/L■
i"
■
H
Hi Great Repair Aid rpBODucTi uMircoy HELPS YOU EARN MORE (Regt/. Tse&t* Mark) Time-saving Repair Data for nearly 900 Radios & TV's. SOLDERING EQUIPMENT Now you can have af your finger- tips Circuits and Data for repairing all the popular TV's, Radios, 'Grams, Record players j^or the and Tape recorders—right back to 1964. A guaranteed money- spinner . . . saves your time, increases your carning-power 1 DISCRIMINATING Compiled by a team of research engineers Newnes RADIO & TV SERVICING not only gives repair information for nearly 60 principal makes bat also ENTHUSIAST includes section of latest de- velopments in the industry. Thousands upon thousands of copies of previous editions sold — it's the most sought-after publication in the trade. Seize this opportunity to see it on free trial. Send now! TELEVISION • RADIO RADIOGRAMS • CAR RADIOS RECORD REPRODUCERS TAPE RECORDERS All these makes covered — Alba. Baird. Bush, Carousel, Cossor, Danseue, Decca, Defiant, Dynaport. Dynairon, E.A.R,, Ekco, Elizabethan, Ever Ready, Ferguson, Ferranti, Fidelity. G.E.C., Crundig. Hitachi. Invicta, Kolster- Brandes, McMichael. Magnavox, m Marconiphone, Masteradio, Motorola, 7 st Murphy, National, Newmatic. Pani, Perdio, Peto-Scott, Philips, Playcraft, Ponadyne, Py_e, Radiomobile, Regen- tone. Revelation, R.G.D., Roberts* n '■ Radio, S.T.C., Sanyo, Sharp. Sinclair, Smiths' Radiomobile, Sobell, Sound. *1 Standard. Stella, Siereosound. Tejetron, Thorn, Trans Arena, Ultra, Zenith. UIRGUITS'DATA 2 VOLUMES • OVER 1,000 PAGES 4 1 iRCitf «OvU"lE tutiNO NEARLY 1,400 CIRCUITS, COM- 19. 9 9 PONENT LAYOUT DIAGRAMS, tiA- DRAWINGS and TABLES Plu* section of latest developments in Radio and Television \ILUSJRA1E.D: >% n; "U L64 BIT INSTRUMENT IN c L,J§ Yours for a week fol L700 PROTECTIVE SHIELD REPAIR HINTS
I~ EASY NO-INTEREST TERMS IF KEPT AFTER FREE TRIAL Buckingham Press Ltd. If under 21 your father must fill up coupon H 15-17 Long Acre, " London, W.C.2 Fn// iVewie APPLY DIRECT TO; I Please send Newnes (BLOCK I.FTrilRS) (Mr., Mrs., Miss) RADIO & TV SER- SALES & SERVICE DEPT. I VICING 12 volumes, 1964-66 models) with- A Mr ess ADCOLA PRODUCTS LTD. out obligation to buy. I If you accept this a ppli- caiion I will post 15/- lick / wfief« cpplicabttM ADCOLA HOUSE I deposit 8 days after re- I The address on ltd is-I ceipt of books, then M) Property ( I GAUDEN ROAD 15/- monthly for 10 Btnlod uolBrnished 1 ' S months, paying £8.5s. Occupation..... LONDON, S.W.4 in all—or return the PoreotsMlooie |_J books. Cash in 8 days Signature furnlshsfllcconi. i" TELEPHONE; MACAU LAY 0291/3 tOO/2228 (flmpnrjry Iddrtss ut GUARANTEED 3 MONTHS | ymuE in VALVES BY RETURN OF FOST Transistorised AMiSntisfactioQ VALVES or MoneyARB NEW Back UNLESS Ouatantee OTHERWISE on goods If retnnwd INFORMED. unused FREE*ithln TRANSIT 14 dsys- WBUEAHCE. P08TA0B 1 t»1»« E-U Sd. per FmorsiU. SSL9ST KCOSt KT89 Ufifi 8/9 1L4 2/3 8K26ST.l 8/9 26Z40 6/67/9 EC 086 6/871- KT91 ,11/-1*1- U24 12/8 1841R6 4/9 18/8918 80F6 8/1 EC 068 91- ET93 6/9 U26 8/8 4/9 8L9SLOQ 71- 80FL1 8/6 SO 160 7/8 ATM 14/- uee FM Tuner 1T4186 4/9 6L18 7/3 SOLI 5 9/6 ECFae 7/8 XT76 8/6 U86 .5'!12/8 2D21 6/98/-
-. Jjsm micRO Fm
rffe/tfr/'/ag' SINCLAIR MICRO FM 7 TRANSISTOR SUPERHET P.M. TUNER/RECEIVER This unique, superbly engineered superhet set for himself have been completely elimi- cfesr/gsts' FM set gives enormous satisfaction both in nated in the Micro FM. It Is ready to use the building and in using it. It is completely moment you have built it. The pulse count- professional in styling inside and out. When ing discriminator ensures best possible built, the performance of the Sinclair Micro audio quality; sensitivity is such that the FM Is fantastic. It is the only set in the world telescopic aerial included with the kit which can be used both as an FM tuner and assures good reception in all but the very as an independent FM pocket receiver just poorest reception areas. The Sinclair Micro whenever you wish. Problems of alignment FM can give you all you want in FM recep- which have previously made it almost im- tion plus the satisfaction of building a unique possible for a constructor to complete an FH design that will save you pounds. TECHNICAL DESCRIPTION 4c Size: Hi' x I Jl' X J* 1 THE EINCLAIR MICRO FM is a completely ★ Powerful A.F.C. cle letf-containcd doubie-purpose F.M. superhet. It uses 7 4c Pulse counting discriminator transistors and 2 diodes. The R.F. amplifier is followed 4c Lew t.F. completely eliminatetafignmant problem* by a self'Osei I latins mixer and three stages of I.F. 4c Tunes from 88 to 108 He/* CRoi? amplification which dispense with I.F. transformers 4c Audio response: 10 to 10,000 c/S ± IdB and all problems of alignment. The final I.F. amplifier 4c Signal to Noise Ratio! 30dB at 30 microvolts produces a square wave which is converted so that the 4c Operate* from standard 9V battery, *elf-cootain*d original modulation is reproduced exactly. A pulse- 4e Plastic case with brushed and polished aluminium (Micro"( om F.M.)vcrf impressedwhich took with onfc the fiveJet counting discriminator ensures better audio quality. front and spun aluminium tuning dial hours to ossemh'e ond worked immerf- One output is for feeding to amplifier or recorder (Signed)iatelK." D.H.VV., Leigh, Heigate, and the other enables the Micro' FM to be used as Complete kit Surrey. an independent self-contained pocket portable. A.F.C. inc. telescopic "I would like to express my complete "locks" the programme tuned in. The telescopic aerial, case, satisfoction with your Micro F-M. aerial included is sufficient in all but the worst signal earpiece and £5.19.6 in quoiitK it certainly equait my areas. instructions tiontpresent on (expensive)o fine design." tuner. Congrotuia- (Signed) London, e.C.4.
SlNCLA'l0 SIKCLAIR MICRO-6 - Build it in an evening MiCfl This is the set to build if you want a minutely sited receiver which will Complete kit including case, aerial, slip into a waistcoat pocket without even showing. It is the smallest set lightweight earpiece and instruction* Isin completelythe world, againstself-contained which a including matchbox aerial looks and enormous. batteries Yet and the it virtually Micro-6 Slays anywhere. Its clever six-stage(a circuit (2 R.F,, double diode detector, A.F.) ensures all you want in a radio today—power, range, quality and A.G.C.selectivity. counteracts It is very fading simple from to build distant and stations,useful to bandspreadhave with you brings always. in THE SMALLEST SET Luxembourg like a local station. There is great pleasure to be had in build- 59/6 IN THE WORLD seening the its white,Micros, gold and and it blackmakes case a andhighly heard acceptable its amazing gift performance. once others have Sinclair radionics l1~d se neujmarkEt road, cambridgE Telephone 5273I
466 SINCLAIR /24w. 12 WATTS R.M.S. CONTINUOUS SINE WAVE \?EkK )
15 WATTS R.M.S. MUSIC POWER (30 WATTS PEAK)
Z.I2 HIGH FIDELITY AMPLIFIER AND PRE-AMP This is the hi-fi amplifier of the volt car battery makes an ideal ★ TECHNICAL SPECIFICATION future—very small, fantastically power source. For mains operation, Size 3*X Ij"* l^* Class "B" ukr»-linear output powerful and with the character- the PZ,3 Is recommended. Because -k Response )5-5O,OO0c/s i IdB -jlr Suitable for 3, 7.5 istics you expect from the most of its size, the Z.I2 can be used for or ISO speakers. Two 30 speakers may be used in expensive equipment available. The car radio, guitar, P.A. system, inter- parallel, Input—2mV into 2kO. -Ar Signal to poise Z.I2 incorporates its own high gain com, etc., as well as the very best ratio—better than fcOdE. ^ Quiescent current con- pre-amp. arranged so that any type hi-fi it was designed for. It is indeed sumption—15mA. of input and tone control circuit is the ideal amplifier wherever the Built, tested and easily matched. Full details are need is for power and quality from guaranteed. Ready for given in the manual supplied with the smallest possible unit. This is immediate use. With every Z.I0, and even for stereo the the approach to high fidelity audio Z.I 2 manual. 89/6 cost is but a few shillings. The Z.I2 reproduction and one which you operates efficiently from any supply can enjoy for remarkably little If you prefer not to cut the coupon out, please between 6 and 20 volts D.C. and a 12 outlay. refer to PE.7 when writing your order. TYPJCAL COMMENT "J haytjutt eomplttedbuild- SENSATIONAL POWER To SINCLAIR RADIONICS LTD. 1 ing the Micro FM. and I em very pleased with the result NEW SUPPLY UNIT 22 NEWMARKET ROAD, CAMBRIDGE I theespecially Z.I2 amplifitr." when linked up to J.G.O.C., Sandwich, Kent SINCLAIR PZ,3 Please send Designed specialty for the very "I am very pleased with it high standards of the 2.12, this very(Z.I2). well," It suits my needs entirely NEW power supply unitited usescircuitry advanced to achieve transiuor- ex- C-TS.. Widnex ceptionally good smoothing. Ripple is a barely measurable or which I enclose I of"Results this world, I am gettingI have demon-ore out O.OSV.power Thetwo PZ.3,Z.I2s whichwith ease,will I' stratedenthusiasts it to who Quite are a scrappingfew Hi-Fi costs— overtheir to valve Z.I2." jobs and changing 79/6 CASHlCHCQUEfMONEY ORDER for £ s. d. \ RJ-V.. Undon. W.3 NAME | FULL SERVICE FACILITIES AVAILABLE TO ALL SINCLAIR CUSTOMERS ADDRESS . I (SuarattLec , 1
i If you ere not completely u 1 ■ satisfied when you re- ceive your purchisefrom us, your money will be SI IE3I < refunded at once in full and without question. ► 467 VARLEY SOLENOIDS FIRST QUALITY PVC TAPE SAMSON'S A.C. 200-250 v. Very powerful. Base R * TV S}' Std. 850 ft. 9/' 5'L.P. 850 ft. 10/6 ELECTRONICS LTD. size 2J' X 2i' X 21 . Pulling spindle 7'Std. 1200 ft. 11/6 3' T.P. 600 ft. 10/6 9-10 CHAPEL STREET length 2 in. 22/6, p.p. 2/6. 3* L.P. 240 ft. 4/- 3'T.P. 1800 ft. 25/6 LONDON, N.W.I SJ-'L.P. 1200 ft. 11/6 5J'T.P.2400 ft. 32/6 Teli PAD 7851 Tel: AMB 5125 LIGHT SENSITIVE SWITCHES 7* L.P. 1800 ft. 18/6 7'T.P. 3600 ft, 42/6 12 Mullard Type ORPI2. 7/6, p.p. P. & P. on each 1/6, 4 or more post free. AUTO TRANSFORMERS 240-110 v., 2,000 Watts, completely enclosed in beaucifuily finished case. SYNCHRONOUS GEARED CYLDON .3 to 4 WATT Fitted with two 2-rin American MOTORS U.H.F. TUNER AMPLIFIER KIT socked, or Terminal Blocks. Neon A.C. 200-250 v. Very powerful 40 complete with comprising indlcitor. On/off twitch and chrome r.p.m. Size 21' X 2i'X 1'. Easily chassis 8? carry handle. 419.19.6, Carr. 10/-. adapted to oscillate op to half a PC.88 and PC.86 x 2i' x r. Also available, completely shrouded revolution. 12/6, p.p. 2/6. Valves. Full vari- orand terminal fitted withblocks. American sockets able tuning. New /T.- Double Please state which type MULTI-TAPPED w wound required. TRANSFORMERS and unused. Size mains Wattage Price Carr. All Primaries 200, 230, 250 v. 41' x 5i' x li". transformer, output transformer, 1.000 f4 !9 6 7/6 Type Sec. Taps Amps volume and tone controls, re- 500 .. £3 IS 0 6/6 A 3-4.5-6-8-9-10-12-15-18. Complete with sistors, condensers, etc. 6V6, 300 £2 0 6 5/6 20-24-30 v 2 29/6 4/- circuit diagram. ECC8I and metal rectifier. 150 £1 19 6 5/- B 3-4-5-6-8.9-10.12.15-18- 35/- plus 2/6 Circuit 1/6 free with. kit. 29/6 P. & P. plus 4/6 P. & P. C 3-4-5-6-8-9-10-12-15.18-20-24-30 v 5 49/6 5/6 400 WATT AUTO D 3-4-5-6-8-9-10-12-15-18-20-24-30 v ... 8 651-7/- 8-watt 5-valve PUSH-PULL TRANSFORMERS £ 6-7-8-10-14-15-17-19-25- By famous maker, fully tropicalised. 31-33-40-50 v 3 49/6 5/6 AMPLIFIER & METAL RECTIFIER Tapped 200 , 210-220-230-240-250, F 6-7-8-10-14-15-17-19-25- Size: 9 X6 X li" A.C. Mains 200-250v. 5 valves. SO -75-65-100-105-j 10-1 SO-160 v. 31-33-40-50 v 6 97/6 7/6 For use with Std. or L.P. records, musical Table top connections, 49,6. Carr. S/-. G 12-18-20-24-30 v 10 77/6 7/6 instruments, all makes of pick-ups and mikes. Output 8 watts at 5 per cent total distortion. VENNER CLOCKWORK SMITH'S 4 MINUTE TIMERS Separate bass and treble lift controls. Two TIME SWITCHES Single-pole switch. IS Amp., 250 v. inputs, with controls, for gram, and mike. Output Transformer contacts. Complete with chrome tapped for 3 and 15 ohms speech coils. Built and tested. £3.19.6. 14-Day one on, one off every 24 bezel and control pointer knob. P. & P, 10/- hours, SA, 250 v. contacts. Com- Size 2 In. dia., depth 21 in. 17/6, condition.plete with 35/-,socket p.p. ahd 3/6. key. Perfect p.p. 2,'6. 8 a n 8, 8 t r FIELD TELEPHONE "MUSETTE" -Iu% E R HE? VENNER ELECTRIC TYPE TELE "f" PORTABLE RADIO TIME SWITCHES ringing.Perfect condition.Complete Generatorwith hand bellset ★ 2i' Speaker. A.C. 200-250 v. Type MDIBP. One ana batteries. £4.19,6 per pair, ★ 6 Transistors Superhet Output on, one off every 24 hours, "30A carr. 10/6. 200 mw. finishedA.C. 250 in_v. contacts-black Bake Beautifully lite case, size 0" X S}' X 4i' Brand new at ic Plastic Cabinet in red, size 4J* HaSB a fraction of maker's price. £3.19.6, FIELD TELE CABLE x 3*"X 11* and gold speaker p.p. S/-. Arms for extra switching, Type "OJ" Single, I/J mile drums louvre. 6/6 per pair. unused. 45/- per drum, p.p. 7/6. •jc Horizontal Tuning Scale. Inc. carrying it Ferrite Rod Internal Aerial. 39/6 strap. Circuit •jr IF 460 Kc/s. Diagram 2/6— ★ AH components Ferrite Rod P. & P. 3/9 free with parts and Tuning Assembly mounted od printed board. if Printed Circuit Board. ★ Operated from PP3 Battery. ★ Tunable over medium and ★ Fully comprehensive instruc- long waveband. tions and point-to-point wiring ★ Car aerial and earpiece D.I.Y. with diagram. socket. TRANSISTORISED SIGNAL GENERATOR Size 5r X 3i' x li'. For IF and RF align- GOODMANS ment and AF output, 700 c/s frequency cover- age 460 Kc/s to 2 Mc/s in switched frequencies. Ideal for alignment to our Elegant Seven and Musette. Built and tested. 39/6. P. & P. 3/6. HIGH ELEGANT SEVEN Mk.II Com bin td Portal) lo and Car Radio FIDELITY The Radio with the " Star" Fcahnei Bina MEim if 7-traniiHor suptrhsL Output MANUAL 350 mW. if Waodan cabinet, littad handle with tllver-coloured A new, larger and more coioutfol edition—revised and completely fitting, »i*e 1211«. x 8i In, x 3i In. up-to-date. It contains articles o< particular Interest to the D.I.Y. ★ Horizontal tuning scale, size 111 In. enthusiast—including special beginners page, advice on stereo, x 2} In. in lilver with black lotterint. ONLY if All ztatlons clearly marked. sfage-buill systems and lull cabinet drawings. Whether building or ★ Ferrlte-rod Internal aerial. improving your own audio set-up or choosing a complete speaker ★ Operated from PPS battery. £4.4.0 system, you'll find it useful and interesting as well as informative. if I.F. neutralisation an etch etaee Ask your Goodmans dealer or send coupon for your FREE copy. 460 ke/i. Plus 6/6 Post & Pocking it B.C. coupled outeat stage with POWER SUPPLY KIT separate AC. negative feed back. to purchasers of Elegant ■ Please send me a free copy of the Goodmans High ■ ★ assemblyA" components,ferrite mounted on rodprinted and tuningbeard. Seven parts, incorporat- I Fidelity Manual ★ Fully comprehensive instructions and ing mains transformer, point-to-point wiring diagram. etc. A.C. mains 200- | Name ...... ★ Printed circuit board, back-printed 250v. Output 9v, 50mA, with all component values. 7/6d, extra. I Address - if Fully tunable over medium and long waveband. a •* Car aerial socket. if Full after-sales service. I P.E.7 ■ 4 In. SPEAKER. Parts list and circuit diagram 2/4. FREE with parts. Shop Hour* 9 a.m. — 6 p.m. Early Closing Wednesday - J GOODMANS INDUSTRIES All enquiries stamped addressed envelope Axiom Worka, WombUy, Mlddtoaa* RADIO & T.V. COMPONENTS (ACTON) LTD. Telephones WEMbley 1200 21 Df HIGH STREET, ACTON, LONDON, W.3 GOODMANS A Diviiion of Radio Rentuet Product! Ltd,
468 TWO-YEAR GUARANTEE On ail our tlimline TV* Sand for fraa titt take your EX - RENTAL TELEVISIONS 17 in. £11.10.0 tl montht' 3 star Guarantee pickJL ■fcTobe -jltValves -^fComponencs w«»i*TiOMAL t^rwva colouredfr.ee list Channel* for all area* t**crmctv* m Demonstrations daily from Large Se/ection Personal collection or Insured Cam 30/- RADIOGRAM CABINETS d£9.10.0 Superbly made and styled in Veneered Cnglitb Walnut UfT UP LID 70 CHANGER 'K-4 AND RECORD STORAGE • COMPARTMENT Post!on S* X S" Twin Speakers \tl/ Diameter; 40 X I6i X I5i Legs I gn. Carr. 30/- Other Models—Send for List RESISTORS 51- per 100. Nov. Mottly ' High Scabs. Assorted. P. & P. 2/-. Overseas 3/S. vW. VALVES £1 per 100. Assorted TV and Radio. SurplusPost 4/6. ex-rental Send (or dismantled list. m -4 LatestRECORD designed PLAYER covered CABINETS cabinets. Takes 49/6. any modern Autoehanger, SINGLE PLAYER CABINETS 19/6. P. & P. 5/6. DUKE & CO. (LONDON) LTD. .. 621/3 Romford Roa.d, Manor Parkt E.12 Liverpool Street—Manor Park—10 mins. Phone: ILFord 600-1-2-3. Scamp for Free List. from hik
semiconductor centers Over 100 IR semiconductor devices are avail- able from your dealer, many with free KOHTAKT instruction manuals and project and experiment details. Look for the floor-standing 'Semiconductor Center,' or the counter-top 1 Minicenter.' 60 EXPERIMENTER SEMICONDUCTOR KITS MOUNTING KITS AND HEAT SINKS THE SPECIAL CLEANER SILICON BRIDGE RECTIFIERS UNIJUNCTION TRANSISTORS FOR INACCESSIBLE SELENIUM PHOTO CELLS CONTACTS INSTRUMENT RECTIFIERS Dm ipwlru' , * KONTAKT 60 deans and AUTOMOTIVE RECTIFIERS protects all contacts SILICON SOLAR CELLS ★ Eliminates high transition SILICON RECTIFIERS (Si KonioVrs/ki resistances GERMANIUM DIODES aMygon#!®* •jr Prevents 'creep* currents THYRISTORS (S.C.R.) ■/If Does not affect plastic materials ZENER DIODES •fc In spray can with 5i' spray TRANSISTORS nozzle SELENIUM STACKS Other Kontakt ffi products are:- Write for the free illustrated catalogue and price-list, also the name and address em" 70 Protective Lacquer 72 Insulating Spray of your nearest IR SEMICONDUCTOR CENTER fRl, 75 Cold Spray for Fault Location 80 Special Siliconized Polish INTERNATIONAL RECTIFIER 100 Antistatic Agent for Plastics HURST GREEN • OXTED • SURREY • Tel.: OXTED 3215 Write for full details of above complete Dealers—write for details of howyoo can start your own range of Kontakt products to;- IR SEMICONDUCTOR CENTER. SPECIAL PRODUCTS DISTRIBUTORS LIMITED 81 PkcadHly, London, W.I. GROsvenor 6482 ^3 semiconductor centers
469 f ADIO & ELECTRONIC IIRADIONIC CONSTRUCTION SYSTEM
ABSOHDIKG AXD ORADTONIC EXXITIIVC!
i" . .1.1? IlunUri'ils ot oluoallonal pstabllsh. 2-^ a,rpl,(,IT" Tpphnleal CoIU jcph. SthiK.ls, th« Arm<-U Forccs- ownprn"f ranitc>' u^InR fnim HaUlonlct to g* > pars tor or cU'oti-onlc ajtr. Instrut-llon. KnthuHlasilu 16 Coun< t rntrcs. '«FraturiHl 'Z In .Sound" and'ndustrlal Trlrvislon Drslen broad for easts. all lirltlsTl Ursirn The system Is beautirutty enBtneereU from top qoaltiy British components. No soMehne. r»=.^0.prtor.,snowlcJ«e ,weJed- Simply arrange components on perforated transparentworKs with full panel, efficiency. position brassYou can connealng then dismantle strip unJcrneath, and build anotherfix with circuir.6BA nuts Your and resultscircuit arc BtHiameeu by out Technical Department and News Letter Service. All parts available separately for conversion or expansion of sets. A No. 4 SET and fi-TflANSISTOR SUPERHET able. Mm ply.?"f Insert "x« soldering" components print and rd tighten circuit nutji. board tot suiicrliet port- No. I Set £5.18.fi, it Circuits (Earphone) aisto No. S Set l'6.19.6. 20 Circuits (Earphone) lOSlC (-ractrft No. 3 Set £10.19.6. _ S3 Circuits (7 x 4in. Loudsiwaher output) .Vo. 4 Set £14.19.6. 3t Circuits (Include c Transistor and reflex suprrbcts) Prices (Post Fret) Full Jelails from: RADIONIC PRODUCTS LIMITED STEPHENSON WAY, THREE BRIDGES CRAWLEY, SUSSEX Tot.! CRAWIEY 28700 Trade Enquiries Invilad Theoretical Circuit Practical Layout Oor '£' Series of basic electronic circuits it available separately. Send for details of El SOS, our do-it-yourself computer.
KT88 82/- QSI202 8/- LY21 FULLY GUARANTEED KTW8I 8/8 QV04/7 8/- 2C34 fiALSW 71- 12AH7 61- 76 8/6 6704 •/- KTW63 2/- VMP40 18/- 2i;4j 22/6 0AMS 8/6 l 12AT7 61- 78 5/- 6064 71- KTZ4I 61- R10 61- VP23 as; 30/- OAMfi 4;- 6K7fi I2AU7 51- 9/6 aoeo 01- INDIVIDUALLY PACKED KTZ63 61- BK72 8/- VP13.1 ar i 18/- SAQS 71- | 12AX7 01- 78 »/- 6680 «/- \ MH4 8/- VRon 2X2 «A«66AQ5W 61-91- sKsn 12AY7 10'- 80 6/6 7193 1/0 MM 61- fillEI2 10/- VS103/30 3.\4 6A88W 9/- OKSH 128.48 8/6 81 91- (476 21- VALVES SJ8 15/- SISOP 16/- 3B7 8/- SA«;C! 80/. SLsn I2BE6 71- 01- 8013.4 25/- AC/HI. 4/3 XE1J 7/- RJ30 12/8 VR150/30 31124 5/- SATfi 4/- 12BHJ 71- 84 01- 8020 01- ACP4 8/- £BS4 1/8 I EL34 10/- OA2 0' SP3SP41 8/8 aiw *- OAUn fiL7
Lmrt HOME CONSTRUCTORS &
ELECTRONICS ENTHUSIASTS RADIO Wa oonridet cot coubsctkm pWMlt (o be tbe flneit raise oo tba home coutnetor market. U on receipt pea lee) not Dompeteni to build (be eet, jon mar retina it as receitai within 7 dan, when the rum paid will he refunded leu postage' DEMONSTRATION STUDIOS CONSTRUCTORS BARGAINS Lasky^s Radio are proud to announce the opening of The "Sixteen1 Multirange their re styled and completely modernised Hi-Fidelity METER KIT and Electronics components store and showroom at: This outstanding meter was featured by Praelical inrelmt pletela the kit Jan. of parts '84 issue.as specified Lasky's by the are designer. able to oOcr the com- 207 EDGWARE ROAD, W.2 EAHOE SPBCIFICATIOR: U-C. volts: 0-2,»-23-30-2J0-S(K> atD.Coorrent; 20,0000/V. 0-50UA, A.C. 0-2,6-30-9SOmA. volts: 0-25-50-260-600 Resistance: at 1.0000-2,0000, n IV. 0-200k0, 0-20 MO. Baslemovement: 40ftA f.8..d. moving coil.MfiA. WithBlack universal plastic shuntcase—3J full xijscale xljin. deflection Controls; current 12is USjCYSBADlOJ lUsj^ position range switch; separate slide ewitch tor A.C. volts— D.C. ohms; ubras aero adiustment pot, meter, meter zero. Data and circuit nvuil- Powerwith all requirements: parts and fullOne 16v.constrootlon and one l.Sv.details. baits. If.P. Complete Terms able separately, 2/8; available. refunded If all [arts LASKY'S PRICE £5.19.6. bought. Pair of I P. A P. 0/- batteries 2/- extra, NEW—LASKY'S MINIATURE TRANSISTOR AMPLIFIER MODULES Incorporating the very latest drcuitry to provide high sensitivity and good quality In Mniuncthm with extreme small size and compactness. High quality Ifewmotket transistors nsed thronghont. Sew foiiturea Include epneioas open layout," Tape Bar, " Sen Service Coiupouente Dept.. All designed to operate on 9v. miniature choiceand Hi-Fi from Dcmonatratkm the largest stocka Studio. in Great Abntutclv Britain—backed new* and by right Latkv'e up to mat date erperienec for your caav ami battery. imme—aynonyiuoua with EtcctroolcB tor over 30 yeara! TYPE PC X. 3 translslor. Input sens. 50 mV., output 150 mW, output imp. REMEMBER LASKY'S GUARANTEE YOU 40Q,ai«2XlXjin. PRICE 27/6 THE BEST IN ELECTRONICS TYPEmW, output PC 8, Imp.9 transistor. 18n, size 2J InpntX 1}X sens. fin..., XmV. PRICE output 22/6 330 TYPE PC S. 8 transistor. Input sens. 8 mV, output 400 inV, output Imp. ISO, size SPECIAL INTEREST I IT MS! 2| X 1} X {in PRICE 25/- TYPE PC 4. 8 transistor. Input sens. 180 mV, output 330 mV, output Imp. 15Q, size TEST METER ADAPTOR 25 x 15 x Jin. PRICE 22/6 Typewhich P.E. enables 230—thlo nny SO la ralctoampa folly trnnaistorfaed D.C. Multimeter device to TYPE PC 6. 6 transistor. Input sens. 8mV, output 3W, output Imp. 3 0, size 6i X be nsed In place of a valve volt meter. Oo the XV. II X lin. PRICE 59/6 increasesrange an, onimpedance the 1060 of V. 1 rangemegohm to Is100 offered megohms. which TYPE PC 7. 6 transistor. Input sens. 8mV, output 1W, ontpnt Imp. an, size 3 X 7ranges: I to 1600 volts, Designed for Immedlute li X tin. .. PRICE 39/6 conBectlonquite suitable to forAvo use 8 andwith similarany other slee 30 maters micronmp but Add 1/- on each lor post and packing meter. SlaeGX 6 X 0 in. Sow and boxed. List Price 7 Oas. LASKY'S PRICE 39/6 SINCLAIR SUPER MINIATURES Post 2;(J. Set of batteries J/S extra. packageWe stock deals. the complete range of Sinclair Super-miniature kits. Write for defoila of THE MICRO-6 miniature radio only l| x liV X liin 22 19 8 THE SLIMLINE 2-trnnsistorpooketradio — 22 9 8 SPECIAL PURCHASE—UHF/VHP TUNERS THE M1CR0-FM. Ituncr/receiver) 25 19 8 Well known British maketa" surplus stocks. Now available tor the flret THE X-20 20 watt P.W.M. Bmplltler 87 19 8 lime to the Home Constructor. Available ready built, tested and guaranteed £9 IB 6 TRANSISTORISED UHF MINIATURE MODEL THE X-10 10 watt nmplMer and pre-smp 19 19 8 Shielded metal cn«e only Si X li X 3in. Fully tunable—complete with Available ready built, tested and guaranteed £0 19 6 two AP 1S9 trans Is tors. LASKY'S PRICE 39/6 THE Z-t2 12 watt amplifier and pte-ampllfier. Fully built and tested tt 9 8 VALVE UHF MODEL (fKurtraW) \/ P -. CJ O A D High grade laminated board with copper strips In nielnl case else 4 x 6 X liin. Fully tunable—complete with PCC86 * trwox-spqrvu — bonded to and pierced with holes. and POC88 valves. LASKY'S PRICE 33/6. Without valves 26/-. Boards Aoeeisotits 43/160442/1803 X 5 lo. 3/8 Terminal pins ■—pkt.oIBO 3/- TRANSISTORISED VHF MODEL I 48/1607 SfXX 531 In in 35/2t- Spot face cutler tool 8/8 Miniature turret type fitted with 12 eete of coils and 3 Motlard AFJ02 transletora. 40/1808 3J X 3i in S/8 Fin inserting tool 6/6 metel case size 4 X 2 X Silo. LASKY'S PRICE 29/6 44/1808 31X1710. 12/8 OrdersPost 8d. of psrltsm 10/- and extra. over pott free. TRANSISTORISED VHF MODEL 2 Sob-mlnlalture turret type fllted with 12 sets of oolle and 3 Mullard AF102 tnmmstors. TRANSISTORS ALL BEAND FEW ASD QDAEAHTEED In metal case size 3 X If X 2ita. LASKY'S PRICE 37/6" GET 81, GET 85, GET 80 2/6; 8J3A, 874P 3/8; 0015. OC71, OC81D 4/8; OO 41. Add 9/8 Poet and Packing on each. OC 73,70. OCOO 82D76, 7/0:OO 81OC 6/8; 201, pair OC £64(10/61; 15/-; AF OO 1X7, 205, OC OC 200 206 8/8,' 19/8: OO OC28 42. OO 24/6; 43. OC 79 8/-. GORLER UT 340 FM/VHF TUNING HEART TRANS FILTERS By BBTJSH CBYGTAL CO. ArsiUWs Ifom itoek. Permeabilitymetal case, biro toned 3 X —21 covering X IJIn. 87Circuit tol08 supplied Me/s. For use with one ECC8S valve. In TO—OlE «J6 kc/s. + 2 kc/s. 1 TO—02D 470 kc/s. ± 1 kc/a. 7/6 EACH LASKY'S PRICE 15/11 Poet 21-. ECC85 valve 9/- extra TO—02BTO—OlD 470105 kc/s.-hke/s. ± 21 kc/s. OT—OlBTF—OlD 465470 kc/s. ± 2 kc/s. ' POSl 60.
207 EDGWARE ROAD, LONDON, W,2 T«l;PAD327l | 42TOTTENHAMCT. RD.,LONDON,W.I Tel:LAN2S73 33TOTTENHAMCT.RD.,LONDON,W.ITehMUS2605 IS2/3 FLEET STREET, LONDON, E.C.4 Tel:FLE2833 Both open all day Saturday. Early doting Thursday, I Both open all day Thursday. Early dosing Saturday. Please address all Mall Orders and Correspondence to 3-15 Cavell St., Tower Hamlets, London, E.I. Tel.: STE 4821/2
LASKY S FOR SPEEDY MAIL ORDER SERVICE
47! CONDENSE. BARGAINS! ELECTROLYTIC 32irf... I'Svolc 2uf fivolt 64uf >volt 3-2uf 64volt •25uf , 3volt lOuf 6volt iSOuf Svolt Suf 70vo)t 2uf, 3volt 2Suf Svolt lOuf lOvoit 2of lOOvoit 20ufBuf . 3volc3vc.lt 30uf fivole lOOuf lOvolt 2uf I SOvolt lOOuf. 3volt 2ufbut Svolt luf SOvolc Bui 275yolt 200uf. 3volt 20uf Svolt BufSuf SOvolt all at I/-?volt each or 9/- ptr dox,SOvolt 3uf . tlvolt 200uf ... l2volt lOOuf ... ISvolt 32uf 4Mf . llvolt 6uf ISvolt 7sour ISvolt Muf 25voltISvolt 6uf . Uvolc Buf ISvoit a-suf ISvolt I SOuf 2Svolt 8 tips ISvflOuf . I Jvolt lOuf ISvolt 3uf 25vott I6uf SOvolt toour. llvoltl2voIt SOuf30uf ISvolt 4uf 25volt _6-4uf ... 40volt all at 1/3ISvoit each or- 25uf11/3 per dozen2Svolt 12'Suf -Wvolt 5,000uf 12volt 4/- each- 25voIt 31- each. PAPER CONDENSERS each doz. 100 1,000 for praitiinl •OOluf SOOvolt 7d. 5/3 291- 67/5/. 000luf •001 uf I.OOOvolt »d, 6/9 37/6 £9/7/6 ■-OOluf SOOvolt -002uf SOOvolt 7d. 5/3 29/- £7/5/- •002uf SOOvolt •OOSufOlSuf 300 A.C. Vd. 6/9 37/6 £9/7/6 -OOSuf SOOvolt •02uf 350volc750volt 7d. 5/3 29/- £7/5/- soldering •02uf 600 A-C. 6d, 4/6 25/- 7/6 per 100. ■luf SSOvolt 1/3 11/3 6i/6 tft/ii'/e £3 per 1,000. •tuf 7S0volc t7id.9d. 5/86/9 31/3 £7/16/3 -35uf 350volt lOd. 7/6 41/837/6 £10/8/-£9/7/6 •Suf (SOvolt I/- 91- 50/- £12/10/- -Suf SSOvolt tli 11/3 62/6 £15/12/6 •Suf SOOvolt 1/6I/O la/O13/6 75/- HO/IS/"£18/15/- SILVER10/- per MICA, J00. CERAMIC, POUrSTTRENE, Mixod typ.a, value., RESISTORS, i watt to 3 watt Close Tolerance, Mixed valuet. Polythene wrappedpost and packing.on cards of 10. Fantastic valuel Only 50/- per 1,000 piui Sl- RESISTORS FOR TRANSISTOR WORK. Low valuet. i watt. 5% 'cads. Excellent quality. 50 for 10/-. Our teleccion only, Computerl - LJntetted, Switching unmarked. Transistors- Excellent Very Value small. at 12/6forNPN or SO. PNP. £1 for 6 I0O. for dozen,. 50/- IOO.'24/5 £12/10/-per Switching 1.000. Transistors, 6 for 10/-. Diodes I/- each, 9/- Ah Tranaistors, components, circuit, to make, 10/- only. LOUDSPEAKERS.. 5... S- .15 Transistors,Sin.. 4tn.. or components Bin,, 10/. each. (excluding meter), 10/.. only. Magnetic, Lapel, 10/- each. With plug and lead. EARPIECES.F,C, Magnetic, S/-each. With plug and lead, ACOShH£ MAKE. MONO 14/-, STEREO 21/-. DIAMOND STEREO M/» G. F. MILWARD 17 Peel Close, Drayton Bassett, Nr. Tamworth, Staffs. Phone: Tamworth 2321 ORDEkS UNDER 10/- PLBASE INCLUDE Ij- POST AN0 PACKING
The SUPER 6 LONG AND MEDIUM WAVE TRANSISTO R RADIO m •if* Component6 traoslstors positions nnd diode. and rcterencea+ 33(tmW. prluted 4. onSupcrhet, buck of board,Perritc roil aerial. cabinet, 11X7i X 3i In. -*• Vinyl covered. *0X4 In. speaker. ★ Wooden 8/-. Free with kit. if Lining up service, if AH parta supplied it Booklet Write for Hat, S.A.E, please. VT0 or X'.P.O. <3/0 with kit). separately. COMPLETE SET OF PARTS ONLY £4 .0.0 OB FVLLr BOUT £4.7.8 Tax & Can. Bali (PLtTS 5/- POST) AM/FM (V.H.F.) RADIO GRAM CHASSIS £!5.IS.O
NEW! jT||yTn The Instant Heat Soldering Kit complete with Chaasla aize 15 x fli x CJIn. high. Sew manufacture. Dial 141 * 41o. la 2 tips, extension barrel, probe and solder. cream and red. 200-2S0v. A.C. only. ... Complete £3 19 6 Picfc-ap. BzL Speaker,ot Ac.,d Gttul P., and Dipole Sockcte. Five pushbuttons— Ask for a demonstrationJ from your local M.:„ SOO-MO ST.; 88-100 Mc/»;' 6-17i, Mc/s.Aligned EZ.80 and tested. rect., ECH81,Tone control. BF89, lOOO-lBOBEABC80, EL84. KOC80. 3ohm speaker required. 91 Cln. Elliptical Speaker 25/-. dealer or fill in the coupon below for full TKBMB: 14.0.0 down and i monthly payments of *8.10.0. Total K.P. price details. ST.«i8.X0.O. Ireland taroolt20/- extra. diagram 8/4. V.H.F. Bipole 12/4. Feeder Bd. yd. Cam to USH8UTTON M,W; B.W.I; tf8,W.2; \'HP; Oram; Btereo STEREOGRAM Gram. Two separate chassis cbannela /or PE/7/66 Stereo Gram with balance control. Also operates with two speakers on RaUJo. Name .. cream and red I5*X 3*. ECC85; ECH81; EF89; 21 X10 ECLSfi; EM84 and Beet, Address TotalJoife H.P.f, ®- price? <»"• *£0.16.0. fald or *5.0.0 deposit and 6 aionthty payments of £4.8.0. BURGESS BURGESS PRODUCTS CO. LTD. GLADSTONE RADIO SAPCOTE, LEICESTER, 66 ELMS ROAD, ALDERSHOT, Hants. SG 1225 KIT (2 mine, from Station and Base*.] Aldershot 22240 Tel: Sapcote 292 Tele*: 34549 CLOSED WEDNESDAY APTEKNOON CATALOGUE 6d, BULK ENQDIBJES INVITED FOE EXPOEX
472 KEDOCO
TRANSISTORISED MODULES BRING TOP-QUALITY TO HOME CONSTRUCTION HI-FI TAPE EQUIPMENT - AT INCREDIBLY LOW COST!
KEDOCO STAR FEATURES ■ Kedoco quality control ensures high product performance — always ■ Transistorised modules ready-assembled for simple, speedy wiring into circuit ■ Units operate from 12 volts — Idea! for out-and-about recording ■ Miniaturization of modules permits compact packaging ■ Complete flexibility in design from eight basic units ■ Money-back guarantee on all products
CLASSIC TRANSISTORISED TAPE EQUIPMENT KEDOCO COMPONENTS 20-WATT AMPLIFIERS TAPE PRE-AMP SSTR/7 A COMPLETE RANGE TO SATISFY ALL All silicon transistor. Zero hum. High gain YOUR NEEDS SS2Q/7 £9/19/* and equalised at 7i" per sec. to give flat response The now well proven model as illustrated com- output. Simple mod. described in accompany- ZENHR DIODE prising pre-amplifier measuring 4-7'.. l-y ing instructions allows equalisation at all speeds. Silicon planar diffused units featuring very and main amplifier measuring d-S' : t 4" both Suitable for all medium impedance heads. sharp knee. Type No. specifies voltage. mounted on base plate and supplied complete Dimensions 40 ; SO ": ISmm. ASSEMBLED Type KZ7-5 KZ5-I with bass, treble and volume on/off controls. 29/4. KZ8-2 KZS-6 MINICLASSIC PRE-AMP SSPA/50 KZ9-I KZ6-2 Tone controlled high gain preamplifier designed KZ6-8 specially for application with the SS3/I0. All 10% tolerance. silicon transistor. Zero hum, requires 12 Slope resistance nominally 10 ohm at SmA, Ij. volt + H.T. Dimensions 70 X 40 3Smm. Dissipation 250mW. Separate inputs for crystal ceramic cartridge Temperature coefficient 0-01% per degree C. and radio. ASSEMBLED 42/-. PLANAR EPITAXIAL 3/11 each MINICLASSIC SS3/9 AND SS3/I0 SILICON TRANSISTOR ^*4 '/}' Two high fidelity amplifiers providing adequate GOLD PLATED. KPS26I2/.' SS20/8 HONS. power for normal domestic listening or portable ALL WELDED KPS27 14/4 A de luxe version complete in itself and ready to equipment. The SS3/9 is the more powerful mount Into your cabinet. Supplied with three and provides a maximum of 6 watts into a 3 ohm Double diffused npn. Suitable from audio to controls mounted on the front of the stove speaker. The SS3/9 provides 4 watts Into 3 RF power applications. Ico less than lOOnA. enamelled chassis and has moulded plastic and ohms and has the advantage of working from a B«bo greater than 20 volts. Power output spun aluminium control knobs fitted as standard. 12 volt rail. Specification; Frequency response, at 28mc/s typically 300mW. Emitter/base A tag strip mounted on the back of the chassis 16c/s to 30Kc/s. Input Sensitivity I volt. Both breakdown voltage greater than 5 volts. in addition to facilitating the L/S and H.T. will operate directly from crystal pickup and Typical Ft 300mc/s. K,c 20 KPS 25 min. 50. connections provides separate inputs for crystal, make complete tape amplifier with SSTR/7. KPS 26 and 27 are two special low level tran- ceramic cartridge, magnetic pick-up, radio and 6 transistor 2 diode. HT 4- SS3/9 18 volt. sistors specially designed for front end ampli- tape recorder. The max. dimensions of the SS3/10 12 volt. Dimensions 50 '. I OS x 22mm. fication. Hio at U = 200pA, 25 and 40 min. whole unic are H' ' 91* ;. 2*. 49/-ASSEMBLED, both models. respectively. Record pre-amp Sr/8 couples SSH/9 to ribbon RESISTORS { WATT HYSTAB SS20/9 19 GNS. and dynamic mic. High gain all silicon tran- 4-7n, 10,27, 100, 150.270.470. IK. I SK.2-2K. A beautiful table model version with its own sistor. 29/4, 3-3K, 4-7K, I0K, I SK, t8K. 24K. 33K, 56K. power supply and In keeping with the modern TAPE OSCILLATOR SSOI3 )00K, 330K, 560K, !M. Sd.each. trend to build hi-fi systems from self contained Complete unit incorporating push pull silicon separate and compact units. Ready to operate transistor oscillator giving adequate erase ELECTROLYTIC CAPACITORS and to connect to tape, gram and radio via power and recording bias. The only unit on SpF. lOpF, 30pF, 50pF. I00/.F. ISV. All at coax, sockets at the back of the cabinet. The the market at such an economical price. Ferrite 1/3 each. amplifier and power supply are housed in an pot tore oscillator. Frequency 50-40Kc/s. MYLAR CAPACITORS attractive pressed steel case finished in a sub- Unit also provides high voltage D.C. rail for I.OOOpF, 2.000pF, 4d. S.OOOpF and O lpF 7d, dued grey stoved enamel and embellished with a the record amplifier. A high efficiency oscil- gilt brushed aluminium front panel engraved lator operating from II volt supply at approx. O OlpF, 9d. •05pF. lOd. 01/«F, I/-. and displaying the four controls. Treble, bass, 2S0mA. Dimensions 90 54 3Smm. volume on/off and three position input selector. COMPLETE 49/4. MICROPHONES Cabinet measurements 12":: i'S' : 2,('. CRYSTAL MICROPHONE RECORD AMPLIFIER SSH9/3 Complete with detachable desk stand; smooth TECHNICAL SPECIFICATION Fully transistorised. High voltage HT. rail slim round design with satin chrome finish. All three models employ similar circuits, have derived from oscillator. Provides substantially Supplied with locking on/off switch, 7 ft. cable. the same electrical specification and are fully constant current record signal. I volt input Response 60 to 10,000 cps. £1.18.0. transistorised. Six silicon planar transistors sensitivity. Input impedance Sk. Power re- and two germanium power. Two diodes. All quirements ImA 75V. derived from SS013 and OMNI-DIRECTIONAL DYNAMIC MICRO- have benefits of negligible noise and distortion, ImA 12V, This is a gain stabilised low dis- PHONE high efficiency, low power consumption, com- tortion circuit. Dimensions 45 '" 40 20min. A beautifully finished professional microphone. pact design and no warm up time when switching ASSEMBLED 45/-. Response 30 to 13,000 cps. Supplied with desk on. The amplifiers are D.C. coupled throughout stand and cable. £3.12.4. (no distortion) and there is a transformerless POWER SUPPLIES LAPEL DYNAMIC MICROPHONE. coupled output having a very low output 30 volt. 3 amp. Ready built and ideal for your I* diameter. Very sensitive and supplied with impedance. Power input, 20 watts peak into Kcdoco Classic and will power 2 of them. 49/4. long lead and plug. 12/4. 3 ohm speaker. Input impedance, selected 18 volt, I amp 59/-, 12 volt, I amp 59/-. .to suit input. Output impedance, 0-25 ohms. Sub-miniature 6 transistor, 3 diode FM Tuner, LEVEL METER 'Bass boost, l2dB at lOOc/s max. Treble boost, Covers 88-l08Mc/», operates from 9U battery. Miniature moving coil meter specially produced 12dB at I6Kc/s max. Distortion 0-1% typical. Accurate tuning. Displayed on horiiontal for level indication in tape recording, £1,4.9. Frequency response. (6c/s to 20Kc/$. Noise, scale. Ideal as FM car radio—:SSSF—£7/9/4 BOdB down on max. output. Power require- ASSEMBLED. All KEDOCO products are fully guaronteed. Should you ments. SS20/7 and SS20/8 only. 20mA Sub-miniature superhet AM Tuner—SS4AM yournot be money completely If purchases satisfied are we returned will Immediatety within seven refund days quiescent. 3 amps peak. 30 volts. completes your hi-fi system—£4/9/4. of receipt.
KEDOCO ELECTRONICS LTD. new showrooms and mail order department Departmentr PE,' 76 Victoria Road, Swindon. Personal callers welcome. open 9 a.m. — ■ 4.301.00 p.m. Wednesaayt
473 Ketall Shop: Z & I AERO SERVICES LTD. as TOTTENHAM COTOT ROAD, LONDON. W.X Tel.: LANi&sm 8403 Opon alldiir Siturd^r Head Office and Warehouse: 44A WESTBOURNE GROVE, LONDON, W.2. Tel.: PARK 5641!2fa OA 2 6A07 SC4 8/6 7B5 obs 6AJ5 6C6 8/- 7B6 10/- 12S12SQ70Tfl/e Y3 EBF89 7/- BP95 6/6 OZ30 81- PL38 101- UBF80 71- osa OAKS 6CB8 (!/- 7B7 11/-71- 14Q7 10/- EBLI 14/- EF98 12/6 QZ33 10/- FL38 16/- UBP84 7/8 OC3 6AK0 6CDOOA17/- 706 71- 1487 EBL31 SO/- EF183 8/- 0234 10/- pjtai OBF89 7/8 OD3 6AL5 ooho e/- 7C7 91- 19A05 IB,8/ ECC84 BF184 8/- KT6a 18/- PL82 UBLSl 11/- IA70T 8/- 6AW0 6CL6 B/- 787 18/. 207.1 14/- ECCflS B/6 EF804 21'- KTSS 22/- PL8S UCC84 10/- IB30T 7/- 6AN4 16/- 6CW4 12/- 7Y4 81- 20F1 14/- BRAND KCC86KCC88 10/-7/- EPP60 10/- N78 15/- PL84 00086 7/- IDAICSQl «/. 6AN3 16/- 6C YG 10/. 7Z4 81- «!■ 19/- 3523 10/- AZ31 ECC18912/. ELS4 11/- K8P1 26/- P1.302 14/- OCF80 10/- IG60T 71- OA KB 10/- GDKO «/. 10C2 181- 2DP4 14/- 35Z4G CBL31 15/- ECF8U 8/- EL37 17/8 N8P2 22/- PL600 15/- U0H21 9/8 IL4 S/8 6AQ56AQ4 6/-8/- 6EA8 11/- 10D1 20P5 12 S6Z40T 8/6 C¥31 ECF82 7/6 EL36 17/6 PABC80 7/9 FL801 10/- OCH42 9/6 INOGT 8/- OARS 6,'- Ofl 14/- 10F1 1*1- SSASO 6/- SSZ5GT 8/- DASO 10/- ECF8B 11/ BUI PO86PC88 12/-JS/- PP6/400 UCH48 81- 1K4 6/- 6 ARB 8/- 8F6 8/- 10F3 81- 'd.j: 10/- DAF91 4/fl ECF804 18/- EL42 PC97 9/8 10/- OOH81 7/- IBS B/- 0AR8 17/8 SP8G »/• 10F18 81- 25L6GT 8/- QOAS 12/- OAF32 6/- ECH21 10/- EL50 PY33 00082 8/8 184 S/- 6A88 6/- 6F13 6/8 10U 7/8 2624G: 00B5 DAF98 7/ ECH35 12/. EL81 FC900 12/- FY80 91- OCL83 10/- 185 4/8 6A80 6/- OKI 4 18/- 10PI3 12/6 ■ 10/- 600060 »P9fi EOH42 9/6 BL8S P0C84 8/6 PY81 6/6 0F41 01- 1T4 8/- 6AS7G 20/- 6P186F17 11/- 10P14 13/- 2SZ6GT 11/ 27/6 UK 3 2 B
YOURSfREE"'7°™
The NewPicture-Book'wayof learning
DACI^ ELECTRICITY(5VOLS) D#%9IW ELECTRONICS(6VOLS) You'll find it easy to learn with this outstand- The books are based on the latest research into ingly successful new pictorial method—the simplified learning techniques. This has proved essential facts are explained in the simplest that the Pictorial Approach to learning Is the language, one at a time; and each is Illustrated quickest and soundest way of gaining mastery by an accurate, cartoon-type drawing. over these subjects.
The series will be of To Selray Book Co. exceptional value in 60 Hayes Hill, Hayes, Bromley, Kent i.'1'. it1 Please send me Without Obligation to Purchase, Basic Electricity/Basic training mechanics and Electronics on 7 Days' Free Trial. I will either return set, carriage paid, technicians in Electricity, in good condition within 8 days or send down payment of 15/- (Basic Radio and Electronics, WHAT THIS MONTH'S Electronics—6 parts) post free. This offer applies to United" kingdom ENTHUSIASTIC READERS SAY only. Tick against set required (only one set allowed on free trial). "... / congraiulale you on their simplicity .. BASIC ELECTRICITY □ BASIC ELECTRONICS H. A., PORTSMOUTH Signature.. "... I have started studying Book 1 and find it first class, an "fdrely new approach in studying what fused to believe was a (If under 21, signature of parent or guardian) difficult subject.. W. S., LEYTON Name A TECH-PRESS PUBLICATION BLOCK LETTERS BELOW FULL POSTAL P.E.7 POST A/QiV for rH/S OFFER // Address .. TWO-WAY STUPENDOUS OFFER—£11 for £2- TOUR MASTER CAR RADIO RADIOS Thedeeerflied Princess below snpsrbet is a OItc commnolcatfon over i mile. rery fine little set that FOLLY traoaUtortoed—ciystal has been eaietaUr eonttolled, hullt-tn telescopic dettgned I or bleb par- aerial—press bat ton operatloo— I or ms nor. Only re- PP3 batteries—pair Inatnunenta cently (troder another Medium and kmg wave (push-button change) complete and reatly to use. name ol course) this perm, tuning—dx translators Including power 47/9/#. plus #/• post and wasradio on oBcrshops, In manyfor output—undoubtedly one ol the nicest car radios tosnraDce. 210/19/6, but we have available today—cnnenlly being sold at 14 gos. been lortnnate In ob- Our price only 19/19/8 ready built and guaranteed These cannot be operated InTT.K. taining the parts at a 12 months. passvery lowthis price saving and on now to TRANSISTOR yon, II you act MULTI PURPOSE SET CASE chasequickly this you lor onlycan pur-89/8 NEON TEST UNIT plus 3/8 post and In- Robust, useful and Instructive—test Insulation—. Very modern cream tnrance. Note these features: • Long and Medium Wave • bong clear —alsocapacity—contlnnity—resistor—volume acts as signal Injector and LT fault controlsfinder— cabinet, lire 51 x 8 x approximatelydial with travelling 360 m.w. pointer # andA.V.C,and slow motion feed back drive • •Dust Push cored pull H.Q.I.F. ootpnt kit comprises neon Indicator—* way wafer switch 12 in. with ehronu handle, trsnslomiers • High selectivity lerrlte aerial • 81* tested transietors —ebonite tubes—reslators—condensers—termi- tuning knob and seals. • Printed drcnit board for fool-proof assembly • Economy ontpnl nals, etc. with dlag. only 7/fl plus 8/6 post and lus. Price 4/6 plus 2/- postage. collcircuit speaker gives •long Cabinet Hie from slie 4PPg Jin. xbattery 3lo. x IJln.• Permanent magnet moving ENGINE REV COUNTER PRIKTED CIRCUIT BOARD You get over 100 parts (list value over 210). In fact everythtag you need or direct with T^.F. citcoit 8/6, superhet 8/6 woaderfnloBcr.and easy to follow Make wiring up eeveral ami aligning while you Instractlons. have the chance. Don't Usemiss them this as presents and yon'U be loved for ever. Made-up chassia 10/- extra. reading FINE Battery 1/9 extra. Data separately 2/6. frequency TUNERS meter 60 pf -with long spindle as Employing•peclat frequency a Illustrated, 1/8, or 12/- doe. WE ARE BEST FOR GARRARD discriminator the Twin 60 p< not quite sneh and because they have been making Instrument I* Just dor.long nplndle, 2/6, or 24/- record players for bo king GARRARD right lor many of the lobs you have wanted to do- are your beet choice—-big range always orlt canas abe portable permanently hutrtunent installed it willas a do re* such counter Jobs in stock. aa measuring frequency of time base—pulse Sheet 1000 28,8. 9. ATM 29. 9.0. generator—dip-Sop, etc., etc, kit comprises: Paxolin 2000 29. 9. 6. ires 2io, 9. o. metal front panel all prepared and stove enamelled Ideal for transistor MOO 27.19. 8. LABSO 225. 0. 0. —moving coll meter. 4 spedally tested transistor projects. Hpcclnl 7/9 for post and Insurance and diodes and all the necessary resUtors and oiler 12 panels fi x allcondensers for 19/8 pinsand 2/9circuit post anddiagram ins. (separately S/8) S in. 5/-. Complete with sendee sheet and templet tunityNOUGHTS to make AND this CROSSES very amusing KAOHUnC—an Item—deecrlbed oppor- CAR BATTERY -THIS MONTH'S SNIP- 40/-postIn Practical paid. Electronics, Kit at IB ewitcbes only FLUORESCENT Veou for Panel flame Switch, etc.—mot tbe'midgct 2ft. JOw 125 Watt Mercury Vapour type but possibly more suitable. 12 lot 10/6, poet Spot Lamp In addition to the normal paid. uses in photography and lighting generally Midget wire ended type 1/8 (Ex. equip.) or 1/9 new. you will find that a spot light shining over your shoulder is a great boon when working MAINS POWER PACK Meal lor cara- on Intricate and micro-circuits. This month MAHS POWER PACE designed to operate tran- van or boat lighting dne to a fortunate purchase we are able to sistor seta and ampllfiere. AdinoUbk output 6 v.- gives thics ■ times aa offer a complete " Philips " ontfit lor about 9 to 12 volts for np to 600 mA (class B working). much light for same current as three ordinary car yonone-fifth a saving of its of proper 80%. Theprice outfit thus comprises showing Takes the place of any ol the following batteries: lamps—use also to light advertWog displays on 126 watt SPOT LAMP (gives approx. same PR1, PP3. PP4, PP6, PPT. PP9, and others. vans and lorries. 12v, 3 amps d.c. complete with light as 600 watt ordinary lamp)—Polyester Kit comprises; mains transformer-rectifier, tube—white enamelled fitting as lllnslrated. tilled choke-starter and adjustable monntlng smoothingcondensers, and zener load diode reeietor, and 6,000instrnctlons. and 100 mfd.Bead 25/19/8, plus S/fl poet and insurance. bracket, with lamp holder—listed at over snip at only M/6, plus 2/6 post. asHalnt Illustrated. operated 2ft.,fluorescent, 20 watt, also 88/-: available Sit.. complete40 watt, <10 we offer the complete outfit in perfect 87/8 both phns 6/8 post and Ins., also for callers order—unused but a little store soiled only only, 4ft,, 40 watt, S9/S; 6ft., 80 watt, 49/6. 17/8 plus 6/8 post and Insurance. TAPE RECORDER BARGAINS DEAC RECHARGEABLE See !n the Dark—INFRA-RED BINOCULARS Capstan Driven, 5 Transistors BATTERIES These nickel cadmium HPKOIPHJATXOir:—200/7,000 c.p.s.— cells have negligible Intenual resistance. These If fed from a high voltage 400 roW, output—double track—twin speed Wilt deliver current yon require, reduce source will enable objects to be (3| and 7J> fast rewind time—Sin. spool distortion and are completely reliable. seen In the dark, provUlng the gives one hour playing with standard tape, Thgy may be recbarged . Indeftnltely. objectsred beam. are InBach theraysol eye tube nn infra- con- weight 7 lb. Sire 8 x II x Sin. Complete Beplocemente for PP3 87/-, V7 lg/9, tains a complete optical lens with batteries, mktophone—tape spool and V2 S2/6, PP9188/-or send for list. system as well as the Infta-red instruction manual. Nothing to go wrong celt These optical systems can DeuiomtrationIf you use a good gladly tape givenand keep nt ourheads Croydon clean. 750 mW TRANSISTOR AMPLIFIER —lightbe used ascell, lens foretc, T.V. cameras(details shop. Special Sup Price This Month 211/11/-, 4 transistors inclnd- supplied). The binoculars form Part of the Army night driving (Tabby) post and Insurance, 6/6. Inputlog two for In posh-pall-crystal or equipment. They are tumsed and believed to be In good working order, bot inagnelio micro- sold without a guarantee. Price 22/17/6 plus 10/- carriage and iosurance. THE "MINY" phone or pick-up— Handbook 2/6. controlBest of onthe mike, spool batterydriven machines,operated 28/19/9, remote scoeltlvltyfeed bock 8loops— ra/v. plus 6/- post and Ins. Price 18/6. Poet and INTERCOM BARGAIN ins. 2/8. Speakers MANAGING CHfiECTOfl 8in.Sin. 18/9:X 4Sn. 6in. 18/6. 18/8; TWO OUT OF SEASON BARGAINS I. 760mounting watt withInfra pnll red swlteh. silica gloss88/6 plusheater—wall 6/6 post and insurance. 3.completely Two-heat waterproofelectric blanketelemeuls element. each 13 Twoyds. Siemens High long; connect both for lull heat <70 watt) and Speed Relay thermalone only balance, for half 10/- 'heat, poet temperature free. control by changeTwo 260 over ohm contact—plat, coils adjustable points tension 7/8. Will save time and Improve efficiency. Ideal in home—office—shop—• Post J/-. sotgery, etc. Complete outfit comprise* Master unit and three sub- When postage is not definitely stated u an extra stations each of which can call the master and have full two-way working. then orders over 28 are post free. Below 23 add Mocganiie Sealed Pots. Another batch of these No wiring problems as sobs fitted with 60ft. twin flex sod they phg into 8/9. has arrived and we can now offer quite a range, bny.eoekcts. Originally Also inoluded sold for is I18/X8/0. packet ol rtapirs—andOUR FKICB—28/6/6, battery. plusNothing 3/6 poet else and to 2namely: meg, all 6K. at 8/- 60K. per dozen10OK. per260K, value, 1 meg.pins 2/9 I meg,post insurance. ondozen, first price dozen, is then9d. each1/- per even dozen, this leesIs only than about one one-tenthdoubted ly ofone the of thecatnlogno best pots price available. and this is nn- ELECTRONICS (CROYDON) LIMITED TnnW Condensers. 3 gang -0005 mfd air spaced standard size with good length spindle. SO/- doz. 102/3 TAMWORTH ROAD, CROYDON, SURREY (Opp. West Croydon Station) ot 3/9 each, post 2/9 up to six; 8/6 per dozen. Timing Condsnssn. BakeDte type, -0006 mfd for tuningS/- each, or post reaction, 2/9 per i lochdoz. spindle, 86/- per doz. or post orders to: Dept. RE, SPRINGFIELD ROAD. EASTBOURNE, SUSSEX
475 NORMA VIENNA #
★ 40 RANGES FOR— D.C. CURRENT & VOLTAGE A.C CURRENT & VOLTAGE TO 30 kc/s RESISTANCE TO 5 MEGOHMS TEMPERATURE OUTPUT ^ Sensitivity of 20,000 Ohms/volt D.C. 4,000 Ohms/volt A.C. ★ Accuracy of NORMATEST 2.5% D.C. MODEL 785 3.5% A.C. to 500 c/s Robust Taut The newest small Multirange Meter obtainable with a specification Suspended Meter Movement comparable to standard-size multirange meters, * Chosen at the Hanover Fair 1964 by a Panel of international Judges for £11-10-0 available from "Good Industrial Design
CROYDON PRECISION INSTRUMENT COMPANY HAMPTON ROAD . CROYDON . SURREY Tel.: THORNTON HEATH 4025 & 4094
HOME RADIO (Hitcliam) Ltd., 187 London Road, Hitcham, Surrey, phone: MIT 3252
MirCHAK> * *
m
n IV Translated into the Queen's English ..." Read all about it." The gentleman is referring to the fact <*• that Reprint No. 12 of the Home Radio Catalogue is hot off the press. As always, its pages (all 210 of them) are packed with good things, things of absorbing interest to every radio and electronics mil- enthusiast. No increase in price . .. better than ever value at 7/6, plus 1/6 post and packing. And Oift/iowj remember, every copy contains five coupons, each value 1/- when used as directed. If you have never j Please write your name and address in block capitals had the good fortune to own one of these famous components catalogues, or if your own copy is now I NAME a bit long in the tooth, send the attached coupon I with your cheque or P.O. for 9/-. Our pleasure in | ADDRESS sending you the catalogue will be exceeded only by I your pleasure in receiving it. \ j HOME RADIO LTD., D.pL PE, 187 LONDON RD., MITCH AM ii 1 476 Practical Electronics
THIS MONTH THE MIGR0BU6 MENAGE The Postmaster General's declaration that the use of any kind of eavesdropping or "bugging" equip- ment is illegal in the U.K. is most welcome. CONSTRUCTIONAL PROJECTS For some time we have noted with apprehension a steady growth of the market in electronic eaves- FUZZ BOX 482 dropping or "bugging" devices—mainly of foreign STABILISED POWER SUPPLY 485 origin. The undue publicity these electronic gadgets have received through bizarre television series and MICROBUG LOCATOR 497 films must be partly to blame for the cultivation of an MICROPHONE MIXER ' 515 unhealthy interest in secret listening among certain sections of the general public. It is to be hoped that the outlawing of these devices will discourage our own manufacturers and retailers from pandering to such (now) illicit demands. SPECIAL SERIES It is probably true that the novelty of these miniature devices may fascinate some of the technically minded BEGINNERS START HERE—21 512 and induce them to conduct genuine experiments, without any real intent to eavesdrop on private CLASSIC COMMUNICATION conversations. To satisfy one's technical curiosity RECEIVERS—BC342 518 is one thing, but there is a real danger that the tempta- tion to continue listening may prove irresistible for some. What might well have begun as an innocent prank or experiment could thus easily develop into a GENERAL FEATURES much more sinister and serious affair. In welcoming the official clarification of the position SUPERCONDUCTIVITY 478 concerning "bugging" devices we appreciate that fully effective enforcement of the ban on their use is largely USING TRANSISTOR DATA 491 beyond the capabilities of the authorities. It is a EXPERIMENTS IN LOGIC frightening thought—but nevertheless a realistic DESIGN—2 503 appreciation of the times—that no one will ever be entirely safe from this menace. And yet there is no reason to accept passively the use of microbugs and their like. Electronics enthusiasts, amateur as well as professional, have an opportunity to apply their NEWS AND COMMENT particular expertise in a worthwhile cause. Elec- tronics which admittedly made the radio microbug EDITORIAL 477 possible also provides antidotes, including means for detection. Such a "de-bugging" instrument, which ELECTRONORAMA 510 can be built by any capable amateur, is featured in our READOUT 520 pages this month. AUDIO TRENDS The anonymous snoopers will be discouraged and 524 their pockets hit every time one of their hidden DETACHED PARTICLES 528 playthings is tracked down and destroyed. As with other kinds of pests, even if we cannot entirely eradicate the electronic variety, we can hold them Our August issue will be published on severely in check. Thursday, July 14 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. Editorial and Advertisement Offices: PRACTICAL ELECTRONICS, George Newnes Ltd., Tower House, Southampton Street, London, W.GJ. Phone: Temple Bar 4363. Telegrams: Newnes Rand London. Subscription Rates including postage for one year, to any part of the world, 36s. © George Newnes Ltd.. 1964. 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. By |. H. B. Gould
Much work has been done in the field of super- scientific curiosity has developed into what promises to conductivity since the initiation, by the then Depart- be a major tool of science and engineering. Its ment of Scientific and Industrial Research, of a national possible applications range from power generating research programme into the applications of super- equipment with ratings of hundreds of megawatts to conductivity in Britain. What, you may ask is microscopically small components for digital com- superconductivity and how is it likely to affect our lives in the coming decade? puters. When a piece of metal is cooled down below ambient room temperature, its electrical resistance falls as the PROPERTIES OF SUPERCONDUCTORS electron scattering caused by thermal agitation grows The temperature at which the change from finite less. There comes a point, however, when the conductivity takes place depends mainly on the strength resistance ceases to fall, for at very low temperatures the of the magnetic field in which the conductor is placed. electrons are scattered mainly by imperfections in the The presence of a magnetic field will force down the structure of the crystals forming the metal. "transition temperature" or even prevent transition But when H. Kamerlingh-Onnes cooled a sample of entirely (the "critical field"). Yet even in the complete mercury into still lower regions of temperature he absence of a field, superconductivity demands incredibly found that the electrical resistance again fell, but this low temperatures, temperatures at which all the gases t0 zero» at a temperature of minus except helium have solidified. 268-95 C. This discovery marked the beginning of Two types of superconductor have been discovered: experiments into the phenomenon known as super- "soft" (also known as "ideal" or "type 1") and "hard" conductivity. (otherwise known as "non-ideal", "type II" or Onnes' discovery was made as long ago as "London"). 1911, little practical use was found for the phenomenon Soft superconductivity was the first to be detected. until quite recently. Nevertheless, these last few years Soft superconductors such as tin, lead, mercury and have seen a radical change in the position, and the aluminium only remain in the superconducting state in effect that for so long had seemed little more than a magnetic flux densities of less than a few hundred gauss. 478 Magnetic fields are unable to penetrate beyond the electricity, in bubble chambers, energy storage, ion extreme outer layers of a type 1 superconductor; drives, and radiation shields. indeed, it was thought for some years that all magnetic The one major disappointment has been the poor lines of force were excluded entirely from a sample behaviour of super-conducting materials when subjected when it entered the superconducting state. However, to an alternating field, when the material no longer we now know that flux will penetrate to a depth operates in a completely "lossless" manner. In fact, dependent on the temperature of the sample and its the losses in a.c. fields have proved to be so high that purity. Another peculiarity of soft superconductors is the power needed to keep the temperature down to the the fact that any electric current entering a super- "liquid-helium" level, more than outweighs the power conductor passes through the outer skin of the sample, that would be lost in ordinary conductors working at down to a depth of the order of one hundred-thousandth room temperature. of a millimetre. Where direct fields alone are concerned, however, the At the present time, many laboratories are conducting picture is more promising. Experimental work has investigations into a range of materials that remain in been in progress in the U.S.A. on a superconducting the superconducting state in very powerful magnetic excitation magnet system for a 600 megawatt turbo- fields. These are members of the class of "hard" generator, and an experiment toward the same end superconductors. Hard superconducting materials are carried out in the U.S.S.R. Academy of Sciences is of two types: alloys such as niobium-zirconium and shown diagrammatically in Fig. 1. This simple intermetallic compounds like Nb3Sn. This last material device is a d.c. generator with what amounts to a has the highest transition temperature found so far: "permanent electro-magnet" supplying the field. An minus 2550C. In hard superconductors, the current is armature borrowed from a ^mall motor runs between not confined to the outer skin of the conductor, but is pole pieces in a soft-iron loop which is broken to admit distributed fairly evenly throughout the whole cross- a superconducting coil. The coil is contained in a sectional area. double Dewar—a laboratory vessel consisting of a. There are other factors besides temperature and vacuum flask holding liquid helium inside another magnetic field that affect the behaviour of a super- vacuum flask containing liquid nitrogen. conductor. One of these 5s the value of the current The superconducting coil (of NbgSn wire) is short- passing through it. Any electric current creates a circuited and a direct current induced into it. The magnetic field, and according to Silsbee's hypothesis, voltage that has been obtained at the terminals of this the critical current for a superconductor, that is the machine is 200 times greater than would have been current which causes a sample to revert to its normal possible using a permanent magnet. In a full-size state, is simply the current required "to produce the turbo-generator, the flux density created by such a critical field at the surface of the sample. Other magnet system would do away entirely with the need for factors that modify the behaviour of a superconductor iron in the magnetic circuit. Not only would this save are mechanical pressure, carrier concentration and a great deal of weight and expense, but the considerable ionising radiation. However, it is the three factors of loss of energy due to this iron would be absent. temperature, magnetic field strength and electric current that bear most directly on the applications of SUPERCONDUCTING BEARINGS superconducting materials. When a conductor is moved in a magnetic field, an electric current is induced in the conductor. If a SUPERCONDUCTING ELECTROMAGNETS block of copper is brought near to a magnet, the eddy To create a magnetic field in an ordinary electro- currents induced in the copper will repel the magnet, but magnet, energy must be "pumped" into the windings; when the field collapses, this energy is returned. No energy at all is needed to maintain the field, just an electric current. Unfortunately, ordinary electro- magnet windings have a finite resistance and energy must be supplied to overcome this resistance. On the DEWAB VESSEL POLE PIECES other hand, if the windings had zero resistance, as would be the case if they were superconducting, we could have what amounts to a "permanent electro- magnet"; for once the field current had been induced to SUPERCONDUCTING flow it would continue for ever, as would the field it COIL creates. No heat would be generated in the windings, so that a very powerful magnet could be made as small as desired without any danger of it melting. Thus the discovery of superconductivity brought to mind the possibilities of extremely powerful electro- magnets weighing pounds or ounces instead of tons. Complicated and expensive water cooling systems, needed on conventional power magnets to carry away the energy wasted as heat, would no longer be needed. But it took the further discovery in the United States of ARMATURE hard "high field" superconducting materials before this dream could become anything more than a dream. mm Bubble chambers, energy storage, ion drives for spacecraft, electron microscopes, radiation shields and MAGNETIC CIRCUIT power transformers could enter the realm of possibility. Despite formidable problems, it is likely that the fig. I. Experimental d.c. generator using a super' superconducting magnet will prove useful in generating conducting field winding
479 FIELD COILS that is. cooled to liquid helium temperatures. On the A SUPEfiCONDUCTIKG other hand, more radical designs become possible RING using superconductors. Fig. 3 shows one such design in diagrammatic form. A superconducting rotor in the shape of a polygon runs^ inside a system of stator conductors. Currents flowing through certain of the stator bars create forces T on the rotor which act perpendicular to the surface of u R ^ t» the rotor adjacent to the bars concerned. As the forces SHAFT are "off-centre" with respect to the shaft, the rotor will turn in the direction shown, i.e. counter-clockwise. In turning, the rotor switches the currents into the next series of bars so that the energised bars are always in the same relative positions to the rotor. Such a machine has been studied in the laboratories of the General Electric Company of America. THIN-FILM CRYOTRON The term ^perconductor is no exaggeration; in a superconducting circuit a piece of silver would act as a Fig. 2. Cutaway view of an experimental form of super- relatively high resistance. Thus, the effect on a circuit, conducting bearing when an element in the superconducting state reverts to its normal finite conductivity, is like turning off a switch. This "switch" can be turned off by tempera- the force is so small that it is difficult to detect under ture, current, a magnetic field or even by mechanical normal conditions. If the copper is replaced by a superconductor, however, there is no resistance to damp out the eddy currents and a heavy block of metal CONTROL FILM can be made to hang in space supported only by the m (LEAD) field of a magnet beneath it. If, in turn, we make this mn superconducting block part of the journal at the end of a iV/frA, shaft, we obtain a bearing that has no friction losses whatever, as the shaft is entirely supported by "field 'M interaction". In Fig. 2, the field generated by the two ■Si coils supports the T-section ring of superconductor which is rigidly fixed to the shaft. GATE FILM (TIN) SUPERCONDUCTOR MOTORS m "Superconducting" motors and generators can be ; i ■f. built on similar principles as conventional machines, but ■ ma with the windings made of superconducting material CONNECTION FILM (LEAD) MAGNETIC FIELD Fig. 4. Diagram illustrating the principle of the crossed- film cryotron (greatly enlarged) O o o o pressure or radioactivity. It is, however, electric o current that controls the behaviour of a thin-film o cryotron. • ROTOR Basically, the cryotron is an extremely simple device, for it involves nothing more than the intersection of two FORCE o metal strips, electrically insulated from each other (Fig. 4). One strip is known as the "gate", the other o O as the "control". The gate is made of a material that permits it to be switched from the superconducting to o. the normal state by the introduction of a current into the control. It is, in effect, a relay. o o . The cryotron can be used to switch the automatic circuitry of a factory or power station, and it can form OSTATOR w BARS part of the logic scheme of a digital computer. How- O O ever, its use in logic circuits is limited by its relatively o O slow speed of operation (relative, that is, to the present- day speeds of computers). As far as computers are concerned, the cryotron is more likely to find its .place in the memory system, a role in which it shows con- siderable promise. If the strips of superconductor are Fig. 3. Superconductor synchronous motor with polyzonal arranged into loops, any currents introduced into these rotor loops will persist until some outside action (such as a 480 +15 C| -269«C +15eC
O o SOURCE o LOAD o % o
DEWAR VESSEL
o o
o n o o o o
T
4>
TT (c)
fif. 5. Basic scheme of superconducting energy store, (a) The source of supply gradually builds up, the current flowing through inductor 1. ot o rate controlled by charging resistance R until the required value Is attained, (b) Switch S3 closes to short-circuit the inductor; switch SI opens to disconnect the supply, (c) To diicharge the inductor, switch 52 closes and switch S3 opens, diverting the current into the load. S3 is a superconducting switch turned off by the field of a small electromagnet current in the "control") determines that they do storage on a large scale is only practical where the otherwise. energy can be pumped rapidly into the store and then released immediately. ENERGY STORAGE Both of these requirements are achieved if the Storing large amounts of electrical energy is a costly inductor is wound with a superconducting material. and sometimes inefficient business. One factor With no resistance losses, the field can be "trickle- common to all storage systems is the great size and cost charged" from a low power source of electricity; the of the stores (accumulators, capacitor banks, the inductor will hold its charge until such time as it is reservoirs of a pumped-storage scheme etc.) in relation required. Fig.'5 shows one way in which a super- to the amounts of energy that they can hold. As was conducting energy store could operate in practice. mentioned earlier, a magnetic field can store energy; Many problems have still to be solved before the but unlike an accumulator or pumped-storage scheme superconducting energy store is able to compete this energy can be released in one intense burst. Its successfully with existing storage methods, but its only real competitor at the present time is capacitor great potential seems to lie in situations where large storage; this can be very powerful indeed. While a amounts of energy (more than 100 kilojoules) are bank of capacitors must be considerably larger than the needed for.release over periods of a few thousandths of inductor of a magnetic store of equivalent power a second. It could, for example, be used to supply the rating, the losses in the latter are extremely high. energy for metal-forming processes of the "exploding- These energy losses, caused by the resistance of the wire" type, or for pumping high power lasers. inductor windings, are so great that magnetic energy 48! by Rl, a more sophisticated means of bias stabilisation being unnecessary as any thermally induced changes of the working point can only introduce additional "fuzz". The signal developed acfoss R2 is applied to the single sided peak clipper diode Dl. Any type of semiconductor diode could reasonably be applied here, point contact or junction types. The value of R3 is similarly non-critical, a choice of resistor between 600 kilohm and 1 megohm proving satisfactory in the prototype.* Squaring of the component tones of the guitar complex wave input is completed by the overdriven amplifier TR2, the output of this being fed to the compound-connected output amplifier composed of l part from the usual tone controls, there are at TR3 and TR4, which together further amplify and r_K \ least three different electronic effects that are improve the squaring by reducing the rise and fall currently In vogue amongst both individual guitar times. players and pop groups. They are; This output is then differentiated by the CR network, (a) Echo or effected by a tape delay made up of C3 and the output potentiometer VRL cr a mechanical delay. This is made evident The resultant spiked positive and negative pulses make as a periodic recurrence of a single sound. up the rasping "fuzzed" sound which can be fed to an (b) Vibrato—sometimes mistakenly called tremolo— amplifier or other effects units by way of SK2. is produced by mixing a fixed low frequency A requirement of this kind of unit is its ability to be oscillation with the guitar signal. switched in and out of circuit without the instru- (c) Fuzz Box—a harsh yet not unpleasant sound mentalist using his hands. This was achieved by using a effected by wave shaping circuits. Here the single-pole changeover switch SI operated as a foot impact of this contrived distortion is most evident switch. This serves the dual purpose of by-passing on low frequencies. the effects box when the switch is not depressed and energising the circuit, thereby breaking the by-pass There are plenty of published designs for echo when foot pressure is applied. As can be seen this units and vibrato units yet there has been little available provides a considerable saving in current. on Fuzz Box circuitry, although considerable interest The setting of the output preset potentiometer has been aroused in the subject. VR1 will be determined by the power output of the Commercial units are. available but the price of these main amplifier and an optimum level can be found by inclined the author to design and build his own. individual experiment, TECHNICAL DESCRIPTION CONSTRUCTION The fuzz box is based on a three stage shaping Since the unit housing would be subjected to con- circuit, shown in Fig. 1, The first stage TR1 is a tinuous foot pressure, it was decided to use an 18 simple pre-amplifier of medium gain the input being s.w.g. aluminium chassis, with the changeover switch applied via an 0-47/iF capacitor C1. The value of this being mounted at one end. This allowed for easy capacitor can however be decreased to O-l^F if fuzz control of switching as the foot is allowed to pivot on bass is not to be used. Base bias current is supplied the box.
s fcaX M. SCIBQR-RVLSKI * 482 Fig. I (right). Circuit rfiogrom of the fo« box with footswitch
5-3 220 5-9 22 kO 1MQ -9V
Bli -4- 0-luF TR2 TR3 TR4 OluF
0-47ljF 0C7 OCli €Lr®c Fig. 2a (below). Layout of VRl SKE components on the tamlnateil AS Ikfl wiring board
B 9 10 11 12 B 14 >5 16 fT Sib • o o • • 0 • o • o o o • o o o o o o o o o o o o o o o o o o o o o 0 0 0 o o o o o o o(Ol o o o o o o VRl • o • o o o o o o o o 0 o o o o o 0 o 0 0 • • o o o 0 • • • o o o •Jl. \tR3 )* SKI o 0 o o o • • • o o o o o (o) o • • - m <\~ o o • • • -P-io, • • • • 0 o o o o 0 *r b o *• 0 o o o • • 0 o o o • 0 • • • o Sfa JR+> I to. 0 o o o o o o o o o o o o o o o o ( o o t • o • o • 0 o • • • o • o o o o • MS ! 0 o o o o 0 o 0 o o o o o o o 0 o lb battery +vt Fig. 2b. Underside of the component board showing holes which are used (black) and copper strip breaks COMPONENTS... Resistors M 68kQ R4 220kQ Assembly of components is made on a piece of R2 3-3kQ R5 3-9kn Veroboard and can be readily followed from the wiring R3 IMfl R6 2'2kQ diagram. Fig. 2. - Stand-off insulators can be used for All ± 10%, iW carbon board mounting but in the prototype a section of barrier terminal strip (block) served equally well. Capacitors CJ 0-47^F polyester 160V It will be noted that the positive line is taken to chassis C2 0-luF polyester 150V by solder tags at the input and output sockets. C3 O-lfiF polyester 150V OUTPUT FILTER Transistors TRI—TR4 OC7I or NKT2M (4 off) A 5T network filter may be found necessary in some amplifiers which have relatively large coupling Diode capacitors (see Fig. 4). Its inclusion is dependent on Dl OAS! Mullard the fuzz quality required. Its exclusion gives a some- what heightened string intermoduiation which, in the Potentiometer« author's opinion, epitomises the "wildness" of fuzz. VRl—Ikl) preset, linear It is kinder to the loudspeaker however to use this Switch filter if much high volume chord work is intended or if SI Single pole changeover switch—S.M.357 Bulgin the speaker enclosure is found to resonate on account of too fierce a fuzz. The filter serves to reduce the Battery harmonic content which is considerable due to the BY I 9V battery. Ever Ready PP3 or Vidor VT2 effectiveness of the squaring circuit. The filter is inserted between the output capacitor and Sockets the output level control. The potentiometer VR2 is SKI-2 coaxial, surface mounting (2 off) adjusted for the desired effect. Miscellaneous Chassis: 18 s.w.g. aluminium, 6in x 4in X 2i-in EFFECTS SWITCHING Verobo^rd: 2iln X l^in. P.V.C. covered wire Terry dip. Solder tags There are three possible methods of installing and using the unit: 483 PftE-AMP ^OUTPUT
__ 1 POWER VRI
VIBRATO
foot switdi 9 Fig. 6a. Footswitch used to Introduce vibrato o o-.o-» a m o o o o ®\L «7D Vtt=4 . . /-.J 1 A*iO O o : BOOST o P ■ 15J >A o- fit GUITAR O'.o-o PICK-UP
50k 1 BALANCE CONTROL FUZZ Bfl
Fig. 6b. Footswitch used to introduce fuxx 1
+: ZSOV 0,C. TO POWER AMPLIFIER Fig, 3. Wirihg details of the unit. The full details of the 22kA centre component, board are shown in Fig 2 3W •!" . 0AZ2OT 2 IOOOUF TO SI 12V (FOOT SWITCH) I FROM TR4 COLLECTOR R7 •.v.- . 3-Skfl 25kn Fig. 7, Method of obtaining a positive low voltage supply from the power ampllfler h.t. C4 SIC2 0*001uF C5 O'OOllF
POWER AMPLIFIER MAINS TRANSFORMER Fig. 4. Pl-fllter connected to the output of TR4 ::<5 240V ^ AC. 5 6'5V 6-3V TO: VALVE MAINS o C.T. HEATERSWPATrD< INin o POWER AMPLIFIER _ GUITAR POWER PICK-UP Slo SZo S3a AMPLIFIER APPRO* -9V FUZZ - VIB. - ECHO _ iC . TREBLE 1000B F BOOST 4^pT2V SIS 152 b 53h 01-4 (SEE TEXT ) —9V Fig. 5. Suggested metftorf of .coup ting four effects'units id the guitar amplifier Input Fig. 8. Rectifying the heater supplies to obtain —PY duxput
484 (a) The unit can be installed in the amplifier itself, either with a separate footswitch dontrol or with raamial control to form a "fuzz channel". (b) As a complete footswitch unit as described earlier ihedriSra:ting all the electronics. The guitar lead plug# into the footswitch unit Itself and the output STABILISED from the unit is connected to the amplifier. (c) As part of ah "effects box" which is external to the amplifier. The remote control of this unit is difficult to :acdiie|e without; either induced Hum or "sydtchpvcr POWER click". However if good coaxial cable and a shielded microswitch are, used then sufficient control is gained by just shorting out fuzz input to fuzz output via the footswitch. This system is really more; suited to the SUPPLY type of unit described earlier. If built into an effects box, one can have.#number of facilities such as echo, fuzz, vibrato, treble boost and so BY P. RUSH, BA (Cantab) on. All that has to be done is to link the required units to switches on a control panel; a suggested set-up is shown in Fig: 5. . Alternatively a footswiteh unit with one switch for each effect can he used. "It is possible to simplify the arrahgeitisftt by making An unstabilised power supply is usually not suitable ,0ne footswitch perform two functions, This "can be for driving a power amplifier since the current taken particularly useful in groups. Forcxample, the rhythm by such an amplifier varies greatly with the signal section would use vibrato/pre-amplifier switching and input. (Here we are assuming a class B output, as is the lead section fuzz/treble boost switching. Examples common with transistor amplifiers.) Because of the of footswi'tching fpr these are shown In, Fig. 6. current variation the voltage supplied from an un- stabilised unit will vary with signal amplitude, resulting FO WEI^ Sl!lPl^liS in distortion. There are a number of different ways of providing power to the subsidiary effects circuits; buttery supplies, STABILISATION separate mains driven power unit, of tapping the h.t. The stabilisation of the supply keeps the voltage from the:power ampfifier. Polarities and connections to the amplifier almost constant no matter what pf the supply are very important, particularly when current is drawn, that is it gives the supply a very low fiSing pnp transistors with a valve poWef amplifier. internal resistance which is comparable to, or better The fuzz box uses pnp tran'istors. than, that of a battery. Taking the first methddTbattery supplies) this should Fig. 1 shows the poor regulation of an unstabi- present fib problems, but remember that transistors lised supply (initial internal resistance about 45 ohms). require a negative supply and npn transistors a positive The stabilisation applied in this unit reduces the internal supply. Never exceed the recommended voltage for resistance to only 1-8 ohms (0«9V drop in supply each effects'unit.: "o voltage at 500mA). The second method (mains driven power unit) can be The basic method of stabilisation is the use of a made up from one of the circuits which have been or Zener diode. This Is a special silicon diode biased will be published in these pages. in reverse. The voltage across it is always fixed by this The third method calls for a certain amount of diode at a characteristic value, provided the supply ingenuity and care. First Of all niikC sure that the voltage is greater. To limit the current through the power amplifier supplies have enough reserve to enable up to about 10mA to be drawn from the h.t., which Will usually be in thefegfqn of about 250V positive. SPECIFICATION This h.t. is not likely to be #abilised so it is advisable tp employ a Zener diode, for example OAE207 or OAZ272 for 9V, to help maintain a steady d.c. supply Input: 200-250V a.c. voltlge. One methpd of doing this iSiishown in Fig. 7; Output 1: 13V d.c. 0-500mA the extra components can be mounted on a small tag (internal resistance I-8 ohms) Board inside the amplifier cabinet This is only suitable for hpn transistors. Output 2: 9V d.c. 0-S0mA Alternatively the 6-3V heating winding on the The power unit described here has outputs amppfier mains transformer can be used if suitably chosen so that the unit Is suitable for supply- rectified and smoothed. This is iUustraled in Fig. 8i ing a transistor radio tuner or pre-amplifier It is important here to make sure that one side, of the (9V supply) and a transistor power amplifier heater winding is not connected tb chassis; it is best to connect the centre tap of. the 6;3V winding to chassis, delivering up to 4 watts (13V supply). The which will also be cdmmbn to; the •'positive" Ime Of the ripple content is negligible and is in- 9V d.c. output. _ dk audible in the output of an amplifier This method is suitable for pnp circuits and is powered by the unit. probably the simplest. Thelpolarity Of the output can It is suitable not only for powering existing be reversed for hpn transistors provided the negative equipment but for providing stable experi- line is conneeted to chassis instead of the positive. mental supplies. Details are given for modi- Almost any low voltage rectifier diodes Of low current fications. rating can be; used, fbr example (5A2()0 or GA90,
485 Zener diode a series resistor, such as R1 and R2 in this unit (see Kg. 2) is needed. The internal resist- ance measured across the diode is equal to the dynamic resistance of the device. This method of regulation is used for the 9V supply. An extension of the basic method is used for the 13V supply. The transistor base voltage is fixed by D2 and so the emitter voltage is only about 0-2V less than the characteristic voltage of D2 no matter what the current. The transistor has the effect of reducing the internal resistance of the circuit even more, here, for the I3V supply, to 1 *8 ohms. '.aw* Such stabilised supplies are not dependent to any great extent on input voltage. This unit has been operated on both 210V and 240V mains with only a minimal difference In output voltage.
SUPPRESSION OF RIPPLE Because the output voltage depends to a slight extent on input voltage, ripple is automatically sup- pressed. The capacitors C2, C3 and C4 incorporated here reduce any remaining ripple to an almost un- detectable level. The values of these capacitors might CONSTRUCTION OF THE UNIT possibly be reduced without a significant increase in The prototype was built on a chassis of heavy gauge ripple, but they are readily obtainable at the values aluminium. The layout used can be seen from Fig. 3, quoted at low prices and are recommended. but this can be varied according to personal choice. It is essential, however, that the transistor is given an adequate heat sink, which is insulated from the chassis, since it must dissipate several watts when the unit is supplying a high current. In the prototype COMPONENTS... the chassis is used as the heat sink with particular care paid to insulation. A mica washer is used to insulate; silicon grease was applied to the surfaces first. Nylon or similar non-conducting screws are essential for Resistors fixing. The diode Dl should also be given a heat Rl I-Ik 10% | watt carbon sink; here it is insulated from the chassis with plastic R2 470Q 10% ^ watt carbon bushes. Heat sinks are not necessary for D2 and D3 Capacitors with the values of components as given, but if run Cl 2000uF elect. 50V near to their maximum power ratings (i and 7 watts C2"] respectively) then a heat sink is advisable. C3 >5000uF elect. 15V The original unit used a Zener diode type VA9-B C4j which is rated at 2^ watts although it tended to get C5 2500//F elect. 12V warm on test. It was decided to replace this with a Diodes and Transistor Brush Crystal Zener type ZS 9-1 which is rated at Dl BYZ 13 7 watts and should suit the application just as well. D2 OAZ 213 (12 volts nominal, watt) D3 ZS 9*1 or OAZ 292 volts nominal, 7 watt) TRI XC H2 (Ediswan) (All available from Henry's Radio and other stockists) Transformer TI Primary 240V a.c. mains. Secondary 24V I A, s type 23 or equivalent (see text) (Samson's \ V Electronics Ltd., 9 Chapel Street, London, N.W.I.) V Fuse FSI IA cartridge fuse and holder Switch SI Double pole on/off (mains rating), -slide or toggle switch Mlscel laneous Two B7G valveholders and plugs. Four wander plugs and sockets. P,V,C. covered wire, mains cable and anchoring clip. Mica washer, 4B.A. nylon screws, and silicon grease for transistor insulation. Alu- minium sheet 16 s.w.g. for chassis S^in X m* x »A drawn 2i»n. Plywood for box 6fin x Sin x 3iin. Fig. I. Graph of the had characteristic—output voltage against had current for a typical low voltage unstabilised d.c. power supply circuit 486 SK5PW FSI -SK( BYZ 3 <--13V M< s,TRI XCMZ SKZ 47011 C 4-vt
240V 24V L.qvr SKJ Main Szooo 5000 bout SKSPinS L CV 5000 5000 SK4 0*2213 25 94 TV*
SK5«fi7 +y« _ SKSPW v Sptoktr Fig. 2. Circuit diagram of the stabilised power unit
The transformer is described in the components list. covered with insulation tape or sleeving. As a further If an alternative component is used make sure that the precaution provide an anchorage point inside the secondary has a minimum resistance of U ohms; cabinet for the mains cable in order to avoid pull on the if not make up to this value with a fixed series resistor. switch terminals if the cable is tugged. With this value the diode DI will not be destroyed The capacitor C5 is used between the loudspeaker by the surge current when the unit is switched on. of the power amplifier and "earth" in transformerless A slide or toggle switch may be used, preferably output amplifiers where one side of the loudspeaker two-pole for safety. If the former is employed as on the would normally be connected to the centre-tap of a prototype ensure that it is suitably rated for mains battery. This capacitor can be omitted if the amplifier operation; some are not. Bare terminals should be to be powered is not of this type.
IU rlH l SIW j^TO nn i ana TO PIN 3 SK5 ■TO PIN 5 SK5 MAIMS TO T1 PRIMARY INSULATING INPUT BACKING RED. AT GREEN PLATE C3 nn \ TP n Fig. 3. Layout and wiring of the power unit. The small com- ponent board on the left and the BLACK capacitors C2, C3, C4 and CS have been moved for clarity. The connections of Tft/ are Jllill GREEN _ SK3 shown looking at the pin side of -9V the transistor. Notice the In- sulation for TRI and the heat IV sink fixing bolt for Dl. Sockets Li SKA SK5 and SK6 are shown dfagram- T9V matlcally; the tags are numbered in a clockwise direction looking at 1*1 SKI the undersides. Dl positive -1JV (cathode) Is connected to the NYLON SK2 stud which should be electri- SCREWS +I3V cally Insulated from its heat sink 3 SPACE FOR MICA WASHER C2.C3.C4 &CS INSULATED WITH PLASTIC SLEEVING TO POINT'A ON TAG STRIP Oc Oh TRI
SK5 SK5
llil
487 In the prototype the outputs were connected to example, suppose we require the unit to provide 13V B7G type valve sockets; a B7G plug and multicore at 500mA. cable connects the unit to the tuner and amplifier. A second socket for further developments and wander- Fig. 1 shows that at 500mA the transistor collector plug sockets to provide supplies for experimental is at 24V relative to "earth". There is thus: purposes were also included. 24 — 13 = 11 volts acfoss Rl. Now the maximum base current is ALTERATION OF OUTPUT VOLTAGES r 500' AND CURRENT RATINGS h - 62.5 mA The unit can be easily modified provided certain precautions are taken. To alter an output voltage — 8 mA substitute a Zener diode of appropriate voltage and so Rl should carry l-2mA more than this, say 9mA. alter the series resistor so that the current through it is Therefore Rl should carry 11/9 kilohms. The nearest either (a) equal to the maximum current needed plus preferred value is 1 -2 kilohms. about i-2mA (D3 and R2), or (b) equal to the maximum To alter the output current keep the Zener diodes base current needed plus l-2mA (D2 and Rl). The as specified and alter the series resistors as described maximum base current can be taken as roughly 1//? above, but in all such cases ensure that the wattage of the maximum current which you wish to draw from ratings of the Zener diodes or the transistor (IIW) the supply. For this transistor — 62-5. As an are not exceeded. ^
0
Vt* tk6 25/8 16 t.w.o. ALUMINIUM 7 >— ' /* *4 - —o 31 FIXING HOLE FOfi MOUNTING IN CASE O 5/ a 3/4H 23/8 1V4- 7/"'8—1 7^ Y c U Va FOLD UP KEY A- Yv DIA. 01 2 HEAT SINK 2 '9 BB.N^KMILL o /8 " TAP/B. A. c= 3/l6 " 5/2 D= H E-/2 INSULATING BUSHES TO FIT Fig. 4. Drilling details of the chassis made from 16 s.w.g. aluminium. The left-' hand flange Is folded twice so that part of It Is U-shaped. A grommet should be fitted to hole "D" for the wires to SKJ and SK6 488 NOT BUILD ONE OFOUR PORTABLE TRANSISTOR All eompanintt mot be pureheitid leparately If detlred. Peru price Hsu and easy build plans available separately RADIOS... at prices stated, Overteat past 101', BACKED BY OUR SUPER AFTER SALES SERVICE NEW ROAMER SEVEN Mk IV 7 WAVEBAND PORTABLE OR CAR RADIO Amazing performance and specification •pr Now with PHILCO MICRO-ALLOY R.F. TRANSISTORS FULLY TUNABLE ON ALL WAVEBANDS • ? sta«M—7 tpan«i«toM and Idiode# Covers Medium and Long Waves, Trawler Band and three Short Waves to appro*. 15 metres. Push-pull output for room filling volume from rich toned 7* x 4' speaker. Air spaced ganged tuning condenser. Ferrite rod aerial for M & L Waves and telescopic aerial for S Waves. Real leather-look case with gilt trim and shoulder and hand straps. Size 9* X 7' X 4' appro*. The perfect portable and the ideal car radio. (Uses PP7 batteries available anywhere.) § EXTRA BAND FOR EASIER TUNING Toul cost of parts now only /C|OAp &p> Parts Price List and easy build plans 3,'. F PIRATE STATIONS, etc, M.I7.U «;,*5/6 (free with kit) NEW ROAMER SIX POCKET FIVE NOW WITH PHILCO MICRO-ALLOY R.F. # 7 stages—5 transistors and 2 diodes TRANSISTORS Covers Medium and Long Waves and Traw- # 6 WAVEBAND!! ler Band, a feature usually found In only the 0 8 stage*—d transistors and 2 diodes most expensive radios. On test Home, Light, Listen to stations half a world away with this 6 Luxembourg and many Continental stations waveband portable. Tunable on Medium and were received loud and clear. Designed round Long Waves, Trawler'Band and two Short Waves. supersensitive Ferrite Rod 1 Aerial and fine NOW READY! Sensitive Ferrite rod aerial and telescopic aerial for short waves. Top tone 2fin. moving coll speaker, built into grade transistors. 3-inch speaker, handsome case with gilt fittings. Size attractive black and gold case. Size "PocKet Five" • 7i x 5} x l}in. (Carrying Strao 1/6 extra.) 5i x li X 3iin. (Uses 1289 battery, medium and long wave EXTRA BAND FOR EASIER TUNING OF LUX, ETC- available anywhere.) version with miniature Toul cost of all 19.6 forti Price List and easy build Total cost of all A'J 11. P. & P. speaker. parts now only 3/6 plans 2/- (free with kit) parts now only 3/6 forts Price List and easy build plans 2/-. (free 29/6 sr- with kit) . TRANSONA SIX NEW TRANSONA FIVE 9 8 stages—6 transistors and 2 diodes "Home, Light, A.F.N. Lux. all at good volume" This is a.top performance receiver covering full C.P., Durham Medium and Long Waves and Trawler Band. High-grade appro*. 3in. speaker makes listening % 7 stages—5 transistors and 2 diodes a pleasure. Push-pull output. Ferrite rod aerial. Fully tunable over Medium and Long Waves Many stations listed in one evening including and Trawler Band. Incorporates Ferrite rod Luxembourg loud and clear. Attractive case in aerial, tuning condenser, volume control, new grey with red grille. Size 6i x 44 x Uin. (Uses PP4 battery available type fine tone super dynamic 2J in. speaker, etc. Attractive case. Size anywhere.) Carrying Strap 1 /- extra. 6| x 4| x 1 Jin. with red speaker grille. (Uses 1289 battery available Total cost of »U CO/A P. & P Parts Price List and easy build anywhere.) parts now only 3/6 plans 1/6 (free with kit) Total «ost of all AJ If. P. & P. Pans Price List and easy build parts now only ^1v 3/6 plans 2/- (Free with kit) MELODY SIX SUPER SEVEN 0 8 stages—6 transistor* and 2 diodes # 9 stages—7 transistors and 2 diodes Our latest completely portable transistor Covets Medium and Long Waves and Traw- radio covering Medium and Long Waves. ler Band. The ideal radio for home, car, or Incorporates pre-tagged circuit board. Sin. can be fitted with carrying strap for outdoor heavy duty speaker, top grade transistors, use. Completely portable—has built-in volume control, tuning condenser, wave Ferrite rod aerial for wonderful reception. change slide switch, sensitive 6m. Ferrite rod aerial. Push-pull output. Wonderful Special circuit incorporating 2 RF Stages, reception of B.B.C. Home and Light, 208 and many Continental stations. push-pull output, 3m. speaker (will drive Handsome leather-look pocket size case, only 6i x 3i x IJin. approx. large speaker), Size 7i x 5J x I Jin. (Uses 9v battery, available with gilt speaker grille and supplied with hand and shoulder straps. anywhere.) Total cost of all /"> OA P. & P. Parts Price List and easy build Total cost of all p.& p. Parts Price list and easy build parts now only 3/6 plans 2/- (free with kit) parts now only £3.19.6 3/6 plans 2/- (free with kit) THE SIG-GEN. A versatile Signal Injector. Something no constructor should be without. This ingenious device generates an audible signal BARGAl through the Audio and R.F. ranges. With variable output. Tele- scopic Probe. Pocket size slim-line case measures 4J* X 3i* x J*. CORNER! Complete set of parts with full instructions. 19/6. P. & P. HEAVY DUTY CELE8TI0N SPEAKERS. 3 ohm. Slightly 1/6. , in errect P.o &fcn P. ■2/6.i ,V P working order. 7" x 4', Only 916. TUNING CONDENSERS. Air spaced, fine quality German QUICK CHECK TRANSISTOR TESTER. manufacture with slow motion drive. 0.0005. With oscillator Checks gain of R.F. and Audio Tran- section. Only B/-, P.&P.J/6. ^ sistors. Also checks for noise level ■ and duds. All parts ready to be Full17*0 M. W. coverage. Fitted coupling coil,By famous oscillator manufacturer. coil, ferrite assembled in attractive grey case with slugs and slow motion tuning with cursor, etc. In original red grille, complete with' Dial, Knobs, and 2f' Speaker. sealed cartons. GIVE AWAY PRICE 10/-. P. & P. 1 /6. Simple assembly instructions firec with set of parts. 39/6. P. & P. 3/6. Callers side entrance Open 9—5 p.m. Barrotts Shoe Shop. RADIO EXCHANGE Ltd Saturdayt 9—12JO pjn. 61a HIGH STREET, BEDFORD. Phone: 52367 489 BI-PAK SEMICONDUCTORS TRANSISTORS VALUE -k so MIXED UNTESTED 10/- 3 OCI39 Trans. NPN Mullard 10/- 2 Drift Trans. 2N1225 Germ. PNP lOOM/Cs RCA 10/- 0 6 Matched Trans. I OC44, 2 OC45. I OC81D, 2 OC81 10/- 4 OAIO Diodes Mullard 30 PIV I amp 10/— 15 Red Spot AF Trans. PNP Factory Tested 10/— 15 White Spot RF Trans. PNP Factory Tested 10/— 4 Silicon Rect. 3 amp. 100-400 PIV Unmarked 10/- m 4 NPN SwitchingTrans. Assorted OCI39.2NI308, etc 10/— 2 10 amp. Silicon Rect. 50 and 100 PiV 10/— 8 Germ. Diodes 4 OA70 4 OA79 Mullard 10/- 1 12 amp Silicon Controlled Rect, 100 PIV 10/- 3 Sil. Trans. 2S303 PNP VCB2S Ic 100 mA Texas 10/- / 10 Assorted Computer Diodes 10/— 4 Zener Diodes 250 mW 5-1 6-8 10-0 12-0 vlts 10/- 4 2G417 Texas Trans. Eqvt, AFl 16/f 17 Mullard 10/— 2 200 M/Cs Sil. Planar Trans. NPN 6SY26/27 STC ... 10/- 2 Bi-Directional Trans. ASY66 PNP STC 10/- 3 Zener Diodes 400 mW 3-3 8-2 15-0 vlts. 5% 10/- 4 Germ. Trans. High Current Mullard OC42 10/— Through this ICS 2 Power Transistors I OC26, I OC35 10/— 5 Sil. Rect. 400 PIV ISO mA I.R 10/- 3 OC7I Transistors Mullard 10/- 3-way Training Method; 3 OC75 Transistors Mullard 10/- 3 NPN Sil. Trans. 70 M/Cs ZT43 Ferranti 10/- MASTER THE THEORETICAL SIDE 1 Power Trans, OC20 100 vlts. 45 watts. Mullard 10/- From basic principles to advanced applications, 5 OA47 Gold Bonded Diodes Mullard 10/- you'll learn the theory of electronic engineering, 4 OA202 Sil. Diodes Subminiature Mullard 10/— quickly and easily through ICS. That's because 2 Low Noise Trans. NPN NF 4 dB 2N929/30 10/- 1 Sil. Trans. NPN VCB 100 200 M/Cs ZT86 Ferranti 10/- each course is set out in easy-to-understand terms, 8OA8I Diodes Subminiature (CV448) Mullard 10/- MASTER THE PRACTICAL SIDE 3 Sil. Rect. 400 PIV. 500 m A BY 101. BY 114 10/- 5 Metal Alloy Transistors Mat Type 10/- ICS show you how to develop your practical 5 Texas 2G344A Trans. Eqvt. OC44 Mullard 10/— abilities in electronic engineering—alongside your theoretical studies. It's the only sure way to One 10/-pack from the above free r/rnmi success. All training manuals are packed with with all orders valued £4 (Four rnrr easy-to-follow illustrations. "FREE" Pounds) or over. 1 MASTER THE MATHEMATICAL SIDE To many this aspect Is a bitter problem. Even LOW COST SILICON CONTROLLED RECTIFIERS more so because no electronic engineer is complete 50 PIV I Amp 8/6 400 PIV 7 Amp 30/- without a sound working knowledge of maths. 100 PIV 7 Amp 10/6 100 PIV 16 Amp 16/6 But new ICS teaching makes mathematics easier Free Circuit Diagrams for Light Dimmers, Speed Con- to learn. trollers, AC Power Switch, etc. with SCR orders. Wide range of courses available include: Radio/T.V. Engineering and Servicing. Closed Circuit T.V., SCOOP PURCHASE NEVER BEFORE OFFERED Electronics, Electronics Maintenance, Instrumentation and Servomechanisms, Telemetry. Computers, etc. Logic Modules All Plug in units NEW! Programmed Course on Electronic Fundamentals and, or, Gates Double and Single Modules, Memory Units, Power Amplifiers, Timer Units, Fanout Multi- EXPERT COACHING FORt pliers, I and 5 amp. SCR Modules, Permanent Memory INSTITUTION OF ELECTRONIC AND RADIO ENGINEERS Units. Power Supply Units 24 vlts. CITY AND GUILDS TELECOMMUNICATION TECHNICIANS Full details on request (Supplied in kit form) ■ CITY AND GUILDS SUPPLEMENTARY STUDIES R.T.E.B. RADIO/T.V. SERVICING CERTIFICATE Unijunction Transistors 2N264^ ISA- RADIO AMATEURS' EXAMINATION Tunnel Diodes IN3720 (TD-5) 15/- P.M.G. CERTIFICATES IN RADIOTELEGRAPHY 6 Sil. Rect, Type BY 100 800 PiV 550 mA 20/- And there are practical "learn as you build" radio 40 Mixed Semiconductors Marked New 40/— courses as well. Our vast stocks change daily with hundreds of Semi- Member of the Association of British Correspondence Co//eges conductor bargains becoming available. We will be glad to put you on our mailing list and rush you our latest stock lists, eqvt. charts, free offers, etc. Just send 2/6 to cover FOR FREE HANDBOOK POST THIS COUPON TODAY 3 months, mailing. I.C.S., Dept. 151, 1NTERTEXT HOUSE, PARKGATE ROAD, LONDON, S.W.11 Minimum order 10/- cash with order please. Add I/- postage and packing per order. NAME By Return Postal Service Mail only. ADDRESS BI-PAK SEMICONDUCTORS 8 RADNOR HOUSE, 93/97 REGENT STREET OCCUPATION- AGE.. 7.66 LONDON, W.C.I INTERNATIONAL CORRESPONDENCE SCHOOLS 490 Tj tma*; X..S | ai Ic J' No. Ic C<«viX) Vc*» ' Vc*o xnA Voiti VoSts mW hi, | niA WNaTatoB 8A 60 30W 85 100 « 32 IA 60 30W 90 f e90 ' 1A 3-6W 70 80 ^ 35 100 S^iS-35® USING n ANSlSTOl%90 SO 16 50 70 80 ™ 70 HSsSiS^" so 15 .70-80 « 50 200 ,W^.^^C*UtLEOT0N« 10 ,s PAfRT S 100 M 1 10 15 50 FrtMn^4 frK wnh«he ** , , ' 1 ■ ■■ iTK- so 20 7S 75 30 OC7J so 30 - 75 75 47 The first part of this article (see May issue) dealt area thermal and electrical contact, to the metal case. with the meanings of the symbols used in the This in turn can be clamped firmly to a heat sink of Practical Electronics Transistor Guide. In this aluminium 05 copper (not steel, because its thermal concluding part, more general matters are explained conductivity is poor in comparison). In the case of a and a table is also provided in which all types mentioned large power transistor, a good heat sink can increase in the booklet are grouped according to application the power-handling capacity enormously—perhaps a suitability. hundredfold. In certain r.f. transistors, the metal can is used for CASES AND ENCAPSULATIONS screening purposes. It is connected internally either The case which contains a transistor is just as impor- to an internal screen or to the collector. tant as the glass envelope which maintains the vacuum and houses the electrodes of an electronic valve. The COMPARABLES AND EQUIVALENTS first function of a transistor case is to keep the dirt out. It is much easier to substitute one transistor for It has been painfully established over the years that the another than one thermionic valve for another. To life of a transistor is very largely a function of the begin with, all currently produced transistors are amount of foreign matter inside it. This is why triodes. Then again, they are usually wired-in, not transistors are assembled under clinically clean, dust- plugged in, and so one is not bothered by variations in free conditions and in atmosplieres of controlled low pin connections. humidity—water is a great enemy of transistors. Thus, in principle, any two transistors with com- , Early types of transistor such as the OC71 were parable electrical characteristics can be substituted smeared with silicone grease and then hermetically for one another. The problem is to be sure their sealed in a glass envelope. Later, metal cans were characteristics are really comparable, and this depends used, with the transistor leads taken out via an insula- on the particular application. ting glass base or "header". These cases are often One thing is quite clear: it is never possible to sub- filled with an inert gas such as helium. stitute a pnp transistor for an npn transistor without The more recent development of silicon planar, modifying the circuit, since a pnp transistor requires a transistors has eased the problem of "encapsulation". negative collector supply while an npn transistor It is possible to treat the surface of the silicon chemically requires a positive collector supply. (The middle during manufacture so as to passivate it, i.e. make it letter gives the collector polarity with respect to the less vulnerable to chemical attack. The process is so other electrodes.) effective that unencapsulated surface-passivated tran- On the other hand, in non-critical applications, quite sistors have been operated immersed in water, a treat- different transistors may do the same job. For ment which would cause more or less instant death to example, a high-voltage transistor, with a collector other types. * voltage rating of, say, 50V may be a perfectly good This, of course, was only an exhibition gimmick, but substitute for a low-voltage transistor in a particular an important side-effect of the planar process is that, circuit. But the low-voltage transistor cannot do with care, silicon planar transistors can be encapsulated duty in the place of the high-voltage one in a high- in a blob of epoxy resin without ill effects. This voltage circuit. This is a case of "one-way" dispenses with the usual hermetic sealing and brings exchangability. down costs drastically. Silicon "epoxy transistors" The Practical Electronics Transistor Guide lists can now be bought for about the same price as com- "comparables", i.e. transistors which can probably be parable germanium transistors. They can be used in substituted for one another in many applications; but all normal environments (living rooms, computers, etc.) not necessarily for all applications—the detailed and some types have passed military humidity tests, characteristics should be consulted if there is any doubt. but designers would at the moment hesitate to put In general, there is enough information in the P.E. them in apparatus which must work in a really hostile Booklet to enable substitutes to be picked out, but atmosphere, e.g. one laden with chemical vapours. occasionally one has to consult the transistor makers' A second function of the encapsulation is to provide complete data. Here are some examples; means of conducting heat from the working parts of the transistor. Most of the power consumed in a Noise transistor is turned into heat at the collector-base If a transistor is to be substituted in the first stage of junction. In high-power transistors, it is quite usual, a high-gain amplifier or receiver, the user must find therefore, to connect the collector directly, with a large- out from the makers1 full data whether it passes muster 491 yvwvwvflF- low noise v/x/x/x/vxAs/v Ac«rt: NKT2I6 NKT226 NKT26S NKT275 2H2926 AAA/^A.-. AMPLIFIER, LOW-LEVEL GENERAL PURPOSE AC M l NKT2I5 OC7I 0C2OI V10/50 A ACISS NKT2I9 OC73 2N2926 AClSi OC202 XB103 25002 NKT223 OC75 OC203 XBI04 2S004 ACIfiS NKT224 OC78D OC430 XBI05 25005 ■SGlzM NKT225 OC8ID V6/4R ZT23 25321 esf^sA NKT264 OC8IDM V6/8R ZT24 25322 NKT213 NKT272 OC82D NKT2I4 VI0/I5A ZT697 2S323 OC70 OC200 VI0/30 A 2 N 706 A 25324 POWER /VWY AF W\Ay - JV\P\AAAA AD 140 NKT402 OGI6 MGT400 OC28 OC20& V30/20P NKT403 OC22 OC29 VI5/I0P MCT600 NKT404 OC23 V30/30NP NKT263 OC30 VIS/20P 2T2270 NKT405 OC24 OC35 V(5/30P 2N4S6A NKT362 NKT452 OC25 OC36 NKT40I V30/I0P 2N4S7A •' Jf NKT45J OC26 OC8IM V30/ISNP 2SOI3 LOW POWER A,F. AND SWITCHING^^^. WW^ ^X >-AAA/ AC 128 ASY83 GET 104 NKT222 OC72 OC20S AC (54 ASY84 GET 105 NKT227 OC76 VFO/ISJ m AC 157 ASY85 GET 106 NKT228 OC77 V( 5/20 IP ACI66 ASY86 GETJM NKT27i OC78 V30/201P AC167 ASY87 NKT2H NKT273 OC8I AC! 68 ASY88 NKT2I2 NKT274 OC82 AC 177 ASY89 NKT2I7 NKT304 OC83 -ip; kpulffii' - ' - iiyip, ASY28 GET (02 NKT2I8 NKT7I3 OC84 ASY82 GET103 NKT22I NKT773 OC204 R.F. AMPLIFIERS, OSCILLATORS & HIGH SPEED SWITCHES A DT I 40 AFZI2 NKTI42 OCI40 ZT706A 2N4I2 API 14 AUYIO NKTI62 OCI4I 20301 2N428 AF1I5 BSY53 NKT6f2 OCff9 2G302 2N585 AFM&ii BSY95A NKT6I3 OCi70 20303 2N697 API 17 MATI00 N KT 674 OCI71 20300 2N706A afM MATIOI NKT67S V6/2R 2G37I 2NI091 AF124 MATI20 N KT 676 XAI01 2G38I 2NI302 AFI25 MATI2I NKT677 XAI02 2G382 2Niii3 AFf26 NKTI2I oc4r XAMI 2G401 2N2926 AFI27 NKTJ24 OC42 XAlll 2G402 2S0I9 API 39 NKTI25 OC43 XAfSI 20414 AFI84 NKTI26 dG44 ZY2I 204(5 AFYI9 NKTI28 OC45 ZT24 i 2G4I6 AppticarioN AFZM NKTJ4I GROUPING 00139 2t49fl 2N4iO c 492 GETA GOLD RING HI-FI TURNTABLE UNIT FORYOUR AMPLIFIER * GOLDRING-LENCO G.99 tncorporates the unique Goidring-Lenco continuously variable speed control and vertical drive features. Machined 8 lb. non-magnetic turntable. Push-button switching. Neon-fit stroboscope. Speed constant within 1% for up to 13% mains voltage change. C21.19.5d. There's a Goldring, or Goldring-Lenco unit to match GOLDRING-LENCO GL68 any amplifier—whether you build it or buy it. At the Continuously variable speed control with a'djusiable click-in positions tor modest end of the scale there's the G.66 integrated standard ispeeds. Arm takes inter-, hi-fi unit that comes complete with pick-up arm and changeable head-slides, and is raised cartridge for as little as 11 gns. Then there's the highly and lowered by on/olf switch. Wired popular GL 68 (see left) and. for the man who wants for mono and stereo. n9.10.7d. the best he can get there's the GL 70 transcription unit with integrated transcription arm at a little under £30, or the sophisticated G 99 without arm, at around £22. Goldring hi-fi equipment includes transcription arms from 7 gns. upwards and a wide choice of cartridges. The coupon will bring you full descriptive leaflets. GOLDRING HI-FI EQUIPMENT To: COLORING MANUFACTURING CO. (G.B.) LTD., 486-488 High Road, Leytonstone, London. E.11. Phase send me descnpiive leaflets on Name Address | □ TURNTABLE UNITS □ TRANSCRIPTION ARMS | O MONO & STEREO CARTRIDGES □ H(-fl ACCESSORIES To: Goldring Manufacturing Co. (G.B.) Ltd., 4*6 High Road, Loytonslsna. London, E.11. Talsphona: Leytonstona 8343 493 NEW EUCTROLYTICS FAMOUS MAKES DE LUXE PLAYER KITS TTOGLAE j TGBCLAR | CAR TYPES 4-Speed Player* 8-tono POST 2/860 ». 2/8 I 100/28 V. 8/600 * BAKER LOUDSPEAKERS Cablneti 17x15 x8!in. High 4/360 v, 2/8 260/26 y. 2/88/- 18/600 v HANDMADE BY CRAFTSMEN 8/460 T, 2/8 1 600/15 v. . 12/- HIGH FIDELITY Sax loudepeaker and 3 watt FREE 18/460 T. 3/-o<- OTo;eovT.8 + 8/460 ▼. O/OV- 16+16/600 y. 7/8 MODELS ALL Famous Make amplifier ready 88/450 ». 8/9 B+ie/4S0v. 3/9m i »uT32 + 32/450v/oo«e. y. «-61- lain. STALWART 15w. n---POST , andbailt. Bur Qnaiily coatroli. output. All Volume Itema 26/85 t, 1/9 18+16/450 T. 4/3 84+120/38060+50/360U • v. 11/811- J or IS ohms £S. J.o. FREEi Bt together perlectly. Special 60/60 T. 8/ 32 + 32/360 t. 4/8 i 100 +200/276 p.12/5 Ilin.STAN D ARD£8. O.O, initrucliona eoabla llin.I2in. DE-LUXEBASS £12.10,0*£9.0.0 aseemhly to 30 350T.-0.1 „9d..3 0.5 1/9;PAPER 1 m!d. TUBULARS SI-; 2mfd. 150?. 3/.. I2in. SUPERB £15.0.0* wiresminutei, to Join. only 5 500?.-0.001 to 0,05 9d; 0.11/-: 0,861/8; 0.5 2/8. ISio. BASS £18. O.O; 12 months' l.OOOv.-O.OOl, 0,0022.0.0047. 0.01,0.02,1/6: 0.047.0,1 8/-- Euaraatea. 0,22, 0.47, 8/-; S.OOOv.-O.OOS, 0.01, 0.022/6; 0.05 3/6. STANDARDLABORATORY MODELS E.H.X. CONDENSERS, O.OOlmtd.. 7kY., 6/6; EOkV,, 10/6. I2in. D.W.I.cone £21. tO.O. TO BUILD EEECTROLYTICS, 1,2. 4.3.8,16,26,50,60.100. I Sin. D.W.I.cone £28.10.0. YOURSELF 500,1,000 mid. 15?. 2/6; 1,000 mid. 60?. 7/6; 2.000/8011/9. -VA' II' CA TA LOOPE FREE/ V-.^EKAMIO. PULSE 800 CERAMICS t. 1 pF. to 10 0.01 pF. mrfl.,to 180 Bd. pF„ DISC 12 kV- CERAMICS 2/6 GSODP MODELS FOB VOCALS POST FREE PRICES SILVER MICA, Close tolerance (plus or minus 4 pP.l,' 5 to BASS LEAD and RHYTHM GUITARS SINOtE PLAYER KITS 5010 80c Fren. res. 80-10.000 cpa. Voice Coils 15 ohms. Hea?y dnty BSR Junior 410. 0,0 ADTCCHASGE KITS TWIN GANG. "0-0""" 208 pF. -176 pF..1.0M 10/6; to 365 5,000 pF., pF., minia- 2/-. 1 BSR 007 SIX.10.0 BSR Monarch £11,10.0 tnre 10/-; 800 pF. atandard with trimmers. 9/-; midget, 7/9; 'Group 25' 'Group 35* 'Group SO Oartard SRP12 211,10.0 Garrard 1000 £12.10,0 midget with trimmers, 9/-; 500 pF. slow motion, standard 9/-: OS SEPARATELY Garrard Mod. 50 £14.10.0 small 3-gang 600 pF. 18/8. Single "0" 366 pF. 7/6. p Player Cabinet 83.10.0 Garrard AT60 £16.10.0 SHORT WAVE. Single 10 pF.. 25 pF.. 60 pF„ 75 pF., iw": Sgns. M;: Signs. ^ ISgns. S watt amplifier 0ac h LOUDSPEAKEKS P.M. 3 OHMS, fitin., 3in.. 4in,. Jin. with speaker 23.10.0 SINGLE PLAY UNITS TDJKNO.in«?Tut, 2Solid dielectric.? . - - Coo100 bepF., ganged. 300 pP.. Coupiers 500 pF.. 9d.3/8 each. 7m. X 4lo., 15/6 each; Sin. 17/6; e/ia. 18/0; 12in. 30/-; AUTOCHARGE DKITS BSR Jaolor £3.10.0 TOIMMERS. Compression cetsmic 30. 50, 70 pF., 9d.: (IS ohms 35,-1; Ipin. X 8ia.22/8; 8in. x Sin. 21/-; Sin. X Bin. BSH Monarch £5.10.0 BSR OD7 £6. 0.0 100 pF., 160 pF., 1/3; 250 pF., 1/6; 600 pF.. 750 pP.. 1/9. 81,-. E.M.I. Doahle Cone 13 J X Sin.. 3 or 15 ohm models, 46/-, Garrard 1000 £8.10.0 Garrard SRPI2 £5. 0.0 Stentorian 101n.HF1012. £5; Sin. HF818.£4. Crossover 86/. Garrard 2M0 £7.10.0 BEST BRITISH PVC RECORDING TAPES Horn Tweeters 3-16 Kelt. 10 w 29/6; 20 w 20 Kc/s. 99/8. Garrard 3000 £8.10,0 GarrardTRARSCRIPTION SP25 £11.0.0UNITS L.P. 71 n. .ISOOtt 19/6 D.P. Tin. 2400!t 29/8 Garrard Mod, 60 £9. 0.0 Garrard A70 £21.0,0 L.P.LP. SiSin. in. 1200tt90011 11/64/9 D.P. 6Jm.6in. ISOOtt1200R 188/64/6 T.V. REMOTE CONTROLLER. ForPbilipjlOTOlllA. Garrard AT60 with Garrard LABBO £26.0.0 Spare Spools 2/6. Tape Splicer 6/-. Leader Tape 4'8 121A, 125A, 142A, 23TG111A. USA 331A, 131A. Stelln diecnst turntable £11.0.0 Garrard 401 £30.0.0 Tape Heads: Coliaro 2 track 28/9 pair. 4 track 70/- pair. 21A,ST1033A. 81A. 3BA,Resdy 43A, to S3A.plug in.Cossor wilh liltCT1910A. 7 way cable,21A. CT2310A. dual pot Volume snd Brightness. OAB1 diode, etc., etc. List Sgns. Q MAX CHASSIS CUTTER MAINS TRANSFORMERS ^ NEW, MAKERS BOXES. OUR PRICE 12/6 POST FREE, Complete; a die, a punch, an Alien screw and key ».250-0-260,80 8 a. 25/-: Ditto mA, 860-0-350,29/8; 6.3 *. 3,5 a. Rectifier MT. 610/300-0-800 6.3 t.1 a. or v.6 JACK SOCKETS St), open-circuit 2:8, close-circuit 4;6. 120 mA., 6.3 ?. 4 a 29/s Lead Socket 8/-. Grnadig 3-p!n 1/8; Lead 3,'6. Tin. 14,6 Iriin. ta'- I Jin. 22/6 MtRlATCTRE 200 ?. 20 mA„ 6,3 ?. 1 a 10/6 Phono Plugs 1/-. Sncket 1/-. Banana Plugs 1,'-. Sockets 1/-. lin. 14,9 ■ iin. IB,'. 2in-3 34/3 JACK PLUGS STANDARD. Screened 3/-. Gruadig 3-pin 3/6. |in. IS/6 liin. 18,6 2a ,. in. MIDGET 2B0 ?. 45 mA., 6.3 ?. 2 a 16/8 WAVE-CHANGE SWITCHES WITH LONG SPINDLES. |in. IS/9 I{in. 37/9 HEATERSMALL, 300-0-300 TRANS. 6.3v. 70v. mA.,1/ a., 8.3 7/8; v. 6.34 a ?. 4 a 10'610 6 2 p. 2-way, or 8 p. 6-wsy. or 3 p. 4-way or 1 p. IZ-way; as. 3/6 Tin. 20,'- 2-jin. 44 3 4 p. B-way, or 4 p. 3-way. 3/6; 8 p. 4-way, 2 water 9/8 18,'- lain. 20/6 I in. sq. 31 6 Ditto tapped see. 1.4 2, 8, 4, 6, 9.3 ?. It amp. .. 10/6 Wavecbange " makits " Ip, 12-way,2p.8-way,3p.4-way 6,GENERAL 8, 9.10,12. PURPOSE 15,18, 24LOW and VOLTAGE. 30 ». at 2 a Outputs 3, 4,&•. 6. 4 p. 3-way, 6 p. 2-way. Prices include click spindles,l CRYSTAL MIKE INSERTS Ditto, I arop., 6.10.16. 20. 25,30. 35. 40, 56, 60.. 29/8 adjuitable stops, spaces, eto., 1 water, 8;6; 8 water, 18/8: H X iln. 6/6; BM3 1 x Jin. 7,6; ACOS IJ >; !in.8;8 Snb-Mio. Mains to 9 ?. 80 mA. X x 11 X liin. 7/6 3 water. 18/-; 4 wafer, 19/6; Swaler, 23/-; egfrawaters, S'S. TANSOY CARBON MIKE with Switch 6/8 ADTOTRANS. 160 w., 0.115 ? 230 25/-; 600 w. 88/6 TOGGLE SWITCHES, s.p., 2/-; d.p., 3/8; d.p.d.L, 4,'-. MOVING COIL HEADPHONES 100 ohms 12/6 ■■ SPEAKER-FRET. Tygan various colours, 52in. wide from (Slightly eoiled but guaranteed) BARGAIN XTAL PICK DP ARM Complete with 10/-ft.; 26io. wide from 5/- It. Samples, large, S.A.E. ACOS LP-78 Turnoverruroover neaqHead anaand styuStyil go/-;80/-; stereoStereo 30/-80/- EXPANDEDEXPANDED METAL. Gold oror SilverSilver 1212 xx 12in.12fn. 6/-.6/-. RETURN OF POST DESPATCH Minimum P.P. Charge 1/6 per order unless otherwise seated. Full List //-, C.O.O. 2/6 extra. CALLERS WELCOME T EH 0 R s D WESTCROYDON RADIO COMPONENTS SPECIALISTS Hie^"n e : T H o 166°* Written guarantee with every purchase. (Export—Send remtttance and extra postage, no C.O.D.) Buses J33. 68 pass door. S.R. Stn. Selhurst. 4-STflTION INTERCOM TRANSISTOR POCKET BOOK by "Asrc* R. G, Hibberd, B.Sc., M.i.E.E., Sen.M.I.E.E.E. VARh £7/15/0 Manager of the Research & Development Solve your communication Department of Texas InstrumentA Ltd. WtaUOna_at.M. w.Transistor Inte. .ProWei""rcom •yetem •»ith (1 masterthis latest and 25/- Postage I/- 3 Sobs), in de-luxe plastic cnblnete for tleak or wail momtlng. Call/lalk/liaten from" Master to Snlw and Subs THE RADIO AMATEUR HAND- Vohunoto Master. control. Operates IdeaUy on one enitnbie 9V battery. for Office, OaloB Factory. switch BO OK. by A.R.R. L.I 966. 40/-. Postage 2/6. Workshop, Warehouse, Hoepital, fihop, etc. Complete TRANSISTOR ETCH ED-CIRCUIT with 3 connecting wires, each OCft. S other aoceesoriee. PROJECTS, by Kyle. 24/-. Postage 1/-. Nothing else to buy. P. & F. 4/0 lu U.K. UNDERSTANDING DIGITAL STAT COMPUTERS, by R. M. Benrey. 16/-. Pottage I/-. FREQUENCY DIVIDER ORGANS.'.by thermostatic CK*faci OWLY - A. Douglas, 25/-. .Postage I/-. TRANSISTORS FOR TECHNICAL soldering iron / COLLEGE, by L. Barnes, 25/-. Postage I/-. for controlled temperature 57 6 KNOW YOUR SQUARE-WAVE A PULSE GENERATORS, by Middleton, Moderalrc bnalneas and home with this latest two-way 21/-. Postage I/-. Miniature Model 50 watt 5S/- midTraaHstor Bub, JnIntercom, etrong plaetioconeisting cabinets of two with unite. chromium Hatter BASIC THEORY & APPLICATION Instniment Model ?(! watt Kt I (Hiepo-Switcfi) etauds.. Elegantly designed to use as two-way loslant OF TRANSISTORS, U.S. Army. 10/-, 79/6 communication eystem—Call/taik/liaten—between two Postage I/-. aa a ! BV BASIC MATHEMATICS FOR RADIO instrument Model 70 watt Hk. II (Magnetic 60 ft. wire. Battery 2/8.° ' P. &hattery. p. 2/6 InComplete D.K. with A ELECTRONICS, by F. M. Colebrook & Contact Breaker) 72/- J. W. Head. 17/6. Postage 1/-. ELECTRONICS DATA HANDBOOK, lifeBoth since Models the thermostatgive excellent completely bit and element eliminates MiiiMiiiifiiieiipffl 75/. by M. Clifford. 16/-. Postage I/-. overheating and controls the reserve heating % 7 Why not In- COMPLETE CATALOGUE I/-. capacity, which makes possible continuous J,,; .j> creaseness bosl-effl- soldering without chilling of the bit. clency with Theideal eonsiscene for printed temperature circuit work. makes these irons Telephone Amplffler with Rotary Calendar andPemHolder THE MODERN BOOK GO. much enableswltI,t, yoult to take down long telephone tneasages BRITAIN'S LARGEST STOCKISTS GARDR0SS ENGINEERING < kolding the handset. A status symboll British and American Technical Books Yes, but very usefulc one, Ou/oaswitch. Volnmo Control. GO. LTD., W00DYARD ROAD, °" ®y-. battery (aupp)led) whlob lasts for 19-21 PRAED STREET Stod to 7 •K* ™ moneyrefu-jded If not LONDON, W.2 DUMBARTON. ,Jl?5?*.1'0SD0!r DIRECT BOTFLIES (PB/7) Phone: PADdiflgten 4/85 Tel.: Dumbarton 2655. 169 KENSINOXOH HIGH STREET, LONDON, W.8 Open 6 days 9-6 p.m. 494 on this score. Makers usually quote a noise figure or noise factor for the transistor under specific conditions of frequency, collector current, signal-source resistance and so on. These can be compared, but take care to make sure that they are really comparable. Example: an OC71 is used in the first stage of a tape recorder. Its noise performance is satisfactory but the j-^W— treble response is poor. Can a high-frequency transistor such as the OC17I be used to remedy this HPS defect? A glance at the makers' data suggests that OUT substitution is possible. The maximum noise figure for the OC7I te 16dB, while that for the OC171 is 8dB, which suggests that the OC171 is much better. But wait a minute! This noise figure for the OC171 is obtained at 500kc/s and lOMc/s, not at a.f. The a.f. figure is 30dB maximum which clearly rules it out for this critical application. Internal Capacitances In tuned high-frequency amplifiers such as i.f. ampli- Fig. I. Simple bias circuit fiers, neutralisation is sometimes necessary to preserve stability. Can an AF117 be substituted for an OC45 in a neutralised 470kc/s i.f. stage? Reference to the makers' data shows that the internal feedback capacitance of the AF117 is quite different from that of the OC45, while the gain is higher. There is evidently some risk of instability. GERMANIUM OR SILICON? There is no difference in principle between silicon ^"Crk and germanium transistors. But there are important practical differences. In the early days of silicon l— OUT transistors, the difference which received most emphasis was that the leakage currents in silicon transistors are much less than In germanium. The effect of tempera- ture is therefore reduced. In addition, silicon devices will withstand higher junction temperatures, and this is of interest in many military aircraft applications Fig. 2. Mixed polarity amplifier where ambient temperatures ar6 high. In everyday applications these properties are not all that important, though sometimes the lower leakages KPH enable simple biasing circuits to be used (Fig. 1) a even at quite high ambient temperatures. This saves components, and may tip the economic balance In favour of silicon even if a silicon device costs more. DRIVER PHP A difference between germanium and silicon tran- HPN sistors which has a bearing on circuit design is that the working base-to-emitter voltage for silicon is about 0-5-1 volt, compared with 0-1-0-3 volt for most germanium devices. This has a bearing on the design of bias networks, and it also means that silicon transis- tors will not work from quite such low voltages as germanium ones. Fig. 3. Complementary output stage Planar transistors have the useful property of "beta hold-up" at low collector currents, i.e. the current amplification factor does not fall off much as the 8o«0fi Dnltudri BoMcontostfM) Base«omoct(iO ccmiao{(N) collector current is reduced. Current gains of 100 or more at Ic=50/iA are not uncommon. This is very Emitter?) Coll«tof(H) Base OxMt useful in low-leve! audio work, because, in general, transistor noise is reduced at low currents. Noise Diffused figures of less than 2dB can be achieved with some transistors. However, though the current gain at low Con«ctar&l+') frequencies is preserved at low currents, the radio- CoilectorM EpHffldal lojier 00 frequency performance falls off. a) ALLOY THANSISTOfi b) ALUJY-OIFFUSED . d EPITAXIAL TRANSISTOR POLARITY: PNP AND NPN (PHP) TMNStSTORtPHF) (NPN) Most germanium transistors are pnp. This is Fig. 4. Transistor structures mainly a matter of convenience in manufacture, although a pnp transistor would have somewhat better 495 h.f. performance than its exact npn twin. With silicon photochemical techniques rather like those used in planar transistors, the npn types are more common at lithography or printed-circuit production. The base present. and emitter contacts are "printed" on the surface of a . ^ all-transistor circuits, there is no special advantage silicon wafer, and this enables their precise shape and m using one type rather than the other. Performance size to be controlled very accurately. and cost are the important considerations. In mixed An essential part of the process is to form a layer of valve and transistor circuits, npn types have the silicon oxide oh the surface of the wafer. This acts as a advantage that the valve h.t. supply can be used very barrier, just like the "resist" used In photo-lithography easily to furnish a collector supply. and printed circuits. It can be etched away where However, the important thing is to remember that required to expose the areas of silicon needed for the both types can be used in the same circuit, often with base and emitter contacts. (Unfortunately, germanium advantage. The circuit of Fig. 2 is a typical example. does not lend itself easily to the technique, because It not only provides component economy, but also germanium oxide evaporates). enables direct coupling between stages to be combined In epitaxial transistors the collector is made up of with a small load resistance for TR1—an advantage two layers: a thick layer of low-resistance material, in wide-band amplifiers. If an a.g.c, current is applied and a very thin, high-resistance layer. The thick to TR1, both transistors are controlled. TR2 may be a layer acts mainly as a mechanical support for the germanium type, but silicon is best for TR1 because it more active regions. The h.f. performance is vastly must have low temperature drift. improved. A simple epitaxial transistor's structure is Another use for mixed-polarity circuitry is the shown in Fig. 4c. Many modern types have complex "complementary" output stage, which enables push- base and emitter areas whose shapes interlock, and pull output to be achieved without using a trans- the base connection is a closed loop, such as a ring, former (Fig. 3). which encircles the emitter connection. At the present time this is the most popular fabrication process, and FABRICATION it has made most of the others obsolescent. The earliest junction transistors were all of the alloy type (Fig. 4a). To form a pnp structure, blobs of p APPLICATION GROUPING type material are placed on opposite sides of a thin The information in these two articles can be used to wafer of n type material and then the whole lot is assess transistor operating data such as that in the ''cooked" at a little below melting point. The p type Practical Electronics Transistor Guide. To pro- impurities pass into the n type material, and the whole vide a quick reference to application suitability, how- art of making this type of transistor is to know just ever, transistors included in the guide have been; when to stop. The best h.f. performance is obtained grouped together under various headings on page 492. when the p type impurities almost meet in the middle, The groupings are to some extent arbitrary, and some but not quite. This is not easy to arrange, and in mass transistors appear under more than one heading because production I5Mc/s cut-offs are about the best average they are general-purpose types. that can be reached (OC44, etc.). Since transistor technology is in a constant state of Alloy transistors, including r.f. types, usually have change, a transistor which is today a candidate for one good noise figures at audio frequencies. list will tomorrow have to be put in another. Early The difficulty of controlling the width of the base r.f. alloy transistors are a case in point: no professional layer led manufacturers to search for alternative designer would nowadays specify the OC45 for a 470kc/s methods of fabrication. One ingenious answer was i.f. amplifier, though he might be inclined to use it as to dissolve away the base wafer simultaneously on a general purpose low level a.f. type. It has been put in opposite sides with the help of two tiny jets of electrolyte the r.f. list here because readers will probably come and an electric current. (This process is the reverse of across it in i.f. stages of transistor portables. electro-plating.) Much better control over base On the other hand, the OC24, which, was designed thickness is possible, and the finished "surface barrier" for use as a high frequency power amplifier, has been and "micro-alloy" transistors can have better h.f. put in the a.f. power list. Why? Because, with a cut- performances than ordinary alloy types. off frequency of only 2-5Mc/s, it has been superseded In the above transistors, the main wafer is the base. for radio frequency applications. But if it ever In later types, however, it ends up as the collector. appears on the surplus market, at a low price, it will In the alloy-diffused type of transistor and the post- be an attractive proposition for a small a.f. power alloy diffused type (PADT) a thin n-type base layer is amplifier. formed on the surface of p-type material by gaseous diffusion. Emitter and base contacts are later alloyed to this layer (Fig. 4b). Familiar types of alloy-diffused transistor are the AF115 series. These transistors are DaaaDDDnDaDaDaDDDDaoDDnaaaDDDooaonDD noisy at audio frequencies, but at r.f. their noise can be very low. In the grown junction structure used in the original § PRACTICAL WIRELESS 8 Texas Instruments silicon transistors, the device is not fabricated from a tiny wafer. Instead, the three layers § ' mY § are formed in a large crystal as it is "grown" from □ ★ Grid dip Meter § molten silicon, by adding the right kind of impurities □ ★ Wide range A.F. Oscillator p at the right time. The crystal is later cut up and leads attached, to form individual transistors. The process □ ★ Beginners' Short Wave Receiver p is wasteful of silicon, and is not used much nowadays, O A" A.G.C. in Tape Recording p having been superseded by the planar technique. The silicon planar epitaxial type of transistor is | On sale NOW 2s 6d § made by an extension of the diffusion process plus □□□□□□□□□□□□□□□appppoDaaoDoonopppDDa 496 • m i THE widespread use of miniature electronic eaves- dropping devices could he a cause of anxiety and cinbarrassmenl for the private citizen, as well as for those presidinfj in board-rooms. I nforlunately. the GPO cannot possibly be expected to track down every short-lived, unauthorised transmission, especially when the signal is weak and the range limited. Radio amateurs and radio control enthusiasts have been justly com- plaining for some lime about the lly-hy-night activities of pirate walkie-talkie operators and. if the trend continues, it may he gloomily predicted that anarchy of the air will overtake us in the future, when all the normal FIND _ radio bands will Ik- jammed solid by individual gibberish. The tiny, transistorised, so called '"hug" can be planted virtually anywhere, to relay private conversa- - THAT tions 100ft or more, to a nearby house or parked car, and the National Press has already brought this threat to the attention of the public. The polenlialilies of its use by criminals are almost limitless. Fortunately though, bugs are self-advertising, and the bug inverse square law of their radiation pattern favours the intended victim. A Iransmitlcr of only a few lens of milliwatts power will produce a strong r.f. field in its immediate vicinity, which is easily delected by a suitable MICROBUG instrument. Equipped with a Bug Locator, the private citizen can do much to discourage the use ol such elec- LOCATER tronic pests. If he finds one he can throw it straight on the fire, or belter still, lake it to bits to use the components for some more rewarding project. Pur- BY □. BOLLEN chasers of bugs will soon find themselves very much out of pocket if their gadgets are always discovered. The purpose here is to describe a fairly simple instru- ment which will detect a suspected "plant" and incident- ally can he used also to locate numerous sources of troublesome electrical interference. ■497 DETECTING TECHNIQUE both of the cascode stage transistors. Although the favoured frequencies for "bugging" are The combination R5, C5, D1, supplies a demodulated in the 27-28Mc/s h.f. band, and the 85-IOOMc/s v.h.f. signal to the base of TR3 via C6, and the audio output band, such strict adherence to any particular set of is taken from R8. TR3 thus acts as an emitter follower. frequencies, on the part of unlicensed operators, cannot A word or two about the types of transistors for be relied upon. Their choice will be largely determined the cascode stage. The BFY19 has been selected for by the receiver they intend to use. It is reasonable to TRI because it has a cdt-off frequency of 300Mc/s. assume that the practical upper limit, imposed by In the common base mode, a BFY18 which has an /r conventional components, will lie at about 200Mc/s. of 200Mc/s is quite acceptable for TR2. These par- Since, at low frequencies, the ferrite rod will radiate ticular transistors will give optimum performance. If, effectively over room to room distances, doing away however, alternatives have to be used, those mentioned with the need for a long aerial, the lower limit might lie in the eomponents list will be suitable—but with a within the long wave band of a domestic receiver. slight limitation to the extreme high frequency Therefore, for the purposes of detection, the need is for response. an uncomplicated receiver covering, say, lOOkc/s to Almost any small transistor amplifier, whether trans- 200Mc/s. former type, transformerless output, or complementary Few commercial receivers will cover this wide range, output, could be coupled to the emitter follower stage and those that do are bound to be cumbersome, com- to supply the necessary drive for the locator loud- plicated, and expensive. Sensitivity and selectivity are speaker. not of primary importance in this present application. The a.f. drive amplifier shown in the right-hand half If the bug is close to the receiver, acoustic feedback will of Fig. 1 is of a type that is fairly common and may, occur by interaction between the concealed bug micro- indeed, be bought complete as a commercial module, phone and the loudspeaker of the receiver, and there constructed from a kit, or it can even be sliced from the will be no doubt as to the nature of the signal. circuit panel of a defunct transistor radio! A simple alternative, avoiding knob-twiddling and To increase audio sensitivity in noisy surroundings, band-changing, would be an untuned wide-band provision is made for low impedance headphone amplifier, capable of picking up any signal within the operation by means of jack socket JKI mounted in the frequency range suggested above, and relying on the handle of the instrument. fact that this nearby signal will swamp all others and make tuning unnecessary. MECHANICAL DESIGN Initially, tests were made with a simple point-contact diode detector and a.f. amplifier, to estimate the degree Microbugs may be hidden in inaccessible places, of sensitivity required, however when placed next to the behind high pelmet boards, inside ventilator gratings, output lead of a signal generator, results were behind or under furniture, to instance just a few unpromising. A stage of r.f. amplification ahead of hideouts. To reach high places, or under obstacles, the the diode was tried. Even then, with a single transistor, locator was constructed as a hand-held boom, with RC coupled for wide band unselective coverage, the amplifiers, aerial, and loudspeaker at the business end, gain was disappointingly low. Finally, a two transistor and battery, switch, and headphone socket in the cascode amplifier gave the desired sensitivity. wooden handle. Another reason for this particular layout was that the THE FINAL CIRCUIT wiring inside the boom tube would act as a counter- poise for the short whip aerial. To minimise strain on The complete circuit of the finalised microbug locator the wrist, weight must be kept low since considerable is given in Fig. 1. leverage results from a boom nearly a yard in length. The left-hand half of this diagram consists of the To this end a lightweight, glued rather than screwed, cascode amplifier TR1, TR2, the detector Dl, and the compact method of construction was chosen. coupling stage TR3. Genera! layout details of the microbug locator are A modulated r.f. signal is picked up and fed to the given in Fig. 2. Individual construction may differ base of TR1, which operates as a common emitter slightly from the prototype, dictated by the sort of amplifier, and is partially compensated by selective components available. It so happened that the feedback resulting from C4 and R4, to offset fall of gain writer's 2in loudspeaker fitted neatly inside the lid of a with increasing frequency. The collector of TR1 is Kodak Microdol-X developer tin. Other tins of directly , coupled to the emitter of its companion approximately the same dimensions should not be transistor TR2. With base grounded to a.c. by difficult to find. capacitor C3, TR2 functions in the common base mode, Perhaps it should be stressed that both tin and tube with a good gain-frequency characteristic needing no were selected, not for screening purposes, but rather for compensation. It will be noticed that C3 is taken to the mechanical rigidity, and it is possible that a much negative rail, the virtual earth of the npn pair. This lighter form of construction would result from the use of arrangement gave the best results at critically high alloy tubing for the boom, and a slim loudspeaker of frequencies. R1, R2, R3 provide joint base biasing for the kind favoured by makers of miniature radios. SKI 00 bU>( —vt AA/560 n I tr uF ft BY T BFY» m; r»d LSI M) m TH4 TR6 -3=2 BFY18 2000 0072 15uF 0072 0072 ywlow - -W RtO RI2 RH ' kOAM Iki WO 150 PJ. Qffl DETECTOR AND COUPUNG StASE "" " _ A.E DRIVE AMPLIFIER fig. I. Circuit diagram of the mterobug locator LOUDSPEAKER AERIAL SOCKET SKI CASCOOE AMPLIFIER S^aa BRASS TUBE 26" HEADPHONE SOCKET JK1 i SOLDER GRILL BATTERY BY I PAXOLIN switch] /g SQUARE WOOD SECTION Of A.F. AMPLIFIER INNER TUBE HOLE FOR CASCOOE AMPLIFIER PANEL HEADPHONE SOCKET A.E AMPLIFIER PANEL l1^ THIN PAXOLIN INSUUTIOM ✓ BETWEEN PANELS > -O ARALDITE -2* HOLE FOR SWTCH LSI WOOOSCREW HOLES HARDBOARD FOR HAROBOARO r*m / COVER DRILL FOR BRASS TUBE (t>) (c) Fig. 2. General constructional details of the mlcrobug locator. (a) General assembly of the complete Instrument (b) The loudspeaker unit, showing how the two electronic sub assembly panels are mounted (c) Details of the wooden handle 499 U'A Note that this does not apply to r,yyt_. R1J the blue and yellow connections TR6 marked "to SI" and "to JK1", 4 respectively. These leads are added at the final wiring-up stage. After this the a.f. amplifier panel should be glued to the loudspeaker TRi 0 frame with- Araldite and tem- RH porarily held secure with rubber bands. .(To hasten setting of this epoxy glue, an assembly may be placed in a cool oven, at around 50 TR4 R12 degrees C for a few hours.) The cascode amplifier unit is built RIO up on another, smaller, plastics (a) component layout board, details of which appear in Fig.4. Here again, a template is provided—see Fig. 4a. After O testing this unit, the final assembly work can be tackled. VC^Nv"':/.'; .' o ■ " o o A considerable amount of care is o O required during this final assembly work. Place the cascode amplifier unit, wiring side uppermost, on the loudspeaker chassis so that ends O o "A" of both panels are facing the same direction. Solder the three flying leads to points PI, P2, and P3 on the cascode amplifier. Note that these leads must he of sufficient (b) drilling template—actual size length to permit routing around the insulating panel which will be sandwiched between the two sub Pt. , P2, , TO SPEAKER TERMSNALW assemblies. Place a piece of thin plastics K-X' TV* board (approximately 2iin x ^in) PJ against the underside of the a.f. amplifier panel, apply glue to the (c) wiring on underside of panel edge of the second sub assembly and fix this latter unit in position on TO JK1 the loudspeaker magnet. Secure the ITR4 wilow completed assembly with rubber bands until the glue has hardened. For future repairs or component replacement the panels may be +vt carefully prised away from the loudspeaker with a screwdriver, and afterwards re-glued. «TR6 HOUSING AND BOOM ASSEMBLY The housing and boom assembly Wut can now be dealt with. o i Cut a circular hole in the lid TO SI of the tin, leaving a narrow rim. Fig. 3. The a.f. amplifier sub assembly Glue some plastic gauze to the outer surface of this rim. Fit the loudspeaker unit inside the lid. If the loudspeaker is a reasonably tight fit, a little CIRCUIT ASSEMBLIES glue will suffice to make this secure; otherwise it may be Construction commences with the two sub-assemblies advisable to bolt the unit to the rim of the lid—this which carry the majority of the circuit components. operation should, of course, be performed before the These are shown in situ in Fig. 2a. gauze is stuck in position. The a.f. drive amplifier is assembled on a piece of Drill a hole in the side of the tin to suit the aerial laminated plastics board, shaped to fit the loudspeaker socket SKI. magnet, shown in Fig. 3. The drawing given in Next drill the base of the tin to suit the outside Fig. 3b is full size and may be used as a drilling template. diameter of the brass tube and solder the tube to the tin. When all components, have been mounted and the A large soldering iron is essential for this purpose. wiring on the reverse side of the panel completed, the Line the interior of the tin with cartridge paper or unit should be tested. Short leads (about 2in long) plastics material. Secure the aerial socket in position should be soldered to points PI, P2 and P3 (see Fig. 3c). and solder one end of C2 to the socket. 500 c*\ci * o o o o o o TR5 /R4\ i y R6 V 07 7 1 •- «TRH 11 l^TRI$ JJ [ii IIIV|ll"l2ITITITnnjil Fig. 4. The cascade amplifier sub assembly (a) drilling template—actual size (b) component layout (c) wiring on underside of panel TO POSITIVE LINE © w -H, c e c e COMPONENTS . . . TR2 TRt + ve r • I _C bTR3 Resistors Rl 2-2kn R8 4-7kn C7+ R2 4'7ka R9 I5kn f^v.%:'!-' /i. 4 -vt R3 JOkH RIO lOkD WM R4 I00£2 Rl I 560Q PS R5 IkO RI2 • IkH R6 22k Rl 3 tOkft TO BASE TO C2 TO NEGATIVE R7 lOkQ R14 150n OF TR4 IN CASING LINE All 10%, ^ watt carbon Capacitors Cl 0-OI/i,F paper C2 lOOpF ceramic tubular C3 O OlftF paper C4 50pF ceramic tubular CS 2,000pF plastic-paper THE HANDLE C6 2^F elect. 9V C7 IS^F elect, 9V The handle is built up from two pieces of |in planed C8 100/xF elect. i2V timber and two pieces of hardboard. C9 100/xF elect. 12V Hie cut outs should be fashioned with a tenon saw AH are miniature types and chisel and the various holes drilled as indicated in Fig. 2c. Two hardboard panels, of identical size and Transformers TI Push-pull driver. Rex LT44 shape, should be prepared—an additional hole for the T2 Output. 3n secondary. Rex LT700 headphone socket is needed in one panel. Assemble (Henrys Radio Ltd.) and glue together the two timber pieces and the hard- board side with the additional hole. Transistors Push the brass tube into the hole at one end of the TR1 BFyi9\ Suitable alternatives: handle. Fit the jack socket, switch and battery into the TR2 BFYI8 J BSY27, BSY29, 2N7S3, 2N744 handle housing. Pass four differently coloured con- TR3-6 OC72 (4 off) necting wires down the boom tube and connect these Diode to the components as shown in Fig. 5. 01 OAS I Secure the handle lid with three woodscrews. Loudspeaker LSI 2 in dia., 30 : Battery BY I 9V layer type. PP3 or equivalent Switch SI Single pole toggle on/off Sockets SKI Wander plug and socket (Radiospares) JK1 Miniature jack socket, with shorting contact Miscellaneous Circular tin 2fin dia. x 2in high (see text). ' Brass tube ^in outside dia., 26in long. Plastic speaker gauze. Laminated plastics board. Timber |in. square. Hardboard, 14 s.w.g. tinned copper wire. Connecting wire. Araldite glue. 501 - \ Hut FINAL WIRING-UP LSt rtd ytllow JK Returning now to the "business end", connect the four wires to the appropriate points on the loudspeaker/ LSI grttn u BY I electronic assembly as indicated in Fig. 5. Connect the w free end of C2 to the base of TRI (see Fig. 4c). Care- fully instal this assembly inside the tin, checking that the various wires are not strained or fouled in any way. To hold the lid in place, and to protect against knocks and abrasions, a slice of bicycle inner tube can be Fig. 5. Wiring diagram for the handle compartment. The stretched over and around the lid and tin, as shown in four coloured leads pats through t#ie boom tube and the illustrations. terminate at the points Indicated en the loudspeaker The aerial consists of a 2! in length of 14 s.w.g. assembly tinned copper wire with a wander plug soldered to one end. \1/ FIELD TESTS It might be useful to mention some field tests carried out with the prototype locator. FEEDBACK At first, the tin and tube were earthed to the battery positive but this was found to attenuate response above LOCATOR about 50Mc/s, probably because of the additional capacitance thus introduced, so the connection was MICROBUG TOBt TRANSMITTER removed. With a long outside aerial plugged in to the locator socket, just about every transmission within skip distance came in at fair volume, dominated by the local R.F. AMPLIFIER B.B.C. Home Service and Light Programme. Tests DETECTOR AND with a signal generator indicated that the limits of A.F. AMPLIFIER usable response were greater than lOOkc/s to I80Mc/s. MICROPHONE LOUDSPEAKER As for sensitivity, with headphones plugged In and a short whip aerial on the Locator, a 60mW radio control Fig, 6. This Illustrates the technique used In detecting transmitter could be clearly detected at a distance of hidden radio mierebugt. The hidden snooping device is 25ft. activated by the operator whistling In a "suspect" area. Another test was with a microphone and amplifier This sound Is transmitted by the bug, and received by the input to the modulation transformer of the signal locator, the audio output of which Is picked up by the bug, and so a self-sustaining feedback loop is created around the generator. When the locator loudspeaker was brought two devices. - The Intensity of the loudspeaker output will close to the hook-up, acoustic feedback occurred—a Increase as the locator is brought closer to the concealed distinctive warbling note. The onset of feedback bug, whose hiding place Is thus soon discovered could be initiated by a sharp whistle from the mouth or, better still, by using a toy whistle to jerk the system into oscillation. "DEBUGGING" PROCEDURE In use then, the mode of operation might be as follows. With headphones connected, the area to be "cleaned" is scanned while the operator emits a few strident whistles. If a bug is close at hand the operator will hear his whistles plus room echos reproduced in the headphones. Next, he will remove the headphones, unplug them from the locator and use the instrument like a feather duster, going round the room in a search for the source of the transmission he has picked up, while still whistling loudly. Sooner or later the warble note from the loudspeaker will give him a clue to the bug's exact whereabouts. The microbug locator can, of course, be used for purposes other than that for which it was especially designed. It will effectively trace sources of electrical interference, check for mains borne r.f., serve as a zero beat detector where two close frequencies are to be compared, or it can be coupled .to the i.f. output of a superhet receiver as a temporary detector and a.f. amplifier. It only remains to wish would be Hemipterists, trappy Bug hunting! ★ EXPERIMENTS in LOGIC DESIGN by S.T.ANDREWS The system shown in Fig. 1.12 last month, although The circuit of a suitable gate can take several forms. capable of adding binary digits in the form of Essentially the requirement is for a form of and gate voltage pulses, has one disadvantage. The input pulses with the gating pulse and the output from the bistable have to be applied simultaneously, and must be of identi- as inputs, as in Fig. 2.1b. The action of this is obvious cal waveform and identical duration. It may well be and it would be quite possible to use an and gate of that two numbers become available at different times, the type shown in Fig. 1.5 followed by a suitable this is especially true if the .numbers are applied by an amphfier. operator punching them on a keyboard, one after the Another version is shown in Fig. 2.2 and this runs other. Obviously some form of storage system is the gating amplifiers off the +9 volt line. In this required, capable of holding the numbers to be added, circuit the bias developed across Rx is sufficient to and preferably capable of holding the result as well. maintain TR4 cut off whatever the state of the bistable, A store which is intended to hold one complete as long as TR3 is conducting. The gating pulse is binary number is known as a register, and the number arranged so that it causes TR3 to cut off for a short is held as a series of on/off signals, each representing time. When this happens the state of the amplifier one binary digit. TTie term binary digit is usually depends on how the bistable is set: if TR2 is conducting contracted to bit and this term will be used from then its collector will be nearly at zero potential and now on, TR4 will remain cut off; if TR2 is cut off then its collector will be at about the potential of the —9 volt STORING BINARY NUMBERS line and TR4 will conduct. Of the various ways of storing binary numbers, the TR4 and TR5 form a voltage amplifier which drives most convenient method in small-scale equipment is an emitter follower output, TR6. In effect this to use rows of bistables, each storing one "bit" of the circuit is an and gate in which only one input is applied number. In the three-input adder five bistables are in the conventional way and the other is used to needed, three to hold the input digits and two to store remove the bias which makes the gate into an and. the output; one of these can be dispensed with later.' Three bistables, and three gated amplifiers, are Using bistables to hold the numbers solves the required to drive one three-input adder. The gating immediate problem of storage, but raises another transistor, TR3 is- common to all three gates, the problem in its place. It is now necessary to provide bottom ends of all three Ry resistors (Fig. 2,2) being some form of gating circuit between the input store and connected to the collector of TR3. The output from the adder itself to prevent the digits from entering the the adder can be coupled directly to the output bi- adder until required to do so. Each of the three input stables, no gating circuits are needed at this point. bistables must have its own gate, but since all three gates will operate simultaneously it is legitimate to SET AND UNSET CONDITIONS consider them as a single unit and draw the block Having devised the circuit of the input gate we have diagram of the adder as in Fig. 2.1a, effectively set the convention for the bistable switch, A set-up of this sort is of far greater use than the We have already explained how a bistable can hold a three-input adder by itself. The binary digits can be 0 or a 1 depending on whether it is set or unset. In written into the bistables at any time and added at the circuit of Fig. 2.2 the convention for use with the leisure by applying a suitable gating pulse to the gate. input registers is: the bistable is set, and holds a 1, when the transistor on the output side (TR2) is not conducting; the bistable is unset, and holds a 0, when the output transistor is conducting. This convention is an inevitable result of the way in which the circuit is arranged. o 3-tNPUT ADDER , Adder ' Input Gating pulse Fig. 2.1a. Block diagram of the adder with storage bi- stables and gating circuits now included Fig. 2.1b. A gating circuit based on an AND gate 503 BISTAWf A -9V II THl TR2 TR4 TR5 TR6 ® I® eon Output to Addtr m +45V TR3 Troisistorji R«d spot/Y«((ow tpot or simllor +9V fig. 2.1. The storage and gating circuits for the adder Input The sequence of events for adding three digits is down one above the other, then the process of addition now as follows: the digits are read into the input will be: (I) Add the extreme right-hand pair of digits, store of bistables in any order, and with any time delay writing the result underneath and, if necessary, writing between writing individual ones. A suitable pulse is a 1 in the carry column of the next stage to the left, then applied to TR3, causing it to stop conducting and (2) Add the digits in this next column, including the allowing the contents of the three bistables to pass carry if appropriate, and again write the result under- through the gates, enter the adder and be added. The neath and, if necessary, a 1 in the carry column of the resulting pulse outputs from the adder set the output next stage on the left. (3) Add this column in the bistables where appropriate. After the gating pulse same way . . . etc., etc. ends all three inputs fall back to zero as TR3 starts to The process is summarised in Fig. 2.3. This may conduct again and the output can be read off from the seem very elementary but it is important to realise what output bistables; the input bistables can all be reset to zero if required. happens when an addition is done on paper, so that an So far, then, we have produced a three-input binary electrical analogy can be produced. adder capable of storing the numbers to be added, THE COMPLETE ADDER adding them when a suitable pulse is applied, and The three-input adder so far discussed can store storing the result of the calculation. We can use a three binary digits and add theTn when required to do set-up of this kind to .build up a complete adding unit so. This is what is needed in each of the vertical which can be made quite automatic, but before going columns in Fig. 2.3 and in order to add multi-digit on to do so a little theory of addition might be useful. numbers one three-input adder is required for each vertical column of, addition. The numbers to be THEORY OF ADDITION added are held in storage units consisting of rows of When adding two numbers, not only in binary but in bistables and it is these which are used as the input to any numerical system, there is a certain pattern to be the adders. There are two rows, each of which is one ..ollowcd. Assuming that the numbers are. written register, and the block diagram of a complete adder is shown in Fig. 2.4. Several points arise from this. The two input registers are on the left and are made STAGE 1 thisinto poirCARRY added. column CARRYdlgit on i»fi. writtw up of some of the bistables that feed the three-input adders. The carry output of each adder, except Th 4 0 1- STAGE 2 into' PCARRY' columnCARRY on M*digit wrimn the last, is used to set the remaining bistable of the subsequent adder, thus the carry signals are passed STAGE 3 t"1"5 P0""" "ddtd. CARRY digit written from one stage to the next. The carry output of the into CARRY column on left. final stage forms the left-hand digit of the final answer. The extreme right-hand adder (the bottom one in Fig. 2.4) will not have a carry signal input since there is no stage on its right, consequently a simpler two- ETC input adder will do in this position. An adder such as this can be extended almost indefinitely by including more three-input adders, the fig. 2.3. Illustrating the 1 0 10 11 0 110 0 1 "repeating unit" is also shown in Fig. 2.4. Each processes involved when CARRY columns ~ additional unit will double the size of number which adding two numbers Result the adder can handle. 504 CARRY J-INPUT 4 s ADDER AOOtft CARRY J-INPUT AOOE8 Z's ADDER R«p«oting Unit m CARRY 2 -INPUT ADDER 1i ADDER One Input Oth«r Input Output Rtgiitir Reqisttr Register Fig..2.4. Logical diagram of complete adder TIMING CIRCUITS CLOCK PULSES Each individual adder in Fig. 2.4 has its own gate In order to make all this happen some form of which, when triggered, will allow digits from the timing chain is required, which must be able to trigger appropriate parts of each register to enter the adder. the gates one after another, in the correct sequence. In the arrangement of Fig. 2.4 these gates must be There is no real harm in a gate opening twice, but it is opened in sequence, first the two-input adder, then best if each one opens only once, at its correct place. the three-input one above it, then the three-input one One method of obtaining the desired result is to above that, and so on, right up the adder. The larger generate a constant stream of pulses all the time and the registers, the longer a complete addition will take, use these to generate all the other special waveforms and the result appears gradually in the output register needed. Such pulses are called clock pulses and are as the addition proceeds. generated in an oscillator which runs all the time the Vs adder 2's adder 4's adder *4 If, ft w. m m ft w ty —* m Terminals at top are digit outputs to indicator unit. Clock-pulse generator and STARTADD generator are not on this board A Two Input bistables F Three input bistables K Sum output bistable P Carry output bistable B Gating transistor G I's adder carry L 3'input adder Q Three input gates C Two input gates H Gating transistor M Three input bistables R Carry OR D Sum output bistable I Three Input gates N 2's adder carry S Sum output bistable E 2-input adder J Carry OR O Gating transistor T 3-input adder Photogroph of the adder built by the author. This is depicted In block diagram form in Fig. 2.4 505 Interpulse stN /Period STARTADD PULSE GENERATOR differentiator The Clock puiset The differentiator (A) produces a constant stream of PulseClock negative-going pulses, each of which is co-incident with the start of a clock pulse. These are AND-gated startt'O-TL1 ''finish finscK _ with the output from a bistable which is set by the TIME trigger pulse used to begin the addition. Jn the resting dirt state the output from (A) is the only signal applied to J START ADOjIDD pulse the and and so there is no output from it. When a adder trigger pulse is applied to the network the bistable changes over and a signal appears at the second input of the and. As soon as the next pulse from the differentiator arrives it passes through the and and f VADO Trigger pube J I INHIBIT triggers the flip-flop into its quasi-stable state. The toilort Timing pubt to 2s time-constant in this flip-flop is set so that the circuit ADDITION adder timing circuit flops.back again after the duration of exactly one clock pulse, so since differentiated signals occur only at the beginning of a clock pulse this circuit ensures fig. 2.5. Logical diagram of STARTADD pulse generator that the startadd pulse, taken from the flip-flop, occurs and waveform of the c/oc/c pu/je exactly co-incidentally with a clock pulse. The output from the flip-flop can be used to drive adder is switched on. (There is one new circuit element TR3 in Fig. 2.2 directly, the base of TR3 being con- to be mentioned here, the differentiator. For the nected to the transistor in the flip-flop which is nor- purpose of this article a differentiator can be con- mally cut off. It is better, though, to have a buffer sidered as a black box which gives out a short voltage transistor between the two sections of the circuit. pulse whenever the input voltage changes suddenly. The output from the flip-flop also passes through a Using the clock pulse as input the output will be a differentiator (B) and is used to unset the bistable. succession of alternately positive and negative-going Successive pulses from (A) do not then cause further pulses, each of which is of very short duration com- operation of the circuit which is thus seen to be self- pared to the input clock pulses.) resetting. In order to start the addition, once the numbers have Fig. 2.5 contains one version of the startadd been written into the input registers, the first available generator, but this can be modified. The flip-flop clock pulse is made to open the I's adder gate. This could be replaced by a second bistable which is supplied requires a circuit which, when triggered, will give a with a constant supply of unset pulses, each at the single output pulse coincident with one of the clock end of a clock pulse. This would require a third pulses, this being done irrespective of the phase of the differentiator. Alternatively the one bistable of clock pulse at the instant the initiating pulse is applied. Fig. 2.5 could be replaced by a flip-flop set to spend In this type of circuit it is sometimes useful to give exactly one clock, pulse duration in the quasi-stable names to particular pulse sequences, thus the constant state, but although this method dispenses with one of stream of square pulses which ultimately controls the the differentiators it is not recommended. The output whole circuit is known as the clock pulse. The pulse from (A) can be applied to the bistable as shown in produced by the trigger which opens the I's adder gate the dotted line in Fig. 2.5. This would be done by an and initiates the adding process can be called the (electronic) switch and would serve to inhibit the startadd pulse. The logical diagram of a suitable startadd generator, and could be used as an additional startadd pulse generator is given in Fig. 2.5; this safety check to prevent addition from occurring while also shows the details of the clock pulse itself. checking the contents of the registers. START ADD pulse OiApuHo Is odder gote -9v R3\ ^R4 RO R(7\ VR2 Rl? R1S Vi: k iri TRZ| TK3 TK4 TR5 TR6 ^<10 t® D ■ R 6 Ri3 ^ RK + 1.5V Trigger Output to next stage 4-5V fig. 2.6. Circuit of a STARTADD generator based on the logical diagram of fig. 2.5 506 A DETAILED CIRCUIT is unset by the pulse from the differentiator, the adder A special version of the startadd generator is given gate closes, and the second differentiator provides a in Fig. 2.6 and although it follows the logical diagram pulse which triggers the 4's adder timing unit. This, of Fig. 2.5 there are some unusual points to be men- of course, is identical with the Ts adder circuit, and tioned. TR1 is the buffer amplifier for the clock pulse will be opened by the next clock pulse. and it feeds a form of differentiator, Cl and R2. From As we have seen, there is no limit to the number of this a stream of trigger pulses pass to the base of TR2 digits which the whole adder can add, the "repeating which, together with TR3, makes up the flip-flop. unit" of Fig. 2.4 beingt repeated as many times as TR5 and TR6 form a bistable which, in the resting desired. Fig. 2.7 Is the*repeating unit of the timing state is set so that TR6 is conducting and TR5 is chain, and again there is. no reasonable limit to the cut off. The collector of TR6 is connected to the number which can be used, each will operate once, collector of TR2 through VR2 and this holds TR2 then reset itself and trigger the next stage. One collector at a low potential making it impossible for "timer repeating unit", as in Fig, 2.7 must accompany it to cease conducting despite the pulses being applied each "adder repeating unit" of Fig. 2.4. In the final to its base. stage of the addition, corresponding to the extreme The instruction to begin adding closes SI and causes left-hand digit of the answer, the output from the the bistable to change over, the collector of TR6 rising timing stage could be used to initiate a process to nearly to the potential of the —9 volt line. The print out the result of the addition and/or unset the inhibiting bias on TR2 collector disappears and the bistables in the input registers. next trigger pulse from TRt sets the flip-flop into its We now have a complete adding unit which can be quasi-stable state. The resulting pulse from it, the made to handle numbers of any size, the numbers being startadd pulse proper, leaves on the 1 's adder output stored before addition, and the result being stored wire to open the adder gate. At the end of the quasi- afterwards. The actual addition is started by applying stable period (which in this case is one clock pulse) the a single trigger pulse after which the process is auto- flip-flop reverts to its normal state, TR4 and C4 provide matic, By itself this adder is not much more than a a pulse which resets the bistable, and a pulse to start toy since in general it cannot do anything which cannot the next stage of the addition leaves via C3. be done equally well by a human operator. However it can be extended to include other mathematical func- TIMING UNIT tions and these will be considered shortly, but first a Each stage needs a single pulse to open the appro- few practical considerations will be mentioned. priate adder input gate, and it is quite easy to make one stage trigger the next. The output from C3 in Fig. 2.6 PRACTICAL CONSIDERATIONS is used to set a flip-flop whose time in the quasi-stable There is no special way of constructing the adder state is about half of one clock pulse. When this and standard circuit techniques can be used. The returns to its stable state it sets a bistable which can writer constructed a small version across a number of only be unset by a pulse at the end of a clock pulse. tagstrips which were fixed to a large aluminium panel. The output from the bistable is AND-gated with the This gave, effectively, a two-dimensional layout in main clock pulse to give the pulse needed to open the which each component and circuit element was easily 2's adder gate. The logical diagram for this is given accessible, but the overall result was rather large. This in Fig. 2.7. unit is shown in the accompanying photograph. The sequence of operations is: a constant stream of Alternatively, tagboards could be used, bolted in unset pulses is applied to the bistable, one at the end of parallel rows, and this would yield a more compact each clock pulse, but these have no effect since it is design but one in which many of the components would unset anyway. The gating pulse from C3 in the I's be inaccessible. The mechanical layout is not too adder occurs at the end of a clock pulse and this important and, like the finer points of the circuitry, triggers the flip-flop. Sometime about the middle of will probably be varied by individual constructors. the inter-pulse period (see Fig. 2.5) this flops back The clock pulse generator is most easily a multi- again and in doing so sets the bistable, during the next vibrator, since this will provide a good square wave clock pulse, then, the and has two inputs, the per- with little variation in frequency. The pulse frequency manent one from the clock pulse line, which is normally is largely a matter of choice, it can be extremely low, 1 c/s ineffective, and now the second one from the bistable. for example, so that the circuit action can be followed This next clock pulse then passes through the and and on a voltmeter, or several kc/s—^though slight modifica- opens the I's adder gate. When it finishes the bistable tions to the circuit would then be necessary. There is no point in trying to make an adder with a very high ClQtk puist clock pulse rate since the long time needed for informa- tion to get into, and out of, the adder would make this quite pointless. Mier oiff INPUT AND OUTPUT DEVICES So far no mention has been made of how to get dift B Information into" or out of the adder. The more To ntxt sophisticated electronic calculators have several sto« methods of exchanging information with their human operators; these include punched paper tape with 5, 7 or 8 tracks, punched cards,' and various forms of. Trvjwr puH* electric typewriter. Mere cost makes all these arrange- ments impossible for the amateur constructor, and a good deal of ingenuity is required when constructing Fig. 2.7. The timing unit for each stage of addition input/output devices. 507 About the best that can be done is the modification Output converters are rather more complex: these of an. ordinary typewriter by the addition of switches take a binary input and produce a decimal output. to the numbered keys (to get information in) and, One experimental type is given in Fig. 2.9 and the possibly, electromagnets attached to the same keys mode of action is thus: the striated wires carry the (to get the results out). This must be regarded as output signals from the adder and these pass through something of an ideal and in most cases a simpler gates to a series of bistables which are arranged to act arrangement will have to be used, for example, a row of as gated amplifiers. The timing unit of the last section small lamps as the display unit. of the adding chain produces an output pulse which We are not concerned in this series with the mechanics initiates printing by setting flip-flop (A). This opens of input/output devices as these will probably be the adder output gates and the appropriate bistables different in the case of each constructor. However, a are set. As it flops back to its stable state it triggers few notes will now .be given dealing with the conversion bistable (B) via a differentiator^ this bistable is and- from one numerical system to the other, i.e. binary to gated with the main clock pulse line, so clock pulses decimal and back again. This requires some form of now enter the decoder proper through the and and converter which can unfortunately get somewhat com- leave at one of the eight outputs. Which output this plex as large numbers are handled, but which can be is depends on which bistables were set and this, of kept reasonably simple with smaller numbers. course, is a property of the adder output. The As an example, a simple decimal-to-binary con- decimal output wires can be made to operate display verter is shown in Fig. 2.8. The number is applied lights or type out the number, as required. by closing the appropriate decimal key which sends a pulse along whichever of the binary output wires is EXTENSIONS TO THE ADDER appropriate. The three binary output wires supply The adder so far described can add two numbers set signals to the input registers. A two-way switch quite efficiently but is unable to do anything else as it is also needed to connect the output from the con- stands. Extra circuitry, however, will increase the verter to one or other of the input registers. It would abilities of the adder and enable such mathematical be possible to arrange things so that pressing a + key operations as subtraction, multiplication and division made the switch change over so that the first number to be performed, as well as certain logical functions, went into one register and the second automatically for example the "non-equivalence" operation. went into the other. The non-equivalence function is useful iu recognising whether or not two numbers are the same, i.e. doing a direct comparison. The exact procedure might be: Strwmi of SETpulsts considering the numbers a digit at a time, write a 0 in oecm. the answer register when the pair of digits of the com- ^7 pared digits are the same, and write a 1 when they are not the same. An example of non-equivalencing is: perform the non-equivalence function between the numbers lOHOOIOll and 1101100010. (Numbers on which arithmetical operations are performed, for ex- ample the above two, are called operands) llOllOOOlo}" operands 0110101001- -result C^0 Fig. 2.8. A simple decimal-to-binary converter Clock v Decimal ^Output £7^ d ft Print Tnooff O Z_4—/ | / j Poise Y Fig. 2.9. A binary-to-decimal converter ADDER OUTPUT 508 5-INPUT ADDER tAflRY- j i1 n SUM i Permanent ApjjroprioU sections unset pulses- of Gate closed applied to Bistable 3-INPUT fiDMR CARRY n SOFT Port of Input Port of Output reqisler | register Fig. 2.10. Conversions for non-equivalence functions In order to make the adder perform this function priate sections, of the circuit into operation; this can it is only necessary to inhibit the carry signals which be called the adder control unit. The whole logical pass from one stage to the next. Three possible ways set-up, containing the adder itself and the control unit, of doing this are shown in Fig. 2.10. An extra gate, can be called the arithmetical unit. normally open but closed in the non-equivalence Since there are several functions which can be called operation, can be placed in the carry output from each into action it is necessary to have some method of three-input adder; the input gate in each adder which telling the adder control which function is needed in a passes the carry from the previous stage can be held particular case. This could be done with a set of permanently shut; a constant stream of unset pulses switches which would be set by hand before each opera- can be applied to the carry bistable at the input of tion, but this would waste a lot of time. A better each three-input adder. If the carry's are inhibited arrangement would be to allocate a code-name or code- in one of these ways (or any other way) then the two number to each function and feed this into the machine operands are written into the input register in the with the numbers themselves. For example, 01 could usual way. A startadd pulse is applied and the be the code for addition, 02 for subtraction, 03 for timing chain operates in the usual way, the non- multiplication, and so on. equivalence result then appears in the output register A complete instruction to the machine would th'en in the usual way. have three parts, A the code-number, or function- Subtraction, multiplication and other operations number, which states which operation is required, can all be done on the adder by putting in extra circuits, and S and C the two numbers on which the operation as with the non-equivalencing. The additional logic is is being performed, i.e. the operands. To add the two somewhat complex and so for the time being only an binary numbers 10110 and 01III the input to the outline will be given of the requirements. machine would be: 01 10110 01111 ADDER CONTROL UNIT and to multiply them it would be: Since all the various functions use the adder to a 03 10110 0111! greater or lesser extent, it can be regarded as the central piece of the calculating machine, and the various The block diagram of the whole machine is now that mathematical operations all use it in their own par- given in Fig. 2.11. ticular way. We thus require an additional unit which If some more extensive form of storage is available is told which function is required and brings the appro- then large numbers of instructions and operands can be stored until required. Since the result of one opera- FuRctwn numbw to Control Unit tion can be one of the operands of another, quite complex mathematical calculations would become possible. The snag, of course, lies in the storage r methods available, or rather the lack of them. Vast m formation WHlt OPtRANDS transferrtd numbers of bistables are impractical due to the in- to nwiiUf creasing possibility of failure and the large amount of space required; core and drum stores are also imprac- tical due to the very high cost and complexity of the ADDER equipment required to run them. Magnetic tape, Control CONTROL used perhaps on a modified commercial tape deck, Circuits UNIT is about the only practical method available to amateurs and even this is expensive and very complicated. Output ■Despite this last discouraging note it is possible for a Register keen constructor (or better still a group of keen constructors) to build some form of. calculating unit, provided that this is not made too complex. The tlnpat r problems involved in building arithmetical circuitry are Registers great, but not too great to be solved, and attempting to solve them is a fascinating branch of experimental Fig. 2.11. Block diagram of complete calculating machine electronics. To be continued. 509 D A I A HIGHLIGHTS FROM THE CONTEMPORARY SCENE i Suppressing Transients in Computers A means of reducing unwanted transient pulses in computer supply systems has been developed by engineers of the Plessey Components Group. These transients are causing increasing errors of calculation in modern computers of high operational speed and complexity. Normal voltage or current pulses for operations are generated by stabilised circuits, but transients in the power supplies can upset the normal function of the pulse generators. An experimental suppressor unit, currently in production for a leading computer manufacturer, is 0> shown, on the left undergoing final tests. - L ' \ V- ' V * v • % i Combining Filter for 1).H.F One of the many items of equipment required for expanding the u.h.f. television services through- out the U.K. is the vision and sound radio frequency combining filter. This picture (left) shows the filter being assembled in the Cambridge factory of Pye TVT Limited. Later, it will be installed with other parts of the transmission system for broadcasting on the BBC2 network. 'Divcoir Characier Dispiay V Televiewers on election night may know that a computer was used for predicting the final election result, but few probably realised that a new system was j used by the BBC for displaying some of the constituency results on the screen. This system, although tried for the first time In this country, has had a successful run in Canada. Known as the RCA "Divcon" (digital to video conversion) system, it accepts data from a variety of sources, stores the ; data and. converts them into a signal suitable for display on television screens (right). Cameras are not necessary for this system since all information is supplied to the transmitter in pulse code form. One interesting feature is that it is not necessary to "rewrite" a complete message in order to change one or more characters. The system responds to all functions carried on an electric typewriter such as shift and back-space. i Numerical Control Development work on the automatic fi control of machine tools has been in ji progress for some years, but the first |. exhibition specially devoted to numerical y control took place at the beginning of If May this year. The picture on the left shows the Emicon SIOOO Positioning Control system, which is basically an analogue computer with electro-mechanical links to the various machine function controls. The nucleus of the system-is a pre-punched paper tape of either five or eight tracks, which is printed in code according to the required milling or boring operations. Complex shapes in two dimensions can be machined under the control of this equipment. Tape Time Announoer ► After the first speaking clock in Sudan, J installed five years ago to provide a service in English and Arabic for the Khartoum area, A.E.I. Telecommunica- I tions Group are supplying five more machines to give a complete service throughout the Republic. These machines use tape recorded announcepients in up to four languages at 10, 15, or 20 second intervals on one inch wide tape. The timing is based on a crystal controlled chronometer, the timed announcements having an accuracy of plus or minus one second per month. The tape used is a heavy duty instru- T mentation sandwich type 489 manu- ' factored by the 3M Company. The oxide coating is completely covered with a thin smooth non-abrasive plastic material to prevent wear to the replay heads. Hence the heads are maintained slightly "out-of- contact" at a uniform distance. BEGINNERS start here... 21 An Instructional Series for the Newcomer to Electronics Following on from the discussion on semiconductor diodes last month, we stated that a transistor can be P n considered as a pair of diodes connected back-to-back. SmaUbOM SaMbkii Now we will investigate the operation of a transistor in J jqUtry some detail. It must be appreciated of course that BY what follows is of necessity an extremely simplified 'Holt*' rtrtamirjq description — but will serve our immediate purpose t *♦ throuo' which is to impart a basic understanding of this most important electronic component. COlltCtOf Bmtr TRANSISTOR OPERATION The action of transistors can be fairly readily Spot on visualised if the forward and reverse ideas in con- cop nection with semiconductor diodes are remembered. Fig. 21.1 depicts a transistor of the pnp type. The II La ecoiltctor BYZ CoKtctor bid* first "diode", formed by the electrodes known as the cumiK batttnr (irittsr' | Icolltctor emitter and base in the transistor, is biased in the bast forward direction by a small battery BYI. The other "diode" junction, formed by the base and collector electrodes, is biased in the reverse direction by a Fig. 21.1. A graphical illustration of transistor action. larger battery BY2. Holes In the f>-n-p /unction transistor move across the first The interesting thing is that the current (heavy, Junction, ana about 98 per cent of them reach the second because of the forward biasing) from emitter into the Junction, arid are swept off as collector current. The 2 per cent forms the base current. Any change in this base base, drifts right on through to the collector. Thus current gives a proportionate change in the current arriving collector current flows in spite of the reverse bias on at the collector, so a few mlcroamps at the base might this second "diode". Only a fiftieth or so of this control many mllUamps through the transistor (emitter to current flows into the base via the connecting lead. collector If a small current signal is injected into the base- Fig. 21.2 (right). This Is one form of transistor construction mitter circuit, the collector current varies in sympathy. In common use Since the collector current is some fifty times greater than the input signal, amplification is achieved. The transistor thus acts as a current to current change reminiscent of the action of the grid voltage in the converter. triode valve.) It is of great interest to note the differences between valves and transistors. Valves are voltage operated WATCH THE POLARITY at the grid, and convert grid voltage changes into current Most transistors at present in use are of the pnp changes through the valve. Transistors are operated type, but npn types are often found and are becoming by current changes at the base electrode. Base current increasingly common. changes produce much greater current changes through With npn types the battery connections (as indicated the transistor collector-emitter circuit. in the accompanying diagrams) must be reversed to To sum up, the transistor can be looked on as two give correct operation. Also, the arrow on the emitter semiconductor diodes back-to-back, but the common symbol is reversed for npn types, as shown in (e) of region (the base) is so thin that current carriers crossing Fig. 20.3 last month. the forward biased emitter-base junction are nearly Fig. 21.2 gives an idea of the actual construction of a all swept straight across the reverse biased collector- common type of junction transistor. The collector base junction. The current actually allowed to reach lead is usually spaced widely from the other two, and a the collector connection is controlled by the base spot of paint is placed on the cap beside this lead to current, not directly by the collector battery. (This is assist the identification. m \ \ N! Nf nH 512 l Now, to put theory into practice, here is a construc- tional project. It is an audio frequency oscillator COMPONENTS... employing two transistors and should be simple to build if the accompanying diagrams are carefully followed. Resistors^ Rl 39kft R5 47kn A TRANSISTOR OSCILLATOR R2 47ka. R6 47k ft First it would be a good thing to remind ourselves R3 IkH R7 Ikn of the two main requirements to be met in all electronic R4 39ka R8 4 7kn oscillators that produce a continuous signal. (In All 10%, iW carbon fact, all vibrators that go on and on, electronic or Potentiometer otherwise.) First we need a source of energy which VRI lOkil linear skeleton potentiometer can be used to operate devices with gain, or amplifi- cation properties and, secondly, an arrangement to Capacitors feed back part of the amplified signal in the correct C1 l^tF elect. 6V C3 O-Oi/iF elect. 6V phase to boost the oscillating circuit. C2 lO^tF elect. 6V C4 0 01/iF elect. 6V In the first oscillator we built (Part 19), a valve Transistors was used as the gain producing device and the phase TRl OC7I was carefully chosen, by selecting appropriate points TR2 OC7I in the circuit, so as to maintain the oscillations in the parallel tuned circuit. Miscellaneous As we have just seen, transistors also have- gain 6r Wooden baseboard. Brass wood screws. Wire amplifying properties, and as a practical example and sleeving. of the use of these devices the present oscillator has been designed for you to build. ACTION OF THE CIRCUIT This oscillator produces a sine wave signal within the Referring to the circuit diagram Fig. 21.3, the base audio frequency range, and does so by means of the of the first transistor TRl receives a small signal from following circuit action. point "A", the junction of the parallel C4 and R8 EV TRl TR2 0 01 0C71 0C71 lOrf C4 R9. IkU I |0-W 4.7 I Fttdback Path Fig. 21.3. The circuit diagram of the transistor oscillator. The output of the two stage amplifier (point " B") supplies its own input (point "A") via the " Wlen Network " of C3, C4 and R6, R8 513 with the series" C3 and R6. This signal appears capacitors C3 and C4. You will probably think up amplified and inverted in phase at the collector of some uses for the audio frequency signal which you TR1. It is fed into the base of the second transistor now have available, and once again the unit is a useful TR2 via C! where it is further amplified and appears signal generator for testing purposes. as a large signal, again inverted in phase, at the col- lector of TR2. This signal is fed into the series/ POINTS ON CONSTRUCTION parallel CR network, and the whole action keeps on repeating—the circuit is oscillating. We will conclude this part with a few ideas concerning Notice the important phase changes as well as the construction. First, remember that transistors amplification that occur. Using two stages means are very sensitive to heat. Keep the transistor leads that the phase is inverted twice, which means in turn long. Complete the soldering operation as speedily that the final phase is the same as the initial signal. as possible so that the component does not become Fig. 21.4 shows the signal relationships in a clear unduly heated. By the way, never let the transistor manner. envelope accidently touch the body of the soldering Which part of the circuit determines the frequency? iron. It is not a coil and capacitor circuit as in the case of The baseboard used in this project is a white painted the valve oscillator. In this present oscillator we electrical fitting board—readily obtainable from mul- have used capacitors and resistors to set the frequency: tiple stores. , INPUT , (pQiwrx] WoedbustboarttfxS* / iCOtiECTORTRI INPUT I Mam edi&ot »d spot TRI TR^ RV.C. cowed trireishmm. thus TK2 (X IPUT m VRt 4- + C4 se Fig. 21.6. The practical layout following the usual mode of construction on a wooden baseboard F/g. 21.4. The relationships of amplitude and phase at various points in the circuit Fig. 21J. The Wien network redrawn to show clearly the series and parallel branches It is a good idea to choose a colour code for the wiring of any electronic unit. This helps greatly in later servicing or circuit tracing. The obvious this is partly in order to show that there is more than colours are red for the positive supply rail and black one method available. We have mentioned the for the negative. Signal paths can be green. The series/parallel CR network, and this is redrawn in Fig. main point is to choose a colour scheme, and use this 21.5 to increase the clarity of our argument. This consistently so that no confusion arises in the future. is a well-known combination of components known as part of a Wien Bridge Network. The oscillator circuit OPERATION is, in fact, a Wien Bridge Oscillator. The network has the property of supplying an output signal in Power for the oscillator can be obtained from a phase with the input, at one frequency only. At all 9 volt dry battery such as type PP3 or equivalent; or other frequencies, the C's and R's shift the phase alternatively the mains operated power unit and filter relative to each other. Thus when the amplifying unit described in Parts 16 and 17 can be employed. section is added, oscillations start to be produced, The output signal from the oscillator can be taken at this one particular frequency only. from the collector of either transistor, via a small We say that the Wien network is frequency selective. capacitor of about 5,000pF. Actually, there is less By changing the values of the capacitors, a different effect on the frequency of oscillation if the collector frequency is obtained, but it is usual to keep the of TRI is used. The other output terminal can be values of both the capacitors equal. In most oscil- either the positive or the negative supply line. lators it is important that the amount of amplifica- Radio enthusiasts can use this oscillator straightaway tion should be just right—not too much, not too little. for morse practice, by employing headphones across In this circuit the gain is adjustable by the potentio- the output, and putting a key in series with one of the meter VR1 which can be set to give the purest note supply leads. from the circuit. Another use, which, we will consider in a later We therefore see that all the requirements for an article, is as the source of audio signals for a component oscillator have been met, and this simple two transistor measuring bridge. When we deal with simple test circuit will produce a sine wave signal over a range of and measuring equipment, the oscillator will be men- frequencies according to the values of the controlling tioned again. 514 In creative tape recording a mixer unit has many uses. Fig.t. Passive mix- It enables multiple sound sources to be individually ing circuit for four controlled as input levels so that a balanced output MieropJwM ,6 Aim channels can be achieved. The monitoring of group instru- 1 AAA- ments or voices from microphone inputs, by way of this unit, can provide flexible levels before amplifica- tion, also acoustic feedback is minimised in the greater separation of microphones and amplifier loudspeaker when using fixed microphone lead lengths. Any type of high impedance crystal or dynamic microphone HierophoM ,5*^2 may be. used. 2 The simplest mixer that can be constructed consists of a purely passive network, as in Fig. I. This suffers from the disadvantage that even on maximum output the Input to a tape recorder or amplifier is less than a single input would be if it was connected directly. .GAIN 3 Output Although "virtual earth" mixers can be used to over- Mierophoni A/V— come this disadvantage, the easier solution is to add an 3 amplifier after the passive network. V t Four Channel by A. FOORD R1 VR1 w— RlZ I C4 IMn ma R5 RB lOOllF 100KA A'7kQ TR2 JK2 w— 2N1304 IMfl iMa TR1 26508 SUF R3 JK5 vR3 W— R6 ma ma Wka W Rtl inn k4 woa 25ur VR4 w— R7 SKI ma ma 27ka OUTPUT -0 2w£ I Fig. 2. Circuit diagram of the four-channel mixer with transistor amplifier 515 THE CIRCUIT the overall gain at a value independent of the variation The circuit diagram is shown in Fig. 2. As can be of transistor current gains normally encountered due seen there are four input jacks, JK1-4, and associated to the spread of the transistor characteristics. Bias gain controls, VR1-4, which allow for selective stabilisation to fix the working points is achieved in monitoring. The individual signals are fed by way of the normal way; C3 and C4 acting as signal by-pass stopper resistors, Rl-4, which isolate their respective capacitors to their stabilising resistors. inputs against level changes in the other channels. CONSTRUCTION Mixing is achieved at the juncture of these resistors and the resultant complex signal is fed. to the base of The unit was designed with an eye for symmetry and TR! by way of Cl. The amplified signal at the compactness which enabled lead lengths to be kept collector is applied to the base of the npn transistor TR2 reasonably short and a point-to-point wiring layout and the output of this is developed across the master to be easily maintained. control VR5 via the blocking capacitor C5, a part of The component disposition and wiring arrangement which is re-routed to the emitter of TR1 by R11. This shown in Fig. 3, if followed, should provide the per- provides negative feedback to the amplifier and fixes formance specifications as set out below. SPEGIFIGATION JK3 JK2 JK Single input impedance-GOO kilohms m VR3 VR2 VR Maximum Output-ZGOmV Frequency Response-20c/s to HOkc/s ± 3dB Overall Gain with any input- approximately x 1 Fig. 3. Component layout and SKI wiring of the four-chonne/ mixer 2 516 COMPONENTS ... Resistors NEXT MONTH! R1 IMQ R7 27ka R2 IM« R8 4-7 ka R3 i Ma R9 iooa R4 i Ma RIO ika R5 looka Rll IkQ R6 lOka RI2 4-7 ka Practlcdl Electronics All 10% j watt carbon mssim Potentiometers VR1 I Ma carbon, log VR2 IMa carbon, log VR3 I Ma carbon, log VR4 1 Ma carbon, log s VR5 IOkO carbon, log Q Capacitors 517 pmnimimiiHimtwiifflitHjs THE BC 342 niiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiilR Origin COMMENT: Four of the six main h.f. communica- This receiver has certain features of resemblance to tion bands allocated to the amateur service are embraced the popular aircraft BC348, dealt with here earlier, within these ranges, though to cover the 21 and 28Mc/s in several respects electrically, though not mechanically. regions (and of course v. h.f.) external converters would For example, it includes two r.f. stages, six switched be needed. bands and several other features in common with the aircraft version—and it is of much the same age, too, Power Requirements being manufactured in quantity in America 20 years If the valves are rewired for 6-3 volts l.t., a mains ago as a general purpose ground station receiver. power unit giving about 3 amps at this voltage and approximately 80raA at 250V will be satisfactory. Basic Circuit Because the BC342 was intended to operate under service conditions from a variety of power sources, space Two r.f. amplifiers, both VT86 (6K7) was allowed for a small mains power to be inserted at the First detector .. VT87 (6L7) rear left. Almost certainly this will be found to be Separate local oscillator VT65 (6C5) for the American supply voltage of 110 to 120 volts, Two i.f. amplifiers, both VT86 (6K7) in which case a step-up transformer to the British 240 Separate beat oscillator VT65 (6C5) volt level will be required. In many samples of this Second detector & audio VT88 (6R7G) receiver this change will have been made already by Output valve VT66 or VTi07 (6V6G) modifying the existing power pack, but the point should be checked at the time of purchase. COMMENT: This valve line-up is typical of that to be found in most versions of the BC342. The com- Controls bination of two radio frequency stages, two i.f. amplifiers and an audio stage driving the 6V6 output stage Central is the frequency scale (with detachable ensure a level of sound output more than adequate for escutcheon) operated by the tuning knob below through most needs. As befits a sensitive receiver the screening a set of sturdy brass gearwheels, and a convenient is exceptionally good, the case, of copper sheet, being vernier logging scale; one rotation of the main tuning virtually "leakproof" from the r.f, point of view. handle _ rotates the logging control through four revolutions—a commendable order of mechanical bandspreading. Waveranges Covered Along the top of the front panel are the aerial alignment control (it operates a 10-210 pF midget Band no. I 1,500-3,OOOkc/s. Band no. 2 3,000-5,000kc/s. trimmer well screened to obviate unwanted pick up), Band no. 3 the crystal phasing control ganged with the crystal 5,000-8,000kc/s. filter switch, and the c.w. oscillator knob. Below, left: Band no. 4 8,000-11,OOOkc/s. Band no, 5 11,000-14,OOOkc/s. the bandchahge switch. Below, right: combined i.f. Band no. 6 14,000-18,OOOkc/s. and a.f. gain control. intermediate frequency COMMENT: Inspection of the control actions and of the general construction of the BC342 discloses its 470kc/s on most versions, essentially rugged construction. The wavechange SIS a 12 volt accumulator and vibrator pack might be the power source. The private user can with no difficulty We present this month the third article ^ rewire all heaters for the more convenient 6-3 volt S our series "Classic Communication service by earthing pin. 2 or 7 of each socket and con- Receivers'*. Intended as a guide to the ^ necting the other to the a.c. low tension rail. ~ prospective purchaser of a high perform* ~ Aerial Input: Two terminals are provided. One SS ance receiver for use on the h.f. bands, this — ~ series gives the basic technical information S may with profit be disconnected and a coaxial socket — he will need without delving too deeply into S substituted (see illustration) to accept low impedance ~ the circuitry. Readers should always make — input for an external tuner unit or converter (in the — sure that a handbook or circuit diagram, S latter case this modification is essential to obviate i.f. SS at least, is supplied with any receiver pur- SS breakthrough). —* chased.. ~ Separating the Gain Controls: An unsightly "spout" at the bottom right hand corner of the front panel conveyed cableform connections to an associated iiiiiiiiiiiiiiiiiiiiiiiiiiiiuiiiiiiiiiiiiiiiiiiiiiiiiiimil COMMUNICATION RECEIVERS Block diagram of the BC342 CRYSTAL Fig' I- FILTER 1st RJ, 2(1(1 H.F. MIXER 1st Lf. 2nd l.F DEMODULATOR VTee VT86 VT 87 VT86 VT86 | AND AUDIO (6K7) (6K7) (6L7) (6K7) (6K7) FIRST AUDIO OUTPUT LOCAL OSC C.W.OSC VT 65 VT65 1605) (6C5) switch goes over with a heavy and positive "clank"; transmitter in some wartime applications. The related within, massive screening of all coil sections is combined microphone and key jacks are redundant and can be with an arrangement of covers readily removable for turned to more useful service, to feed a second headset, inspection purposes—though they need not be for perhaps. The "spout" should be removed, the resulting trimming, for all signal frequency inductors "are access- orifice being covered by a blanking plate and the ible from the back, and are clearly identified, as indeed combined gain controls separated and mounted on it are all stages and their major associated assemblies. as shown in the illustration. The refinement of internal screening puts the oscil- The redundant switch labelled "Rec Send" can lator section of the gang capacitor in a separate box, either be removed entirely or used to switch on the an Insulated spindle conveying the drive from the other mains power unit. three sections of the gang. The three position switch'furnishing a.v.c. or manual The spread of each amateur band is as foiiows, control will upon being turned to the left (to "OFF") using the main tuning knob as handset and the vernier mute the receiver output. as bandspread: Capacitors—the usual warning: The age of every BAND REVOLUTIONS SCALE WIDTH BC342 means that many capacitors will be suspect— I-SMc/s 5i 1 in and it is better to test these for leakage before switching 3-5Mc/s ' 5| l|in on rather than wait for smoke to emerge from the 7-OMc/s li ajn case! Even better, ask for a demonstration of the set 14-OMc/s 5| 2 in before purchase. Used as an i.f. strip for I44-146Mc/s, tuning over the popular range of 14-16Mc/s required no less than DON'T BE DISAPPOINTED . . . 22tj revolutions—an admirable degree of bandspreading. We receive many requests for back numbers but many have to be disappointed because Recommended Basic Modifications stocks are limited. Don't fet this happen to you. Make certain of Heaters: Pairs of valves have heaters series connected, your copy of Practical Electronics every with suitable l.t. equalising resistors where appropriate, month by placing an order with your local to permit use in the field (in a military sense!) where I newsagent or bookseller. I 519 KevioaM cantata Sir—I wonder if any of your I \ readers can suggest an answer to a problem that I am faced with. I am designing a machine to play any piano. Briefly, the method is A SELECTION FROM OUR POSTBAG that the music will be played first by a pianist on a specially adapted master piano. This adaptation will consist of electrical contacts being placed beneath each of the 85 Healthy and recent series, I felt, concentrated notes plus the sustaining pedal, the too much on valves and this is one contacts being wired to 86 tracks on constru. five field where the tremendous specially wide magnetic tape. When Sir—If the tone of this letter advantages of transistors- must any note or the pedal is pressed, an appears to be one of criticism I hope render valves obsolete. impulse is recorded on the appro- that it will be received in the spirit In a nutshell, this is a plea for priate track on the moving tape. intended—i.e. healthy and con- devices which are really worth- The playback can be on any structive. while. I hasten to add that worth- piano, by means of the following: For years most relevant technical while devices have appeared in The playback mechanism is con- magazines have issued a succession your publication but the ones tained in a casing, the length of a of "Process Timers" for photo- quoted, in my opinion, do fall keyboard, and can be placed on the graphic and other uses. I observe short in value. keyboard of any piano. There Is from the June issue that another D. Coney, an additional mechanical device to version is published. The world Lincoln. be clamped to the left pedal, to of electronics can be so useful to reach over and motivate the right the amateur (and professional) Your comments concerning the timer for photographic processes were particularly pedal. photographer. What a pity, then, of interest since we are proposing to The tape is played back over 86 that we do not appear to explore it publish details of a rather more ambitious magnetic heads, each impulse fully. From the description given device within the next few months. charging an electro-magnet which it would seem to me that the purely This device will be designed specifically motivates a plunger above one audible device implied would have for colour prints. of the 85 notes on the keyboard, been very useful some 20 or 30 We have already published a design or the sustaining pedal. Thus the years ago. I can see no point in for an electronic flash gun. However, in view of the considerable interest shown entire piece of music is replayed. constructing a device purely for the However, the problem is: Can sake of constructing it and which in this particular field, we shall be offering another design next month. the velocity at which each can do little more than simpler (and Finally, with regard to your comments individual note is struck by the perhaps cheaper) devices- which concerning the Radio Control of Models pianist on the master piano be already exist. series, I should explain that this was faithfully recorded by the impulse The photographic timer would intended primarify os on introduction to and transmitted to the playback have been of use in the days when, the subject, and no attempt was made to plunger? It is quite essential, of say, film development was carried introduce detailed designs. We hope course, to record and transmit the out by hand in the darkroom. to publish constructional projects for radio control in the future.—Ed. comparative velocities of the But, surely what the photographer various notes, for without this there requires these days is firstly, an can be no expression in the music interlocked enlarger lamp and when replayed. timer. Secondly, assistance in deter- I am assuming that impulses at mining correct exposure for given the recording stage and electro- negatives and preferably that this ffl Pfli magnets at the playback stage are information be automatically the best means to employ for this coupled to the timing device. I m mechanism. Commercial devices such as this Percy Kramer, already exist and so surely it would London, N.W.ll. be not too difficult to produce an amateur design. A method which might be helpful here, in A comparable device for use New Zealand calling obtaining control over the expression, with production of colour prints Sir—I have been interested in some would be by means of d.c. recording would also be most acceptable but techniques and use of mognet/c amplifica- of the pictures you have shown in tion. here, I would agree, we may be too your 73 Page and thought you A recently developed type of playback ambitious. might like one from overseas. head uses a ferrite core, and is sensitive I would also be interested in more New Zealand changed its licence to direct unchanging mognet/c fields, and information with reference to elec- plate system a couple of years ago to magnetisation of the tape at very low tronic flash equipment. There and I managed to hunt down the speeds, and even provides an output when appears to be a gap here which has one in the photograph which has the tape is stationary! This is because not been adequately filled. an added interest with the "88". the ferrite is arranged to comprise a In passing, I must also express Best of luck to you and your saturable reactor. some personal disappointment in If the pulse is picked up by means of page. an iron-cored search coil situated near the lack of detailed constructional ZL2RP, the piano mechanism of each individual information on transistor trans- Lower Hutt, note, it may be passed on to o mognet/c mitters for Radio Control. The New Zealand. amplifier. Small magnets may be attached 520 Enjoy yourself and Save Money I by Building Heathkit models A wW* rang* of well designed quality kit sets to choose from A KIT FOR EVERY INTEREST... HOME, SERVICE WORKSHOP, LABORATORY Eue of membly is guaranteed AUDIO Even fop thote without previout experience—by the comprehentive, Cabinets, Turntable units, Mono and Stereo Amplifiers, Pick-ups, yet simpte. step-by-scep construction manuals supplied with every Speakers, Speaker Systems, Mono and Stereo Control Units, Tape Heathkit model. Pre-amplifiers, Tape Decks, Transistor Mixer. Save £ £'* building the models RADIO Heathkit units cost considerably less than comparable pre-assembted AM/FM and FH Tuners, Transistor Radios, SW and Communication equipment. You cannot buy the parts any other way as cheaply. Receivers. Guaranteed performance Every Heathkit product—assembled in accordance with our com- TEST INSTRUMENTS prehentive construction manuals is guaranteed to meet published A wide range of Audio Test, Home Workshop, Service and Laboratory performance specifications, or your money will be cheerfully Instruments. refunded. AMATEUR GEAR Convenient credit term* A wide range of equipment. By taking advantage of our credit terms—you can enjoy your mode) MISCELLANEOUS right away—and pay for it in easy monthly instalments. Deferred Hobby kits for the youngster. Tool kits, Intercoms, Electronic Organs, terms available over £10 in U.K. PA/Guitar Amplifiers, etc. TRANSISTOR SIGNAL VALVE TV ALIGN. •SCOPES POWER SUPPLIES TESTER GENERATORS VOLTMETERS GENERATORS Instruments Test, Service. Home Worksho J In. LOW-PRICED OSCILLOSCOPE. Model TRANSISTOR TESTER, Mpdel IM-30U. Un- 05-2. Ideal for servicemen. Compact: 5*X 7i' matched in quality, performance and price. Pro- 8 in. DE LUXE VALVE VOLTMETER,Model XI2'. Wt. 9J lbs. "Y" bandwidth,!c/s—3 Mc/i, vides complete d.c. analysis of PNP. NPN transis- mIM-I3U. 7 ranges. Measures Res. icto and 1,000 dc volts Mn 0-1.S in to7 ranges.1,500V T/B 20 c/s—200 ke/s in 4 ranges- Kit £22.18.0. tors and diodes. Internal battery for tests up to Modern styling, with gimbal mount. Kit £18,18.0. Assembled £30.8.0. 9v. Kit £24.18.0. Assembled US.IO.O, Assembled £26.^8.0. Freq.R.F. SIGNALcoverage fromGENERATOR. 100 kc/i-100 Model Hc/s onRF-IU. six TV ALIGNMENT GENERATOR, Model toMULTIMETER. 1,500 v A.C. and Model D.C. MM-(U.ISO txA Rangesto ISA 0-1.SvD.C.; bands on fundamentals and up to 200 Hc/s on HFW-I, 3.6 to 220 Mc/s on fundamentals. 0.2 to 20 MO. in. 50uA meter. Kit £12.18.0. calibrated harmonics. Kit £13.8.0. Assembled fixedUnique and electronic variable markersweep generatorsoscillator. (5Built-in Mt/s Assembled <18,11.0. £19.18.0. . - crystal). Kit £37.18.0. Assembled £47,10.0. Sin. FLAT-PACED OSCILLOSCOPE. Model FULL RANGE OF MODELS IN DECADE RESISTANCE. Model DR-IU. Range IO.I2U. Lab. performance at utility 'scope price. 1-99,9990 in I n steps. Kit £10,8.0. Assembled 'Y bandwidth 3 c/s to 4-S Mc/s. TB 10 c/s to 500 kc/s FREE CATALOGUE £14,8.0. in 5 steps. Built in Ivcalibrator. Dim.:8}'wx SfMPiT SEND COUPON BELOW TO H' h x 17* deep. Kit £35.17.6. Assembled Dept. PM, Gloucester DECADElOOpcpF to 0.111CAPACITOR. itf in 100 uuf Model steps. DC-IU Kit £7.S.O.range, £45.15.0, Assembled £10.8.0, Miscellaneous construction ■MALVERN" EQUIPMENT "OXFORD" LUXURY TRANSISTOR TRANSISTOR GENERAL COVERAGE CABINET. Will house all your Hi-fi equipment. PORTABLE, Model UXR-2. Beautiful solid RECEIVER, Model GC-IU. Frequency coverage LeftKit £18.1.0"in the (inc. white." P.T.). SizeA wide39i xrange 32 xof 21! other in. leather case, LW and MW Coverage. Kit 580 kc/f—30 Me/s in S bands. Kit £37.17,6. cabinets. £14,1833 (inc. P.T.) Assembled £45.17.6. RG-I.GENERAL Freq. COVERAGEcoverage 600 kc/s-1.SRECEIVER. Mc/s. Model1.7-32 20 + 20W TRANSISTOR AMPLIFIER. HI-FI FM TUNER. Range88-1 OS Mc/s. Available Mc/s in 6 switched bands. Many features incl. Model AA-22U. Outstanding performance for in two units, sold separately. TUNER (FMT-4U) J lattice crystal filter. Kit £39.16.0. Assembled price. Send for full spec. Kit £39.10,0, less 10.7 Me/s IF £2.15.0 (inc. P.T.), IF AMPLIFIER £53.0.0. cabinet. Beautiful cabinet £2.5.0 extra. Total(FMA-4U) Kit £16.8.0. power supply and valves £13.13.0. 6W QUALITY STEREO AMPLIFIER. Model S-33H. An inexpensive stereo/mono amplifier. The Berkeley SPEAKER SYSTEM. New JUNIOR ELECTRONIC WORKSHOP. Ideal for use with the Oecca Deram lightweight construction gives faster assembly. Professionally Model EW-I, 20 exciting experiments can be pickup. Modern attractive styling. Kit £15.17.6. styled walnut finished cabinet. 2 speakers cover made. Special solderless connections. Kit Assembled £21.7.6. 30 c/s—17,000 e/s. Only 7i'deep X 26* h X 17* £7.13.6 (inc. P.T.) STARMAKER-33 TRANSISTOR PA/Guitar wide. Kit £18.18.0. Assembled £23.0.0, TRANSISTOR MIXER. TM-I. A must for AMPLIFIER. Full 20 warn (33 watts IHFM) SSU-I SPEAKER SYSTEM. A practical the tape enthusiast. 4 inputs, 9 v, battery heavyoutput. duty Four speakers. inputs onCompact two size.channels. Tremolo. Two solution to the problem of a low-price speaker operacien. Kit £11.16,6. Assembled £16.17.6. Elegant cabinet. Kit £44.19.0, Assembled system. Two speakers. {Bookcase) £11.17.6 All prices quoted are mail order. £59.10,0, legs or castors extra. P.T.) (inc. P.T.) (With legs) £12.12.0 Kit (inc. See the complete Heathkit range in the FREE catalogue RECORD PLAYERS TAPE DECKS CONTROL UNITS QUALITY r—Y HI-FI STEREO and MONO TRANSISTOR SW RECEIVERS FM A AM/FM CABINETS AMPLIFIERS PORTABLES TRANSMITTERS RADIO TUNERS SPEAKER ^ViV-V.VV.V SYSTEMS Welcome To Our To DAYSTROM LTD., DEPT. PM-7, GLOUCESTER, ENGLAND LONDON HEATHKIT CENTRE Please send me FREE BRITISH CATALOGUE (Yes/No) 233 Tottenham Court Road We open MON.-SAT. 9 a.m.-5.30 p.m. Full details of modeI($)..„ THURS. 11 a.m.-2.30 p.m. American NAME Telephone: MUSeum 7349 (BLOCK CAPITALS) WHEN YOU ARE IN TOWN. WE HOPE Catalogue I/- p.p. ADDRESS. THAT YOU WILL VISIT US THERE (Yes/No).. PM-7 521 VARIABLE VOLTAGE TRANSFORMERS INPUT 230/240v. A.C. 50/60— TRANSISTOR ELECTRONIC OUTPUT VARIABLE 0.260v. 1 LIGHT SENSITIVE SWITCH BRAND NEW Carriage Paid.l Kit of parts, including ORP(2 Cad- Buy direct from the importer,! mium Sulphide Photocell, Relay, ORGANS FOR THE AMATEUR keenest prices in the country." Transistor and Circuit, etc., price All Types (and Spares) from 25/- plus 2/6 P. & P. ORP 12 in- by Douglas. 19/- i to 50 amp. from stock. cluding circuit, 10/6 each, plus OPEN TYPE (Panel Mounting) 1/-P.&P. TRANSIST0R SPECIFICATION AND j amp, £3. 3. 0. I amp, £4. 17. 6. A.C. MAINS MODEL f SUBSTITUTION HANDBOOK, by Tech- 2}- amps, £5. 12. 6. Incorporates Mains Transformer, Rectifier press. 16/- SHROUDED TYPE and special relay with 3, 5 amp mains c/o lamp, £4. 10. 0. 2.5 amps, contacts. Price inc. circuit 47/6 plus 2/6 BENCH SERVICING MADE EASY, by £5. 17. 0. 4 amps. £8. 7, 6. P- & p. Middleton. 25/- S, amps, £9. 0. 0. 8 amps, 50 AMPS £13. 10. 0. 10 amps, £17. 0. 0. NEW! PHOTO ELECTRONIC COUNTER TRANSISTOR ETCHEO-CIRCUIT PRO- 12 amps, £19. 10. 0, IS amps, Can be set for counts of up to 500 per JECTS, by Kyle. 25/- £22. 0. 0. 20 amps, £32. 10. 0. minute. 210-250 v, A.C. powered. - Kit of HOW TO BUILD PROXIMITY DE- 37.5 amps, £65.0. 0. 50 amps, ■ Components including photo celt. High £85. 0. 0. I speed non-resettable counter. Transfor- TECTORS & METAL LOCATORS, by ikW PORTABLE TYPE mer.relay, etc., together with clear circuit Shields, 21/- 2.5 amps, Portable £9. 17. 6. I diagram. £3.2.6, plus 2/6 P. & P.- KNOW YOUR SQUARE-WAYE & PULSE 100 WATT POWER SANGAMO WESTON GENERATORS, by Middleton. 22/- RHEOSTATS (MEW) Type S32 2s Edgwise Meter SOLAR CELL & PHOTOCELL, experi- m 250 Micro-amp,, scaled in dB's, New AVAILABLE IN THE 29/6, P. & P. |/-. menters' Guide, by Hoberman, 25/- FOLLOWING VALOES MULLARD REFERENCE MANUAL OF 10 ohm, 3 a.; 25 ohm, 2 a.; 50 ohm, 230 V. A.C. MOTOR"MOTOR and REDUCTION GEAR BOX TRANSISTOR CIRCUITS. 13/6 1.4 a.; 100 ohm, I a.; 250 ohm, .7 a,; Reversible vs h,p. I.4S0 r.p.m. 500 ohm, .45 a.; 1,000 ohm, 280 mA; dia. J* long shaft. Mounted in anti- COMPUTER CIRCUIT PROJECTS YOU 1,500 ohm, 230 mA; 2,500 ohm, .2 a. rib ration cradle. CAN BUILD, by Boschen. 22/- Diameter 3im. Shaft length Jin., Supplied complete with pre- dia. Jjin. All at 27/6 each. P. & P. 1/6. cision 20—1 reduction gear box ELECTRIC GUITAR AMPLIFIER HAND- and pulleys. BOOK, by Darr. 24/- NOW ALSO AVAILABLE Made to highest standard for computer work. Ex equip. IN 25 WATT First-class condition. Price £3.5.0. P. & P. 7/6. KN0W YOUR SIGNAL GENERATORS, 10 ohm, 1.5 a.; 25 ohm, I a.; SO ohm, by Middleton. 21/- .75a.: 100 ohm, .5 a,; 2S0 ohm. .3a; SOUND POWER OPERATED • METERS All prices include U.K. postage ' SOOohm. .2 a: 1.000 ohm. ,15 a; I.SOO EX-ADMIRALTT HEAD l2^' Plush Round ohm, .12a.: 2,500 ohm, .1 a; all at AMMETERS Where possible 24-hcur service guoronteed 14/6. P, & P. |/6. AND BREAST SETS IP in 'nJi0-1,0-5, ' 0-10, 0-15, Two such sets connected 0-20 Amp, All 21/- "CABY MULTI-RANGE TEST up will provide perfect each, p. & p. extra. UNIVERSAL BOOK GO. METER Model B40. D.C. vole, intercom. No batteries , A,C. VOLTMETERS 0-5 v., 2-5 v. at 10.000 required. Will operate I 0-25. 0-50. 0-150 V. 12 LITTLE NEWPORT ST., LONDON, W.C.2 ohm per volt. Ideal for up to ^ mile. Price 17/6 | All 21/-each, p. & p. (Leicester Square Tube Station) transistor circuit test- each plus P. & P. 3/- or • extra. 0-300 V. A.C. ing- A.C. and D.C, 32/6 per pair. P. & P. S/6. | m/c Rectifier £1.9.0. volt, l0v.,S0v.,2S0v„ 500 v.. J.OOOv. at 4,000 UNIVERSAL DEMONSTRATION TRANSFORMER ohm per volt. Resis- A complete composite apparatus, com- tance. 2K ohm, 200 K Scemyl Type prising a Transformer and electro- ohm, 2 megohm, 20 magnet with removable coils and The most accurate __ megohm. pole pieces. Coil tapped for Price Includes Test Leads, Battery, 230v, 220v, I lOv, 115v; 6, 12. Instruction book, Packing and Post 36, HOv. A.C. These coils are pocket size (U.K.). £6.2.6, 3 additional models also used for D.C. experi- available from 54/- to £14.14.0, ments. _ Complete with all Leaflet gladly'senc on request. accessories as shown. £17 + CALCULATOR Q 10/- carriage. Leaflet on 34R SILICON SOLAR CELL request. — in the world u^ 10 scriesn connected output NICKEL CADlUM"BAfTERY the.? efficiency' of selenium. sunlight. As 30used times to Sintered Cadium Type, l.2v. 7AH. Size: height 3i", width 2rx Hr. Weight: approx. 13 ozs. Ex R.A.F., power Earth Satellites. 37/6. P. &p. 1/-. tested 12/6. P. & P. 2/6. 230 VOLT A.C. GEARED Send a postcard S.T.C. SILICON POWER .RECTIFIERS MOTORS RS300 Series. All types 1.5 amp. wire ended. RS3I0. today for free 5 r.p.m. I.7lb. Inch £2.9.6. P. & P. 2/6 100 v. P.I.V.4/-, RS330, 300 v. P.I.V. 6/-, RS340, 400 v. 80 r.p.m. ■261b. inch £2.2.0. P. & p. 2/6 P.I.V. 7/', RS3S0. 500 v, P.I.V, 8/-, RS360. 600 v. P.I.V. booklet, or if you u — ' " RS380, 800 v. P.I.V. 10/-. 4 can be used to ' * LATEST HIGH SPEED MAGNETIC COUNTERS make 3 amp. bridge. Not Seconds. Brand New prefer, send 75/- Mm 4 figure '0 impulses per second. Type I00O.4.I ohm C qperation T e Stock. Postpaid. oiV 5 0- at . n - 7P '00A. SOOohm coil, SOLENOID. Overall length 31", stroke i' forthis invaluable m « ' ^9: Pe'" '9 - Type '00B, 2,300 ohm coil. to i*. Maximum push 8 oz. 12-24 v. D.C. '||j 1/6 P & p operation. Any type, IS/- each, plus operation, D.C. resistance 35 ohm. Price 8/6. spiral slide rule P. & P. 1/6. on approval. L.T. TRANSFORMERS All primaries 220-240 volts. ULTRA VIOLET"BULBS" VJiv Type No. Sec. Taps Price Carr. Easy to use source of U.V. for dozens of with money back I 30, 32, 34, 36 v, at 5 amps...... £3.5,0 6/- practical and experimental uses, 30,40, SO v. at 5 amps £5.5.0 12 volt 36 watt A.C./D.C. SBC 6/6. guarantee If not I 10, 17, 18 v. at 10 amps £3,10.0 12 volt 60 watt A.C./D.C. SBC 8/6. 6, 12 v. at 20 amps £4.17,6 P. & P. I/-on above items. 17, 18, 20 v. at 20 amps £5.12.6 Transformer to suit the above. Input 200- satisfied. 6, 12, 20 v. at 20 amps. £5.5.0 240 v. A.C., 12 volt 36 watts. 16/6; P. & P. • 24 v, at 10 amps £3.15.0 2/6. Input 200-240 v. A.C. 12 volt 60 watt, /pnTi 28, 29, 30, 31 v. ac 21 aipps £7.10.0 10/- 22/6. P. & P. 3/6. CARBIC LTD. \booklet oh (Dept. PE5), \reooest SERVICE TRADING CO 54 Oundonald Road All Mail Orders—Also callers: Personal callers only 47/47 HIGH STREET, KINGSTON on THAMES , 9 LITTLE NEWPORT STREET London. S.W.I9 Telephone; KINgston 9450 LONDON, W.C,2 Tel.; GERrard 0576 522 paid for out of the membership fee of 10s Od per year. CAN YOU HELP? If anyone is interested in starting Letters for inclusion under this heading should be as brief as possible. Replies should be made an electronics group elsewhere 1 direct to the readers concerned. A SELECTION FROM OUh HOSTUAb would be very pleased indeed to give them any help they may Sir—I would be very much obliged if require based on my own experience any reader could let me know where continued when 1 started the St. Cyres I can get the March 1966 issue. Electronics Group and this club. R. Schofield, 23, Alwyn Avenue, to the mechanism of each note in order to We have other very interesting Litherland, Liverpool, 21, induce a pulse in the search coil. There projects lined up for the future and Sir—Could any of your readers is thus, in the master piano, a search supply me with the January J966 coil and magnet, and a magnetic amplifier also hope to publish a Newsletter issue. 1 will pay full charge and of for each note which may be sitaoted giving details of our activities, course postal rates. either in the piano itself or in the ancillary together with reports on affiliated C, J. Dee, 13 Vulcan Crescent, North equipment. groups. Starting next September Hykeham, Lincoln, Lines. The output of each magnetic amplifier we will show technical films at may be arranged to be d.c. of one meetings and have discussions on Sir—I am interested in purchasing polarity only, and this is used to activate them, as well as our special back numbers of Vol. I. I am willing the recording head coils. projects. to pay" cost price of each copy and Upon playback the saturable playback postage, heads will react to the d.c. magnetisation Cyril Bogod, A. Clement, 14 Greepmill Road, (which is proportional to or a function of Penarth, Longtown, Cumberland. the original pulse), further magnetic Glam. amplifiers would then activate the Sir—I have been trying to obtain the e/ectro-mognetfc actuators, causing the following copies; November 1964 fceys to be struck with a force related to to September 1965 inclusive. I am the original. flegenerative feedback willing to pay a fair price for these It appears that magnetic amplifiers Sir—I would be obliged if you copies in reasonable condition. would have certain advantages over could help with a point of elec- John Carrell, 41 Atkinson Road, valves or transistors in this app/icotion, tronics theory. Sale, Cheshire, Not the least would be the high sensitivity, power obtainable, and better controi over I am at present working on a Sir—Could any of your readers the energy transfer charocfer/stics. project to design a school -elec- supply me with the • February and Possibly with a system of this nature, tronics course, approached via March 1966 issues. timing problems would be a big factor, and semiconductors. One of the • R. B. Summer, Bruce House, Stowe, it may be possible to achieve best timing circuits 1 have constructed is a Buckingham, . oniy by making a simultaneous audio perfectly conventional, RC recording of the master piano piece and coupled, three stage amplifier using Sir—I need the December 1964 and correcting the master tape after careful three GETIH transistors. January 1965 copies to complete my comparison with the audio recording. set of issues. You will no doubt find there are many The amplifier functions perfectly M. Beeforth, 2 Sunset Rise, Mean- technicai difficulties involved in this while I used a 9V bench supply^in the wood, Leeds 6, Yorkshire. project. It is quite a hefty development laboratory. Recently the l.t. unit job. I hope my suggestion of magnetic was being changed and I used in its Sir—Please would any reader send amplifiers and a saturable ferrite playback place a 9V battery. The amplifier me an August 1965 issue. head is of some help.—AJ.8. immediately produced a very high P. Ashford, 24 Sunningdale Road, audio frequency oscHIation. When Denton, Manchester. the input terminals where shorted British amateur Sir—If any reader has the November together the oscillation reduced in to March 1965, also May and Septem- electronics club frequency but emerged at full gain ber 1965 issues, complete with blue- from the loudspeaker. prints, to dispose of I would pay him Sir—I am writing to inform you Returning to the bench supply a fair price. that the St. Cyres Eiectronics the oscillation disappeared. Using A. J, Campbell, "Uplands", 101 Group has changed its name to separate 9V packs for each stage Oliver's Battery Road, Winchester, The British Amateur Electronics also removed the oscillation. Hants. Club. I have not yet found a theoretical The aim of the B.A.E.C. is to explanation for this effect. Can Sir—I would be very grateful if any fulfil a similar function in the field you shed any light on the problem? reader of Practical Electronics of general electronics to that per- could sell me a handbook for P. Green, HalHcrafters Model S-38A. formed by the British Amateur Beckett Park, M. A. Batt, Post Office, Rokewood Television Club in its own Leeds, 6. Junction, Victoria, Australia. particular field. I am very grateful to Mr. D. Mann, the Hon. Secretary The impedance of the 9V battery wos Sir—I would be grateful if any reader and Mr. Grant Dixon a founder providing regenerotive feedback. The could sell or loan me information on member of the B.A.T.C. for their internal impedance of a battery increases the cells, lens system or a suitable help and for allowing me to copy a with its discharge state. power supply for "Tabby, Type E", infra Red binoculars. large part of their constitution. Since the loop gain of the unit is J. C. Duncan, 18 Grove Park, The first project this session will greater than unity, with the input Wanstead, London, E.U. be an electronic shooting gallery grounded conditions ore right for the amplifier to function as a phase-shift which we hope to have ready to oscillator. This might be proved by demonstrate to the public in aid of inserting a low value potentiometer in the charity by August. All the com- Back humbers are usually very quickly ex- battery lead. If this is varied you will hausted. We strongly advise all our readers ponents wilt be supplied to the probably find that the pitch of the that a standing order be placed with their news- members free by the club, being osciflation will change.—C.G. agent to avoid any future disappointment. 523 A Commentary on Souna Reproducing Equipment ny Clement Brown ■■y This -month, more than the usual variety of tech- nical developments compete for attention. Not only were many new products introduced at the Audio Fair, but a wealth of American equipments, many of them unfamiliar to British enthusiasts, were also shown at an exhibition in London. BETTER RECORD REPRODUCTION As far as British and some imported disc equipments Leak stereo pick-up are concerned, the Audio Fair provided confirmation of trends that were apparent during the last year or so. already familiar model but has the high compliance of Greater understanding of pick-up requirements have 6 taken us well beyond a quest for wider response: 20 x JO- cm/dyne and a vertical tracking angle of manufacturers can now claim more success in lessening 15 degrees. An elliptical stylus is fitted, and there is a the audible effects of distortions inherent in record new method of stylus arm mounting to give better reproduction. Tracking distortions can detract more protection against damage. from clear, musical results than any other flaws in the Further down the price range is the CS91/E, the audio system are likely to do; but disc reproduction most recent version of Goldring's ceramic stereo at its best is superior to anything achieved with other cartridge. Compared with the familiar CS90, it programme sources. can be tracked at a lower pressure; the compliance Customers for pick-ups of really high quality will is higher and there is an elliptical tip. This cartridge of course look for such features as low playing weight, exemplifies what is being done to offer a good standard smooth response and high head compliance. However, of performance with reduced record wear—at moderate there can be no warranty of secure tracking and good cost. performance unless the pick-up presents a small In the more advanced arms, intended for very low mechanical impedance to the groove; hence a greater playing weights, the reduction of pivot friction is emphasis on small effective tip mass (as low as 1 essential. It is equally vital to ensure that connecting milligramme) and the taming of resonances. The mass wires passing round the pivots do not introduce of arm/head combinations are further reduced in appreciable friction or torque. This particular snag recent models. does not arise in a new laboratory arm by Audio & Design, who have ingeniously incorporated mercury NEW PICK-UPS baths in the pivot pedestal. Signals from the head pass, via small electrodes, through the mercury and Leak's new stereo pick-up, an integrated arm and thence to the lead-out cables. head, is a variable reluctance design intended to track at 2 grammes. The tip mass is quoted as less than 1 AUDIO ELECTRONICS milligramme. Other specification points include 10 x 10_8 cm/dyne compliance, channel separation of On the electronics side of audio the application of 25dB at 1,000 c/s, and average output of 6mV. An transistors is clearly the focus of interest. This is elliptical stylus is fitted. The arm, which features a a time of steady development, and performance stan- viscous-damped unipivot, has a raising and lowering dards are gradually being raised. One of the most device. Price is £26 16s. 6d. interesting amplifiers in the popular price range is A new version of the Ortofon moving-coil head, imported by Metro-Sound, is basically similar to the Audio & Design pick-up and mercury bath BUILD 0VEI^ ^ ft# ft# I b ■# CIRCUIT/EXPERIMENTS -hiast&r ete&ramcs the |^rnakit way No maths — No unnecessary theory NO PREVIOUS KNOWLEDGE NEEDED BUILD A PROFESSIONAL CATHODE RAY OSCILLOSCOPE Learn how to READ AND DRAW CIRCUIT DIAGRAMS RECOGNISE, HANDLE AND UNDERSTAND every type of modern ELECTRONIC COMPONENT OVER 40 EXPERIMENTS — including:- Valve Experiments # Square Wave Generator Transistor Experiments # Morse Code Oscillator Electro-magnetic Experiments # Simple Transmitter Basic Amplifier % Electronic Switch Basic Oscillator 0 Photo-electric Circuit Basic Rectifier 0 Basic Computer Circuit Signal Tracer 0 Basic Radio Receiver Simple Counter 0 A.C. Experiments Time Delay Circuits D.C. Experiments This complete practical course will teach you all the basic principles of electronics by carrying out experiments and building operational apparatus. You will learn how to recognise and handle all types of modern components, their symbols and how to read a complete circuit or schematic diagram. The course then shows how all the basic electronic circuits are constructed and used and HOW THEY ACTUALLY WORK BY USING THE OSCILLOSCOPE PROVIDED. An application is given in all the main fields of electronics, i.e. Radio; control circuits; computers and automation; photoelectrics; counters, etc., together with rules and procedure for fault finding and servicing of all types of electronic equipment. For a new and exciting approach which gives a real understanding of electronics In an entirely practical way— this course has no equal anywhere to-day. r POST NOW FOR FREE COLOUR BROCHURE 1 To: BRITISH NATIONAL RADIO SCHOOL, READING, BERKSHIRE Please send free Brochure, describing your LERNAKIT Oscilloscope Course without obligation, to: i NAME I ADDRESS etOCK CAPITALS PLEASE OR WRITE IF YOU PREFER NOT TO CUT COUPON (No representatives employed) P.E.7.66 L J British National Radio School 525 KING'S TELE-SERVICE CO. The hard-to-find man Electronic Engineers is the man with (Sole distributors for Radio Bleep Ltd.) advanced technical Micro-Miniature Components knowledge Micro-Microphones. In the field of Electronics today the greatest demand is for men to fill the positions of skilled Flea Size Transistors. technicians and support engineers. These are the 'hard-to-find' men for whom the way ahead to Full range of American Tunnel rewarding and Interesting Jobs lies wide open. Diodes. Perfect for high frequency CREI HOME STUDY COURSES offer advanced oscillation at excess of 100 m/cs at technical education to the man who realises that technical knowledge must be current and up-to- only 1.5 volts. date if progress is to be made in a world in which new ideas, new techniques and new applications Condensers you need a magnifying develop almost overnight. lens to see. CREI COURSES ARE AVAILABLE IN:— Electronic Engineering Technology Prototype Printed Panel Division Automation & Industrial Electronic Engineering Nuclear Engineering for your Panels. Communications Engineering Aeronautical & Navigational Engineering All Photographic Resist Materials Television Engineering Servomechanisms & Computer Engineering and Developers available. Space Data Systems Radar & Servo Engineering Miniature Resistors. Mathematics for Electronic Engineers City & Guilds of London Institute: Subject 49 & Supplementary Studies Subject 300. Call and see us and bring your magnifying lens For further information write to : C.R.E.I. (London) (Dept. P.E.2) 105-107 DAWES ROAD WALPOLE HOUSE, 173/176 SL0ANE ST. LONDON, SW1 Telephone: BELgravia 8662 FULHAM, S.W.6 International Division of Capitol Badio Engineering Institute, Washington, DC FULHAM 1668-2998 526 the Goodmans Maxamp, which employs silicon transistors. Others include a new Elizabethan model: it is a shelf-mounting unit, catering for magnetic and ceramic pick-ups and rated at 10 watts per channel. The price is 39 gns. Howland-West showed prototypes of transistor amplifiers which are due for production in August. System One, as the first model is called, incorporates a new type of output stage and is rated at 12| watts per channel. A power response of 20-20,000 c/s is claimed. A second model, System Two, is also promised. Tape recorders, especially portables, are mostly transistorised, and exceptions to the rule become fewer. On the other hand it is noticeable that many Elizabethan Princess stereo amplifier professional machines depend on valves: this is true . Finally a note on audio from the U.S.A. The of the Brenell and Ferrograph recorders and some other American manufacturers, at their recent hi-fi show, top-class instruments seen recently. were seeking U.K. agents for their products. Of Decks include two by Scopetronics. Their type course, some firms—for instance Dynaco, Fisher and 825, costing £49 10s., has 1% and 3|in/sec speeds, Shure—already sell in this country. Nevertheless and the selection of speed is effected by changing over there are untapped riches of which one hopes to see the number of poles in the capstan motor. Four heads more in the future. Price levels are generally high, can be fitted. A larger deck, type 1150, operates at but the exhibition provided much evidence of technical 15 and 7iin/sec and accepts spools of up to lliin ingenuity and smart design. diameter. AMERICAN PRODUCTS SPEAKER SYSTEMS Firms represented by Delrama included Acoustic New speaker systems and drive units continue to Research, whose excellent speakers and turntables arrive in variety. Among the compact systems are have received limited attention in the U.K. before. the Decca Kelly-Mini and the Leak Mini Sandwich. Other turntables included two Rek-O-Kut models and The latter employs methods of design and construction the Marantz zero-tracking-error model, which has a already made familiar in the standard Sandwich radial pick-iip arm. Empire, Grado and Pickering system. Other small speakers are the Rectavox Ambi were among the pick-up specialists. Tape equipment (£36 IOs.), the Sonotone Solent (£18) and the Truvox included high-quality machines by Crown and Ampex, LS.120 (19 gns.). the latter's reputation being such that 800 and 2,000 Among the new floor-standing speakers is the KEF series recorders were used for demonstrations by the Concord, the successor to the Duette. This nice- other exhibitors. looking model, measuring 24in x 15in x 9|in, sells Only one or two of the many speaker firms can be at £39 19s. Constructors should note that a brochure mentioned. Although compact models seem fairly of enclosure designs is available from .KEF Electronics popular, there are at least as many large, heavy-duty Ltd., Tovil, Maidstone, Kent- The latest big speaker systems on the American scene. Those by J. B. from Wharfedale is the Teesdale (£52 10s.), and there is Lansing and Sherwood are intended for large rooms also a new 12in drive unit, the W12/FRS. and gracious living. Nearly all American speakers are multi-unit systems with crossover filters. KEF Concord loudspeaker cabinet The first thing one notices about the tuners and amplifiers is the predominance of smart metal control panels. Then one becomes absorbed in technical matters, notably the wide use of elaborate transistor circuits (no expense spared). Some power ratings seem unnecessarily high, even taking low efficiency speakers into account; but obviously a generous power reserve means small distortion under practical conditions. Some names to look out for are CM, Electro-Voice, Mclntosh and Sherwood. As befits the size of the market, American enthusiasts enjoy an impressive choice, and the chances are that we shall be sharing some of it with them if things go well. Scopetronics 82S tape deck detached particles JOHN VALENCE TABS ON THE DABS Coupled with this plan is the Well I suppose it is no good intention to overhaul ail relevant preaching standardisation and then Quite a bit of controversy has standards. The Ministry of Tech- raising objections in particular arisen over the Home Office nology is now responsible for spon- instances. The balance seems now suggestion that perhaps everyone's sorship of the British Standards decidedly in favour of Hertz and I am fingerprints should be recorded as Institution -and so will have a direct afraid we shall soon be saying a part of the campaign to stamp out influence upon its deliberations. reluctant good-bye to our old friend crime. There will be bitter argu- "c/s". But it won't be easy to ments about whether or not this is an readapt oneself after years of writing infringement of individual liberty. GOODBYE TO C/S ? kc/s, Mc/s and plain c/s. This apart it is not altogether certain So far as symbols and abbreviations that the proposal Is feasible from a used in electronics are concerned, technical point of view. there is already a fair degree of RATHER SHATTERING Classifying the "dabs" of some conformity between different Those Jiving in the vicinity of a 60 million people would be quite an countries. major airport will readily accept the undertaking even for that prodigious But one important case where we claims made for the demoralising machine the electronic computer. do differ from the continentals is in effectiveness of the "Curdler." However some experts think that there is a good chance of sorting out the fingerprints by measuring the sines and cosines of the arches, loops and whorls which make up fingerprint patterns. At anyrate, IBM for one are busily Investigating this possibility. Where will all this recording and tabulating of persons end? Will the ■ ill A stage ever be reached where it will be possible to locate instantly any individual through the medium of an implanted device—as a colleague of SQUAD mine suggested the other day? RIO Perhaps a -somewhat nightmarish thought, but it is reasonable to suppose that technology will be called upon to play an ever increasing role in the fight against crime. GETTING IN STEP Whether we ever get into, the Common Market or not—we shall at least be going metric. The com- " I said ft would be no good at a pop festival—they're dancing to It!" mitment has already been made by the Government and more recently the terminology used for frequency. This, In case you have not already the Minister of Technology While we have been quite happy heard, is the latest device for quelling announced his intention of establish- with cycles per second and the unruly mobs. A kind of super ing a nationwide calibration service. abbreviated form "c/s", it has long public address system with a built-in This has been decided upon with the been common practice In other noise generator, the Curdler has been full encouragement of industry as a countries to use "Hertz", and the devised to bombard troublesome further step towards getting our house shortened form "Hz", for this crowds with a raucous output of such in order and in tune with other purpose. intensity and tonal character that the countries. The Americans, although 3,000 disorderly elements are well and truly Not least of the reasons behind miles or more from Europe, have now stunned, frozen in their tracks, and this decision is the handicap our decided in favour of "Hertz" and the finally compelled to retreat with export trade is suffering because of change is already , apparent in hands clamped to ears. They are the present lack of authenticated technical literature originating in the luckier in this respect than some calibration certificates for certain U.S.A. In face of this, can we in this householders who just have to sit and measuring instruments and equip- off-shore island hold out much take it when another VC10 or 707 ments made here. longer against our close neighbours? shrieks its way over the roof tops. 528 LAFAYETTE HA-4J TEST EQUIPMENT COMMUNICATION PORTABLE OSCILLOSCOPE CT.52 a RECEIVER 10A compacte/8.40 tc/s. (9'X8*X Band 161*)width general1 Mc/a. purposeMnllard "scope. PG 7/6 T/B 2}* CHT. Forope»»UoBOn200/260 v.A.C, Supplied complete 7 valves plus Rectifier. 4 Bands, ttfldkc/s- with metal transit case, strap, teat leads, and visor hood. Qcclc'&C) 31 Mc/a. "S" Meter—BFO—ANL—Band- Brand new. 422.10.0. Can*. 10/-. Supplied complete with Mm >'ewspread £4 Tuning.0m. Carr. 200/250 Paid. v. A.C. Brand InstruetloM. OS/B8/U OSCILLOSCOPES LAFAYETTE HA.230 AMATEUR High quality Portable COMMUNICATIONS RECEIVER American OscIUaacope. 3* Supenedea model HE-SO. 8 vslvet + rectifier. C.r.t. T/B 3 c/b-60 kc/» X ERSKINE TYPE 13 DOUBLE Continuous coverage on 4 bands. 650 K«/e— Amp i 0-500 ko/e Y 30 Me/s. Incorporates 1 HP & 2 IP stages, Q Amp: 0-2 Mc/s. Power BEAM OSCILLOSCOPE Multiplier, B.P.O.. AJ)t, "8" meter. Electrical 0 requirements 105-125V. Time base 2 c/e-760 kc/s. Calibrators at bandapread, Aerial trimmer, etc. Supplied brand newA.O, Suppliedcondition, in brandfully 100 kc/» and X Mc/a, Separata Y1 and Y2 newAlso and available guaranteed. in aem] *33. Kit Form.6.A.E. SS tor gns. lull details. tested. 426. Carr. amplifiers up to 5.5 Mo/a- Operation 10/-. 8uf table 230/U6v. working110/230 order.volt A.C. 427/10/-. Supplied Carriage in perfect 20/-. LAFAYETTE HA-SSA Transformer 16/9. AIRCRAFT RECEIVER TE-20 RF SIGNAL GENERATOR Accurate wlda range signal 108-138 Mc/s. High selectivity and generator covering 120 kc/8.-280 Includingsensitivity. 6CW4 Jncorporntes Nnvlstor, 28 HPtubes stages (or «■ Mc/s on 6 bands. Pirectly 11 tube perlommnoe. solid state power attenuator.calibrated. OperationVariable 300/240R.F. supply, adiustable squelch control, slide v. A.C. Brand new with In- o rule dial, built In 4ln. speaker and Iront structions, 412.10.0. P. i p. © o Suppliedpanel phone brand, jack. new 220/210V.and guaranteed. A.C. 7/6. Ground119.7.6. PlaneCarr. Antenna 10/-. 68/5.108-J7S - Mc/a 8Jt.E. for details. HAM-I COMMUNICATION LAFAYETTE NUVICTOR RECEIVER LAFAYETTE TB-46 6 valve snperhet receiver covering 860 GRID DIP METER Kc/s—30 Ho/s on 4 bands. Special fea- RESISTANCE CAPA- Compact true one hand operation. tures Include ailtle rule dial. Bandapread CITY ANALYZER Frequency range 1.7-180 Mc/s. 280v. speaker.tuning. Operation'B' meter. 230/240B.F.O. v. BuiltA.C. BrandIn 4* 2 PF—2,000 MFD. 2 ohms— New with Instructions, 18 QMS. Carr. 10/- © 200 Megohms. Also checks AC operation. Supplied complete S. A.E. for details. insulationImpedance, 200/260v.turns ratio,A.C. with all colls and Instmeiiona. 412.10.0. Brand New 415. Carr, 7/6- Carr. 5/-, MAIN LONDON SINCLAIR TRANSISTOR AMPLIFIERS TE22 SINE SQUARE WAVE AGENTS FOR ZI2 Amplifier 89/6: Power Pack 64/-; X10 Amplifier Built AUDIO GENERATORS NOMBREX EQUIPMENT CODAR 48.19.9, Kit 15,19.9; X10 Power Pack 64/-: X20 Amplifier EQUIPMENT BuUt 40,19.6, Kit 47.19.6. X20 Power Pack 44.19.6. Sineko/s. 20on cps 4 bands. to 200 Transistorised Audio Generator 10-100,000 o/a. All Items available as Micro Pit Radio Kit 45,19.6. Micro 6. 69/6; TH750 amp Square: 20 cps to Sine or square wave, 419X5,0. advertised Kit 38/6; Micro amp 28/6; Micro Inleotion 27/6. Post Paid. '20 kc/s, Output Transistorised Signal Generator 160 ko/s. impedance 6,000 350 Mc/s. 410.0.0. TRANSISTORISED I 2-WAY RADIOS ohms. 200/240 v. Transistorised100 M«g£J, 1 pMOOtiF. resistance 46.capacity bridge XO- TWO-WAY ] Superbplete with quality. all accessories Com- A.C. operation. Transistorised Induction bridge lirN-lOOH. TELEPHONE NewSupplied and Cnaran-Brand 418. Mains operated Transistor power supply and fully guaranteed. teed with Instruc- nnit, output l-15v. up to 100 mA. £6,10.0. INTERCOM. 3 Transistor 47,10.0 pr. tion manual and leads. 416. Cart. 7/6. All above post paid with battery. Operative over nmaitngly. 4 Transistor 11 gn>, pr. long distances. Separata « Transistor 417.10.0 pr. CLEAR PLASTIC PANEL METERS buttons.coll and 2-wlre press connection. to talk 10 Transistor 422.10.0 pr. First grade quality. Moving Coll panel meters, available JOOO's of applications. Post extra. (S.A-'B. for ea-stook. 8.A.B. for fllostrated leaflet. Discounts for Beautifully finished In- full details). quantity. Available as follows; Type JfE. 38P. 1 21/32(n. ebony. Supplied complete 'V't square fronts. with batteries and wall lO0d)-lOOuA 27/6 SOOmA 22/9 brackets. P 500-0-5flOiiA 22/9 aoOmA 22/9 100V B.C. . 22/9 46.10.0, pair. P. A P. 3/6. 1-O-lmA .... 22/8 000mA. 22/6 300VlaoVB.c,. B.C. . 22/8 VOLTAGE 1mA. 22;8 760mA. .. 22/9 500V B.C. . 22/9 MASNAVOX 363 TARE DECKS STABILIZER 2mA 22/6 1A P.C, .. 22/6 750V B.C. . 22/922/6 New 3-speed tape deck, supersedes old TRANSFORMERS 6mA...... 10mA 22/922/6 2A B.C. . 22/0 15V A.C. .. 22/6 Coltaro studio deck. 2-track 410.10.0. Input 80-120V. OO/cA 32/6 20mA 22/6 6AP.C.3V B.C. .. 22/8 C0V A.C. .. 22/9 4-track 418.10.0. Carr. Paid. and 160-240v. lOO/rA 29,8 50mA 22/6 10V B.C. 32/822/8 300V160V A.C. .. 22/6 Constant output 200uA 27,6 100mA 22/6 20V B.C. 22;8 600V A.O. 22/6 PCR3 RECEIVERS HOv. or 240v,, 600/rA 26/- 150mA.. 22/9 60V D.C. . 22/6 "8"MetcrlraA 29/622/6 Absolutely brand new 3 wave bands ISO- 240New watte. Guaranteed. Brand IHWWWInA .. 29/8 POST EXTRA. Larger sizes available—send for lists. 48.19.6.650 metres Carriage and 2,3-23 10/6. mc/s Plug-In with circuitpower 410.10.0. Carr. supply 12 volt d.c. 19/6. 230 volt a.c. 7/9. TE-SI NEW TS-76 20,000 O.P.V. PUSH 85/-, VARIABLE VOLTAGE 20.000n/YOLT BUTTON MULTI-TESTER TRANSFORMERS MULTIMETER Simple operation, AMERICAN TAPE Brand New—Fully D.C. volts up to First grads quality American tapes. Shrouded. Input 230v. 0/8/60/1201,200V. A.C. 1,000 v. A.C. volts Brand new, Biscoonta for qmrniltles, Volte.50/60 c/a. Ontpnt 0-260 0 / 3 / 30 / 60 / 300 / op to 1,000 v. 3in., 226ft. X,.P. acetate. 4/. 1 Amp,, £4.10.0 600 1 3.000V. D.C. Resistance op to aiin., 600ft, P.P. mylar 10,'- 2.6 Amp .... 45.17.6 0 / 60uA / 12 / 300 5to., 600ft. sld. plastic 8/8 6 Amp 49.0.0 MA. P.C. 10 megohm. Current Sin., 900ft. L.P. acetate 10/- 8 Amp 413.10.0 0 / 60K / 6 Meg. O up to 250 ' mA, 61m, l.aooft. P.P. mylar 15/- 10 Amp 417.0.0 85/-. F. A P. 2/6. Decibels — 20 to 6in.i 1.800(1. T.P, mylar 85/- 12 Arop 419.10,0 4- 36 db. 46.6.0, 6iln.,BJIo., l,200ft.3,800ft. P.P. acetatemylar 212/6 2.620 AmpAmp Portable—432.10.0 MODEL PV-58 VALVE P. b P. 2/-. 6Jtn. 2,400ft. T.P. mylar 48/- Metal Case with Meter* VOLTMETER MOBEL 600.30,000 Vim,7io., l.SOOfl.1,200ft. std.L.P. mylaraceUte I1S/.2/8 Fuses, etc. 49/17/6. IX meg. Input. 7 D.C. o.p.v. O/.6/1/2.6/10/ 7to., X,800ft. P.P. mylar...... 20/- SILICON RECTIFIERS volt ranges. 1.6- 05 / 100 / 260 / 600 / 7iu., 2,400ft. P.P. mylar 26/- 200 V.P.I.V. 200mA 1.600 v. 7 A.C. volt 1,000V. B.C. 7ta. 3,900lt. T.P. mylar 68/9 400 v. P.I.V. 3 amp. 4,000ranges Peak1.6-1.600 to Peak. v. 0 / 2.6 / 10 / 25 / Postage 2/-. Over 43 post paid. 1,000 v. PJ.V. 650 mA Reastance .2 ohm to l.OOOv.100 / A.C.250 / 600/ 800 v. P.I.V. IKKtmA 1,000 megohm.. Deci- 0 / W/xh / 5 / 60 / 400800 v. P.I.V.PXV. SOOmAS amp bete—lOdbto +65db. SOOmA. 12 amp. CALLERS WELCOME ! 70 v. P.I.V. 1 amp, Supplied brand new D.C. Open 9 a.m. to 6 p.m. every day Monday J60 v. PXV. 165mA leadswith andinstructions, probe. 0 / 60K / 6 Meg. 160. to Saturday. Trade (applied. Ulscounta lor qoanttlles. Post es 412/10/-. P. & P. 3/6. PoetPald.Meg fl. £8/17/8 (RADIO) LIMITED Phone: CERRARD 5204/9/55 Cables: SMITH EX LE5QUARE 3-34 LISLE STREET, LONDON, W.C.2 529 Practical Electronics Classified Advertisements The pre-paid rate for classified advertisements is I/- per word (mlmmum order 12/-), box number 1/6 extra. Semi-displayed setting £3.5.0 per single column ipch. All cheques, postal orders, etc., to be made payable to PRACTICAL ELECTRONICS and crossed " Lloyds Bank Ltd." Treasury notes should always be sent registered post. Advertisements, together with remittance, should be sent to the Advertisement Manager, PRACTICAL ELECTRONICS, George Newnes Ltd., Tower House, Southampton Street, London, WC2, for insertion in the next available issue. TAPE RECORDERS, TAPES, ETC. MISCELLANEOUS FOR SALE /confimi ed) " P.E." MOTORIST AIDS. Home Aids. Bonanza TAPES TO DISC—using finest professional Project?. Vibrato Unit. Burglar Alarm. equipment—45 r.p.m. IS/-. S.A.B. leaflet. Transistor Tester.- Portable Ratemeter. FOR SALE. Osellloseopes — Galvanometers — DERO Y, 62 Heat Bank Lane, Lancaster. Compact Power Unit. A.F. and R.F.- Signal Everehed & Vlgnolles Meggers. Also other Tracer. Pipe and Cable Locator. Electronic items and components. Free list. Stamp Candle. Servo System. Minlprobe Signal please. R. & E. MART, Box 9, GJ.O.. Generator. Simple Digital Computer. Fire Tunbrldge Wells, Kent. SERVICE SHEETS Alarm. System. Neon Novelties. Doorphone. Audio Oscillator and Valve Voltmeter. Water Level Alarm. New Look Tape Recorder. TRANSCEIVERS SERVICE SHEETS for all makes Radio, T/V, General Purpose Sealer. Echo L" nit. Noughts W.S. 38 A.F.V. New condition. Complete Tape Recorders, 1925-1966. Prices from I/-. and Crosses Machine. Transistor and Diode set of valves, 17/8, p. HOME STUDY COURSES In Practical Elec I International Corretpondence Schools ] tronics. Free Brochure without oblieatlon INTERNATIONAL | (Dept. 152), Intertext House, Parkgato Road, from; BRITISH KATIONAL RADIO SCHOOL, Reading, Berks. I London, S.W.I 1. CORRESPONDENCE NAME Block Capitals Please SCHOOLS A.M.I.Meoh.E., A.M.I.E.R.E. City & Guilds, ADDRESS G.C.E., etc. Become a Technician or Techuo- logtst for high pay and security. Thousands of passes. For details of Exams, and Courses :n all branches of Engineering, Building, A WHOLE WORLD Electronics, etc., write for 156-page handbook OF KNOWLEDGE I 7.66 —FREE. B.I.E.T. (Dept. I25k), London, W.8. AWAITS YOU I L. 531 SITUATIONS VACANT (continued) RECEIVERS AND COMPONENTS (continued) SPECIAL OFFER A CAREER IN AUTOMATION I Watt S.T.C. 300 MC/S N.P.N. Silicon Planer. 100% Transistors. Limited Stocks. £1 for 6. junior electrical 3/- each. OC44, OC45. OC70. OC7I, OC8I, OC8ID, OC200, testers Gee 16, Get 20. 4/- each. AF114, AFI15, AFI16, There are stilf a few vacancies in our Test Department for techrjically AFI17, OCI70, OCI7I. minded boys and young men. These openings form first-class introductions to the growing field of 5/- each. OCI39. OC140. Get automatic electrical control. The work demands an enquiring and 7, Get 8, Get 9, XCI4I, BY 100, methodical mind—reliability, accuracy and enthusiasm are most important. OA2II. Those appointed will be encouraged to study for recognised SUN SOLAR CELL KITS qualifications and a paid day-release scheme to Technical College is in operation. Working conditions in an entirely new building are 24 Page Booklet on Experiments excellent and there are ample opportunities for advancement—many Inc. 4 Solar Celts II/- Set. of our senior executives entered the Company through the Test Department. G.P.O. DIAL TELEPHONES 20/- each. 35/- pair. • Send 6d. for full lists: inc. S.C.R. experienced senior Zeners. C u r s o n s test engineers 78 Broad Street Canterbury Experienced men are also required for the Final Inspection Department. Applicants should possess a minimum of O.N.C, or Kent equivalent and have practical experience of testing and adjusting automatic electrical cdntro) equipment. Apply with full details of education or experience to: R. &R. RADIO & TV SERVICE Mr. G. W. Hanson, Dept. P.E. Head of Test Department, 44 Market Street, BACUP, Tel. 465 LONDEX LTD. NEW VALVES I 42 Croydon Road, 6K8. WENTWORTH RADIO la Wentworth Court, Alston Road, Barnet, Herts GENUINE HIGH QUALITY COMPONENTS BAR 3087 GENUINE LOW PRICES RETURN OF POST ORDER AND QUOTE SERVICE OC44 2/6 OC45 2/6 OC7I 2/6 BARGAIN OF THE MONTH i - iW RESISTORS 100 - 22M 2d. OC72 2/6 OC77 3/- OC8IO 2/6 AW 10% MINIATURE lOO-JMSd. .OC201 OC8I 2/6 OC200 3/3 AC128 3/3 CERAMIC CAPACITORS 4d. 30/- 100 MULLARD BRAND NEW API 15 3/6 AFII7 2/6 OCI70 3/- SILVER MICA I0PF-I000PF 6d. OC24 10/- 10/6 each OC35 10/- GET853 12/6 HI-STABS 1% iW I/- MAT100 7/9 MATI0I 8/6 MATI20 7/9 P.P. Sd. 2 or more Post Free MINIATURE TRANSISTOR ELECTROLYTICS, MAT12I 8/6 OA95 1/- BY 100 6/- WHITE SPOT 9d. OA9I I/- FULL RANGE 1/2. MAGNETIC EARPIECES 4 PIN TRANSISTOR SOCKETS 9d. 250MW ZENERS 4/- each WITH PLUG 3/-. CRYSTAL 4/4 MINIATURE POTS. LIN. 5KO, I0K, I0KLOG, 2SK. 50K. tOOK, 250K, 500K, IM, 2M. 2/- each We welcome emjuiries for all types of components. Lists. S.A.E. Terms, cash with order, P.P. add 9d. for orders under £2 534 SENSATIONAL HALF PRICE OFFER! THE FAMOUS 3*. 'Continental' & RADIOGRAM AT The TUNCH tjoti nZm/I HALF PRICE! >122 Masni>lc«ni S(«r««ph»nle Radio- pram Chassis complete with two TO" elliptical loudspeakers, plus a Mona/Steroo 4-spoad HOLE PUNCHES automatic record changer. Instant Type i* diameter 6/10 ea. Screw-up Type Only £29-19-6 J|" diameter Toggle switch 8/6 8/6 Easily fitted • Luxembourg and Caroline i" " B7G "I .. Na soldering or Technical received at full strength 1' .. B8A, B9A 9/6 knowledge neeessory ir 10/2 „ • Usten to U.S.A., Russia, Africa. r 10/8 Pits almost any cabinet with Canada and oven Australia 11/8 minimum trouble diameter Int. Octal 13/4 „ Modernises your old radiogram • Unique Lewis Radio 365 day '6/2 „ guarantee, even en ail the valves 18/10 Built-in ferrlte rod aerial 89G 21/8 .. Piano key switching • All British moke 24/4 „ SPECIAL terms available of £7.10,0 deposit followed by 18 monthly Meter 33/2 ,, payments of £1.9.1 (total H.P. £33.13.6) + postage & packing 15/- extra. Complete Set £9.3.6. No extra charge for postage and pocking in the U.K. INDIVIDUAL CABINETS SUPPLIED ON REQUEST Now supplied by: Send your cheque or P.O. today for £8.5.0 while Stocks last to Def>t. PE76 TOMPKINS & LONGMAN LTD. LEWIS RADIO. 100.CHASE SIDE, SOOTHGATE LEWIS 237 GIPSY ROAD LONDON, N.I4. Telephone: PAL 3733/9666 WEST NORWOOD, S.E.27. Tel.: Gipsy Hill S000 CRESCENT RADIO LTD. TRANSISTOR 40 MAYES ROAD WOOD GREEN, N.22 POCKET BOOK BOWES PARK 3206 R. G. Hibberd, B.Sc., LONDON'S ELECTRONIC CENTRE M.t.E.E., Sen.M.I.E.E.E. BEST QUALITY—KEEN PRICES TRANSISTOR AMPLIFIERS A comprehensive guide to H.r v. EG 1004 4 Trans. PusK-Pull t Watt Harrow. EG2004 4 Trans. 250M/W £1.16.0£3.14.6 the characteristics and use of Eagle. EG304 4 Tnms. 3 Watt £3,13,1 the various types of transistor Sinclair. ZI2 12 Wan £4. «.6 .. X10 10 Watt £6.19.6 now available. The manu- .... X20 20 Watt £9,19.6 facture of the various types TRANSISTORModel TELEPHONE 300 £3.0.0 AMPLIFIER of transistor, up to and in- TRANSISTORHarrow. INTERCOM HP2S £3.19.6 {Baby Alarm) cluding the latest epitaxial Peerless.TRANSISTOR WT.300A Range TRANS/CEIVER Third of Mite £7,19.6 planar, field of effect and These cannot be operated in U.K- metal-oxide silicon transis- TRANSISTOR MAINS UNITS PMTypoPP9 Type 33/617/6 tors, is described in detail in TRANSISTOR EAR PIECES order to make dear the Crystal and Magnetic Types Fitted 2.S or 3.S SOME MORE EXAMPLESPlugs 3/9. FROM OUR LARGE imm different characteristics of SELECTION OF TRANSISTORS cm. each. Includes notes on the OC8ID 3/6 OC78 5/6 OCet 4/6 OCI70 1/6 use and handling of transis- OC44 4/6 OCI71 5/6 tors, and chapters on solid OC45 4/. AFI17 4/6 OC76. PICK-UP 4/- CARTRIDGESOC26 ..11/6 slate circuit techniques and, Special Line Complete with UP and Std. recent developments, Other_ . types In stock—BSR..Stylus B/6 ACOS, COLLARO from 17/6 2-f'x S'. About 280 pages, CABY.HULTI-METERS Ml about 200 line diagrams and AI0 £4.)£3.14.0 1.6 photographs. 25s. B40NH200 £5.11.6£6. 3A We have largeTMK itoekg 500^ of Electronic£9.17,6 Components From your Bookseller, or in case of difficulty, 27s. from in stock and feel that a visit to our promises would1 be tor your advantage. GEORGE NEWNES LTD. , SOUTHAMPTON STREET, W.C.2 /• f? « Catalogue showing our stocks of andMullard, vast component Newmarket, stock. Texas, Maids Transiitors. Please Include postage with orders. 535 MARCONI CRYSTAL CALIBRA- BUILD THIS 37mcs TOR No. 5 HKII I Mc/i precision REMOTE CONTROL TRANSMITTER crystal calibrator complete with spares HEW RANGE U1F. AERIALS FOR an PARKERS SHEET FOR HI-FI METAL FOLDING m h rt i n AND F.M. MACHINES OUULxAJLo+^iJbc* HEAVY VICE ' yr£#KA^ 50 PR0FESSt0NAL genrouslyMARTIN desifinedAUDIOKITS «crie» compriia or^ luUy-tr»iv»n in- sistorised units by means of which you can S£IF- SP^Ki moZI T™. 20 WATT INTEGRATED simplebuild upmono a hi-fi amplifier assembly system starting and withadding a STEREO toinstallation, it to make for a wellfully under integrated £30, This 20-wact can be stereo used GET THIS AIR DRYING HAMMER FINISH withtape-heads, low output microphones, as we 11 as crystal etc. pick-ups, Building radio, is YUKAN Aerosol spraykit contains 16 ozs. fine NOW! I ADD-ON UNIT SYSTEM pleasantly easy. Quality is outstanding. Now quality durable easy instant spray. No stove baking units for making an FM Tuner are available for required. Available in Grey, Blue, Gold, Bronze at F.M. TUNER adding to Audiokit assembl ies or usingseparately. )4/ll at our counter or IS/I I, carriage paid, per THE EASY WAY TO BUILD AND SAVE pushbutton self-spray can. SPECIAL OFFER : I can plus optional transferable snap-on trigger handle Leaflet on request. ("mahtin electronics LTD. I . 154-155 HIGHST.,BRENTFORD.MIDOXl (value 5/-) for 18/11 carriage paid. From good stockists |1 Martin Leaflet on Audio kits □ . Choice of 13 self-spray plain colours and primer (motor car quality) everywhere. FM Tuner □, please. also available Martin Electronics Ltd j NAME - Please enclose cheque or P.O. for total amount to: IS4-IB5 High 8L, Brentford, ADDRESS j YUKAN • DEPT. PE/7 * 307B EOQWARE ROAD • LONDON - W.2 MMdtaex. /SLeworth II6J/2 I 536 VALUABLE NEW HANDBOOK IB AMBITIOUS ENGINEERS Have you had your copy of " Engineering Opportunities " ? The new edition of "ENGINEERING OPPOR- TUNITIES" is now available—without charge— THIS BOOK TELLS YOU to all who arc anxious for a worthwhile post in •fg HOW to get a better paid, more interejf- Engineering. Frank, informative and completely ing job. "R HOW to qualify far rapid promotion. up to date, the new "ENGINEERING OPPOR- •R HOW to put some letters after your name TUNTTIES" should be in the hands of every and become a key mon . . . quickly and : person engaged in any branch of the Engineering easily. •R HOW to benefit from our free Advisory industry, irrcspectiveofage, experience or training. and Appointments Depts. •R HOW you con take advantage of the 1 chances you are now misting. On SATISFACTION OR R HOW, irrespective of your age, education or experience, YOU can succeed in any REFUND OF FEE' terms branch of Engineering. 156 PAGES Of EXPERT This remarkable book gives details of examinations CAREER - GUIDANCE and courses in every branch of Engineering, Building, etc., outlines the openings available and PRACTICAL INCLUDING describes our Special Appointments Department. EQUIPMENT TOOLS Baiic Pcutkal and Ihtote- The specialist Elec- ti{ Coursci (or bcqlnnffi in tronics Division of WHICH OF THESE IS Radio, I. V.. tlectronio.EK., ll.i.E.T. A.MJ.E.R.E. City S 6uildl HOW offers you n YOUR PET SUBJECT? Radio Amateurs' Exam. real laharalory train- R.T.E.6. Cerlilirale ing at home nit It MIICII. KNGINKrUINfi J'-LEC. KNGINiaatlNC; P.M.C. Certllkalc practicn! cquipmem. Gen. Me, h. Mir.—Mainien- General Eleclricul Eng. ■— Pratlital Radio Ask for details. ««<•«? Mir. — Dirset Mir. — Jnstallarions— Draug/irsnian- Radio ATefexIsion Setwdng Toot Ooxign —i SI we I ship ■— Jlhwiititiliiig Eng. — Praditai Elcrtromrs Me in I Work — 11 'ehliiiR '— Refrigeration — Eleni. Elec. Eletlronin Engineering Mig. Put tern A! tiki tig — Science — Elec. Supply — Autsmalion B.I.E.T. Inspect ion - Drouslilsnmmhip Mining Elec. Eng. •— Aletallurgy — I'rnituction Mig, AUTO ENGINEERING You arc bound to benefit from reading RADIO KNCINEERING General Auto Eng. — Auto. "ENGINEERING OPPORTUNI- Genera! Radio — Rtiilio it Maintenance — Repair ■— TIES", and ifyou are earning less than TV Servicing — TV Eng. — Auto. Diesel Maintenance — £30 a week you should send for your Teleconinirinicolhiis — Elec- Auto. Electrical Equipment-— tronics—•Sound Recording— Garage Muiingenieni. copy no ir—FREE and without A nloiiiatiotl—Prncticnl Radio obligation. —Radio Anuilmr.i' Exam, RLILDING General UnUding — Healing CIVIL KNGINEERING & Ventila lion ~ Plumbing General Civil Eng. Muni- — Arcliiiectr/rc ■—• Corpeniry cipal Ens- — Sli iirltiral Eng. — Painting — Decorating — Sanitary Eng. — Road Eng. Specijicalions rf Qnaniilics ■ TO B.I.EX, 316A COLLEGE HOUSE, •V. sunup if posted in Hydraulics—A lining— 11 'uter — Surveying — Arcfiilecluia! 129-31 WRIGHTS LANE, W.8. Supply—Petrol Tech. Draughtsn lanstdp. an unsealed envelope. | I Please send me a FREE copy of "ENGINEERING \ WE HAVE A WIDE RANGE OF COURSES IN OTHER SUBJECTS IN- OPPORTUNITIES." I am in/eresled in (slale subject, I CLUDING CHEMICAL ENG., AERO ENG., MANAGEMENT, INSTRU- I exam., or career). MENT TECHNOLOGY, WORKS STUDY, MATHEMATICS, ETC. Which qualification would increase your earnine power? I a'm'■ol<:h'E."sa . k^'M S'E" A.M.I.C.E., A.M.I,E.R.E., B-Sc.." |nahe | Moiu ARI-BA- A-t-O.B., A.M.I.Chem.E.. A.R.I.C.S,. EDUCAT ON E A-M.I.Mun.E., CITY & GUILDS, GEN. CERT. OF ■ ADDRESS ■ BRITISH INSTITUTE OF ENGINEERING TECHNOLOGY 3I6A COLLEGE HOUSE, 29-31 WRIGHT'S LANE, W.8 I | WRITE IF YOU PREFER NOT TO CUT THIS PAGE rr m n vGF RGE N X NE S THE CHAPFf R.VFR P»K^ AnHr uani '| Y - LIMITED, Tower House. Southampton Street. I.ondon, W.C.2. Printed in Ennland by a,vv 1 ;,nd Rhodesia: ^ ?' Sole Agents for Australia and New Zealand- GORDON & GOTCH fAkiil r r