


BYX20-200 


«/- 


GET 1 02 


5/4 


GET 103 


4/4 


GETIII 


10/- 


GET573 


10/- 


OCI9 


5/- 


OC20 


33/- 


OC22 


11/- 


OC23 


23/- 


OC24 


19/- 


OC25 


7/- 


OC26 


11/- 


OC28 


11/- 


OC29 


IS/- 


OC35 


»/6 


OC36 


13/- 


OC4I 


3/6 


OC42 


41- 


OC43 


»/- 


OC44 


»/- 


OC4S 


l'l- 


OC7I 


3/- 


OC72 


4/6 


OC73 


3/- 


OC7S 


3/- 


OC76 


3/- 


OCBI 


3/- 


oca id 


3/- 



OCB2 

OC82D 

OC83 

OC84 

OCI23 

QC 1 39 

OCI40 

OCI69 

OCI70 

OCI7I 

OC200 

OC20I 

OC202 

OC203 

OC204 

OC20S 

OCP7I 

ORPI2 

ORP60 

ORP63 

ORP93 

ORP90 

OAS 

OAI0 

OA47 

OA70K 

OA73 

OA79K 

OABIK 

OA6SK 

OA90K 

OA9IK 

OA9SK 

OA200 

OA202 

OA2I0 

SX63I 

SX636 

SX63B 

SZ20C 

61 SV 

SVC I 



4/6 

4/3 

3/6 

4/- 

11- 

12/- 

11/- 

*/- 

4/- 

6/- 

6/- 

10/- 

13 - 

8/- 

11/- 

I 0/6 

19/6 

97- 

8/- 

9/- 

!•/- 

19/6 

3/- 

41- 

1/6 

1/6 

1/6 

1/6 

1/6 

1/6 

1/6 

1/6 

1/6 

1/- 

2/- 

7/6 

7/- 

10/- 

12/- 

13/- 

93/- 

19/9 




2N38 1 9FET 1 1 !- 

2N3826 6/- 

IB4QK10 19/- 

I8I00-MOS 54/- 



smcum 

ADTI40 12/6 

STI4I 5/- 

ST140 §/- 




NTEGRATED 
CIRCUITS 

Epoxy T05 8 

lead nL 900 Buffer 

vD 11/- 

,uL 914 Dual Gate 

a ii/- 

uL923 J-K Flip 
Flop Q 14/- 
4-page reprint on 
tC usage circuits 
data, etc. 2/6 



J.E.D.E.C. 


2N385A 




2N1BBA .. 


13/- 


2N696 


9/- 


2N706 


4/- 


2N706A , . 


6/6 


'2N7II 


776 


i 2N 1 1 32 


10/- 


2NI302 


51- 


2N 1 303 


51- 


2N 1 304 


«/- 


2N 1 305 


61- 


2NI306 


8/- 


2NI307 


8/- 


2NI308 


10/6 


2NI309 


10 9 


2N2I47 .. 


17/- 


2N2I60 


14/9 


2N2646 . . 


10/- 


2N3436 ., 


6/9 


PLANAR 




BARGAIN 




2N2926 Yell 


OW 


4 for 10/- 




NEW G.E. 




Over 1,000 tran- 


slator and dtodc 


types ex stock. 



GUARANTEE: All the above-listed semi-conductor devices are Brand New, First Grade, and 
guaranteed. We will replace at no charge an/ device found to be faulty. Further: all devices 
carry the Manufacturer's name or Trade Hark, type number and batch number. We do not 
offer for sale devices often described as "new and tested" or bearing re-marked type numbers, 
these often have a short and unreliable life. LST COMPONENTS 




Resistors: i Watt 5% Miniature type, 
low noise— high stability. 10, 12, 15, 
18. 22, 27. 33, 39, 47, 56, 68, 82 and 
decades to 820K. 1-25 pieces, 4d ; 
25-99, 3d ; 1 00 pieces or over, 2d each, 
10% tolerance, i Watt, I Meg, to B-2 
Meg., same price. 

Preset potentiometers. Standard or 
Subminiature types, 20% tolerance, 
Lin. vertical or horizontal. 
100. 250, 500 ohm, Ik, 2 -5k, 5k, 1 0k, 
25k. 50k, 100k. 250k. 500k, I Meg, 2 5 
Meg, 5 Meg. All at 1/6 each. Discounts 
for quantities over 12 of I value. 



COMPONENTS 

7 COPTFOLD ROAD 

BRENTWOOD ESSEX 

BRENTWOOD 7904 

24 HOUR POSTAL SERVICE 



"X" LINE MODULES 

Send for details of 
our range of ready- 
built solid-state 
circuits, amplifiers, 
sirens, light flashers, 
etc. 



FAIRCHILD AF 11 
20W SOLID STATE 
AMPLIFIER KIT 
£8.8.0 Complete 

Includes Printed circuits 
board, Semiconductor!, 
Resistors, Capacitors, 
Heat sink and short 
circuit protection com- 
ponents. S.A.E. for 
details. 



1968 CATALOGUE 

34 pages — 

NOW AVAILABLE 

send 1/6 stamps 



POST * PACKING 9d 

per order 

EXPORT ENQUIRIES 

WELCOME 



TRANSISTOR MANUALS 
O.K. New Edition 29,<<J 
R.L'.A. Latest Edition 87/8 
+ 2/8 Post & Packing 



RETAIL AND WHOLESALE 
SUPPLIED 



REDUCED PRICES 
2NI073BPNP I20v 60W I.SMHi (TO-41 can) 
10,'-. 2NI290 Electrically as 2NI07JB {TO-3 can) 
10,'-. Ex-equipment, tested, either type 5/- each, 
5 for 20/-. Rechargeable bate, DEAC 12.2v 450 
mA/hr 17/S, P. & P. 2/6. P/cct board Edge Con- 
nectors, 0.2 matrix, 12 way 2/6, 1 7 way 3/-, 22 
way l/o, 30 way 4/6, 32 way 5/-. 2W pots, 1" 
spindle, 5k, 2k, Ik, 500, tOO ohms. I/-. Pre-set, 
min, pots jW 270k, 1 00k, 330, 270 ohms. 9d. 
Terms C.W.O., Min. order 3/-. P. & P. I/-. 
S.A.E, for list. Mail order only. 
T. L.WILLIAMS 
2 CHESTNUT CLOSE, ADDLESTONE. SURREY 



STUDENT ELECTRONIC SERVICES 

194 Regent Road, Sal ford 5 
We stock a wide range of Resistors i and 
i watt. 

Buy individually OR try the S.E.S. Pre-Pack. 
Stocks now include Potentiometers — Log, 
and Lin. 
Enclose 6d . for complete price list 



FANTASTIC OFFER ! ! ! 

Computer printed circuit boards. 
Comprising transistors, diodes, reiiiton, 
etc* Ideal for constructing amplifiers, 
receivers, etc, etc. 

Price: 3 boards for only 10/- P. ft P. 2/-. 

TELE-RADIO (1943) LTD. 

IS9 Edgware Road, London, W.2 



SUPER QUALITY NEW RESISTORS 

Carbon fi/m, tow noise, high stops: 

Power Range Series Per doz. Per 100 

*W S%SIO to330ktl E24 1/10' M/6 

iW 10% In to 4-7 [] EI2 +^d per resistor 

1/9 
2/2 
3/3 



13/6 
17/- 

25/10 



Jtt iuy i 14, m t r u 
W 10% 4 7() to I0MQ EI2 

±W 5% 4-7[) to I0MO E24 

IW 10% I0Q to I0MQ EI2 

1/6 per 100 less in IOC's of one ohmic value. 
Please state your choice of values. 

Quality Carbon Skeleton Pre-iet*: 1000,250(1,50012, I ko, 2kll, 2-5kfi, 5kO, 
IOktl,20kO,2SkQ,50kO, lOOkfl, 250kQ, SOOkfl, I M0.2MO, 2-5MO, 5MO, I0MO. 
Available in horizontal or vertical mounting, I/- each. 

Low Cost Volume Controls! I00O, to I0MO, I in., 2/3 each: Ska toSMQ.log.. 
2/3 each. 

Log. Stereo: lOOkQ, 250kfl , SOOkO, I M Q. 2Mo, US., 9/-. O.P.sw. 12/6. 
Ceramics: 100, 220, 470. 1.000. 2,200, 4,700 P F, SOOV, 5d: 0005. 001. 0-02. 
0-OSuF, 50V, 5d. 

Electrotytics: S, 10, 25, SOuF, 10V, S, (O^F, 25V, »d; 100, 200^F, (0V, 25,50^F, 
2SV. I/-. 
Sub- min. C426 range: all values in stock. 

PICK OF THE NEW SEMICONDUCTORS 
Silicon, many types including; 

BCI 07, 45V, I] (25-500. 4/-. BCI67, S0V, 1 25-500. 3/-, 

BC108, 20V, 125-900, 3/1 1. BC 168, 20V. ! 2S-9O0, 2/6, 

BC 1 09, 20V, 8 240-900. 41-. BC 1 69. 20V, 240-900. 2.'». 

BCI09 and BCI69 are low noise types, BCI67, BCI6S and 8CI69 are plastic 
Best Value For: 

Power: 2N3055, I ISW, I00V/I6/6; 2N3054, £1, 
Field Effect: MPFI05, gm 2 to GmAIV, 10/-; 2N3BI9, 14/6, 
VHF and Fast Switching: BSX20 ft. 600MHz, 4/6. 
High Gain: 2N3390. B400-I.250. 6/-. 

Low Noise: 2N3707, 5/-; 2M339IA, 5/6; 2N40S8 (PNP), 5/6. 
Sub-Miniature: SCI 22. 30V. 50mA, BOmW. 250MHz. 6/6. 
Low Cost: 2N2926, 18V. 120MHz, 1/6 (our colour selection) 
Also: 2N3702, 2N3703, 2N3704, 2N3705, 4/- each; BCI09C, 4/3; BFY50 3/3, 




Germanium, many types including: 

RP, VHF: NKT603F, 6/-; NKT6I3F, 5/9; NKT677F, 4/5. 

Low Noise: 2G308, 6/9; 2G309, 7/9; NKT275, 3/8. 

PEAK SOUND PRODUCTS 
CIR-KIT No, 3 Pack, 12/6. Adhesive copper 5ft >, ±in or .'.in. 2/-; 100ft • Jin 
or Am, 30/-. Perforated board 0-ltn matrix Sin x 3Jin, 4/-; 2£in •; 3|in, 2/6; 
2in x 3t'm, 2/-. Also SA-8. Stereo Amps at attractive prices . 
TRANSISTORISED STEREO AMPLIFIER AND PRE-AMP 5AB-8 

Complete kit of this very popular amplifier. 

16 watts 

total output, £10.10.0 

Power supply kit, £3 

Cabinet, £1 , 



IS", B DISCOUNT an whole order and post free when pur chasing en SA6-67 

The most successful amplifier of its kind yet, A real money saver. 

Old-Timers: 2NI302, 2NI303, 3/6; 2NI304, 2NI305. 4,-: 2N1306, 2NI307, 6>; 

2NI30B, 2NI309, 7/11. 

High Power: NKT403, 14/10; 2N2I47, 16/9; matching, I/- pr. 

Complementary Output: AD 16 1 INPN), 9,'-; AD 162 (PNP), 9/-. 

Silicon Diodes: 

Low cost: IS940. 30V. 75mA. 1/3; OA202. 150V, 160mA, J/-: BY238. 850V, 

500mA. 3/11; IN5054, BO0V, IA, 4.9. 

Zener Diodes: 400mW. S%, 2 7V to 33V (E24 values), 3/3. 

Germanium Diodes: OA47. 1/9; OA70. 1,9: OA8I, 1/6; OA90. l/3;OA91, l/ll 

OA95. 1 13. 

ALL GOODS BRAND NEW • NO SURPLUS • FAST DELIVERY 

Discounts: 10% over £3; 15% over £10. 

Post and Packing; I,'-; free on orders over £1. 

Catalogue: Send I - stamps — includes data on all types in stock and many 

equivalents. 

ELECTROVALUE 6 MANSFIELD PLACE. ASCOT, BERKSHIRE 



381 



RECEIVERS AND COMPONENTS (continual) 



ADROI ELECTRONICS 



Lord Alexander House 
Water house Street 
Hamel Hempstead, Herts 



OC28 
OC3S 
OC36 
OC44 
OC45 
OC70 
OC7I 
OC72 

oca i 

OCI40 
OCJ70 
OCI7I 
2N696 
2N697 
2N706 



5/- 2N2646 

7/4 2N2926 

8/6 2N3Q53 

1/9 2N3055 

1/9 2NI482 

2/ J 2NI720 

2/- N KTI 24 

2/- N KTI 25 

1/3 N KTI 26 

4/4 NKTI27 

2/3 N KTI 28 

12/4 NKTI29 

4/4 NKTI4I 

Sj- N KTI 42 

4/3 NKTI43 



12/4 

5/- 
10/- 

19/- 
5/- 
4/4 

a/4 

s/- 
s/- 

8/6 
S/9 

S {~ 
S/9 

5/- 
4/9 



NKT2! I 
NKT2I2 
NKT2I3 
NKT2I4 
NKT2IS 
NKT2I6 
NKT2I7 
NKT2IB 
NKT2I9 
NKT22I 
NKT022 
NKT223 
NKT224 
NKT225 
NKT226 



4/9 
4/4 
4/4 
J/4 
3/4 
1/1 
'/» 
4/1 
4/7 
4 8 
4/- 
4/1 
3/6 
3/6 
8/9 



NKT227 

NKT22S 

MKT60I 

NKT6I2 

NKT6I3 

NKT674 

NKT675 

NKT676 

NKT677 

TK20C 

TK40C 

OAS 

OA8I 

OA200 

OA2I0 



8/3 
4/1 
S/9 
4/8 
4/9 
5/- 
4/- 
4/1 
4/1 
1/4 

V- 

1/- 

& 

«/* 



BRAND 

NEW 
G 

U 
A 
R 
A 

N 

T 
E 
E 
D 



Send 94. stamps for complete list* Transistors. Rectifiers, 
Integrated Circuits, Etc. 



Cosh with order please. Postage 9d. 
Airmail extra 



R 6c R RADIO 

51 Burnley Road, Rawtenstall 

Rossendale., Lanes 
Tel.s Rossendale 3152 



VALVES BOXED, TESTED * GUARANTEED 


EBF80 


3/- 


PCC84 


3/- 


PY82 


^^ 


EBFS9 


3/6 


FCF80 


3/- 


UI9I 


4/» 


ECC82 


3/- 


PCF82 


3/6 


U301 


4/6 


ECL80 


31- 


PCL82 


4/- 


6F23 


5/- 


EF80 


1/6 


PCL83 


4/- 


I0PI4 


3/- 


EF85 


1/- 


PCL84 


5/- 


2QP5 


3h 


EFI83 


3/4 


PL36 


3/- 


30FS 


3/4 


EFI84 


3/6 


PL8I 


41- 


30LIS 


*/- 


EYB6 


4/- 


PL83 


41- 


3DPI2 


4/6 


EL4I 


s/- 


PY33 


tl- 


30CIS 


Sh 


EZ40 


4/6 


PYBI 


1/6 


30PLI3 


S/6 


EBC41 


4/6 


PY800 


3/6 


30PLI 4 


5/6 



POST, ONE VALVE 9d. TWO TO SIX 6d. 
OVER SIX POSTPAID, 



BI-PAK SEMICONDUCTORS 



(DEPT. E) 



8 Radnor House 
93/97 Regent St 
London W 1 



UNIJUNCTION 

■ ITJC Eqvt. 2X3846, T /Z 
U 140 TIS43, BEN 3000* / ° 



SIL. REaS TESTED 

PIV T40mA 3 A 10 A 30 A 



M 

toe 

•00 
800 
600 

con 
ISO 
800 

;r)'jn 



a/o 

4/- 
4/8 
4,9 



■/- 4/0 9/0 

■/) 3/0 •/- 15/- 

2/0 4/0 6,8 20,- 

8/- 4/8 •/- 22/- 

o/- 9i- ta- 
rn 9/6 30,'- 
71- 10/- 37,'- 
Bj- 18'- 40/- 
8'- 10'- 17/6 50,- 



SCR's WJWB8T PRICE 
* V LARGEST RANQE 

PIV 1AMP 7A ISA 30 A 

26 — 7/0 — 80/- 
50 7/0 8/6 10/8 35/- 
100 8/8 10/- 167- 45/- 
200 18/8 15/- 80,'- 65/- 
300 15/- 20/- 25/- — 
400 17/0 29/- 34/- 80- 
600 30/- 40/- 46/- 85/- 
600 — 40,'- 60/- — 



SCR MANUAL 25/- 

3rd Edition. P.P. 2,'fi 



OfiP 12 Q/£ 
ORP 60 °/ w 

OCP 71 EACH 



SYLVAN I A (USA) 
IN2I BMR 
MATCHED PAIR 
MICROWAVE 
DIODES 

1 IK21B and I IN21BR S 
BARD MIXER DIODES 
15;- per pair. Brand Sow 
in Manufacturers Original 

Packages. 



* QUALITY-TESTED VALUE PAKS * BARGAINS * 



2 DHlt Trims. 2N1226 Germ, FNF lOOMu/e 10/- 

B Matched Trans. OC44/45/8I/81D 10/- 

[6 Red Spot AF Trnos. PNP . - 10/- 

[8 AVhlte Spot RF Trana. FNP 10/- 

5 8 II (ton Reels. 3 A 100-400 P1Y 10/- 

2 10A Silicon Rcets. 100 F1Y 10/- 

2 OC1 140 Irani. NPN Switching 10/- 

1 12A SCR 100 PIV 10/- 

3 All. Trans. 2S303 TNP 10/- 

4 Zener Diodes 250in\V ;(-12V 10/- 

■A 200Mc,'a Sil. Tram. NTN BSY26/27 . - ■ 10/- 

3 Zener Diodes 400mW 33V 5% Tol. ... 10/- 

4 High Current Tran:". OC42 Eqrt , 10/- 

2 Power Transiitora 1 OC28 1 OC3S . . 10/- 

5 Klllcnn Beets, 400 V1V 260mA 10/- 

4 OC75 Transiatom Milliard Type 10/- 

1 Power Trans. OC20 )00\ r 10/- 

4 OA202 Sll, Diodea Kub-miii 10/- 

2 Low Koine Trana. NFS 2N92M/30 10/- 

1 Bit. Trana NPN VCB 100 ZT86 10/- 

H OAS 1 Diodes Sub-niiii 10/- 

4 OC72 Transistors 10/- 

4 OC77 Transistora 10/- 

3 Metal Alloy Trana lit on Mm. Type 10/- 

4 Sil. Recta. 400 PIV OOOmA 10/- 

4 OET884 Trans. Eqvt. OC44 10/- 

5 rt£T883 Trans. Eqvt. OC43 10/- 

2 2N708 Sil. Trana. 300Mc/s N PN 10/- 

5 CT41/45 ficrm. Trnns. PSP Eqvt, OC71 10/- 

:* OT31 LF Low Noise fierni. Tram. PSP 10/- 

8 IN9I4 Sit. Dkides 75 PIV 75mA 10/- 

OA95 Germ. Diodes Sub-niin 10/- 



3 NPN (Jerm. Trans. NKT773 Eqvt. AC180 10/- 
10/- 

10/- 
10/- 
10/- 
10/- 
10/- 
10/- 
10/- 
10/- 
10/- 
10/- 



OC22 Power Trana. tier" 

OC25 Power Tram, (ieriu 

OC73 Milliard Trans 

AC 128 Trans. PNP High tiain ... 
AC127/128 Comp. pair PST/SPS 
2S 1307 PSP SwitchinK Trana. ... 
CG62K Germ. Diodes Eqvt. OA71 

AF118 Milliard Type Trans 

Assorted Germ. D^dea Markeil . 

AC126 Genu. l'NP Trana 

1 A Germ. Beet. 200 PIV 



1 ORF61 Phut u -conduct ivo cell 10/- 

4 Silicon Reets. 100 PIV 700mA 10/- 

3 AF117 Trans. Mullard Tv-pe 10/- 

7 OC81 Type Tran* 10/- 

3 OC171 Trans. Mullard Tjik: 10/- 

8 2K2928 Sil. Eposy Trana 10/- 

7 OC71 Tvpe Trans 10/- 

!5 Trana. HeatsinkB fit T018, S012, ctt. . . 10/- 

2 2S701 Sil. Trana. Texas NPN 10/- 

3 12V Zenere 400mW 10/- 

3 IW 5.6 Zenera 10/- 

4 OA10 Diodes Mullsrd 10/- 

5 20417 Eqvt. AF117 10/- 

8 OA70 Diodes Mullard 10/- 

4 OA47 Gold Bonded Diodes 10/- 

2 I0A 600 PIV 811. Recta. 1S425R ...... 15/- 

2 Zener Diodes 20W 18 and 22V 16/- 

1 2N910 NPN Sil, Trans. VCB100 «0Mc/» 16/- 

2 1,000 PIV Sll. Rects. l.SA R8310 AF . 15/- 

3 BSY05A Sil. Trans. NPN 200Mc/s .... 15/- 
3 OC200 Sil. Trans. 15/- 

2 SH. Power Rects. BYZ13 16/- 

1 Sil. Power Trans. NPNIOOMc/s TK201A 15/- 

8 Zener Diodes 3- 16V Sub-tobi 15/- 

1 2N1132 PNP Epltailal Planar Sll, Trnns. 15/- 

3 2N607 Epitaxial I'ltuinr Trana. 811 16/- 

4 Germ. Power Trans. Eqvt. OC18 Mullard 16/- 

1 I'll I Junction Trans , 2N 2646 Eq v t . D5E2 9 16/- 

2 Sil. Trans. 200Mc/a 80\'eb ZT83/H4 . . . 16/- 
I Sil. Planar Trans. NPN 100 Mc/s BSY25 15/- 
1 Tonnel Diode IN 3720 ( TD5) G.E 15/- 

1 I"nJiunctionTranB.2N2160TO-5canfi.E. 16/- 

2 Sil. Beets. 5A 400 PIV Stud Type 15/- 

2 Oerm. Power Trana. OC28 15/- 

1 Tunnel Diode AEY11 10o0Mc/h 8TC. . 15/- 

3 2N2732 Sll. Epoiy Planar HFE22S nla\. 16/- 

6 BY 100 Type Sil. Recti 80/- 

25 Sil. and Germ. Trans. Mixed, all marked 

New 30/- 

10 Xew Power Trans. OEC Eqvt, OC16/26 30/- 



FREE 



One 10/- Pali ol your own choice 
free with orders valued £4 or over 



BI-PAK 7 




"SPECIAL" 

SILICON PLANAR 

TRANSISTORS 
• SIMILAR 2N706 

J^ONLY I/- 
each 



■«> 



NPN FULLY 
TESTED 




* QUALITY-TESTED DEVICES * 



ACI25 2/3 

AC176 , 5/6 

AF139 10/- 

AFZ12 10/- 

BC107 5/- 

BC108 6/- 

BC10B 6/- 

BCY3.1 5/- 

BCY34 6/- 

BCZI0 5/- 

BCZ11 «/- 

BFYOO 71- 

BFY51 7/6 

BFYoS 7/6 

MAT10O 8/- 

M.1T120 8/6 



NKT773 41- 

NKT781 6/6 

OC44 .■■■ 1/8 

OC45 1/8 

ST140 8/- 

ST141 4/- 

2N6S0 */B 

3N697 5/- 

2N1000 4/8 

2N1300 4/- 

2N2147 15/- 

2K2804 8/- 

2N3819 16/- 

2N3820 - 25/- 

2S303 5/- 

3S303 */- 

•■JS30-1 6/- 



ftLUT 

10/- 

PER PAK 



120 Glass sub-mi[i Germ. DIODES 



K1N6 OF THE PAKS "SUPER-PAKS" 
UNEQUALLED VALUE AND QUALITY 
BRAND NEW UNTESTED SEMICONDUCTORS 
SATISFACTION GUARANTEED IK EVERY PAK 



60 Mixed Germ. TRANS. 



75 Gold Bonded Germ. DIODES 



40 Lite DC81, AC128 Berm. THAHS. 

60 Silicon 200mA sub-min. DIODES 



40 Sil. Planar NPN TRANS. 



16 Top-Hat Sil. Rect. 750mA 



50 Sil. Planar DIODES 250mA 



20 ZENERS 1 wan mixed volts 



150 Mixed Sil. Germ. DIODES 



20 BAY50 charge storage DIODES 



12 Epoxy Sil. Rects. 



30 PNPSil.PtanarTrans. like2H113Z 



6amp Sil. Rect. Sim. BYZ13 Type 



30 TO-5 NPH Sil, Trans. BFY50, 
2N696 Type 



30 Germ PNP AF Trans. TO-5 like 
ACY17-22 



30 NPN PNP Sil. TRANS. 



10 3A Sil. RECTS. (Stud Type) 



30 Like BGI08 Sil. NPN TRANS. 



12 l.SA Sil. RECTS. Top 



30 AF Germ Alloy TRANS. 



10 1A Glass Sil. RECTS. high volts 



30 MAOT's MAT series PNP TRANS. 



20 Germ. 1A REGTS. GJM series 



25 3D0M/CS NPN Sil. TRANS. 



30 Fast Switching DIODES IN914 



Overseas 



Our vast stocks change daily with hundreds of Semi- Minimum Order 10/-. CASH WITH ORDER 

conductor bargains becoming available. Juit send 2/6 ! PLEASE. Add I/- postage and packing per Order, 
to cover 3 months mailing of our latest stock lists, j GUARANTEED by return postal service, 
eqvt. charts, circuits, etc. I add extra for Airmail. 



BI-PAK GUARANTEE SATISFACTION OR MONEY BACK 



382 



RECEIVERS AND COMPONENTS 

(continued) 



Trintiitor larrlte rod aerials, M\v and KW Sm long. 

5/- no data. 

Smalt 7 traDiittor radios ideal for BpHres. or repair, 

in maker* liases with 4 nickel cadmium batteries, 

battery charger, leather case, start (Oiled nnd no 

nutir.iHirr, bargain •> 22 8 + -2 • P. ,v I' . 

Double gang potentiometer!, 250k + 200k log.. 

500k + 6fi0k I In, 3 - each. 

Ferrlte rodi, ,', 31 in, 01 each. 

Disc oeramior, l.nOOpf [P.C, type) ehort leads, 3d 

each: Hi do* (6TO VWi. 

Transistor capacitor*. OlmF 50 VW, 4d each; 8/- doz. 

»iiF 8VW. M: 4mF 64VW, SOrriF 8VW, lOOmF 

BVW, lOniF 12VW. 6d each; lOOmF BVW. ISOmF 

12VW. SSDinF BVW. Sd each; -iOOmF 16VW . 

SOOrnF 9VW 1 '-. 

Set ol 3 transistor double tuned LP. transformers 

UTOk.-m, 10'- with circuit. 

Mixed baa ot silver mica capacitors, 100 (or 8 -. 

Mixed bar o( silver mica and tabular ceramics, 

100 (or 9<- (our selection). 

Traniiitors, fiT-lftB (OC45) 1,8 each. 

Zener diodes. OAZ247 B,.'8. OAZ224 3,8. IB7051A, 

I87076A 8/8. 

P.C. board, ilnule sided. ft in. thick, appro*. Sin. :<2in. 

4d; 41n.x4>ln., 9(1. 

Folfittrene capacitors, 1.000 pF 6%, S.OOOpF 11%, 

3d each; g/8 doi. (30VW). 

Silver mica capaclton, 25, 30, 47, 40. 75, ?2. 137, 

220, 330, 375. 500, l.OOOpF, wire ended, .150 VW; 

80. 230. 300. 370. 505, 680, 1,100, 1,600 pF. P.C. 

type, 200V W. 

Minimum order 5.'-. 

POSTAL SERVICE ONLY. Poatane; under £1. 

1/8; £\ to «2, 2/3. Over £3 post (rec. S.A.E. (or 

lists. 

A. J. H. ELECTRONICS (G8A0N) 

5BWAVERLEY ROAD, THE KENT 
RUGBY, WARWICKSHIRE 



STUDENT ELECTRONIC SERVICES 

194 Regent Road, Salford 5 

Constructional aids — including 
Assembly Stand (each individually 
made by craftsmen). 

LEKTROKIT— the biggest money and 
time saver since the 
safety pin ! 

Everything to construct a pro- 
fessional job, from a variety of 
boards, pins to chassis plates and 
rubber feet. 

Special introductory kit in 2 sizes. 

Write now for complete price list 
AND sample resistors, enclosing 6d, 



TRANSISTOR CAPACITORS (ELEC- 
TROLYTIC) 

5 00 mfd 4V 64 mfd 40V l6mM 25V 

320mfd 10V SO mfd 10V lum'fd 25V 

250mfd 4V 30mfd 10V e-4mfd 64V 

200mfd 16V 25mfd 25 V 4mfd 64V 

lOOmfd 16V 20 mfd 12V I mfd 25 V 

I/- each. 9/- per doz. Min. order 10/- 
TRANSISTOR PANELS— OC45 or equiv., 
20 Tor 20/-. JO— IS/-, 50—35/-, 70—45/-, 40— 
10/-, 60 — 40c, 80— 50,'- Postage 2/- per panel 
Brand new STC sit. EPT planar transistors 
300 Mc/s 350 mW, all at 2/- each. 2N743, 
2N753. 2N9I6, BSY26. BSY28, BSY6S, BSY18, 
BSY95A. BSY29 

TRANSISTORS OC4S. TK22C ® I/- each. 
OC76. OCI 39, 2G302, OC8I , OC44 8, 2/- each. 
GET 1 20, OC83, IN 1 308, OC72, NKT2I6 @ 
41- each. OC23, NKT452, NKT453 W 6/- each 
10 watt heat sink drilled for power trans, 5/-, 
I.OOOmfd 30V 4/-. 3.000mfd 10V 2/-, T.V. 
capacitors 100 + 200 + 400mfd 27SV 7/6, 
100 + 2O0mfd 300V 5/6. 

W.W. POTS 5, 10, 25, 50, 100. 250. 500 ohms, 
Ik, 2k, 2-5k. 5k, 1 0k. 25k, 50k, 1 00k, not 
preset!/- each. Min. order 5/-. Postage 1/- 
ZENER DIODES— 2-4, 2 7, 3 6, 4 75, 5 25. 
5-75. 6-2, 68, 7-5, 91, 13, 15, 16. IB. 20, 27. 30, 
33 volts, 3/6 each, mostly I watt 
POLYSTYRENE CAPACITORS 350V: 180. 
270, 330, 390, 470, 560, 680, 820pf. 1 ,800, 2,200, 
2,700, 3,300, 5.600. 6.800. 8.200 
I2SV: 1,200, 1,500. 1,800, 2,200, 2,700. 3,300. 
3,900, 4,700, 5,600, 6,800, 8,200. 012, 015. 
BOpf ceramic 200pf S.M. any selection 2/< doz. 
4-40pf trimmers 41- doz. 

BRAND NEW BOXED CHASSIS, contain- 
ing 2— OC35, 2— OC29 12 WW resistors JO/-. 
Postage 1/6. 

STEREO POTS, Less switch, single spindle. 
I meg -r I meg log and I meg log -r 1 meg rev/ 
log, 7/6 each. 

NEW CROSS RADIO 

6 OLDHAM ROAD, MANCHESTER 4 



RECEIVERS AND COMPONENTS 

(continued) 



RESISTORS 

5 watt carbon Film 5% 

All preferred values in stock from 

10 ohms to 10 megohms 2d. each. 

Send S.A.E. for free sample 

CAPACITORS 

Mullard Miniature Metallised Poly- 
ester P.C. Mounting, all 250V D.C. 
working. 0-01 mf, 0022mf, 0047mf, 
0-lmf. 0-22mf, all at 6d. each 

Hunts tubular (mf 200V working 
at 3d, each 

Send 6d. stamp for extensive list of 

low priced Electronic Components, 

Instruments and Equipment 

Please include I /- postage and packing 
on all orders under £1 

Dept. P.E.11 - 

BRENSAL ELECTRONICS LIMITED 

CHARLES STREET, BRISTOL 1 



PHOTO ELECTRIC CONTROL 

QVQTT1I Comprises a light source unit with 
OIuILitI optional Infra Hed Biter and lens 
system to force the light. Also a 
photo-electric Relay control unit. Both housed in 
metal ca&es for bench or wall inn mat hit*, sensitivity 
control, mains on-oft switch. Works from 23Q/240V 
a.c. Mains, Can be used as a simple on-off switch by 
breaking the beam of light (invisible if Infra Red 
Alter is asedl and as such It will operate as a burglar 
alarm, or will open doors, etc. Also in conjunction 
with a counter or other equipment it will per Jam i 
many functions ht the factory or /Q I Q A 
warehouse. * 1VT. I 7.%I 

P.M. WIRELESS MICROPHOHE 

84.104Mc/s. Transistorised. Operates from 9V 
battery. Complete with arlditiontil secret tie clip 
microphone. List £12/ 10.'- ON XV £jL I C A 

These cannot be operated In l*.K. a^w, I J.v 

TBAHSISTORISED FK TTJHEB 
« TKAS8I9TOR MKiH QKALITY USER. 
SI2EOSLY6inx 4in X 21 In 3 l.F. stages. Double 
tuned discriminator. Ample output to feed most 
Amplifiers. Operates on BV batterv, Coven^e 
8S-108Mi::b. Ready built ready for tjL I "F f. 
use. Fa ntastic value for money "' * 

FM MULTIPLEX STEREO ADAPTOR 

Printed circuit biscuit, 4 trans. 6 fC IQ i 

diodes 9V with lull instructions fcrf " ' '* v 



BSR TAPE HEADS 
R£« 39/6 pair 



BSH TAPE HEADS 
■ALL \Q If. 

4 TRACK JT /° f 3 " 



REFLEX CONE TYPE 
WATERPROOF SPKR. 
watt. 8 ohm. 300- 
lfl.OOOc's PA £A C A 
* Music Uelav fc^'J'W 



MULTIMETERS \J I 

from J ' t / 



LOUDSPEAKERS. J'Q 
40ohni.21"80ohin. 3/0 



IT TWIN CONE 10 M/ 
watt, la or 3ohm Oil/" 

!'29/6 



TWEETER 1*i ohm 
10 watt, I8K-CPS 
CROSSOVER NET- in/ 
WORK 1« ohm If/" 



SUPER SILICOH RECT. T.V., etc, 1.200 P1V 
800mA. 8'-; or complete with Instr. resistor, 
condenser, 7/B; 400 PIV HW 8A, «;-; 200 PIV HW 

6A, t!-. 

Stamped envelope fur lull selection an I hargaiu 
oilers In Multimeters, Radios, Baby Alarms, Inter- 
coms, Walkie-Talkies, Rectifiers ami Eagle Lists. 
UNDER £1— P. & ¥. 8d. OVER £1 post free. 
C.O.D. 3/6. 

DURHAM SUPPLIES 

17SF, Durham Road, Bradford, 8, Yorkshire 



PLEASE MENTION 
PRACTICAL ELECTRONICS 

When Replying to 
Advertisements 



The RADIO AMATEURS 
HANDBOOK 45/- 

1968 Ed. by A.R.R.L. Postage 4/6 

COLO U R TV PAL SYSTEM, by Pateheu. 
4M/-. P. & P. 1/-. 

F.E.T. CIRCUITS, by Turner. 25/-. P. & P. 
I/- 

BRIDGES AND OTHER NULL 
DEVICES, by Turner. It/-. P. & P. I/-. 

ABC'i OF TRANSISTORS, by Mann. 
20/-. P. & P. I/-. 

RAPID SERVICING OF TRANSISTOR 
EQUIPMENT, by King. 30/-. P. & P. I/-. 

HI-FI YEAR BOOK, I96S EDITION, 
IS/-. P. & P. I/-. 

101 WAYS TO USE YOUR OSCILLO- 
SCOPE, by Middleton. 21/-. P. & P. I/-. 

COMPUTER CIRCUIT PROJECTS 
YOU CAN BUILD, by Boichen. 24/-. 
P. & P. I/-. 

TRANSISTOR SUBSTITUTION 

HANDBOOK, new 7th edition. 15/-. 
P. S P. I/-. 

SILICON CONTROLLED RECTI. 

FIERS, by Lycel.- 21/-. P. & P. I/-. 

Where possible 24-hour service guaranteed 

UNIVERSAL BOOK GO. 

12 LITTLE NEWPORT ST., LONDON, W.C.2 
(Leicester Square Tube Station) 



"PLUS-3" MAINS CONVERTER 



Provides three separate 
switched output voltages 
6v„ 7iv. and 9v. D.C 
Suitable for all types 
of transistor equipment, 
radios, amplifiers, record 
players, etc Attractive 
case with indicator light, 
ma ins lead, output socket, 
plug and lead. Size 
41' X 3i' X 21*. 




P. & P, m 



(Extra lead with din plus (or cassette recorders 7/t) 
Mains unit for Ft-Cord 202A f4.15.lt. p. & p. 5/,. 

R.C.8. PRODUCTS (RADIO) LTD. 

(Dtpt P.E.), 31 Ollnr Road, London, E.17 



REPEAT OFFER OF CIRCUITS 

• NOUGHTS AND CROSSES MACHINE 

• BINARY ADDFR MD SDBTRACTOR 

• FOOTBALL POOL COMPUTER 

• KULTIPLYIN6/0MDING AHALQBUE COMPUTER 

• SIMULTANEOUS AND QUADRATIC EQUATION SOLVERS 

All these circuits for 4/6 post 6d. Diagrams 
(9 pp.) text (26 pp.) parts and price lists. All 
purely electrical designs. We are the leaders 
in rhis field and can put a dare en the publi- 
cation of each circuit to show that we were 
the first. Our machines have appeared at 
exhibitions in this country and abroad, before 
learned societies and the TV cameras and 
have even made money Tor charity. 
Again showing that we lead, we have under 
development a new circuit, which will Add 
and Subtract Binary numbers both in parallel 
and serially as in a full scale computer. The 
formation of the Sum and Carry is shown step 
by step. This will prove an invaluable aid to 
teaching binary arithmetic and computer 
method. Full details available shortly. 

PLANET INSTRUMW CO., 25(E) DOMINION AY., LEEDS 7 



383 



ERSiN 




for quick, 



Contains 5 cores of non-corrosive flux, instantly 
cleaning heavily oxidised surfaces. No extra flux 
required. Ersin Multicore Savbit Alloy also reduces wear 
of copper soldering iron bits. 



&&* 



SIZES 

HANDY SOLDER 

DISPENSER 

Contains 10 ft. coil 
of 1 8 s.w.g. Ersin 
Multicore Savbit 
Alloy. 2/6 each. 



SIZE 15 

SOLDER 

DISPENSER 

Contains 21 ft. coil 
of 60/40 Alloy, 
22 s.w.g. Ideal for 
small components, 
transistors, diodes, 
etc. 3/- each. 




SIZE 12 

jf Ideal for home 
~ constructors. 
Contains 90 ft. 
of 18 s.w.g, Ersin 
Multicore Savbit 
Alloy on a plastic 
reel. 1 5/- each. 




BIB MODEL 8 
WIRE STRIPPER 
AND CUTTER 

Strips insulation 
cleanly and 
quickly, fitted 
with unique 8 
gauge wire 
selector. Plastic 
handles. 9/6 each. 



* 



From Electrical and Hardware shops. If unobtainable, write to: 

Multicore Solders Ltd., Heinel Hempstead, Herts. 



SHORT WAVE ONE VALVE 
RECEIVER KIT 



39/6 + 2/6 P.P. 



PEAC ANALOGUE COMPUTER KIT III STOCK 

UNIT 'A' COMPLETE £26.0.0 + 1 5/- P.P. 

Punched aluminium panels and 
case for above £4.17.6 + 5/- P.P. 

CLUBMAN Mk. I KIT COMPLETE £6.17.6 + 5/- P.P. 
Without metal work £4.12.6 - - 2/6 P.P. 

CLUBMAN Mk. II KIT COMPLETE £10.17.6 + 5/- P.P. 
Without metal work £8.12.6 -;- 4/6 P.P. 

EXPLORER KIT COMPLETE £4. 2.6 + 2/6 P.P. 

STABILIZED POWER SUPPLY KIT 0-20V. 500ma 
COMPLETE £4.17.6 + 5/- P.P. 

COMBINED AUDIO OSCILLATOR AND FREQUENCY 
METER £17 + 10/- P.P. 

PORTABLE TEST UNIT KIT 
FLUORESCENT CAMPING LIGHT IN STOCK 

S.A.E. FOR TRANSISTORS, SEMICONDUCTORS, FULL LIST 

700 TYPES 

3 SILICON RECTIFIERS, BY 100 TYPE 10,- 

10 MIXED MARKED TESTED TRANSISTORS 10/- 

40 UNMARKED UNTESTED TRANSISTORS NEW 10, - 

1 LIGHT SENSITIVE CELL ORPI2 8/B ' 
25 MIXED UNMARKED TESTED TRANSISTORS 10/- 

2 TRANSISTOR COMP. PAIR AD 16 1/162 16 - 
P.P. I/- 

OUR COMPONENTS CATALOGUE 5 - Post Paid with 10;- worth of 
discount vouchors. 

OLRUS ELECTRONICS LTD. 

748 HIGH ROAD, LEYTONSTONE 

(NEXT TO GREEN MAN} 

LONDON, E.11. Tel. 01-989 2751 

CALLERS WELCOME— CLOSED ALL DAY FRIDAY 



HTOH SPEED HAGIfETIC COTJHTERS (4X1X1 in). 4 digit. I2/24/4SV. (elate 
which) B/8 each, P. 6 P. 1/-. 

COPPER LAMINATE BOARD (8 1 X fllX i.in). 2/fl eueb. 5 ior 10/-. 
BB-8ETTABLE HIGH SPEED COUNTER (3 x 1 X Sin). 3 digit. 12/24/48 V. (state 
which) 8B/B each. 

BULK COMPONENT OFFERS 
104 Capacitors SOpF to .ifiF. 

260 Carton Resistors i & jW. (Transistor types), 
360 Carbon Besistors i * IV. 
100 Ceramic Capacitors 2— lOOOpF. 

25 Vitreous V[W Resistors (0%). 

12 Precision Resistors ('1% several standard values Jiidiadctlj. 

26 Close Tolerance Caps. (2%). 

12 Silicon Diodes 600 p.i.v. 750 HI. a, 

4 Silicon Rects. 400 p.t.v. 3 amp. 

8 Silicon Beets. 100 p.i.v. 3 amp. 

60 Silicon Trans. (2N706/708. B8Y2B/20. BCY41/42 types.) I'uuuirkcd, Untested, 

60 Silicon Diodes 200 m.a. 100 p.i.v. Sub. Mm. 

ANY ITEM 10/-, ANY 6 ITEMS IS. 



8.C.R.. (Thyristors, CRS1/20 S/8; CRS1/40 7/8; CRS3/10 7/S; CRS3/30 8/0; 

CBS 3/40 10/-: CRS3/50 12; 6 each. 

'WOO' TYPE RELAYS (es. new equip.) 10 for 25/- (our choiie) p.p. 5/-, 

PATTRIGK & KINNIE, 81 Park Lane. Romford, Essex 
ROHford 44473 




PEAK- 
SOUND 
8 + 8W. 
TRANSISTOR STEREO AMPLIFIER in kit form 

BoJJd Oil lor £9.10.0 (4/8 post). Power Pack Kit £2.10.0 (4/- post;. Cabinet (tee 
ilMttration) 50/- post paid or £14.10.0 the three items pott paid. Parts List Booklet 
and loll detallt 1/8 (Eree with kit). A.E.I. Circuil of 14 Trantistori; SW per Channel 
Into S to 15 ohm Speaker. 50m V input. Ceramic. Crystal Cartridge, Radio Tuner or 
Output from Tape Recorder may be need. 20 to 20,000 Hi ± 3dB. Neg. Peed Back 
1MB. 12Jn. X Sin. high X Bin. Cabinet, Clr-Eit Board Construction. Bass. Treble 
and Vol. Control, lor A.C. mains of 200-250V. Bast Cat and Lilt; Treble Cut and 
Lilt, rally built 13 extra. Delivery by return ol post. 

66 ELMS ROAD 
ALDER SHOT, HANTS. 

Alderebot 22240 
CATALOGUE Sd. 



GLADSTONE RADIO 

(2 mine, from Station and Buses.) 

CLOSED WEDNESDAY AFTERNOON 




BAKER MAJOR £8 



The remarkable quality and performance 
of the "Major" makes possible truly 
brilliant and rich sound from a single 
loudspeaker. It recreates the entire 
musical spectrum from 40 to 14,500 c.p.s. 
The unit const tt» of the latest double 
cone, woofer and tweeter cone together 
with a special Baker magnet assembly 
Alcomax II having a flux density of 
14,000 gauss and a total flux of 145,000 
Maxwells. Bass resonance 45 c.p.i. 
Plated 20 watts. Voice coils available 3 
or 8 or 15 ohms. Price £8, or Module 
version as illustrated with tweeter, 
crossover and baffle, £10.19,6, 



Baker Reproducers Ltd 



Bensham Manor Road Passage, Thornton Heath, Surrey. 01-684 Io65 



4fl page Enclosure 

Manual 5/9 Pose Paid. 



rk 



WKAH $0 PGOFCSStOAfAL Ttf£ 

S££F'%Y^Sik YW&W A£ROSOL WAY- 

— - # 



M/AU/7 HP BLACK WRWKCe 
WOW! OR (CRAC K Ce) f;„; s h e$ 



Yukan Aerosol spray tit contains 16 oats- fine quality, durable easy instant 
spray. No stove baklnj required. Hammers available in jriy, blue. gold. 
bronie. Modern £j|ihe'l Black Wrinkle (Cut lie) ill at M/ll it our 
counter or 15/1 I, carriage paid, per push-button lell'lpny cm. Also 
Durable, hoc and water resistant Black Mitt finish (11 on self-spray 
tins only) 13/11 carriage pile. 

SPECIAL OFFER: I can plus optional transferable inap-on irini'Aiii:!: 
(value 5/-) for 18/11. carriage pud. Choice of 13 Sill-iprty plain celourc 
and primer (Motor cir quality) alio available. .-_-- --. 

Plane ant ota cheque or crossed P.O. for total amount to; l£Z~- 

YUKAN, DEPT.PE76 307*. EDGW ARE ROAO, LONDON. W.2. 

Wt tuppl y many C ov* r n men t De pi rtmen ti. Mu nici pal Aucno ri tin. tnstitu cu 
and Leading Industrlil Organisations — We can jupply you too, 

I Op« n all day Saturday, Closed Thursday afternoons, eeeeae 



.■San a !-',■'' 
corr.peid 

ZrfK Cntwndte 
Citat loceuer 
Mttolt'ci Ccr Slut. 
tVonie ffrtO Gold- 




384 



VALUABLE NEW HANDBOOK 

ID AMBITIOUS 





Have you had your copy of "Engineering Opportunities"? 



The new edition of "ENGINEERING OPPOR- 
TUNITIES" is now available — without charge — 
to all who are anxious for a worthwhile post in 
Engineering. Frank, informative and completely 
up to date, the new "ENGINEERING OPPOR- 
TUNITIES" should be in the hands of every 
person engaged in any branch of the Engineering 
industry, irrespective of age, experience or training. 

On ' SATISFACTION OR 
REFUND OF FEE' terms 

This remarkable book gives details of examinations 
and courses in every branch of Engineering, 
Building, etc., outlines the openings available and 
describes our Special Appointments Department. 

WHICH OF THESE IS 
YOUR PET SUBJECT? 

ELECTRONIC ENG. 

Advanced Electronic Eng. — 
Gen. Electronic Eng.— Ap- 
plied Electronics — Practical 
Electronics —Radar Tech.- — 
Frequency Modulation — 
Transistors. 
ELECTRICAL ENC. 
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cipal Eng. — Structural Eng. 
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— Hydraulics — Milling — 
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Radio — Radio tfi TV Servicing 

— TV Engineering — Tele- 
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ance Eng. — Diesel Eng. — 
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Metal Work — Welding — 
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— Metallurgy — Production 
Eng. 

AUTOMOBILE ENG. 

Advanced Automobile Eng. — 
General Auto. Eng. — Auto. 
Maintenance — Repair — 
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THIS BOOK TELLS YOU 

it HOW to get a better paid, more inter* ft- 

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ir: HOW you can take advantage of the 

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•jr HOW, irrespective of your age, education 

or experience, YOU COM succeed in any 

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132 PAGES OF EXPERT 
CAREER • GUIDANCE 

PRACTICAL INCLUDING 

EQUIPMENT TOOLS 

Basic Practical and Theore- The specialist Elec- 

tic Courses fori e$inne« in ironies Division of 

Elections, Radio. T.V., Etc., B.l.F.T. 

A.M.I.E.R.E. City & Guilds SOW offers you a 

Radio Amateurs' Exam. real laboratory train- 

R.T.E.B. Certificate ing at home tvith 

P.M. 6. Certificate practical equipment. 

Practical Electronics Ask for details. 

Electronics Engineering _^ _ — m ^^ 

Practical Radio f» I 

Radio & Television Servicing i^B« B » il» I m. 

Automation ■*•■•■■• ■ • 




You arc bound to benefit from reading 
"ENGINEERING OPPORTUNI- 
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WE HAVE A WIDE RANGE OF COURSES IN OTHER SUBJECTS IN- 
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TECHNOLOGY 

BERKSHIRE 



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NEW! SOLID STATE HIGH FIDELITY EQUIPMENT British made 



POWER AMPLIFIERS— PRE- AMPLIFIERS— POWER 



G I idpi i crc W a proudly preie nt this new range ol Audio Euuipment developed irom Dinsdale 
OUrrLI to jf]t, tl — each unit or system will compare favourably with other professional 
equipment jelling at much higher prices. Briet detail) are below: — 



iwnrnK.-sir »■ 

W m ft # m 
— — - - 


^ MF3 
SP6-2 






■ DUO VTffTI IrYMO — 

.a- .._. „ r: — — • 

iiir-iii- -ii4'- ~'dk" -ii- *>^ 


•W 1 -ta- .-an- HR -it- «5r— • 1 9 






J^- 




COMPLETE FULLY ILLUSTRATED 
BROCHURE FREE ON REQUEST 11 and 21 



V 



■J> 





Syitcm Compriting Price 


• 


A 


5 watt mono lor /III 1 A 
3/S ohm speakers * ■ V.JM 


• 


1 


12 watt rnooo lor /|7 l-l £ 
3 to 5 ohm ipeaken *■ ■ ■** ■ * ■<? 


• 


2 


IS watt mono lor /|i n / 
IB to 18 ohm speakers 61*1. IX. O 


• 


4 


24 watt mono two channel lor /1ft 1 C ft 
18 to IS ohm ipeaken t AW, 1 3 .U 


* 


Q ! 20 watt mono.stereo lor it A A A 
O is to 16 ohm speakers WiMM 




O 2* watt mono/stereo for f ?£ 1 C 11 
7 8 to 6 obo retaken MW. 1 3.W 

M 40 watt mono, stereo for f)<t [flft 
1 ^ 7! to la ohm ineskers W7.ll/iU 



- 



MANY OTHER SYSTEMS AVAILABLE 
Send lor loll detail! 



THE FINEST VALUE IN HIGH FIDELITY - CHOOSE A SYSTEM TO SUIT YOUR NEEDS AND SAVE POUNDS 




VHP FH TUNER 
87/105 Mc/9 Transistor Superbet. (Joared 
tuning. Terrific quality and sensitivity. 
For valve or trai»*i&tor amplifiers. 4 N x' ; K 
'Jiin. Complete with dial plate. 5 Mullanl 
Transistors, Plus 4 Diodcs. 
AiL lor Brochure 3 
TOTAL COST 
TO BUILD £6.19.6 '•*■*'« 




FH STEREO DECODER Brochure 4 

7 Kullard Transition. Printed Circuit 
Design with Stereo Indicator. For use with 
my valve or traosistor FH. Uses pot 
cores to Hullard design and iter, and silicon 
transistors. As used by BBC. and G.P.O. 
Complete Kit Price £5^ | Qq P.P. 2,6 



BUILD A QUALITY TAPE RECORDER with MARTIN RECORDAKITS 

383 DECKS* . 

* TWO-TRACK. link £10.10.0. Amplifier. 
£14,18.6, Cabinet ami -speaker 7e;ns. Complete 
kits with microphone Tin. 1 .200 It. tape, apare 
spool. 

Today's Value £4&. 29 gns. PP. 18,9 

* POCK-TRACK. Deck £13.10.0. Amplifier 
£16,18,6. Cabinet and epcaker 7 ens. 
Complete kits with microphone Tin. 1.200ft. 
tape, spare spool. 
Today's -i<* _ 
Value £50 SI gtlS. P.P. 18/6 




\€> 



m 



Ask tor Brochure 5 



MW LW 80ALITY 
TRANSISTOR RADIO TUBES 
Fully tunable superbet with excellent sen- 
sitivity and selectivity. Output up to 
i volt peak. Complete with Iront panel, 
etc. 9 volt operated. For use with any 
amplifier or tape recorder. 
TOTAL COST 
TO BUILD £3. 1 9.6 p - p - B ' 8 



TRANSISTORS - SEMICONDUCTORS 



COMPLETELY NEW 1968 LIST OF 1000 
typqs available from stock. Send for 
your FREE COPY TODAY. (List No. 36) 

• S.C.R's from 5/- 
■sr FIELD EFFECT TRANSISTORS from 9/4 
-k POWER TRANSISTORS from 5, - 

* DIODES AMD RECTIFIERS from 2/- 
24 page Illustrated Brochure as above includ- 
ing Valves and Quartz Crystals. 1 - post paid. 



GARRARD DECKS 

all the LATEST MODELS 





COMPLETE 
RANGE IN 
FROM £5.19.6 STOCK 

Send lor illustrated Brochure 16 ft 17 



I<l T AL£ 0ST T0 BUILD 99 GNS. 

r Build this instrument stage by stage In your own hor 
A truly portable instrument lor all enthusiast*. 



ELECTRONIC Art for brochure ? 



Also READY BUILT AND 
TESTED 128 gns. 
Deferred terms 
available. 

DEPOSIT £36.8.0 and 12 
monthly payments of 
£9. Total £144,8.0. 
KIT ot PARTS Deterred 
terms: — DEPOSIT £29,18.0 
12 monthly payments ot £7. 
TOTAL COST £113,19.0. 
ORGAN COMPONENTS 
We curry a comprehen- 
sive stock of organ cum* 
portents for TRANSISTOR 
AND VALVE FREE 
PHASE desigus. Brochure 10 

EXPORT PRICES 




Build the PRACTICAL ELECTRONICS 

FLUORESCENT CAMPING LIGHT 
AS DESCRIBED IN MARCH.I966 Edition 
Total Cost including Construction Data 
Less Metal work pai/ POST 

and Tube >"/0 2/6 

All items ovo/loofe separately 
ASK FOR PARTS LIST No. 43 



TRANSISTOR CAR RADIO 
Send tor Brochure 15 



(qI^Ji 



British Hade G-Transistor MW/1W. 
IS volt 3 watt output. Push-button 
wove- change. Supplied built, boxed, ready 
to use with Speaker anal Haiti.'. Car 
fixing kit and iitnnu,facliirers" current 
guarantee. Special Bargain Offer. Positive 
or Negative Earth. 
5 Fush-bultoo ifc-luxc (Q I Q Z P.P. 

or — Earth 



i a 




7-TRANSISTOR 
MW-LW SUPERHET 
PORTABLE 



NEW! 



New pi'iutud circuit design with full power 
output. Fully tunable on both mw/lw 
bands. 7 Transistors plus diode, pusfa- 
pull circuit. Fitted 5 inch speaker, large 
fertile aerial and Milliard transistors. Easy 
to build with terrific results, AH local, 
and continental stations. Siic 10 <7X3Jin. 
TOTAL COST 

TO BUILD £jk I 9.6 PP - 4;8 

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TRANSISTORISED 
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PRICE "ggf 

Power Sopply £14.0.0 33 

30 Audio Generator £19.10,0 34 

31 R.F. Generator £18.10.0 35 

32 C.R. Bridge £10.10.0 26 

33 Inductance bridge £20.0.0 29 
27 Signal Generator £10.10.0 14 
66 Inductance bridge £13.0.0 14 

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BUILD THE PRACTICAL WIRELESS 

I.C. F.M. TUNER 

AS PER DECEMBER, 1967 ISSUE 
TOTAL OO I A POST 

COST 1/6 

Including R.C.A. CA3I04 Circuit and 
Layout Diagrams. Parts List No, <tOA 
BUILD THE PRACTICAL WIRELESS 

SWITCHED F.M. TUNER 

AS PER AUGUST. 1967 ISSUE 
TOTAL fjit POST Parts List 
COST f I JO 2/6 No. 39 

I 1 With Circuit and Layout Diagrams. 

PRACTICAL ELECTRONICS 

GLiSSANDOVIBE 

85- P °6 ST 

AS PER FEBRUARY. 1968 EDITION 
Parts List No. 42 



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