RADIO- ELECTRONICS in ALL ITS PHASES CANADA 7St I

Home , Free FM, KGNC, KLCN, KMUS, KMYC, KTSJ

MAJOR EDWIN H. ARMSTRONG JUHE F A T H E R OF F M 1948

30c RADIO- ELECTRONICS IN ALL ITS PHASES CANADA 7St i

These "sound jurors" record their preferences as they listen over test circuits.

Tal by "Sounc Jury"

Ttie engineer in the foreground talks over the test circuits which the other engineer sets up on a "circuit simulator."

AFTER Bell Laboratories operation, a "sound jury" listens in. behalf of you and millions of other engineers have designed a new talk- An actual performance test is set up telephone users. ing circuit, they measure its charac- with the trained ears of the jurors to Targets of the transmission engi- teristics by oscilloscopes and meters. supplement the meters. neer are: your easy understanding of But a talker and a listener are part As syllables, words, and sentences the talker, the naturalness of his of every telephone call, and to satisfy come in over the telephones, pencils voice, and your all- around satisfac- them is the primary Bell System aim. are busy over score sheets, recording tion. To score high is one of the So, before the circuit is put into the judgment of the listeners on feats of Bell System engineering.

B E L L T E L E P H O N E L A B O R A T O R I E S

Exploring and inventing, devising and perfecting for continued improvements and economies in telephone service 1

THIS Vacuum YOU BUILD THIS Radio Cir- YOU PRACTICE Radi,. s,rvie YOU PRACTICE "FM" Servi YOU BUILD Tube Power Pack, make changes cuit early in Course with Solder- , . ith this Tester built troni Mg on this Frequency Moduli. which give experience. learn . you ing Equipment and Radio Parts ... I. 1 send. Also use it to help tion (FM I Signal Genernter how to locate and correct power I send: practice mounting, con- ,:.rii EXTRA MONEY fixing built with parta I supply: learn necting. soldering Radio parts. , iehbrs' Radios. by repairing circuit defects. pack troubles. '

YOU BUILD THIS A. M. Sig- YOU PRACTICE signal trac- nal Generator which provides this complete Super - You Get PRACTICAL EXPERIENCE amplitude- modulated signals for neterudyne Circuit you build with ninny tests and experiments. enrts I send you, use it to con - With This Superheterodyne Receiver gives you practical experience. luctmany tests and experiments. YOU BUILD THIS complete, powerful Radio Receiver that brings in local and dis- N. R. I. gives you ALL the r tant stations. Radio parts . . . speaker, tubes, chassis, transformer, sockets, loop antenna, etc.

BY PRACTICING IN SPARE TIME WITH BIG KITS OF PARTS I SEND YOU I WILL

Do you want a good -pay Job in the fast- Business is booming. Trained Radio Tech- TRAIN YOU growing Radio Induat ry-or your own Ra- nicians also find profitable opportunities dio Shop? Mall the Coupon for a Sample In Police, Aviation, Marine Radio, Broad- 64 -page book, "How to Be casting, Radio Manufacturing, Public Ad- AT HOME Lesson and my dress work. Think of even greater oppor- a Success in Radio-Television -Electronics," tunities as public demand for Television. both FREE. See how I will train you at FM and Electronic devices continues to MY COURSE home --how you practical Radio expe- get grow ! Send for FREE books now! rience building, testing Radio circuits with /NCL UPES Bit; KITS OF PARTS I send! Find Out What NRI Can Do For You Mail Coupon for Sample Lesson and my FREQUENCY Many Beginners Soon Make EXTRA FREE 64 -pnge book. Rend the details Money in Spare Time While Learning about my Course, letters from men I /NODULAT/ON, The day you enroll I start sending trained ; see how quickly. easily you can EXTRA MONEY manuals that show bow get started. No obligation ! Just MAIL TEL EV/S /ON, to make EXTRA money fixing neighbors COUPON NOW in envelope or paste on a Radios in spare time while still learning! penny postal. J. E. SMITH, President. Dept. FX, ELECTRON/CS ICs probably easier to get started now National Radio Institute. Pioneer Honte Study than ever before he, the Radio Repair Rodio School. Washington 9. D. C. I TRAINED THESE MEN Has Own Radio Service Good Span Time Business GL/ f/Om SAMP EELESON FREE "I have my own Radio and "I have been getting receivers Television sales and servicing to repair right along, and with MR. J. E. SMITH, Pres.. Dept. SFX, business. I get enough repair N. R. I. methods I don't have National Radio Institute, Washington 9. D. C. jobs to keep me going right to spend much time on them." along. " -ALEXANDER KISH, -S. N. STRICKLAND, Mail me FREE Sample Lesson and 61 -page book about 34 Pershing Avenue. Carteret, 191 Dale Homes. Portsmouth, how to win success in Radio and Television -Electronics. New Jersey. Virginia, No salesman will call. Please write plainly.) Age Name Address VETERANS City Zone State Cheek if Veteran You get this training in your own home L -J under G. I. Bill- Mail Coupon. APPROVED FOR TRAINING UNDER GI BILL

IL\DIO- CItAIT, June, 1148. Voiotia. XIX, No. 9. Published monthly by Itaderaft Publications, Inc., 29 \Cortldnetw. Street, Soringflrl.l a. Mass. I:atercd as sn,erd class matter at Post Orrice, Springsold, Mass., under the Act of March J. 1879. JUNE, 1948 Capitol Radio Engineering Institute- Pioneer in Radio Engineering Instruction Since 1927

Here's how you can figure on a BETTER dos in RADIO- ELECTRONICS, Broadcasting, Television, Servicing, Manufacturing

Add CREI Technical Training to Your Present ence, you must fortify yourself with up -to -date technical knowl- Radio Experience. Then (:et That Better Radio Job edge to qualify for the better jobs and to stave off the new competition war -time brought -.Make More .M >y -Enjoy Increased Security. that activity has into the field. CREI has a course of training for you. You will find our proved 'tou can't plan your future on a slide rule. But you can take type of training practical and thorough. Whether your future a measurement of your own capabilities. lies in broadcasting, television, servicing, manufacturing or any Look at the successful radioman. You'll find that he's the branch of communications, you will find that you can "go all the fellow who looked and planned ahead. Today, you have the same way with CREI" from introductory, basic principles to advanced opportunity -at a time when radio's technical progress has gone training, and on to specialized fields of radio -electronics. beyond the supply of technical Alanpower. Never before have so Send for, and read. our interesting 24-page booklet. It men you had the to step ahead - many like opportunity into better explains our self-improvement program, courses and what CREI paying jobs jobs that offer real interest and security in any ... can do for you. It will give you a good idea how practical and one of the many fields that urgently need competently expanding easy -to- understand our training is, and why many thousands have trained men. enrolled for CREI courses since 1927. You can't say, "I don't need more training." Every ambitious radio technician needs more training. No matter what your experi- VETERANS! CREI TRAINING AVAILABLE UNDER G. I. BILL

If you have had professional or amateur radio experience and want to make more money, let us prove to you we have the training you need to MAIL COUPON FOR FREE BOOKLET qualify for n better radio job. To help us answer intellig ^ntly your inquiry -please stale briefly your CAPITOL RADIO ENGINEERING INSTITUTE background of experience, education and present position. 16th & Park Road, N. W.. Dept. Nag. Washington 10, D. C. Gentlemen: Please send your free booklet, "CREI training for your better job in Radio -Electronics," together with full details of your home -study training. I am attaching a brief resume of Capitol Radio my experience, education and present position. Cheek field of grew teat interest: PRACTICAL RADIO- ELECTRONICS PRACTICAL TELEVISION BROADCASTING '1 AERONAUTICAL RADIO ENGINEERING Institute RECEIVER SERVICING ELECTRONICS Engineering INDUSTRIAL An Accredited Technical Institute NAME STREET Dept. RC -6, 16th and Park Road, N. W., Washington 10, D. C. CITY ZONE STATE I AM ENTITLED TO TRAINING UNDER 6. I. BILL. York 170 Broadway San Francisco (2) 760 Market St. Branch Offices: New (7) R. J RADIO -CRAFT for 3

You build this fine modern Superheter- odyne Receiver and other units, with the complete standard parts we send you. This valuable eeulp- ent becomes yours use and keep

Get these 2 8/G GOOKS If you are already employed in the great Radio industry, you know how great the demand is for trained. experienced servicemen, operators and technicians. You Inn v how fast the fRFF! field le growing and haw important It AD IU Is to keep up with new developments to S F.M.. Television and Electronics. The Radio PMANUAI industry is alive with opportunity for the qualified technician whose knowledge is up.te- the- minute. You can be an FM and Television specialist . . . get into the lucrative Radio NOW! New Professional Service Field . own a business of your If you prefer. National Schools of Los Multitester Included! Angrles,for almost 10 years a practical resident This versatile le,' Is portable and and home study trade school, has put Into ef- complete with teat i :. I !, rrlen. Simple to fect its New 1948 Training Program. This operate, accurato and tependablo. You will be program, adapted to National's Master Shop able to quickly locate trouble and adjust the most Method Home Study ('ourse. can qualify you delicate circuits. You can use the Multitester at In your .pare Limo as a Radio and Television hone or on service calls. It is designed to meas- technician. For details of this Program fill ure AC and DC volts, current. resistance and out and mail the coupon below. decibles. You will be prom] to own and use this ralmntdr irref,-.,Mna1 Inslnumid-

SHOP METHOD HOME TRAINING from a Technical Trade Resident School

LEAR National >.I,,ds brings Its exelusive Shop Method et' training right into your own bent. You can learn the most up-to-date approved practical training projects, systems and modern circuits item the very beginning to your spare time. here is sound and practical home training -the development of experienced BY DOING Instructors working with students right in the shops, NEtt' Television and Ittoadcast Studios and Experimental Laboratories of NATIONAL SCHOOLS --one of the most advanced teimllal trade education centers world. Work with Real Ex- in the perimental Equipment Take Advantage Now of these Outstanding Features Furnished without of National Schools' 1948 Training Program '\..uo cad Si -Insu,' 194s t nur.,t is planned to prepare you for real WOMBS In Radio Extra Cost as Part of f. h -ri wet Wul Éleetradcs. Experimental equipment supplied with the Course has been completely revised to your National kilo*l(< give you the most up-to -date practical experience with new circuits. new units. etc., right In your own hone. Training New Television Lessons have been expanded to give you training in the latest laa r developments In this important field. The 1948 Course includes a Professional Multitester (shown above) for your 4r u x in spare or full -tine Radio work. Send Coupon Natialon Schools gives you advanced training -the ev key to the better positions in Radio, Television. BOTH HOMESTUDY EXPERIENCE IS THE BEST TEACHER. You and prove to Electronics. learn by experience with the exclusive National AND RESIDENT You are sent standard Experimental Equipment, COURSES OFFERED Shop -Method of Home Training. With the appa- yourself what 6 Including tubes and accessories. for building ratus sent you, you actually build various types of YOU can modem Short tt'ave and Standard Broadcast Super- standard equipment-a powerful superheterodyne redo heterodyne Receiver. All equipment becomes your ceiver, a signal generator, an audio oscillator, low in RADIO and nemesia' property. power Radio transmitter and other units. You make National Schools' nearly ro years of experl- APPROVED

7 r in Technical Trade . testa and conduct experiments that show you the why TELEVISION! Training FOR and how of Radio. You understand what makes the modern shops and laboratories . highly trained various elements because instructors are back of your time -tested Training of Electronics operate you Plans for brighter VETERANS actually see them work for you. Not only do you gain future. by method splendid experience this of learning, but you CHECK COUPON receive valuable equipment you will use on the job in the practice of your profession as a Radio Technician. Mail the coupon and learn what this means to you. NATIONAL SCHOOLS LOS ANGELES 37, CALIFORNIA EST. 1905 ll MAIL OPPORTUNITY COUPON FOR QUICK ACTION MEMBER: NATIONAL COUNCIL MufRRR NATIONAL HOME or TECHNICAL SCHOOLS grimy COUNCIL (Ma'il in se Examine the exelinive National Shop Method of Home Training. NATIONAL SCHOOLS, Dept. RC -6 Penn/Pe pen o carol See for yourself how mind and practical It is. Be convinced 4000 South Figueroa Street, Le. Angeles 37, Cal,fernla that you ran learn Radio, Electronics. Televlelm- quickly and easily In your spare tine. This trial le ABSOLUTELY FREE. Mall Mad rue FREE the two hooks mentioned In your ad. Including a sample Ire,,, of hour course. tho coupon here for the honks that tell you the complete story of I understand 00 salesman will call on roe. National Schools Master Shop Method of Home Training In Radio. Electronics and Television. NAME AGE This is the :MODERN SYSTI111 OF TRAINING: it matches the rapid progress constantly being made In Radio. Television and Electronics. It is TIME TESTED. ton. Natteral Schools has been training men for more ADDRESS than a of a century. is the very same training that has helnrd third It CITY ZONE -` thousands to more pay and greater opportunity. You owe it to yourself-- Your future -to read the honk "Your Future In Radio. Electronics and í l Check here if veteran of World War II Televlsia' -FREE to you when you send In the amava.. JUNE, 1948 4 //,sWeI'$

TO EASY FM & TV SERVICING The big profits in service lie in repairing FM and TV receivers - of which thousands are already in use. Fast, efficient service demands visual alignment of sound and video ii. amplifiers. McMurdo Silver, world- famous builder of Laboratory Caliber Electronic Test Instruments, gives you the quick, accurate answers. Use 909 or 911 with any good 'scope, follow the simple, clear pictorial instructions and you'll master FM and TV alignment in "no time flat."

FM /TV SWEEP SIGNAL GEN- ERATOR WITH CRYSTAL 911 MARKER OSCILLATORS. Covers 2 thru 226 megacycles in three bands upon accurately calibrated 3 -range dial without band -switching! Out- put variable from zero to 1/2 volt. One graduated knob sets linear electronic FM sweep to anything between 40 Kc. and 10 megacycles -low enough for sharp communication FM to high enough for the biggest TV sets. Provides saw -tooth horizontal synchronizing voltage to 'scope at 2x power line frequency giving steady, stable mirror -image trace on your 'scope of i.f. - and r.f. - amplifier selectivity curves. Two panel knobs control amplitude of marker. frequency "pips" produced by two built -in low -drift 1 and 5 mc. crystal oscillators. These marker "pips" let you determine precisely correct pass -band in TV i.f. alignment . also serve as standard -frequency signals for checking calibration of all types of re ceivers, signal generators, etc.

FM /TV SWEEP SIGNAL GEN- ERATOR. Already America's most 909 popular sweep signal generator. Model 909 is identical to Model 911 above except that it does not include crystal marker oscillators - uses your present AM signal generator to provide variable - frequency marker "pips" when desired. Using any good 'scope and following the clear, concise pictorial instructions, Model 909 makes you master of FM and TV visual alignment . the only method guaranteeing fast and perfect i.f. alignment. Thou- sands already in use by smart service technicians , and in the laboratories and factories of FM and TV sit manufacturers prove it to be exactly the instrument you have demanded. Convenient portable size matches all Silver LCETI - turns your shop into a modern service laboratory.

'Psis-vs slightly hiehv frost of aocAir..

Send for 1948 -1949 Catalog of NEW LCETI Test Instruments LABORATORY CALIBER OVER 37 YEARS OF RADIO ENGINEERING ACHIEVEMENT ELECTRONIC 7/ C sWe"Z -. Of-r TEST EXECUTIVE OFFICES: 1240 MAIN ST., HARTFORD 3, CONN. INSTRUMENTS FACTORY OFFICE. 1249 MAIN ST., HARTFORD 3, CONN. RADIO -CRAFT for .i

Get Your ALLIED Catalog Now Get More for YourMoney in Every Way Get Everything New in Your Radio...

Ay.

Se* i-ot Radio's Leading Buying Guide 172 Pages Packed with Value Here's how to get the most for your Rodio dollar! A TYPICAL VALUE! Use ALLIED'S great 1948 Catalog, the Buying Guide that brings you everything in radio and electronics at lowest, money -saving prices. ALLIED has every- The New NATIONAL NC -33 Receiver thing for Servicemen, Soundmen, Engineers, Amateurs and Builders. Complete selections of latest Packed with Professional Features -A Great Buy! home radio and Television receivers, test equipment, P. A. Systems and amplifiers, Amateur gear, thou- NOW -enjoy the thrill of owning the National NC -33, the sensa- sands of parts, tubes, kits, tools, books - ready for tionally brilliant new communications receiver. It's built to highest fast shipment. Get the advantages of the most fa- engineering standards -easy to operate -delivers top -notch reception mous service in radio - expert handling, helpful on broadcast and short-wave bands. Perfect for SWL's and beginning personal attention, money -saving values! Send today Amateurs. Covers 500 kc to 35 me continuously in 4 bands. Main for your copy of the ALLIED tuning dial is calibrated for easy location of all important amateur, 172 -page Catalogg --the most police and foreign bands. Band -spread dial operates over entire fre- complete in Radio. quency range. Has automatic noise limiter; adjustable pitch BFO, universal antenna input; built-in 5" PM speaker; headphone jack; com- Everything in Radio fortable, glareless tuning dials. Self- contained in attractive modern for Everyone in Radio cabinet, finished in smooth gray. For real enjoyment and dependable all- around performance nominal at cost, the NC -33 takes top honors. -. Comes complete with tubes. Operates on 105-125 volt, 40 -60 cycle lx AC, or »C. Stock No. 97-596. NET, FOB Chicago $6595 '4 Terms: $13.19 down, S5.08 monthly for I months. IMMEDIATE DELIVERY ON THESE FAMOUS NATIONAL RECEIVERS Notional HRO7 $299.36 National NC- 2- 40D...... $225.00 j

National NC 57 89.50 National NC -46 . 107.40 National NC -173 189.50 NEW! National HFS National NC183 269.00 Receiver -Converter 125.00 Send for Radio's Net FOB Chicago. Prices subject to change without notice. Leading Buying Guide Attractive Time Payment Terms. Trade -ins Accepted.

ALLIED RADIO CORP. 933 W. Jackson Blvd., Dept. 2 -F-8 THE WORLD'S Chicago 7, Illinois Send FREE 172 -Pag ALLIED Catalog. LARGEST Enter order for National Model .. Enclosed $. .. ._ .... _. Full Payment RADIO Pert Payment (Balance C.O.D.1 Send ALLIED Eosy Payment Plan details and order blank. SUPPLY Nome HOUSE Address City ton. State - - -J JUNE, 1948 s

CATHODE RAY TUBES THE 5BP1 ... $1.20 BEST TUNING 1 BUYS UNITS

BC 191 & BC 371 T1' 611. 3000 kc to 4311m LOWEST kr. TU 911 -7700 to 111.1(00 kc. TU 1011- 10,000 to 12.:1111 ke, TU 22 It 350 to 650 ke. TU 26 112uu 3BP1-$1.25 5FP7-51,75 to 500 ke. will supply closest unit to Specified 3FP7-51.20 5JP2-$4.00 PRICES Frequency at time of shipment. Each $2.25

TRANSFORMERS MICROWAVE TUBES AD Primaries -117 V 60 cycles DYNAMOTORS (Magnetron;) d5102: 1'80 vet a 55 ma, 6.3 v. a 1.2 amp, V. Tube Freq. Range Pk. Pwr. Out. Price .3 2.131 2820.2860 me-05 Kw $15.00 5 51101 1100 . @ 70 ma, tapped 42 550 V. (for 2.121 -A (725 -A) 9315 -9 Ils n 50 Kw $25.00 with I1. W. rect.) 52.ì5 2.122 3267- 3333 me 265 Kw $15.00 2.126 2992 -31119 me 275 Kw $15.00 FILAMENT TRANSFORMERS 2.127 2965 -2992 mc 275 Kw $15.00 . 5123: 6.3 vet a amp. 0.: vet @ I ' op $2.15 2.131 2820 -2860 me 285 Kw $15.00 4 a 8.14 V. 2.5 amp $2.75 27 volts am,. 6.Ì a 2.122 2780 -2820 me 285 13163:1100: 2. v. se 1.75 amp, 5 v. @ 3 anti. 6.5 v. If Kw $15.00 atop. 0.5 V. 00 8 inn). $5.35 2.138 PKG. 3249 -3203 me 5 Kw $25.00 Doughnut Xfmr. Two 5.1 v. windings a 5 .nap. each. 2155 PRO 9345 -9405 me 50 Kw $25.00 15,0011 volt test $7.50 :4131 24.110 me 35 Kw $17.50 No. 5058: 0.3 VCT @ 2A. 6.3 VCS a 2A 12.25 W.E. 700 -A 100 V test $1.35 680 -7101ße Kw $30.00 No. 5100: 6.3 VCT a 1.2 A, 5000 W.E. 720 -BY 2800 1000 Kw Nn. 51156: 6.3 PCT 44 0 A, 6.3 VCT 88 2.2 A. 0.3 VCT 50 $25.00 - 2 A $2.50 y1AGNETS for 2321 -A 1725 -A1. 2322. 2726, 2327. 2131, Io 5057: 6.3 VCT 4t 1 A. S VCT a 3 A. 5 VIII' @ r A 52.50 2.131. 2J32 and 3.131. each $8.00 UX 6800: 5 V 45 5.5 A. 5 V @ 5.5 A. 29.000 Volts Teat Field Strength Distance Between Pole Face Prim $24.$0 PE 73 CM II:.E.1 Power supply for lIC 375 (Gauss) Pole Faces Diameter Input: :8 VDC Output: 111110 VDC @ 356 POWER CHOKES 9850 96" :S - $8.00 hb @e ma 51.50 31a. New $4.95 Hy 150 with 1500 I%' In $8.00 111y @ 800 Ma. 7.5 Ohms $5.95 BD 77101 Power supply for BC 191 1000 Adjustable Dual Choke: 2-2 Hy 0 100 Ma. 5 .90 spare ruse links. etc. Input 14 v.d.c. Output Dual Choke: 7 75 .ta. 11 Hy @ 60 Ma 51.50 (Electromagnet) 296" to 3" 2%" $12.00 y a 111.50 1000 V. @ 350 ma. New $9.95; Army Ite- Klystrmh-- 2K25'725Á 5 h @ 125 $5.95 $7.75 25 h a 65 Ina $1.10 ussue, 02. .rond. 1'1'1 101 -C Input 13/26 VDC @ 12.6/6.3 A. MODULATION TRANSFORMERS (salad: 400 VDC @ 135 Ma. 800 VDC ' MINE DETECTOR AN, PRS I ..1.14 to and serve,. uf 2 In pull 6n7 pl:te 20 Ma. 9 VAC 00 1.12 A. new $3.49 Will Indicate buried metallic & nonmetallic objects, such as rh ...... 5.85t-'1 Posh 211 . rl.li tu 1d;te ,f sun, 211 S1.95 Pt: 86 N, Input: 28 VDC, Output: 2511 water pipes. x'er pipes. troc roots, water pockets. etc. Uses 316116tes and 1 LC @ 60 ma With filter $1.95 st meter for aural and visual Indicators. Operates ( 1(l principlo of changes in radiation resistance An ideal gad., t 18 VDC A, Out. DAG 33A Input; @ 3.2 f r Inge . gealogi:is hntnr -,1(v n. rs. Nsw, sons l,I ste.... $12.75 ARC -5 ACCESSORIES Poi: 450 VDC @ 60 51a. $2.45 With Kilter i,, 521.65 CONVERSION COILS FOR ARC -5 TRANSMITTERS Dyl :0: Inpu4 28 VDC Gz 7 Ma. Output: 540 VDC 250 Ma. l'ow'er supply for M.O. Coils P.A. Coils Antenna Free. Range (? Loading Coils Sell 274 modulator $3.95 CERAMICON CAPACITORS $1.00 each 51.00 each 5.55 each DM 23350: Input: 27VDC @ 1.75 A Out 6029 5 7247 2 6033 3.4 Mc. (Erie. Centralab) $7.50 per 100 5 58034 4.5.3 me. put: 285 VDC @ 75 Sia. $3.50 :6030 39293 Mc. .'. mmf 67 mmf -1- 20 % 032 56035 7.9.1 051 21: Input: 14 VDC. Output 235 Vim' 5 mmf +5 % 100 mmf rt5% CONVERSION KIT. nsistinéof 1 -al -O coil. I.V.A. con, cool 90 Ma. l'ow'er supply for IBC 312 52.49 In any one frequency ,_ 4 mmf '.5mmf 115 mmf 2 % :.ANTENNA COIL. particular 55. Input 12 vdc @ 25 amp. Output $2ge.00 l'E 8.5 ram? ...... ±.5 mmf 120 mmf -.VI ARC No. 6558 variable receiving pacitor. 82 m f /se,'. 500 vdc @ 400 ma. (slightly useri) $4.95 +5% 8 a rotors. Worm drive 11 mmf 240 mmf -.3'; Iton , 3 ver thons. .03" spacing. 11D -AR 93. Input: 28 vdc @ 3.25 amp. .0tot ... stnit vdc Pioneer. 15 mmf .....±-2.6 mmf 250 mmf No.spa ng9Ó, rotors. 1(g eapu.-14m, 22.3 -145 Output: 375 @ 150 ma. w5032 mes. Each 41.00 New $4. 48 mmf 2r¡o 500 nun( ,.i- 15-30'1 20.2 mod 50 +5ri TRC x822 VaoVar. Xmlg. -I tt 5i.óó VII' 10 O l'ow'er supply. nsing 2 IYnamo- mmf -.20% 1000 mmf worm drive'. 90:1 rdr 60 mmf -.3(ó ingleRrevr. Rtg a' racks $1.00 Input: 24 -28 vdc. Output: 1000 Dual mtg. racks freer.) 2 r`400 ma. 230 vile @ 100 ma. New: tom. Shock mounts for rack $1,50 able with relays, filters. etc. BI-N SILVER-MICA BUTTON CAPACITORS FOR Bettis $1.00 DUAI. CONTROI. foxf:S IliS $40.00 (Erie, Centralab) $9.50 per 100 it 19 power pack t dynamotor). Input: IL 186 mmf -'-2 5mm f INSULATORS ode or 9.4 anip. Output: 275 vile @ Dut 175 mmf 5mmf rita 500 vdc @ 50 ma. New, copteletrt in 500 mmf 1 , tä1 rase wiib 2 plugs. filters, etc...56.95

1,51 :51 -It, Input: 28 valse. @ 1.25 atop. ANTENNA. AN /122 -A. Used in I Isms',: udros -k -rays for I nnputl 2711 .d.r. @ 70 ma. New with high gain and dinclivit'. each dipole clement is X 12' long. incited terminal bis $3.25 made of 9i," tubing. Excellent for that new 6 or 2 -miler beam. Don't MISS this great value. z_5 0sÁ .0515. Input: 12/24 valse. @ 4/2 $5.65 each or 4 for S20.00 *581 p. Output: 506 r. Le. (- 50 ma. Cmm ,1.ut square shape. size 714"x41/6 x3 ".$3.95 ANTENNA AN /104 -A. Tho famous al- handle antenna. used Ideal for mobile wave, 7.A/USA 05t8. Input: 12/24 .d.e. (ñ- with the SCR 522. quarter because of or 2 units can be used s I amp. Output: 275 v.d.c. @ IIO na. 12 its streamline construction; to a for 2 meters or for @ 3 amp. Compact Square. i sire forni dipole TV and FM reception. b.Lr. of 7'z- x914 "x3" $4.25 Cmislsts copper sheath 21" long moulded about s woolen tupport, with 83 -111 coax connector. 5.75 ea.. or 2 for $1.35. 1,51-25: In 12V1C 2.3:\ Out 2250DV'C 'u $2.49 AN, 128.A. For high gain and direethity on 2 meters. Consists *584 *582 *650 *48{ of 2 vert leal eletnetits working against a squire reflector, Ont NS 3. 1111 -42: In 14VIO. 515/1030 VDt approx. 3'24'. Impedance js 50 ohms $40.00 5050: Lapp-bowl fee,) lam. Similar to NaD(ah:,l 215 '260 ma and 2 VDC $3.95 Siade d 11611 itualily glazed porcelain. Fits 2 r hole. 140.600 MC DIRECTIONAL ANTENNA 64a_ L x 3" Ilan. v $1.50 5584: Fred-Otto. Mlade fir steatite. similar to National XS 1. INVERTERS 140 -310 Mc cone and 300 -600 Mc cone. each consisting of 2 end fed ware conical sections with enclosed matching stub Fits 14s. (hole. 5' 1, x I ". dlam. half Ea. 5.49 or 4 for $1.50 t'R 200 -A. Input: 28 ed.e @ 38 Amp. for reactance changes with changing frequency. New, won- holds twine: line also. L Output: 80 volts orb 500 volt -amp, 800 S. pieta with mast. attys. cables. carrying chest $49.50 :582: Antenna feeder support. r Leland Eleetrie. New. complete with In z 11k' .Ilan. Hole size: V. Each 5.17 or 10 for 51.00 -urtino book. relays. filters, le...$12.50 Control Unit BC 1073 : :um'. except Is Lang. I'll 218-15001 25-28 cd.c. @ 92 Consists of pulse- generator and peter which measures 5581: SUMO as .582, it 1% volts. 15n0 colt amps. ,tio Each 5.12 or 12 for $1.00 nina IL'. 300 frequencies from 150 to 210 nu. The ipulse generator makes an IClry trie. Nrnv sellent sew with 248C: Antenna support insulator. Made of fine quality stea- ladnnd 535.00 square -wave aloe variable pulse -widths. V-. I. I'v- , ana. $20.00 'rho w meter e n be nualilled 117 tite, with nickel plated reinforeed ends. Non "plosiv Into a a1'li? oscillator. s VAC. GO rio operation. w /tubes $50.00 4' 1, x dé' dlam. Es. $.25

SONAR SOUND GIBSON GIRL EMER- RELAYS HEADSETS Ro a s u rn rr g x wile, contacts I, and headset - GENCY XMTR a msuas a1c .25 Dynamic mike mold DETECTION UNIT @ ,\ high quality. enleleut unit. 7220 -24 Contactor. SPIT, 24 -28 , ,,,I In 1t -19 taon States. d Ida1 for de lstìug units,- water snm,la. \like Transmits auto- contacts 400 amps SL20 i, lmrs complete, new $2.75 ' 11th 1611 rw 1 minx in s'm.ds, matie SOS signal 10771SF, Antenna changeover. DI'h I; :- it 80110 ohms mope lanes G stile usa a Inn- -.oó Ì5 aJsein Oldie salt rnst al, witch is loua on 500 kc ewer- c1. 28 vdc S rubber cushions. Canes with 8' cord Dines more sensitive than quartz. It gency wave. Can alh,l slag PI. 2.i New 5P.ä5 completely enclosed a slid cors manually keyed MINIATURE RELAYS HS 30 headset. insert type headset sound detector va. to h1( - transmit addi- x1591!_ ) tuts out background nobso and low brigaiall.i usedaxed in harbor defense. il ( size: assures tional Intoriaitnn. -28 vdc. 515:\ 10059 -11 5.70 15o,í d1ms1 Cnnp L,l to an andin amplifier this r1( ' ^r -- 4' 41'07, Y2 and high fidelity. A MUST for even' valuable No Batteries re- DPDT, 22 -28 vdq 300 duns 560 be found to have many ap a ham at this price $ .85 the h\haha silt which . Hand r .PDT. 21 vile, 300 oluns, ]lull prri)aimis. Its 560 Nfnir to niait 8000 ohms output,$ .35 contains 7 miermlioto milts.. $12.50 cranked ...$25.00 - 55S7,4

All merchandise guaranteed. Mail orders promptly filled. All prices, F.O.B. New York City. CROSS POINTER Send Money Order or Check. Shipping charges sent C.O.D. INDICATOR Two 0 -200 microam pere movements, 3' EQUIPMENT CO. case. many applica- COMMUNICATIONS tions $2.50 131 C. Liberty St., New York City 7, Digbyg b Y 9 -4124 RADIO -CRAFT for

114 I Put You to Work with Your Hands to LEARN RADIO! You Build Receivers! You Make Typical Defects Occur and Make Tests to Prove the Theory!

o D to MAKE MONEY! LOW COST TRAINING - EASY PAYMENT PLAN! You Learn at Home How to Build and Test Dozens and Dozens of Circuits - Simple and Complex! w YOU DO F. L. SPRAYBERRY, PRE S, IDE NT of the SPRAYBERRY OVER 175 ACADEMY OF RADIO. TMs INSTRUCTIVE is the man who directs your study. His years of EXPERIMENTS experience and Radio "know -how" assure you of the finest in home Radio Training YOU BUILD ALLTHESE TESTERS AND MORE! I gire you a fine, moving -coil type Meter Instrument on Jewel Bearings - with parts for a complete Analyzer Circuit Continuity Tester. You learn how to check and correct Receiver defects with professional speed and accuracy. You'll get 70 t10 90100 valuable experience and 65 practice 60 building this Signal Gen- eratormulti and Set has Long and purpose Short Wave Tuning.. Tester. All Sprayberry Equip. Makes a Is yours for KEEPS. breeze out of fixing Radios and you done have to spend money on ready made Equipment.

SPRAYBERRY HOME TRAINING is PLANNED to MAKE MONEY for you FAST! I train you with regular professional Radio Equip. the finest kind of "bends" experience. And you get ment. I tell you exactly what to do how to do ... it right in your own home. In no time at all, you'll ' . -- it. You handle Radio Parts, see them operate, be ready for a business of your own or a good job learn what they're for. With the fine I Soldering, wiring, connecting Radio Kits supply, in Radio, FM, Television, you learn how to build Radio Circuits, construct / parts ... building Circuits with your Radar, Industrial Elec- own hands - you can't beat this your own Test Equipment. I'll show you how to method of learning. When you con - cause typical Radio defects so you can watch and tronics, etc. Alow's +v! struct this Rectifier and Filter, Re sistor see how they act. You learn the latest methods for the time to get and Condenser Tester, etc., you '4 get a really practical slant on Radio trouble -shooting repair. All ! 00 and this adds up to started I-_s t that leads to a moneymaking future MI MI MI MI VETERANS! SEND FOR MY SPRAYBERRY ACADEMY OF RADIO F. L. Sprayberry, President Approved for VALUABLE Room 2068, Sprayberry Building, Pueblo, Colorado Please rush nly FREE o i s or "Mow to MAKE MONEY in RADIO lEC G.I. Training TRONICS and TELEVISION' and "NOW to READ RADIO DIAORA , SY'MSOLS." Under Public FREE BOOKS! D Cheek here if a veteran. Name Laws 16 and 346. Age . "How To Read Radio Diagrams and Symbols" ! Mail Coupon A wonderfully complete new hook. which explains in Address simple English how to read and understand any Radio for Full Set Diagram. Includes translation of all Radio sym- C tv Details. bols. Send for this volume at once! It's free! With State ' I'll send you another Big Free Book. describing In detail my Radio Electronic Training! 11 IME - u (Mai! N. envelope or paste s,, pe y po.tra..11 , JUNE, 1948 u

eommand j'ei- CATHODE 97[ RAY TU8E5 ten1a,n

3 CP I Ind. Screen, .95 Relay 3 DP 1 -A Ind. Screen .95 3 FP 7-A 1.35 Antenna Relay Unit BC.442A or RE. 3 HP 7 1.45 2.ARC5. Originally used on Commend antenna odd 25c each to cover Set .SCR274 t. Contains on NOT ICE 191s milivolt me- postage and handling' changeover relay, a thermo- ter, with an external 54 amp. We need room. That's why we're The meter stole reeds R.F. 5 FP7 1.75 couple. slashing our already sensational prices on linear scale calibrated 0 to 5 CP I 1.95 current on these limited quantity items. Our 10. All new. A truly sensational buy at 5 BP 1 2.45 itock is definitely limited, so rush your only 'add 25c to cover postage 5 HP I 245 $1.95 order now, to be sure not to miss any of and handling.'. these unusual bargains. 'odd 35c each toc r and handling postage 500' $995 [ P ANTENNA 7 BP 2.65 Ó 7 CP I 3.25 FORMAT/ON STICK 'odd 40c each to cover 3 CONDUCTOR Originally used in con. postage and hondling' junction with the Automa. TELEPHONE WIRE rif 9 GP 3.50 tic Pilot. Contains innume 3 conductor Braided AO 3 roble gears and resistors; BUY Shipped express, charges a potentiometer and Con. insulated copper & steel telephone wire. is collect trifugal Governor. Really It Used primarily on aircraft & Marine ADF made of copper for con- an elec- a gadgesecrs paradise, and Systems, Loop LP21A contains ductivity, and steel for These have a truly unusual buy of on. tric motor and selsyn. loops ALL strength. Worth at least but ly $1.95. Add 40c to been removed from salvage aircraft, NEW: 3c per ft. Yet due to an are guaranteed to be in excellent working cover postage and hand- exceptional buy, we can condition. ling. now offer it at less than Shipped Express Collect lc a (t. Shipped Express Collect Rieloireórri6iiss WIBC 450 BRAND NEW CONTROL WORTH DETECTOR BO X MINE A LOT Triple remote control box for Corn. MORE mend Receivers 'SCR 274 N Series Equipped with 3 tuning dials, 3 volume R5 or 433G, controls, and 6 selector switches. Used, /ARN7 but in excellent condition, a steal at either of these Radio only 51.50 ea. Add 25c to cover pos- Compass Receivers tage and handling. complete with tubes. l4eal for conversion for home reception. complete (except batteries' in original case Used but good. A real Each contains STEEL OXYGEN TANK unit on instruction Manual. Good 9S buy of only SDv . for detecting objects under the earth's surface. 'Shipped express PHANTOM Requires one 6 volt and three 4 -5 volt batteries col. 'Shipped express charges collect' lect) ANTENNA These tanks ore approdmote- ly 44" long by 6" in diameter. I2VOLT 50 AMP They will stand up to 400 lbs. 79S LIMITED pressure, and have an outlet on either end threaded with stain SUPPLY darda" pipe thread. A real buy AT A transmitting at only 51.50. 'Shipped Express Jefil(r45 antenna, for use on Charges Collect.' These generators are ex. ALL approximately 450 cellent for truck or bus use. [W: MC. Complete with They also will make a fine standard coax con. power supply for your radio nectar. A weather- shock or nice light welder. proof unit. Add Brand new in original boxes 25c to cover hand. as pictured with pulley, ling and postage'. $9.45 each or with keyed shaft less pulley $7.95 IS. I Squadron Signal Genera. each. tor 'Navy Type CML- 60049 'Shipped Express Collect' used for Type ZA Glide path equipment. Frequency range 9095 roc. modula- Due to customs regulations which require ex- Amplitude ted variable frequency; audio cessive paperwork and packaging complications, we oscillator tuned to 60 cycles. [NOTE cannot accept orders for shipment outside the United R F level measured by self con. All merchandise subject to its prior States or possessions. tamed VTUM. Contains 0 -50 sale, minimum order $2.00, No micro-amp meter. C.O.D. orders accepted. Michi. Recordinc wire. New on o gon residents must odd 3 State .006 Stainless Steel recording Shipped Express Collet sales tax. riginol spools as used by Army and Navy re.

6532 EAST McNlCHOLS DETROIT 12 , MICHIGAN tC/11.11.1/05.&vrARROADely c/ Sorte RADIO -CRAFT for 4 9

E. B. De Vry, President DeForest's Training, Inc. is NFR

Profit Through Training in RADIO-ELECTRONICS Prepare at HOME or in our CHICAGO LAB- ORATORY to get REAL MONEY, a BETTER

JOB, or a BUSINESS OF YOUR OWN . . . . Our business is helping men ... and young men ... get into a well -paying future in the highly profitable fields of RADIO - ELECTRONICS. During the past sixteen years we have trained many men who desired better jobs or businesses of their own. We can effectively provide you with this same opportunity either in our new, modern Chicago laboratories or in the privacy of your own home. VETERAN TAKE YOUR Both our (I) Chicago Laboratory and CHOICE (2) Home Study training are accepted If you choose to come to Chicago, we shall find comfortable under the "G. 1. Law." If you quality, the Government will pay cost of either training you select. living quarters for you. If you train at home, we shall send you modern, practical equipment. In either of these two methods, you will have the supervision of some of the finest instructors in the country. Fill in coupon below and we shall send you, absolutely FREE, full information about our program of building men for better opportunities in RADIO - ELECTRONICS. DeForest's Training. Inc. also includes in- Mr. E. B. De Vry, President struction in FM Radio, Television and Industrial Electronics. DeForest's Troining, Inc. 2533 N. Ashland Ave., Dept. RC -E6 If you prefer to remain at home, you receive eight (8) big Chicago 14, Illinois kits of radio parts and assemblies from which you can work Please show me how I may get started toward a good job or a busi- out dozens of fascinating radio circuits to gain practical ex- ness of my own in Radio -Electronics. perience in your own home. In addition, you receive a 16 mm. motion picture projector and 12 information- packed reels of Nome film which help you learn faster ... easier. You also get mod- Age em looseleaf lessons with handy fold -out diagrams. Address Apt EMPLOYMENT SERVICE City Lone State When you complete your training our effective Employment Service helps you get started toward a real future. Mail cou- If under 16, check here Ifa dlscharaed Veteran of World War II for special information. check here. pon below today .. . do not delay.

CHICAGO. Associated with the DeVRY Corporation DeForest's Training, Inc. ILLINOIS Builders of Movie & Electronic Equipment

JUNE, 1948 s 10

JUNE 1918- Special FBI Issue EDITORIAL RADIO The Rising Tide of FM by Hugo Gernsback 17 COVER FEATURE CRAFT Frequency Modulation -1922 and 1948 by Edwin H. Armstrong 20 I near,' rat, ng SNORT WAVE CRAFT TELEVISION NEWS FM (Pages 21-61) RADIO & TELEVISION Tmnemark r,eistcred 11. S. l'a Lela Olttrc FM Fundamentals by John B. Ledbetter 21 FM Receivers 22 by Bob Stang 25 -HUGO GERNSBACK FM Sweep Generators Editor-an -Chic) Advantages of FM by Leigh L. Kimball 26 FM Tuners 28 FRED SHUNAMAN, Managing Editor FM Receiver Servicing Technique by Milton S. Kiver 30 Simplified FM Receiver Uses Crystal Detector by Robert E. Altomare 32 M. HARVEY GERNSBACK, FM Discriminator Circuits by Douglas H. Carpenter 34 Consulting Editor by H. Secor 36 FM Receiving Antennas W. ROBERT F. SCOTT, W2PWG, FM Receiver From War Surplus Radio BC -624 by Robert C. Paine 38 Technical Editor Complete FM Station List .. 40 ANGIE PASCALE, Glossary of FM Terms compiled by John B. Ledbetter 44 Production Manager Foreign News (Page 68) I. QUEEN. W2OUX, Editorial Associate Ralph W. Hallows 68 Report From Britain by Major ELMER FULLER, Shortwave Editor

Construction (Page 68 G. ALIQUO, Circulation Manager Modern Crystal Receiver by W. V. Nutall 69 JOHN J. LAMSON, Servicing (Pages 71 -74) Advertising Director ALFRED STERN. Promotion Manager Return of the Veteran by Emmett Brightwell 71 Production -Line Technique for Service Shops by Jack King 72 Audio (Pages 75 -76) In Our Next Issue Connecting FM Tuners by Albert Loisch 75 INGENIOUS TEST INSTRUMENT TELEVISION POWER SUPPLY Amateur (Pages 77 -79) DOUBLE BRIDGE VOLTMETER A Sailplane Transmitter by Fritz Compton 77 On the Cover: Test Instruments (pages 7 tl1 -711 Economy Voltmeter by Homer L. Davidson 80 Departments The Radio Month 18 Technotes 46 Radio -Electronic Circuits 62 New Patents 64 Question Box 66 Try This One 67 New Devices 70 Communications 82 Book Reviews 87

''NEW LOOK" FOR RADIO -CRAFT Major Edwin H. Armstrong, Father of FM, in the shadow of our RADIOCRAFT introduces a new format this For the greater convenience readers, anten- month. All articles on the same subject are grouped together. `Sign -posts" are placed of one of the latest nas used for FM broadcasting. on each page, identifying the subject. Continuations (except where unavoidable) will be eliminated in the next few issues. We trust you will like the new classified and systematized R.amOCRAFT. Let us have your reactions! Chrornatone by Alex Schornburg

ABC PAID CIRCULATION 6 MONTHS TO DEC. 31, 1947 -102,688. (Publishers Statement) PRINTED FOR JUNE ISSUE -153,000.

RADCRAFT PUBLICATIONS, INC. Hugo Gernsback, President; M. Harvey Gernsback, Vice President; G. Aliquo, Secretary Contents Copyright, 1948, by Radcraft Publications, Inc. Text and illustrations must not be reproduced without permission of Copyright owners. RADCRAFT PUBLICATIONS INC. PUBLICATION OFFICE 29 Worthington Street, Springfield 3, Mass. Address all correspondence to N. Y. office. EDITORIAL AND ADVERTISING OFFICES 25 West Broadway, New York 7 N. Y. Telephone REctor 2.9690. BRANCH ADVERTISING OFFICES: Chicago: 308 W. Washington Street, Chicago 6, III. Tel. Randolph 7363. Detroit: Frank Holstein, Manager, Room 402 Lexington Bldg., 2970 West Grand Blvd., Detroit 2, Mich. Telephone Madison 7026.7. Los Angeles: Ralph W. Harker, Manager, 606 South Hill St., Los Angeles 14, Calif. Tel. Tucker 1793. San Francisco: Ralph W. Harker, Manager, 582 Market St., San Francisco 4, Calif. Tel. Garfield 1 -2481. -CRAFT, June, 1948, Volume XIX, No. 9. Published monthly on 25th of month preceding date of issue. Allow one month for change of address. RADIO be add d to When ordering a change, please furnish an address stencil impression from a recent wrapper All communications about subscriptions should the Circulation Manager, Radio -Craft, 29 Worthington St., Springfield 3, Mass.. or 25 West Broadway, New York 7, N. Y. $6.00 for three SUBSCRIPTION RATES: United States and possessions, Mexico, Central and SouthAmerican countries, $3.50 a year; for two years; $8.00 years. $7.50 two for three years. Canada, $4.00 a year; $7.00 for two years; $9.50 for three years. All other foreign countries, $4.25 a year, for years; $10.25 179 Elizabeth FOREIGN AGENTS: Great Britain: Atlas Publishing and Distributing Co., Ltd., 18 Bride Lane, Fleet St., London E.C.4. Australia: McGill's Agency Dreef 124, France: Brentano s, 37 Avenue de l'Opera, Paris 2e. Holland: Technisch Bureau Van Beerle, Bemelmans & Co., Heemsteedscbe, Street, Melbourne. Sts. Heemstede. Greece: International Book & News Agency, 17 Amerikis Street, Athens. So. Africa: Central News Agency, Ltd., Cor. Rissik & Commissioner Street, Johannesburg. Middle East: Steimatzky Johannesburg; 112 Long Street, Capetown; 369 Smith Street, Durban, Natal. Universal Book Agency, 70 Harrison 14 Lane, ,Middle East Agency, Jaffa Road, Jerusalem. India: Susil Gupta (Distributors) Co., Amrita Bazar Patrika Lt., Ananda Chatteriee Calcutta. RADIO -CRAFT for r II

PHOTOFACT Publications

moos x ar. Help You to Success! .,sivU,t rs't; .., COURSE 13-8 1ElE°.'SU Have more practical, useful, complete ÇFT NOJ V FOLOfR ;-J -¡ data than you can get anywhere else...

READY NOW! PHOTOFACT VOLUME 4 NOW RUNNING IN CURRENT Includes First Three TV Course Installments! FOLDER SETS Latest companion to popular Volumes L 2 and 3 PHOTOFACT - brings sour file of post -war receiver service data right up to July 1948! Most accurate and com- lit-re's the first practical, successfully proved plete radio data ever compiled . an absolute Television instruction for the Service Technician' MUST for all Servicemen. Everything you need to know for faster, more profitable servicing. in Now - at no extra cost to you - you can pre. handy, unified form. Includes: Exclusive Standard pare for profitable Television servicing without Notation schematics: photo views keyed to parts taking time off from your business. If you can lists and alignment data: complete parts listings and proper replacements; alignment. stage gain, service a Superheterodyne, the PHOTOFACT circuit voltage and resistance analysis; coil resist- Course will teach you clearly and simply how to ances; dial cord stringing: disassembly instructions: service a Television Receiver. Telegrams, letters record changer repair instructions. Order Volume and 'phone calls by the hundred acclaim the Your Price 4 today - et's the only service data that meets your actual needs! first installment of the $500 Television Course - Each Volume, which appeared in PHOTOFACT Folder Set No. Vol. 4. Modelt from Jan. 1, 1948 to July 1, 1948 in DeLuxe Binder 38. If you haven't started the Course (which is run- Vol. 3. Models from July I, 1947 to Jan. 1, 1948 ning in current PHOTOFACT Folder issues) - be Vol. 2. Models from Jan. 1, 1947 to July 1, 1947 sure to get PHOTOFACT Sets No. 38. 39 end 40 today! Stay ahead of the game with PHOTOFACT! 18" Val. 1. ml post -war models up to Jon. 1, 1947 1947 Automatic Record Changer Manual Don't Miss a Single Installment! Nothing like it! Covers more than 40 different post. war models. Absolutely accurate, complete, author- Dial Cord Stringing Guide itative-based on actual analysis of the equipment. Shows exclusive "exploded" views. photos The book that shows you the one right from all angles. Gives full change cycle data, ad- way to string dial cord. Here. for the justment data, service hints and kinks. complete first time. in one handy pocket -sired book, parts lists. Shows you how to overcome any kind are all available did cord diagrams cov- of changer trouble. PLUS-tor the fist time - ering over 2300 receivers. 1938 through complete, accurate data on leading Wire. Ribbon. 1946. Makes dial cord restringing quick simple. Pays for itself in time saved Tape, and Paper Disc Recorders. 400 pages; 8' 'r -'x and II "; hard cover: opens flat. Don't be on single dial cord repair job. A "must" without this manual. ONLY E$4. 957,7 for every service bench and tool kit. Order today! ONLY Si c Woo

41 Radio Receiver Tube Placement Guide The book that shows you exactly where to replace BOOST YOUR EARNING POWER! each tube in 5500 radio receiver models. Covers I receivers Irons 1938 to 1947. Each tube layout Moil This Order form SAMS & CO.. INC. is illustrated by a clear, accurate diagram. Saves to HOWARD W. 2924 E. Washington St., Indianapolis 7, Indiana time - eliminates risky hit -and -miss methods, especially when the customer has removed tubes from My (check) (money order) for S enclosed. the set. A handy pocket -sired 192 -page book. Send Photofact Sets -38, _39, _ ..40. indexed quick reference. use it for You'll profitably ($1.50 per Set). every single day. Order several copies Send Photofact Volume 4 (including Sets Nos. 31 for your bench and outside calls! ONLY D1.LSL through 40) in DeLuxe Binder. 18.39.

Vol. 3. Vol. 2. Vol. 1 (518.39 each). Automatic Record Changer Manuel, $4.95. HOWARD W. SAMS & CO., INC. Tube Placement Guide, $1.25. INDIANAPOLIS 1, INDIANA Diel Cord Stringing Guide, $1.00.

Export -Ad. Auriemo -49 Brood S1. New York 4, N. Y. -U. S. of America Send FREE Photofact Cumulative Index. Conoda -A. C. Simmonds t Sons, 301 King St, East- Toronto, Ontario Name PHOTOFACT SERVICE Address "The Service that pays for itself over and over again" City State

JUNE, 1948 L t$Sf Sftecía&f Do not fail to closely examine this list of bargains. We believe that every item listed below is a sensational value that soon can never he repeated. All equipment advertised herein is unconditionally guaranteed to the customer's satisfác- tion to this extent: Return any item advertised within five days after delivery for full refund except transportation charges (both ways).

(A) IGNITION SWITCH r across face and 2" deep. Has off position or will switch to either or both of two circuits 5.60 (B) BENDIX SCINTILLA MAGNETO SWITCH TYPE CRZ -43AA AIRCRAFT 4" high s 4" wide x 3" deep. Contains one off -on toggle type switch. two rotary type RADIO RECEIVER switches each with oft position and two on Another item for the VHF experimenter. Con. positions. 5.75 tains ten tubes: 6- SH7's, 2- 6H6's, and 2- BC- 1155 -A SYNCHRONIZER (C) CUTLER- HAMMER SWITCH ASSEMBLY 7193's. Relays, condensers, resistors Amphenol Another Invaluable unit for the Television and VHF ex- Consists of four DPST bathandle toggle connectors, dynamotor, carbon pile voltage reg- perimenter. Contains 19 Me. IF strip using 5- WE7I7A switches, each rated at 20 amps 125 volts. ulator and numerous other parts. Weight ap- tubes. A total of 24 tubes included. consisting of 6- with connectingnn straps. Price per assembly W E717A's, 2- 6SL7GT's, 2-SAC7's. 5-6SN7GT's. 2- prox. 32 lbs. Size, 12 "W a II "H of four $1.00 $6.95 6N7GT's. 2- 6L6's, I- 6V6GT, 2- 6AG7's. I -6AC7, (D) CIRCUIT BREAKER x8 "D and I -6H6GT. Other parts included are 6 pots, 10 30 amps. 2 "x2 "xs. ". Automatic push to re- Amphenol 8318 chassis connectors and umerouss con- set. New 5.50 densers. resistors, and transformers. Weight I "W W$1 /.75 (E) HEAVY DUTY TOGGLE SWITCH 22 lbs. Size 21"L x II} x 73/4"H. PRICE CH type C -5A DPST 20 A. 125 V. 5.35 (F) HEAVY DUTY TOGGLE SWITCH CH type AN- 323.10 DPDT Momentary Contact 30 A. 125 V. 5.35 (G) SOUND POWERED TELEPHONES Shipping weight about 7 lbs. per pair. Require no batteries or external source of power. Will operate up to several miles with two wire circuit. or use one wire and ground, lightweight. Brand new. Price per pair 519.50 (H) HEAVY DUTY TOGGLE SWITCH CH type C -2 DPDT Center oft 30 A. 125 V 5.50 (l HEAVY DUTY PP -51, APQ -9 RECTIFIER -POWER UNIT AN-3022-6B SPDTTCenCenter of 30 A. 125 V. $.25 HEAVY TOGGLE SWITCH 4110 cycle 115 V. Contains 4 -5R4GY tubes. 2 -4Mfd. 1000 V. DC condensers. 2 MI d. 1500 V. DC con (3CH type AN3 125 -1 27 2B DPST 20 A. V. 5.25 densers, 406 -2000 cycle transformers. power resistors. (K) MICRO -SWITCH etc. Weight 38 lbs. Size 21 "L x 5'é "W x $4.95 Weather - proof, metal clad. 10 A. 125 V. type YZE "TROTN SPST normally open. 5.35 BC -800A RADAR TRANSMITTER & RECEIVER Loaded with tubes and components for the VHF experimenter. Contains 19 tubes including 1- 955, 3- 956's, I -2C26 1 -5U4G, I -2X2, I -6SN7, 7- 6AC7's, 2 -65L7í T's, I- 6V6GT, and I- 6H6GT/G. Several HF tuned circuits, 7 amphenol chassis fittings, sockets, 24 V. blower and motor (will operate on 110 V. AC), 2 -4Mfd. 600 V. condensers, and many other resistors and parts. Weight approx, 40 lbs. In a metal case 12'/z" x 111/2"H x 8 "D $14.9 5

SN -7C APQ -13 SN8/APQ-5B Sensational offer for Television engineers. Contains 19 Mc, IF strip containing WE7I7A tubes. Other HE Contains 31 useable tubes consisting of 6H6's, 5- 2- strips containing 2 -6AK5's. 3- 6SL7GT's. I- WE7I7A. 3- 6AC7's, 2- 2050's. I -6SA7GT. VR105's, 10 2- 4 -6SN7GT's, 2- 6N7's. 2- 6L6's, I-6H6. 3- 6AC7's. -OAG7's. 7-- 6SN7GT's, I -Vß75. 2- 6SL7GT's: 1 -OAG7's, I-6V6. A total of 26 tubes, Other parts I-6N7. Other parts such as 17 Shallcross pre vision wire-wound such as DPDT relay. 7 pots, 12 Amphenol 831R chassis resistors of 30.000 120.000. DYNAMOTOR PE1OIC connectors. and numerous condensers, toggle switches, 150.090, 250,000. 20,000. 200.000 and 100.000 x 14" long. Shipping weight and transformers. ohms value. Site about 4" dia. ItF chokes. variable ondensers, Relay DPDT. variable condensers, 420 Weight Size 2(YL x 111/2"W Amphenol and Cannon connectors, tap switches, approx. 15 lbs. Made to order for BC -645A appros. 25 lbs. $19.50 networks and transformen make this another in- Mc. Citizens Band transmitter -receiver. Input x 7?. "H, PRICE valuable parts item at the advertised low price. 13 or 26 V. DC- output 400 and 800 V. DC and Weight 28 lbs. Contained in aluminum cue 9 V. AC. Brand new in original lr, "Lail .'W x 7t'H. 83.95 PRICE $14.95 sealed cartons

LS -3 SPEAKER ARGON INCANDESCENT LAMP 6" PM type, homed in 2 watt pear shape with regular AC type heavy metal case. Con- screw base. NEW 35c ea. tains output transformer Sold carton of ten only. NMI to match 4000 ohm impedance. Used but guaranteed okay. Size about WESTINGHOUSE MERCURY -VAPOR PP -2 APQ -5 POWER UNIT 8 "18"x4 ". Shipping weight Battery h e e bulbs. Commercial 6A. Style 400 cycle. 115 V. Contains 10 tubes as follows: 2- socket. For 6 or 7 batteries approx. 10 lbs. Has lack 259116. for screw 5U4G's, I- 6X5GT, 4-6Y66's, I- 6SL7GT. 2- VRI50- for plugging in oed to re- charged at one time -2000 to 3000 hours 30's and numerous condensers. transformers and re- Ideal for with spectral high resisting glana. $3.95 istors. Weight 17 lbs. Size 21'L x 5'1/2a'W x $5.75 BCYr.348 receiver. r$8.50sP NEW 7s.-H. PRICE

RADIO -CRAFT for I:t

lit

T -26 /APT -2 RADAR TRANSMITTER RECEIVER AND POWER Contains tunable VHF circuit using 2-JAN CTL 703's or BC -314 RECEIVER

368AS tubes. Other tubes are 2-5R4GY's, I I SUPPLY FOR APN -4 -2X2, -807, Frequency coverage 150.1500 Kc. in 4 ranges. Two I -6AG7 2 -6AC7's, and I -931A. Other parts such as RF stages. 1st detector. two IF stages, second Contains 16 tubes: I -6SN7. 1 -6SL7. I-6H6. 24 V. DC motor and blower, HV. condensers and trans- detector. RF oscillator, CW oscillator and audio. 4 -6SK7. i R105.30. I -V -6517. 2 -2X2. I- formers, terminal strips and Amphenol connectors, knobs, Total, 9 tubes. 14 V. DC at 5.3 amps. input to 5U4G. 3-6B4G. I -6SA7. Shipping $19.50 fuse holders, etc., make this unit invaluable for parts alone. dynamotor. Easily converted for 110 V. AC. Use weight 32 lbs. headphones or speaker or both. Weight applox. 45 lbs. Size 21 "L x 10/2 "W n ¢ New, with manual 589.50 73/4"1-1, , in metal case $ MARKER -BEACON Used 569.50 RECEIVER Can be adapted to redo controlled devices. Was used by pilots to flash a signal lamp on aircraft Instrument panel when in range of a beacon trans. mitter. Responds to modulated signals over a variable range of 62 to 80 Me. Tube plates and fil- aments operate directly from 24 V. DC. Can be adapted for radio control of experimental apparatus opening garage doors, etc. Circuit diagram and parts list included on either model shown below: ANTENNA KNIFE SWITCH BC- 357 - contains 12C8 andd 12SO7 tubes and Has 2's" porcelain i nsulator bakelite base. heass T- 4" sensitive el (size 39 /APQ -9 RADAR TRANSMITTER blades long. Single Pole Double Throw S .7. ,- x 5'.á'` Loaded with VHF parts and tubes such as 2 -RCA 8012's, 3Y4 -). r $2.95 Double Pole Double Throw 1.00 I -931A, 2- 807's, I -6AG7, 2- 6AC7's. The RCA 8012's are Triple Pole Double Throw 625 rated at 50 W. input to 500 Mc. Contains variable parallel. BC- 1033 - contains 6SH7. 6SL7 and 12SN7 plate oscillator silver plated, ventilating blower and tubes. sensitive relay motor, ceramic tap switch, pots, terminal strips, gears, (size 54' x 413.50 counters, etc. Weight 36 lbs. Size 22 "L z I0'/2 "W 5'r4' x 3'á "). P x 72%4 "H. PRICE $9.75 OXYGEN TANKS

Cy- Aviators oxygen breathing bot- tles. Non -shat- INDICATOR SCOPE terable. Choice of two types. ID -41 APQ -13 (A) Withstands About 6" diameter by 15" deep. Contains I -5FP7. 2000 lbs. pres- 1-6A K5 tube.5 Grain of Wheat 3 V. pilot light, magnetic deflection yoke. condensers. $6.95 sure. resistors. potentiometers- sockets. (B) Withstands 500 lbs pressure. SPERRY A -5 AUTO PILOT WILLARD LEAD ACID CELLS CHOICE AMPLIFIER RACK 35.95 ca. Contains 115 V. AC voltmeter and 350 -450 cycle Frequency meter. A total of 4 amplifier chassis com- A plete with following tubes included in rack: 2- 1631's, 6- 1632's, 3- 1633's, 3- l634's, and 2 -1644 INTERPHONE tubes. Numerous transformers, resistors and con- AMPLIFIER densers make this unit invaluable for parts. Weight 38 lbs. Size 12 "L z 14 "W s 101/4 "H, PRICE $6.95

SCR -522 TRANSMITTER - RECEIVER 6 V. INew) (Dry -charged) $3.00 Operates from 100 -156 Mc. Easily adaptable to amateur radio, fire department, taxicab purposes, for mobile or 6 V. (In metal carrying case) (Add electrolyte fixed station installation. A redhot item the specific gravity 1.265) for amateur (Drug st erri $4.00 6 -10-11 meter rig. In excellent condition. Complete with all tubes, dynamotor, and remote control, and not beat -up. Shipping weight 45 lbs. .. $24.95 DYNAMIC HANDMIKE Same as above except not in excellent High impedance type-with press -to -talk switch condi- $14.95 that shorts microphone when released and operates tion and not guaranteed condition a relay or other circuit when depressed. Designed Beautifully constructed in gray finish sturdy metal for close talking PA and mobile communications rabinet. Operates on 24 V. input. Complete with Dynamotor for SCR -522. Size about 13" x 8" x 5" high. service. Speech is brisk and clear. Made to stand dynamotor. Has I and volume -6V6 1-6S37 tube, Shipping weight about 35 lbs. necessary rough handling. Black wrinkle finished. Has 6 ft. control. carbon or magnetic microphone input. Delivers all power for the SCR -522 transmitter 8 receiver. Can be op- 3 conductor shielded rubber covered cable and Fastened to sturdy resilient mounting on rubber. standard amphenol plug. Made by from 28 V. ElectroVoice Site 6' a 7- s W'. Shipping weight $3.45 erated DC or coupled to gas engine $ for the Signal Corps. Comparable mikes 14 lbs. or electric motor mechanically .. 4.95 list at $28.00. SPECIAL. EACH $7.95

Unless Otherwise Stated, A ll of This Equipment (s Sold As U sed

130 W. New York St. WITHHAL ALL Indianapolis 4, Ind. Orders Shipped F.O.B. Collect JUNE, 1948 11 itì OFD PhiCFSDQk r PUSH No. S -3006 START STOP BUTTON No. T-1640 starting o'r TRANSFORMER Designed for push stopping of the transmitter. Here is a rugged trans to. -rc1 the rig. +t Fast St built to Army specs. Hero.. KITS button red. Wally sealed with Fran].' TUBE button is black. Tubes Start Terminals for easy soldo,L. completeS $17.95 Give your rig that profes- Primary 115 v. GO eyes. CR522 appear- 58 ma. Tubes sional $1.25 Sec. No. 1 8.5 v. et di Comitte $7.95 - goes ...... Sec. No. 2 5.4 v. Ot 3 a. S 34f Tubes Sec. No. 3 6.4 v. de 6 a. of $7.95 for No. N -268 $2.49 Specify Model Numbers POWER SUPPLY VIBRATOR 12 Macle by Mallory. volts input. Delivers 19U Perfect No. T 406 volts Or 85 ma. for mobile receivers. MODULATION BC -348 Owners Lo -drain battery cur- to rigid TRANSFORMER for BROADCAST BAND rent. Made 61,6 CONVERTER in Army specifications. Designed for n 807 final. 348 without any alteration a small Convert that BC takes tubes as modulators, Our special $3.50 mod sour set teto 450 and compact joh to handle receiver. ust tune your om done on a converted panel erate pow',- r. forget it. All tuning is means 1600 ke.- double conversion vering 550 to Fidelity and Higher $3.25 High Sensitivity. Excellent Selectivity-complete lessbchassisitdiall anschematic lull instrutons- 6.50 handle l'aa.a knobs. Terrific Buy at P W" laanet. tuning GG Molts, M4214 r \ buy No. 1 .t wonderful / designed MIKE 1 DYNAMIC /.- cute ra faro -. a Ripplele aÌ deed to talk switch reproducing the hov t' lias Uush METER BEAM fully designed for the famorry 200-EA. 5- ELEMENT 2 quenches, but Model dlIwle driven element. All- aluminum Mark 11 Transmitt, KIT. Folded impedance coaxial $3.89 construction. Feed with low can be used anywhere- net price wonderful value -- Blarl. able. Amateur Only two to a customer. Bakelite Frame. and Complete with 3 ft. rubber cord $1,75 DUAL RELAY No. R-4602 60 cy Relay 1'1.55 plug H-487 2 110v No. Mounted on one frame. Both relaYs No. M -462 double pole. One 31/2 INCH "S" METER MOUNTING BASE i single throw. One Circuit, ANTENNA on throw. Used in a Bridge mobile ant. 1 Here is a unit for mounting your canan be paral elá will give you accurate heavy gauge steel with rubber independ- on your surplus the car- made of or used readings housing enables your k ently. receiver or receiver not handle s 50 $1.89 meter. Uses shock without breaking. sWill equipped with long, r': diam. $1.69 light for lighting meter lbs. 16 feet $2.20 each face. No. M-248 2 VOLT STORAGE $4.95 MIL MOVEMENT No. B-4011 21/2rr 0-1 BATTERY oN,ms Basic Wonderful for mobile No. D-4064 -,I wherever a equipment. A rugged plas- nt Is nc Ied fm you DYNAMOTOR II I mil tic case will allow BC- ec I- nasic trr lu Used with the popular V t r in to use this battery with- Radio Receiver. 12 volts $2.95 about break- 312 ma. out worrying input-235 volts 4U 90 age - 30 amp capacity Output complete with filter balls on side tells when Can. recharging. mounted in . FOR THE 522 battery needs $2.49 DESIGNED Size 5"x3" $3.49 TRANSMITTER x4"

No. C -641 A Four Band Selector Unit T.6042 BC -312 No. FROM THE 1 the r mo- POWER TRANSFORMER UNITS Which replaces - R.F. su(Y ! \au V.T. which tor allow (ti. 'travy Duty 750 volts Contain ngr you to with a Igo m 150015 to 18 Mc. Has for cö 250 ma. to be Installed h` $3.00 lias tap-perfect for a ceramic band switch each -d salt or ally t nit 10 minutes ..... supply t from any coil. Each oneinos,ope these change needing air pad- application high coil is tuned with an voltages. Sire 564" your own receiver ',4" wide 5" deep. weight der. Build No. 3-651 DI HEPTAL SCOPE signal generator with this 21 ibn. assembly. mar- --- SOCKET ' velous Buy at .. , $1.98 tailor $5.45 14 1 " Socket ,eJ for high Fete nitl 1 _:, item F-604 $1.49 No. ENS NAVY FY O l'gngdrte with 5 foot router cord. low Im- pi; pedance suey., has a chin band whichThris adjustable phones are very sensi- and deslgn,sl for No. 11 -3040 tive se " Here is a Buy -Dual Grinder rugged $1.7¡ 5 HEAVY DUTY again in stock Easily opened. Completely sealed 1/3 horsepower VIBRATORS Large enough to use motor t you any 6 Prong Base moisture when closed. the house Type A Standard outahle at beats at any place nk around 6 volt. Type 13. for tuning units this will save you Synchronous designed waterproofing is necessary. hours of labor. as above but where long .. endless =pail Same 4'<," high. 5'4" wide. 84" ^ for 110 v. $36.50 l J- Either Type $$1.09

20 °o DEPOSIT ALL PRICES WITH ORDERS NIAGARA RADIO SUPPLY CORP. F. O. B., N.Y.C. UNLESS RATED 160 GREENWICH STREET NEW YORK 6, N. Y. RADIO -CRAFT for A

WANT YOUR FCC COMMERCIAL LICENSE IN A HURRY? Use Cire Training and Coaching Service- and Get Your "Ticket" in a Few Short Weeks! Thousands of new jobs are opening up-FM, Television, Get your license without delay. Let Cleveland Institute Mobile Communication Systems. These are only a few of prepare you to pass FCC license examinations, and hold the radio fields which require licensed radio technicians and the jobs which a license entitles you to, with CIRE stream- operators. lined post -war methods of coaching and training. Your FCC Ticket Is Recognized in ALL Rad io Fields as Proof of Your Technical Ability More than ever before an FCC Commercial Operator's Employers frequently give preference to the license holder, License is a sure passport to many of the better paying jobs even though a license is not required for the job. Hold an in this New World of Electronics. FCC "ticket" and the job is yours! Hundreds of Satisfied, Successful Students hare taken the first "I class phono license ex- "I passed the FCC - examination In radio- "I hare had my 1st class radio -tele- "After sending In Lesson E-9 I amination and reeelv,.i my first class ticket last telephone 2nd class. at Detroit on June license since Vareh of this year, Saturday. phono talk the commercial operator's May :11. In dosing I must say yours Is 3rd. and I want to thank you for your and plan to continue with your course license a minnt inn for class excellent radio 2nd re. and I really appreciate your readV asslstance 0x my instructor Se v. since' I find It a great help In studying radiotelephone, and It. E. One passed ¡wiltilt stol the service you have rendered io.i I o f ir.,.. ui ter," I received the license last meek." Student >. Student It 2779N12 Student =2772N1

I can show YOU HOW TO PASS

FCC RADIO OPERATOR'S EXAMS

If you've had any practical radio exprienee- amateur. Army. Navy. radio servicing or other, my time proven plan can help you. too, on the road to success. Fill out the CIRE training coupon below and mail it. I'll send you. FREE, the entire story. and coaching Edw. H. Gaillard Vice President makes it EASY c to get your + SAMPLE , FCC ticket FCC TYPE EXAM 1 ' ..Ay EVEN °`E4 we* o ,; ,, yi WITH ir \`f e'` THE NEW CLEVELAND INSTITUTE OF RADIO ELECTRONICS EXAM RC-6 Terminal Tower. Cleveland 13, Ohio I want to lop,w hmv I can get my FlX' tleket In a few abort weeks. Send me your nil: t: e.d1le6 "I10w In l'asa FCC License Examinations" tdoes not cover exams for Ainsleu, I inmsel as wolf as a sample FCC-lyno exam and Catalog A. describing opportunities h. 11.0110 -Electronics.

NAME

ADDItEFs

' 7TY ZONE STATE C7 Veterans check for enrollment under G.I. Bill NO OBLIGATION - NO SALESMEN ti 1 JUNE, 1948 Ili

Z BOOKS IN IN THE RADIO DATA BOOK

The only Radio Handbook of its kind! .. . 1148 pages, 12 sections, each a complete coveroge of one rodio subject.

Together, the 12 sections form the most complete Radio Handbook you can BUY! Easy to read ... A quick reference!

Plan every operation in radio and electronics with the Radio Data Book. This new radio bible will be your lifelong tool ... you will use it every day, on the board, at the bench, in the field! Use it for engineering, construction, troubleshooting and testing. The RADIO DATA BOOK will be your invaluable aid in design, experiment and in layout. It will help make your production better, faster and easier. In any and every operation in radio and electronics, you will use the RADIO DATA BOOK! The RADIO DATA BOOK is a work of complete authority, prepared by engineers with many years of practical experience. They have been assisted by the Boland & Boyce staff of editors skilled in preparing electronics manuals for the U. S. Signal Corps for many years. These men have worked for several years gathering material for this book . all the knowledge of radio principles and operation . all the statistics . all the newest developments in electronics every possible angle and detail. Eighteen months were spent di- gesting this material into the most concise, the clearest. and the most readable form. The result is this invaluable manual The RADIO DATA BOOK. Whether you use this book for general reference, for scientific instruction. or for education, one thing is certain -the practical help. the daily use- fulness you will derive from it will prove to be worth many. many times its astonishingly low price!

Here's a description of just ONE section- Section 5, Sound Systems: This section covers the planning. selection of components, and assembly of complete P.A. installations. Every type of unit and material used in a sound system is described. and HANDSOMELY analyzed. Components are classed as to size and type of P.A. installations in which they should be used. Tables and charts BOUND IN RED & GOLD are given from which to determine power and ratings. Micro- phone and speaker construction are described and illustrated 12 sections ... 1148 pages ... Completely Illustrated in detail . . . placement in auditoriums, etc., for proper acoustical results is explained and illustrated. Patterns of SECTION 1. THE 150 BASIC CIRCUITS IN RADIO. the different types of microphones are illustrated as are the SECTION 2. COMPLETE TEST EQUIPMENT DATA. proper methods of wiring up the various units. etc. SECTION 3. TESTING, MEASURING AND ALIGNMENT. The above is just one of the twelve big sections in the RADIO DATA SECTION 4. ALL ABOUT ANTENNAS. BOOK. We wish we had room here to describe all twelve in detail, but SECTION 5. SOUND SYSTEMS. just look over the list of sections, and you will see why this is the best SECTION 6. RECORDING. radio handbook money can buy. Send in your order for the RADIO DATA SECTION 7. COMPLETE TUBE MANUAL. BOOK today! SECTION S. CHARTS, GRAPHS AND CURVES. SECTION 9. CODES, SYMBOLS AND STANDARDS. SECTION 10. 50 TESTED CIRCUITS DESIGNED FOR OPTIMUM PER- FORMANCE. SECTION 11. DICTIONARY OF RADIO AND ELECTRONIC TERMS. Coming Soon! SECTION 12. RADIO BOOK BIBLIOGRAPHY. 12 complete books in one only $5.00 The VIDEO HANDBOOK Less than 42c per book! Everything in Television in one Complete Textbook. this coupon to your jobber- -Or direct to: Over 500 pages completely illustrated. BOLAND & BOYCE, INC., PUBLISHERS This new handbook will be invaluable to everyone concerned with 460 Bloomfield Ave., Montclair, N. J. Television. Everything from the basic theory of the technical aspect of Please send me: 1 enclose full pay- television through the design and characteristics of receivers' to final : ment. The Radio Data Book at $5.00. installation, operation, and maintenance is covered. This is a com- I enclose $1.00 and pletely new book that includes all of the latest developments in the The Video Handbook at $5.00. will pay balance to field -the components discussed are of the newest design -the Prac- Both Books at the Special price of $9.00. postman on deliv- tical maintenance described is a result of intensive study of the equip- ery. ment placed in operation during the past few months. There are five completely illustrated sections in the VIDEO HAND- NAME BOOK, each over a hundred pages long. Each section completely covers. ADDRESS The VIDEO HANDBOOK will be out October 15th. but we have ZONF received a flood of orders already. To insure your getting a copy in CITY printing -mail your order now. the first STATE The VIDEO HANDBOOK is $5.00 alone, or you can order it with tl.e RADIO DATA ROOK and get both books at the special price of $9.00.:_.nd in the coupon today!

RADIO -CRAFT for Editorial n THE RISING TIDE OF FM

3,/11, In the midst of its boom, still rises rapirlll.

By HUGO GERNSBACK

IN the middle of April, when this was written, there ent -and one or two high -fidelity regional FM networks. were in actual operation in the U.S. 463 FM broad- Instead of strictly independent FM programs, the casting stations. In addition the Federal Communica- present trend is unmistakably toward a solid duplica- tions Commission has authorized 564 more FM station of those broadcast by the AM stations. More and tions which are as yet not on the air. Besides the above, more do AM broadcast station owners invest in FM 88 more applications are pending. As soon as the latter transmitters. And as soon as they do so they now in- are in operation. we will therefore have 1,115 FM broad- variably duplicate the programs which are broadcast by cast stations in the U. S. This does not by any means their AM transmitters over their FM transmitters as represent the saturation point. Con- well, even though this means sac- ceivably between 3,000 and 4,000 rificing high -fidelity transmission JII IIIIIIII I I IIII I I II111111111111IIIIIIIIIIIIIIII IIIIIIIIIIIIII IIIIIIIIIIII IIIIIIIIIIIIIIIIIIIII_ FM stations can operate success- to ordinary network standards fully in continental U.S. without This Special FM Issue (100-5,000 cycles). E. undue overcrowding. is Dedicated to Moreover, the exigencies of eco- Why so many stations? The rea- nomics will make it necessary for son of course is that the effective Major the independent small -town FM transmitting radius of an FM sta- transmitters to take the high - tion is its optical horizon -in flat Edwin H. Armstrong grade, sponsored AM network pro- country from 25 to 35 miles, in grams originating in New York hilly or mountainous regions from Father of FM and Hollywood. This is but a repeti- 35 to 100 miles. The topography in tion of broadcasting history when the U.S. being preponderantly level, RADIOCRAFT is happy and proud g early independent small -city AM it follows that over 85% of the to dedicate this special number on =_ broadcasters found it necessary to FM stations will have an effective E FM radio, to Major Edwin H. Arm. g become affiliated with the big radio range only an strong-scientist, radio engineer and =_ transmitting of inventor extraordinary. networks. average of 35 miles radius. Hence The reason for such affiliation many more are needed g Few radiomen in U.S. history have g transmitters g achieved the towering stature of Arm. _ is a purely economic factor: no to cover the entire country. small-center independent g strong. His unprecedented and epoch - g FM sta- The present trend indicates that g making basic discoveries: the super-uper- tion can possibly afford to pay for in a foreseeable time the U.S. will heterodyne, superregenerat ion, and a continuous stream of high -class undoubtedly be converted from AM frequency modulation will forever programs. Besides, the American to FM. The reason is simple: once make him one of Radio's Great Im- public has been educated to the big - a radio set buyer has listened to the mortals. feat ure, big -star radio programs. much clearer, practically noiseless Armstrong, who is professor of If the FM stations do not broadcast and staticless radio reception of an electrical engineering at Columbia these features, then FM would be FM receiver, he will shy away from 1- University, is now in the prime of doomed to failure. Clearly this will AM. This is indeed what is now E his eventful and productive life. Let not come about, and the present happening all over the U.S. It also us wish him a long and healthful tendency future, in the full knowledge that supports this view. explains the present FM boom, both he will bestow more of his priceless That the public's listening trend in transmitters being erected and gifts on radio and all of us. is unmistakably toward FM is receivers sold. clearly shown by the radio receiver Here are the latest FM receiver zlanlou minnulnuunmmun uuuuamuuan I IIIIII I I I munnmulllllllllllG manufacturers. There is first of all statistics: There are now in use a huge output of pure FM radios. (up to April 30) 2,022,547 FM receivers, which figure Next we have an even higher output (at present) of includes FM tuners (converters) and AM -FM sets. FM tuners that can be attached to old -style AM re- Radio manufacturers are producing now about 148,000 ceivers to bring in FM programs. Then, we have com- FM units monthly. These figures are compiled from bination AM receivers with FM, to bring in both types RMA and independent sources. of programs. Finally all the newer and better television At one time it was thought that FM would be a sets are also equipped for FM, making reception much completely independent adjunct to radio broadcasting more pleasurable. in America. It was felt then that every FM station How long will it be till the entire U.S. broadcasting would disseminate its own programs, or that there facilities have been completely converted to FM? From would be a country -wide high- fidelity FM network which about 8 -10 years might be a conservative estimate for would actively compete with AM stations and AM net- 85% to 90% of our transmitters. But from 10!'; to 15rí works. This did not come about, although there are of of them may remain AM for much longer -in fact some course many independent FM stations which originate of the larger stations may continue to transmit AM in- their own programs- mostly phonograph music at pres- definitely. JUNE, 1948 18 I The Radio Month

RELIABLE FM RANGES may extend were again very strong on the follow- Finch Telecommunications, Inc., is ap- far beyond the horizon, K. A. Norton of ing morning when the station began proved by the FCC. Mr. Finch is now the Bureau of Standards reported last broadcasting at 6:25 am. The mechan- negotiating for the construction of six month. Experimental research under- ism responsible for the strength of these FM stations in northern New York, taken by the Bureau has shown that fields and for the comparative absence with the idea of using them in a fac- atmospheric "ducts" and boundary lay- of fading is considered to be atmospher- simile network as well as for FM broad- ers in the lower troposphere both reduce ic refraction. casts. the attenuation of high- frequency radio From analysis of the field- intensity These facsimile papers would furnish waves with distance at points beyond data obtained by the Bureau, it appears farmers with a permanent record of the line of sight. These results are ex- that external receiving antennas may be livestock prices, weather reports and pected to provide a firmer basis for the used with considerable advantage for farming tips, as well as news flashes prediction of the service and interfer- reception of FM broadcasts at points far and pictures. Such a service would also ence ranges of FM broadcasting sta- beyond the horizon of the transmitting provide a big market for rural adver- tions; they should also aid in the solu- antenna. The FM fields from stations at tising. tion of problems that may occur in con- large distances may be expected to reach nection with other uses of the spectrum their maximum levels in the early morn- TWO -WAY RADIO for funerals is above 30 megacycles. ing hours during the summer months; planned by the Catholic archdiocese of Variations in the density of the at- at these times effective ranges up to sev- Chicago. An application filed with the mosphere within a few hundred feet of eral hundred miles may he expected. FCC last month to set up a permanent the ground provide differences of re- land station and two mobile field units fractive index which can increase the AUTOMATIC CODING and decod- at Mt. Carmel cemetery near Chicago. curvature of a radio wave by an amount ing of confidential information is now Radio communication among ceme- equal to or greater than the curvature possible with a new magnetic recording tery workers would eliminate confusion of the earth. Known as ducts, these system, the Codit Company of Chatta -. when several funerals are handled, ac- characteristic changes in the refractive nooga, Tennessee, announced last month. cording to the petition submitted by the index of the air near the surface of the Rev. William P. Casey, cemeteries di- earth become more and more effective rector. in bending radio waves as frequency increases. A PAGING RADIO little bigger than For the overland propagation paths a package of cigarettes may solve the which are usually involved in frequency problem of reaching doctors or business modulation broadcasting, effective at- men in theaters or city streets, it was mospheric ducts are to be expected after revealed last month. the sun sets and the earth begins to cool According to Sherman Amsden, pres- the atmosphere. Under favorable cir- ident of Telanserphone, Inc., New York, cumstances this cooling may continue the little receivers would be tuned to throughout the night with the formation the frequency of a special transmitting of a duct of great width. The received station. Each subscriber would receive fields would then be expected to reach an identifying number (his own private their peak values early in the morning station call). Telanserphone, which is a Magnetic disc machine codes as it records. before the sun has had opportunity to telephone- answering service, would re- destroy the duct by warming the earth. The system consists of a specially ceive important messages and immedi- This general behavior has been ob- coded plastic tracking disc. The disc is ately start broadcasting the subscrib- served for the fields of FM broadcast placed over a paper or plastic record er's call. The subscriber need switch his station WCOD at Richmond, Virginia, on a turntable, and the grooves in it radio on for only a few moments to lis- as received at the National Bureau of act as a guide for the needle which ten through the list of calls being Standards in Washington, D. C. On controls the movement of the special re- broadcast. If his is among them, he August 4, 1947, for example, the station cording arm. As the arm moves across telephones to the service and receives began broadcasting about 6:25 in the the surface of the record, it records the his message. morning. Throughout the day the fields voice magnetically on the iron- oxide - gradually increased until a little after coated surface. midnight. At this time the received field The magnetic pattern cannot be un- increased markedly, and the fading, derstood or analyzed without the use which had occurred at a fairly rapid of an identical tracking disc during rate during the day, decreased both in playback. Since each purchaser receives amplitude and frequency of occurrence. a set of identical discs, and no other The calculated field intensity corre- discs are made to the same pattern, he sponding to propagation in a vacuum has his own private code which cannot over a fiat earth was exceeded for the be deciphered. half hour just prior to 1 am, when the station went off the air. Presumably this FACSIMILE NEWSPAPERS will favorable propagation condition lasted soon be broadcast in rural areas if a throughout the night since the fields plan suggested by William G. Finch of EQUIVALENT SMOOTH PROFILE USED IN HEIGHT FIELD INTENSITY CALCULATIONS IN XMITTING ANT. RECEIVING ANT. R- R 4. R\ Receiver is practically cigarette -pack size. 2KßR 2K With this system, a single set of bat- 50 60 70 80 90 100 110 120 IK teries should last three months, accord- :0O 13 0 ing to the designer, Richard Florac of 0 10 150 DISTANCE IN MILES 160 New York City. No entertainment which would tempt the user to run the radio (4/3 EARTH RADIUS USED TO CORRECT FOR STANDARD 0` for long periods will be broadcast-only ATMOSPHERE REFRACTION) K =1000 R= RIVER paging calls, weather reports and Profile of the path between Richmond, Va., and Washington, D. C., over which tests were made. emergency news. RADIO -CRAFT for The Radio Month i19

MACHINES THAT LEARN were re- THEATER TELEVISION using the CANADIAN FM LICENSES now ported last month by the Philips Lamp delayed technique was presented for the number 44, it was stated last month in Works of Eindhoven, Holland. The ma- first time in a sneak preview at the reply to a question in the Canadian chine in question is an electronic tele- Paramount Theater in New York City Parliament. At least 11 stations are in phone switching apparatus of great last month. active operation. These FM stations are complexity, similar to a computing ma- The broadcast consisted of two am- located in four provinces, from New chine. ateur boxing bouts. It was sent by 7,000 Brunswick to British Columbia, and Usual switching equipment goes megacycle microwave relay from the range in power from 250 to 3,000 watts. through the same blind search until the arena to the top of the Daily News In addition to the stations already dialed number is located and the call Building and from there again relayed licensed, at least four more applications put through. But this machine learns to the top of the theater building. have been received. to distinguish frequently- called num- At the theater, the telecast was trans- Of the stations now in active experi- bers, and when a number is called often, posed almost instantaneously onto 35- mental operation, five are under the it can make the connection more rapidly. millimeter film by a special recorder, Canadian Broadcasting Corporation. It makes "intelligent" short -cuts. and the film was projected through the The remainder are privately owned. The invention, it is stated, can be ap- standard 35- millimeter projector. Only While definite frequency assignments plied to mathematicians' electronic com- 66 seconds elapsed from the time a scene have not yet been made the stations now puters. In a factory where machinery was telecast to the time it appeared on operating are all working on fre- is run by control apparatus, it would the screen. In the strict sense this is quencies between 93 and 106 mc, and it speed the most common operations. And not television, but rather delayed video. is expected that the Canadian FM band if new jobs were developed, the machine will approximate that now authorized might learn those, too! LICENSING for New York City's for United States FM broadcasting radio technicians will remain a dead stations. PASTEURIZATION BY RADIO issue till next Fall at least, city council- takes less than one second, the Radio man Stanley Isaacs promised last month. AUTHORIZED DEALERS are Corporation of who America reported last This, said the originator of the measure discovered reducing list prices on fixed - month. In the process, the bacterial to license radio repairmen, is to "give price television receivers have been count of milk drops from 50,000 to 100, the industry a chance to clean up its dropped by the Allen B. DuMont Lab- an unusually low figure. The milk is own problem." oratories, Inc., Victor E. Olson, receiver homogenized at the same time by the Reason for the respite is the encour- sales manager, revealed last month. He action of the rapidly fluctuating electric aging progress being made by the As- also disclosed that the company has dis- field on the tiny oil droplets suspended sociated Radio Servicemen of New York continued franchises of dealers who milk. 'n the (City). The ARSNY has formed griev- have transshipped merchandise to non - ance committees to handle customer authorized stores. complaints against any radio repairmen, A shopping agency has been engaged RADIO -ELECTROCUTION whether Association members or not, is to watch retailer activities in states Readers -especially radio techni- now sponsoring a course of technical which have fair trade laws. cians-will do well to read the item lectures, and is planning to co- operate below with extreme care. A house- in organizing for New York City a FM TRANSPORT RADIO has been hold radio can be dangerous! This is Town Meeting of Radio Technicians installed on 250 Greyhound buses oper- the second report of a double electro- (similar to the Philadelphia meeting) ating midwest routes, Motorola an- cution in the bathtub due to a mid- late this summer. nounced last month. This system per- get radio. The other one was that of mits bus dispatchers to keep in constant a mother and three -year -old child. TELEVISION may not reach "a good communication with all buses and ter- The child caught the line cord and share" of the population of this country, minals in the network. The transmitters pulled the radio into the tub. It is Joseph H. Ream, executive vice- presi- and receivers are housed in a special the duty of radio servicemen to point dent of the Columbia Broadcasting Sys- compartment at the rear of the bus (see out to customers potential dangers in tem, declared last month. Rural sections, photo below). (especially) midget a.c -d.c. radios. he continued. will be beyond the service The busses also have a small speaker If a radio is used in the bathroom, range of television stations, and that built into the headrest of each passen- it must be permanently installed - "very probably" smaller cities and ger's seat. An individually operated bolted firmly to a shelf at a distance towns may never be able to support sta- switch gives the passenger a choice of from the tub or wash -howl. The same tions. either one of two radio programs. precautions are necessary with kitchen radios. A set near the sink can be as deadly as one near the bathtub! A small radio caused the death by electrocution last month of two small girls in Binghamton, New York. The girls, Wanda Thompson, 12, and Marlene Monell, 11, were killed in the bathtub when the radio to which they were listening fell into the tub. The 117-volt current was sufficient to cause instant death under the cir- cumstances, the coroner reported. Investigators reported that Mar- lene had often taken the radio into the bathroom, set it on the tub and listened to programs during her evening bath. Ironically, the father is an electrical- appliance repairman. He was called out on an emergency refrig- orator job during the evening and was not at home at the time of the accident. This bus installation provides communication for the driver and programs for passengers. JUNE, 1948 20 tovcr Feature Frequency Modulation- áT 1922 and 1948 4,,Je

The system now popularly known as FM operates with less than one -tenth of the distortion of the best AM system, and improvement in this direction is not yet at an end. A new era of realism in the transmission of music with all its tones and dynamic range has become a practical possibility. As everyone also knows, the problem of static, both natural and man -made, has ceased to be a problem. FM reduces noise to 1 /100th of its energy on an AM signal on the same frequency, and since the system operates in the very high frequency ranges, still further immunity from atmospheric static is obtained. It is clear, therefore, that the inventing and engineering responsibilities of those men who worked to bring about this Co o rtrsg of Forts s. il,y,n:ine: photo htl Erie School new era in broadcasting have been successfully met and Armstrong revisits the Yonkers room, scene of his early work. their duties successfully discharged. Their work is clone. The question now is squarely raised: Will the public get Rodio Broadcasting -1922- ( Looking Backward ) the benefits of this work to which it is most certainly en- the bill? The responsibility IN the year 1922, when broadcasting was just getting under titled, since in the end it pays to see that it does no longer rests with the inventors and way, amplitude modulation was the method employed. engineering that Nobody called it amplitude modulation, because most those who have engaged in the creative To it brought FM into being. It rests upon the administrative people didn't know there was any other kind. them and most heavily was simply "modulation." governmental bodies, upon the broadcaster, on. page 55) Nonetheless, the idea of varying the wave length of the (Continued signal, or its frequency, could be found in the text books more than fifteen years before broadcasting started. As a practical reality, however, it was still an idea and all attempts to make use of the method had resulted in failure. In the nineteen -twenties, the characteristics of the wave resulting from modulating the frequency were examined by some very able mathematical physicists. The consensus was summed up in a conclusion appearing in a paper in the Proceedings of the Institute of Radio Engineers in 1922 in the words: "Consequently this method of modulation (frequency modulation) inherently distorts without any compensating advantages whatsoever." So amplitude modulation became enthroned as the accepted method of doing the job. Now many of the readers of this article remember the great amount of effort that was put forth in the nineteen - twenties, or earlier, to discover or invent a "static eliminator". They will also remember that the people who put any great amount of emphasis on, or expressed any great amount of hope in, the possible solution of the problem, were considered rather visionary -a bit "queer ", in fact. In 1928, again in the Proceedings of the Institute of Radio Engineers, we find the consensus of the art at that time in a mathematical demonstration of the fact that static, like the poor, will always be with us." So ' it appeared in the early nineteen -twenties that the broadcasting art was destined to he forever limited by the vagaries of the forces of nature and the imperfections of the amplitude modulation system, wherein a "radio" sounds like a "radio" and not like a musical instrument.

Radio Broadcasting -1948- ( Looking Forward ) But as everyone now knows, those pronouncements turned out to be false prophecies. Some discoveries were made, and what were regarded as axioms in the art had to be rewritten. Men working on an arm of the pioneer FM antenna at Alpine, N. J. RADIO -CRAFT for Fn 121 Ell Fundamentals Why k:/ radio is free from many of 1 h draa /iiii%S of 1-/ hroudinMling By JOHN B. LEDBETTER

FREQUEN 1" modulation is not new. Since the early (lays of broadcasting various attempts have been made to utilize some form of FM as a means of overcoming radio disturbances and other disadvantages of AM broadcasting. Early attempts were un- successful because any advantages gained by use of FM were lost in the receiver, and because a frequency -modulated signal produced less than one - tenth the power of an amplitude -modulated signal. It remained for Major Edwin H. Armstrong, professor of electronics at Columbia University and inventor of the superheterodyne and su- perregenerative circuits, to develop and introduce the system which is the basis of present -day FM. Advantages of frequency modulation over amplitude -modulated systems include 1. immunity to static and man- made noises, 2. freedom from fading and interference, and 3. high -fidelity reproduction. Other gains are greater efficiency and economy of transmitter operation, increased service area, and lower -power requirements. Noise can generally be classified as being either impulse or random. Impulse Author checks frequency on built -in scope at WCTS, Cincinnati. Motor is noise contains bursts or pulses which control above hand. occur separate at or infrequent inter- form output carries all frequency vals. This is the this issue, another weakness of present - type produced by electric deviations of the original razors, ignition systems, power signal faith- day broadcasting is the interference- lines, fully. Applied to the discriminator, by and other electrical equipment. Random these complicated fading -which ruins re- noise variations produce an audio output ception at night in large sections of the pulses overlap or run together to which varies in amplitude. form a continuous sound. country. Examples of The ratio detector uses no limiters, random noise are thermal agitation and but operates tube hiss, both by distinguishing between Fading and interference disturbances which origi- the ratio of signal strength above and nate in the receiver. Atmospheric dis- Radio waves consist of two compo- below the mean carrier frequency. Since nents, turbances and precipitation static are this ratio varies the sky wave and the ground wave similar to random noise. according to the modu- (Fig. 1). The sky wave is emitted sky- lation in the frequency- modulated wave, When this noise is received by an but ward from the antenna and reflected remains constant or nearly so in back AM receiver, it is detected and ampli- noise and amplitude- to earth at (listant points by the fied modulated signals, ionosphere. The ground wave along with the desired signal. Such only the frequency modulation affects travels noise -or even an interfering AM sta- the output. along the surface of the earth. The tion -can be objectionable even though ground wave proper may be subdivided its intensity is only 1Ç- that of the de- IONOSPHERE into two parts, the surface wave and sired signal. the spare :vase. It is the surface wave When such noise is picked up by an which determines the daytime coverage FM receiver, it passes through the con- ____ _. of AM broadcast stations. At night verter and mixer stages just as in an C broadcast frequencies may be trans- AM set. The FM detector, however, is ....,.ñ,..--n7flAxqrn mitted long distances by the sky wave. designed to detect only variations in ARTN The result is that the AM signal is re- T- XMIT TING ANT. ; R- RECEIVING SKY frequency of the applied signal, not ANT.; A- wAVE , flected at a number of different angles. B- SPACE WAVE (DIRECT PORTION); C- SPACE WAVE (GROUND - changes in amplitude. Two methods are REFLECTED and appears at a number of different PORTION); D- SURFACE - common. In WAYS. i distant points. Many times the Foster -Seeley discrimi- e, C L D ARE ALL COMPONENTS OF THE GROUND WAVE. the interfer- nator circuit, one or two limiter tubes ing station is located thousands of miles Fig. 1 -Wave propagation FM precede the detector. These are i.f. at frequencies. front the point of interference. stages which operate at low plate and Thus one of the worst enemies of good FM owes its freedom from fading and usually zero grid voltages. As a result, reception is defeated at the start. Cer- station interference to the fact that at their output cannot exceed a certain tain types of noise which are actually high- and ultra -high frequencies, the amplitude, and, if they receive a rea- frequency- modulated do get through to sky wave is generally not reflected back sonably strong signal, the output ampli- the audio output, but these are rare and to earth by the ionosphere, but continues tude is uniform at the maximum of almost negligible. out into space in practically a straight which the limiter is capable. This uni- As pointed out in another article in (Continued on page 53) JUNE, 1948 FM IIÉCEÍVERS

: "::;! ,

, ..; : . ,:' ,...... I-The coaxial tuner is shown behind the tuning condenser of the Motorola 77XM. FM 2-This Belmont Model I IAF21 has I I tubes and uses a quarter-wave indoor antenna. 3-Rear view of the National NC-I 08T. The receptacle is for power fo e.f. amplifier. 4-Espey-7B. This chassis and speaker are available for custom-built installations. 5-Capacitors tune FM and AM r.f. sections in the Farnsworth ' GK-084 to GK-087 sets. 6-Stewart-Warner A92CR3 to A92DR6. The FM and AM permeability tuners are ganged. 7-This II-tube chassis is used in the West- inghouse Models H-164, H-166 and H-167. 8-The REL 646 is a commercial type set with field-strength and tuning indicators. 9-The r.f. sub-chassis of this Philco Model 48-472 is shock-mounted with rubber. 10-Urrder chassis of the Belmont . ... Models Model I IAF21 shown in the center of fop row. 11--Chassis of Westinghouse H-161 and H-168. Note the novel dial arrangement. RADIO-CRAFT for

123

FM receivers, fundamentally alike. used by Philco, differs from both com- vary in mon types. The circuit of this section is elan, details and use compo- shown in Fig. 1. It is designed around the FM 1000 nents unknown to older radio sets tube, the No. I and 2 grids of which are connected in a modified Colpitts oscillator circuit tuned FM broadcasting has to mushroomed by an r.f. stage) one or more i.f. ampli- the 9.1 -me i.f. with LI and CI -C2. The from an entertaining curio into a fiers, one or more limiters (in some full -grown industry in a compara- types of circuits) a di.sci'inlinator, an tively few months. Set manufac- a.f. amplifier and a power supply. All turers, spurred by the ever- increasing sets are designed along these Bues, but number of FM broadcasting stations, a number of them have outstanding dif- are now breaking records for producing ferences clue to different engineering FM receiving equipment. There are a approaches to identical problems. few straight FM receivers on the market but most manufacturers are produe- Differences in discriminators ing sets for receiving both FM and AM The ratio and Foster -Seeley discrimi- broadcast stations. nators are the most popular types in use The Ware Inductuner, described on page 24. The prospective purchaser of an FM today. The latter type normally requires oscillator set often circuit is coupled to the platt- finds very- little technical in- one or two limiters following the i.f. through the electron formation available on stream. The plate any set he may amplifiers. These add to the sire and coil 1,2 is also consider. This tuned to 9.1 me. Its hand - article and the data in over-all cost of the finished product. width is the accompanying increased to about five times table may supply The ratio discriminator does not require the width of the sonic of the lacking information, limiters. FM signal by the 5,600- as well Cheaper and more compact ohm swamping resistor across as give a brief review of the main fea- sets can therefore it. The be made with this cir- signal from the third i.f. amplifier is fed tures of the more common receivers. cuit. (FM detectors are discussed in an- into The typical the No. 3 grid. The coupling be- FM receiver consists of other article in this issue.) tween circuits causes a mixer -oscillator (sometimes preceded the oscillator to The locked -in oscillator discriminator (Continued on following page) OUTSTANDING CHARACTERISTICS OF THE BEST -KNOW

? 7q .... ó j ? É . tñ A a bé 4. ^É ó i ö F A É Q C\ Q f F f Q e O 4 pó i .Q p= .. \ C e\ O ` _ .1 r:F Ó Q 4.1 Q ÿ i ADMIRAL Fold. 7C64 FM -AM 8 8/7 P I FM Rollo dole S E 10 PM 5Y3 (Ch. 811) P A.C. Changer 6587 Y, 6ÁU6, 1 AM Loop bÁ15, ADMIRAL 6517, 6V6, (2) 6BA6 Fold. - 7C73 FM -AM 9 9/7 P 2 FM' Rollo d'ple S-E 12 PM 5Y3 (Ch. 9A1) P A.C. Changer 6587 -Y, 6L5, 6V6. I AM' loop ADMIRAL 6517. (41 6BA6 9814 Fold. to P 2 FM' Ratio d'ple 9816 FM AM 6587 -V, bÁ15, 6507, 9 9/7 C I AM' loop (Ch. 981) S-E 12" PM 5Ú4G A.C. Changer 6V6, (4) 6BA6 AIRLINE y. -wae 6" 9 (WARDS) FM-AM 9 9/6 C None Ratio Hank 748R S -E oval SY3 A.C. Phono 6C4, 6AT6, 6V6, -1814 C None LOOP ED Input 6A1.S, (4) 6BA6 14 -wave AIRLINE FM -AM 9 9/6 C None Ratio Hank S -E 10- ED 5Y3 A.C. Changer 6C4. 748R -2702 C None 6AT6, 6V6, Loop 6A15, (4) 6BA6,

Changer, (3) 6BA6, 68E6, AIRLINE FM-AM' 10 9/6 C I FM Ratio Loop S -E 10 ED 5Y3 A.C. Tuning 616, 6A15, 74WG -2705 C None 6A16, Loop Ind. 6V6, 6U5/6G5 1/4 wave BELMONT FM -AM I I 11 /8 C None Ratio Honk 11ÁF41 P -P IO" ED 5Y3 A.C. Changer (4) 6BA6, (2) 6C4, C None Loop (2) 61(6. 6AT6, 6ALS

CROSLE FM -AM" 8 8/7 C None F -S None S -E PM or ED 5Y3 A.C. Chonger 12) 65G7, 6AC7, 7F8. 38CR C None Loop 6116, 6V6, 6507 CROSLEY Changer C 1 FM None 148CP, FM Tuning (3) 6SG7, (2) 6507, -AM' 14 13/9 C None F -S Loop P -P 148C0 12 PM 5U4 A.C. Ind., (2) 6V6, 65A7, 6116, PB' 6AC7, 7F8, ESPEY 6SH7, 6E5 Chaule Fold. 6BA6, 7F8, 7AH7, FM -AM I I 10/7 C 1 FM Ratio d'ple P -P IO" PM 5Y3 A.C. None 75117, 7A6, 78 C None 6507, Loop 7F7, 707, (2) 7C5 FARNS W ORTH GK -084 FM -AM 8 8/6 C 1 FM Roto Fold. to -087 S -E PM 5Y3 A.C. Changer (3) 6517, 6587 -Y, C 1 AM d'ple 6AG5, 658, 6V6 Changer, Fold. P -P 12 FREED -EISEMAN Tuning 6H6, 6U5, (2) 6SA7, FMAM' 21 16/11 C 1 FM F -S d'ple w oofer 12) SU4 A.C. Ind. (2) 651(7, 6517, (3) 615, 30, 32 C I AM LOOP 3" FM (2) 616, (2) SU4, (3) tweeter Squelch 6AG5, MOTOROLA (2) 6SG7, (2) 65117 77ÁM41 te 77XM448 FM' AM None W 6 6/5 Co -an F -S Hank' S -E 5" PM Solen. AC /DC9 Chonger (2) I2BA6, 5085, I9T8, 77FM21 to C None Loop 77FM23 17,677, 128E6 Changer MOTOROLA PS inner" (21 6V6, 7W7, 6507, FM AM" 10 8/7 Co -a. None Ratio loop P -P 12" ED 5Y3 A.C. 107F31 (motor 65X7, 6ALS, 707, C I AM loop 7F8, 6SG7 trolled) NATIONAL NC (3) 6SG7, 6114.6, 6AG5, -108T, FM I1" C 1 FM Ratio None S -E 5" PM 5Y3 A.C. Tuning NC-108R 6C4, 6116, 6517, 6V6, - Ind. 6U5/6G5 (table cot tiluled on folloi'ing page) JUNE, 1948 211 FM

. óo g. ?° ° o ó é é ré O. ..>. v é áp w' e nA a tf ° ° ó .4. .s tk d tD C i F F\ j .p F ó ' Ta w° w Ar r ro d r° á v` Fold. OLYMPIC M Ratio pole P -P 12 ED 5Y3 A.C. Changer 7 FM.AM 10 10 /8 i -V25, 934 C 121 6507, 6 A15 (2) 6K6 -936 C 1 FM 4 . 6 Hank. S.E oval 11723 AC /DC 14F8, (2) 14H7, 7 7/6 C 1 FM Ratio PHILCO fM -AM FM 12ÁW6, 14X7, 50A5 C None loot/ 48 -472 Changer ED 5U4 A.C. PB Tuner, (2) 6BA6, 6AU6, 7A7, 1 FM l -1 Hanks P.P PHILCO C 7F8, 7AF7, FMI000, None Loop 12-M Scratch 48 -1290 FM -AM" 13 11/9 C Elimin. 6507, 7E7, 7F7, (2) 6V6 Changer Fold. 14" Auto. PB 6AU6, 7E5, 757, FMI000, PHILCO P -P woofer 5Ú4.G A.C. Tuning. (2) 7H7, 7F8, C 1 FM l -I d'ple 48 -1274, FM -AM 16 13/12 5" Scratch (3) 615, 7E6, n7, 7E7, C 1 AM Loop 48-1276 tweeter Elimin. 12) 6L6 Fold. A.C. Changer d'ple P -P 12' PM 5V3 RCA VICTOR FMAM 10 9/7 C None Ratio (21 6BE6. 6BA6, 12Ì16K6 C None loop 710V2 field Strength (5) 7ÁG7, (2) 7C5, 6 SU4 A.C. an9 Tun- 121 7F8, A6, F -S None P -P None 644 6 FM 12 12 C 1 FM d.

STEWART- 12H6, 6406, Hank SE 5" PM Selen. AC /DC WARNER FM -AM 7 7/5 C 1 FM Ratio (3) 12BA6. Loop Á72T1 to C None A72T4 STEWART- A.C. Changer (3) 6BA6, 6AL5, Fold. S -E 10' ED 5Y3 FM -AM 9 9/7 P I FM Ratio -Y, 6507, WARNER dple 6SB7 A92CR3 P 1 AM 65)7, 6V6 A92CR6 131 6BA6, 68E6, 6AU6, CAR 6H6, 6Ái6, 65C7, Nona P -P PM SY3 AC CARLSON FM'sAM 11 11 /8 P 1 FM Ratio 121 6V6 1 loop 1210 P AM WESTINGHOUSE 6BA6, 616, A6, Ratio Fold. H -161, FM -AM 8 8/6 C None Changer 616, 6A76, 6AU6 d'ple S -E 8" ED'. 5AZ4 A.C. H -168 C None loon (Ch. V-2118) WESTINGHOUSE (2) 7f8, 6AU6, 10 /8 1 FM Ratio Fold. H -164, FM -AM II'. C A.C. Changer 6AT6, 6H5. d'ple P -P 12" ED 5U4 1 H -166, C None 6BA6 62)7 Loop H -167 ZENITH S -E PM Semen. AC /DC 1 FM F -S Honk. (3AU2BA FM's -AM 7 7/6 P , 1 E6, 7H820 Loop (Ch. 7E01) C 1 AM 10 On series 77 FM only to 108 Mc PB Push -button - FM - 88 - amplifier 11 - P us 5.6 to 12.2 -mc bond 1 First stage grounded -grid AM - 540 to 1600 kc (opprorr) - 12 Any combination of 6 AM or FM stations 2 Conventional ri. amplifier - C Condenser tuning - 13 replaced by meter in NC-108R - Plus the 9 to 15.5 -mc short -wave bond - 6U5/6G5 P - Permeability tuning 3 - to 4 Plus the 9.4 to 11.9 -mc short -wove bond FS - Foster -Seeley discriminator - 14 Plus 44 to 15 5- c bandd 6 Double superheterodyne L-1 - Lockedin oscillator - 16 10" speaker on Model H -168 6 Plus 2.5 to 6.7 and 6.7 to 18.5mc bands - PM - Permanent magnetic dynamic - 17 Changer on Model H168 only 7 Push buttons for tone control and BC tuning - ED - Electro - dynamic - 18 -A 65C7 phono preamplifier is included an Models PP Push pull 8 - FM antenna in line -cord - straight o.c. H -166 and H -167 -E`5 - Singleended 9 - Series 77XM only, others 19 - Plus 6.2 to 9.9 -mc and 12 to 17.5mc bands

follow a doubler supplying the heterodyning and both television bands (44 to 216 ntc). "lock -in" with the i.f. signal and is a its variations. The current through the signal. This reduces oscillator drift. The General Electric Guillotuner lines type of tuner is modification of the "butterfly" tuning load resistor R1 is linear and inversely The co -axial ca- Thus in Motorola FM radios. The high unit, and combines inductance and proportional to the frequency. used and the other are converted to Q of this type of tuning circuit makes it pacity in circuit unit. It, frequency variations mentioned above, were linear a.f. voltage changes. The a.f. sig- possible to dispense with r.f. stages to tuning systems nal is taken from Rl and fed to the a.f. eliminate images. Indeed, so selective is amplifier through a decoupling network. the circuit that Motorola uses the low 4.3 -mc i.f. which was standard in sets Various tuning methods built for the old FM band, thus obtaining certain advantages in stability, gain, 6K The most noticeable difference in FM 15 receivers is usually in the r.f. or front and ease of adjustment inherent in the Pof end. The methods of r.f. tuning include: lower intermediate frequency. in- . 1. Varying a capacitor across a coil. Some of the Motorola models are - KTIOOKO AF AMP' 2. Varying the permeability of the teresting also in that they use a Foster limiters. coils by movement of an iron or brass Seeley discriminator without R +225V with a slug through the cores. The manufacturers claim that Fig. I-Philco uses this locked -in oscillator. elements like signal tuned in exactly, noise impulses 3. Using special tuning some length in the Decem- the Mallory -Ware Inductuner, the Guil- tend to balance themselves out across described at the two diodes of the discriminator. ber, 1947, issue of RADIO -CRAFT. lotine or co -axial lines. is a fea- of the Philco Models 48- The Inductuner, one of the simplest An electronic squelch circuit The circuit Freed -Eisemann Models 30 1274 and 48 -1276 is one of the most of all tuning circuits, is a set of induc- ture of the r.f. tors mounted on a rotatable form. Slid- and 32. These sets use separate FM and interesting of those reviewed. The uses using a 6AU6 r.f. pentode, is ers make contact with each inductor, AM tuner circuits. The FM tuner circuit, AM uses a standard standard. The 7F8 oscillator has some the amount of inductance varying as the 10 tubes. The tuner half the form is turned. This type of tuning cir- 4 -stage plus tuning eye superheterodyne original features. It operates at broadcast band required to beat with the sig- cuit has an enormous range, and is used covering the standard frequency on page 52) nal to produce the i.f. The other half is with success to tune across both the FM (Continued RADIO -CRAFT for FM

SI,-r 906 Ja=Lson 64i cck 288X FM SWEEP GENERATORS INDEX OF POPULAR FM -AM SIGNAL GENERATORS By BOB STANG CROSS JACKSON HICKOK SILVER G. E. TRIPLETT R C A -53A FEATURES 641 288X 906 YGS -3 3433 WR

T11 E radio serviceman who is to con- must spend a por- Frequency range 100 kc to 100 kc to 90 kc to 100 kc to 100 kc to tinue to succeed fundamentals 160 mc; 160 mc; 170 mc; 150 mc; 170 mc; 85 -110 mc; 10 bands 8.3 -10.7 mc tion of his time keeping up with 8 bands 7 bands 8 bands 7 bands in his field. technical developments FM maximum 0 to 0 to Not 0 to 25 kc steps With the advent of FM, television, auto- deviation range ±400 kc ±450 kc variable ±750 kc to ±150 kc ±400 kc control, noise silencers, matic frequency FM sweep Var. from Var. from suppression, not to 100 to 60 or 400 400 cycles 100 to 60 or and dynamic noise frequencies cycles mention a number of developments at 10,000 cycles cycles or 400 kc 12,000 cycles 400 cycles 60 present in process, the serviceman is Output calibration Calibration Calibration to keep his technical meter; None, db meter; Magic eye; Meter, not hard pressed 5 ranges; meter built 5 ranges; no calibra- Calibrated knowledge at a level high enough to en- 0 to 100kmv in 0 to 100kmv tion in my None satisfactory job. This able him to do a Amplitude 60, var. 100 60, 400 var. 60, 400 var. 60 need is recognized by the number of new modulation to 10 kc 0 to 15 kc 400 100 to 12 kc 400 -- - technical magazines which have sprung in cycles de- Only 60 into being concurrent with these 'Scope Yes velopments, as well as the increased synchronization Yes cycles No Yes Yes circulation of the "old reliables," and Phasing control Yes No No No No NO books the large number of pertinent Variable amplitude published. The enterprising technical modulation r, 0 to 80 r; No 0 to 50'7, 0 to 100'; No - man therefore has reams of material at Voltage regulation Yes No Yes No Yes No his disposal. Accuracy 2 of 1 `'; ; While technical know -how depends Fixed freq. how anxious each service- standards - Set by beat - Set by beat- partly upon no beat adj. ing against ing against man is to obtain it, the problem of required int. crystal 1 % int. crystal 1% 2' ; test equipment is an selecting proper Type of dial Glass Glass Plastic Plastic Rotating Glass other matter entirely. The only informa- protected; protected; protected; protected; wire protected; available Knife -edge Fixed Rotating Rotating pointer Fixed tion on the subject generally pointer; pointer; dial; dial; over pointer; is catalogs which, Fixed Rotating Fixed Fixed etched Rotating from manufacturers' scale while very useful, are naturally biased dial scale pointer pointer panel in their own favor. More information Serviceman's price $159.50 $159.06 $116.50 $195.00 $157.50 $162.50 evaluating equipment features is for de- needed so that the prospective buyer can Today's most useful piece of test equ'p- erator. This instrument, if properly weigh function against cost, and decide ment, with the possible exception of the signed, can be used in conjunction with what is best for his individual needs. oscilloscope, is the FM -AM signal gen- (Continued on page 60)

General Electric YGS -3 'Hpott 3433 RCA WR -53A JUNE, 1948 .261 PAn ADVANTAGES OF FM The listener to frequency -modulated programs hears more stations and better music undam- aged by interference, natural or man-made. By LEIGH L. KIMBALL*

THE frequencies from 88 to 108 receivers in use today. They are com- over -all system has the megacycles required fre- today embrace the finest mon pieces of living room furniture, quency response and meets system distortion of aural broadcasting which whereas ten years ago a superhetero- specifications. has been available to the public dyne receiver operating at 100 mega- The advantages of FM since the beginning are not limited of radio history. Yet cycles would have been even a labora- to high -quality program transmission not so long ago it was believed that any tory curiosity. only. FM offers real benefits to broad- frequency above 30 megacycles was lim- Now comes the question -of what use cast listeners who live beyond the nor- ited strictly service to as far as the hori- and what advantage is this new system mal nighttime service ranges of AM zon and that the generation of large of broadcasting to the average person? transmitters. amounts of power these at shorter wave The first advantage is the well -known The degree to which AM broadcasting lengths was an impossibility. It took one of high audio fidelity. The chart in deteriorates at night is amazing. Mil- World War to inspire the II miracles of Fig. 1 shows the extended audio range lions of listeners in this engineering which country who have made it pos- possible with FM. Full frequency re- live in rural and semirural areas night- sible to develop kilowatts of power in sponse to the limits of human hearing is ly experience a tremendous reduction in the vicinity of 100 megacycles. possible because the 20- megacycle width available AM program service. The The miracles were not confined solely of the FM broadcast band accommo- number of stations in the country has to transmitting developments. Receiv- dates wide -band stations with ease, more than doubled since the end ing -tube design of the also advanced. keeping whereas the approximately 1- megacycle war. Right now, there are more than step with transmitter research. A tre- wide AM broadcast band poses a prob- 1,970 AM stations on the air or under mendous amount of research was also lem of frequency conservation. In addi- construction. undertaken As a result, most of them on high -frequency antennas tion wide -band FM is inherently free are operating and v.h.f. propagation. under increased interfer- The accumulated from noise. ence conditions at night when sky waves experience led the Federal Communica- The FCC has set up frequency -re- tions Commission to assign FM broad- sponse standards and requires compli- casting to the 88 to 108 -megacycle band ance with these standards within + or which only a few years before had been 1 - db from 50 to 15,000 cycles. Dis- CPS considered an absurd assignment for tortion requirements are as follows: IS" broadcast service. Modulating Maximum N11 How greatly FM has progressed since Frequency Permissible its original assignment to this frequency (Cycles) Distortion (r,"c) 50 to 100 3.5 1211 band is illustrated by the fact that there 100 to 7500 2.5 Ilk a are now a number of FM broadcast sta- 7500 to 15000 3 tions operating with effective power in 011 Before a license is issued, the larger txcess of 200 kilowatts. It is estimated e11 FM Stations are required to submit ac- that there are over 1,620,000 FM es home tual measurements from microphone 'Chief Engineer WASH -FM. Washington, D. C. terminals to antenna showing that the 111 UNITED 4TATES 1570 51(

4 Al 011 2s `a>ii1`` \ Ì Í s ` ,-m 11 1000 ` ,, I 1\`Ì'- Fig. I -FM reproduces the full audio range. 4X' -ú cover tremendous distances compared to ground -wave coverage in the daytime. After sundown, these sky waves may travel halfway or further across e e the country, to interfere with any or all i (61 other stations on the same channel. In =1\r the early days of broadcasting, when there were fewer stations, sky -wave '`L transmission was a boon -people de- o _1 nr#4.00-: veloped their first keen interest in radio e1EL0 INTENSITIES (MV/M) by sitting up into the wee small hours DA' M11 - to listen to distant stations. today. aT l00o ItC But sky -wave propagation in the form of w.p WILL a[ FREE Of TIIa1MdIC 1 interference from other stations on his Ma[ FOR 50i Or M VEAN channel has become a plague to the broadcaster. the map above shows how serious are the effects of static on ordinary AM transmissions. Many Of the AM stations now licensed, 851 southern areas can have atisfactory radio program service only with static -free FM. (more than half) are class I-V locals, all RADIO -CRAFT for FA1 1:; of which are crammed into six of the antenna height of 500 feet. If the an- channels on a population basis. Smaller 101 channels available for AM broad - tenna height is greater than 500 feet, cities capable of supporting relatively casting-an average of about 142 sta- the radiated power must be scaled pro- few stations have been assigned relations per channel. These stations range portionately but in no case may the tively few channels, and the larger cities from 100 to 250 watts and serve a radiated power exceed 20 kilowatts. As have been assigned correspondingly radius of anywhere from 20 to 50 miles an example, the radiated power must be in the daytime, depending upon fre- reduced to 3 kilowatts for an antenna quency and soil conductivity in the area. height of 1,000 feet. Incidentally, this At night, the interference-free coverage illustrates graphically the relatively tre- of a local station in most areas is re- mendous effect upon coverage of height duced to something less than a 5 -mile as compared to the effect of power. radius, due to interference from all the The minimum power in Area II is 2 other stations on the same channel. kw and the minimum antenna height is 350 feet. No limit is placed upon the FM coverage area is practically con- 102 stant. The distance signals can cover power and antenna height of class B is roughly the stations in Area II, provided that the at this high frequency ex- same during day or night. Interference new station does not interfere with less isting stations. Consequently, stations in from other FM stations is much sprawling than with AM because the desired FM this area are able to serve the rural area. A considerable number of be only twice as strong as IN MILES signal need issued DISTANCES GIVEN the interfering signal on an adjacent construction permits have been channel to blanket it completely. A de- for 450 -kilowatt stations. As an example of the way the tenta- sired AM signal must be 100 times Fig. 3-Approximate ranges of FM stations. stronger than an interfering AM signal. tive allocation plan works, 20 class B have been assigned to serve the of factors, a greater channels larger numbers of channels. Because Because of these entire metropolitan area of New York methodical planning by the FCC, the number of FM stations can be assigned City on a constant day- and -night basis. for FM more com- most efficient channel usage in a given area, and can give In addition to these 20 channels, there facilities has been assured. than a smaller number broadcasting plete coverage are 13 class A channels available to The map in Fig, 2 illustrates what This is a much more of AM stations. serve local interests, making available coverage may be obtained by FM sta- effective system for all concerned -the a total of 33 FM stations in the New predic- buying advertiser, tions according to the coverage broadcaster, the time- York area. tion system set up by the FCC. It com- and the vast majority of listeners. Be- The pattern is the same throughout pares the predicted coverage area of cause of the stability of FM coverage, the coverage ac- for the FCC to set up a the country. In general and wherever one FM station with it was possible (Continued on page 60) tentative allocation plan to serve as an practical, cities have been assigned allocation guide for FM broadcasting OLIIAMA CO I co throughout the country. The plan pro- . I wt. vides for two types of FM broadcast »....I MEASURED COVERAGE -I stations. The first is the class A station, designed to serve small communities and towns other than the main city of an area and its surrounding rural area. These stations are limited to an effective radiated power (effective radiated power = transmitter output power X antenna power gain X transmission line efficiency between transmitter and antenna) of 1 kilowatt and an antenna height of 250 feet above the average terrain. Twenty FM channels have been set aside for use by class A stations. The second type is the class B station, designed to render service primarily to a metropolitan district or principal city and its surrounding rural area. The allocation plan also divides the United States into two areas to tailor the class B stations to the different needs of the country. Area I includes southeastern New Hampshire; all of Massachusetts, Rhode Island, and Con- necticut; southeastern New York as far a,...... north as Albany- Troy -Schenectady; all of New Jersey, Delaware, and the Dis- trict of Columbia; Maryland as far west as Hagerstown; and eastern Penn- sylvania as far west as Harrisburg. These are generally the more densely populated areas which can better support a larger number of FM stations, as re- but other sections may be added .:.o quired. The rest of the country is in I o.. i ...... -;;;.i_» ,nña Area II. .,mate o ..... Class B stations in Area I are licensed on,.R.,/ m,..,l...1 .. ° to operate with not less than 10-kw ef- ,-oK...... R.... fective radiated power with an antenna r l l .. height of 300 feet and a maximum of 20 -kw effective radiated power with an Fig. 2- Correlation between predicted and actual coverage of typical FM broadcast station. JUNE, 1948 PM 281

I-The Edwards Fidelotuner, a long- lines device. 2-The Brooks FMT-10 uses 8 tubes plus eye and rectifier. 3- Espey tuner, an FM-AM receptor. 4- The Meissner 8C is a compact and efficient unit. 5-Collins Audio Products

Deluxe FM-AM tuner uses 11 tubes for FM including voltage regulator and rectifier. 6-The Dongene FM-AM tuner is another large ¡ob. 7-The Browning. one of the pioneer AM-FM 9 tuners. 8-Approved Electronics tuner,

featuring a special curved long-lines circuit. 9-The little Pilotuner is one of the best-known units. 10-The De Wald is a device which receives an FM signal and puts out an AM signal in the

manner of a phonograph oscillator.

RADIO-CRAFT for s FM - - -- 129

FM tuners may be almost as satisfactory as complete receivers to listeners wills good AM receivers

FM is no longer the coming form of fidelity type as required for best results. radio broadcasting. It has arrived! The would -be FM listener has as wide There are now more than 500 FM a choice among FM tuners as among stations actually on the air, and receivers. They vary as widely in char- 1,000 are expected before the end of the acteristics as in price. Small 5 -tube jobs year. Yet many listeners are still with- are available for the person who wants out FM receivers. There are two main a simple, low -cost tuner. The listener reasons for this lack. Supply of FM who lives far from FM stations will receivers has not been equal to the de- prefer to use a bigger one, with (at mand (at least until very recently) and least) two i.f. stages and possibly also many owners of good AM receivers have an r.f. stage. The listener in a big city, hesitated to buy a new set just to get with many powerful FM broadcasters, the extra FM band. will be more interested in the r.f. stage FM receivers to suit all tastes and as an interference eliminator. For the purses are daily becoming more avail- same reason, he will be attracted by the able, so the problems of the first group double- conversion feature of some of are rapidly reaching the vanishing the circuits. Other units are equipped point. For the second group -those with with AM tuners as well, and need only the fine AM receivers -an FM tuner an excellent amplifier and speaker to may well be the answer. They are read- be a high -fidelity receiving system. ily available, their cost is lower than Among the most interesting technical that of a complete receiver (varying variations are those in the tuning cir- Permeabilty -tuned coils of the Brooks tuner. $130 for straight FM cuits. Two-the Edwards Fidelotuner from about $30 to Circular long lines tuners), and they can be attached im- and the Approved -use modified long - mediately to any radio which has a lines circuits. In the Edwards tuner, In the Approved Electronic Instru- phonograph input. If the radio is not so these lines are straight, approximately ment set, the long lines are ingeniously equipped, the local serviceman can in- 5% inches long, and % inch apart. One bent into a semicircle. The shorting stall one easily. set tunes the r.f. and the other the oscil- blocks thus have a rotary motion and For worth -while FM reception, the lator section of the 6J6 converter tube. are attached directly to the tuning original receiver must have an excellent The two sets of lines are mounted below shaft. The lines also have end coils and audio end. If not, quality will be little each other in polystyrene end blocks trimmer condensers, though tracking better on FM than on AM. Where nat- and are tuned by a pair of shorting adjustments may be made by moving ural static or electrical interference strips, mounted in a polystyrene block the shorting blocks slightly on the ruins AM reception, the listener may and moved along the lines by the dial shafts, to which they are attached with find it desirable to get interference -free cord. Both sets are loaded with small setscrews. reception with an FM tuner, even coils and are tracked with trimmer con- Effect on performance does not ap- though his AM receiver is not a high- densers. (Continued on page 52) CHARACTERISTICS OF THE MORE POPULAR FM TUNERS LINE NO. DISCRIM- OTHER R.F. MIXER I.F. LIMITER TUNER AND MODEL OPERATION TUBES INATOR FEATURES 6AL Approved Electronic Inst 7Y4 6AG5 6J6 2-6SH7 6SH7 G.C. 6AL5 6U5 tuning 8 6AK5 6BE6 3 -6AK5 2 -9001 Brooks 6X4 F -S indicator 6BE6 6H6 separate AM external 8 6BÁ6 2-7AG7 2-6SJ7 Browning RJ -12 6C4 F -S channel a.c. 6H6 6U5 tuning -10 7 6AU6 7F8 2 -6AÚ6 2 -6SJ7 Browning RV 80 F -S indicator a.c. 6AK5 6AL7 9 6J6 3 -6AG5 2-9001 6AL5 Collins Audio Products 6X4 6C4 indicator V -R tube, Audio Products FM- a.c. 6AG5 1 -6AK5 Collins 9 6J6 2-9001 6AL5 audio channel AM Tuner 5Y3, GT 6C4 2-6AG5 6AL7 indicator -d.c. 12AL5 125A7 a.c. none 14ÁT7 4 -146A6 none De Wald 35W4 5 F -S oscillator 6BE6 6H6 separate a.c. 8 6BA6 2 -6SG7 2 -6SJ7 Dongene SY3 6C4 F -S AM channel a.c.-d.c. 6H6 long -lines Fidelotuner 5 none 6J6 2 -6SH7 6SH7 Edwards selen. F -S tuner ckt. 6BE6 6AL5 also AM tuner a.c. 6BA6 2-65G7 none Espey 512 5Y3-GT 6 6C4 ratio 6U5 indicator 4-6AG5 6AL5 a.c. none 2 -6BA6 none Meissner 8C 6X5 -GT 7 6C4 ratio AM channel, external 4 -6AG5 6AL5 Meissner 9 -1093 9 none 3 -6AG5 2-9001 F -S 6U5 indicator pack 6C4 separate a.c. 6á 5 6BA6 6BE6 2-6BA6 none ió5 Pilotuner Selen. JUNE, 1948 301 FM FM Receiver Servicing Technique The author aiisrussos and sairos many proaüiaaaa t. Mel üa FM roooi roa .s. em- By MILTON S. KIVER phasizes iisuaai oaüiivaaaoaa/ Mel ieaaeïw.

WHEN an FM receiver is audio system are functioning, when must be taken not to disturb the place- brought in for repair, sev- neither AM nor FM signals are reach- ment of other parts. eral preliminary tests can be ing the loudspeaker. The FM detector, in 98 out of every applied to localize the troubles 50n0 C1,12-.0001 r ñ3 -1 AUDIO quickly. In many cases these tests save AM and FM receiver differences A the serviceman considerable time. I 155 ;OUTPUT Standard broadcast AM and FM re- RI a I Many present FM receivers combine ca ceivers differ basically in two respects: 1 AM and FM in one unit. If the set is R2 C2 .0051 normal on frequency of operation and type of de- the AM bands, but completely tector. L_ inoperative when turned to FM, then DE-EMPSASiS NETWORK the trouble must be in some portion of The FM band is from 88 -108 mc. At 6ÁL5 (T m.StC) the receiver which deals exclusively these frequencies, the usual variable Fig. I -The well -known Foster -Seeley circuit. with the FM signal. The audio amplifier condenser and coil arrangement is not too satisfactory. Such tuners are still 100 receivers, is usually either one of and the power supply can be eliminated two types: immediately. Separate i.f. coils are used found in some receivers, but most re- for each signal, and an open or short ceivers are tuned by keeping the capaci- 1. The Foster- Seeley discriminator, may exist in the FM coils. Open leads tance fixed and varying the inductance. 2. The ratio detector. can be discounted because, in practically Thus, Zenith employs permeability tun- In the Foster -Seeley circuit (Fig. 1) all combination circuits, the i.f. coils are ing, G -E uses guillotines, and Motorola the audio output voltage is developed connected in series. An FM coil may resorts to tuned lines.* Replacements in across the resistors Rl and R2. This have shorted out, but this is not a com- the r.f. section must be exact duplicates voltage is passed through a de -em- mon occurrence and may be discounted of defective parts. Connecting leads phasis network to the audio am- at first. should be kept short, and special care plifier. The network reduces the ampli- Phonograph attachments can reveal tude of the higher- frequency components M. S. /Giver, "FM and Television Design," whether or not the power supply and Deremóer, 1947, RADIO-CRAFT. of the audio signal. This is necessary because the transmitter boosts the amplitude of these frequencies to reduce noise which accompanies the signal. The frequency characteristic of this detector is the S- shaped curve in Fig. 2. Its linear portion is the useful section of the curve. A certain amplitude of output voltage is derived for every frequency variation. If the curve is off - center (Fig. 3 -a) or the center section is not linear (Fig. 3 -b), distortion results.

10.6MC 10.7M; 10.9M;

Fig. 2 -A good discriminator curve is linear. The Foster-Seeley discriminator is almost always preceded by a limiter stage whose function is to remove all amplitude variations from the incoming signal. If the frequency variations are accompanied by amplitude variations, these will be detected by the diode rectifier tubes and appear as distortion in the reproduced audio signal. The limiter is generally a sharp cutoff tube operating at low plate and screen voltages, and with grid -leak bias (Fig. 4). The bias across Rg varies with the amplitude of the signal, and tends to level off all amplitude variations. The low plate and screen voltages permit the tube to saturate easily. As long as the Service engineer at Howard W. Sams checks an FM receiver, using visual alignment method signal is sufficiently powerful to drive RADIO -CRAFT for RA1 I31

the limiter to saturation, reception is it. The r.f. choke (Fig. 5) obtains its audio amplifier is tested by applying an noise-free. The hiss heard between sta- voltage from Ll through C5. a.f. signal to the grids of the audio am- tions illustrates what happens when the The change from the balanced to the plifier tubes. limiter is not saturated. unbalanced circuit will affect the method The FM detector is next. Connect the Since the voltage across Rg varies of aligning the detector. To align the sweep signal generator to the grid of with signal amplitude, a vacuum -tube unbalanced detector, first connect two the tube preceding. the FM detector. Set voltmeter or oscilloscope at this point 68,000 -ohm resistors in series across R1. it to sweep 300 kc above and below the indicates how well the r.f. and i.f. am- Connect a vacuum -tube voltmeter be- i.f. center frequency. Connect an oscil- plifiers have been aligned. tween points B and C. Adjust the trim- loscope across the output terminals of mers for zero reading on the meter, with the detector. a signal at the intermediate frequency. The shape of the S -curve on the oscil- For frequencies above and below this loscope screen tells the complete story point, the voltage will be either positive about the operating condition of the de- or negative, to produce the character- tector. If the coupling network connect- istic S- curve. ing the FM detector to the previous In summary, then, FM receivers have stage is not properly tuned or centered; several test points which help the ser- the S -curve appears as shown in either viceman to localize defects in the circuit. Fig. 3 -a or 3 -b. In either case, the sound For receivers employing the Foster - output is badly distorted. Adjust the Seeley type of discriminator, a test trimmer condensers (or iron cores) in point exists in the grid circuit of the the discriminator primary and secon- preceding limiter or at the output of dary windings to correct this condition. the discriminator. In the ratio detector The primary controls the linearity of an indication can be obtained at point A the center portion of the S- curve, while or across the audio output. the secondary adjustment affects the centering of the S- curve. The necessary instruments Fig. 7 shows the S -curve when the is 1. A sweep signal generator, with fre- band width of the tuning circuits too is when quency ranges from 5 -15 mc and narrow. The output distorted the incoming signal is fully modulated, Fig. 3 -a, top and 3 -b, bottom -Curves like 80 -110 mc, a maximum frequency these will produce a a.f. and the voices appear "hissy" and distorted signal. sweep of 750 kc being desirable on realign Some receivers have two limiters in both ranges; "raspy." The solution is to the series. In this case, the point is 2. A vacuum -tube voltmeter; circuits. test To obtain points on the dis- shifted from the grid circuit of the first 3. An AM signal generator with a marker criminator curve, connect the AM sig- limiter to a similar position in the sec- frequency range from 5 -125 mc; nal generator in parallel ond limiter. The lowest readable signal 4. An oscilloscope. with the leads of the sweep generator and tune it to voltage should be used, when testing, bSJ7 in order not to saturate the first limiter the frequency to be checked. If the fre- stage. occurs, the meter IF 50uut quency is 10.7 mc, a wiggle (Fig. 8) will If saturation 11 t TOfM be visible at the 10.7 -mc point on the will not indicate each change in signal DISCRIM I S on oscilloscope screen. amplitude. Rg 50e -curve the Check the extent of the linear portion of the The ratio detector is shown in Fig. 5. 02 S -curve by shifting the frequency of Changing voltages across Cl and C2 pro- TEST POINT -SEE TEST 22e 100e ?' duce an audio voltage across R3 which 6+ the AM generator. When the must be made with an passes through a de- emphasis network Fig. 4-A limiter precedes the discriminator. test AM generator, the process is lengthened to the audio amplifier. SDYYI 6AL5 C1,C2 -.004 considerably because only one point can 5 A Points for the repairman be tested at a time. Here is how to pro- RI TOAVC ceed in such a case. The voltage between point A and t For the Foster-Seeley discriminator ground depends upon the strength of 33e T R2 (Fig. 1), connect the generator to the the incoming carrier. If the incoming grid of the preceding tube. Next, con- is broadcast signal replaced by voltage ALL CORDS nect a vacuum -tube voltmeter between e+ 15 _.005 AUDIO from a signal generator, then the volt- point A and ground (Fig. 1). Set the age at A will be maximum when the i.f. Fig. 5 -The original ratio defector circuit. signal generator to frequencies 25, 50, transformers are aligned. 75, and 100 kc above and below the Since the audio output voltage is devel- 8AL5 A intermediate frequency. Voltage read- oped across R3, point B is a good spot to 04.1 LI .11. L2 ings should be the same for frequencies place the oscilloscope when the ratio de- I equally above and below the center fre- tector is being adjusted. When the pri- quency. Equal values indicate a linear mary and secondary of Tl are properly \1 9+ discriminator characteristic. If the re- aligned, the audio output is zero when sponse is not linear, then the primary the incoming signal is precisely at the .005 15e C2í004 and secon Lary discriminator windings i.f. center frequency. Signals with fre- AUDIO quencies above and below this point will produce negative and positive voltages Fig. 6 -A variation of the ratio detector. at R3. Thus, the S -curve of Fig. 2 repre- FM receivers can be repaired with sents the characteristics of a ratio de- only a vacuum -tube voltmeter and an tector, as well as the Foster- Seeley de- AM signal generator. But time is money tector. Since the ratio detector does not to the serviceman, and all four items are 10.640MC 10.7MC ,0.760MC respond to amplitude variations, it does required if repairs are to be made in the not require a limiter. shortest possible time A sweep signal A variation of the ratio detector is generator produces the full circuit re- shown in Fig. 6. Comparison reveals sponse in one pattern; an AM signal that point B in each diagram is actually generator can provide information con- Fig. 7 -A curve with too narrow band -pass. at the same point in the circuit. In cerning only one point at a time. must be readjusted. place of the r.f.c. of Fig. 5, we now have The general procedure for trouble The method of testing the ratio de- L3, which is inductively coupled to Ll shooting an FM receiver by signal trac- tector depends upon its form. If it is and receives its reference voltage from ing is the same as for AM sets. The (Continued on page 58) JUNE, 1948 ., PM 3 1 at

Simplified FM Receiver Uses Crystal Detectoi'

By ROBERT E. AL70MAREALTOMARE

AS the result of many pre%iuus located at considerable distance from tapped at 's turn from the hot end. The experiments, I decided to de- broadcast stations. In addition, it pre- mixer plate circuit is made inductive by sign an FM tuner that anyone vents loading of the mixer tank by the L2. This coil consists of 15 turns of No. but the greenest beginner could antenna and minimizes oscillator radi- 22 enameled wire wound around a 3/16 - easily construct. Simplification was the ation. Cathode bias is supplied by the inch diameter, 1,500 -ohm resistor. Re- chief objective. The tendency toward 220 -ohm resistor connected between turn all ground connections in this cir- instability is minimized by reduced cathode terminal No. 2 and ground. Ter- cuit to the same point on the chassis, stage gains and correct physical circuit minal No. 7 is the return point for the preferably to the frame of the tuning layout. Circuit values are kept well be- screen and plate bypass capacitors. The capacitor. low the critical point, allowing possible plate load inductor Ll has an induct- The oscillator is a Hartley type and wide variations. ance of 4.250. It is available com- tunes 10.7 me higher than the incoming The tuner has four tubes: 6AG5 -r.f. mercially (Electrical Reactance type signal frequency. Make the oscillator amplifier; 7F8- mixer-oscillator; 6BA6 165), but a substitute can be wound coil of 1% turns of No. 14 bare tinned -first i.f. amplifier; and 6AG5- second with 50 turns of No. 30 enameled wire wire wound on a % -inch form. The os- i.f. amplifier. A 1N35 dual germanium on a 100,000-ohm, 5/32 -inch diameter cillator tap connection is not critical. crystal unit is the detector, although a insulated, carbon resistor. The effective Attach it to a point about '/2 -turn from 6AL5 dual -diode can be substituted with Q will be about 65. the plate end. equal results. A 5Y3 -GT rectifier is em- A 15,000 -ohm resistor reduces the Fig. 2 is a suggested circuit layout for ployed. plate voltage to approximately 145, and the oscillator. Wiring is simplified, and The frequency range of the receiver also acts as a decoupling resistor. The the leads are short. was extended to 86.3 -109.3 me because screen voltage is 150. The resistor in the The oscillator is coupled to the mixer some constructors, however careful, control grid circuit reduces any ten- through a small capacitor, Cl, made by might end up with too much capacitance dency to oscillate. If the circuit does not twisting two 1 -inch lengths of No. 18 across the tuned circuits and a reduced oscillate, omit the resistor. insulated wire together. Solder one wire tuning range. It is better to recognize The r.f. tuning coil is self -supporting. to terminal No. 1 and the other to ter- this possibility in advance and avoid the It is made of 2% turns of No. 14 tinned minal No. 8 of the 7F8 socket. Capaci- disappointment of a limited tuning wire, % -inch inside diameter. Solder it tance can be reduced by untwisting the range. between the stator terminal of the tun- wires. The two r.f. chokes in the 7F8 ing condenser and to the same ground and r.f. 6AG5 filament leads consist of The tuning section as Rl. One and one -half turns of hook- 25 turns of No. 26 enameled wire, wound The complete circuit is shown in Fig. up wire interwound with the r.f. coil is on 68,000 -ohm, % -watt insulated re- 1. The r.f. section is tuned by a three - suitable for a 300 -ohm folded dipole. A sistors (L4, circled 7 and 8). gang variable capacitor. Each section 72 -ohm antenna will require only a has its individual trimmer. These are single loop of wire for coupling. The i.f. amplifier section set initially at one turn from maximum - The tuner has two i.f. amplifier capacitance positions. Mixer and oscillator stages. The r.f. amplifier is conventional, but The mixer tuning inductor is similar to The 1st i.f. amplifier tube is a type it is especially useful if the tuner is the r.f. coil. The coupling condenser is 6BA6; the second, a type 6AG5. Differ-

Above -Chassis view of fhe set. Right- Under- chassis, showing coils. RADIO -CRAFT fo 133

8AG5/RF 7F8 8BA8/1F1 6AG5 /Ir-2

4145V SOµµf CERAMIC +250V 1.2 +242V +242V SHIELD7 s N : 3 s DISÇR.TR. 3004 DIPOLE q0V 1H35 1 +ISOV U ' I 338 rREMOVE 10 I F-- I- +

+9V IL i ,1_29 j 1.28 5 L - .0010ERAMIC 478 158 .001 CERAMIC 18 I8 SEE TEXT 5 - VOL.CONT. IMEG . ... SEE TEXT ¡CI .` .004 X 758 .001 AF \\ -2V 252V I.IN /10W /WW OR VALUE TO SUIT PO ER TRANS MICA +340V \ 5V/ 2A \\ 2 15- 450v _15 2e SRAMIC 6 =.03/600V U7VAC 325v CERAMIC L. ®SW 1 SOMA re 6. 5-235µµf AT AVERAGE TRIMM. lE T71NLl 325V T \ \ \ 5Y3-GT 14 4I bl 1 83Y/1.2Á 2-* 7fO8 4j 6846 4`A2S 416AG5tRFl 8 =1000 ALLCONOS -If- I lì O Il Fig. I -The schematic. The 1N35 crystal is actually two IN34's, carefully matched for equal output. Circled numbers refer to Fig. 2. ent tubes were used only to emphasize d.c. voltages should agree with those be loosened for maximum output, re- that different types are usable. indicated in Fig. 1. Measure the oscil- duce inductance by spreading turns. The i.f. transformers are slug -tuned lator grid voltage with a vacuum -tube Now align the discriminator trans- to 10.7 mc. Any make can be used. voltmeter. Lack of oscillator grid volt- former. Connect two closely matched Orient the 6BA6 and 6AG5 sockets age means an inoperative oscillator. 75,000- to 100,000 -ohm resistors across and the transformers to keep the grid This might be due to a bad tube, parts a and plate leads comparatively short. or wiring. CONDENSER:60NG C H A S S I S Assemble the components of the sec- If all voltages are approximately cor- MIX.GND LUG CI u ond i.f. amplifier stage on a terminal rect, align and track the tuner. A signal 8+ BO ,;U15>> MOUNTING board in their entirety. generator is practically a necessity. MIX.TR.1M. 06-r; LUGS A The final stage is a modified ratio de- Connect it between the mixer grid and I- ©1/ TN tector. Audio output is taken from a ground and adjust the i.f. transformers OSC.TRIM ,;f, tertiary winding on a standard discrim- and the primary of the discriminator ' OSC.TAPLEAD inator t4j O transformer. Make this winding transformer for maximum d.c. voltage GOSC.GND LUG of 5 turns of No. 26 sec wire, wound across resistor R. over the cold end of the primary, and in TO FIL. CIRCUIT To align the r.f. section, apply the Fig. 2- Detail of part of r.f. section. Numerals the same direction ( Fig. 3). Connect the signal generator to the dipole input hot end of this winding to the center on socket indicate pin numbers. Circled ones tap terminals through two 300 -ohm carbon refer to points on schematic. Cl is a of the secondary The single coil. other end sup- resistors (70 -ohm resistors for a 72 -ohm twist of wire between pins I and 8 (gimmick). plies audio output. This lead also con- dipole). Set the signal generator to R. Place the common lead of a d.c. nects to ground through a .004 -µf mica 109.3 mc and completely unmesh the capacitor. It will be necessary to re- v.t.v.m. at the junction of these resistors tuning capacitor. Now adjust the oscil- and move the coupling capacitor normally lator trimmer for maximum voltage the hot lead at point X, below the connected between the plate lead and discriminator transformer in Fig. 1. output across R. There will be two Adjust the center tap of the secondary winding. voltage as is opened. the discriminator transformer peaks the trimmer for zero reading on the meter. The dis- The 75,000 -ohm resistor and .001 -µf The second is the correct one. condenser form a 75- microsecond de- criminator is then correctly aligned. Now decrease the frequency of the Now repeat the alignment process. For emphasis network to neutralize the pre - same emphasis inserted at the transmitter to signal generator and at the time increase the capacitance of the tuning REMOVE reduce noise. A 1 -meg volume control capacitors, continually following the sig- PLATE LEAD allows control of the output. PR I.WINOING.. nal at the same time, until the SEC. WINDING Note that the output of a ratio dis- tuning is meshed. criminator is half that of a conventional capacitor entirely If the signal generator reads about 86.3 mc, the discriminator for a given signal input. 6+ LEAD volume oscillator is correctly adjusted. Automatic control can be SECONDARY CENTER TAP added easily to this FM tuner. It is pref- If the generator frequency is con- NEW WINDING erable to control only the last i.f. stage, siderably different from 86.3 me when Fig. 3 -The ratio detector winding details. although sometimes it is also desirable the oscillator capacitor plates are "all more detailed information, see the ar- to control the r.f. stage. Fig. 4 shows in," the oscillator inductance is incor- ticle on page 30 of this issue. the circuit for applying a.v.c. to both. rect. For a lower frequency than 86.3 6AG5(RF) 6AG5(IF'2) mc, decrease the oscillator inductance by VOLUME Physical layout spreading the turns and repeat the CONTROL Take care to align the tuning capaci- whole procedure. If the frequency is greater than 86.3 mc, increase the oscil- tor with the dial. Place the r.f. tube close 2MEG to the r.f. section of the tuning capaci- lator inductance by squeezing the coil. tor; the 7F8 should side -straddle the If necessary, wind another coil with an 2.004 mixer and oscillator sections. See Fig. 2. additional quarter -turn. Mount all the main components first, To align the r.f. and mixer sections, Fig. 4- A.v.c. applied to r.f. and last I.f. and then wire the power supply and set the signal generator to 109.3 mc and The builder can often persuade a filament circuits. Keep the r.f. stage fila- again set the capacitor to minimum, tun- local serviceman to permit the use of a ment choke at least 2 inches away from ing in the signal. Adjust the r.f. and signal generator at his shop for align- the r.f. coil. Next wire the discriminator mixer trimmers for maximum output. ing the tuner. In the event no signal and the ii. circuit. Test and align the Now retune both the signal generator generator is available, the alignment i.f. stages with a signal generator at this and tuner to 86.3 mc and check the r.f. process becomes complex and perhaps point. Hook up the oscillator, mixer, and and mixer trimmers. If either of these impossible. Possibly a station could be r.f. stages, following Fig. 2 closely. must be tightened the corresponding in- tuned in and the extremities of the Before trying to "get music" from ductance is too low and should be in- band then approximated, if the i.f.'s the tuner, check all the circuits. The creased by squeezing. But if either must are aligned with a 10.7 -mc signal. JUNE. 1948 FM 311 * fifi DISCRIfflIflATOR CIRCUITS

Most FM circuits paroUel their corresponding AM equivalents. The

FM discriminator, or detector, introduces some totally new feotures By DOUGLAS H. CARPENTER

FREQUENCY modulation has today The i.f. amplifiers must pass this takes too much time to be practical. As stepped into the limelight both in its same 200 kc while operating at a much a representative case the Pilotuner was own right, and as the sound portion lower frequency. The Pilotuner for in- aligned by a qualified man using the of television transmission. Success- stance has a center i.f. of 10.7 mc. It is tedious AM generator-output meter sys- ful servicing of this equipment requires necessary to broaden the natural sharp tern. It took more than half an hour. a thorough knowledge of circuit opera- response of the i.f. parallel resonant cir- A recheck with a sweep generator and a tion. The visual system of alignment cuits to accommodate this 200 kc band. scope showed slight lack of symmetry of with a cathode-ray oscilloscope and a These circuits may be shunted by resis- both the i.f. and detector patterns. The sweep generator has been covered in re- set was then aligned in five minutes with cent articles. This method is the accept- the sweep generator and scope. ed way to do a fast, accurate job. In addition to possessing the above equipment FM limiter circuits the serviceman should have a good 'IIII., liniiter-tIi ... irninator was the working knowledge of the methods em- first popular system of FM demodula- ployed to convert the frequency-nudu- tion. This type of receiver is not manu- lated radio signal into the final usable factured as extensively today as the audio. If these circuits are understood, ratio detector type. It may be found in troubles pointed out by the oscilloscope higher-priced receivers, and it requires may be more readily located. a greater number of stages to guaran- The r.f. and mixer stages of an FM tee immunity from noise. receiver do not differ basically from The limiter makes certain that AM those of a normal AM set. Referring to noise which may be present with the FM the schematic of the popular Pilotuner signal is removed before the signal we see that the circuit is similar to that reaches the discriminator (detector). of a normal broadcast receiver right up This is done by operating a tube or tubes to the detector circuit. This particular at low plate and screen voltages so that unit is a complete, well-designed FM re- The Pilofuner, a typical standard FM tuner. they saturate easily (are operated to ceiver (lacking only the audio system) full output with a low value of grid sig- and is representative of the type of cir- tors, or coils of low Q may be used to nal drive). Thus the signal which cuit that the serviceman may expect to obtain a more or less fiat top response. reaches the discriminator is of constant encounter. Another system uses critically-coupled amplitude. The two-stage or cascaded The r.f. and i.f. sections of the re- dual i.f. transformers. An amplitude limiter is superior in that it will reach ceiver must pass a 200-kc band width loss of not more than 2:1 at points 75 saturation (allow no further change in without too much amplitude variation. kc either side of the resonant center fre- plate current) with lower grid signal This is no problem for the r.f. ampli- quency is considered satisfactory re- drive. This allows noise-free reception fier, as it is not very selective in terms sponse. of weaker signals. Noise variations of of 200 kc when operating throughout Alignment of these amplifiers requires course can be reproduced as audio if the the high-frequency FM band. Maximum an FM sweep generator and a good os- input signal is too small. The limiter gain is desirable in this stage, however, cilloscope. It is perfectly possible to system would not then function proper- to keep the signal-to-hiss ratio at low align a FM receiver with an AM gen- ly, as it would not be driven hard enough signal levels high. erator and output meter only, but it to saturate. This suggests the use of sharp cutoff tubes in the limiter circuits and high gain in the i.f. system. The FM discriminator I'Iie di«tinsin:stor is the detector of the FM set. It follows the limiters, and its purpose is to convert a signal which is varying in frequency into a usable audio voltage. Fig. 1 is the schematic of a back-to-back phase-shift discrirni- nator. If the primary circuit Li-Cl is tuned to the resonant frequency it looks like a pure resistance. The voltage fed to the secondary (L2-L3-C2) is made up of two parts. The first is the voltage across the secondary due to inductive coupling, and the second that which is fed to the secondary center tap through Cc. The phase relations of these two voltages are such that the currents pro- flED duced by rectification in the two diodes Circuit of the Pilotuner referred te above. (Condensed horn RADIO-CRAFT, September, 1947) flow through the load circuit (R1-C3-R2. RADIO-CRAFT for FM I35

C4) from opposite sides, and buck each amplitude variations that come in with pened no voltage would be applied to other out. The net result is that no volt- the received signal. the diode input circuit, and conduction age appears at the audio terminals. would be stopped momentarily. The When modulation is applied to the The ratio detector large stabilizing condenser has a charge carrier its frequency shifts above and The ratio detector is a discriminator established across it and has a relatively below the resonant center frequency. If that requires no preceding limiters. It is long time constant. This tends to hold the carrier changes from resonance to a therefore not necessary to build up the the audio output at the last average higher frequency the input circuit looks input signal to as high a level as would level, and the disturbance would not be capacitive, and the induced secondary be necessary to insure saturation in the noticeable to the listener. This detector current leads the voltage. This shift in limiter -discriminator receiver just dis- would not be effective for interference phase causes the current produced by cussed. Less i.f. amplification is re- of long duration that satisfied the above the inductive coupling to combine with quired, and no limiter stages are need- requirement. Complex voltage of this that fed to the secondary through Cc in ed. The production cost of this type of type is rare indeed, however. such a way that one diode has more receiver is much less than the limiter - Summing up the advantages of the voltage applied to it than the other. The discriminator type, and the ratio detec- two systems, it may be said that the rectified current of this diode increases, tor is used in many lower- priced sets. limiter- discriminator type of FM set is while that of the other decreases. The The discriminator circuit responds to slightly superior to the ratio detector currents in the secondary load circuit a change in the average amplitude of system, but requires a greater number are no longer equal, and an audio volt- the carrier. The voltages developed of stages for the same practical effect. age is produced. If the carrier changes across the load circuit in the example The ratio detector is found in the ma- to a frequency lower than resonance the just given were proportional to the ap- jority of currently produced sets be- input circuit looks inductive, and the plied signal, but note that the ratios of cause of its lower cost. This conforms current lags the voltage. In this case these voltages were the same. In the with the present policy of manufac- the other diode has more voltage applied first case the voltages across the two turers to produce large numbers of FM to it, and the complete load circuit has load resistors were 5 and 15, or a ratio receivers at a reasonable price. a voltage across it in the opposite direc- of 3:1. In the second instance the volt- An entirely different system of FM tion to that of the first instance. ages were 30 and 10, but the ratio was detection, employed by Philco, uses a The frequency of the audio voltage de- still 3:1. The ratio detector works on weakly oscillating tube. A heptode spe- pends on the rate the carrier is shifted changes of this ratio between the volt- cially designed for the work, it has two above and below the resonant frequency, ages developed across both halves of the grids. One of these is the grid of the and the magnitude depends on how far load circuit. Because of this it is insensi- oscillator circuit; the input signal from the carrier is shifted from resonance, as tive to amplitude change. the i.f. amplifier is applied to the other. this determines the amount of current The ratio detector (Fig. 2) works on An oscillator has a well -known ten- unbalance in the load circuit. the principle of separating a fixed d.c. dency to "lock in" with (follow the fre- voltage into two parts. The ratio be- quency of) another oscillator tuned near tween these two voltages is the ratio of its frequency. Oscillating tubes have an- the voltages applied to the separate other tendency even better known to 7,i diodes. This voltage difference is caused amateurs. Their frequency varies with by the change in carrier frequency pre- variations of plate current. This type of LUDIC viously explained. The capacitors C3 and C4 are of equal value, and together with Rl and C2 AVC 4 form the diode load circuit. The recti- -óa(- fied currents of the two diodes are in series in this case and create a voltage Fig. I- Back -to -back (Foster-Seeley) circuit. drop across Rl. The voltage developed 4MM The width of the frequency band that across this resistor depends on the av- may be passed without amplitude change erage strength of the applied signal. depends upon the Qs of the respective Capacitor C2 is large and is an effective coils and the degree of coupling between bypass for audio variations. The Pilo -

them. The closer the coupling and the tuner uses an additional small bypass AUDIO lower the Q, the wider the linear re- shunted across this high -value condenser s sponse. The audio voltage difference de- to prevent the larger one from acting Fig. 2-Circuit of the common ratio detector. pends, however, upon the amount of like an inductor at higher frequencies. voltage applied to the diodes, and it is At resonance the current will flow frequency modulation is a very undesir- desirable to keep the Qs as high as pos- around the series circuit and there will able feature in simple AM transmitters, y cible, and passing no more than the be voltage drop across Rl. No voltage and one that the ham dislikes. frequency excursion required. will be fed to the audio system, because These two old and heretofore harmful Since the discriminator responds not the ratio of the voltages across C3 -C4, features were used to produce a detector only to changes in frequency but also is 1:1. If the carrier deviates from res- of frequency variations. A circuit (see in magnitude of the applied voltage, it onance more voltage will be applied to Fig. 1, page 24) was devised which is sensitive to amplitude variations such one diode than the other, and the ratio would increase both these tendencies. as noise. If a carrier causes the voltage of the voltages across C3 -C4 no longer The oscillator is so designed that it locks across the two load resistors to be +10 will be equal. The total voltage across in with and follows faithfully the fre- volts across one, and -10 volts across the load circuit has not changed, but quency variations of a relatively small the other, no voltage will be developed simply the ratio of the voltages across signal applied to its input grid. across the audio terminals. C3 -C4. This is realized as useful audio The second feature was used in re- If the carrier shifts away from the output. The total voltage developed verse. Changes in the oscillator's fre- resonant frequency a certain number across 111 of course depends on the quency are made to produce changes in of kilocycles the voltage across one re- average strength of the carrier applied. the plate current. Thus the detector cir- sistor will increase to +15 volts, while The voltage at the top end of this re- cuit receives a frequency -modulated sig- that across the other will be -5 volts. sistor therefore makes an excellent nal and puts out an amplitude -modu- The voltage delivered to the audio sys- source of a.v.c. lated one. tem is then +10 volts. If the carrier re- The large capacitor that shunts the Other methods have been and are be- ceived were twice as strong the voltages load resistor is called the stabilizing ing used to detect FM signals (such as would be 30 and 10, and the audio sig- condenser, and serves an additional pur- slope detection with superregeneration) nal would be twice as great. This system pose. A separate variation of the proper but the above are the most important therefore is rarely used without pre- phase and amplitude could heterodyne to systems, and practically the only ones ceding limiters to wash out undesirable zero the FM signal itself. If this hap- the repairman will meet. lk JUNE, 1948 36 FM

FM Receiving Antennas H. W. SECOR

BEST reception on FM is possible For a more accurate calculation, use a The plastic twin -lead usually gives only with an outside antenna. The correction factor of 7.5% for 98 mc and very satisfactory results if it is care- indoor antenna is more liable to % -inch diameter tubes or rods for the fully installed and kept away from pick up interference from power dipole. metal tanks and pipes. To avoid inter- The factor varies with the frequency ference pickup, the flat line is sometimes and the diameter of the antenna ele- given a twist of about one turn per foot. ments. Some manufacturers supply antennas The ordinary simple dipole does not with center impedances as low as 14 have an even response over the 88-108 - ohms. These must be matched to the mc FM band. A broad -band antenna is (usually) 300 -ohm input of the receiver. needed for tuning over the wide fre- A simple matching section may be com- quency range. The folded dipole, illus- puted and installed as shown in Fig. 5. A- BENDING or WAVE; B HIGH ANTENNA, SIGNAL OK, C- LOW trated in Fig. 3, has been widely adopt- Let us assume these factors for an ANTENNA, NO ORAL OB-OBSTRUCTION ;FMX -FM XMI TT ER ed for FM because of its broad fre- example: Frequency to which antenna Fig. I- Line -of -sight may be exceeded by FM. quency response. is to tune, 98.75 mc; impedance of lines and electrical apparatus, and gen- The frequency response of a simple transmission line, 300 ohms; input im- erally delivers a weaker signal to the dipole can be broadened simply by over- pedance of receiver, 300 ohms. input terminals of the receiver. lapping the inner ends of the two ele- The matching section is a short lead The higher the FM antenna can be ments, as shown in Fig. 4. The dipole (about tQ wave length long), inserted erected, the stronger are the signals, in elements are made slightly longer than between the antenna and the 300 -ohm most cases. If the antenna is low, it may % wave length. This extra length transmission line. The impedance of the be impossible to receive all the stations makes the antenna inductive. The in- matching section is equivalent to the in the area. FM signals follow the line - ductance is compensated for by intro- square root of the product of the two of-sight to a great extent, and the reducing a capacitance, created by over- impedances to be coupled, or ceiving antenna should therefore be as lapping the inner ends of the tubes. Impedance of matching lead = high as possible. There is some bending V14 X 300 or V4200 = 64.9 ohms. of the signal due to refraction (Fig. 1). A choice of three different impedance This accounts for satisfactory reception lines is available: 75 ohms, 150 ohms, of FM programs at distant locations, and 300 ohms. The nearest value in this even when the receiving antenna is not case is the 75 -ohm line. AVç as high as theory might demand.* /l To compute the length of 75-ohm line The receiving antenna should be tried required for the matching section, we in several different locations. Sometimes RODS OR TUBES use the following formula: moving it from one end of a roof to the 11811 X Y opposite end spells the difference be- L (inches) = tween poor and good reception. Flexible f(mc) X4 indoor antennas, when used, can be test- The value of Y is chosen from the 75n LINE TO SET ed in a number of different positions - following tabulation: Y for 75 -ohm under the carpet, on the wall (hidden matching section = 0.69; for 150 ohms, behind a picture), etc. Keep all FM an- SIMPLE DIPOLE FOLDED DIPOLE Y = 0.77; for 300 ohms, Y = 0.82. F is tennas away from metal masses, metal the antenna frequency in mc.'Substitut- fg2 I TO SET fig pipes, and electric wires. ing 0.69 in the formula gives: L Figs. 2 and 3 -The simple and folded dipole. 11811 X 0.69 Simplest FM antenna Impedance matching (inches) = = 20.63. The simplest FM antenna is the di- The average simple dipole has ap- 98.75 X 4 pole (Fig. 2). It is usually cut to reson- proximately 75 ohms of impedance at TUBE, REAR VIEW FROM 98 mc, fy, ' TOP SHOWING -. ate at the center of the FM band. the center, at its resonant frequency. \ CONNECTIONS The length of the whole dipole is t/z The impedance of a folded dipole is wave length at 98 mc, or 56.7 inches. about 300 ohms. Since the average FM fig 46 Each leg of the dipole is one -half this receiver has an input impedance of 300 WORE THAN I/4 WAVELENGTH or 28.3 inches. ohms (RMA standard), the folded di- For general purposes the half -wave pole can easily be matched to the re- length in feet is found from the formula ceiver with a 300 -ohm transmission line. A 75 -ohm antenna might be coupled to CENTER 492-6% the receiver (300 -ohm input impedance) IMPEDANCE 14nÿ , L = where f is the fre- through a 75-ohm co -axial cable. An IMPEDANCE MATCHING f impedance matching network should be SECTION 1/4 installed between the end of the co- WAVELENGTH quency in mc. The 6% corrects for axial cable and the receiver. Co -axial SOLDER JOINTS effects due to the capacitance added by cable has the advantage of being shield- )(MISSION LINE OOn LINE the insulators at the ends of the dipole. ed and not subject to interference pick- fig4Ar III TO SET figs up, as is the case -lead "Television and FM Antennas," H. W. Secor, with the twin flat Fig. 4- Overlapping fo broaden band. Rwmo- CaArr, January. 1948. plastic line. Fig. 5-A dipole antenna with a reflector. RADIO -CRAFT for F1 137

Fig. 5 shows how the matching sec- represents a good compromise, since it suitable for FM. If the length of the tion is connected between the 14-ohm an- has a fairly sharp pattern, with broad reflector is adjustable, vary it too for tenna and the 300 -ohm line to the re- frequency response and easy matching maximum signal. ceiver. The joints between the 75- and to a 300 -ohm line. It is often best to turn the antenna 300 -ohms lines must be soldered and At points remote from the transmit- for the strongest possible signal from taped well to protect them against the ter, where greater signal strength is the weakest stations. The strong signals weather. required, the antenna height can be in- will take care of themselves. Keep the creased. Or an antenna made of two or more dipoles, one above the other, can be used (Fig. 6). There are several types of omnidirectional antennas. One of them, with the elements arranged in the form of a cross is shown in Fig. 7. A quarter -wave matching section usually connects the two dipoles. Where it is difficult to pick up a sufficiently strong signal from all the desired stations with one antenna, the use of several antennas may be helpful. Several dipoles can be erected at different locations or one below the other, each one facing the desired station. A simple switch or jack- and -plug arrange - Fig. 6-A sensitive and directional antenna. ment permits the operator to connect The directional characteristic of the any one to the receiver. An alternative Courtesy Ward Products Co. folded dipole can be improved by adding is to use one antenna which can be Fig. 7-An omnidirectional type of antenna. a reflector. The impedance is somewhat rotated. Sometimes the antenna requires lead -in cable away from metal tanks lower (approximately 250 ohms) when tilting at an angle because of changes and pipes, and support it away from the the reflector is about 14 wave length in the polarization of the high -fre- . building, wall and roof with suitable from it. It is common to match this com- quency waves. high- frequency insulators. Anchor it in bination to a 300 -ohm transmission line. place so it cannot sway in the wind. The small mismatch does not interfere Tuning the FM antenna Bring the cable into the building with a satisfactory signal pickup. It is While FM antenna adjustment is not through suitable insulators. One method common to space the reflector about 0.15 too critical, care should be taken when is to use a sheet of polystyrene in place wave length behind the antenna. it is erected. of a glass window pane, passing the If a director element is added to a Mount the dipole broadside to the lead -in through a hole drilled in the folded dipole, the directional pattern is transmitting station. Adjust the length center of the polystyrene panel. still further sharpened -an aid in cases of the dipole elements for maximum Connect a vacuum or other approved where interference is severe. Since these signal strength, and also the gap be- type of lightning arrestor to the lead -in. parasitic elements make the antenna tween the inner ends of the elements. Attach the ground wire to the nearest frequency-sensitive and cause response About 1 to 11/2 inches is a common gap water pipe or a piece of pipe driven over a narrow band, they are not the length. Experiment with the distance into moist earth. Some types of anten- best solution of the antenna problem. between the reflector and the dipole for nas do not require separate lightning A folded dipole with a reflector only best results -about 14 wave length is arrestors.

DIRECTORY OF FM RECEIVER MANUFACTURERS ADMIRAL CORPORATION FADA RADIO & ELECTRIC CO., INC. PHILCO CORP. 3800 Cortland St., Chicago 47 30 -20 Thomson Ave., Long Island City I, N. Y. Tioga & C. Sts., Philadelphia 34, Pa. AIRADIO, INC. FARNSWORTH TELEVISION & RADIO CORP. PILOT RADIO CORP. Melrose Ave. & Barry Place. Stamford, Conn. 3700 E. Pontiac St., Fort Wayne I, Ind. 37 -06 36th St. Long Island City I, N. Y. AIR KING PRODUCTS CO., INC. FISHER RADIO CORP. RCA VICTOR DIVISION 170 Fifty -Third St.. Brooklyn 32. N. Y. 41 E. 47th St., New York 17, N. Y. Camden N. J. ANDREA RADIO CORP. FINCH TELECOMMUNICATIONS. INC. REL: RADIO ENGINEERING LABS.. INC. 27 -01 Bridge Plaza North, Long Island City I, N. Y. 4th & Virginia Sts., Passaic, N. J. 35 -54 36th St., Long Island City I, N. Y. ANSLEY RADIO CORP. FREED RADIO CORP. RADIO TELEVISION PRODUCTS CORP. 41 St. Joes Ave., Trenton 9, N. J. 200 Hudson St., New York 13, N. Y. Grass Lake Mich. APPROVED ELECTRONIC INSTRUMENT CORP. GAROD RADIO CORP. RAYTHEON MANUFACTURING CO. 142 Liberty St., New York 6, N. Y. 70 Washington St. Brooklyn I, N. Y. 55 Chapel St., Newton 58, Mass. A.R.F. PRODUCTS. INC. GENERAL ELECTRIC CO. REMLER COMPANY, LTD. 7627 Lake St., River Forest Ill. Electronics Park, Syracuse 1, N. Y. 2101 Bryant St., San Francisco 10, Calif.

AUTOMATIC RADIO MFG. F CO.. INC. THE HALLICRAFTERS CO. SCOTT RADIO LABS., INC. 122 Brookline Ave. Boston 15, Mass. 4401 W. Fifth Ave., Chicago 24, III. 4541 N. Ravenswood Ave., Chicago 44, III. BELMONT RADIO CORP. HOFFMAN RADIO CORP. SENTINEL RADIO CORP. 5921 W. Dickens Ave.. Chicago 39, III. 3761 S. Hill St. Los Angeles 7, Calif. 2100 Dempster St., Evanston, III. BENDIX RADIO HOUSTON RADIO & TELEVISION CO. SONORA RADIO & TEL. CORP. East Joppa Road Baltimore 4, Md. 1612 N. Main St., Houston 9, Texas 325 N. Hoyne Ave., Chicago 2, III. BROOKS ELECTRONIC LABORATORIES HOWARD RADIO CO. THE SPARKS -WITHINGTON CO. 621 Main St., Waltham Mass. 1735 Belmont Ave., Chicago 13, III. Jackson, Mich. BROWNING LABORATORIES, INC. INTERNATIONAL DETROLA CORP. STEWART- WARNER CORP. & Detroit 9, Mich. 742-750 Main St. Winchester, Mass. Beard Chatfield Aves., 1826 Diversey Parkway, Chicago 4, III. BRUNSWICK RADIO & TELEVISION LEAR, INC. STROMBERG- CARLSON CO. 244 Madison Ave. New York 16, N. Y. 110 Ionia Ave., Grand Rapids 2, Mich. 100 Carlson Rd., Rochester 3, N. Y. COLLINS AUDIO PRODUCTS CO. LEWYT CORP. SYMPHONIC RADIO & ELECTRONIC CORP. P.O. Box 368 Westfield, N. J. 60 Broadway, Brooklyn II, N. Y. 292 -298 Main St., Cambridge 42, Mass. COLONIAL RADIO CORP. THE MAGNAVOX CO. 254 Rano St. Buffalo 7, N. Y. Ft. Wayne 4, III. TELEVOX, INC. Y. CROSLEY CORP. MAJESTIC RADIO & TEL. CORP. 451 South 5th Ave., Mt. Vernon, N. 1329 Arlington St. Cincinnati 25 Ohio 900 N. State St., Elgin, Ill. TEMPLETONE RADIO MFG. CORP. DeWALD RADIO CORP. JOHN MECK INDUSTRIES, INC. 100 Garfield Ave., New London, Conn. 440 Lafayette St. New York 3, N. Y. Liberty St., Plymouth, Ind. VIEWTONE TELEVISION & RADIO CORP. DONGENE LABORATORIES INC. MEISSNER MANUFACTURING DIVISION 81 Willoughby St., Brooklyn 1, N. Y. 95 Van St. New York N. Y. MAGUIRE INDUSTRIES INC. WARWICK MFG. CORP. DuMONT LABORATORIES, INC. Bellmont & 7th St., lait. Carmel, III. 4640 W. Harrison St., Chicago 44, III. 2 Main Ave., Passaic, N. J. CORP. OF AMERICA WATTERSON RADIO MFG. CORP. CORP. MINERVA EDWARDS FM RADIO 238 William St., New York 7, N. Y. P.O. Box 840, 2700 Swiss Ave., Dallas I, Texas 168 Washington St, N¡4ew York 6 N. Y. WELLS -GARDNER & CO. ELECTRICAL REPRO6ECTIONS CO. MOTOROLA, INC. 4545 Augusta Blvd.. Chicago SI, III. 2701 N. Kildare Ave., Chicago 39, III. 1644 N. Ada St., Chicago 22, III. WESTINGHOUSE ELECTRIC CORP. ELECTRO -TONE CORP. NATIONAL CO., INC. 48, Mau. 2519 Wilkens Ave., Baltimore 3, Md. 221 Hudson St. Hoboken N. J. 61 Sherman St., Malden RADIO & PHONOGRAPH CORP. NOBLITT-SPARKS INDUSTRIES, INC. WILCOX -GAY CORP. EMERSON Charlotte, Mich. Ill 8th Ave. New York 11, N. Y. 13th St. & Big Four RR. Columbus, Ind. ESPEY MANUFACTURING CO., NC. OLYMPIC RADIO & TELEVISION INC. ZENITH RADIO CORP. Chicago 39, III. 528 E. 72d St., New York 21. N. Y. 34 -01 38th Ave., Long Island dity I, N. Y. 6001 Dickens Ave.. 1948 381 RM

Left, a front view of the converted set. Note the construction of the dial. Below, under -chassis view. R.f. section is on right side.

FM Receiver Frone mar Surplus Radio BC -624

By ROBERT C. PAINE TM reception is possible with several surplus sets. The author tells how to convert the BC -624 receiver.

THE BC -624 is still one of the most cuits. This tube is mounted under the tance of 20 -54 µµf. This has a possible popular surplus items on the mar- chassis. The latest model, the BC- 624 -C, tuning range of V54µµf /20µµf= 1.64/1. ket. It is well liked by amateurs is a scarce item on the surplus market. The FM band, 108 me to 88 mc, requires and experimenters who have con- It uses a 12H6 (VT -214) in an elec- a range of 1.23/1. This means that the verted it for receiving AM signals on tronic squelch that replaces the mechani- condenser, as it stands, has an excessive the 2 -meter band. (Detailed instructions cal system used in earlier models. Any tuning range, which results in more for converting the BC -624 for 2 -meter of these models can be used in making difficult alignment and a more crowded reception were given by Mr. L. W. May, this conversion. tuning scale. The capacitance ratio is W5AJG, in the September, 1947, issue Equipment circuit alterations changed with trimmers and padders as of RADIO -CRAFT. He described the con- shown in Fig. 1, where C is main If your BC is the version of the companion transmitter in -624 in a rack with the condenser, Cp, the small parallel trim- the April, 1947, issue.) In this article transmitter, remove it by unscrewing mer in the red -painted visible built on the main condenser, and we will show how it can be converted screws when the Cs is 5 -µµf rack is out of the a -35 mica trimmer mounted with little effort to a standard wide - cabinet. The next step in series with the coil. Since the entire band FM receiver. is to remove the mechanical channel tuning range of selector which turns the condens- the condenser is actu- This set is available separately or as tuning ally somewhat less than 90 degrees and a component of the SCR -522 -a receiver ers through cams. These cams are fast- the active ened with Bristo stations come close together, and transmitter combination designed screws that can be re- a tuning dial with an expanded scale is moved with a No. 8 Bristo wrench after desirable. The author used a planetary the cement that prevents their shaking type (National) with a long pointer loose has been removed with carbon attached to the dial. c, tetrachloride. Remove the a.f. transformer (295) c Co and the plate relay in the mechanical The R.F. circuit squelch circuit. Take out the crystal The circuit of a BC -624 converted for mounting FM operation is shown in Fig. 2. Signal Fig. Trimmers and padders adjust tracking. strip, the tuning coils, power I- plug, and terminal strips near the 12C8, Corps nomenclature, in parenthesis, and for use on the 100- to 156-mc band. The 12J5, and 12AH7 tubes. The i.f. ampli- color codes have been entered on the tube line -up is as follows: 9003 (VT- fier is used as is, with only minor diagram to aid in tracing the circuit. 203) r.f. amplifier; 9003 mixer; 9002 changes, but the second detector and The front end of the set is rewired with (VT -202) harmonic amplifier; 12AH7 audio system are completely rewired. the 9002 in the oscillator circuit tuned (VT -207) crystal oscillator and squelch The 12C8, 12J5, and 12AH7 are re- by the center section of the condenser. relay control tube; three 12SG7 (VT- placed with a 6SN7, 6K6, and 6X5, re- Self- supporting coils are used in the an- 209) 12 -mc i.f. amplifiers; 12C8 (VT- spectively. tenna, mixer, and oscillator circuits. They 169) second detector; a.v.c. and first There are two variable condensers: are 3/8 inch in diameter and are wound a.f. amplifier; and a 12J5 (VT -135) one has three gangs, and the other has with No. 14 wire. Ll is 2 turns placed second a.f. amplifier. two. These have split stators and in- about 1/4 inch from the grounded end of There are several versions of the BC- sulated rotors. Each section has a ca- L2. L2 has 6 turns, spaced to 15/16 624. The BC -624 -A is one with minor pacitance of approximately 16 to 50 µµf inch; L3 has 6 turns, center tapped and electrical or mechanical improvements. which makes them ideal for tuning h.f. spaced to 7/8 inch. L4 is identical to L2. The BC- 624 -AM is the BC -624 -A modi- circuits. The original i.f. transformers were fied-either in the field or factory -to Assuming a circuit capacitance of 4 designed for AM circuits, and their include an additional tube for delayed µµf in parallel with the tuning con- band width is too narrow for FM re- a.v.c. and automatic noise limiter cir- denser. we have an available capaci- ception. The band width should be 200 RADIOCRAFT for -FIM 139

I2H8 9003 9003 éw I2SG7 12SG7 125037 RF MI 15T1F 2ND 1F 006 3RD IF TIf__i C2 25MPf I 25uPf I -

LI g 5.3 L2` CI,C2-10Npt 330

.00035 35K .005 28K .0008 2MPf 6X5aCT IO 212-A. .212- 20 5 212-FG412-0 61u.-TERMINALS+rd L 5 S 25.4 250-300V L3

9002 TERMINALS 296' 100K 4604 osc 5 FILTER CH. OR 243 ON TRANV2961 SV 5 .W 12.6V FILS AMP, 5K 6K8 6SN7, 6016 IYIVAC K =1000 ALL CORDS -6E_ 4 6.3V FILS OUTPUT 2

2 -The schemafic. Replacing the 35,000-ohm resistor in the detector circuit with 15,000 ohms will improve high -note reproduction. to 300 kc. The band can be broadened a white -black -green wire), since it is de- and connecting an output meter to the by using inductive coupling with only sirable to retain this feature of the audio output. The i.f. transformers are one coil of the i.f. transformer, con- original circuit. then stagger -tuned to transmit a band nected as an inductance loaded with a 200 to 300 kc wide at 12 mc. For the r.f. low- resistance grid leak, as shown in The power supply unit, C. (see Fig. 1) is varied in the r.f. Fig. 3. The new parts added are en- Since the i.f. tubes have 12 -volt fila- and mixer circuits to obtain the desired closed by dotted lines. The coils are ments, we used an ordinary receiver range (somewhat greater than 88 -108 stagger -tuned to different frequencies transformer with 6.3 -volt and 5 -volt mc). (We adjusted the set so the oscil- close to 12 mc to give approximately filament windings connected in series - lator frequency is 12 mc lower than the even gain over a band of 200 -300 kc. aiding to produce 11.3 volts, which will A ratio discriminator transformer, Ti, suffice for the 12 -volt tubes. The 6.3-volt must be built to take the place of the terminals can still be left available for PRI SEC L.- 4th i.f. transformer (294). For this the 6.3 -volt tubes. A cathode -type recti- 1 9i a 455 -kc, fier, such as the 6X5, can be used for the purpose the author rewound 4.8K ' NOT USED iron -core i.f. transformer which hap- B- supply. A choke and condensers of pened to be available. The two coils of standard values or components of the 6+ T.006 wound set can be used in the power -supply filter the BC -624 i.f. transformers are Fig. 3- Coupling inductance in plate circuit. on separate, rigidly spaced forms, and circuit. The output transformer (296) it is impractical to vary their coupling. has a choke winding between terminals signal frequency). The oscillator is The arrangement of the discriminator 2 and 3 that can be used with con- tracked at the low- frequency end by ad- coils and the connections for the ratio densers (212 -A) and (212 -B) in the justing Cs, and at the high -frequency detector are shown in Fig. 4. The num- metal -cased condenser can. This can end by adjusting Cr. The coil can be ber of turns and values of tuning con- also contains two 5 -µf, low- voltage units squeezed together or spread apart as re- will vary, depending that were used to bypass the cathodes quired. Alignment is checked by varying densers Cl and C2 with a tun- on the particular coil form used. The of the 6SN7. You can mount the power the inductance of each coil primary and secondary windings should transformer in the space formerly oc- ing wand. The powdered -iron slug low - each be tunable to 12 mc. If you follow cupied by parts that were removed. TI the specifications given below, Cl and C2 will be about 10 µµf each. Aligning the set Fig. 4- Right, a 3- winding trans- A % -inch form was used for the dis- The set can be best aligned with an FM signal generator; however an AM former must be criminator transformer. The primary The tertiary do. To align the discrirttinator wound. winding has 19 turns and the tertiary type will is the primary. is con- over has 4 turns. The secondary is a bifilar transformer, the AM generator The secondary is i.f. winding made by doubling a length of nected to the grid of the third tube a bifilar winding. wire and winding 16 turns on the form, and a high- resistance or electronic d.c. T h e transformer keeping the turns close together and voltmeter is connected to the a.v.c. lead must be connected parallel. The doubled end of the wire is at A (Fig. 2). The primary is then as shown below. the center tap, and the open ends are tuned for maximum output at 12 mc. the ends of the secondary. All coils in The meter is transferred to point B and the discriminator transformer are the secondary tuned for zero output at wound with No. 30 enameled wire. 12 mc. When the signal is shifted away The audio system follows convention- from 12 mc the d.c. reading will increase value and then drop off, al lines and is easy to construct. It has to a maximum 4.8K A is connected reversing polarity and going through 8+ .006.1. a 3 -stage circuit. 6SN7 CI,C2 IOU.+ as a resistance- coupled cascade ampli- zero as the frequency goes from above fier working into the 6KG pentode power to below 12 mc. These maximum values ers the resonant frequency and the cop- amplifier. It is shown in the lower right should be equal. There is some inter- per slug raises it -the condensers or corner of the complete diagram in Fig. action between these adjustments so it coils must be adjusted according to the 2. The original output transformer may be necessary to repeat them. indication obtained. (296) was not designed to handle power To align the tuning unit and the i.f. The receiver conversion outlined above so it may be necessary to use a standard stages with an AM generator, the ratio results in a reasonably good FM re- output transformer designed to match detector is temporarily converted into ceiver. It is sufficiently sensitive to bring the 6K6 if good quality is expected. The an amplitude- modulation detector by in stations to a distance of about 30 d.c. output of the detector is connected grounding one end of the discriminator miles away, with only a 3- or 4 -foot wire to the original a.v.c. lead (identified as transformer through a small condenser as an antenna. JUNE '949 1'°I Complete hM station List WGHF of New York City come in al- WANTED: FM SCOUTS most nightly, sometimes with very FM is a new art in Radio. Much of it remains to be learned by engineers. The behavior strong signals. The distance is approxi- of radio waves in the FM band is still understood imperfectly. According to theory, mately 190 miles. N.Y.C. stations FM signals should not reach much beyond the horizon. Yet often they do. In some R-CBS -FM, WGYN, WNBC -FM and cases extraordinary DX reception has been reported. \\'NYC -FM are also heard occasionally, RADIO -CRAFT readers can render the radio art a distinct service in reporting such and WTRI, Troy, and WGFM, Schenec- phenomena as well as others, to us regularly. We will publish such information as well tady, are heard practically every night. as the "FM Scout's" name in this department. Some excellent reports have already been received. Address all letters to FM Department, c/o this magazine. To make FM reports really valuable, THE EDITORS scouts should furnish the following information: RESPONSE to our last month's call amplifier, he has received \VKIL -FM 1. Make and model of receiver(s) for FM scouts has been encourag- Kankakee, Illinois, and WCSI -FM, Co- used. ing. Several excellent distance reports lumbus, Indiana. Both these stations are 2- Type of aerial and transmission have been received. A number of others in the order of 250 miles from his loca- line and its height above ground. may or may not have been records, but tion. His antenna is a Ward television 3. Airline distance to the transmit- the reports did not give enough informa- folded dipole shortened to tune to the ters whose signals are received. good FM band, and he is "atop highest tion to determine exactly how the the 4. Time of reception and duration of reception was. Reports have also in point in St. Louis County." period in which signals are re- some cases given the reputed distances Thomas Gray of Arlington, Virginia, ceived. (often based on road mileage) to the reports reception of WCBS -FM and stations reported, instead of the air -line WGYN, New York City, about 215 miles Please get all the above dope into distance. away, on a pre -war G -E converted to your next report! Only then can infor- Best distance was reported by Jack the new band. Another long -range re- mation be gathered which will not only Wulfmeyer of Valley Park, Missouri, port was filed by Lincoln A. Wood of be of real interest, but may also add to (20 miles southwest of St. Louis). Ayer, Massachusetts. He reports that the world's knowledge of the behavior Using a Pilotuner with a Masco 35 -watt W2XEA, Alpine, New Jersey, and of very -high frequency radio waves.

STATION LOCATION FREQUENCY STATION LOCATION FREQUENCY STATION LOCATION FREQUENCY (mc) (mc) (mc)

KAGH-FM Pasadena, Calif. 98.3 KOMB Des Moines, Iowa 92.3 WAGE -FM Syracuse, N. Y. 98.5 KAKC-FM Tulsa, Okla. 94.9. KONG Alameda, Calif. 104.9 WAIR -FM Winston-Salem, N. C. 93.1 KALB-FM Alexandria, La. 96.9 KONO-FM San Antonio, Texas 92.9 WAJL Flint, Mich. 107.1 KALW San Francisco, Calif. 91.7 KOPP-FM Ogden, Utah 103.9 WAJR Morgantown, W. Va. 99.3 KAMT-FM College Station, Texas 94.5 KOPY Houston, Texas 98.5 WAKR -FM Akron, Ohio 97.5 KARMFM Fresno, Calif. 101.9 KOZY Kansas City, Mo. 98.1 WAMS -FM Wilmington, Del. 96.1 KBEE Modesto, Calif. 103.3 KPDR-FM Alexandria La 99.7 WAPO -FM Chattanooga, Tenn. 94.7 KBIX-FM Muskogee, Okla. 98.5 KPFM-FM Portland, Ore. 97.1 WARM -FM Scranton, Pa. 105.7 KBMT Son Bernardino. Calif. 99.9 KPNI Palo Alto, Calif. 101.7 WASH Washington, D. C. 97.1 KBTR Minneapolis, Minn. 98.5 KPOR Riverside, Calif. 97.5 WATG -FM Ashland, Ohio 101.3 K BU R-FM Burlington, Iowa 92.9 KPRA Portland, Ore. 95.5 WAIL -FM Atlanta, Ga. 97.5 KCLI Los Angeles, Calif. 105.1 KPRC-FM Houston, Texas 102.9 WAYS -FM Charlotte N. C. 107.7 KCMC-FM Texarkana, Texas 92.5 K V-FM Pittsburgh, Pa. 98.1 W BAB -FM Atlantic City, N. J. 100.7 KCRA-FM Sacramento, Calif. 96.1 K W-FM San Francsco, Calif. 103.7 W BAM New York, N. Y. 98.7 KCRK Cedar Rapids, Iowa 96.9 KRBA-FM Lufkin, Texas 95.5 WBBB -FM Burlington, N. C. 101.1 KCRW Santa Monica, Calif. 89.9 KRBC-FM Abilene, Texas 96.9 WBBM-FM Chicago, Ill. 97.1 KCVN Stockton, Calif. 91.3 KRCC Richmond, Calif. 104.5 WBCA-FM Schenectady, N. Y. 101.1 KDI:A-FM Pittsburgh, Pa. 92.9 KRFM Fresno, Calif. 93.7 WBCM-FM Bay City, Mich. 96.1 KDYL-FM Salt Lake City, Utah 98.7 KRIC-FM Beaumont, Texas 99.5 W B EN -FM Buffalo, N. Y. 106.5 KE'A-FM Los Angeles, Calif. 95.5 KRJM Santa Maria, Calif. 103.1 WBEZ Chicago, Ill. 91.5 KENO-FM Las Vegas, Neb. 103.9 KRKD-FM Los Angeles, Calif. 96.3 WBGE-FM Atlanta, Ga. 95.5 KERN-FM Bakersfield, Calif. 94.1 KRLD-FM Dallas, Texas 92.5 WBGO Newark, N. J. 91.1 KFABFM Lincoln, Nebr. 97.9 KROC-FM Rochester, Minn. 94.7 WBIB New Haven, Conn. 100.7 KFAC-FM Los Angeles, Calif. 104.3 KRON-FM San Francisco, Calif. 96.5 WBIK Chicago, Ill. 96.3 KFOK-FM Sacramento, Calif. 96.9 KRSC-FM Seattle, Wash. 98.1 WBKY Lexington, Ky. 91.3 KFI-FM Los Angeles, Calif. 105.9 KRVM Eugene, Ore. 90.1 WBML-FM Macon, Ga. 100.7 KFM8FM San Diego, Caff, 101.5 KSBR San Bruno, Calif. 103.5 WBNB Beloit, Wis. 107.3 KFMX Council Bluffs, Iowa 96.1 KSBS Kansas City, Kans. 105.9 WBNU Aurora, III. 103.9 KFMY Fort Dodge Iowa 102.7 KSCJ-FM Sioux City, Iowa 94.9 WBNY-FM Buffalo, N. Y. 92.9 KFOR-FM Lincoln, Nebraska 102.9 KSEI-FM Pocatello, Idaho 96.5 WBOC-FM Salisbury, Md. 97.5 KFPW-FM Fort Smith. Ark. 94.9 KSEO Durant, Okla. 107.3 WBOE Cleveland, Ohio 90.3 KFSA Fort Smith. Ark. 107.7 KSFH San Francisco, Calif. 94.9 W BOW -FM Terre Haute, Ind. 101.1 KFSH San Francisco, Calif. 94.9 KSJO-FM San Jose, Calif. 95.3 WBOX-FM Louisville, Ky. 100.7 KFU O-FM St. Louis, Mo. 104.1 KSL-FM Salt Lake City, Utah 100.3 WBRE -FM Wilkes- Barre, Pa. 98.5 KFXD-FM Nampa, Idaho 101.9 KSPI-FM Stillwater, Okla. 93.9 WBRL Baton Rouge, La. 98.1 KFXM-FM San Bernardino, Calif. 95.1 KSTP-FM St. Paul, Minn. 102.1 W BT -FM Charlotte, N. C. 99.9 KFYO-FM Lubbock, Texas 99.5 KSUI Iowa City, Iowa 91.7 W BTM -FM Danville, Va. 97.9 KGAR-FM Garden City. Kans. 99.3 KTFIFMl Twin Falls, Idaho 99.7 WBUR -FM Burlington, Iowa 92.9 KGBS-FM Harlingen. Texas 95.3 KTOK-FM Oklahoma City, Okla. 104.3 WBUZ Bradbury Heights, Md. 96.7 KGDM-FM Stockton, Calif. 92.9 KTRH-FM Houston, Texas 101.1 WBYS-FM Canton, Ill. 100.9 KGKB-FM Tyler, Texas 101.5 KTRN Wichita Falls, Texas 97.3 WBZ-FM Boston, Mass. 92.9 KGKL-FM San Angelo, Texas 94.5 KTSJ Topeka. Kans. 99.5 WBZA-FM Springfield, Mass. 97.1 KGLO-FM Mason City, Iowa 101.1 KTUL-FM Tulsa, Okla. 97.1 WCAC -FM Anderson, S. C. 101.1 KGNC-FM Amarillo, Texas 104.3 KUGN-FM Eugene, Ore 99.1 WCAO -FM Baltimore, Md. 102.7 KGO-FM San Francisco, Calif. 106.1 KUOA-FM Siloam Springs, Ark. 105.7 WCAP -FM Asbury Park, N. J. 107.1 KGPO Grants Pass, Oregon 96.9 KURV-FM Edinburg, Texas 104.9 WCAU -FM Philadelphia, Pa. 98.1 KGW-FM Portland, Ore. 100.3 KUSC Los Angeles, Calif. 91.5 WCBS -FM New York, N. Y. 101.1 K1-1.1-FM Hollywood, Calif. 101.1 KVCI-FM Chico, Calif. 101.1 WCBT -FM Roanoke Rapids. N. C. 98.5 KIDOFM Boise. Idaho 106.1 KVEC-FM San Luis Obispo, Calif. 99.9 WCEC -FM Rocky Mount, N. C. 100.7 KIMV Hutchinson, Kans. 105.7 KVNJ-FM Fargo, N. D. 92.3 WCFC -FM Beckley, W. Va, 101.3 KING-FM Seattle, Wash. 94.9 KVWC-FM Vernon, Texas 98.7 WCFR Fall River, Mass. 100.9 KISS San Antonio, Texas 99.5 KWBR-FM San Francisco, Calif. 97.3 WCHA -FM Chambersburq, Pa. 95.5 KIXL-FM Dallas. Texas 104.5 KWBW-FM Hutchinson, Kans. 93.1 WCIL -FM Carbondale Ill. 100.7 KJBS-FM San Francisco, Calif. 98.9 KWGS-FM Tulsa, Okla. 90.5 WCJT Louisville, Ky. 99.7 KKLA Los Angeles, Calif. 97.1 KWIL-FM Albany, Ore. 101.7 WCLO -FM Janesville, Wis. 99.9 KLCN-FM Blytheville, Ark. 96.1 KWK-FM St. Louis, Mo. 99.1 WCLT Newark, Ohio 100.3 KLOK-FM San Jose. Calif. 98.5 KWLK-FM Longview, Wash. 104.3 WCMW -FM Canton, Ohio 94.9 KLZ-FM Denver, Colo. 94.1 KXEL-FM Waterloo, Iowa 105.7 WCNB Connersville, Ind, 100.3 KMBC-FM Kansas City, Mo. 100.5 KXLW-FM Clayton, Mo. 101.1 WCOA -FM Pensacola, Fla. 98.9 KMBT San Bernardino, Calif. 99.9 KXOA-FM Sacramento Calif. 107.9 WCOD -FM Richmond, Va. 98.1 KMFM Monroe, La. 104.1 KXOK-FM St. Louis, Mo. 93.7 WCOH -FM Newnan, Ga. 92.3 KMPC-FM Hollywood, Calif. 100.3 KXYZ-FM Houston, Texas 96.5 WCOL -FM Columbus, Ohio 92.3 KMUS Muskogee, Okla. 101.5 KYFM-FM San Antonio. Texas 101.5 WCOU -FM Lewiston, Me. 93.9 KMYC-FM Marysville, Calif. 99.9 KYSMFM Mankato, Minn. 103.5 WCSI Columbus, Ind. 93.7 KN BC-FM San Francisco, Calif. 99.7 KYW-FM Philadelphia, Pa. 92.5 WCTP Greensboro, N. C. 98.7 KNX-FM Hollywood, Calif. 93.1 W2XEA Alpine, N. J. 92.1 WCTS Cincinnati, Ohio 01.9 KOA-FM Denver, Colo. 95.7 W2XMN Alpine, N. J. 44.1 WCTW New Castle, Ind. 03.' KOAD-FM Omaha, Nebr. 92.9 WAAT-FM Newark, N. J. 94.7 WCVS -FM Springfield, III. 02.9 KOCS-FM Ontario, Calif. 93.5 WABF New York, N. Y. 99.5 WDAE -FM Tampa, Fla. 05.7 KOCY-FM Oklahoma City, Okla. 94.7 WABX-FM Harrisburg, Pa. 100.9 WDBQ Dubuque, Iowa 03.3 KOKX-FM Keokuk, Iowa 102.7 WACE-FM Chicopee, Mass. 100.3 WDLB -FM Marshfield, Wis. 03.9 KOMA-FM Oklahoma City, Okla. 105.9 WAFM-FM Birmingham, Ala. 99.5 (Continued on. page 42) RADIO -CRAFT for 41

MONEY BACK GUARANTEE- We believe units offered for sale by mail order should be sold only on a "Money- Back -If- Not -Satisfied" basis. We carefully check the design, calibration and value of oll items advertised by us and unhesitatingly offer all merchandise subject to a return for credit or refund. You, the customer, are the sole judge as to value of the item or items you have purchased. The Model 88 -A @OMBIN7I TION SIGNAL GENERATOR AND SIGNAL TRACER The ultimate in signal tracing procedure is achieved by the Model 88, for the use of this model, enables you to use either the broadcast signal itself or the signal injected by the Signal Generator. This is especially useful of course when servicing "dead" or "intermittent' receivers. The Model 88 you will find is the greatest time -saver ever provided for by combining a full range Signal Generator and Signal Tracer into one unit the set up time for interconnecting, etc., is entirely eliminated. Signal Generator Specifications: * Frequency Range: 150 Kilocycles to 50 Megacycles. * The R.F. Signal Frequency is kept completely constant at all output levels. This is accomplished by use of a special grid loaded circuit which provides a constant load on the oscillatory circuit. A grounded plate oscillator is used for additional frequency stability. * Modulation is accomplished by Grid. blocking action which has proven to be equally effective for alignment of amplitude and frequency modulation as well as for television receivers. * Positive action attenuator provides effective output control it all times. * R.F. is obtainable separately or modulated by the Audio Frequency. Signal Tracer Specifications: * Uses the new Sylvania 1N34 Germanium crystal Diode which combined with a resistance -capacity network provides a frequency range 85 of 300 cycles to SO Megacycles. Simple to Operate -Clips directly on to receiver chassis, no tunine The Model SS comes * complete with all test ONLY controls. leads and operating NET * Provision is made for insertion of phones of any impedance, a instructions. 8 standard Volt -Ohm Milliammeter or Oscilloscope. The New Model 606 TUBE & SET TESTER A COMPLETE TUBE TESTER Tests all tubes including the n w cost -sear miniature loctals such a the 12AT6. 12A116, 35W4, 5085, 11723, etc. Tests by the well -established emission method for tube quality. directly read on the scale of the meter. Tests shorts and leakages un to 3 Megohms in all tubes. Tests leakages and shorts of any one element against all elements in all tubes. Tests both ointes in rectifiers. Tests individual sections such as diodes. triodes, pentode, etc.. in multi- Purpose tubes. A COMPLETE MULTI -METER ti D.C. VOLTAGE RANGES: O to 7.5 15 75 150, 750'1.500 Veils 6 A.C. VOLTAGE RANGES: O to 15 30.150 306, 1,500 3.000 Volts 4 D.C. CURRENT RANGES: Oto 1.5'15 150 Ma. 0 to 1.5 Amps. LOW RESISTANCE RANGE: 0 to 2.000 Ohms (1st division is 110th of an ohm.) 2 MEDIUM RESISTANCE RANGES: 0 to 20.000,206.000 Ohms Model 606 comes housed i a beautiful hand rubbed $ .85 HIGH RESISTANCE RANGE: oak eabinet complete with n portable cover. test leads. 0 to 20 Megohms tube charts. and detailed operating instructions- ONLY NET 3 DECIBEL RANGES: 47 -10 to +38 +10 to +38 +30 to +58 0.8. 20' DEPOSIT REQUIRED ON ALL C.O.D. ORDERS

PARK PLÑC: GENERAL ELECTRONIC DISTRIBUTING CO. NEW YORK 798

TUNE, 1948 Complete FM Station List 421

STATION LOCATION FREQUENCY STATION LOCATION FREQUENCY STATION LOCATION FREQUENCY

WDLM Chicago, III. 95.5 WHPE-FM High Point, N. C. 95.5 WMLL Evansville, Ind. 94.5 WDNC-FM Durham, N. C. 105.1 WHTN-FM Huntington, W. Va. 100.5 WMLN Mt. Clemens, Mich. 106.3 W DOS-FM Oneonta, N. Y. 99.1 WHVA Poughkeepsie, N. Y. 104.7 WMMW -FM Meriden, Conn. 95.7 WDRC-FM Hartford, Conn. 93.7 WHYN-FM Ijolyoke, Mass. 93.1 WMNE Boston, Mass. 100.5

WDTR Detroit, Mich. 90.9 W I BA-FM Madison, Wisc. 101.5 WMOT -FM Pittsburgh, Pa. 94.5 WDUL Duluth, Minn. 92.3 WIBG-FM Philadelphia. Pa. 94.1 WMRC -FM Greenville, S. C. 94.9 WDXY Spartanburg, S. C. 100.5 WIBW-FM Topeka, Kans. 102.5 WMUN Muncie, Ind. 104.1 WEAW Evanston, III. 96.7 WIBX Utica, N. Y. 96.9 WMUR -FM Manchester, N. H. 95.7 WEAU-FM Eau Claire Wis. 94.1 WIL-FM St. Louis, Mo. 97.3 WMUS -FM Muskegon, Mich. 100.5 WEBC-FM Superior. Wis. 92.3 WINC-FM Winchester, Va. 92.5 WNAM -FM Neenah, Wisc. 98.5 WEBR-FM Buffalo, N. Y. 96.9 WINX-FM Washington, D. C. 96.3 WNAV -FM Annapolis, Md. 99.1 WEEU-FM Reading, Pa. 92.9 WIOD-FM Miami, Fla. 97.3 WNBC -FM New York, N. Y. 97.1 WEEX Easton, Pa. 98.3 WIP-FM Philadelphia Pa. 93.3 WNBF -FM Binghamton, N. Y. 100.5 WEFM Chicago. III. 99.5 WIS-FM Columbia, S. C. 94.5 WNDB -FM Daytona Beach, Fla. 94.5 WEHS Chicago, III. 97.9 WISE-FM Asheville, N. C. 102.5 WNDR -FM Syracuse, N. Y. 102.5 WELD-FM Columbus, Ohio 97.1 WIST Charlotte, N. C. 104.7 WNLC -FM New London, Conn. 99.5 WELL-FM Battle Creek, Mich. 102.1 WITH-FM Baltimore, Md. 104.3 WNYC -FM New York, N. Y. 93.9 WENR-FM Chicago, III. 94.7 WIUC Urbana Ill. 91.7 WOAI -FM San Antonio Texas 102.5 WERC-FM Erie, Pa. 99.9 WIZZ Wilkes -Narre, Pa. 103.3 WOHS -FM Shelby, N. C. 96.1 WESB-FM Bradford, Pa. 97.5 WJAS-FM Pittsburgh, Pa. 99.7 WOPI -FM Bristol, Tenn. 96.9 WEW-FM St. Louis, Mo. 95.1 WJBC-FM Bloomington, Ill. 101.5 WOPT -FM Oswego, N. Y. 104.7 W EW S-FM Cleveland, Ohio 02.1 WJBK-FM Detroit, Mich. 93.1 WOTW -FM Nashua, N. H. 106.3 WEXL-FM Royal Oak, Mich. 04.3 WJBY-FM Gadsden, Ala. 103.7 WOWO -FM Fort Wayne, Ind. 96.1 WFAA-FM Dallas. Texas 97.9 WJEJ-FM Hagerstown, Md. 104.7 WPAD -FM Paducah, Ky. 96.9 WFAH-FM Alliance, Ohio 01.7 WJEM Springfield, Ohio 103.9 WPAG -FM Ann Arbor, Mich. 98.7 W FAS-FM White Plains, N. Y. 03.9 WJHP-FM Jacksonville, Fla. 96.9 WPAM -FM Pottsville, Pa. 95.5 W FBL-FM Syracuse, N. Y. 93.1 WJJW Wyandotte, Mich. 103.1 WPDX -FM Clarksburg, W. Va. 95.1 WFIL-FM Philadelphia, Pa. 02.1 WJLB-FM Detroit, Mich. 97.9 WPEN -FM Philadelphia, Pa. 102.9 WFJS Freeport, Ill. 02.5 WJLK-FM Asbury Park, N. J. 94.3 WPIC -FM Sharon, Pa. 102.9 W FM D-FM Frederic, Md. 01.5 WJLS-FM Beckley, W. Va. 99.5 WPLH -FM Huntington, W. Va. 102.5 WFMI Portsmouth, N. H. 07.3 WJMC-FM Rice Lake, Wis. 96.3 WPTL Providence, R. I. 91.5 W FMJ-FM Youngstown, Ohio 05.1 WJNO-FM West Palm Beach, Fla. 98.7 W AM -FM Miami, FIa- 94.9 WFML Washington, Ind. 06.5 WJOB-FM Hammond Ind. 92.3 W DI Quincy, Ill. 105.1 WFMO Jersey City, N. J. 03.1 WJPF-FM Herrin, Ill. 98.5 W XR -FM New York, N. Y. 96.3 WFMR New Bedford, Mass. 98.1 WJPG-FM Green Bay, Wisc. 101.1 WRAL -FM Raleigh, N. C. 101.5 WFMU Crawfordsville, Ind. 02.9 WJTN-FM Jamestown, N. Y. 93.3 WRAK -FM Williamsport, Pa. 100.3 WFMY Greensboro, N. C. 97.3 WJW-FM Cleveland, Ohio 104.1 WRBL -FM Columbus, Ga. 93.3 WFMZ Allentown Pa. 95.9 WKAP-FM Allentown. Pa. 100.7 WRC -FM Washington, D. C. 93.9 WFNC-FM Fayetteville, N. C. 98.1 WKAT-FM Miami Beach, Fla. 93.1 WRCM New Orleans, La. 97.1 W FN S-FM Burlington, N. C. 99.9 WKBH-FM La Crosse, Wisc. 93.1 WRGA -FM Rome, Ga. 106.5 WFOB Fostoria, Ohio I05.6 WKBN-FM Youngstown, Ohio 98.9 WRGK La Grange, Ill. 103.1 WFOR-FM Lincoln, Nebr. 102.9 WKBR-FM Manchester, N. H. 100.1 WRLD-FM West Point, Ga. 102.9 WFRO-FM Fremont, Ohio 99.3 WKIL Kankakee, Ill. 100.7 WRLD-FM Lanett, Ala. 102.9 WFRS Grand Rapids, Mich. 92.5 WKJG-FM Fort Wayne, Ind. 106.1 WRNY-FM Rochester, N. Y. 97.9 WFUV New York, N. Y. 90.7 WKNB-FM New Britain, Conn. 103.7 WROL -FM Knoxville, Tenn. 97.3 WGAL-FM Lancaster, Pa. 101.3 WKNP-FM Corning. N. Y. 106.1 WROV -FM Roanoke, Va. 103.7 WGAN-FM Portland, Me. 101.9 WKOK-FM Sunbury, Pa. 94.1 WRRN -FM Warren, Ohio 107.9 WGAY-FM Silver Springs, Md. 102.3 WKPB Knoxville, Tenn. 93.3 WRUN -FM Rome, N. Y. 105.7 W G BA-FM Columbus, Ga. 95.1 WKPT-FM Kingsport, Tenn. 98.5 WRUC Norfolk Va. 102.5 WGBG-FM Greensboro, N. C. 100:3 WKRG-FM Mobile, Ala. 99.9 WRXW Louisville, Ky. 95.1 WGBR-FM Goldsboro N. C. 93.3 WKRT-FM Cortland, N. Y. 99.9 WSAL Saginaw, Mich. 98.1 WGFM Schenectady, N. Y. 99.5 WKWK-FM Wheeling, W. Va. 97.3 WSAN -FM Allentown, Pa. 99.9 WGH-FM Norfolk, Va. 96.5 WKY-FM Oklahoma City, Okla. 98.9 WSAP-FM Portsmouth, Va. 99.7 WGHF-FM New York, 61. Y. 101.9 WKYC Paducah, Ky. 93.3 WSAR-FM Fall River, Mass. 103.7 WGNB Chicago, Ill. 98.7 WLAD-FM Danbury, Conn. 98.3 WSAV -FM Savannah, Ga. 100.3 WGNC-FM Gastonia, N. C. 101.9 WLAN-FM Lancaster, Pa. 96.9 WSBA-FM York Pa. 103.3 WGOV-FM Valdosta, Ga. 92.5 WLAV-FM Grand Rapids, Mich. 96.9 WSBF South Bend, Ind, 101.3 W G PA-FM Bethlehem Pa. 95.1 WLAW-FM Lawrence, Mass. 93.7 WSFA -FM Montgomery, Ala. 103.3 WGST-FM Atlanta, Ga. 94.1 WLBR-FM Lebanon, Pa. 00.1 WSGN -FM Birmingham, Ala. 93.7 WGTM-FM Wilson, N. C. 106.7 WLDS-FM Jacksonville, Ill. 00.5 WSHS Floral Park, N. Y. 90.3 WGTR Boston, Mass. 99.1 WLET Toccoa, Ga. 02.9 WSIC-FM Statesville, N. C. 105.7 WGUY-FM Bangor, Me. 93.1 WLEY Elmwood Park, Ill. 07.1 WSJS-FM Winston -Salem, N. C. 104.1 WGYN-FM New York, N. Y. 97.9 WLIN-FM Merrill, Wis. 01.7 WSLS -FM Roanoke, Va. 99.1 WHA-FM Madison Wis. 91.5 WLOB-FM Claremont, N. H. 06.1 WSM -FM Nashville, Tenn. 103.3 WHAD Delafield, Wis. 90.7 WLOG-FM Logan, W. Va. 03.3 WSMB -FM New Orleans, La. 102.7 W HAV-FM Haverhill, Mass. 92.5 WLOS-FM Asheville, N. C. 04.3 WSNJ -FM Bridgeton, N. J. 98.9 WHBC-FM Canton, Ohio 94.1 WLPM-FM Suffolk, Va. 97.9 WSON -FM Henderson, Ky. 99.5 WHBF-FM Rock Island, 98.9 WLTN Lewiston, Pa. 97.9 WSOU South Orange, N. J. 89.5 WHBS-FM Huntsville, Ala. 95.1 WLVA-FM Lynchburg, Pa. 97.5 WSOY -FM Decatur, III. 98.7 WHCU-FM Ithaca, N. Y. 97.3 WLWA-FM Cincinnati, Ohio 101.1 WSPA -FM Spartansburg, S. C. 98.9 W H DH-FM Boston, Mass. 94.5 WMAR-FM Baltimore, Md. 97.9 WSPD -FM Toledo, Ohio 101.5 W H EF-FM Rochester, N. Y. 96.5 WMAS-FM Springfield, Mass. 94.7 WSRK Shelbyville, Ind. 101.3 WH FB-FM Benton Harbor. Mich. 99.9 WMAZ-FM Macon, Ga. 99.1 WSRS -FM Cleveland Heights. Ohio 95.3 WHFM Rochester, N. Y. 98.9 WMBD-FM Peoria, Ill. 92.5 WSTC -FM Stamford, Conn. 96.7 WHIO-FM Dayton, Ohio 99.1 WMBH-FM Joplin, Mo. 96.1 WSTP -FM Salisbury N. C. 106.5 WHIS-FM Bluefield, W. Va.' 104.5 WMBS-FM Uniontown, Pa. 105.7 WSTV -FM Steubenville, Ohio 103.5 WHKX Cleveland Ohio 100.7 WMCF-FM Memphis, Tenn. 99.7 WSVA -FM Harrisonburg, Va. 100.7 WHKY-FM Hickory, N. C. 102.9 WMCK-FM McKeesport, Pa. 104.9 WSYR -FM Syracuse, N. Y. 94.5 WHLD-FM Niagara Falls, N. Y. 98.5 WMCP Baltimore, Md. 94.7 WTAD-FM Quincy, III. 99.5 WHMA-FM Anniston, Ala. 100.5 WMFR-FM High Point, N. Y. 99.5 WTAG -FM Worcester, Mass. 96.1 WHNY-FM Hempstead, N. Y.' 98.3 WMGM-FM New York N. Y. 100.3 WTAL -FM Tallahassee, Fla. 103.9 WHO-FM Des Moines, Iowa 100.3 WMIN-FM St. Paul, }vlinn. 99.5 WTAR -FM Norfolk, Va. 97.3 WHOP-FM Hopkinsville, Ky. 98.7 WM IT Winston -Salem, N. C. 106.9 WTCN -FM Minneapolis, Minn. 97.1 WHP FM Harrisburg, Pa. 97.3 WMIX-FM Mt. Vernon, Ill. 94.1 WTFM -FM Tiffin Ohio 98.3 WTHT -FM Hartford, Conn. 106.1 WTIC -FM Hartford, Conn. '96.5 WTJS -FM Jackson, Tenn. 100.7 WTMA -FM Charleston, S. C. 95.1 WTMJ -FM Milwaukee, Wis. 93.3 WTOC -FM Savannah, Ga. 97.3 WTPS -FM New Orleans, La. 95.7 WTR F -FM Bellaire, Ohio 95.1 WTR I -FM Troy, N. Y. 102.7 WTRT -FM Toledo, Ohio 99.9 WTSP-FM St. Petersburg, Fla. 102.5 WTTH -FM Port Huron, Mich. 99.1 WTTR Boston, Mass. 104.1 WVAW -FM Cheviot, Ohio 96.7 WVUN Chattanooga, Tenn. 98.1 WWCF Greenfield, Wis. 94.9 W W DC -FM Washington, D. C. 101.1 W W DX-FM Paterson, N. J. 107.1 WWHG Hornell, N. Y. 105.3 WWJ-FM Detroit, Mich. 97.1 WWLH New Orleans, La. 100.3 WWNY-FM Watertown, N. Y. 100.5 W W PG -FM Palm Beach, Fla. 97.9 W WST -FM Wooster, Ohio 104.5 W WVA -FM Wheeling, W. Va. 98.7 WXHR -FM Cambridge, Mass. 96.9 WXLW -FM Indianapolis, Ind. 94.9 WXNJ -FM Plainfield N J. 103.9 WXYZ-FM Detroit Mici 10'.I RADIO -CRAFT for ìr 43 SENSATION I LU A LUE THE NEW MODEL 770 Specifications:

6 A.C. VOLTAGE RANGES: AN ACCURATE 0- 15/30/150/300/1500'3000 Volts 6 D.C. VOLTAGE RANGES: POCKET 0- 71/2/15/75/150/750 /1500 Volts -SIZE 4 D.C. CURRENT RANGES: 0-1%/15/150 Ma. 0-1% Amps. 2 RESISTANCE RANGES: VOLT -OHM- MILLIAMMETER 0-500 ohms 0-1 Megohm

(Sensitivity 1000 Ohms per volt, THE MODEL 770 Comes complete with self- contained bat- e teries, test leads and all operat- Features: ing instructions. * Measures A.C. Volts, D.C. Volts, D.C. Current and Resistance. * Compact- measures 31/6" x 5 %8" x 21% ".

* Uses latest design 2% accurate 1 mil. D'Arsonval type meter. * Housed in round -cornered, molded case. * Beautiful black etched panel. Depressed letters filled with permanent white, insures long -life even with constant use. THE NEW MODEL 247 + TUBE TESTER Checks octals, loctals, bantam jr. peanuts, television miniatures, magic eye, hearing aids, thyratrons, the new type H. F. miniatures, etc. Features: * A newly designed element selector switch reduces the possibility of obsolescence to an absolute minimum. * When checking Diode, Triode and Pentode sections of multi -purpose tubes, sections can be tested individually. A special isolating circuit allows each section to be tested as if it were in a separate envelope. * The Model 247 provides a super sensitive method of checking for shorts and leakages up to 5 Megohms between any and all of the terminals. * One of the most important improvements, we believe. is the fact that the 4 position fast -action snap switches are all numbered in exact accordance with the standard R. M. A. numbering system. Thus. if the element terminating in pin No. 7 of a tube is under test, button No. 7 is used for that test. ONLY Model 297 comes complete with new speed -read chart. Comes housed in handsome. hand -rubbed oak cabinet sloped for bench 90 use. A slip -on portable hinged cover is indicated for outside use. 9NET Size: 10 %" z 8 (t " z 5% ". THE MODEL 650 - AN A.C. OPERATED SIGNAL GENERATOR 9 RANGE: 100 KILOCYCLES TO 105 MEGACYCLES

* RF obtainable separately or modulated by the Audio Frequency. * Audio Modulating Frequency -400 cycles pure sine wave-less than 2% distortion. * Attenuation -3 -step ladder type of attenuator (T pad). * Uses a Hartley Excited Oscillator with a Buffer Amplifier. * Tubes: 6J5 as R.F. Oscillator: 6SÁ7 as modulated buffer and Mixer; 6SL7 as audio oscillator and rectifier. Model 650 conies complete with coaxial cable, test leads and instructions. Housed in heavy gauge grey crystalline $ cabinet with beautiful two tone etched front panel. Size 91/2" x 10" x 6" NET PRICE:

MODELS ARE OFFERED ON MONEY-BACK4F-NOT-SATISFIED OUR POLICY BASIS. AL ITEMS AVAILABLE FOR ATE SHIPMENT FROM STOCK. GUARANTEED TO BE EXACTLY AS DESCRIBED -ALL RH \ \I) NEW -NO SURPLUS. 20% Deposit Required on all C.O.D. Orders MOSS ELECTRONIC DISTRIBUTING CO.DEPT. RCEWYORULTOrNTREET

JUNE, 1 9 4 8 Glossary of FM Terms

Compiled by JOHN B. LEDBETTER

amplitude distortion. Result of nonlinear action blanket effect. Tendency of an FM signal to sup- note. To avoid this type of interference, strength in the grid -cathode or plate -cathode circuit ut an press completely a weaker signal on the same of the desired station need be only ten times amplifier, causing frequencies to appear in the channel. This effect is largely due to action in that of the undesired signal. output which were not present at the input. the receiver limiter circuit. conditional grant (CG). Authorization for a new amplitude modulation (AM). A system of broad- carrier shift (carrier deviation). The amount (in FM station provided certain terms or conditions casting in which the amplitude or strength of the cycles) by which the center frequency departs are fulfilled. radio wave is varied with modulation. from its assigned value. Deviation limit set by construction permit (CP). Authorization to pro- antenna gain. A measure of antenna strength; FCC is 2.000 cycles. ceed with construction of a new station; issued determined by comparing the power ratio between carrier wave. The unmodulated component of the after previous terms have been met. the antenna under test and a standard antenna wave emitted from the transmitter. cross-modulation. The impression of one stations having a gain of one. Ratio is determined by the center frequency. The exact assigned frequency modulation on the carrier of another. Modulation Poynting vector or by measuring radiation re- of an FM transmitter when no modulation is ap- from both stations may appear simultaneously. sistance. plied. Also known as resting frequency. idle fre- de- emphasis network. An arrangement at the re- antenna height (above average terrain). Actual quency, carrier frequency. or mean frequency. ceiver, usually consisting of a 100,0110ohm re- physical height above average or mean height of channel. A station's assigned frequency. Width sistor and a .001 -pf condenser. for reducing pre - terrain to top of antenna. of AM channels is 10 Ice, FM channels 200 kc emphasized frequencies to their original values. antenna height, effective. Ratio of the total signal (FM frequencies 88 -108 me correspond to chan- demodulation. Action by which a frequency-modu- voltage at the receiving antenna to the strength nels 201 -300). lated signal is converted into audio voltage. of the radiated wave. (in a quarter -wave vertical wire antenna, effective height = 2/a x actual characteristic impedance (or resistance). When deviation ratio. The frequency swing (75 he height.) referring to a transmission line. the value of re- divided by the highest audio frequency. sistance which will match that of the line and composed antinodes. See Nodes. dipole. A directional receiving antenna, completely absorb the transmitted energy. Other of two ,,..¡-wave length elements placed end-to- atmospherics. Static or electrical disturbances values will result in loss of power through re- end and insulated at the center. caused by storms. flected energy and standing waves. direct frequency modulation. A way of produc- audio compressor-expander. A limiting type of class A station. One intended to serve a coming frequency -modulated signals in which the audio amplifier designed to compress audio peaks munity or town, other than the principal city in master oscillator stage is modulated directly. to a predetermined level, and to increase low - the area. and surrounding rural area. Minimum usually by a reactance tube (or tubes) connected level passages to a desired value. power, 100 watts, maximum, 1 kw. with antenna across its tank circuit and the reactance varied terrain. Twenty class A audio 250 feet above average at an audio rate. The small frequency swing thus peak chopper. An amplifier designed to channels are by frequency to keep a desired provided. obtained is increased multipliers peak amplitudes from exceeding the correct value. value by instantaneous clipping of those peaks. class II station. One serving the metropolitan district or principal city and surrounding area. or direct wave. The component part of a space suave audio peak limiter. An amplifier in which the which from gain is quickly reduced and then slowly restored a rural area removed from large cities. Minimum travels in a straight line transmit- 10 with an ting to when instantaneous peaks exceed a predetermined power east of Mississippi, kw an- antenna receiving antenna. level. tenna height of 300 feet: maximum power. 20 discriminator. A demodulator circuit (correspond- kw with 500 -foot antenna. West of Mississippi ing to the second detector in AM receivers). As- audio response. The degree of fidelity inherent in power in excess of this maximum is granted if any or sists the limiter circuit in removing or suppress. part of equipment transmitting receiving need is shown. Sixty class 13 channels are pro- ing amplitude variations in the frequency -modu- audio signals. vided. lated signal. Discriminator circuits are employed system automatic frequency control (a.f.c.). A for co -axial line. Transmission line for coupling in some types of direct -FM transmitters to sta- correcting the master oscillator frequency in FM transmitter to antenna; composed of one copper bilize the carrier frequency. transmitters. Modulation is applied in series with conductor placed within another of larger diame- doublet. A receiving antenna whose physical the control grid of a reactance tube, whose trans - by ceramic conductance (and oscillator ter and insulated from it spacers. length is short compared to wave length. Large reactance across the Outer conductor is at ground potential; inner end capacitance causes an even distribution of tank) is varied accordingly. A degenerative feed- conductor carries the energy. Line is made air- is used to oscillator current throughout the conductor. Similar other- back circuit heterodyne the tight and filled with low -pressure gas to mini- wise to the dipole. frequency to an intermediate frequency to minimize moisture content. mize frequency drift. (In some receivers, a.f.c. dynamic noise suppressor. An amplifier equipped is used to compensate automatically for incorrect common channel interference. A possible form of with electronic gate circuits which effectively dial settings.) interference appearing as cross -talk or as a beat eliminate noise and record- scratch frequencies without apparent effect on music. dynamic range. Difference in level between loud- A MODERN HIGH -POWER FM TRANSMITTER est and softest sounds contained in a broadcast, i.e., symphony and concert offerings. effective radiated power (ERP). The product of transmitter output times antenna gain. A transmitter running 5 kw into an antenna whose gain is 6 has an effective radiated power of 30 kw. elevation. The height of an antenna site above sea level. equalization, line. Treatment of a telephone or network line, in which the frequency response is extended to suit broadcast purposes. equalizer.Anatwork designed to change the audio - frequency response of a circuit. Equalizers may be inserted to give a certain cut-off point to improve noise rejection, or to extend the normal response characteristics of a line. field strength. The strength of a radio wave, expressed as voltage stress produced in space by the wave's electric field; usually expressed in microvolts or millivolts (per meter). folded doublet. A doublet type of receiving antenna whose elements have been doubled back on themselves to form an effective loop. frequency deviation. Frequency swing, or amount of departure from the resting frequency with modulation. frequency deviation range. 150 kc maximum (75 kc each side of center frequency). The 25 -kc portion at each extreme edge of the range is used only as a guard frequency. frequency dividers. Stages of radio -frequency amplifiers, used to divide and compare the frequencies of the modulated oscillator and n crystal standard. The difference voltage is applied to a motor control system to correct for drift. frequency modulation (FM). A system of radio broadcasting in which modulation is accomplished by varying the carrier frequency width, while the carrier amplitude remains constant. Band width of FM channels is 200 kc; maximum frequency swing is 75 ke each side of center. frequency monitor. An electronic instrument em- William H. Pitkin, the chief engineer of New York City's Municipal Broadcasting System, ployed at the transmitter to indicate departure. makes an adjustment on Station WNYC -FM's new Western Electric I O-kilowatt transmitter. (Continued on page 49) RADIO -CRAFT for 4 =13

A GREAT FIRST!

NEW... Sensational TRANSVISION Development now offers LARGE -IMAGE DIRECT -VIEW TELEVISION at low cost! BIGGEST VALUE in TELEVISION! Model 10BL TELEVISION KIT with FM Radio Features Beautiful CABINET with BUILT -IN LENS . . . Gives LARGE 120 Sq. In. Picture.

Roto- picture effect: Picture "rotates ", giving the appearance of being in focus and clearly visible from every angle! Uses 10" Electromagnetic Direct -viett Picture Tube. Features new -type cabinet with built -in lens which magnifies, clarifies and heightens contrast of the picture. The lens also creates the effect of apparent rota- tion of the picture. so that when the observer moves. the picture still seems to be in focus and clearly visible from any angle. ECONOMICAL KIT, EASY TO ASSEMBLE. In t ' t of value, this Telcvis' kit provide- the opporttulily of acquiring a LARGE -IMAGE direct-view television set at a VERY LOW PRICE; also very economical from a tube replacement angle. This model is available in KIT FORM, for easy assembly; no technical knowledge required. Simple step -by -step instructions are included. Sates as much as 50 over the cost of receivers 1r N.'r similar picture Magnitude. TECHNICAL DATA: Model 10131, uses a 10" Elea tro- magnetic Direct -view Picture Tube; has plete F.M. Radio whith conies completely factory -wired; receives all channels in any area; supplied complete with antenna and lead -in wire. The LENS is 15" x 11 ". giving a picture size of approx. 10" x or 120 sq. 12" in.; the highly- styled cabinet measures 26" wide x 17" high x 19" deep, available in Ma- iogan.. Walnut or Blonde finishes.

PRICES: Transvision MODEL 10ßL Television Kit, with FM, 10" tube, cabinet with built -in lens, antenna, 60 ft. lead -in wire...... List $359.00 MODEL 12RL, same as IOBL except that it uses 12" tube, giving picture area of 130 sq. in. List $389.00

SCOOP! New revolutionary MODEL 7BL Television Kit with specially designed CABINET with BUILT -IN LENS. t.-4 Elecn'orLd is Picture Tube Cive. :ill square inch picture of superior quality FEATURES: Though it has a 7" tube. the effect is equivalent to a 10" set because the built -in lens magnifies the picture. Also picture performance is superior because the lens clarifies and heightens contrast of the image. Picture "rotates" apparently, as the observer stoves, giving the effect of always faring the observer. This is effective to a very wide :eagle. Pre -tuned for 5 channels.

PRICE: including cabinet with built -in lens, antenna. 611 ft. of lead -in wire Net $189.00 TRANSVISION "SERVICE NOTES" The Key to Successful Television Servicing Transvision's "Service Notes" is a compilation of confidential Tele- vision Notes and Information. the product of experience with over 20.000 television receivers. now made available to the publie. The "Service Notes" is a most valuable compilation of instructions and data on Magnetic and Electrostatic Television Receivers. Though compiled in the course of servicing Transvision Kits. the information is applicable to any type of television receiver. "SERVICE NOTES" is complete with photographs and diagrams. The information is worth a small fortune. The cost is low. LIST $2.95 higher west of Mississippi; all prices fair traded. For further information see your distributor, or write to: TRANSVISION INC., Dept. RC, NEW ROCHELLE, N. Y.

J U N E 1 9 4 16 I 'recli.II/tcs

. . I.F. TRANSFORMER REPAIRS PHILCO MODEL 18 I.f. transformers in some older receiv- The oscillator in this set sometimes War Surplus Bargains ers have special trimmer assemblies and operated intermittently. A complete are therefore difficult to replace. If a check of the oscillator revealed a high - NAVY CRV -46151 AIRCRAFT coil in one of these transformers be- resistance short across the oscillator RADIO RECEIVER comes defective, and it is impossible to coil. Coil replacement was the cure. obtain a replacement transformer, here WILLIAM PORTER, is an easy way to repair the unit. Lafayette, Indiana INCLUDING Measure the space between the two CASE windings, and cut through the core piece $1950 just below the top coil. Then remove OVERHEATED RESISTORS the bottom coil of a standard i.f. trans- When a shorted bypass condenser is former of the same frequency, also by replaced, also change the dropping re- cutting through the core. sistor through which the current was Roll a piece of thin cardboard and drawn. The resistor has usually been Four bands, including broad- use it as a dowel to fit the two coils to- overheated sufficiently to cause it to cast (195 -9.050 gether. Make sure the spacing between change its value considerably. RC). Circuit is is HENRY VAN ZUYEN, six -tube super- the coils the same as before. A little heterodyne with mechanical band change. Pow- cement on the joint completes the re- Hanford, Calif. ered from self -contained 24 V. DC dynamotor. The sets are complete with tubes, mounting pair. rack and remote controls. No cables or plugs. ALBERT LOISCH, Darby, Pa. CROSLEY MODEL 86CR ARC -4 TRANSMITTER & REC. The molded wire -wound filter resistor between the two filter condensers is fre- . TUBE REPLACEMENT If a 2W3 half -wave rectifier is not quently fpund to be open. Substitution of a good -quality, 10 -watt cures the ixcwDixs available to replace a defective one, an unit trouble cuss OZ4 can be used in its place. Merely permanently. connect the two OZ4 plate pins together WILLIAM PORTER, at the socket and plug in the tube. Lafayette, Indiana PETER CASELLA, New Orleans, La. . MAJESTIC MODEL 460 If the receiver oscillates and squeals . CHEVROLET MODEL 985538 but all the voltages are correct, check A replacement was unobtainable for the main filter condensers. In some cases Operates on any of its 4 predetermined crystal the defective antenna coil in this set, controlled frequencies in the range 140 condensers of MC. and these may lose enough ca- Complete with tubes, remote control, ¡unction substitute antenna coils did not give pacitance to cause oscillation long be- box, shock mounting base and connecting good results. I finally used a 4 -pie, 2.5- plugs. This unit is ideal for amateur fore any hum can be noticed. UHF or mh r.f. choke mobile telephone. Operates from self -con- with a lead to the 6SA7 WILLIAM B. THORNE, tained 24 V. DC dynamotor. grid off tapped between the first and St. John, N.B., Canada TELRAD 18 -A second pies from one end. The lead from FREQUENCY STANDARD the upper three pies went to the antenna and the other lead to the a.v.c. CROSLEY MODEL 146C5 Checks signals in the range of 100 Kc. to 45 The set then played perfectly with a Noise heard when the r.f. is Mc. with a high degree of accuracy. Self -con- tube tained power supply is 110, 130, 150. 220. and 66 -inch auto antenna. tapped and which is not due to a bad 250 V. 25.60 cycle AOI Complete with tubes, PAUL STANLEY, tube is usually caused by a defective dual crystal, and instruction book, $24.95 Brand new. Price P Chatsworth, Ga. .001 -pf screen bypass condenser. Re- place T -17 -B Carbon Microphones the condenser with a ceramic -type . RECORD CHANGERS condenser, and check the stage for any Handmike 95c A frequent complaint on several possible misalignment which may have makes of is occurred during servicing. HEADPHONE automatic record changers EXTENSION that the turntable slows down after ARTHUR L. JOHNSON, CORD 50c playing two or three records. This Hutchinson, Kansas trouble can be eliminated on most fric- WILLARD LEAD ACID CELLS tion- drive-type changers by applying a STEWART- WARNER MODEL 517146 6 V. (dry chgd.) $3.00 General Cement Resin Stick to the in- 6 V. (in metal carrying case, dry chgd.) $4.00 side rim of the turntable. A frequent complaint on these sets is (Odd electrolyte, specific gravity 1.265-drug- store). LYMAN E. GRAY, an intermittent drop in over -all sensi- Alexandria, La. tivity, resulting in only local stations Art '13 Control Head With being heard. The trouble is due to in- Connecting Plug creased resistance of the soldered ter- $2.50 . AUTOMATIC MODEL 640 In these models a loud hum which is minals of the secondary of the first i.f. DYNAMOTOR MODULATOR not caused by defective filter condensers transformer insidd the shield can. Re- UNIT $1.95 and which cannot be controlled by the solder the connections or replace the volume control, is often the fault of an transformer. Antenna Relay Unit $1.25 excessively long volume control ground ARTHUR L. JOHNSON, lead. If the size of the filter resistor is Hutchinson, Kansas INTERPHONE AMPLIFIER changed to 2,000 ohms at 2 watts, hum $1.95 will also decrease appreciably with PHILCO 38-I16 CODE 125 practically no change in performance. A common complaint on this model is All Prices F. O. B. Indianapolis ARTHUR L. JOHNSON, a broken dial support. The dial is Hutchinson, Kansas mounted on its axis by a single strip of TERMS: CASH WITH ORDER celluloid which often breaks. The dial . RCA MODEL 1X2 will then not turn with the tuning con- If the set is very weak or is suddenly denser. Repair by cementing 4 pieces of AMERICAN SURPLUS reduced in volume, but the tubes test clear celluloid around the rear of the good, check the a.v.c. filter condenser. dial with transparent cement. If care- PRODUCTS CO. Replacing this condenser with a new one fully done, the repair cannot be seen 537 N. CAPITOL AVE. usually clears up the trouble. from the front of the cabinet. WILLIAM PORTER, D. L. Fuqua INDIANAPOLIS. IND. Lafayette, Indiana Fairfield, Iowa RADIO -CRAFT for 17

Au,1948 and F.M. A1cznua/ BIGGEST BARGAIN IN RADIO DIAGRAMS Make these two new mammoth volumes your moneysaving source for data on all recently released receivers. Learn about modern circuit developments, be ready to repair any new radio no matter how complex. You pay only $2 for each of these large manuals. With these two volumes on your workbench there is nothing else to buy, nothing else to pay -a whole year of radio diagrams and service data yours for a couple of dollars total. Again Supreme Publications beats all competition and gives radio servicemen greatest bargains in service information. Other volumes for previous years described F.M. and Television New 1948 Manual below. No -risk examination granted to servicemen, Use this new giant manual of Be prepared to repair ' kly factory instructions for trouble- all new 1948 receivers. In this big -QUICK shooting. repairing, and align- single volume you have clearly - FIND ALL RADIO FAULTS DOUBLE ment of any 1947 -194' F.M. and printed. large schematics. needed Television set. Every popular alignment data, replacement parts You can speed -up and simplify radio repairs with make, including new F.M. tuners. lists. voltage values, and informa- AM -FM combinations, and all tion on stage gain, location of SUPREME PUBLICATIONS Manuals. Service all radios types of television receivers. De- trimmers, and dial stringing, for tail circuit diagrams, theory of almost all recently released sets. faster, better, easier, save time and money, use these operation, test hints, alignment Makes toughest jobs amazingly most -often -needed diagram manuals to get ahead, earn data, including both meter and easy. Find faults in a jiffy. oscilloscope methods. This is the Speed -up all repairs. The time more per hour. For the remarkable bargain price (only material you near) to fix any saved on your next job will pay you of having in your modern F.M. or Television set. the $2 bargain price for the $2 for most volumes) are assured Don't turn this profitable work complete manual -after that you shop and on the job, needed diagrams and other essen- away for lack of knowledge and use it FREE. A worthy com- information. Use this newest panion to the 7 previous volumes tial repair data on 4 out of 5 sets you will ever service. Supreme manual to save time used by over 120.1100 shrewd radio and money on your very next servicemen. New manual covers Every popular radio of all makes from old- timers to new F.M. job. Data presented on 192 models of 42 different manufac- 1948 sets, including F.M. and Television, is covered. large pages, SH.,x11 in. turers. Giant size: Sturdy, manual -style $ I..x11 ", 192 pages + $ 00 Clearly printed circuits, parts lists, alignment data, and binding. Just pub- o des. Manual - style lished. Special price.. lint'. Price. only.. helpful service hints are the facts you need to improve your servicing ability. Save hours each day, Models Made by: R.C.A., Zenith, every day, begin to earn more by making re- Philco, Sears, Fada, pairs in minutes instead of hours. Let these Emerson, Belmont, manuals furnish you with diagrams for 80% Detrola, Crosley, of all sets. There is no need to spend large G.E., Westinghouse, space- wasting manuals, or ,114>.`-t - Often -11;eedt1tl Arvin, M aj es t ic, sums for bulky, to Stewart -Warner, buy additional drawings every few weeks ; be Admiral, Delco, wise, use SUPREME Manuals to get the most 1947 Stromberg.Carlson, in diagrams and service data for the smallest Wards, West'n Auto, Sparton, Motorola, cost. Act today and be money ahead with RADIO and mata others, Supreme Publications. plc1GRAI`IS Information wert f creicbig

1 K. p, 'WPM PIrBLIGr10Pla SCIlEME 2OO Feted Supreme l 'ingrani Siannals and Record Changer Books you amt to ex:uui m' Use coupon to order manuals for examination Send the convenient no risk trial rot pun, rue the manu Ils in som Iran Llaue or Include ali POP ular set. from 1920 to 1918 'shop for 10 days at no risk. Derlde fur yourself that Supreme Publications are tic greatest 'aloes i Hire data. You must be completely satisfied. or return manuals and receive Your 1 money back Record Changers Manuals 1 NO RISK TRIAL ORDER COUPON Post -War Models Pre -War Models M Service expertly all modern usim life) oust what you need ea repair quickly record changers. Jr to follow SUPREME PUBLICATIONS, 9 S. Kedzie Ave., Chicago 12, ILL. needed ad- merle record changers. manual ones, pick and repairs. views. la M photo- cps, rotions. undratsrs, Ichanic, and Ship the following manuals on under your 1948 graphgraphs 11 exploded ')fact largo size: Hundreds of and trial 8th x 11 61.50,. 144 fern filled pages. al 128 large pages;1.50.; slza guarantee of satisfaction or money -back. 1947 PRICED Price only 81.50, pnettwld. 8 x 11 Inrhea.inches. Price, only $loe. New F.M. and Television Manual.. 82.00 1946 AT ONLY See Your Radio Jobber or Send Coupon ---)o. 1942 13 Post -War Record Changera 1.50 s2 1941 Pre -War Record Players & Recorders 1.50 1940 I , EACH am enclosing 6 send postpaid. 1939 ,uwrenc Pucatons Send C.O.D. I am enclosing $ deposit. 1926-1938 - $2.50

PUBLISHERS OF RADIO BOOKS. MANUALS. ANI) DIAGRAMS Name:

9 South Kedzie Ave. Chicago9 12, Illinois s Address: M JUNE 19 4 8 18 INSTRUMENTS HEATHKIT LEARN SAVE BUILD Ideal for Schools, Training Courses, Laboratories- Service Shops, Hobbyists.

HEATHKIT NEW 1948 HEATHKIT 5 INCH

S I G N A L G E N E R A T O R K I T OSCILLOSCOPE KIT

Every shop needs a good signal generator. The Heathkit fulfils every servicing A necessity for the newer servicing technique need, fundamentals from 150 Kc to 30 in FM and television at a price you can afford. megacycles with strong harmonics over The Heathkit is omplete, beautiful two color 100 megacycles covering the new tele. panel, all metal s parts punched, formed, and vision and FM bands. 110 V 60 cycle plated and every part supplied. A pleasant supply. transformer operated power evening's work and you have the most inter- 400 cycle audio available for 30 ° esting piece of laboratory equipment available. modulation or audio testing. Uses 6SN7 the features large 5BP1 tube, as RF oscillator and audio amplifier. Check - 5" Complete kit has every part necessary compensated vertical and horizontal amplifier: and detailed blueprintsi and instructions using 6517's, 15 volts to 30 M cycle sweep .50 enable the builder to assemble it in a generator using 884 gas triode, 110 V 60 cycle few hours Large easy to read calibra- NOTHING ELSE power transformer gives 1100 volts negative tion nient x x 4 4 Convenient size 9" 6" ". and 350 volts positive. TO BUY Weight 4tzpounds` Convenient size 8,2- x 13" high 17" deep, weight only 26 pounds. $39.50 HEATHKIT SINE AND SQUARE WAVE All controls on front panel with test voltage and ext. syn post. Complete with all tubes and NOTHING ELSE TO BUY AUDIO GENERATOR KIT detailed instructions. Shipping weight 35 lbs. Order today while surplus tubes make the The ideal instrument for checking audio price possible. amplifiers, television response, distortion, etc. Supplies excellent sine wave 20 cycles 74 NEW to 20,000 cycles and in addition supplies square wove over same range. Extremely HEATHKIT VACUUM TUBE low distortion, less than 1°0, large cali- VOLTMETER KIT

brated dial, beautiful 2 color panel, 1 °ó

precision calibrating resistors, 110 V 60 The most essential tool o rodio mon con have, now within the reach of his pocketbook. The Heathkit VTVM cycle power transformer, 5 tubes, detailed $34.50 is equal in quality to instruments selling for $75 00 or blueprints and instructions. R.C. type cir- more. Features 500 mp meter, transformer NOTHING ELSE power supply, l';, glass 'enclosed divider resistors, with 11 TO BUY cuit excellent stability. Shipping ceramic selector switches, megohms input resistance, linear AC and DC scale, electronic AC reading weight 15 pounds. RMS. Circuit uses 6SN7 in balanced bridge circuit, a 6H6 os AC rectifier and 6X5 as transformer power supply rectifier. Included is means of calibrating four scant hou as time less than HEATHKIT SIGNAL TRACER KIT four pleasant hours, and you have the most useful test instrument you will ever own. Ranges 0 -3, 30, 100, z4 . SOI Redues service time and greatly in- 300, 1000 volts AC or DC. Ohmmeter has ronges of ELSE creases profits any service shop. scale times 1, 100, 1000, 10M and 1 megohm, giving NOTHING Uses crystal diode to follow signal from range .1 ohm to 1000 megohms. Complete with TO BUY antenna to speaker. Locates faults im- detailed instructions. Add postage for 8 lbs.

mediately. Internal amplifieravailable I for speaker testing and internal speaker H E A T H K I T available for amplifier testing. Connec- tion for VTVM on panel allows visual CONDENSER CHECKER KIT tracing and gain measurements. Also d tests phonograph pickups, A sand checker anyone can afford PA systems, etc. Frequency range to 200 to own. Measures capacity and leakage Mc Complete ready to assemble. 110 V from 00001 to 100 MFD on calibrated 60 cycle transformer operated. Supplied scales with test voltage up to 500 volts. with 3 tubes, diode probe, 2 color $19.50 No need for robles or multipliers. treads panel, all other parts. Easy to assemble, NOTHING ELSE detailed blueprints and instructions. resistance 500 ohms to 2 megohms. 110V TO BUY Small portable 9" x 6" x 414 ". Wt. 60 cycle transformer operated complete 6 pounds. Ideal for taking on e with rectifier and magic eye indicator calls. Complete your service shop with tubes. this instrument. Easy quick assembly with clear detailed blueprints and instructions. Small con- $19.50 venient size 9" x 6" x 434 ". Weight 4 HEATHKIT HIGH FIDELITY NOTHING ELSE pounds. This is one of the handiest in- TO BUY AMPLIFIER KIT struments in any service shop. Build this high fidelity amplifier and save two- thirds of the cost. Push pull output using 1619 tubes (military type A WORD ABOUT HEATHKIT INSTRUMENTS 616's), two amplifier stages using o All Heathkit service instruments are supplied complete in every 111_2il dual triode (65N7), and o phase in- way grey crackle cabinets, 2 color calibrated all tubes, verter give this amplifier a linear reproduction - panels, test leads (where required) etc. All are 110 V transformer operated. equal to amplifiers selling for ten times this price. Every and Calibrations are complete and exact, 1% precision resistors are part supplied; punched formed where needed. chassis, transformers (including quality output supplied s14.95 Heath engineers are ready to assist and advise. to 3 tubes, and -8 -15 ohm voie coil), controls, Heathkits are sold direct to customer, order from this ad. All are NOTHING ELSE complete instructions. Add postage for 20 lbs. guaranteed. TO BUY 12" PM speakers for above $6.95 7 LvrlvrE BENTON HARBOR, MICHIGAN 1,r1111111r RADIO -CRAFT for F11, 149

I GLOSSARY OF FM TERMS (Continued from page 44) A MUST Sptiona FOR FM in cycles, from the assigned center frequency. ¡s1oW.j frequency multipliers. Stages of radio-frequency idCEt & amplifiers operated as doublers, triplera, etc., to TELEVISION provide the required order of multiplication. In FM transmitters the frequency is multiplied many SERVICE times before it reaches the final stage. ON/41 I.ITY frequency shift. The departure of a wave from QUALITY its assigned frequency. ECA SHOPS! full license. Final authority to operate a commercial FM station. Issued after station has operated satisfactorily on CP (construction permit) and has met all requirements as to field- strength measurements, proof-of-performance TELEVISION testa, program commitments, etc. FN& ghosts. Secondary wave reflections which reach the receiving antenna out of phase with the initial wave. Ghosts are the result of reflections from the ionosphere, or from hills, apartment Sígal buildings. or other structures, and are more p prevalent in low spots or areas of low signal 5wSweep strength. In FM, the result may be garbled. R distorted reception. 0 ground wave. The part of a radio wave which de- ENERA pends entirely on conductivity of the earth's sur- G face, and reflection from it, for propagation. The 5 ground wave is composed of a surface wave and a 9 space wave. The space wave in subdivided into a direct wave and a ground- refected Wave. s coMVLE ground- reflected- wave. The component part of a space wave which is radiated from the transmitting antenna and reflected from the earth's surface to the receiving antenna. grounded -grid amplifier. A radio-frequency amplifier (final stage) in which the grid circuit is at ground potential, the input and output resonant circuits being provided by filament and ///! IDAWlJrI O/i.w/ii! plate, respectively. guard band. The 25 -kc band width at the extreme ends of each FM channel, used solely to prevent interference to adjacent channels. Here's great news for FM and TV Service Shops! A new, top harmonics. Even or odd multiples of the funda- quality sweep signal generator -product of a manufacturer with mental wave frequency. vast resources, advanced engineering "know- how ", and war- high fidelity. The faithful and exact transmission or reproduction of audio-frequency signals. time experience In producing test equipment. DIRECT FROM THE FACTORY-at a phenomenally low price! GENERAL INFORMATION image response- Tendency of a receiver to pick up spurious frequencies equal to twice the i.f. insulation frequency plus or minus the radiq frequency. High frequency Images are eliminated by adding an r.f. stage or FRONT PANEL CONTROLS FREQUENCY RANGE TUBE LINEUP Throughout otherwise increasing selectivity. 3 BANDS r Maximum output indirect frequency modulation. See Phase Modu- Sweep width 500 KC Io lation. epp,.. 10 MC (No bond switching 6(4-Fixed frequency 500,000 U7Y interference, adjacent channel. Cross- modulation Phasing control necessary) modulated oscillator Power required 105 -125 (2 to 227 Megacycles) Volt 50 -60 AC effects produced when two signals of near -equal Tuning vernier control 10 lo 35 Wotte strength are assigned to channels adjacent to 6(4- Continuously Power line filter built la each other. Effects are much more pronounced in 1 ratio 2 -77 MC variable beat frequency AM than in FM systems. Selecto switch FM- IF-CAL Special Midline Capacity 40 -154 MC tuning condenser interim operation. The period during which sta- RF Output control oscillator tion operation is maintained on low pend- power. 151 -227 MC Pilot light line indicator ing installation of the regular transmitter or 60 cycle horizontal sweep 6(4- Mixer -Cathode antenna system. output Calibration and reference Geoerotor output con be follower output tube scales ionosphere. (formerly known as the Kennelly - Amphenoi RF output shielded used either frequency Heaviside layer). Ionized layers of gases existing in the upper parta of the earth'. atmosphere, connector Dial scale length 5Y3- Rectifier tube modulated er pure RF usually at heights between 30 and 260 miles. Radio waves striking these layers are reflected, the amount of reflection depending on layer FM FRONTEND height, wave frequency. degree of ionization, and RADIATION LOOP AND other factors. Complete with 3 tubes, ALIGNMENT WAND including Magic Eye. ionosphere storms. Disturbances in the iono- $1.101 MC. sphere which seriously affect radio transmission Provides loose coupling. above 500 kc. These disturbances are closely Checks loop - oscillator For use with 10.7 MC linked to the 11 -year sun -spot cycle; their ap- tracking. Increase. ef- I.F.B., hIeb Q res- pearance can result in unpredictable behavior. ficiency of receiver's onant tuned lines. alignment or mistrack- Heavy sliver overlay even at FM frequencies. Ing. Enables the service on lines red con- Kennelly- Heaviside layer. See Ionosphere. engineer to make gela tactors. High fre- measurements. Profes- quency insulation appearance limiter. Last i.f. stage or stages of a receiver ; ar- sional and throughout I -RF esulti. May be und on eny'slgnal C e stage. detector, ranged to overload so that plate current is satur- enerator. Complete with operating and ated cut off on alternate half -cycles. This 95 oscillator. Large T' and Instructions. allderule dial. C $1595 action removes amplitude variations and leaves floated. bon- mlcrophonle. only the frequency -modulated component of the f signal. In phase -modulated FM transmitters, a limiter is employed to remove residual amplitude fluctuations. AM SIGNAL GENERATOR linearity. The ability of a system (r.f. or a.f.) to maintain an output voltage or percentage in S RF bands. Frequents coverage 1001CC -75 MC. External modulation from 40 to 30,000 cycles. Internal modulation at 490 cycle.. Phase shift audio direct proportion to the input voltage. oscillator and Internal modulator. A.C. 105 to 120 volts. 50 to 00 cycles. line- of-sight. The approximate distance the Special Hammarlund variable condenser: 3 step RF attenuator Continuously to variable RF -AF attenuator control. Ultra stable two terminal RF oscillator. horizon, or about SO to 50 miles; formerly sup- Pilot light line Indicator. Cathode follower output tube. Modulator per- posed to be the limiting factor for FM transmis- centage continuously variable from front panel. Internal or external. 0 to sions. Actual range approaches two or more hori- tom,. Heavy 16 -gauge steel cabinet. Complete with 4 Island- e/a zons, due to reflection and refraction character- ard brand) tubes. Amphenol eo -axial connecting cable. ground $ (/5°/ istics of the earth's surface. cable. operating instructions and guarantee. /ie marker frequencies - Frequencies produced by a signal generator to identify frequency deviation limits and to measure discriminator response in BACKED BY ECA WITH R.M.A. GUARANTEE. FOR PROMPT DELIVERY, RUSH YOUR ORDER receivers. Used in conjunction with an oscillo- TODAY TO DEPT. RC 20% DEPOSIT REQUIRED. NEW YORK CITY. scope to obtain visual patterns. -6. WITH ORDER F.O.B. modulation. Act of applying audio frequencies to a radio-frequency wave. ELECTRONIC CORPORATION OF AMERICA modulation index. The frequency swing (fre- 353 WEST 48th STREET NEW YORK 19 Y. P LONE: CIRCLE 6 -1985 quency deviation) divided by the audio frequency. The index varies directly with the audio-frequency WRITE FOR ECA CIRCULAR ON PARTS AND ADDITIONAL EQUIPMENT. JUNE. 1948 50

Mg an opening or slit extending full length on one side. ratio detector. A demodulator circuit which replaces both limiter and discriminator in FM receivers. Popular especially in lower -priced seta. reactance modulator. A tube (or tubes) connected in shunt across the master oscillator plate tank. Application of audio voltage to the reactance grids varies the reactive plate current, causing the oscillator frequency to vary at an audio rate. reflection coefficient. The vector ratio of a re- ABSOLUTELY NO KNOWLEDGE OF RADIO NECESSARY flected ground wave to the original wave. Value depends on conductivity and dielectric constant YOU NEED NO ADDITIONAL PARTS! of earth, frequency. and angle at which the wave THE PROGRESSIVE RADIO KIT Is the ONLY COMPLETE KIT strikes the earth. Operates on 110 -120 volts AC /DC. Contains everything you need. Instruc- reflector. An antenna element somewhat greater tion Book, Metal Chassis, Tubes, Condensers, Resistors and all other nec- than r4 -wave length, mounted on a dipole an- essary radio parts. The 36 -page Instruction Book written by expert radio tenna to improve signal pickup and increase PROGRESSIVE Instructors and engineers teaches you to build radios In a professional man- re- ner. The first circuit built is a simple ate -tube detector receiver. Each suc- jection to unwanted signals. SCOOPS! ceeding circuit incorporates new arrangements of detectors. RF and AF response, response curve. Output amplifiers. This le variation (with kit excellent for learning the principles of receiver. frequency) of an amplifier i.e., an amplifier flat transmitter and amplifier design. It is used In many radio schools and within FM COIL & CONDENSER colleges. All of the commonly-used detectors are used. including diode. grid xt 2db dyer the audio range is said to have leak. plate and infinite -impedance: The transmitters are designed with good response. The response curve is plotted Hartley and Armstrong oscillators, using screen -grid and control -grid modu- graphically with the aid of a calibrated audio Designed for operation on 88- lation. Both vacuum tube and selenium rectification are employed in these Oscillator. 108 MC (new band), contains 2 circuits. The circuits are designed to provide excellent performances. Alto- gether. fifteen circuits service area. primary. The IF transformers. 1 Limiter are constructed, including 11 receivers. 1 audio area in which recep- amplifier, and 3 transmitters. Tho acts start with tiOn is satisfactory Transformer, 1 Discriminator simple circuits of 1 tube under all conditions. Minimum plus rectifier, gradually grow more complex, and finish with several examples field strength for primary Transformer, 1 RF coil, 1 cd' reception in rural radio sets using three tubes plus rectifier. areas is 60 microvolts for FM Variable condenser. Schematic PROGRESSIVE stations. Due to and wiring instructions. Excel- RADIO KIT ONLY $14.75 threshold noise and static, primary field strength lent for schools, experimenters SPECIAL FREE OFFER for AM stations is required to be 10 times this Electrical value, or 500 microvolts. Urban (residential( and Radio Hobbyists and Radio Tester sent absolutely FREE with each Progressive field strength requirement Price only $4x95 Radio Kit. PLUS F REE membership in Progressive Radio Club. Entitles for both services is you to free expert advice and consultation service with licensed radio 2000 to 6000 microvolts. teehnicins. Write CONDENSER KIT for further information or ORDER your KIT NOW! service area, secondary. Area in which field 50 Paper Tubular Condensers. strength falls below the values set for primary Values from .002 mfd to .1 mfd. coverage. Reception is good under favorable con- 400 V. DC to 600 V. DC. ditions but poor under unfavorable conditions. Only $1.95 shot effect. Noise introduced into a receiver RESISTOR KIT through a variation in electron emission from HIGH FIDELITY, HUMLESS. AMPLIFIER. the cathode, usually 100 Carbon Resistors, It Watt., SEVEN TUBE PERFORMANCE originating in the grid and RMA color- coded. Values from plate circuits of the first tube. When static and This newest Progressive Kit will enable you outside noises are of 120 ohms to 2.2 megohms $1.50 to build newly -designed. high fidelity, no consequence, the noise humless within a receiver is governed by shot 10 -10 MFD. 450 W.V. DC Elec- amplifier. thermal effect and trolytic Condensers Beautiful aluminum custom- punched chassis, agitation. 65e etched the and volume control plates. aide Designed by former bands The frequencies which appear on each 20-20 MFD. 150 W.V. DC Elec- Western Electric engineer. aide of the center frequency a Condensers Ideal amplifier for televinan kit or set. FM tuner. AM as result of modu- trolytic 30e instantaneous tuner. microphone, lation. Since these frequencies decrease in ampli- 40-40 MFD. 150 W.V. DC Elec- Electrifypyourlmueial by connecting them to the Progressive tude as their width increases, no side -band inter- trolytic Condensers 45e Amplifier by means of a contact mike. ference is likely outside the assigned channel. Amplifier can be readily modified to match the OE reluctance pick -up. Antenna and RF Coil Set Separate mike and phone input. Regulated power signal -to-noise ratio. Ratio of the desired signal (Broadcast stant voltage supply maintains con- to background Band) 59e supply. I)C heater supply, whether amplifier is used on AC or superimposed noise in a re- or DC, provides humless operation by eliminating esthode- ceiver. The highest possible 6e Alnico Slug Speaker.. $1.69 hum. Contains degenerative heater leakage ratio is obtained feedback for improved frequency response. when the only noise present in the receiver is Selenium Rectifiers 79e balanced phase inversion and push -pull beam power thoroughly decoupled output. Every stage that of thermal agitation in the input circuit. Midget to Improve low-frequency response and to prevent Soldering Iron 35 Watts motor-boating. completely variable. sky wave. The part of the transmitted wave 110/120 volts Sev -tubee UL approved 69e n erformance Dees 2 selenium rectifiers. beam power am- which travels skyward and is (usually) plifiers. 1 high -mu reflected 55 Watt pentode mike amplifier. 1 twin -triode inverter, back tq earth by the Soldering Iron UL ap- and 1 voltage regulator tube. phase ionosphere. At ultra -high proved $1.90 frequencies the sky wave is virtually unaffected Progressive AMPLIFIER KIT 75 Watt (less Tube' and Speaker) only $15.75 by ionospheric reflections, and hence is not nor- Soldering Iron UL ap- mally reflected to proved $2.40 TUBES for Progressive earth. Amplifier Kit 1- 128L7, 1- 12877, 1 -VR75. 2- 12A6's. Long Nose Cpleteom Bet space wave. The portion of the ground wave Pliers and Cut- Only $3.00 which is projected ters $1.45 from the transmitting antenna toward the receiving antenna. It is de- PROGRESSIVE RADIO BUILD A 5 TUBE AMPLIFIER - - only $5.95 pendent on two components, the direct wave and Ideal for phonograph. FM tuner or the ground- reflected wave. TOOL KIT tifier. microphone. Has 5 tubes including rec- contains 75 Watt Kit is complete with tubes. chassis, volume control. the control, special temporary authority (STA). 110/120 Volt radio paru, hook -up wire, solder and instructions. Authority soldering Iron, long nose PM. speaker We can provide a 4 -inch given by the FCC to operate on a temporary pliers with mounted output transformer to fit on chassis. priced & cutters, scrèwdriver, insulat- at $1.95. Or use this kit with your own basis while conditions of a regular CP are being output. speaker. It has 5 watts C ed alignment tool $3.25 more than enough to drive a 12 -inch speaker Only 5.99 5 met or completed. standing wave. The energy that exists at one or ESPEY CUSTOM more -BUILT AM -FM HIGH FIDELITY RECEIVERS--ModeI No.7 -BC points along a transmission line as the re- 1. AC Superhet AM FM receiver. 7. HighFidelityy sult of mismatch or improper AM.FM reception. 12. Loop antenna for AM termination, The 2. Frequency Modulation Circuit. S. Full -range combenation b a s. and Folded ratio of standing waves 3. 11 finest quality tubes, including treble tone control. Dipole antenna for FM reception depends on the amount rectifier. S. 13 supplied. of mismatch and the resultant watt (memmum) Push- Pull 13. Provisions for strength of the 4. dual purpose tubes give 15 AutliñcOutputtube ..tern., antennas. reflected portion of the initial wave. performance. 10. 10 inch PM speaker with Alnico 14. Wired for phonograph operation. V agnet. 15. Licensed studio-transmitter link S. Automatic volume control. 11. Indirectly der RCA and Raasl- (STL). An ultra -high- s. Full -range volume control. illuminated 'slide- tine patents. frequency transmitter -receiver arrangement for rule" dial. 16. RMA listed. connecting Your Price 584.00 525.00 deposit required with studio to transmitter where regular C.O.D. orders wire lines are undesirable or impractical. Since line-of-sight distances usually are involved, CRESSIVEOnwarre QUAN- PROGRESSIVE ELECTRONICS transmitter power requirements are very small. TITY pSicca CO.,Dept.RC-14 stiräldP° be on Beam antennas are employed. 497 UNION AVE. BROOKLYN All c.o.O. orators 11, NEW YORK Shipped Collect. surface wave. That portion of the ground wave which travels along the surface of the earth. phase angles have changed during Propagation at FM frequencies depends on both the process of the surface and space components of the ground GLOSSARY OF FM TERMS modulation. wave. (Continued from phase modulation. The indirect method of page 49) taining ob- thermal agitation. Noise generated by the ran- frequency modulation. Consists of a crys- dom motion of electrons tal- controlled oscillator whose output is split into within a conductor; two paths, one usually introduced into a receiver through the voltage (for given frequency), and inversely containing a 90- degree phase - first tube. It is with the audio shifting network and the other a balanced modu- important that thermal noises be frequency (for a given audio volt- lator. kept to an absolute minimum in FM receivers. age). The modulation index is large at low fre- A series of multipliers are used to increase quencies and small both frequency and modulation index to the turnstile. An antenna consisting of two half - at high frequencies (i.e., for a values. wave sections crossed at right maximum frequency deviation of 75 kc, an audio Proper Phase modulation was the method angles and fed 90 frequency of 15 kc will first employed by Major Armstrong. degrees out of phase. A number of these radiat- have an index of 5; ing sections may be stacked horizontally [75/151. 1,500 cycles produces an index of 50; 150 polarization, horizontal. Orientation of a trans- to in. cycles = crease antenna gain. Stacked sections are called 500, etc.) For the highest audio fre- mitted wave so that its lines of force (electric bays. quency (15 kc), the modulation index is called the field) are parallel to the ground. FM antennas deviation ratio. are horizontally polarized, since this method gives turnstile folded dipole. A receiving antenna com- nodes, nodal points. The pointe improved noise rejection. posed of two folded dipole sections crossed as a in an antenna turnstile and fed as such. High efficiency, system or transmission line where amplitude polarization, vertical: Wave orientation so that with a standing wave of the non -directional characteristics, is possible with is zero. Points where the ampli- electric field is perpendicular to the ground. this arrangement. tude of a standing wave is at maximum are (Elliptical polarization is a combination of ver- called antinodes or loops. Antinodes appear mid- tical and horizontal fields; a certain amount may wave guide. A hollow conducting tube used for way between node points. be said to be present in either plane.) transmission of ultra-high and micro-wave frequencies; employed in v.h.f. relay systems. peak shift, limiter. A shifting of the resonance pre -emphasis. Deliberate transmitter equalization peak of the limiter input transformer, due to to increase voltages of high audio frequencies Weir stabilizer. A frequency control system using the loading effect of signals strong enough to beyond their normal in order to improve the a standard crystal oscillator, mixer, discriminator, cause grid current flow. signal -to -noise ratio and detector to compare the difference voltage and to bring the modula- between phase distortion. The result of harmonica or tion index up to that of low frequencies. standard and carrier frequency and feed multiples of range the result to a frequency- correcting feedback frequencies whose relative pylon. A cylindrical transmitting antenna, hay- circuit RADIO -CRAFT for 51

SENSATIONAL BARGAINS 'n V1/AR SURPLUS OPTICS YOU CAN EASILY MAKE ASSEMBLE YOUR OWN BINOCULARS! Telescopes. Magnifiers. Photographic Gadgets and Hundreds of Experiments with these Low Complete Optics! Complete Metal Parte Cost Lenses. Save More than S/z Regular Cost To Translate Millimeter measurements: 25.4 GOVT'S 7 x 50 BINOCULARS mm. equals one inch. Here's an unusual opportunity to secure a TERRIFIC BARGAIN- BUBBLE SEXTANT fine act of Binoculars at a substantial saving of money. Offered here are complete sets of Optics and Metal Parts for the 7x50 Binoculars. These components are new and all ready for assembly. We sup - ply full instructions. Limit - I set of Metal Parts and I set of Optics to a customer. METAL PARTS-Set includes all Metal d'art.--Complete- ly finished -for assembly of 7,50 Binoculars. No machining required. Bodies have been factory hinged and covered. .\ sturdy Binocular Carrying Case Is optional with each . of Metal Parts. Stock #842- F...$39.40 Postpaid, plus 84.80 for Ca,e 844.20 both the Binocular Optics Total NOTICE! If you buy OPTICS-Set includes all Lenses and Priams you need for and the Binocular Metal Parts, your purchase assembling 7x50 Binoculars. These Optics are In excellent becomes subject to 80% Federal Excise Tax. Be condition- perfect or near perfect-and have new low sure to add amount covering tax to your remit- reflection coating. cannot be filled Stock #5102 -F -7x50 Optics 825.00 Postpaid tance or your order These Army Alr Forces Bubble Sextants cost the Govt. about $125 each. A real bargain at our price of $12.501 Included with Bubble Sextant shipment is wooden Carrying Case. 5 spare waxed paper discs, flashlight with rheostat for night use (uses ordinary flashlight ARMY'S 6 x 30 BINOCULARS! sells-(not fumlehed) aux. 2-power Galilean Telescope Allen wrench 1 spare marking point. Wartime used. BUT COMPLETELY REPAIRED. COLLIMATED AND any Sets shown below. Optics and Metal Parts Are Available for Monocular, Light bulb has No Carrying Case with For Complete Details. Write for PUT IN GOOD WORKNG ORDER. COMPLETE OPTICS & METAL PARTS Model (Vi a Binocular). been tested-Bubble is in working condition. Because of model)- Every- Bulletin : 14-F. not satisfied MI3A1. 6x30 Binoculars (waterproof Binocular Optics and the Binocular wartime use, we make this guarantee: If thing you need -ready for assembly. When finished will If you buy both the that Sextant is exactly as represented. return within 10 factory costing $102 to $120. The Metal l'arts. your purchase becomes subject to 20% be refunded. Full directions for look like a regular job }Arlan Tax. Ile sure to add amount covering tax days and money will , or near -perfect condition. Federal Optics are new, in perfect your order cannot be filled. use accompany each ahipnnent. Have new low coating. Metal Parts are now to your remittance or Stock #924 -F 812.50 Postpaid and perfect. all esenpletely finished. No machining re- with Complete VARIABLE DENSITY ATTACHMENTS Satre SEXTANT as above but BRAND NEW and quiredBo and covered. POLARIZING Automatic Electric Averaging Device and Illuminate) instructionsdes included. BINOCULARS Postpaid FOR - Averaging Disc for nighttime use. Govt. cost 8217. Though Stook :830 -F $40.00 brand new we have rechecked Bubble and Collimation and plus $8.00 tax -Total 548.00 An amazingly ERective unit for controlling amount of GL'ARANTF.E perfect working order. METAL PARTS ONLY -Model M -13A1. 6130 Binocu- light reaching your eyes. Cuts down glare in sky and Stock :933 -F 322.50 Postpaid described for over -water observations. Easily snapped on and off mar lars. No Optics. Same Metal )'arts as CONDENSING LENSES -Seconds. but suitable for En- Stork 6830 -F. the eye- ups of American-made 7x50 Binoculars. Govt. Metal Parts $25.00 Postpaid cost $5.30 each. i irrors and Spotlights. Stock #832 -F-6x30 Stock fa 1061-F-61/a" dia., 9" F.L 82.50 Postpaid Metal l'arts). OPTICS FOR 6x30 BINOCULARS-(No Stock #20.000 -F ' 82.00 Postpaid Stock :1080 -F -5" die.. 7" F.L $1.50 Postpaid Perfect and low reflection coated. Condensing Lenses- $15.00 Postpaid also adaptable to Govt. We have a Limited Quantity of Stook #5130 -F MOW(' Polarizing Attachment seconds-ranging from 414" to 814" in die. with various alight seconds. 0x30 Binoculars with substitution of sputa' eye -cups. SAME OPTICS AS ABOVE -Coated, but Postpaid focal lengths. Send for Free Bulletin titled "SIISCEL- Stock : 5124 -F $12.75 Postpaid Stock #20.010 -F -6130 Eye -cups 75e pr. LANEOUS (X)NDENSING LENSES -F." 35 MM. KODACHROME PROJECTING LENS SET - Consists of 2 Achromatic Lenses for projecting. plus 2 Condensing Lenses and piece of Heat Absorbing Glass SIMPLE LENS KIT -Some govt surplus, some com- 6 POWER GALILEAN TELESCOPE -(Commercial Sur - with directions. nome few clnstructednofiAluminuma7'c Stock :4029 -F $3.10 Postpaid mercial surplus. some chipped rejects, perfect. long. extends gr.t Com- coated . In any event an excellent bargain. Contain- to ing Plano Convex. Double ('mirez. Concave. !tllnlscus plete with carrying case. lengths. 8 POWER ELBOW TELESCOPE Lenses. Dia. range 5mm to 40mm. Assorted focal Stock :941 -F $3.00 Postpaid Stock #5 -F55 lenses S 5.00 Postpaid Stork # 10 -F-80 lenses 310.00 Postpaid $200.00 DRIFT METER for $5.60 Set :1 -F- "Our Advertising Spate! " -15 lenses for s1.60 Postpaid, plus 10 -page idea booklet. For ttmying ULTRA CLOSE -UP SHOTS. microphotography, experi- These wero used for deter- mental optics, magnifying mail for making a two power mination of drift and true f /10 Telephoto Lens. "Dummy Camera." 6edarhrome air speed. You can adapt Viewer. DETACHABLE REFLEX VIEWFINDER fol to other usen or take apart 35mm cameras, etoreoscople viewer, ground glass and to get two mounted Achro- enlarging focusing aids. TELESLY)l'ES. low power matic Lenses - Mirrors - M icnacupes and for many other uses. Field Lens - Pantograph Engraved Scales- Sponge -- Our Price $17.501 NEW 50 -PAGE IDEA BOOK "FUN WITH Rubber Discs metal parts Govt. Cost $200.00! - In- Big 2" diameter objective. All lenses Achromatic. Amica EDGE LENSES" and other components. ar. a CHIPPED weighs 4 lbs. prism the image. .trument red. used condition but guar- wide s the eutra and Slightly us Contains for perfect working uorder. W'elgln 5 Ilse. Can be fascinatingscinating usest of all Lenses in sots listed above Stock :942 -F 85.60 Postpaid anteed only 81.00 Postpaid. carried lint a triflo bulky. Stock #943 -F $17.50 Postpaid LENS CLEANING TISSUE -1st quality. sheet size AIR FORCES GUN SIGHT 11'17!5^. Made to govt. specs. Free Of abrasivos. High POLARIZING OPTICAL Wet st rngth. Stock :721 -F -500 sheets 51.00 Postpaid With Polarizing Variable Density Attachment -Can he RING SIGHT used as Slide Viewer, or take It apart an you an get Mangle Con- LENS Polarizing Variable Density Attachment. Used in gun sights- especially for shot- MOUNTED PROJECTING cave Mirror. Reflector Plate, Metal Reticle, Window, (Unmounted). SYSTEM -F.L. 91.44 mm. Oust Right. The Polarizing guns. As you look through, you see a series of rings that Speed Lamp housing, Ring and Bead on your target. No front sight required. right for 35mm. Projectors). attachment alone is worth many times the price of entire you eupor1[npoee of Fie Outside die. of mount at Filters mounted with small Increases degree of accuracy. Length of mount unit. Consists of 2 Polarizing 84.00 Postpaid of 60 mm. handle which rotates one around the other. May be usci Stock #2067 -F ceendi mm. in Photography, Research. Experiments, as Light Dim CONDENSING LENS SET -Consists of 2 Condensing Stock : 4033 -F $3.00 Postpaid mer. etc. Lensoa with diameter of 2". Used for making 35mm ptoJectors OT many other pumosos. THREADED OUTSIDE MOUNT Stock :908 -F $5.00 Postpaid Stock #4034 -F 75e Postpaid FOR FOCUSING ABOVE SYSTEM We have literally millions of war surplus lenses and (Not Illus.) Stock :715 -F. Same unit Without PWrizleg Attachment Prisms for sale at bargain prices. Write for catalog "F" free! SIAM Postpaid Stock #916 -F $2.50 Postpaid -.ant Order by Set or Stock No. Satislaction'Guaranteed

EDMUND SALVAGE COMPANY a o. AUDUBON, NEW JERSEY JUNE, 1948 FM

in a standard rack -mounting panel, is GREATEST SELECTION IN COUNTRY also designed for monitoring and com- LOWEST PRICES mercial applications. NEW-STANDARD BRAND-Min. Order $5.00 It is a straight FM receiver using 10 tubes including rectifier. It uses one QUANTITY PRICES ON REQUEST TUBE stage of r.f. . amplification, separate mixer and oscillator tubes, a 3 -stage i.f. 0A4G 81.06 3C6 1.28 6N7 .88 12DP7 ....14.95 49 .88 832A 2.95 00 .50 3C24 .69 6N7GT .88 I2F5GT ... .59 50 1.56 833A 39.50 amplifier, a ratio detector and a 2 -stage 0Y4 .88 3D6 .89 6P5GT .88 12H6 .59 50A5 .88 836 1.15 01-4 50 3E29 2.95 8Q5G .98 1215GT .54 50135 .72 837 2.50 a.f. amplifier with a meter tuning indi- O74 .88 3LF4 1.06 606G/6T7G 1.06 1217GT . .72 50L6GT .59 838 4.95 cator and a built-in 5 -inch PM speaker. A3 .72 3Q4 .72 607 .72 12JP4 60.00 50X6 .88 841 .69 A4 1.28 305GT .88 6R7 .88 I2K7GT .59 507607 .59 843 .69 A variation is the NC -108T. It is A4P 1.28 384 .72 6S7 .88 12K8 .88 53 .88 845 4.95 AIT 1.28 4-654 14.50 638GT . .88 12Q7GT .59 55 .72 860 3.00 mounted in a metal cabinet, with a tun- A50 .88 4.125* 27.50 66A70T .59 12547 .59 56 .59 861 50.00 A6 1.06 4-250A 37.50 6SC7 .72 123C7 .72 57 .72 864 .69 ing eye replacing the meter. The manu- MG .88 5BP1 1.49 6SD76T .72 12SF5 .59 58 .72 866A .89 facturer ABS 1.06 5BP4 4.95 6SF5 .59 128F7 .72 59 1.06 868 1.95 calls these sets receiver- tuners B4 1.28 &CPI 3.95 85F7 .72 12SG7 .72 7017131 1.56 872A 1.95 and recommends their use with an ex- B5/258 1.06 5FP7 3.95 6SG7 .72 128H7 .72 71-A .72 874 1.95 87G .72 51P1 9.95 66147 .72 12517 .72 75 59 876 4.95 ternal amplifier and speaker for best B25A 4.95 5R4GY 1.29 6.617 .59 1281(7 .59 75TL 2.96 884 .98 827 4.95 514 1.28 6SK7 ' .59 128L7GT .88 76 .59 902 4.95 reproduction. 838 ' 4.95 5TP4 20.80 68L7GT .88 128N7GT .88 77 .59 920 2.95 C50 .88 5U40 .54 GSN7GT .88 12507 .59 78 .59 950 1.06 CB 1.06 6V40 .88 6SQ7 .54 128R7 .72 79 .88 954 49 C7G 1.06 5W4 .88 6SR7 .39 12X3 .98 80 .42 955 .49 D5GT 1.28 5X491 .60 6557 J2 12Z3 .88 81 1.28 956 .75 FM TUNERS D7G 1.06 5Y30T .38 6ST7 .98 1444 1.06 82 .88 957 .49 from. page D8GT 1.28 5Y4G .50 617 1.06 14A5 1.56 83 .88 9584 .69 (Continued 29) E5GP 1.56 5Z3 .60 6115 .72 14A7 .88 83V .88 959 .49 E7G 1.28 5Z4 .88 6U6GT .72 14136 .88 84/6Z4 .59 991 .50 F4 .88 6A3 1.08 6U7G .59 1487 1.10 85 .72 613 .95 pear be notable, as F5G .88 6450 1.56 6V6 1.06 14B8 .88 89 .72 614 1.75 to -tube for tube - F6 1.28 646 .88 6V6GT .72 14C5 .88 99V 1.56 616 . 1.39 the Edwards was somewhat more sen- G4GT .88 6A7 .72 6V76 .72 I4C7 .88 99% 1.56 619 .29 G6GT .88 6A8 .72 6W7G .88 14E6 .72 100TH 12.95 622 1.75 sitive than the average of the tuners H4G 72 6485/6N5 .88 6X4 54 14E7 .88 1144 .69 624 .98

HSGT . .60 6487 1.06 6X5 .54 14F7 .88 117L78T 1.28 625 .49 tested and the Approved somewhat less H6G 1.06 6AC5GT .88 6Y60 .88 14H7 1.06 1178178T 1.28 626 .49 16G 1.06 64C7 1.06 6Z7G . 1.28 1417 1.06 11707137 1.28 627 7.95 so. .72 1.28 L4 .72 6AD7G . 1.06 6ZY50 14N7 1.06 117P7GT 629 .59 Most LA4 1.06 6AF6G .88 7A4 .72 1407 .88 117Z3 .72 642 4.95 of the rest of the tuners use LA6 1.06 6AF8 .88 7A5 .72 1487 1.06 11726GT .88 851 1.25 standard coil- condenser combinations, LB4 1.06 6465 1.06 746 .72 14117 .88 120A 12.95 2050 .89 LC5 1.06 6AG7 1.06 7A7 .72 14W7 1.06 121A 2.65 2051 .49 with such variations as brass -plate tun- LC6 1.06 6A15 .99 7A8 .72 14X7 1.06 2058 4.50 5514 3.95 LE3 1.116 6AK5 .99 7AE7 .72 14Y4 .88 211 .96 5516 5.95 ing condensers to minimize drift. The LDS 1.06 64K6 .88 74F7 .72 154P4 110.50 215A 3.00 5562 10.00 FMT -10, LH4 1.06 6ÁL5 .72 784 .72 15E 1.50 2170 7.50 7193 .39 Brooks however, has a per- LN5 1.06 641_7GT 1.06 7E15 .72 I9 1.06 250R 7.95 8005 4.95 meability-tuning system, varying the N50 .88 6A05 .72 787 .72 20 1.56 250TH 19.50 8011 2.95 P22 11.50 6406 .72 788 .72 204P4 270.00 252A 4.95 8012 4.95 frequency with movable brass cores in P5GT . .88 6ÁT6 .80 7BP7 295 22 1.28 259A 4.95 8016 195 05G7 .88 6.4U13 .72 7C4 1.08 23134 .49 304TL 1.98 8020 595 the r.f., mixer, and oscillator circuits. .72 134 1.06 6B4G 1.06 7C5 23D6 .98 307A 6.25 8025 3 95 T4 .72 6B6G .72 7C8, .72 24A .72 310 4.95 9001 89 Another outstanding feature is the 24G .69 316A .89 9002 69 TSGT . .88 687 1.06 7C7 72 1.06 double superheterodyne circuit. It is U4 .72 688 1.06 7E3/1201 2546 1.06 3508 4.95 9003 49 U5 .88 6846 .72 7E8 .72 25A7GT .88 394A 4.50 9004 49 found in most of the larger tuners with- -V .72 68E6 .72 787 .88 25C6G 1.06 417A 19.95 9005 9e 2A3 1.06 6B GO 2.40 7EP4 17.95 25L6GT .59 450TL 24.95 9006 49 out an r.f. stage. In this circuit, the 2A5 .72 6C4 .80 7F7 -88 2575 1.28 531 49.50 CEQ72 195 2A6 .88 6C5 .60 7F8 1.06 25Z5 .54 701A 4.95 CK1005 39 oscillator operates at half the input fre- 6C6 .72 767 1-06 25Z6 .72 703A 7.50 CK1006 69 2A7 .88 19.40 quency minus half the intermediate fre- 2API 2.95 6C80 1.06 7GP4 20 .59 705A 2.95 EF50 79 2B7 .88 604 1.95 7H7 40 27 .54 70M 24.95 EL225 1 95 quency. The incoming signal is thus 2022 .69 606 .80 717 1 2807 .75 709A 9.95 FM-1000 1 56 .75 6E5 .72 71(7 1.06 30 .72 713A 1.65 GL434 4.95 to . heterodyned half the input frequency 2C264 715B 19.95 60 2C34 98 6F5 .60 7L7 80 31 .88 GL446A 2 2040 2.60 6F6G .72 7N7 40 32 1:06 717A 1.85 HF100 395 plus half the intermediate frequency in 2.60 6F6 .72 7Q7 .72 32L7G1 1.28 721A 3.95 HY69 295 2C43 7R7 .88 1.06 5.95 HY75 125 the first converter tube (or the first half 2C44 1.75 6F7 1.06 33 72348 1.06 34 725A 12.50 I 25 2021 1.89 6FeG 1.06 767 1.06 HY615 of a double -triode converter). This fre- 48 6G6G .88 777 1.06 35/51 .72 750TL 49.50 HVE1146 1 25 2E5 1.06 800 2.25 2E22 1.50 61(6 .60 7W7 35A5 .72 RK12 195 quency is then heterodyned by the same 1.06 1.10 11 B22 4.37 6H6GT .60 7X7 35L6GT .59 801A 495 2E24 .46 802 2.95 2E25 3.95 614 3.95 7V4 72 35W4 RK60 79 oscillator to exactly the intermediate 2E30 .54 108P4 34.95 3573 .72 805 4.95 995 frequency in the second converter tube 2JB51 {p5 615GT R1(73 616 1.06 10CP4 42.20 35Z4GT .50 807 1.25 720 I 95 1.10 or section. 'ñ 10YP4 49.50 35Z5GT .46 808 2.96 7740 295 2X2 617GT 6 The Browning (one of the first on the 3A4 -72 618G 1.06 12A8 .89 37 .59 8 0 7.95 1.06 VR75 3A3GT 1.92 6K5GT .88 12A7 38 .72 811 1.95 VR78 75 market), one of the Collins Audio, the 12A8CT .72 39/44 .59 812 2.95 3API 285 6K6GT 54 NR90 76 60 12AH7GT . .88 41 .59 81211 6.50 Dongene, the Espey, and some Meissner 3B7 I.OB 6K7 12AT6 .59 42 .59 813 7.95 V RIOS .75 3B22 4.95 61(8 .88 12AU6 .72 43 .59 814 5.95 VRI50 . .73 models are combination AM -FM tuners. 3B23 4.95 6L50 .88 124U7 .88 45 .59 815 2.30 VTI27A 3.00 Some of these have completely separate 3824 1.95 616 1.29 121340 .72 45ZSGT .59 826 1.25 VUI11 1.50 3B25 BLBG 1.06 I2BE0 .72 48 .88 8298 4.95 WE532A 4.96 AM and FM tuners; others combine the 3BP1 2.95 61.7 .88 12C8 .89 47 .88 830B 5.25 Z225 1.36 i.f. channels. The Meissner 3 -1093 and 20% DEPOSIT WITH ORDER UNLESS RATED the Browning RJ-12 were constructed without power supply, obtaining their g ALI. TYPES LISTED ABOVE IN STOCK NOW BUT SUBJECT TO PRIOR SALE voltages from the amplifier with which 160 GREENWICH ST. they were intended to be used, or from NIAGARA RADIO SUPPLY CORP. NEW YORK 6, N. Y. an external pack. Both companies find it worth while to supply self- powered tuners, the 9-1091 and RV -10, respec- ! tively. Collins Audio Products, and pos- FM RECEIVERS sibly others, have done the same. (Continued frotn page 2.1) A feature phonograph users may well look for is the phono -FM switch provided in a few of the models. The phono- and the 6.2- to 9-me and 12- to 17 -mc It uses eight tubes in the r.f. section and graph is attached to the tuner, a switch short -wave bands. This section shares has two panel-mounted meters -one permitting selection of either FM or its first al. amplifier and tuning indi- used as a field strength meter and the phonograph operation. cator with the FM section. There is a other as a tuning indicator. It includes Another departure from the beaten special bass -boost a.f. amplifier on the a 10 -watt a.f. amplifier on a separate track is the De Wald tuner, which does tuner chassis. The power amplifier and chassis. not 'require any attachment to the re- power supply are on a separate chassis. The Model 648 is a similar set de- ceiver. Its output is an oscillator sim- Output is 20 watts, to a co-axial speaker. signed for use in a vehicle with a 6 -volt ilar to that of a wireless record player. The REL Model 646 is a dual-band d.c. supply. This set is for use in making While such a device cannot reproduce FM receiver designed primarily for mobile field -strength surveys. the high fidelity of FM transmission, demonstrating and station monitoring. The National Model NC -108R, a set since it transforms the signal to AM, RADIO -CRAFT for 53 it may be useful in special applications cator tubes are not counted in the "num- where it is not desired to disturb an ber of tubes" column, though they are existing set to add a phonograph input listed in addition to the functional tubes. and where interference and electrical Where a separate oscillator is used in disturbances make FM reception (even the mixer Circuit, it appears directly with only AM quality) desirable. below the mixer tube. Two mixer tubes Characteristics of the more common- indicates a double superheterodyne. Ab- ly available FM tuners are given in the breviations are: seien., for selenium rec- table. Only the FM channels of AM -FM tifier; and F -S, for Foster- Seeley dis- tuners are considered. Rectifier or indi- criminator.

Under- chassis view of Edwards Fidelotuner, showing the selenium rectifier. The long -lines tuning apparatus is above the chassis.

FM FUNDAMENTALS (Continued from page 21) 25 Ceramicon Condensers is low. FM carrier power line. Transmission depends on the space carrier power Provide ultimate stability. Temperature wave. remains constant at all times (Fig. 2-b), the power merely being distributed in coefficient is determined by the ingredi- High -fidelity reproduction the side bands ,on modulation. In AM ents of the ceramic dielectric; control- The useful audio -frequency range ex- systems, 100% modulation refers to the lable to within very fine limiting values. tends from about 20 to 15,000 cycles maximum or peak amplitude allowed; Color coded. Flexible pigtail leads. Shpg. per second. For good fidelity in repro- in FM, it refers to the maximum fre- wt. 1 lb. duction, a broadcast station must be quency swing. capable of handling all these fre- To meet the high- fidelity require- APS511 -Your Cost 690 quencies. Instruments such as the snare ments of FM, all station equipment drum, violin, piccolo, and oboe, and even must be capable of passing the entire Crystal FM Converter require the full range. hand clapping, audio range with very low distortion Change old FM (40 -50 MC) to new Since AM stations are assigned to chan- in and noise levels. Total distortion few moments and at lowest nels only 10 kc apart, high -fidelity modern equipment is kept to approxi- FM in a transmission at broadcast frequencies is mately 1.5 db, and the noise level 65 db cost. Efficient operation; this is a su- out of the question. Network lines and below program level, or better. Fre- perior device. No loss of signal. Easy to most remote lines are equalized to cut quency response is fiat over the entire install. off all frequencies above 5,500 cycles per -!- 1 db. APS700- range to within Your Cost second. Rebroadcasting does not introduce aloa FM channels are 200 kc wide, and sta- feedback or heterodyne effects. A group Only tions are allowed a maximum swing of of stations can be linked to form a net- 75 kc on either side of the center fre- work of any size, the only limiting fac- quency. This leaves a spare 25 kc at tor being the distance between stations. either end to serve as a guard band to Each successive station must be within prevent adjacent channel interference. reliable receiving range of its prede- The wide channel permits broadcasting cessor. the entire audio range. Other FM advantages IL NOW As previously mentioned, the carrier t power of an FM station remains con- it York stant. This allows the tubes to be run 10@ SIXTH AV Fig. 2-a Fig. 2 -b closer to their recommended operating rat St-, Boston 10 The signal strength of an AM station characteristics, and efficiency is in- al Ave, Newark 2 varies with modulation (Fig. 2 -a), creased, especially in the final r.f. stages reaching its peak at 100% and decreas- where an efficiency of close to 70% can ing correspondingly with lower levels of be maintained. modulation. Noise may cover the softer Due to FM's superior ability to con- Ctweitel \""'^"' passages of sound completely when the quer interference and static, a lower- RADIO WIRE TELEVISION, INC. Dept. JF-0, 100 Sixth Avenue, N. Y.13 f cni tEi) No. APS511 @ 69c each AVOW INPUT Send quantity ( ) No. APS700 @ $6.00 each quantity t ) BUFF. FREO.MULt1 POWER AMP.t- ( ) order ( ¡KULOSC.,- BUFF. -{ Enclosed: Check money 111111 I Send Catalog ( ) New Flyer C12 ( a1L.M00. Name ...... XTAL OSC. Address State Fig. 3 -Block diagram of FM transmitter using the Armstrong indirect method of modulation. City Zone.... JUNE, 1948 54 --- FM FUNDAMENTALS (Continued from page 53)

SET- BUI LOER'S power transmitter, with greatly reduced operating voltages and cooling requirements, can be used. This reduces over- all operating expenses. Costs can be scoot! lowered still further by using an antenna system with a power gain as high as 6 or 8. Tuning Unit - - The modulation system employed in FM transmitters also represents a sav- Newest Type, ing. In AM, the carrier power is increased 50% under 100% modulation, Permeability and four times on peaks. The cost of the additional power is high, especially Complete, including large stations. Since an FM transmitter separate iron core oscillator, tracking coil, is modulated and built -in- mica trimmers. in the oscillator stage, the May be used to cover the broadcast modulator unit employs inexpensive re- hand in either AC or AC -DC receivers. Has worm gear drive for ceiving -type tubes. iron slugs, rigid metal frame only 1," x 13.1" x 378". Extra This discussion would hardly be com- long tuning shaft. Moisture proof coils wound on plastic forms. plete without describing the methods of generating FM waves. Two basic sys- Nothing equal at twice the price. Full instructions included. $125 tems are now in use: the indirect or Shipped C.O.D. or postpaid with cash order within U. S. A. Armstrong method, and the direct method. The indirect system (Fig. 3) con- WA0TTERSON SALES CO. sists of a crystal -controlled oscillator whose output is split into two P. O. BOX 84D DALLAS I, TEXAS paths, one of which is fed through a 90- degree phase- shifting network, and the other contains a balanced modulator. When these two paths are again combined, the How to repair result is a phase -modulated signal, i linear up to ±30 degrees. The frequency RADIOS . deviation, however, is very small. The necessary 150 -kc swing is obtained by multiplying This manual shows you MARJ the oscillator output to a r high frequency. This frequency is then how to handle 95% reduced to a low value by heterodyning of all service problems it with a second crystal oscillator. It is then put through another series of mul- Here's a highly practical radio tipliers to raise it to the final frequency. repair manual which leads you This system allows a higher order of in easy steps to a complete un- frequency swing than if simple fre- derstanding of 95% of all radio servicing quency multiplication is used. jobs. It covers the modern superheterodyne A.M. receiver, as well as phonograph -com- In the more simple direct method of bination service problems and auto radio frequency modulation, a reactance tube problems. Detailed "how- to- do -it" explana- controls the master oséillator, which tions enable you to put your finger on ex- usually operates at one -sixteenth the actly what needs to be done. output frequency. The oscillator output is fed through multiplier and buffer ELEMENTS OF stages to the final power amplifier. Automatic frequency control RADIO SERVICING To control the transmitter frequency, a portion of the oscillator's output volt- BY William Marcus, co-author of "Elements of age is passed through a chain of fre- Radio" and Alen Levy, Instructor of Radio Me- v chanics, Manhattan Trade Center for Veterans quency dividers until the frequency and Chelsea Vocational High School. reaches a very low value (5,000 cycles 471 pages, 6 z 9, illustrated, $4.50. in one commercial transmitter). A tem- This radio servicing handbook is easy -to-read and perature- controlled crystal oscillator is There is no other radio like Hallicrafters easy-to-understand. It breaks the superheterodyne into natural stages. and analyzes it thoroughly used as a frequency standard. Its output precision -made Model S -38. Four bands from a service standpoint, covering everything is also passed through frequency di- bring you thrilling land, sea, air commu- from setting up the signal generator to the push - pull output stage. Attention is given to the most videra until its frequency is identical to nications from all parts of the world commonly used testing equipment -the multi - that from the first chain of dividers. plus finer qualify on your favorite broad- meter and signal generator. Schematic diagrams help make this book a practical on- the-job manual. The outputs of both divider systems are cast program. Perfect for den, library, then applied to balanced modulators office. Extra clear, strong reception any- whose outputs are 90 degrees out of 10 FREE where. AC DC. Write for Catalog P38 DAYS' EXAMINATION phase. Each output is amplified and and where to buy. t A '50 McGraw -Hill Book Co.. lee.. 330 W. 42 SL. N.Y.C. IB (in one system) applied to separate Model S -38 . . Send me Marcus and Levy's Elements of Radio Serv- icing for 10 days' examination on approval. In 10 days windings of a 2-phase Inductor motor 1 will send $4.50. plus a tow cents postage. or return whose shaft is connected book postpaid. (Postage paid on cash orders.) to a frequency- compensating capacitor in the tank cir- hallikrafters RADio Name cuit of the modulated oscillator. Any Address difference between the center frequency Ger o Hallicrahen and listen for the Gatti- Hallinafters City and State of the modulated signal and the crystal mobile, radio- equipped expedition now operating via short wave Irons the Mountains of the Moon, Company standard produces a beat frequency Africa. whose THE HALLICRAFTERS CO. Poeition RC-6.48 direction of drift operates the 4401 W. Fifth Ave., Chicago 24, Illinois L__ea-- mamamamm ,.MMMM- --4-. motor to adjust a compensating circuit. RADIO -CRAFT for 4- PM +55 A very effective method for producing frequency modulation uses balanced reactance tubes. The RCA BTF -3B FM transmitter employs this system. A modulated Hartley oscillator is link - coupled to the grid circuit of push-pull reactance tubes. The r.f. voltage appearing on each grid is 180 degrees out of phase with the opposite grid, and 90 degrees out of phase with its respective plate. One reactance tube produces a plate current which leads its plate voltage by 90 degrees and functions as a capacitive reactance across the modulated oscillator. The other tube's plate TO INTRODUCE THE NEW current lags its plate voltage by 90 degrees and acts as an inductive reactance across the oscillator tank. Since the plate current from these tubes is directly proportional to the amplitude of the audio-frequency signals impressed en their grids, the result is a proportional change in frequency of the modulated oscillator at an audio rate.

FREQUENCY MODULATION (Continued from page 20)

of all upon the manufacturer. It is on the operations of the manufacturer that the spotlight of public opinion is now focused. For over two years, as everyone knows, the efforts of a very large part of the industry have been centered on the manufacture and sale of equipment that is already obsolete; that is, AM sets without an FM band. A small part of the industry is engaged in practices which bid fair to bring back the days of the "blooper" - sets which oscillated directly into the antenna. And there have been still EXCLUSIVE others who have engaged in the equival- WITH OLSON/ The ent of selling an automobile without a AKRAD Condenar gearshift, i.e., an "FM" set without evelopb h our proper noise -suppressing facilities. of eres.. alear years IIIIIIIIIIIIIIIIIIII by OLSON PLEASE: All these things the public will find RadioLY Warahouta1 EXTRA VALUE! Only ONE Akrad to a cus- out in due course. They will then turn tomer at this special low AKRADS are manufactured so to the sets of the manufacturers which price. You must use the efficiently and In such great outside give them genuine FM performance. QUANTITY that we save on the coupon. No orders USA. Offer expires AUG. I, But why put a substantial part of the cost, AND SO DO YOU. public to all that trouble and loss? 1948. the WHY DO WE MAKE THIS OFFERT Well, we think the AKRAD Condenser is Is it not time that radio industry OVERLOADING of responsibility to TERRIFIC and we think you'll agree after you try one. Watch the cultivated a sense the long SHELF LIFE of an the public? Is it not time, if they fail so an Akrad will take without breaking down; check up every AKRAD Condenser with a 100% GUARANTEE -so get do, that their responsibilities be Akrad. We back to one NOW from OLSON, the Radio Parts King of America. A REAL INVESTMENT pointed out to them by the editors of the for only a DIMEI trade and technical journals so clearly that they cannot fail to understand VALUABLE COUPON! ,11I II'idlf*fl rl'IIÌt./ them? .ii11fir fe ÌI All the old- timers remember that SEND THIS COUPON WITH ONLY 10e TO when the Superheterodyne was invented there were a flock of devices known as Infradynes, Ultradynes, Superdynes, etc., but that eventually the art stand- OLSON RADIO WAREHOUSE INC. ardized on the basic Superheterodyne MINN principle. So it will, of course, be with 71 E. MILL ST., DEPT. 123 AKRON, OHIO the FM system. Whether the manufac- `Ç turing industry has learned that lesson -and you will receive one 8 MFD 450 V. "AKRAD" CONDENSER. Hurry) or whether it will have to learn it all Offer expires AUG. I, 1948. over again will be made clear within the coming year. NAMF The opportunity, however, to give to (PLEASE PRINT) people a service infinitely better than ADDRESS they have had since broadcasting start- C= how AWN ed is here, and history will record CITY STATF well the receiver manufacturers took advantage of the opportunity which has ¡ ;ll:'I;':'ump'ú:.'.tis:',.'n`mi.v''Lty''1¡;'I \ been laid on their doorstep. JUNE, 1948 56

RADIOMEN'S HEADQUARTERS WORLD WIDE MAIL ORDER SERVICE!!! BUFRAD CAR RADIO ANTENNAS All of our car radio antenna. are made of triple plated Admiralty Brass Tubing, complete with low loss shielded antenna leads and high quality fittings. SIDE COWL -BR -1, 8 sections extend to 66 ". Your price-single units-$1.60; in lots of 12-11.35 ea. SKYSCRAPER -BR -2 has 4 heavy duty sections that extend to 98 ". Your price- single units-12.45; in Iota of 12 -12.25 ea. TILT ANGLE-BR -3, may be adjusted to all body contours. 3 sections extend to 66 ". Single unit price - 11.50; 12 lot price -11.25 ea. VERSATILE-BR -4, single hole fender or top cowl mounting may be adjusted to conform with all body contours. 4 sections extend to 66". Single unit price- 12.90; 12 lot price -12.75 ea. THE MONARCH -BR -6, single hole top cowl mounting, 3 sections extend to 66 ". Single unit price- 11.90; 12 lot price-$1.75 ea. AFTER SEEING OUR ANTENNAS AND COMPARING, YOU WILL NEVER BUY ANY OTHER MAKE!

BENDIX SCR 522 -Very high Frequency Voice Transmitter -Receiver -100 to 156 MC. This job was good enough for the Joint Command to make it standard equipment in everything that flew, even though each set cost the Gov't $2500.00. Crystal Controlled and Amplitude Modulated -HIGH TRANSMITTER OUT- PUT and 3 Microvolt Receiver Sensitivity gave good communication up to 180 miles at high altitudes. Re- ceiver has ten tubes and transmitter has seven tubes, including two 832's. Furnished complete with 17 tubes, remote control unit, 4 crystals, and the special wide band VHF antenna that was designed for this set. These sets have been removed from unused aircraft and are guaranteed to be in perfect condition. We include free parts and diagrams for the conversion to "continuously variable frequency coverage" in the receiver. The SCR 622 complete with 24 volt dynamotor sells for only $37.95. The SCR 522 is also available with a brand new 12 volt dynamotor for only 142.95. BRI Bß2 BR3 BR/ Bß5 FLUORESCENT LIGHT BALLASTS. Single 30 or 40 FILTER CHOKES: 200, 300. 400. 500 ohm light duty AUTO RADIO DEALERS! ATTENTION! watt.5i.68; Dual watt High Power -S9e; 200 or 300 ohm heavy duty -99e; 250 ma 33 40 Factor- 53.75. ohm, made for U.S. Navy. fully shielded-11.9S: 75 Nationally advertised brand of 1948 car radio which HEADPHONES- Highest quality Signal Corps head- ohm 125 sua -25c or 25 for 34.25; "Meissner typa" sets with 12' cord and plug 11.25. 5' rubber covered core will fit practically any car and every pocketbook. Six yaichcords with phone plug and socket -45e. 25e;;Choke- conden`ser2Scombination. Ideal replace tube superheterodyne with three gang condenser and LINE FILTERS --110V -each unit contains two 2 mid. 6%" sample, Dealer oil filled condensers and a 15 amp. iron core choke. 11ÓV. CIRCUIT BREAKERS lof Magnetic type: Follow- speaker. $32.20 for or price 129,97 ing Current Hating" in Stock: 1.25. 3, 4, -8 Amps. each, in lots of two or more. Till. filter has innumerable uses such as oil burner Please specify. each. ten 31.95 is an item no serviceman who line fill SEVEN ASSORTED TRANSFORMERS-81.9S; Here that repairs auto V1iI RECTIFIERS-My discc type1 yy', 1, 1.2 I.F. Five radios should be without. Nationally advertised ATR suitable for convening¡n tale la Asstd. Oscillator Coils-S9c. battery eliminator that supplies filtered 12 AC,p for supplying portable radios, METER RECTIFIER-Full wave, may be used for re- perfectly convening DC to ACUrapplications, and also placement, all typas á test equip- VDC or 6 VDC at 14 amps, from 110 AC $36.00 may be used In low current charters-90c. ment-91.25. HalfWaavvice SOC 1948 MODEL MUTUAL CONDUCTANCE TUBE TESTER. $49.95 No possibility of good tubes reading "Bad" or bad tubes reading "Good" as on dynamic conductance testers or other ordinary emission testers. Attractive panel and case equal to any on the market in appearance. . . Large 4 %' meter. . Calibrated micromho scale as well as a Bad -Good scale.... Front panel fuse... Individual sockets for all tube base types -voltages from .76 volts to 117 volts and complete switching flexibility allow all present and future tubes to be tested . regardless of location of elements on tube base. . Indicates gas content and detects shorts or opens on each individual 1 section of all loctal, octal and miniature tubes including cold cathode, magic eye and voltage regulator tubes as well as all ballast resistors. Name of the nationally known manufacturer withheld because of special price offer. Model "C "- Sloping front counter case $49.95 Model "P "- Handsome hand -rubbed portable case 54.95 Built -in- roll chart with either of above $5.00 extra. POWER TRANSFORMERS -Half-aheli type, 110V, 60 c,' MICROPHONES-All nationally Contertapped 11V winding. Specify either 2.5 or 6.3V filament known brands. Bullet crystal - AT LAST YOU CAN AFFORD when ordering. $5.45; Bullet Dynamic-$7.45; For .4.5 tube sets - 650V. 40MA. 5V & 2.5 or 8.3V $1.49 Mike Jr.-60e; Handy Mike - A LABORATORY STANDARD For 5-6 tube sets -650V, 45MA. 5V & 2.5 or 6.3V 1.75 90e; Lapel Mike -93e: SHURE For 6 -7 tube sets-675V. 505IA, 5V A 2.5 or 6.3V L90 T -17 MIKES, with push to talk For 7 -8 tube sets -700V. 7OMA. 5V & 6.3 or two 2.5V 2.35 switch -99e. MICRO VOLTER For 7 -8 tube sets 705íA, 5V & 6.3 (25 Cycle) 8.60 -700V, 20 AUTO COIL FORMS. In- The famous Measurements Corp. 51adel 78E, 5 Tube For 8 -9 tube sets- 700V -9OMA, 5V -3A. 2.5V -3.5A. cluding 11 2.5 -10.5A ceramic. 3 polystyrene, Laboratory Standard Signal Generator (that sold new, 2.85 and 6 fber, all useful sires N. Is For 9 tube sets 5V & -4A 2.85 -50e. FOB Boonton, J.. for $310.00 net) available -lt -700V, 63V in perfect rendition for 25 to V 9 5V VARIABLE CONDENSERS: 350 60 cycle. 115 AC op- For -15 tube sets -600V. 150MA. & 6.3V 2.95 now CONDENSERS -PAPER TUBULAR 600 WV- .001, .002 005 SIMFD, 5 gang -$L95; 4 gang eration. Until this -$1.49; 3 gang 7.5 to 20 Is the sort of topflight -Sc; .01, .03 -9e; .1 -10e; 25 -23e: 5 -35e: ELECTRO- -83e: lab equipment that dis- LYTICS: 8mfd 200. -20e; lomfd 35v -20e; 30mfd 150v -23e; MMFD, 1750v spacing. extra long shaft Hammarlund -89e- criminating buyers have 20 /20mfd 150v -35e; 30/20 150v-46e: 50mfd 150v -43e; 8mfd only vainly hoped would 475v -34e; 16mfd 350v -65e: OIL CONDENSERS: 4mfd 600v minlatllre variables, 25 ACHED 49e; 2mfd 600v -29e: 3X.lmfd 600v -29e. -39e; 50 MMFD -49e; 75 81ß4D--59e: 100 MMFD be released at a bargain -69e; 140 MMFD -79e. prlce. Worth every cent SPEAKERS -These PM speakers are the finest that are available INTERRUPTION FREQUENCY COILS for super -n- the manufacturer asks. All have heavy Oteraide Alnico V magnets. generative receiver. or the tremendously popular FM but available FOB Buf- 3'/a $1.15 5 fer $6.60 adapters for standard broadcast sets. Iron core with falo while our limited 4' 61.15 6 for $6.60 resonant frequency of 50 KC -39e; Air Core, 100 KC supply lasts for only 5' $1.10 10 fer $9.50 -29e. $59.95. 6' $1.50 6 for 68.70 30 MC IF TRANSFORMERS. double slug tuned -25e. Such companies as Ad- 7' (Cr Radio Sire) . $4.50 6 for $21.50 30 MC VIDEO AMPLIFIER PLATE COILS-Slug miral Corp. and John 8' 10 oz. .. $395 6 for $20.50 tuned -25e. Meck, Inc., have ordered 8' 21 oz. .... 64.95 6 for $26.50 REMOTE CONTROL UNIT: Aluminum cas. 4.3x2' from a and repeated 10' 21 fig. .. 50 6 for $30.00 containing 2 potentiometers, triple pole switch, 4 knobs, many limes on these 78 12- 21 oz. .... 7.96 6 nor $42.00 gear mechanism. counter and phone lacks-59e. generators for use In Medel 76 -E Standard Sig - their labs and produo- nal Generator. II tion line testing. - - - .- "REMEMBER THAT A STANDARD IS - - AS RELIABLE AS ITS MAKER." ------ONLY RT -1579 consists of a three stage cascade 6877's and SF6 output stage high gain, high fidelity amplifier with 60 cycle, 110V power supply on the same135Sx14% chat. CLOSING OUT OUR WAREHOUSEOUS FORT INCOMING STOCK 4 sic which Is protected by a substantial steel cover over tubes and parts. Slade by Western Electric with typical quality components such as a busk,' newer transformer AIRPLANE INTERCOM AMPLIFIER-Complete with 4 tubes in aluminum case $4.95' and oil condensers. this unit Is obviously intended to ' "SO" RADAR P.P.I. SCOPE, complete with 9 110 V tubes, Selsyn motor and self- contained give years of trouble -free service with no more need 'power supply designed to run on the AC supply on LST and PT boats. Various ranges from for repairs than a telephone. Disconnecting one wire 2 to 80 miles. The most satisfactory scope available for navigational radar or panoramic tele- each, from the special Input and output filiar., will re- vision applications. Nationally as by sult In as high a fidelity amplifier as can be obtained. advertised surplus at $100.00 others. Our price only $39.95 Your coot with tubes, diagram and parts list included AIRCRAFT MARKER BEACON RECEIVER-Complete with dual purpose tubes and sensitive -514.95. relay to control external circuits from received signals. Just the receiver you have been waiting RT- I655 -11 tube crystal controlled superhet re- for to control models. open doors from a distance, etc. PRICED AT only $6.96 ceiver for 24 -28V DC operation. Beautiful daasb and cabinet. Uses latest tube types Including 7 miniature 6A35'e. Tubes and schematic supplied. e A A Akio ò Only a few available at 614.95 SELENIUM RECTIFIERS. The new miniature rectifier that more and more manufacturers are using. Order some of each type so you will be ready when these receivers require servicing. Make extra money by installing them in old seta. A 1 types are rated at 180 V.A.C. 25 MA $ .45 10 For 1 4.00 75 MA .70 10 For 6.50 60 For $31.00 100 For $69.90 100 MA .76 10 For 7.00 50 For 32.50 100 For 59.11 150 MA .89 10 For 7.50 50 For 35.00 100 For 66.91 200 MA 1.05 10 For 10.00 50 For 47.50 100 For 99.90 250 MA 1.25 10 For 12.00 60 For 57.50 100 For 110.00 DO NOT ASSORT TO MAKE QUANTITY Cable Address: BUFRAD Minimum order 83.00 -All prices subject to change -25% deposit with C.O.D. orders BUFFALO RADIO SUPPLY, 219 -221 Genesee St., Dept.6 C. BUFFALO 3, N. Y. RADIO -CRAFT for 5 7 4-

RADIOMEN'S HEADQUARTERS n WORLD WIDE MAIL ORDER SERVICE!!! DUE TO POPULAR DEMAND WE REPEAT THESE TERRIFIC BARGAINS Three assorted new MICROPHONES, including push -to -talk type $1.49 Ten assorted R. F. Chokes including high frequency types $ .95 Five assorted AUDIO or FILTER CHOKES One Hundred assorted RESISTORS $1.95 Ten assorted JAN CABLE CONNECTORS, including SCR274,522 and BC375 types $ .99 Six assorted OIL FILLED CAN TYPE CONDENSERS, all with mounting brackets $1.49 METAL & BAKELITE KNOBS -(no wooden knobs) $ .39 Ten assorted $1.49 Six assorted VARIABLE CONDENSERS, including butterfly types Six assorted POWER and AUDIO TRANSFORMERS, all new $1.98 bakelite R. F. COILS shielded and unshielded $ .99 Six assorted isolantite and can be above ten assortments totaling over $12.00 at the unbelievable bargain prices listed purchased The guaranteed to be as advertised. together as one lot at a super -special total price of only $10.00. All merchandise containing 3.7F7, 1.7Y4, 3.7NT. d potentiometers. numerous re,tstore. filter and contains two power ßT3463 T tube amplifiers and six sensitive plate relays. A military Aluminum gear box 18x8x7 that bypass condensera. alter hokes. power and audio transformers, 6 amazing teplesa control proportional tao c ion rtinirod for lierons. rudder ful electric motors and two matched gear trains. evelopment that provided of the rdinary type would deflect the rudder nd elevator. In the original application. A control gears in all varying in size from % to 4 inches in or . The eult arbitrary the blownnamtender be converted to rotate t correction awast the plan continued Ñcourse. or the correction ld diameter. This unit is readily Idlerbe th . increase tuel Ullon ad lapsed time In use $3.0 0o great. taming series of tackings and would grenuy in bridge beam antenna or any other similar reaching Ñe objective. This phenomenal unit. with Its 9 amplifiera na six 5000 ohm relays ircuita, will accurately ntrol any 3 0operations, related or unrelated, in inutely adjustable uniquely quart Native variations in either forward reverse directions. 9',7'x8' black crackle aluminum case. Brand ew in original carton. $9.95. BC -221 FREQUENCY BRAND NEW INVERTERS AND DYNAMOTORS METERS with calibrating PE BA: A 24 to 32 V DC input, to 80 V. AC regulated output converter $12.96 and 19.95 Crystal calibration PE 19A: A 24 to 28 V DC input. to 80 V AC at 800 cps output ) frequency a stepup transformer with each of the above ao that 110 V AC it available from either charts. A precision (We include 98e 27 V DC 295 V DC @ .5 MA output is useful for input $5.95 standard that 27 V DC input. Output 300 V t9 150 MA. 150 V ®® 15 MA and 12 V ®® 5 Amp. for Input. Output 300 V @ 150 MA, 150 V @ 15 MA and 12 V @ 5 Amp. $12.00 innumerable applications 12 V DC $15.00 13 or 28 V DC input. Output 800 V DC. 400 V DC @ 135 MA. and 9 V AC service field the above laboratory technician, (By running on 8 V ta small experi- . and dynamotor 0 111 preside gond source of 12. 400 or 800 V DCeicltation. man, amateur, menter at the give away GENERAL ELECTRIC price of only $36.95,

150 WATT MODULATION TRANSFORMERS -10 watt. metal case figs 30 sett, open-tine. $1.95: 40 watt. cast aluminum case. $2.95 TRANSMITTER Class "R" input transformers, out aluminum cue, $1.95 Transceiver audio transformers. 65e: Transceiver modulation transformers. 115e. Cost the Government $1800.00 of each of the fdlow- MINIATURE PLIERS SET contains one All Cost to you $44.501!!! ing: Needle nose. flat nose, parrot Dose, standard nose. contained In a leatherette wee. Your cost- $1.98. consieting of 5 sockets ranting in alze trer.amitter used in U.B. Army SOCKET WRENCH SET This is the famous from 5/18 to 54' and a handle-79s. bombers and ground stations. during the war. Its will strip up to 1000 wires have been proved in service. AUTOMATIC WIRE STRIPPERS design and construction per hour, a handy tool for any service Job--63.52. under all kinds of condition,. all over the world. The entire frequency range is covered by means of plug - in tuning unite which are included. Each tuning unit RT -1248 15 -TUBE circuits designed GENERAL ELECTRIC h.n L.]. 'i rv. - e J, and condenser. and antenna tuning -all frequency range. Transmitter and accessories are finished to Operate at tup tfllcic,i y no .1:1 Its partirulnr Here TRANSMITTER -RECEIVER black crackle, and the milliammeter toltmeter, and RE ammeter are mounted on the front panel. In operate on specifications: FREQUENCY RANCE: 200 to 500 KC and 1500 to 12.500 KC. (Will POWER watts) on any two Instantly selected. are the compensated, and TERRIFIC -(20 10 and 20 meter band with plight modification). OSCILLATOR: Self -excited. thermo easily -adjusted frequencies tram 435 to 500 Mc. Transmitter 211 tube, and equipped with pre Re- hand calibrated. POWDER AMPLIFIER: Neutralised class "C" stage, using uses 5 tubes including a Western Electric 816 A as final. antenna coupling circuit which matches any length antenna. MODULATOR: Clans -13--um uses 10 tubed Including 955's, u first detector and oscilla- practically which furnishes 1000V at 350 MA. ceiver trene- two 211 tubes. POWER SUPPLY: Supplied complete with dynamotor tor. and 3-7117's as IF's. with 4 slug -Pined 40 Mo. IF operate set from 110V AC. SITE: 2141x231954 inches. Total shipping Complete instructions are furnished to tuning tubes, dynamotor power supply, five tuning units, antenna unit operateand any sort of xternal equipment Weight 200 Ibs.. complete with all are guaranteed to be 8reei ys designedi7io7 and the eseentist plugs. These units have been removed from unused aircraft but when actuated by received signal from a similar set elsewhere. in perfect condition. Originally designed for 12 volt operation. poser supply Is not included, u it is a cinch for any amateur to connect this unit for 110V AC. using any supply capable of 400V DC at 135 MA. PE -109 32 -Volt DIRECT CURRENT POWER PLANT The ideal unit for use in mobile or stationary service in the Citizen's Radio Telephone Band where no license is nereebarY. This power plant consists of a gasoline engine that is direct coupled Instructions and diagrams supplied for running the RT -1248 in or FM transmission or to a 2000 watt 82 volt DC generator. This unit is ideal for use in transmitter on either code or voice AM reception. for use u a mobile publlo address system. as on 80 power or to run or locations that are not serviced by commercial 110 FM broadcast receiver. as a Facsimile transmitter to Mc. for many of the surplus items that require 24 -32V DC for operation. receiver. as an amateur television transmitter or receiver. The price of this power plant is only $58.95. We can also supply remote oontro relay hookups, for Golgor- Mueller counter appliw- or from only for $53.90. If a converter that will supply 110v AC from the above unit marine or mobile use. tha dynamotor which ooneither any 16 -32V DC source for $12.95. 12 or 24V DC and supply all power for the set is only $15.00 Due to the fact that the PE -109 cornea to us sealed in a heavy steel -strapped govt. case, it additional. is impossible to inspect the individual units to determine if they are new or need, or what "as is,' In general they represent the condition is if used. Consequently we must sell them SENSATIONAL SCOOP -Brand new 1948 model 7% a terrific bargain. H.P. twin cylinder outboard motor made by the world's second largest manufacturer of outboard motors. Regu- TERRIFIC VALUE -PORTABLE ELECTRIC DRILL lar price everywhere $169.95. Our amazing price on at the peak of the seasonal de- brand this hard -to-get item less than price mand is $142.95, or $135.00 each in Iota of three or Only $19.95 (equipped with Jacobestablishedeared luck nd Key.eNot an Intermittent duty drill. but a full else rugged tool. Most convenient type switch, natural grip handle. and balance like a six shooter. more. Precision at gears-turbine type cooling blower -extra long brushes. No stalling under hastiest pressure because of powerful 110 Volt AC -DC motor and multiple ball thrust CO.'S latest (rearing. UJNIVFJI.SAL MICROPHONE Other bearings self -aligning lifetime- lubricated Chrysler 011lte type. model recorder platform with high quality re- Made for toughest year -In and year-out service in plant or on construction lobs. cording amplifier complete with all necessary Amazing perpetual factory guarantee enures you tf a lifetime of trouble -free use. record, and If not with drill after trhd. controls for volume, tone, playback, 25 °, deposit on C.O.D.'s. Full refund (you pay transportation) pleased public address applications. Unit features crystal SCR -274N COMMAND SET playback and magnetic recorder head attached by special pantographic arrangement for mak- The greatest radio equipment value in ing absolutely linear recordings. Complete With history all tubes and matched speaker. Everything sup- A mountain of valuable equipment that includes 3 but cabinet for $46.95 receivers covering 190 to 660 KC: Cl to 6 MC; and 6 plied the to 9.1 MC. These receivers use plug -in coils, and consequently can be changed to any frequencies de- TUBES-All. types In stock. 60% eC On all tubes if ordered ired conversion. Also included are two Tun- in lots of 10 or more. without TRANSFORMERS -All types fu stock. AUTO- TRANSFORM- ing Control Boxes; 1 Antenna Coupling Box ; four ERS: Steps up 110v. or steps down 220v to 110v- $1.95. 28 V. Dynamotors (easily converted to 110 V. opera- FIL. TRANS.: 6.3v. 20 Amps. -$1.96: Universal Output Trans. tion) two 40 -Watt Transmitters including crystals, 8 Watt-89e; 18 Wat- $1.29; 30 Watt -$1.89. AUDIO TRANS- and Preamplifier and Modulator. 29 tubes supplied in FORMERS: R. Plate to B. Odd. 3:1 -79e: R. Plate to P.P. all. Only a limited quantity available, so get your MIKE TRANSFORMER in Removed from unused and in Midget Output fo AC-DC seta-439e:seta -69e: order fast. aircraft for T -17 shore microphone, similar to UTC Diner type -$2.00 guaranteed electrical condition. A super value at Stancor SR or DB mike to line or grid-41:95. $29.95, including crank type tuning knobs for re- knobs receivers can't be ceivers. Without these the MIDGET BASIC I WATT RIG supplied complete with poly- tuned. and are only useful for parts. Don't buy styrene coil forms for 3 ham hands. fila, over ails- x l' x 254' without knobs! We also include one 60 cycle. 110 to high. Includes practically all necessary put*. Details on page 24V filament transformer for receiver-FREE. 89 of January 1948 QST. Your cost $1.50. Minimum order $3.00-All prices subject to change -25% deposit with C.O.D. orders Cable Address: BUFRAD BUFFALO RADIO SUPPLY, 219 -221 Genesee St., Dept. 6 C. BUFFALO 3, N. Y. JUNE, 1948 581

FM RECEIVER VALUABLE SERVICING TECHNIQUE (Continued from page 31)

SERVICE balanced (Fig. 5) connect the vacuum - tube voltmeter between point B and AIDS! ground. The procedure is the same as for the Foster -Seeley discriminator, A. TROUBLE TRAC- For the unbalanced ratio detector ING -for checking (Fig. 6), conneot all AC-DC Radio Re- two 68,000 -ohm receivers. sistors in series across Rl and the B. RADIO SERVICE common lead of the vacuum -tube volt- STANDARD RATE meter BOOK - gives pricing to point C. Connect the other lead on all radio repairs. to point B. The rest of the alignment is RADIO WORK C SHEET complete the same as for the balanced ratio de- details of the- service tector. Job. D. RADIO SERVICE Limiters, i.f. amplifiers RECORD - handy form of 100 numbered When a receiver becomes noisy, check service job tickets. the limiter stage. Limiters become noisy when their grid -leak A. "TROUBLE TRACING IN AC -DC "RADIO SERVICE circuits open or B. STANDARD voltages rise above RECEIVERS" normal. Under these RATE BOOK" conditions it will require considerably 60 pages packed with essential servicing data The standard of fair dealing. Contains complete stronger in AC -DC sets. Each part thoroughly analyzed, details for turning out a clean repair job at a signal voltages to saturate the causes, effects and remedies discussed in detail. fair Divided tube, and Fifty price. into six sections covering the limiting action is impaired. case histories with their logical solutions. each general type of set. Registry of electronic A check of Easy to understand, technical verbiage held to manufacturers and thorough coverage of crys- the i.f. system is made a minimum. Equivalent to 6 years tal cartridges with photos of 51 different types. quickly. Connect the vacuum -tube volt- practical experience $1.00 Spiral bound, edge indexed, attractive green enamel cover $1.00 meter across the limiter grid -leak resistor. Connect the output lead of the C. "RADIO WORK SHEET" D. "RADIO SERVICE RECORD" AM signal generator to the control grid Don't hide your light under a bushel. Use the Book of 100 numbered service job tickets in 8 of the first i.f. stage, and the ground WORK SHEET to acquaint your customer with part form. Designed for practical service use. lead to the receiver the complete details of his repair job. Shows Series available-1001-1100, 1101 -1200, 1201- chassis. Set the sig- 38 minor repairs and adjustments in handy 1800, 1801 -1400, 1401 -1500. 1501 -1600, 1601 -1700, nal generator to the i.f. center frequency. check -off listing. Everything shown. No 1701 -1800, 1801 -1900, 1901 -2000. Space pro- hidden charges ÓOC vided for dealer rubber The vacuum -tube voltmeter needle will per 50 sheet pad stamp eI,ZS ea. deflect when the i.f. system is functioning. If the signal path is broken, AT PARTS DISTRIBUTORS EVERYWHERE Write for catalog move sheet the generator toward the limiter to reveal the defective stage. OELRICH PUBLICATIONS, 4135 N. Lawler Ave., Chicago 41, III. Sets with ratio detectors usually have no limiters. In these instances, place the v.t.v.ra. at point A in Fig. 5 or 6. The indications will be the same as with the meter in the limiter grid circuit. To align the i.f. amplifiers, connect FIDELOTUNER the vertical input terminals of an oscilloscope across the grid -leak resistor FOR MAXIMUM in the limiter stage and the sweep sig- F-M nal generator between the converter (or LISTENING PLEASURE! mixer) tube control grid and ground.

CONVERTS A N Y R A D I O RECEIVER or SOUND MARKER AMPLIFIER i for F -M Fig. 8- Marker signals identify frequencies. Adjust the signal generator for a 100-kc sweep about the i.f. mid -frequency. A curve as in Fig, 9 will be obtained if the New and revolutionary tuning principle* makes system is aligned. EDWARDS FIDELOTUNER most efficient F -M When the receiver contains a ratio de- CONVERTER on the market today! All the tector, connect the oscilloscope between great advantages of F-M reception are yours, point A on Fig. 5 or 6 and ground. with this compact, efficient sew tuner. Five The i.f. stages tubes, plus selenium rectifier. can be aligned with an AM signal generator. The process Edwards Fidelotuner, in as cabinet, shown, requires considerably more time because ready for your F -M Listening Pleasure, size I I" long, 6" wide, 63/4" high. most i.f. transformers are overcoupled. To parr prva r List Price $38 50 peak an overcoupled transformer, (Slightly higher West of Roclies) load the primary with a 1,000 -ohm re- DISTRIBUTORSI Some territories sill open. uta sistor, and adjust the secondary trim- We invite inquiries. Write for literature. TT:P.o mer for maximum response. Then s3á ól Menufectur.,d by f& "" :i7 switch the loading circuit to the secon- ...m.n.., e..., .err_ dary winding, and adjust the primary EDWARDS r,..: F-M RADIO CORP. by for maximum response. This is done for 168 Washington Street New York 6, N.Y. i.7..74/%77--; v: each set of i.f. transformer windings. RADIO -CRAFT for RA 59 The AM signal generator feeds its signal into the grid of the tube preceding the stage containing the transformer under adjustment. Connect the indicat- i Ig voltmeter in the limiter grid circuit at point A in ratio detectors. With a sweep generator, we observe the full response at once, and artificial loading is unnecessary. In testing the r.f. section of FM receivers, it is best to start at the oscillator. The oscillator is the most critical stage in the front end and most likely NEW COMPLETE e4KC42R to be at fault. Measure the voltage between the control grid and cathode of the oscillator with a v.t.v.m. to determine whether or not it is functioning. RADIO The voltage may have any value be- s- tween -2 and -10. Too low a value may be due to a bad tube or low operating / voltage. If the plate and screen voltages CATALOG are correct, change the tube. Measure IGO VALUE -PACKED PAGES the grid voltage on all bands since the Mail coupon for FREE copy of this great, new tube may not function at some fre- Concord Catalog -a vast, complete selection of everything in Radio, Television, and Test Equip- quencies. This may be due to defective ment. Thousands of items ... latest 1948 prices. 23 pgs. Radio and Television LOWER prices on finest -quality RADIO SETS, PHO- switching or to the fact that a tube - NO- RADIOS, RECORD CHANGERS RECORD Sets 62 pgs. Radio Parts oscillates more at low frequencies. PLAYERS RECORDERS -wire and lilac PORT- ABLES, AMPLIFIERS. COMPLETE SOUND SYS- and If the oscillator is operating satisfac- TEMS TESTERS. Latest listings of all well-known, 18 pgs. Sound Amplifiers dependableppT radio torily, connect the 'AM signal generator 4 212.04 SATISFIED CUSTOMERS CANNOT BE Accessories 23 pgs. Ham Gear WRONG! Concord's quarter -century reputation for to the receiver input terminals. Tune Customer Satisfaction is the reason Radio Men (the 9 pgs. Electronic Test Equipment Experts who Know) keep coming back to CONCORD. the receiver and the signal generator to At CONCORD, YOU MUST DE COMPLETELY the same frequency. Place the vacuum - SATISFIED or your money will be refunded. 'Nail COUPON TODAY! tube voltmeter in the grid circuit of the CONCORD RADIO CORPORATION, Dept. 144 limiter or at point A of the ratio detec- 901 W. Jackson Blvd., Chicago, 7, III. tor. If set is operating Na Yes, rush FREE COPY of the comprehensive new Con- the satisfactorily, Radio Catalog. (Please Print) the meter will be deflected. If there is cord no response, change mixer or converter RADIO CORPORATION Nome CHICAGO 7 ATLANTA i tubes, measure voltages at the elec- MI W. J Ire. 215 Peechime St. Address.:,, Donnta ,.n Ch c.ao' ,.n.hc 221 W. M.dn.n trodes, and make resistance checks. City & Zone State r

WIRE & TAPE RECORDING COMPONENTS STOP! LOOK! -ORDER NOW Essential "hard -to -get" basic parts for con- LEOTONE'S VALUE -PACKED "SUPER" structing units described in "Radio News," RADIO PARTS ASSORTMENT. This iv sous Feb., '48. chance to stock up on new & dismantled qual- WIRE RECORD- PLAY -ACK HEAD. ity radio & electronic parts -17 FULL precision built Triple -Coll (record. POUNDS of COILS, TRANSFORMERS. pplayback ) d pIn plug -In type. )Ño Ided houMnß SUB. ASSEMBLIES, SPEAKER ACCESSOR- m.6MC I0.7MC IO.SMC grooved for accuratelyccu telyy Y' IES, WIRE, SOCKETS, etc., etc. All grooved for maximum O ellty $2.95 Fig. Response curve of an FM i.f. system. sensitivity. For replacement these AND MORE for only 9- (1aÚ3 WIRE SPOOL NUB. Polished alumi- CO -AXIAL CONNECTORS 83 -1SP The serviceman must not rearrange num. Takes nasdard wire spool (1 %' angle hole). shaft hole. deep .39 (PL -259) or 83 -1AP right any of the components on the underside %' %' adaptor. Each 29e. 4 for $1.00 PERMALLOY OUNCER LAMINA. 4' PRECISION ETCHED DIAL. Cali- of the chassis, especially small coils. It TION& Hydrogen annealed. Specifical- brated 0 -100 over 180'. Plated brass. ly for use in oonstructtng TAPE REC- y. setscrew .39 mincer hole is impossible to emphasize too strongly ORD- PLAYBACK HEADS. Per JK -24 JACK. Circuit opening long tome. laminations .40 frame. Takes standard 9 way phone the criticalness of these high -frequency MAGNET WIRE-- Sufitcient to wind lone complete TAPE READ. plug. 2 %' circuits. Many of them, especially the 5 n P.E. -35t ít28 P.E.-59e 10 a1 .223 compensating con- 030 SEC-45e Kit of all 3-451.25 oscillator, contain R91-4 RECORDING MOTOR. Haag SENSITIVE D.P.D.T. RELAYS. densers to compensate for changes in duty, 110V, 60 cycles. Adaptable to Famous m ke. 3/18' silvered oon- WIIIE. TAPE or DISC RECORD & tai's with protective plastic taus - abaft. 8 in``. 18- 28V.DC. 160 ohm coil. the electrical characteristics of the tun- PLAYBACK. 5/16. O.D. %' NEW sq. 3 %' deep. Las turntable, mtg. 134'x %'x1 %' BRAND - 39e. 15 $5.00 ing condensers and the coils. If one of pplateg & rbs. drive wheel Shea. ONLY fir these condensers becomes defective, the srL circuit is detuned. The serviceman ALNICO ERASE MAGNET for TAPE OR 250 OHM LINE TRANSFORMER to 8 ohms. 5 equal \l'IltE. '1 ' (hips; polished poles. %'x %'x taps, 0 to -IGdb. 1 :xrellent low -less matching to 1 or might conclude that the circuits merely %-. 3/16 gap 99 more remeda speakers. Diagram lnd. 69e. f for 1.25 Send for latest Illustrated ALNICO MAGNET t require alignment and readjust them. supplement. However, it will drift during each TUBES! TUBES! warm -up period, and the drift may be HANDY RADIO PARTS KITS 1 TUBES! OSC. 10 asstd. .98 All in perfect condition, but in unsealed sufficient to shift the r.f. circuits out of 01 -R.F., ANTENNA & COILS. cartons. Most types in stock at up to 80% 03- MOULDED BAKELITE CONDENSERS. list. Every tube guaranteed 90 days. range of the signal. The set will have 50 asstd. .00001 to .2 mfd. 200- 600WV. off Clearly marked 2.95 1x20. 27 Or 31 .29 to be retuned each time it is turned on. 04- TUBULAR BYPASS CONDENSERS. 50 *24, 42. 75, 77, 78, 6H6 er 6K7 ...... 39 asst. .001-to .2 mfd. 200 537, 39. 5Y4. 5U4. 6A4, Another frequently encountered de- Get on mar mailing new. 6A7, 6A8. 687. 6C5, 6F5. G00WV. Standard brands. yLeotoneMlna 2.49 Conne-Puy 615. 8J7. 6L7. 6SÁ7, fect is a howl caused by the speaker PROMPT SERVICE ON ALL SPEAKER PHONO or 12SK7 49 59 -WAFER SOCKETS. ICK -UP REPAIRS 6SF5 vibrating the oscillator tuning slug. Min. Order $2.00 20% deposit on COD's SIA7, 1H5. 6U5. 6X5. 12 asstd. 4 to 7 prong .25 - 7A7. 7Y4, 50 w 5065 .59 Place a fiber spacer between the oscil- 510 - VOLTAGE - DI. TUBE CARTONS. Plain. VIDERS. 10 asstd. multi - Miniature (l' aq.x2V') lator and the mixer slug shafts to elimi- tapped. High wattages In- Per .96 cluded 1.88 OT size 0(1 %' sq.x3% nate the vibration. This effect may be- 012-MICA PADDERS Per 100 1.25 come noticeable only as the volume con- & TRIMMERS. 15 asstd. Medium (1% sqx4V4') Incl. multiple & ceramic Per 100 1.49 trol is advanced, but the remedy is the base 69 Large (2' sax?) Per same. Howling may also be due to 527±1% Wire Wound. MAKERS OF CONES ANO FIELD COILS 100 1.79 Std. Makes. 1W. 10 asstd NEW 'YORK 7, N.Y. 1.98 65.67 DEY STREET speaker vibrations reaching the oscilla- -5 "LAMINOID" TRANS- 528- ROTARY SELEC- WORTH 2.0284 LUCENT PANELS. I le tor sections of the gang condenser. TOR SWITCHES. 6 amt. 0M'ti' sq. Rat with gray standard make'. Multi - C O SO = T OF kIDIO PARTS harking for d,rmaticr or Mount the gang condenser on a rubber deck & commie Input 1.75 lusulating purposes .35 ea. cushion or a felt strip to stop this howl. JUNE. 1948 .+F11¢ r:+ ,.:..í:.:.. ..:.. L _. .... : .k...>--e->H+w.E +» «t..+.erwir!. +-!r {qy

Pik 4111i- 60 I pattern may be viewed on the 'scope and measured directly in kilocycles on the deviation scale of the generator. FM SWEEP FREQUENCY: Ability to vary the deviation rate is useful. It permits a point -to -point oscilloscope check through the whole set from speaker to antenna with one setting of the signal generator. Yar:Y1SIr:,1 OUTPUT CALIBRATION: It is almost im- Complete Line of possible to design a signal generator ASSDIfit Y whose output voltage doesn't drop as t TELEVISION ASSEMBLY'S the frequency is increased. Response curves therefore have little meaning unless the output level can be corrected with frequency. In addition, a calibrated direct -reading meter can indicate the signal -to -noise ratio, sensitivity, and gain per stage. This is a quick way to WITH DUMONT INPUTUNER find a defective tube or circuit. AMPLITUDE MODULATION: A variable ,r; 10" Champion model audio oscillator included means an additional instrument at the same price. 2731° It can be used externally to test audio response, speaker and cabinet resonance. The Dumont Imputuner tunes continuously from 44 to 216 megacycles 12" Champion model without a break, VARIABLE MODULATION PERCENTAGE: covers all 13 channels as well as FM, amateur, and 303.10 aviation channels. For ease and convenience of operation no band Standard feature -should be included switching of any kind is required when but not critical as to percentage of vari- tuning from channel to chan- 15" Champion model nel with the imputuner system. Just one simple operation to reach ation permitted. any desired station. 393.10 OSCILLOSCOPE SYNCHRONIZATION: Un- less a 'scope is synchronized, it will be IMO impossible to get a stationary pattern. Clip leads can be used to pick up external synchronizing voltages but are in- convenient and apt to introduce phase distortion. OSCILLOSCOPE PHASING: A phasing All Television Assemblies are complete and in- control eliminates a double image on the clude: 29 RCA Tubes -plus CR Tube -Heavy Duty 'scope. Phasing can be adjusted with a RCA 6.8 oz. slug 12" PM Speaker -Specially de- potentiometer and condenser hung on signed dipole antenna with 60 ft. lead in. the horizontal input terminal, but the 10" Standard model 12'Standard usual objection to haywire applies. model 15" Standard model Accun4cI: Usual standards prevail. 229.50 2595° 349.50 , E Should be weighed against the type of Superior performance is obtained with a new IF Video & Sound IF Strip pointer and scale, since ability to read 25% DEPOSIT- (Pat. Pend.) aligned, wired, pretuned, tubed and tested. All circuits are calibration is equally important. Opti- BALANCE contained on one chassis ready to use with the front end unit supplied. mum arrangement would be highest ac- C. O. D. This front end will handle 13 channels and is aligned and tested, mounted curacy obtainable plus a large dial, on a separate chassis. Mercly connect B plus filament and output IF leads preferably protected and having a to the television chassis. It is not necessary to make any RF alignments. knife -edge pointer. These units utilize a clipper circuit which filters out ignition noises. DIAL TYPE: Protected dials retain calibration better than unprotected ones. A large dial and thin pointer permit ,S1-420, RADIO COMPANY more accurate reading of calibration. 509 ARCH ST. PHILADELPHIA 6, PENNA. ADVANTAGES OF FM (Continued front page 27) FM SWEEP GENERATORS (Continued front page 25) tually obtained. The correlation between the two is good. In general, field meas- a 'scope for optimum alignment of all FREQUENCY RANGE: Continuous cov- urements have shown that FM stations FM and AM receivers and tuners. FM erage from 100 kc to at least 110 me is are obtaining coverages very close to receivers must be properly aligned to essential to cover all services. All fre- what has been predicted. take advantage of the high -fidelity and quencies should be fundamental - not Fig. 3 illustrates the approximate noise -free characteristics of the Arm- harmonics. - ranges of various classes of FM sta- strong and ratio -detector circuits. NUMBER OF BANDS: More bands mean tions. There is considerable variation The following is a list of features better dial accuracy. However, an exces- due to local conditions, but they are incorporated in different roughly as follows: types of FM- sive number of bands is time consuming. Radius AM signal generators, with a descrip- FM DEVIATION RANGE: Must be at in miles tion of each type. The cross index lists least ±150 kc wide to permit visual 13.5 -Class A station, 1 kw effective popular makes of FM -AM signal gener- analysis of wide-band FM receivers. An radiated power, antenna height ators and the features each includes, as additional narrow deviation range per- 250 feet, in Area I with the maxi- well as their relative prices. Experience mits accurate alignment of i.f. stages of mum permissible interference un- indicates that wide -band television high- fidelity AM receivers. Calibrated der FCC standards. sweeps combined with such instruments variable deviation is a valuable feature 52.0 -Class B station, 20 kw effective are impractical and prohibitively expen- since it enables direct reading of i.f. radiated power, antenna height sive. A separate restricted -range r.f. band width which indicates fidelity re- 500 feet, in Area I with the maxi- generator with 10-mc sweep has proved sponse. For example, if the i.f. signal is mum permissible interference un- more satisfactory. fed into the converter, the discriminator der FCC standards. RADIO -CRAFT for 1 FA 161 38.0 -Class A station with no interfer- ONLY 50c EACH ence such as would be the case for all but the most densely populated $5.00 SET OF 10 sections of Areas I and II, power and height as above. Iet 65.0 -Class B station in Area II, power and height as above. These Books Keep You On Your Toes! 102 -Class B station in Area II de- Here are a total of 640 pages of downright practical knowledge to help you keep punching away effec- at the unknown factors of radio until you have mastered them. Every one of the 10 is worth many signed for rural coverage, times its 50c price if you will just apply a small portion of the information gained to your daily tive radiated power 160 kw; an- work. You'll be glad you have the complete set handy whenever you are trying to work out like the easy -to-read type -the clean - 1580 above particular problem In construction. testing or servicing. You'll tenna height feet cut printing -the smart, modern. flexible covers, and the great number of illustrations. They all average terrain. (Radio KRNT, help to make learning a pleasure. Order as many as you need today-better still, make it all 10. under construction at Des Moines, Iowa.) No. 20 -HANDY KINKS AND SHORT Today, there are more than 500 FM CUTS. A carefully edited compilation of time savers. Kinks on Antennas -Power stations on the air, and the FCC has au- Supplies -Teat Equipment- Servicing -In the Shop -Phonographs and Amplifiers- thorized the construction of over a thou- Coils and Transformers-Miscellaneous. sand FM stations to date. The existing 400 stations provide pri- No. 30- UNUSUAL PATENTED CIR- I- CUITS, 1944.1946. A gold mine In new mary service to an area in which 60 book -ups! A selection of unusual circuit,. many a result of wartime research-of great million people live, and it is expected value to anyone Interested In electronics, on the Control Circuits- Detector. and Amplifiers that 1,000 FM stations will be air -Power Supplies -Miscellaneous Circuits - by the end of 1948. These stations will Foreign Circutta. serve 117 million people -84% of the No. 31 -RADIO QUESTIONS AND population of the United States. ANSWERS. Answers to most frequently asked questions. Clear schematic.. Ampni- fiers-Receives- Trammltten- Meters and should crack down on per- .,n. .,I Test Equipment- Intorphonos -Power Sup- The FCC plies-Phono Amplifier-P. A. Systems. sons or companies who have secured patented, circuts construction permits for FM broadcast No. 32-ADVANCED SERVICE TECH- 1944-1946 NIQUE. An up-to -date collection of Infer stations but have failed to erect a sta- motion for the advanced serviceman: Visual Alignment- Tracking Problems- Negative tion, says the FM Association. A resolu- Feedback -Tone Control Circuits - Adding effect urges that the FCC Microphones to Seta- 5latehing Loudspeak- tion to that 1111041ill ers- Remote Juke Bone,- Servicing Record be asked to "investigate carefully" all Changers-Hum Elimination-FM Servicing. applications for extension of time where SO rias Ne. 33- AMPLIFIER BUILDER'S construction permit holders have not put GUIDE. Invaluable for the designer and their stations on the air within the time builder of audio equipment. Tells how to build a wide variety of amplifiers. Detailed specified. radio design Information on: Push -full -!Ruse questions Inversion-Bus and Treble Roosters-Vol- radio ume Expanders- Resistance Coupling -In- test QUIZ ternal Feedback. RADIO answers instruments By HAROLD GLENN No. 34- RADIO- ELECTRONIC CIR- CUITS. An extensive collection of circuit Check your radio knowledge. Any diagrams, with brief. to -the -point descrip- cor- IA110CIAfI tions of each, Including: Intercommunica- question may have more than one tions Systems-Power Supplies- Balancing AA010CIAfI LIIAA1f rect answer and, in at least one case all circuits -V.T. Voltmeter,-Amplifers-Re- ceiven - Phono Amplifiers - Short Wave answers are correct. 58 lant Adaptors-Electronic Relay,. 50 cots 1. Mercury -vapor rectifiers are used No. 35- AMATEUR RADIO BUILDER'S for their (a) low voltage drop, (b) high GUIDE. For the "ham" who builds his (c) heavy current I'rartical, down -to -earth. Tells you peak inverse voltage, how to Build: A 2 Meter Band Acorn elementary handling. Tube Set -Miniature Communication. Re- radio ceivers -Long Linos Transmitter-Begln- 2. The condenser -input filter is good ner's Transmitter - Preeelector - Rotary servicing for (a) light loads, (b) low output volt- Beam Aerial -Power Supplies. etc. heavy loads. ages, (e) No. 36-RADIO TEST INSTRUMENTS. 3. A swinging choke is used to (a) A MUST for overt' radio man. This latest IA110CIAII 1111511 book on building test equipment Places em- vary the bias, (b) improve voltage reg- phasis. practical Signal Portable d es Meters - 50 uni ulation, (c) handle more current. Bench Multi- checker-- Signal Generators- 4. Condenser -input filter circuits re- Tube ti teckera-Eleclrooio Voltmeters -and quire insulation protection for voltages many Others. (a) equal to d.c. output plus a.c. input, No. 37-ELEMENTARY RADIO BERV ICING. For the radio man who knows (b) 1.41 x d.c. output, (c) 1.41 x a.c. nrApliCer little about servicing. Row to get started, builder's even more Important, how to keep go- input. iradng: Planning the Service Shop-Equlppmg 5. most common method of cou- guide the Shop Syotematic Circuit Checks -Sig- The nal Tracing Methods- Servicing the Midget pling r.f. stages together is (a), resist- -Soldering -Servicing Volume Controls - ance, (b) transformer, (c) capacitance. 110w to Service Speakers. I/111C1Af1 1n1Á11 6. Capacitance within a tube is be- No. 38 -HOW TO BUILD RADIO RE- CEIVERS. This book contains a sufficient tween (a) plate and grid, (b) plate and variety of sets to appeal to every radio fan. grid and cathode. Seems Includes: Short-Wave, Broadcast, Portable, cathode, (e) A.C. Operated, Miniature and Standard 7. The deflector plates in beam -power Receivers. Complete poll- winding data. tubes take the place of (a) control grid, (b) suppressor grid, (e) plate. 8. A supercontrol radio amplifier has the least amplification when (a) the RADIO-CRAFT LIBRARY SERIES grid is most positive, (b) the plate is at the saturation point, (c) the grid is RADCRAFT PUBLICATIONS. Dept. 68 See Your Radio Dealer Supply You. Use Coupon most negative. 25 West Broadway. New York 7, N. Y. If He Can't means (a) Send me the volumes (500 each, postpaid) checked. My radio dealer Is El All 10 9. Selectivity in a receiver Books $5.00 louder signals, (b) sharper tuning, (e) unable to supply. O El 34 grid bias. I imams 8 29 has (a) Your Name 30 35 10. The output transformer (Print Clearly) high primary resistance, (b) step -up Address 31 36 turns ratio, (c) low secondary resist- Dealer's Name 32 37 ance. (See page 82 for an8wer8) Addreu o-33 036 JUNE, 1948 621 Radio-Electronic_ :i.rcuits

SWITCHLESS INTERCOM USING OLD TRANSFORMERS BUZZER A talk- listen switch in this 3 -tube Practically every radio serviceman 1\s.GNO -1 SW ON POL intercom amplifier is not required. The and experimenter has several old power 2 .t -41/4/V2'.506 +T1.511 switch is replaced with a resistor net- transformers that have been saved from 5 MxTAI work which operates like a hybrid coil junked sets. With a few other parts and o y in a telephone repeater. Ordinary audio- a little work, these transformers can be 3 r frequency transformers are used in the put to practical use. 0 1 OO,IPHAaJE hybrid circuit. Potentiometer R is of Two transformers connected as in Fig. 1 can be used to burn metal filings l9- .00d and dust from between variable condenser plates. Be sure to disconnect all wires

to the variable condenser before apply- 15 11.114 16 ing voltage. Position one or two usually supplies enough voltage for this work. 500K Positions three and four may be used 17 10K B 19 20 for finding breaks in power cords and o--yVqr o o ;indb 21 similar jobs. IOOK 22 23 IM 24 Open speaker fields can sometimes be made serviceable again by applying the If it is not already insulated, the high voltage to the defective winding. buzzer should be wrapped in sponge This tends to arc over the break and rubber or cotton enough to absorb all weld the wires together. the sound. ROBERT GUGANNONI, HV SEC 4 Aightstown, N. J. the screw -driver adjustment type. It is (Other parts or values may of course varied until no howl or feedback is be substituted in this instrument if de- heard from either speaker. If 5,000 -ohm sired.- Editor) magnetic speakers are not available, use PM speakers with 5000 -ohm output HV II7VAC SW transformers. ot 9 Further adjustment of the potentiom- SPWITCH 9 eter is not necessary if the leads to the L-p FIL 0 speakers are not varied in length or //NEON 4 other important changes made. Fig. I -How to obtain variable high voltages GEORGE C. RECKENTINE, for various jobs in the radio service shop. 0 *PHONE JACK Fort Wayne, Indiana O6 In Fig. 2, the 6.3- and 5 -volt windings ® ®o are in series with the prim>3ry, thus 9 10 ONE -TUBE REFLEX RECEIVER forming an autotransformer. If the The reflex receiver shown here brings transformer has a tapped primary, sev- a local stations in with good volume. It is eral voltages above and below the line Qo ° built into a cigar box and uses a mere 12 13 14 handful of parts. Q Instead of the conventional coil and 15 16 le tuning condenser, this set uses a coil from a permeability tuner a mov- and 19 20 able iron core to tune it. The different +POT.017 stations are selected by moving the core 0 0 in or out of the coil. The choke L is also 21 22 23 24 a coil from a permeability tuner, but PANEL 5 " WOE -10141614 CASE 3 "DEEP has a fixed iron core. Fig. 2 -A variable -voltage transformer. With PHONO -RADIO CONVERSION an untapped primary, a switch to throw the line from No. Ito 4 will supply below-line voltages. A 3 -tube phonograph amplifier can be readily converted to a combination radio voltage are available for testing. A set phonograph merely by making a few can then be tested under the same condi- circuit changes. The additional parts tions that may be encountered in the TANI .00025 home. (In some areas voltage is higher .00025 B+ 90V than normal, while in other places it is ANT E- 7.59 - A +1.5V lower.) Certain types of "intermittents" in COIL 1 e A -B {H receivers will manifest themselves much

In operation, the signal is amplified faster, too, if the set is tested at a STAI PICKUP by the tube and is rectified by the 1N34 higher-than -normal voltage. crystal diode in the plate circuit. The required are few -an antenna coil and a.f. signal is fed back by the trans- SUBSTITUTE BOX tuning condenser, 2 fixed condensers, a former to the tube where it is further This substitution box can be used for resistor, and a single -pole double -throw amplified. The signal is heard in head- receiver testing and general experi- switch. phones connected between plate and menting. This set has good volume on local screen. If desired, a small PM speaker The buzzer generates a signal for stations. can be connected across the output ter- aligning and testing i.f. and a.f. cir- JOHN ZVERLOFF, minals. cuits. A crystal detector is used for sig- Akron, Ohio ARTHUR S. BEAN, nal tracing in r.f. circuits. All connec- (But probably not too much selectiv- Baltimore, Maryland tions are brought out to pin jacks on the ity. However, such an attachment may (This receiver was tested by RADIO - panel. receive a strong local station -in the CRAFT and was found to bring stations The panel is a 5 x 10 -inch piece of 114- absence of interference -with better in with good volume and medium selec- inch thick plywood, and the plywood box quality than a high -priced superheter- tivity.- Editor) is 3 inches deep. odyne.-Editor) RADIO -CRAFT for Radio-Electronic Circuits

Our 26th Year Quality-Price-Dependability NATIONAL COMPANY COMPONENTS -`-' ATTENTION!! Direct Calibration Dials--51 Drive Ratio t ALL SCR522 ACN -754' W a S' li $3.00 OWNERS ICN W a 5' lE with illuminated scale $6.00 EE Control -7'4' SONS W z 4 7/16' II $3.00 -w for SCR C Brand MCN -8% W a 254' II $2.70 The Nome of RADIO New in Original Park- NPWO Clew Drive 20:1 Ratio: Shaft per- ing: Conslets of 5 push pendicular to Panel with Micrometer t S' button ewltchea. 5Weet- $7.20 y om Electric Pilot \s- PWOGer Drive 20:1 Ratio; Shaft Par YOU MAY BE LOOKING FOR ombllee, with Pilot allot to Panel with Micrometer Ulal 'V$9.00 ITEMS Bulbs and Dimmer, and WE CARRY A COMPLETE LINE OF NATIONAL Fedrral type Seiuli um Bert i lievs. 1e0 511 , each.. 50e lever Switch all finished PARTS i RECEIVERS De Jur W. W. 20.000 Ohm l'ot. 12 watt 49e 4 In Black Crackle. Order ARC -5 (banana Plugs silver plated. per dozen 10e yours Today P1. -259 Coaxial Plugs Sliver Plated. 190 Ea.. per . s tor 100 $1 5.00 only $1.25 ea. APC -25mm( Shyer Plated Air Trimmer ISe 150 Watt, 5 ohm. W. W. Rheostat 4' Diameter $1.95 Antenna Plug 46 -1'S -1 10 for $1.25 for :.2A 15e ea. APC -50mmf Silver Plated Air Trimmer 15e CARDWELL VARIABLE CONDENSERS 40 for $1.25 ET- 27 -AD: 27mmf split stator 15 platee per section .070 Air Gap [Menthe Insulation i4' Shaft $I.29 STEEL CHASSIS 11 per section. 7 x 7 8 2 63c 10 x 14 a 3 5190c Eli- 35 -AD: 35mmf split stator platee x 17 a OIL FILLED CONDENSERS .030 Air Gap Lolanllle Insulation 54' Shaft. $1.05 7 a S 2 73e $1.28 In- 7 a 11 a 2 eOC I Mfd., 750 VDC, Sprague 15e 51P- 2d-GS: 26 mmf -7 plate .070 Air Gap Mycale: a a 17 s 3 51.2? 7 x 13 x 2 7 Mfd., 380VAC. C.E. 98e nation S4' Shaft $1.29 s a 10 x 3 875 13 x 17 x 10 Mfd., 330VAC. (LE $1.25 Nt;V- 150VS: 150mmf 35 plate. .070 Air Gap 5lyealet 3...... 52.22 8 a 14 x 3 93c All Slack Wrinkle Finish 10 Mfd., 600VDC. Capeeitren 96e Insulation i4' Shaft $1.95 16 Mfd., 400VDC. W.E. Co 96e 2050 -AS: 50mmf -21 plate. .030 Air Gap Isolantlle Steel Cana and Coxes 69e Insulation. Screw Driver A .U. 95e 4 : 4 x 2 88c 8 10 a 10 $2.06 2 Mfd. 1000VDC, Aeroroa a 5 a 3 Inc 12xx 7 x $3.66 0.1 Mfd., 7500VDC. 0.E $1.50 s s 8 a 9 51.41 11 x 12 a 8 32.25 2 x 0.1 Mld., 7000VDC, O.E. $2.00 METERS 6 a e a e 95c Is $2.35 I MM., 5000VDC, Solar $2.95 5 -0.5 Amps. D.C. Charge and Discharge Seale Slop, eg 4Ftronl =Meter Case. Cut cor 3 inch Meter. 2 Mfd., 10000VDC, C.D $13.95 63 ' Slot 92< 0t-1 Amp. RF, O.E. 2' Round $2.45 All Slack Wrinkle Finish 100 Amp-6 volt U.C. 3' Scale, 414" Square. Gray lin WIRE ish with shunt. A Swell Buy $2.95 D ynamotor- 5047 -D.C. Input 27 volta (4 1.75 amps. Out- amps. continuous dutY95e No. 10 Copper Enamel 100 Ft. Lengths Each $1.75 0 -100 MA 2' RD $1.95 Put Lengths Each $1.25 5 BrandI o 075 No. 12 (baler Enamel 100 Ft. by New. Input Enamel 100 Ft. Lengths Each 83e DM -43A Dynamotor. Manufactured O.E. No. 14 Copper TUBES At Real Prices 24r Amps. 7500 (RPM; output 515 /1030 / 300 Lead Ileetie covered. 100 ft $1.95 ® 23 Q2 ohm Twin Green Screen. New $1.45 2'8v. 215/260 mllllamps: Shored. Special.. 95 72 ohm Co -Aa Cable To per FY.. 100 ft $6.75 511PI. CR Tube 5' (0 8322A, Dual Beam Power Tetrodo. New $2.15 3 Rubber Covered Cable per Ft 3e Conductor 6i6. 'twin Triple Sllnlature. New 50e Selenium Rectifier Full Rave 68 VAC Input 48VDC 3074, Triode, 100 Watt Power OuOtput. New. ea. f Output .5 Amp. $1.50 35Ó C5-0 IAL RELAY-S.P.o.T. Dual Cou with Armature Pivoted between eollo. All tacts normally upon operates 220 -250 25% with order. balance C.O.D. All prices WIRE WOUND volts.8000 ohmseach con contacta Rated 2 amps If not rated 110VAC. Ideally suited F.O.B. our warehouse New York. No order under $2.00. for balanced or bridge typa POTENTIOMETER circuits where limited r- We ship to any part of the globe 100.000 ohm, precision made. avaÌlable. Foi only.. 95C G. R. typo. 25 watt. diameter. Brand new ' $1.95 O.E. 2500 Ohm Relay_ LEEDS RADIO CO. 5.P.S.T. 111A D.C.. 5 prong Heineman Circuit Breakers. PluE In type. hermetically sealed. 75 Vevey Street Dept. RC6 oleos 95c 95cBrand New COrtlandt 7 -2612 New York City 7

117 VOLTS ON AUTO RADIO Auto radios may be tested by this power supply without the use of a storage battery. A 6X5 rectifier tube and a 6.3 -volt filament transformer are used to supply B -plus voltage to the set. In operation, the rectifier tube and vibrator are removed from the receiver under teat. The cathode of the 6X5 is connected to the input of the d.c. filter in the receiver. The positive battery lead and a lead from the chassis are connected directly to the transformer Philip Rand started a new trend to secondary with the two short leads real, badly- needed receiver -selectivity shown. This provides filament voltage with his Q -5er. Byron Goodman carried for the tubes. This will, of course, be an it forward with his "Lazy -Man's Q- 5er ". a.c. voltage; since auto sets are designed We applaud both steps, but felt that filament voltage, the test supply even more could be attained by special for d.c. give every ham super -het, new or old, the "New Look" may introduce some hum, but for check- design to really will not be selectivity QST advocates. ing purposes this usually Our answer is Model 805, 100kc. I.F. Amplifier. Connect it between your important. last i.f. secondary and your audio volume control and you get a small boost in gain. But what you really get is single -side -band selectivity -a selectivity 5 6X5 curve 2.4kc. wide across the flat top, skirts falling so steeply as to be only 4.7kc. broad 1000 times (60 db.) down, only 7.2kc. wide 10,000 times down! As Byron Goodman says of this new look selectivity, it will "cut thru the TO DC FILTER ON QRM and pull out the desired signal like nothing you ever saw or heard ". RECEIVER Take Model 805, only 3 7/8" wide, 4 15/16" long, 5 5/8" high, make 6 simple 117V AC connections to your 455/465 kc. i.f. receiver, (which can usually supply 6.3 V. ac. at .75 Amps. and 110 to 250 volts d.c. at 25 ma. to the 805) and you TO CNA SIS OF RCVS have that post -war receiver with the "new look" Model 805 Price, less 1 - 6 BE6, 1 - 6 BA6, 1 - 6C4 tubes, only 518.90 Test the vibrator before removing it, Model 805K - kit complete less tubes, $15.90' by attaching the two 6 -volt a.c. leads *Prices slightly higher West of Radars. battery -leads of to the filament -or Send for Catalog the radio. If the vibrator purrs, it is OVER 37 YEARS OF RADIO ENGINEERING ACHIEVEMENT trouble may be See these and other. probably O.K. If not, the McMurdo Silver in it. LCETI instruments at. -712`774441d-c.574e,c,. 1740 MAIN ST HARTFORD 3 COBB' A. P. NIELSON, your favorite jobber. EXECUTIVE OFFICES Seattle, Wash. FACTOR., OFFICE 1749 MAIN 5T.. HARTFORD 3 CONN JUNE. 1948 641 New Patents HIGH -VOLTAGE REGULATION resonant circuit tuned slightly off that of the parallel circuit. This gives a maximum change of George C. Sziklai and Robert R. Thalner, impedance between the two frequencies. Princeton, N. J. As an example of size, a 1 -mc vibrator has the (Assigned to Radio Corp. of America) following dimensions; outer and inner diameters Patent No. 2,435,414 are respectively .267 and .25 inch, and thickness .01 inch. The material may be aluminum or 30,000 Many high -voltage supplies for television are molybdenum, and the Q is higher than 5,000. now derived from sweep circuits. Saw -tooth The magnetic field has a strength of about 10.000 pulses are amplified and rectified to produce the gauss. RADIO SERVICE - d.c. Unfortunately, regulation is not too good with this method. This patented invention uses a pentode instead of a diode for the rectifier. Good REMOTE TECHNICIANS READ regulation is obtained because the plate- current OPERATION OF characteristic of a pentode is a horizontal line MOTORS when control and screen grid voltages are con- Richard G. Clapp, Haverford, Pa. stant. (Assigned to Philco Corp.) Patent No. 2,435,423 Suitable' for driving small clocks or other motors by microwave power transmitted from a distance, this system is especially useful for operating small synchronous motors which may require an accurately controlled frequency but which are not located near a 60 -cycle line.

PULSE XMITTER SYNC MOTOR The triode shown is the saw -tooth voltage amplifier. The high -voltage pulses appear between plate and cathode of the pentode, and rectified - current flows through the filter A to the output XMITTER ANT RCVR NIT terminals. The screen grid voltage is kept constant because it comes from the d.c. plate supply, A magnetron or other pulse -type transmitter, as shown. The control grid bias is derived from operated directly from the a.c. line. radiates 60 the voltage drop across B. Two d.c. currents flow pulses of high -frequency power per second. These in opposite directions through R. One is supplied pulses are picked up, detected by a crystal X, by the B -power supply; the other is rectified and shock- excite a resonant circuit tuned to 60 current from the pentode. The grid bias may be cycles. The nearly sinusoidal oscillations are am- adjusted originally at the potentiometer. plified and can be used to operate a clock or The output voltage tends to fluctuate with other motor. changing loads and potentials. When it rises, the pentode grid becomes more negative, causing plate current to drop. When reduced, it causes IMPROVED PENTODE TUBE higher current. plate Therefore the output volt- Robert Adler, Chicago, Ill., and age is compensated. John G. Prentiss, Berwyn, Ill. (Assigned to Zenith Radio Corp.) EVERY MONTH Patent No. 2,426,681 This RADIO new type of pentode makes possible very MAINTENANCE today fills a breach that QUARTZ CRYSTAL high amplification in a single tube. has existed in the radio field for a long time. Al- SUBSTITUTE, The area of ready 30,000 servicemen read RADIO MAINTE- Robert Adler, Chicago, Ill. the plate is smaller than that of the third grid. NANCE every is This grid is also closely wound. The remaining month because it devoted en- (Assigned to Zenith Radio tirely to the Radio Service Technician. Corp.) elements are roughly similar to those in the The RADIO MAINTENANCE staff specializes in Patent No. 2,435,487 usual pentode tube. the preparation of articles on every phase of Quartz crystals are important in many types Radio Maintenance in series form which may be of communication f- filed and used for reference. The circuits. However, the raw leading articles material is cover everything for the radio serviceman on not abundant and must be carefully Television, FM and AM; Test Equipment; Elec- chosen to avoid even minute flaws. In addition tronic Appliances; Tools; Antennas Alignment; it is difficult to cut to the required shape and Troubleshooting; Repair; Construction; Pick -ups size, thus adding to the cost of the finished crys- and Sound Amplification and Reproduction tal. The mechanical substitute for a quartz crys- Equipment. Also, in RADIO MAINTENANCE tal described here is suitable for use at fre- each month there are departments on hints and quencies from about 260 kc S kinks, the latest news of the trade, review of to roc. trade literature, radiomen's opinions, new prod- The principle of operation is shown in A. ucts and news from the organizations. All articles A coil or loop and a washer- shaped metal disc With this construction the third grid can con- are presented in a step -by -step precision style, are placed in a magnetic field. The loop is sup- trol the plate current, becoming a control grid. clearly illustrated with schematics, accurate plied with current from an external source and In addition it controls the screen current. This photographs, specially prepared drawings, white induces a secondary current in the washer. Ar- is because the total cathode current remains ap- on black charts, color diagrams, isometric pro- rows show the directions of jections and exploded views. these currents at a proximately constant for a given control grid particular instant. The washer current is ac- potential. Therefore any plate current variation RADIO MAINTENANCE is not sold companied by its own magnetic field. is accompanied by a corresponding and opposite on newsstands The reaction of both fields on the washer variation of screen Current. The Binders in beautiful green simulated leather causes it to vibrate, as shown by the four ar- new tube may be connected as shown in stamped in gold are now available for your rows. When the loop current reverses, so does the schematic. The screen circuit contains a load RADIO MAINTENANCE magazines - see the the force on the washer. Actually, the loop is across which amplified voltage is developed. This current issue of RADIO MAINTENANCE for supplied from a high- frequency source and the voltage is transferred to the third grid which information. washer element vibrates at the same rate. There controls plate current. The output voltage exists is some frequency at which maximum vibrations across the plate load. In effect this tube is RADIO MAINTENANCE MAGAZINE RC6 are obtained, depending upon dimensions of the connected as two triodes in cascade. 460 Bloomfield Avenue, washer. 1 Montclair 5, N. J. There is aleo a regenerative effect in the new Please send me RADIO MAINTENANCE for tube. As described previously, a more negative I year at 53.00 Bill me later third grid reduces plate current and therefore C increases screen current. This reduces the screen 2 years at Payment enclosed n $5.00 o voltage. Since the screen potential is coupled Name to the third grid through the condenser. the original potential of the third grid is intensi- Address fied. With suitable design regeneration is present without sustained oscillations, City-State An output of several volts may be obtained when the input is in 'Occupation the order of millivolts.

Title ) Employed by a b I----- CIRCULAR SWEEP CONTROL Alden Packard, Kanmore, N. Because of the mutual reaction between the Y. Independent Serviceman - Dealer Serviceman - (Assigned to Colonial Radio Corp.) Service Manager -Dealer -Distributor Jobber. loop circuit and the vibrating element. a high - value of impedance is reflected into the loop cir- Patent No. 2,436,447 cuit. The entire mechanical unit is equivalent to This invention may be used with a circular the electrical network at B. There is a parallel - sweep oscilloscope in radar detection and for resonant circuit in series with a resistor and an measurements of rotating machinery. In a radar inductance. The inductance may be resonated with installation, for example, a saw -tooth current an external capacitance C to produce a series- flows through deflecting coils and causes the RADIO -CRAFT for «r..»...;

New Patents 165 electron beam to move at a constant rate away from the center of the screen and then to be returned abruptly. The deflecting coils rotate fe-SweetesrMusie continuously around the 'scope tube so that the radial path of the beam also rotates and scans the entire surface. A bright spot on the pattern shows the location of an object within the field of the transmitter. RENDING OERECTING COLS of_ (WONG TABE Heaven e from this NEW, IMPROVED

Y C rB+ MAGNETIC

VARIABLE FOR SIMULTANEOUS CONTROL OF AMPLUTIl0E ANO ZERO POSITION OF BEAN

} To expand the pattern on the screen for closer PHONO PICK -UP study requires that the saw -tooth current be in- H I G H F I D E L I T Y creased. The deflection current is actually composed of two parta: the amplified saw -tooth current and the average or static plate current. If only the first component is increased (by greater amplification), the beam will travel out further but will also be returned to a point beyond the center of the pattern. This is because the center point of the radial path is determined by the average or static plate current which has 'not been changed. In the circuit shown, resistor It controls negative feedback and tube amplification. At the same time it adjusts the average value of grid bias. The resistors in the cathode and screen -grid circuit and resistor S are determined by experiment. Design is correct when the d.c. plate current changes in the same ratio as the amplification. when R is varied.

THYRATRON REGULATOR Donald R. Gibbons, Belmar and Harry L. Chaney, Red Bank, N. J. (May be used by the U. S. Government without royalty payment) Patent No. 2,435,961 $ Profit and Exquisite A thyratron may be used as a regulator tube for very high currents. The regulator circuit is shown in the figure. An upper transformer wind- Record Reproduction... ing has an R -C network to displace the thyratron grid voltage compared to the plate voltage. JOBBERS SERVICEMEN turn service calls into The lower winding supplies high voltage to the ...... thyratron plate and the plate of a tetrode through profitable sales with ease. This new LEAR Reluctance Pick - a diode rectifier. The tetrode voltages are stabilized by VR tubes. Up transforms "flat" old- fashioned sound into full -toned Rectified output from the thyratron is filtered and appears at the output terminals. Some of this modern reproduction! voltage is fed to the screen -grid of the tetrode This new, Improved High- Fidelity Reluctance Pick -Up is LEAR engi- through an adjustable resistor S. If the output voltage should drop, the screen grid becomes less neered to excel in quality of performance ... and priced for positive and less current flows through T. The thyratron grid potential becomes more positive your profit. Replaces millions of old style crystal pick -ups than before, and the tube conducts earlier each now in use! Jewel stylus eliminates needle changing holds cycle to compensate for the reduction in output - voltage. surface noise to a bare minimum. It performs a miracle of The advantages of the thyratron in this circuit are low voltage drop and high current -carry- modernization - assures full tonal beauty of sound wherever ing capacity. In addition the control is gradual. a characteristic usually associated only with installed. vacuum tubes. List this "hot" seller in your catalog! Service men who feature the THYRATRON new LEAR Magnetic Pick -up will pick up extra profits every -in now for price list AC LINE day! Cash -write complete discount today! To complete your LEAR Sound Service: i New, Improved LEAR PRE - AMPLIFIER, List Price -$9.90 To provide additional amplification with use of MP -103 LEAR Magnetic Pick -up. Can be connected directly to old crystal cartridge input. High voltage and filament wires provided for connection into existing equipment. Two -position switch permits high -fidelity response to finest quality recordings. Power rectifier (top) No. PA -103 (not shown here) -LEAR Tone Arm Assembly is stabilized by the with MP -103 Magnetic Variable Reluctance Pick-Up Car- combination of a di- tridge, List Price $15.50. ode rectifier, a tetrode and two voltage - Designed for high -fidelity reproduction of 10' and I2'recor- regulator tubes. Tet- dings. Spring counter-balance provides "feather touch" 17 grams stylus pressure on record. This rode plate and grid - operation -only voltages, rise and fall reduces record wear to a minimum. Handsomely finished with a.c. and output in brown metallic. voltage, varying the factory Representatives-Distributors: A fete choice current through T and territories are still available for these and other thereby causing thyra- fine LEAR Electronic Products. Write today tron voltage grid vari- giving details. ations that will coun- full 110 Ionia Ave. N. W. Grand Rapids 2, Mich. teract the change. JUNE, 1 1948 6 I question Box

LOOP ANTENNA and a small battery- powered amplifier. A. This multimeter circuit should meet I would like to have a diagram of I wish to attenuate all frequencies above your needs. All parts values are shown. a highly directional loop antenna for 100 c.p.a. when desirable. N.A.R., The accuracy of the'meter will depend use on the broadcast band. The response Pittsburgh, Pa. on the accuracy of the shunts and mul- should be maximum in one direction in- tipliers. The 150 -ohm resistor across the stead of front and back as in the usual A. The amplifier in the diagram will output of the a.c. rectifier should be ad- give sufficient type.-E.V.P., Ordnance, Ore. gain and output under justed to draw 1 ma. The 1,400-ohm normal conditions. Should greater gain resistor in the direct current line may A. Here are circuits of two directional be needed, a CK510AX could be substi- be made variable to compensate for any loop antennas. In circuit A, the loop is tuted for the first CK512AX with a 25% inaccuracies in measuring the internal used as a sensing antenna as well as a increase in A- battery drain. If less resistance of the meter. directional loop. For best unidirectional power output is permissible, a CK522- effect, throw S1 to "balance" and adjust AX could be used in place of the CK506- C until the signal has equal intensity AX. 3 -3001( IN SERI ES 2-2.SMEGINSERIES each side of null position. After the .. 9001 2001A/600n .,o RECORDING IXVO. .. INV ` loop is balanced, throw Si to "sense" ., AMPLIFIER 2 225N 2w SMEG 4 Please print a diagram of a re- IN SER. 5 450K and rotate the loop for maximum signal. `500Vo.A0.j - cording amplifier using a 6SJ7, 6SQ7, 11eo500V IW 2.514EG 161 1.17, CLOSE WOUND ON 24' FRAME and a 6L6. I want to use a 10 -nui d.c. Ac« 250VOIMr. -d1Mro250V meter for indicating recording levels if ACV AT 1 DCV Al DCV 1.25MEG possible. The recording head is the IRa /V 90K .00035-.0005 LI IA 4- OHMS SNn/V ohm magnetic type. S.K., Honolulu, 100Vo3111/ 1NMo 100V ÇL TO RECEIVER - CURR. 500K MEN T.H. 4511 0000 50VoMA, AA ARAM 50V 9 -160,. f SDuul A. Input circuits for a microphone and IPST 25011 914 SW SI . SENSE a playback pickup are provided in this 10VOJ. .. L2 BALANCE KM}ISÓ .00035-.0005 recording amplifier. Monitor phones can COM be used when recording. The recording Ckt. A- Simple direction finding loop input. level meter is used with a full -wave 10- SMA + METER RECT o200NA SEN E ANT or 15 -ma meter rectifier. Shield grid and ,r--51.01 IN SHIELD plate leads to the 6SN7 input. 11.41( - oIMA ADJ HST M I7 CLOSEWOUNO ON 24. FRAME 150ZERO 450 SEE TEXT FOR 11,13,14 MULTIMETER ZOMA I CI -.0003510.0005 I have a 200 -microampere d.c. meter 40 ,DC ' 1 SHIELD with a 600-ohm internal resistance. I RX1 22.6/2W SOMA CURR. would like to use this as the basis for a o 4AFI, RCVR INPUT TUBE multimeter with a.c. and d.c. voltage A X IO 227/.5W a o RAN ranges to 1,000 1 2501A volts, d.c. to ampere. t 9X10 2.5K 1.5 The meter has a resistance scale cali- 11,41 SW TUNING COND IN RCVR I.A brated up to 2,000 ohms. I would like to o .5 use this and have additional scales to OHMS±IIII 4.sv o CON AVC read up to 2 megohms.- K.L.L., Bloom- - ington, Ind. Multimeter with a 200 -microampere movement. Ckt. B-An improved direction -finder circuit. CK512AX C 512 AX CK 506 AX Circuit B is similar, except that the 5,000 -ohm potentiometer is adjusted for best phase conditions. It has the advan- MINE IN .0 GAIN 30KO tage that the loop is shielded and the OUT.PLUG length of the vertical antenna, which .0001 PRI. IMP r XTAïT°1 must be used in this circuit, can be '.1 adjusted for optimum signal strength. MAG The signal from the vertical antenna CI' 502AX 61I GND J through the potentiometer and L2 CK 512 AY 54321 RED DOT should be equal to, but not greater than, 60011 - . DPST SW OUT PU1 FOR EITHER MAG.OR X7AL UNIT the signal from the loop. -Ali- CORDS 150V t LSV A - .MOFF 22.5 -45V B - The parts list for both units is: An electronic stethoscope which uses three of the subminiature hearing -aid type tubes. Ll- Approximately 1 millihenry. Can be winding from i.f. transformer. 6SJ7 6SN7 L1A -Wound to match receiver input. L2- Approximately 240 microhenries. 250n Can be secondary of standard r.f. coil 6 IMEG with turns added or removed. 1M. 4 fr L3 -250 to 500 microhenries, closely 5 a 4W. NORMAL - coupled to Ll. 6.5W. MAX L4- Inductance to match other tuned 25 50V MAG. CUTTER coils in receiver. Loosely coupled to f-- X 6/450v 12N/2W ' t270V Ll or coupled for best signal transfer. K 1M C- Differential -type variable capacitor, approximately 50 -µµf. Cardwell type PHONO IN .05/400v ei`é/90MA ER-60 -AB may be used. 5Y /2A ON-OFF SW ® ELECTRONIC STETHOSCOPE ZF 117VAC --105i600V Z. 325V90M I am a physician and my hearing is T^ 325V impaired to the extent that I have g1 2 1 eo trouble hearing heart sounds (J5 to 60 PHONO ON-0FF 10MA DC 6.3V/3A P L FILS c.p.s.) with an acoustic stethoscope. I RECOR.LEVEL INDICATOR want to build an electronic instrument using a lapel-type crystal microphone This medium-power recording amplifier uses a 10- milliampere meter as level indicator. RADIO -CRAFT fog . Try This One-- I67 BASS COMPENSATION A small iron -cored coil in the voice - coil leads of a speaker provides a very effective form of bass compensation. The ntroduces... inductive reactance of the coil increases with the frequency, thus decreasing voice -coil current at high frequencies while passing lower notes. P. C. DIMITZACOPOULOS, St. Johns, P. Q., Canada (The inductance may consist of a small filter choke, iron -cored r.f. choke, Unexcelled in Performance Remarkably Low in Cost or other inductance having values between 100 mh and 5 henries. Experi- Designed to satisfy the most critical profes- ment with different values for best re- sional or amateur, the Collins "Super 20" sults.-Editor) offers unsurpassed value in an FM RECEIVER. The advanced 20 -Tube circuit features: Arm- strong FM, built -in stabilized power supply SPEAKER CLEANING KINK and audio amplifier capable of 10 -watt out- To remove bits of iron or steel from put; new 6AL7GT tuning eye, connections for between the pole and voice coil of a 2 types of phono pick -up, output imped- loudspeaker, insert a screwdriver into a ances to match 4 to 20 ohm voice coils and coil of insulated wire and energize the 500 ohm line, and variable bass and treble e coil with d.c. to make a powerful electro- tone controls with attenuation and boost for magnet. Keeping it in the magnetic Write Today for Complete Details upper and lower registers. field, run the end of the screw -driver all around the space between the pole and the voice coil while moving the one COLLINS Audio Products Co., Inc. forth. This will remove n.ag- back and P. O. BOX 368 WESTFIELD, N. J. WE. 2 -4390 netic material. E. S. COLEMAN, Dallas, Texas ASTATIC MIKE -k ,,, TURNER MIKE i SHURE Here's s HOT ¡ High quality crystal / ' 14' ^\ T1 %B value for YOU! hand -mike, midirec- PICKUP ARM MOUNT \` High quality crys- ` tional, wide range Here is a quick way to substitute Push Button tal mike. Can be response. One -piece ñ used ; ; L' Carbon Mlke either as = °!a responuetion. 2s/s' phono pickups on a record player. % hand mike or desk _ I diem. by 1'/z' thick. Remove the hinge at the end of the C mike. With Stand. Complete with at- 88 Base and 7 ft. tached 100 -ft shielded mike pickup arm and replace it with a phone ie. Cable. cable. A truly wonderful buy, plug. Mount a phone jack in the base of With Cord , for only the pickup arm swivel. The exact mount- and Plug 75 SPECIAL i7 ing varies with the different types of arms. GENERAL INDUSTRIES DETROLA UNIT AUTOMATIC To change pickups, merely remove HOME RECORDING RECORD another. VALUE elegemed _?'-gyp one and plug in 639.95 7 /1 CHANGER ALBERT THOMAS, JR. -, Plays 12 $19.95 - - Inch records Cleveland, Ohio i automatically. Crystal pickup. ii A low priced Special 7-___::-_ ' recording and - plybk unit - -- toatutrrecords $14.49 \ i - \ / CLEANING RADIOS on to 10 & 12 inch records. Consists of iO' turntable. of crystal pickup base plate 15 WEBSTER I attach a rubber hose to the outle; frand front RECORD CHANGERS "1' records. a vacuum cleaner and use the air b:ast Model #156 Plays 12 -Ten or 10- Twelve Inch TUBE PHONO AUTOMATIC STOP CRYSTAL PICKUP to blow out the dust from cabinets, 2 Reg. - with G.E. sections of OSCILLATOR MM speakers, chassis; and other el5pickup : dmpr mnyliter0 $LY9rJJ using Complete with tubes. ostra. radios. This is more effective than 35Z5. 12SK7. Use with a cloth or a brush. record player, and tune 0 section telescopic aerial any radio. 100 Asst. Resisters. IRC. etc. f1.79$1.79 The air blast also removes many in n,, 1 Wired. noises can- 25% Deposit. Bal. C.O.D. Plus Charge. scratching and hissing that $4.75 Write for Latest Catalog not be found easily. 3 Tube PHONO AMPLIFIER Volume $4.95 a. FLOYD STORY, and tone control. ALL WIRED with Tubes. $4.95 BONAFIDE RADIO CO. Pick UO with O.I. $4.95 St.,Dept. K, N.Y.7,N.Y. Springfield, Il!. motor 89 IA Cortlandt

HIDDEN ANTENNA RADIO PANEL LABELS Many modern homes have metal -li Ted Commercial -looking letters for your THESE VALUES be easily made. The materials COMPARE laundry chutes running from the upper radio can NATIONALLY KNOWN BRANDS floors to the basement. These make ex- needed are: clear speaker cement, an INDIVIDUALLY BOXED indelible pencil, and a small slab of 024 88 12AT6 59 cellent antennas. The lead -in can be .sol- IT4 88 12BA6 69 dered to the metal lining and brou smooth unglazed porcelain about 2 x 2 x 1R6 88 12ßE6 69 inches. 185 68 128A7 69 the room through a hole drilled into 1/4 384 88 125K7 69 the side of the chute close to the wall of Print the letters on the porcelain slab 3Q4 88 12SQ7 59 with the pencil. Then apply a thin coat- 5Y3GT 42 35B5 69 the room. In most cases, the lead -in can 6X5GT 59 35L6GT 69 it along the ing of cement to the letters with a soft 6K6GT 59 35W4 49 be concealed by running 49 brush, allowing it to dry for about 1/z 6V6GT 69 35Z5GT baseboard molding, or possibly under a 25Z6GT 69 50B5 69 carpet. hour. After it has dried, peel off the 25L6GT 69 50L6GT 69 should be made cement, trim the edges, and glue it to DEDUCT 10% IN LOTS OF 50 OR MORE A preliminary check Bargain Bulletin with an ohmmeter to make sure the the equipment with transparent glue, Write for Free Illustrated chute is not grounded. such as Duco cement. JOYCE RADIO DISTRIBUTING HOLLYWOOD 28. CALIF HOWARD A. MILLER W2WLl STANLEY J. ZUCHORA, BOX 2068 Rochester, N, Y Detroit, Mich. JUNE, 1948 Foreign News 681 Report From Britain By Major Ralph W. Hallows RADIO -CRAFT EUROPEAN CORRESPONDENT

truck contains the mixer, which allows are line grids corresponding to a fre- either of the two cameras carried to be quency of 1.0 me for checking uniform- faded in or out as required. Each cam- ity of focus over the whole screen. The era has a battery of lenses of different pattern is completed by a broad black focal lengths in a turret. When either of horizontal bar on a white background the turrets is being rotated, its camera above the circle and by a narrow white is automatically cut out and the other bar on a black ground and a narrow automatically cut in, to avoid all chance black bar on a white ground, one on SOMETIME ago I of one particularly annoying effect. The each side of it. The scan width of these wrote that it apparatus must be amazingly robust, narrow bars is about 0.25 microsecond. w a s strange for its journeys were made in winter You can guess what a boon these pat- that there time. I know the countries visited -and terns are, not only to engineers who should be so little their roads. There is nothing wrong design televisers, but also to service- interest in tele- with complicated electronic equipment men and to televiewers who know some- vision in France. which can be unpacked, erected, tested thing about the works of their receivers. By that I meant interest amongst tele- and be in full working order within five viewers and potential televiewers; for hours of its arrival at Oslo, Norway. The component show French technicians are most actively The images are said to be of as It would have been surprising, if I concerned with this branch of radio. good quality as those of the movies. may so put it, had there been anything What must be one of the most advanced With an 819 -line definition and the 10 new about the show recently held in me bandwidth, I can well believe this. London by the British Radio Component I don't know, though, that I'd care to Manufacturers. We learnt during the swap jobs with the designer called upon war anything that we didn't already to produce at a popular price, 819 -line know about making compact, robust, televisers able to do justice to a 10-mc fully tropicalised components. Progress transmitted bandwidth! then was -and still is-chiefly in the di- Keeping them on their toes rection of ruggedness, standardization of performance and miniaturization. I'd like to see what the new French What one expected was exactly what gear would make of the latest test pat- one did find -a wide range of small, tern (Fig. 1), transmitted for an hour well -made and sturdy bits and pieces, each morning by the BBC's television often backed by performance certificates system. It was designed jointly by the from the National Physical Laboratory, BBC, and the British television manu- which corresponds in many ways to the facturers to show up almost any fault American Bureau of Standards. Two Fig. I -BBC's new television test pattern. you can think of in a televiser. The points, though, specially impressed me. background of the pattern is a mesh of The first was the ingenious ways in outfits in the world -if, not the most black squares separated by narrow which certain severe shortages in raw advanced-is the French mobile demon- white lines. In the middle is a white materials -steel is one of the most stration equipment, which has been circle containing two vertical grids of acute -were overcome by the ingenious making a tour of Switzerland, Belgium, black and white lines, arranged in use of substitutes. Secondly, I welcome Holland and Scandinavia. The system blocks corresponding to frequencies of the realization by component designers has an 819-line scan coupled with a 1.0, 1.5, 2.0, 2.5 and 3.0 mc. The circle that any separate part of a radio or transmitted band -width of 10 mc. also contains a vertical bar, composed television receiver should be so con- The outfit is housed in a small fleet of five squares graded in tone values structed that it is easily mounted, con- of trucks. One of these contains the 50- from white through two shades of grey nected, and checked, not only in the fac- watt 200-mc transmitter. The same to black. At the corners of the pattern tory, but also in the serviceman's shop. In the bad old days of the past far too many components seemed to have been designed with a view to making things as difficult as possible for all who had to handle them. Two highlights Two of the many good exhibits struck me as being well in the brain -wave class. The first of these is a kit for determin- ing the temperature of soldering iron bits in the quickest and simplest way. Books and articles on soldering have a way of recommending a bit temperature of so many degrees centigrade, but don't tell how to measure it without a pyro- meter, which is a pretty unlikely piece of equipment in the amateur's work- shop. The kit consists of a number of cards, each containing a length of special wire which melts at a stated temperature. Simple, as many good things Easily- serviced British radio which 'opens like a flower" on release of a single bolt. are, but very useful! RADIOCRAFf ;o- I I,

Construction 4 169 MODERN CRYSTAL RECEIVER By W. V. NUTALL / Better Products for the Radio Industry A1N34 germanium crystal diode and parts of a permeability -tuned i.f. 1 transformer are used in this efficient NEW G -C crystal set. It is simple to con: truct STATIC CHASER NEW G -C and has good volume and selectivity. INJECTOR and POWDER TUBE PULLER Unlike most crystal sets, the primary Tire static coil instead of secondary powder kits Makes it easy to remove or In- the is tined. -improve sert miniature tubes . simple The tuned antenna circuit is an impor- auto radio fo operate. Inserts or extracts reception. tubes where fingers will not tant feature of this receiver becat.se it Eliminates reach-into hard -to-reach provides a much greater signal strength wheel static Inter- places. Saves time and at the headphones ference. New pow- money. Ends tube break- than if the secordary der is blown into age, prevents burnt fingers. were tuned. all the inner tubes-easy to use. For No. 5093 -Miniature Puller List 1.65 every car owner! S To construct the receiver, take No. 5093 -D Display of 12 List tl:e i.f. No. 5604- Injector for G-C Static $19.90 transformer apart and unwind the sec- Powder List $1.50 ondary coil until it is about 70% the No. 5605-G-C Static Powder Packet for 5 tires List $1.00 size of the primary winding. Remove the No. 5606 -Kit-One Powder Packet and NEW G Injector -C FIELD iron slug from the secondary List $2.50 core, cut CHASS EZ the coil mounting board in two, and NEW G -C mount each part as shown in the draw- MINIATURE Holds almost any radio ing. chassis in position! Has Warm the wax holding the coils special sible hooks TUBE PIN for flanged type chassis PAT. PEN0. STRAIGHTENER or, to tilt chassis back if necessary. Made with slide adlustment -fakes only 5 seconds to In- Eve Radio Man needs a tube pin stall. No parts to lose -will wear out. A straielhtener for the new miniature real convenience for the radio serviceman! glass tubes. Each man should have 2 No. 5207 Chess E: List $3.65 or 3 -one to carry with him and several fastened to his bench. No. 5191 List $1.00 are G -C Products at leading Have you seen the new G -C ava iloble Write for Speedex Wire Strippers ... write distributors. for illustrated literature. Of our new your'COPY catalog_ RADIO DIVISION DEPT. D illustrated

GENERAL CEMENT Mfg. (o., Rockford, III., U.S.A. Manufacturers of over 3,000 products Soles offices in pri,,c)pol rill.,

.S0o035-.0005 to the forms with the heat from the soldering iron (carefully), and move the coils up flush with the ends of the forms. The wiring is straightforward. One Slg^Uf loreceivN lead of 13y approach the 1N34 crystal is soldered to rV1Ci h9 Speed a to Ire Dynamic fM one of the secondary coil terminals 1Lnd Modern, ent problems, -S-S -S tells HOW in the other lead is fastened The Simple, adjustmenty - directly to the ment and to learn simple, direct language. phone OI'sgn complex jack. Make sure that the rotor of Nothing to Purchase equipment New 9th edition now off the press. the condenser is connected to ground to No _ non-obsolescent 100 pages of valuable information. prevent detuning due to Universal Basic Tesl body caps.ci- only tance. Employs Available iron all leading rodio ports and Selectivity is determined by the pcsi- equipment distributors or directly from factory tion of the iron slug in the primary cir- at only 40c per copy. cuit and by the coupling between the ^RECISION APPARATUS COMPANY, Inc. 92 -27 Horace Harding Blue., Elmhurst 4, N. Y. primary and secondary coils. The sac - ondary coil is moved back and forth, to make this adjustment, by turning the wing nut. PEN -OSCIL TELEVISION RECEIVER -$1.00 Antenna is -LITE length not critical, but it mo tetest oscillator ffor .0 Complete instructions for building your own television is an important the evict t ; alignmentintt Self ruminer. 16 pages- 11x17' of picture., pictorial dia- part of receiver P owered from grams. clarified schematic., 17 -.2r complete schematic 000 Yellen uu h.f. Outputfrom tw a to 125 diagram chassis layout. Also booklet of alignment is worth a little extra effort. Maxim. m l .t u.ed by Signal Corp. e Writ. for ilownformation. Instructions, voltage a: resistance tables and trouble- signal strength is obtained along :ts shorting hints.-All for $1.00. GENERAL TEST EQUIPMENT length, so pointing it toward a more d: s- CERTIFIED TELEVISION LABORATORIES 38 Argyle Ave. Buffalo 9, N. Y. tant station will bring in the staticn. Dept. C, 5507 -13th Ave., Brooklyn 19. N. Y. Placing it at right angles to a strong local transmitter permits weak signals to be heard more clearly. With a 50 -foDt JUST OPENED! antenna and with a steam pipe for a RADIO -CRAFT needs more photos of New FEDERATED Branch ground, at least 10 stations from 200 o service shops and service benches. We ALLENTOWN, PA. With completely stocked a tn,use and .bowroom., 400 miles away have been clearly will pay $6.00 for each 6x8- or 8x10 -inch featuring all andato brands In Radio. Electronic heard. Parts. A Equipment. IF YOU'RE AROUND -DROP An average of three more-distant sta- glossy photo accepted. Do not "dress up" IN AND SAY HE.1.1.01 your bench, st tions are heard four or five nights a but take a bone -fide photo, FEDERATED PURCHASER Inc.,icl;;;ems 1fes week the year round. preferably with men working. PHONE: Allentown 3 -7ee1 JUNE, 1948 701 'l`w I evices

FM GENERATOR HI- FREQUENCY TUNER TELE SYNCHRONIZER TUNING CONDENSERS Radio Corporation of America Allen B. Dumont Laboratories, Inc. Allen B. Dumont Laboratories E. F. Johnson Company Camden, N. J. Passaic, N. J. Clifton. N. J. Waseca, Minn. are WR -53A is an FM signal gen- Continuously variable frequency cov- Type 5030 A is a portable television These new air variable condensers Model the ever built commercially. erator providing output on the 88-108- erage from 44 to 216 mc without band synchronizing generator especially built smallest switching is provided by the new Type for field use. It provides mixed driving, They are available in three models: 7047 Inpatuner. It is designed for re- single, differential, and butterfly types, ception of FM AM, and television in and four different capacitances. all services within this range, using the The single type is an adjustable pad- Mallory Ware Inductuner as a tuning der for trimming r.f., i.f. and oscillator unit. The tuning unit comprises three Circuits. It is available in 1.55 to 5.14µµf, tuned circuits; grounded -grid input, 1.73 to 8.69 µµf 2.15 to 14.58 µµf, and and oscillator. Over -all gain is 2.6 to 19,7 µµf. mixer, type approximately 15. I.f., ratio is about The differential switches capac- 1,000, and image suppression is in the ¡tance from rotor to either of two sta- order of 100. Input impedance is 73 tors, and also shifts the tap on a capac- ohms. itance divider. Capacitances are 1.84 to Three -hole mounting simplifies instal. 5.58 µµf, 1.98 to 9.30 µµf, 2.32 to 14.82 and 2.67 19.30 or un- µµf, to µµf. me FM band, either modulated The butterfly type is used wherever It generates an FM modulated. also a small split -stator condenser is re- on the 8.3- 10.8 -mc band for i.f. signal quired. Four models include 1.72 to alignment. The sweep width is vari- to different requirements 330 µµf, 2.10 to 5.27 µut, 2.72 to 8.50 able suit blanking, and synchronizing signals for µµf, and 3.20 to 11.02 µµf. for wide -band reception. transmitter testing, television develop- Features include: single hole mount - The consists essential- sweep circuit ment, and laboratory work. e to pre- ly of an electron -coupled oscillator The master oscillator can be locked vent turning, beryllium by push-pull reactance ern contact modulated to a 60-cycle 117-volt line, or run free. and frames. tubes. A buffer amplifier between the spring, steatite end Half -line driving pulses for differen- Spacing is .017 inch and the break- oscillator and output eliminates fre- Dimensions are lotion in receivers. tial delay techniques are available for is 750 r.ms. 2 with load. Ter- -CRAFT down voltage at mc.- quency shift changing T/t x 3 x 3 inches. -RADIO cable hookups. RADIO -CRAFT minals are provided for obtaining de- A regulated power supply and au- flection voltages for an oscilloscope. OSCILLOGRAPH totransformer make the unit inde- The unit measures 131/2 x 9444 x 7:4 pendent of line-voltage variations. COLORED TV LENS inches, and weighs 15 pounds. -RADI Electrical Instrument Co. Hickok Dimensions are 91/4 x 171/4 s 191/4 inches. Celomat Corporation CRAFT Cleveland, Ohio Weight is about 50 pounds.- RADIO- New York, N. Y. RECEIVER The Model 505 oscillograph is de- TV -FM signed primarily for. FM servicing. It The Vue -Scope is a blue -tinted tele- lens Sightmaster Corp. uses the new 511PI 5 -inch cathode -ray SWEEP GENERATOR vision magnifying which reduces N. Y. tube, and contains such features as a eyestrain and glare. New York, Clarkston Corporation The lens is made of two preformed The Model IS-C -II is a wide- and narrow -band FM signal gen- Sightmaster for modu- Los Angeles, Calif. lucite sheets. The convex front sheet 24 -tube table -model combination tele- erator with provisions lating it from an external source A new type of sweep frequency gen- is clear and the flat rear sheet is such as a microphone or phono pick - erator, the Clarkston Model 125, pro- colored. Both sheets are first bonded up. Additional features are a demod- vides a regularly recurrent changing together and the hollow space filled ulator, for permitting a modulated r.f. signal to be viewed on the screen, and a phone jack to permit any signal to be heard on headphones. There isi also a sinusoidal sweep with a phasing control. This instrument is designed for align-

for testing audio and electrical vision and FM receiver. It uses a IS- pattern tube arranged for direct equipment. inch picture is produced by viewing. Video amplifier band width The complex signal photoelectrical ly a sychro- with clear mineral oil through a small is 4.5 mc. The FM receiver section has scanning disc. The Modulation on opening which is sealed afterward. a ratio detector and tunes from 87 to nously-rotating the disc is the photographic reproduc- 109 mc. Two speakers are provided for a precision pattern. Frequency NEAT' WE(DED JOINT improved frequency response. The an- tion of 1 range on 60 cycles is from 40 cycles tenna input impedance is 300 ohms. - i BLUE LUDTE REM LENS 10 are at I, 3, 5, RADIO -CRAFT to kc. Marker pulses 7, 9, and 10 lac. Output is 50 mw into TOOLS a 500 -ohm line. Internal impedance is TV SET ALIGNMENT 200 ohms. Approved Electronic Instrument Housed in a metal cabinet 15 3/16 x Corp. 8 z 8 3/16 inches, it weighs I81/2 pounds. -CRAFT New York, N. Y. RADIO These alignment tools consist of a r.f., .f., and discriminato cir- radiation loop made of 1/4 -inch alu- ment of CLEANER cuits.- RADIO -CRAFT CONTACT minum tubing and an alignment wand Walter L Schott Co. with a 6 -inch antenna loop at one end of a wooden rod and a rectangular ELECTRIC -EYE KIT Beverly Hills, Calif. aluminum plate at the other. The radia- Tec- Tronic Laboratories, Inc. N o -O x is a tion loop acts as an antenna for the De- neutral chem- FOCUS ADJ signal generator and provides loose Chicago, Illinois ical contact coupling between the generator and Model AK 115 is a new photoelectric - cleaner and lu- the receiver. The alignment wand is eye amplifier construction kV offered to bricant for use LENS SUPPORT used to check tracking between the in electronic and r.f. and oscillator stages of a receiver. electrical work. They are designed to be used with any It dissolves cor- TABLE receiver that has a built -in antenna. rosion and is es- In use, each end of the alignment pecially suited for L CIFAR WOTE FRONT LENS wand in turn is held between the radi- cleaning noisy vol- MO: MINERAL OIL (SEALED IN t ation loop and the receiver antenna. ume controls, f :FRAME If one end causes the reading of the switch and relay output meter to increase and the other contacts, and wip- A mounting bracket permits horizon- adjustment for screens end causes a decrease, the two stages ers on tuning con - tal or vertical are not tracking and alignment is densers.-RADIO- of different sizes. Dimensions of the 10 x 13 inches 131/4 CRAFT lens vary from to x 19 inches.- RADIO -CRAFT experimenters. The kit contains a phototube, amplifier, drilled chas- LIGHTNING ARRESTOR sis, sockets, relay, and all oth- PHONO NEEDLE er necessary parts. When complet- Radio Corporation of America ed the amplifier measures 51/2 x 4/z Duotone Company Camden, N. J. - x 21/4 inches. It operates on 117 volts N. Y. Model 202611 lightning ar- New York, a.c. or d.c. -RADIO -CRAFT The RCA nylon phonograph restor is designed for FM and television A new shockproof body needle reduces surface noise and installations. It has a plastic tipped to fit around 300 -ohm trans- needle talk. It has an osmium- MOLDED CAPACITORS designed a nylon mission lines. spring steel shaft set into Sprague Electric Co. The transmission line is placed in an bumper which acts as a shock absorb- North Adams, Mass. open slot in the plastic body and a These new phenolic -molded tubular plastic cap it screwed down firmly, condensers are usually smaller than causing four sharp prongs to pierce ordinary paper condensers of equal the insulation and contact the wires. rating. They are heat- and moisture -re- It avoids cutting and splicing of the reduces noise. The radius sistant, noninflammable, and are con- line-usually necessary with other er and also servatively rated for operation from types of arrestors-which distorts in- of the osmium tip is .0028 inch plus or -40 to +85 degrees Centigrade. coming signals. minus .0001 inch. The needle shank is are available in all The arrestor is mounted on any in- duralumin and has a milled surface for necessary. If both cause the meter The condensers car. in 200 -, 400-, 600-, 1000 -, door water pipe with a flexible metal one -way insertion into the pickup reading to decrease, the oscillator and capacities RADIO -CRAFT r.f. sections track. -RADIO -CRAFT and 1,600 -volt types. -RADIO CRAFT ground strap.- RADIO -CRAFT tridge.- RADIO -CRAFT for # Servicing I71 RETURN 000000000000000000000000 OF THE VETERAN e By EMMETT BRIGHTWELL e TOP VALUE OFFERS Kit Model FM -7, w` PLEASE TEAR OUT AYEAR ago RADio- CRAFT and a Self- Contained Table Model Fre- THIS ADV. AS REMINDER other journals devoted to the quency Modu- interests of radiomen were lated Radio Re- filled with ceiver Kit wails and editorial Model FM -7 has a comment about the difficulties encoun- frequency range of tered by craftsmen 86-110 Mc., can also then being dis- be used as a TUNER charged from the military services. with a high quality amplifier. A phonoiack is provided ln the rear These complaints ranged from no of the chassis with double pole, double throw credit, no parts, no wholesale switch for feeding signal to either the radio contacts speaker or to the phonoiack. An additional to flat refusal of manufacturers to rant lack for connecting extra loud speaker Is included. The sales franchises for standard products. R.F. section of the kits is pre - assembled at the factory. This kit uses 2 IF stages, I And there were beaucoup grounds for limiter and I discriminator. Minia- ture tubes used throughout. Complete with all the complaining; both wholesalers tubes including beautiful bakelite cabinet, and manufacturers preferred to cling ready for assembly. to their wartime outlets, knowing full Kit Model 210, a well that be Three Way Port- it would many months - able Receiver years, maybe -before there would be Model 210 operates 4 enough goods to go round. on either AC or DC o r self . contained Recently I got to wondering if condi- batteries ... power tions had changed so, switch conveniently -if how. So I located on front of looked in on several veterans who had set so that "bat - managed, since discharge, a Eery" or "AC or to get toe- DC" may be se- hold again in the radio service field. lected without open Some of these were ing case. Five inch Alnico 5 permanent dy- willing to discuss namic speaker. Case covered with fine grade conditions, some were not. leatherette material. Complete with tubes, ready for assembly. RADIO FACTS The most articulate of the few who AND FIGURES Kit Model S -5, a 1 would submit to an interview was Joe One Band Re- AUDELS RADIORANS GUIDE -914 Pages, 633 Illus. Solorzano, who operates a s ceiver .rations, Photos, Wiring Diagrams, 08 Big Chapters, neat, if nail, covering RadioTheory, Consfruction,Servicing include Model S -5 ... this radio and appliance store, the Strand radio kit contains keg Important Data on Developments In Television, Radio Shop, the following fea- Electronics and Frequency Módulafion, Review. at 3339 Twenty -Third Questions & tures: improved su- and Answers, Calculations Testing. Street, San Francisco. perheterodyne Highly Endorsed- Indhpensable for Ready Reference cir- and Joe, before entering the service, was cuit, built -in loop Home Study. antenna, PM Alnico $4 COMPLETE PAY ONLY SI A MONTH an experienced radio repairman. In fact, e speaker, streamlined Step up your own skill with the recta and figures of airplane dial, wide your trade. Auricle Mechanics Guides contain Preo. in the Coast Guard where he serve], he e Seal Inside Trade Information In a bandy form. tuning range 550Kc- Fully Illustrated and Easy to Understand. HIBgbl was found so good that instead of I eing 1600Kc, 5 tubes (including rectifier), 115V, AC- Endorsed. Check the book you want for 7 aays- put through DC, 12SK7 IF 12SA7 converted, 12S97 Det. and Free Examination. a radioman's training e 1st audio, SOL6GT output and 35Z5GT e rectifier. Send No Money. Nothing to pay DOettnan. course, he was assigned to teaching Complete with tubes, including beautiful Bake- lite cabinet, ready for assembly. w-. -- CUT HERE -11111 others. e - - Many other kit models On discharge his problem was not to e available. e Write for Catalog M MAIL ORDER get parts and supplies. It was to find a e AUDEL, Publishers,49 W.23 St., RAW store any room enough Ñ °fRK -or large t) set RADIO KITS COMPANY Please send me postpaid for FREE EXAMINATION book. marked tic) below. Il I ilorino to keep them 1 agree 50 up in. He finally secured the locaticn he ,I SI In 7 Days book orae,ed e 120 Cedar Street New York 6, N. Y. on eaCh and further now occupies. Its area is not more mall $1 monthly on each book Until I have bald price than -othenwse, 1 will return them.

250 square feet; one 10-foot cot nter RADIOMANS GUIDE, 914 Pages . . $4 ELECTRICIANS EXAMINATIONS, across the entrance to the service de- 250 Pages . 1 WIRING DIAGRAMS. 210 Pages 1 partment leaves just space enougt for Now ELECTRIC MOTOR GUIDE 1000 Pages .: 4 ELECTRICAL Joe to pass edgewise (Joe still has an You Can Become DICTIONARY, 9000 Terms . 2 ELECTRICAL POWER CALCULATIONS. 425Pps. 2 edgewise) to and fro. HANDY BOOK OF ELECTRICITY, 1440 Pages 4 Joe has about $2,500 invested he in ELECTRONIC DEVICES 216 Pages 2 e A Prospector! ELECTRIC LIBRARY 1x1 vol.. 7000 Pgs., 11.50 vol. fixtures, in test equipment, in stock. He OIL BURNER GUIDE, 384 Pages .. , . , , 1 REFRIGERATION & Air Conditioning, 1280 Pgs. 4 is a facile worker, turns out guaranteed Here Is One Of POWER PLANT ENGINEERS Guide, 1500 Page: nf/ .\el PUMPS, Hydraulics Air jobs, seldom has a comeback, tests tubes The War's Top Secrets tt, & Compressors, 1658 P 4 free, collects a basic service charge on WELDERS GUIDE. 400 Pages l BRAND (NEW) BLUE PRINT READING, 416 Pages 2 every repair job, hardly ever does ;l re- SHEET METAL WORKERS Handy Book, 388 Pgs 1 ARMY MINE SHEET METAL PATTERN LAYOUTS, 1100 Pgs 4 pair outside the shop, and the only thing AIRCRAFT WORKER, 240 Pages 1 he will do to a receiver in the owner's DETECTORS! MATHEMATICS & CALCULATIONS,700Pgs 2 MACHINISTS home is run a Portable: Will Detect Handy Book. 1600 Pages . . 4 a tube test. METALLIC and NON- MECHANICAL Dictionary 968 Pages 4 METALLIC objecta; AUTOMOBILE GUIDE, 1700 Pages 4 Joe uses various avenues of acver- Very Sensitive; using DIESEL ENGINE MANUAL, 400 Pages 2 tising. He keeps a running ad, with 955 Tube In detecting MARINE ENGINEERS Handy Book, 1280 Pages 4 fre- head; two tube ampli- MECHANICAL DRAWING GUIDE 160 Pages . 1 quent copy changes, in the neighbor rood fier using two IN5gt: headset; or micro- MECHANICAL DRAWING & DESIGN, 480 Pgs. 2 newspaper, he distributes handbill:. pe- phone: also 150 micro MILLWRIGHTS & Mechanics Guide, 1200 Pgs. 4 meter; Power supply; CARPENTERS & Builders Guides (4 vols.) 6 riodically, and after nightfall his win- 3 -45 -v: one 6 -v.: or PLUMBERS & Steamfitters Guides (4 vols.) 6 2 3 -v. batteries. Com- dows MASONS & Builders Guides (4 vols.) . . 6 are a blaze of electric light and Less plete with Instr. MASTER PAINTER & DECORATOR, 320 Pgs 2 neon signs. I-tutorial.; packed in original cases; /tapa. GARDENERS & GROWERS GUIDES (4 vols ) 6 He thinks his window displays wgt. 106 I.M. ENGINEERS and Mechanics Guides :lave Nos. 1, 2, 3, 4, 5, 6, 7 and 8 complete 12 F.O.B. N. Y. the best drawing power. He is inaigu- tree Answers on Practical ENGINEERING 1 rating a follow -up letter system tc old $17.50 ENGINEERS & FIREMANS EXAMINATIONS , 1 customers with a view of (Less Batteries) encouraging Ihrs and monopolizing repeat business. 826.40 But Joe has not to been able W Ith Batteries this day F.O.B. N.Y. to get a dealer franchise. He sells a few NO C.O.D. lafrarliS Occuonlesg off -brand receivers. But good, for Joe Send Order to liasiM0Y0a 01/ .,an tell a good receiver by just exanin- COLUMBO TRADING CO., INC. .ng the layout and the parts, and he 304 Canal St.. Dept. RC!. New York 13, N. Y. AUNE, 1948 721 krvici>.s wen_auean" -VI E[ C C 1\ for YEIRes! RETURN OF THE VETERAN (Continued from page 71) VOLUME CONTROLS aims in near future in the Made by a nationally known manu- all the time at customer satisfac- thing startling the facturer. Standard noise -free carbon tion. field of television or any other depart- construction - %" bushing - do He thinks shaft, 8" long -complete with switch. "I not feel that just because a man ment of radio or electronics. Ideal all purpose replacement control. was in the service he should feel en- the industry will stick closely to proven Full range of sizes -with attached switches! things for which a In the following Ohms titled to any special consideration from items and designs, 10M- 25M- 50M- 250M- 500M -1 Meg -2 Meg either the public, the manufacturers, or market already exists, things which are 59c Ea. $55.00 per 100 Assorted a ready sale, and that The above are ten avidity products --do net confuse the financing agencies," Joe said. "After known to have them with cheaper controls on the market new. all, free enterprise A "GREEN" SUPER SPECIAL is based upon free STANDARD VOLUME CONTROL competition, and a WITH SWITCH serviceman 500.000 OHMS radio olmi famous and popular control. Mfg. type. 500,000 may as well realize complete with D.P.S.T. switch and mtg. nut. 2%' shaft. All brand new. A terrific bargain. while 29c that,if he is to stay they last in business, it will FREE! FREE! be because he can RESISTOR COLOR CODE GUIDE do a good job; he with every order can't rely wholly upon public good CODE KEY a will to get business Type J38 - and goods and Made to U.S. Army Sig- e\:._ nal Corps specifications at _ money to finance a cost several times our price. liar bakelite them." base 8/16" thick. Every one brand -new in individual box. The writer liked Special Each 95C Joe's shop,his INSULATED RESISTORS methods of doing 100-500.000 ohm ? watt and, Plus or minus 10% R.M.A. Cola Coded. business, Reg. Price $8.00 SPECIAL $2.00 above all, his attitude, so well that INVERTED SCREW CAN CONDENSERS he took a picture of These seen are manufactured to operate . tisfact. rib under the Joe doing a job at severest conditions. Etched foil his workbench. construction. Completely Insulated. Û generate negative and pr Joe does not think leads for each section. Pal nut furnished with each there are too many condenser. Satisfied customers and a well -planned advertising campaign help to Cap. Mfd. W.V. Each shops. He is 8 475 .69 service make Mr. Soloranzo's small radio and appliance shop profitable. 12 475 .81 making a living for 20 5 8 +8 475 1.915 his family of four. He believes he could this attitude will tie up most manufac- 40 450 .99 do a great deal better if he had more turing equipment and raw materials for TUBE SPECIALS space in a higher-income community. a long time to come. BRAND NEW-STANDARD BRAND scarcer And in the meantime, a lot of the Our Our But with store space growing Type List Special Type List Special and scarcer, and rentals going higher radionic wonders of today will become I A7GT 1.80 .72 35W4 1.15 .46 IH5GT 1.50 .60 35Z5GT 1.15 .46 and higher, he thinks he will quit look- the has -beens of tomorrow without hav- 2A7 2.20 .88 7OL7GT 3.90 1.56 6A K5 3.90 .95 75 1.50 .60 ing for a better location and make the ing caused a single ripple on the waters 6C4 1.50 .25 6AC7 2.65 1.06 of interest. 618 2.65 .79 0V4 3.90 .88 best of what he has. public 117L7GT 3.55 1.42 25Z6GT 1.35 .54 Joe is not looking forward to any- Joe, you see, is conservative. 358 1.0 .72 OTHER SPECIALS PRODUCTION -LINE TECHNIQUE FOR SERVICE SHOPS 20 Amp Auto Fuses. SFE 100..$2.00 14 Amp Auto Fusee, SFE 100.. 2.00 By Jack King Rubber Male Caps .05 .5- -600 V Tubular Condensers .24 RGANIZING your servicing routine 3. Examining the receiver to deter- RESISTANCE LINE CORDS O has definite advantages. For ex- mine its faults; Individually boned In the following Ohms ample, 4. Correcting the faults and repair- 135 220 330 List $1.20 ea the sequence may run: 350 SPECIAL ing the radio; 2550 1 0 1. Receiving the radio; 200 300 49c Ea. 5. Returning the set to the customer;

2- walnut wall Bellies, sturdily constructed S 3.7 2. Identifying the set by attaching a 6. Receiving payment and ringing the O.I. Dual Epeod Phono Maas- 331/3-78 Real heavy duty a clone out 17.5 tag; cash register. Section Auto Antenna, side cowl mount. 26 to 66'. low loss leed 1.3 Duotono genuine Sapphire Needle, 5000 plays .49 '-450 Ohm Dynamic Speaker with 501.6 output Trans. a few at 1.9 Aeutic Dynamic Microphone, Bullet type, com- 10.95 $1. 30 Min. $91.95: FANS ITE IS Recording Wire -15 fMin. 0a CALL 60 Mln. 3.25 Socket Wrench Sete. self container with 6 wrench sizes .31 TUNES 152-162 MEGACYCLES Nylon 1J Crystal Cartridges List $8.80 True F.M. Superhetrodyne LIST Our Price 3.69 6 Tube (miniatures) 25' Rubber covered Hanks .16 including rectifier. 115 Volts, A.C. -D.C. 5 Inch 15 Watt--tear 11 -E Mazda Lampe .07 speaker. Clear vision dial. 91/2 a 61/4 a 51/4 Turner Crystal Microphones with 100' Mie deep, walnut veneer cabinet. Shipping weight 6.95 99s Cable. For the price of talc. Cable Sche- Portable Record Player with Auto. changer, 3 51/3 lbs. Highest quality components. tubo built -in amplifier, 5' speaker. beauti- matic inside bock cover. 2 stages high gain ful brown carrying case 32.47 10.7 Megacycle I.F.S. High Selectivity. Dis- ALL MERCHANDISE BRAND NEW criminator Detector. Guaranteed reception gaol. yes AND 100?. GUARANTEED from your local F.M. Transmitters with at- Ierluded NO SECONDS! NO REJECTS! NO OFF -BRANDS! tacked antenna, from cabs, police and others. F.O.B. STANDARD BRAND MERCHANDISE ONLY Ready to plug in and use. Inds lip 'o Deposit required with C.O.D. Orders. All $10.00 Cash orders FOB New York. Minimum orders $8.00. SOME CHOICE DEALERSHIPS With Order STILL AVAILABLE - RE FIRST - WRITE less C.O.D.

GREEN RADIO DISTRIBUTORS RADIO APPARATUS CO. THE HOUSE OF BARGAINS POLICALARM 729 NORTH BANCROFT ST. Electronic Supplies & Equipment RECE1VEk INDIANAPOLIS 1 ì, INDIANA 482 SUTTER AVE DI. 2.4444 BROOKLYN. N.Y. RADIO -CRAFT for Note that there are six definite steps. RADIO A certain amount of time is requi:red to perform each operation. In a factory FM CONDENSER & TROUBLESHOOTER'S time study analyses of the work: per- COIL KIT (88 to 108 Mc) HANDBOOK formed are made to see how time can be saved Eliminates useless by eliminating unnecessary testing on 4 jobs steps, or by conserving the time of spe- out of 5 cialized individuals by diverting c srtain parts of the work to less-well -trained persons. Why not apply this technique to servicing shops? In the above se- ...YOUR quence, 3 and 4 require actual technical knowledge. COMPLETE Why, then, waste the time of thct tech- fP nical man by having him deal wilt the PRACTICAL RADIO V riable Condenser i Limiter CoJ customer? Who wouldn't rather deal Discriminator Coil Antenna Coil ' Oscillator Coil Schematic Diagram with a good- looking blonde? At ti Ties it Two I.F. Coils Instructions SERVICE LIBRARY Thi Kit contains the vital parts needed to build an is admittedly essential FM Tuner r Radio and for modernizing that the service- Pre-War all other partspar FMtandard. a4s95 man be present to talk with the custom- } ...in two er, but in most cases his time can to con- AUTO RADIO served and he can Tube SuPerbetem- concentrate on techni- dynexhrree T Gang Con- giant denser Powerful Long books cal work if suitable people are employed Distance Reception Fib All Can, Easy In- to do the routine jobs. stallation Mounting What factors enter into step 1? First, Rrnekeb Included MODERN RADIO the owner should be queried abort the $29.97 SERVICING complaint. Leading questions sho ild be Net A complete guide to troubleshooting, instrument's, circuit asked. The following are typical: analysis, repair. 1. What sort of trouble are you hav- TOM THUMB ing? CAMERA RADIO LEARN TO WORK BY MODERN, PROFESSIONAL METHODS 2. Is the noise heard at all times of Precision Built Ex- i Tone Quality the day or only at particular times? Fcellentull Vision Slide -Ruin Train for the big pay jobs! Dial The Ideal Vacation 3. Does the hum appear after the set Companion A PORTA- Ghirardi's MODERN RADIO SERV- BLE RADIO for Battery has warmed up or immediately? Operation A HIGH ICING is a complete, 1 vol. course in all GRADE CAMERA with Re- phases of professional radio -electronic re- 4. Do you hear the Rex Lens Using Standard distortion at once 227 Film 16 Pictures. pair. Tells how to make preliminary trouble or does it take some time to develop? checks on difficult jobs; how to analyze any 5. Do you wish an $ 28.75 circuit and its components; how, when and estimate first or Net will it be all right to go ahead and re- where to use all types of test instruments Less Batteries and interpret their readings to track down pair the set? the trouble-even how to start a service (It is usually safer to give an esti- BROOKS RADIO DIST. CORP. business of your own. Everything is ex- mate.) 80 Vesas, Street, Dept. A, New York 7, N. Y. plained simply and thoroughly. 706 clear The tag which identifies the set (step The Trade Mark illustrations and 723 self -test review ques- of "Time-Tested ILLINOIS tions make study easy. Complete 1300 -page 2) should be attached firmly to the Quality" book only $5-or see special combination radio's power cord. price offer below. The tag itself may be streamlined, CONDENSERS CUT TIME IN HALF ON just as streamlining is in used produc- COMMON SERVICE JOBS tion -line methods. The first thing of importance is the owner's name. This is RI= BELONG Work faster make more money placed at the top of the tag and is the Almost 4 out of 5 radio repair jobs IN THE BEST can be handled as easily as falling off a log! first thing written down. The nutr.ber of Just look up the model of the set to be the tag and the date should also be at fixed. Chances are Ghirardi's RADIO' the top. Then, the owner's addres,f, tele- Electronic Sets TROUBLESHOOTER'S HANDBOOK tells phone number, receiver make and model exactly what the trouble is, exactly how to fix it. Gives common troubles, their symp- number, serial number, and nature of toms and remedies for over 4800 radios by complaint. Td facilitate filling out the 202 manufacturers. Hundreds of additional tag, such words as hum, noise, intermit- pages contain tube data; transformer trouble listings, alignment charts and doz- tent, etc., may be printed on the tag, ens of diagrams, etc. for faster, better serv- with a small box or space. opposite each ice on any radio ever made. Only $5-or see word. This eliminates the necessity of special combination offer. retelling the story to the serviceman. MONEY SAVING OFFER! He can glance at the tag and quickly Let Ghlrardi's RADIO see what the complaint is and wt at the TROUBLESHOOTER'S NANO- -4114111116 BOOK save time, help you make job entails. more money on common service Read these L11lG-0. lobs. Let MODERN RADIO SERVICING train you in truly GIANT The actual servicing scientific servicing that can pave -.__:1G=,w your way to the big money Jobs. books for Step 3, examination of the receiver to Get BOTH big books at the spe- 5 DAYS determine its faults, may require con- cie/ price of only $9.50 for the two 1$10.50 foreign). Use coupon siderable time. Intermittent receivers today--et our risk! ... at our may take hours to repair Look fo Illinois for a complete line instead of min- of electrolytic capacitors for every risk! utes. The time required can be Cu'; down electronic application and radio re- Dept. RC -68, Murray placement use. Hill Books. Inc.. by first of all making certain that the When you need 'a 232 Madison Ave., New York 16. N. Y. capacitor has technician has that superior ability to Enclosed find $ for books checkedµ or a thorough technical send C.O.D. Irlo C.O.D.'S withstand extreme temperature outside U.S.A.) and I ill training and Pay postman this amount plus few cents postage. In really knows the funda- changes, that's manufactured to ex- either event.e. may "return books within 5 days for complete y re mitbnce. mentals of radio. acting specifications. that's time - [ Without basic knowl- MODERN RADIO SERVICING edge, efficient servicing is out tested through 14 years of high qual- IS (55.50 outside U.S.A.) of the ity production experience -you want RADIO TROUBLESHOOTER'S HANDBOOK question. SS ($5.50 outside U.S.A.) an Illinois condenser! SPECIAL MONEYSAVING OFFER Good, conveniently arranged, test Both of above big books only 59.50 equipment WRITE FOR OUR LATEST CATALOG (520.50 outside U.S.A.) is a big help in diagnosing Name trouble. Depending on a nontechnical assistant to test tubes is not good prac- ILLINOIS CONDENSER CO. Address City a Zone State tice. Most of the bad tubes rr.ay be ti

JUNE, I 9 4 8 -4 Ilevvicialp

caught by the inexperienced person, but THE often a tube which shows an intermit- ONLY $89'50 IS COST, tent short or leakage on the tube tester SUPER VALUES will get by all but the technician. Short- ening this step, then, depends greatly on technical knowledge and good test from MID-AMERICA! equipment. Cheap and inaccurate test equipment results in loss of time and Stromberg -Carlson DYNATENNA money. Thought directed toward efficient placement of the equipment on the bench is well worth the effort. This famous -make FM mitting station. Illus- antenna has been ad- trated instructions Once the fault has been located, it vertised and sold for and all necessary must be corrected (step 4). This invari- many times the low hardware. A screw- ably means that a part must be. taken price MID -AMERICA driver Is only tool out of stock or ordered. Naturally, the asks? Covers both FM needed for assembly. bands. Delivers PM Dynatenna Is seam- more parts kept in stock, the faster is reception at Its best. less, heat -treated. the service. It is always easier to take Complete with 60 ft. of all aluminum . for the SENSATIONAL -NEW- IMPROVED a part out and install it than to order it 300 -ohm twin lead -In. will withstand from a distributor with attendant red Line is standard ap- severest weather. 10 INCH proved flat -type, solid tape and delay. But the stock that can dielectric with weather- be kept on hand is usually limited be- resisting Insulation. $495 KIT cause of lack of space and money. An anywhere TELEVISION Mounts each analysis over a period of time (say six easily ... vertically or less tubes horizontally to match $4.45 each Complete with 13 channel tuner, all parts and months) 'of the parts ordered can be polarization of truss- In lots of 3 easy step -by -step following instructions and made. Certain parts will be ordered and schematics. re- ordered. In rural districts there may $89.50 less tubes be a demand for battery radio parts. Kit complete with all tabes $149.50 Cost of cabinet $25.00 Portable and a.c. d.c. radios may be Using the new 13 CHANNEL TUN-EB. which Is pre - widely used in d.c. districts, necessitat- wired and factory aligned for the entire television spectrum. The kit builder merely Installs this unit ing repeated ordering of a.c. -d.c. chokes, into his chassis and makes three connections. Contains an R.F. stage oscillator and mixer. It is extremely 150 -volt electrolytic condensers, and small and compact. Using new I.F. coils whim pm- high -voltage -filament tubes such as 43's, vide maximum gain and picture definition. Sound reception is high Quality F.M. for complete listen- 35Z5's, and 50L6's. If the demand for PERMEABILITY TUNER ing Build pleasure. a really HOT 6 or 6 -tube AC DC superhet receiver! SAME TELEVISION KIT -7 INCH, omelet* less the past six months is known, the next Takeo place of old -style gang condenser, of and antenna tubes complete with all tubes $99.50 coils: regular 465 KC intermediate frequency. MA -2167 $59.50: six months' demand can be fairly well Complete with permeability tuned oscillator coil. predicted. Parts which are very often 4's 255' x 2W; 2W diameter dial drum. Com- $ 24 IMMEDIATE DELIVERY FROM STOCK píete with diagrams for buildings and 6 tube sets. used, therefore, should always be kept Order MA -216e Loop Antenna . . . . !go ELECTRONIC 3 in stock. Order MA-2 i4 Drilled, punched Chassis Mee 762hopolifazl INSTRUMENT CO. A convenient and neat storage sys- Dept. RC 42 WARREN ST. N. Y. 7, N. Y. tem, with bins or compartments, kept BANTAM 1- WATTER clean and orderly, is necessary to avoid wasting a lot of time looking for parts. BCR -746 -A tuning unit used as foundation for Some service shops look like haywire Bantam 1- Watterde- may be scribed In Jan. 19480ST. nightmares. Resistors neatly Makes tiny crystal - sorted in drawers or boxes. Paper and controlled CW mmkter. Measures only 3't' long. OPERATES electrolytic condensers similarly may be 2 t ' high. I4 wide. Re- quires only 155 volts 'A ". 30 to 90 ENTIRELY kept in proper order. Tubes should be volts "B ". Draws 8 to 15 ma nder load. Supplied lesa244t stocked in orderly fashion for easy plug- FROM 110 In coil MA-907 and identification. VOLTS AC /DC Correcting faults also depends on the SPECIAL AUDIO TRANSFORMERS technician's skill. Replacing a loudspeaker cone or a dial drive cable can Exceptionally high -quality universal output transformer for up to 12' speakers. Rated at 12 watts. Matches any single, THE METER MASTER be a tricky job which takes more time push- poll or parallel tubes to 6 -8 ohm voice coil. 12' color coded leads. 2'high with 2:5' mounting centers for instalia than necessary unless skillfully done. FOR RADIO REPAIRMEN, e a a tion on chassis or speaker. Complete with Instruc- ! 11111 Time in analyzing the necessary for matching tube impedances. IAA-1205A1205 41 STUDENTS, . e . HAMS. spent to speed is worth while. Hermetically sealed 200 ohm Single 3000 -ohm to 4 -ohm Precision resistors elim- RANGES: steps servicing CT to50,000 ohm grid. Use as voice coil output for 50Ió4 inated by means of sliding Low .1 ohms the shop employs more one man, microphone transformer 36I4, etc. 1W high on $ Resistanos: If than resistors. No complicated 500 ohms line -to-grid, etc. 255- CD( mounting centers. A e` to High Resistance: 0 -I each one can specialize in certain types :1(x115'. MA -1262 Vs7Y NIA12511 . . .. YaIY switches to confuse you. Special damn decreases Meg./10 Meg of work. Servicing of record changers, Current: 0.1 / 10/ l O0 m.a. crowding at high resistance D.C. Volts: 0. 10/100/- for example, calls for more mechanical Heavy Duty Noise Filters end of ohmmeter scale by 500 /5000 automatically increasing A.C. Vats: 0-10 /100 /- than electrical or radio skill, and some Rated on l0amps, 116 -volt AC. Measures only l'xlW'square. internal voltage. 30 min- 200 Install right in amplilers, receivers and other equipment utes to assemble. men are able to do this work better than where line noises must be kept at minimum. Na- large COMPLETE KIT one 3%s' meter insures accu- best in- tionally -known manufacturer. MA -2164 . . . . t77 with others. Some men are at their racy. Meter sale blank INSTRUCTIONS Filter for mobile power sat stalling or repairing auto radios. plies- Rated 10 amps, 8-30 V DC. except for 1 ma. range. Case not Included. Has additional 2 mfd, 100 VDC condenser. 2' high, COO Calibrations easily print- Bulky circuit manuals are somewhat 2' square...... MA2165 . . . . . of t71 ed I4 $16.75 OADaa TODAY difficult to handle and take up consid- SPEAKER SPECIALS erable room on the test bench. If the METER MASTER diagrams are taken out and filed in a All with Heavy ALNICO 5 Slugs BOX 51 BERKELEY, filing cabinet, a single diagram at a 3' /= PM MA- 2062.. 4x80velPM MA CALIF. $1.39 -2187 $1.39 time may be removed as needed. 5' PM MA -2071 . , $1.39 6' PM MA2189... $1.95 Step 6, receiving payment and ring- ORDER FROM THIS AD! ing the cash register, is the easiest of Quantities are so limited, get your order In nowt Minimum 25.000 tones the order shipped, 82.50. Send 25% deposit, balance C.O.D. repaired loud speaker paper PROVE all in many respects, and yet the hard- Get on MIDAMERICA's CONE PATCH cement saves you TIME and MONEY. mailing list to receive BIG BAR- CONE musical cement. positively does not before it can be performed the GAIN BULLETINS that list latest, greatest buys in radio PATCH. est, for parts, electronic equipment. Send orders to Desk RC -66. produces all musical vibrations. IS almost Invisible preliminary five steps must be finished. and stronger than r w. 100,7s satisfaction s guaranteed or oney refunded. Cash and carry is a good rule to follow. Peal cant brings folio. 12 CONE SIZE bottle of CONE l'ATCII -KIT $1.25 postpaid. Free. VOICOIL. solution, Paper debts are of no value. Arguments for wamedd V.C. Canes. Inquiries invited from salesmen and jobbers. will be avoided by giving clear estimates RADIO RESEARCH PRODUCTS expecting the customer to pay W. MOLLOY, Director and 6417 Harker Ave. Chicago 37, Illinois promptly when the work is done. RADIO -CRAFT for 75 CONNECTING FM TUNERS By ALBERT LOISCH NOW AVAILABLE ! MANY radio receivers have a 7bscfieeeeea 6" 9E,

VOL. CONT

RADIO

TUNER VHONÓ, OR PICKUP e Y o./ 1e+ LOW Fig. I-- Connection circuit for modern sets. LOW PRICE! switch to the phono position switches MASTER- REMOTE INTER -CONS the tuner or record player into the audio Push button selection for r to S remote stations section of from this quality baia 4 tube, 2 watt Master station. the set and disables the radio Several remotes can be "paged" at one time. Remote section. stations con originate call to Masts Very simple to install with any 3 conductor cable. Sturdy, good Many of the older radios use the an- looking wood cabinets, walnut finished Moste, H M II T IE cient biased -grid detector. Fig. shows 12x7/ x6t/a ", Remote 61/4 X7k4" 2 Ne. 32A234X, Master Station end $29,95 how to connect phono One Remote -ONLY 4 a jack to a detec- No. 32A235X, Additional tor of this type. Remote Stations -ONLY $7,88 No. 2A113, 3 Conductor A separate bias resistor is V used to get Cable- 100 Foot 2.60L Pea the correct grid voltage for phono oper- COMPOSITION RESISTORS ation. In the phono position, THE "DOUBLE TWENTY" the switch FLUORESCENT cuts out the high -bias resistor and UNIT You never have to guess about the resist- Plugs in Any Outlet ance and wattage of any Little Devil switches in on one of lower value. Hangs in Any Position resistor. To calculate the size of the new re- Underwriter's Approved Every unit is not only color -coded but individually marked for quick, sistor, divide the desired bias voltage by Improved heavy steel, high reflection baked white positive identifi- enamel inside, gray outside. Hangs anywhere, with cation. Millions used in entice' war gmp- wire or chain, in a "jiffy." With 6 foot attached GRID &AS DCL MIIIVO cord rood tooeplug s n any outlet. Ideal for your ment. Standard RMA values from 10 ohma hobby repair shop, store etc. Shipped com- to 22 megohms, in 34, 1, and 2 -watt sizes. plete with two 20 lamps. Size 2St/+x9s/4x5% ", wt. 10 lbs. Tol. ±10%. Also ± 5% in 34 and 1 -watt sizes. No. 30A60 6 et Spec. Lech $8P 28 Lech. $7.73 Available Only Through, OHMITE Distributors 67, WRITE FOR YOUR COPY OF CATALOG No. Ohmite Manufacturing Co. 481 IF YOU DID NOT RECEIVE IT. 4896 Flournoy St., Chicago, Ill.

BURSTEIA-APPL Í EE

1012.14 McG£E STREET. -'"")""`Y . i XARS4S CITY 6, MISSOURI Fig. 2-Connecting phono to older receivers. the cathode current. For example, if ;he required bias voltage is 13.5 and -;he current is 5 ma, at this bias voltage, GREYLOCK then the value of the resistor is: A Dependable Name in 13.5 RADIO TUBES - 2,700 ohms QT. Olass. d Mini Tyres. All TubindividuallyTubas e Sexed. .005 123117, 135417, E0L6. 12A711. 12EÁ.. 135E6, 35W4. 5055 each son Receivers with biased 156. 155. 174, 354. 3434, GARS, SACS. 6aC7, grid detectors AQ6, 55E5, DIAS, SAUS, Bale. 6X4 esci, a usually have volume 331.7. 70L7. 117L7 each S9c r.f. controls which All Tubas carry RNA BO -Day Guarantee permit cutting the sensitivity to zero. If the set does not have PM SPEAKERS this control, it + Alniee No. S a

WRIGHT VERIFIED SPEAKERS They Glorify the Tone WRIGHT, Inc. 2234 University Avenue St. Paul 4, Minn.

D001 sAC CONNECTING FM TUNERS Circuit of the automatic vacuum -tube timer. from page (Continued 75) voltages used. Low -voltage, high-current tubes are slower heating and cool- with high -gain audio amplifiers, it may nated, try feeding the input voltage ing, giving longer timing periods. The be necessary to shield all the input leads from the pickup or tuner to the second small battery types give shorter cycles. to the audio tubes to prevent instability. audio stage. Tension of the relay springs also has a Remove any remaining instability by Where the receiver's volume control marked effect on the frequency of oper- connecting a small carbon resistor of has no effect on the signal from the ation. from 10,000 to 50,000 ohms in the input pickup, it will be necessary to mount an Any tube may be used in this circuit, additional control either on the receiver from a diode up to the more complicated IST AP I- chassis or at the pickup. Some FM tun- types. Grids may be either connected to ers have a volume control already in- the plate or left floating. I have used a stalled. If the pickup is of the high - 6H6 with diodes in parallel operating impedance type, connect a potentiometer with as little as 1.5 volts on the plate. directly across the two leads, (Fig. 4). The plate current is then sufficient to The exact value will depend upon the 1,500 -ohm relay Fig. 3-Grid resistor eliminates instability. operate a very sensitive impedance of the pickup, -usually from at about 0.55 ma. On and off periods circuit of the first audio stage (Fig. 3). 50,000 -ohms to t or tfi megohm. See were about 15 seconds each. Do not use the resistor unless the shield- the manufacturer's recommendation. The timer is suitable for starting ing fails to clear up the trouble. In all Hl IMP. PICKUP motors or lights periodically for display of audio oscillation, check the by- purposes. If a single -pole, double -throw cases TO AUDIO GRID pass and electrolytic condensers, and the VOL CONT. arrangement is available on the relay, decoupling filters before making any the oN position can close one circuit changes in the circuit itself. Motor - while the ore position closes another. boating or other forms of oscillation Fig. 4-A high -impedance pickup and control. The circuit is also readily adaptable to often appear when the switch is thrown time -delay uses, such as turning on to the radio position, due to the extend- An FM tuner is designed to connect to high voltage to a mercury -vapor recti- ed wiring and the capacity of the switch. a high -impedance circuit, so if it is fier after some predetermined time in- If the oscillation still cannot be elimi- necessary to attach a volume control to terval. I.Q. RADIO -CRAFT for nfg.«.nye..«r..-wAMr614H+.a[-4Ai.Nsf.Hie , . . «N..KOa`tïr M

Amateur 177

RADIO EN! GET THIS S00444 Valuable "newt OF "150 NEW RADIO DIAGRAMS %0" 1 EXPLAINED" í=-

to to 1 Satisfaction GUARANTEE Here's a sensational "get ac- Gliding enthusiast Fritz Compton with the 1/2 -watt transmitter he made for his sailplane. quainted" offer I This big, new "I pers onally book, "150 New Radio Dia- suerantee that at grams Explained" is yours, the end of 1 year absolutely FREE I It contains from date of re- circuits and data on the latest ceipt. my Applied Television seta. Practical Radio Radio and A Easy -to-read, 81,,x 11" size, Sailplane Transmitter set will hare earned for you at with full instructions on how least 10 times its to read and use diagrams. Be- By FRITZ COMPTON amt. or YOU mu longs in every radioman's kit. rennin it and I'll return every cent HOW TO GET SAILPLANE pilots often you paid." take advan- places" if used with a beam or properly BOOK tage of thermals and other currents tuned long-wire antenna. Ed.) B. W. Croke, Pres. YOUR FREE aloft to make motorless flights of a hun- You get this book Free just for looking over -without cost dred miles or more. Generally, the pilot The flea -power circuit or obligation -the sensational lands in a convenient pasture or mead- The 3S4 new 5- volume Coyne set "AP- transmitter uses a 7 -mc tri- PLIED PRACTICAL RA- ow to await the arrival of his ground tet oscillator, doubling to 14 me in its DIO." It's just off the pry. crew with tow car and trailer. Dur ng plate 'circuit. The Here's everything you want to final stage is a 3R4, know about radio. from basic a flight the usual procedure is for he Heising modulated with a class -A 3A4 Principles to up-to -the -minute ground crew to try to average 20 to 25 amplifier. The oscillator coils Ll and L2 Television and FM I PA, shortwave, dviat'on -auto radio, multibands, tele- m.p.h. over highways in the general are interwound on a 1 -inch form. Each transmission testing instruments and trouble- direction of the flight. When conditions has eight turns of No. 20 d.c.c. wire. shooting short -cuts, phototubes, etc., all clearly It explained. Shows how to construct, install, serv- aloft force the pilot to alter his course, is preferable to use different colored ice all types of apparatus. Step -by -step photos the ground crew may be many miles wires to simplify making connections to break equipment down before your eyes I Newest testing methods. Hundreds of subjects, over 150Q away when he lands. the coils. The 14- and 28 -mc tanks L3 pages, almost 1000 illustrations, diagrams. Writ- During the 1946 National Soaring ten for home training and field reference-a° complete, so up-to -date and practical that every man Contest at Elmira, N. Y., the author interested in radio should see it. completed a 151 -mile soaring flight to a point near Trenton, You can how much N.J. Midnight found NO him in a field SEND MONEY canu mean to clover with his sailpla'1e, your future, without cost or obligation. I'll send still awaiting the ground crew and sail- "APPLIED PRACTICAL RADIO" postpaid, for you to look over for 7 days FREE -and with it, plane trailer. The landing had been made the Radio and Television Diagrams book as an 8 hours earlier, and the ground crew outright Gift I This book is yours to keep free contacted some time later by telephone whether or not you decide to keep the 5- Volume Set In 7 days, either return the 5 -Book Set and through contest headquarters owe nothing or pay $3 then and $3 a month until at El- Rear view of the 10 mira. After this experience, author -meter plane transmitter. $16.75 is paid. Or you can save $1.75 by paying the $15.00 cash price. built this 1/z -watt, 10-meter transmitter and L4 are self -supporting coils with an for keeping in contact with the grou:ld inside diameter of s/a inch. They have Use Coupon crew through a receiver in the tow cE.r. 19 and 10 turns, respectively. Both are Now! The half -watter was designed for lc w wound with No. 14 enameled wire, YOU ARE NOT battery drain and light weight-weight spaced the diameter of the wire. The BUYING THE 5. is a critical factor in the performance antenna coil L5 is two VOLUME SET turns of insulated WHEN YOU SEND of sail planes. Miniature tubes were used wire interwound with the cold end of THIS COUPON. for compactness. (Although this urit L4. One end of the antenna coil is You are merely A asking to see the was designed for use in a sailplane, it is grounded and the other goes to an in- books free for 7 an ideal unit for use on a bicycle, motor- sulated on days. Free Beek jack the front panel. The Offer Is limited- cycle, small boat, or even on a hike. antenna is 71/a feet of wire. so mall coupon to- (We'll bet that this little rig will "go (Continued on page 78) day. 3A4 7250NC 2 t 10ONC 15 VAL 3 1p le B. W. Cooke. Pres., Coyne Electrical & Radio School r 500 S. Pauline St., Dept. A8-TI. Chicago 12, III. Send me the NEW 5 -Volume Coyne Set. "APPLIED PRACTICAL RADIO" for 7 days FREE examination LI Also send New Radio Diagrams Explained"01 u a FRË L 4.55 -BIAS MICA .__..Oki NAME AGB opsT sw2 °NOr 0V 11 Co USED ADDRESS ALL .001,00 P -P PENTODE OUTPUT TRANS A -/B- ALL .001,002 CONDS ARE MICA TOWN ZONE.... STATE The sailplane ansmitter uses ` t three dry -cell tubes -oscillator, amplifier and modulator JUNE, 1948 Amateur 781 k-

3 HOURS A SAILPLANE 110tu Make Your Own ti TRANSMITTER i tttl`¢I CONTINUOUS OPLAY Q li[t ITH THE (Continued from page 77) MAGNETAPE RECORDER! RECORDS A midget 200 -ohm microphone trans with RISCO 3 -way Home Recorder former is mounted below the chassis at the audio -frequency end of the trans- "Snapshots in Sound" mitter. The microphone jack is on the front panel. A small 41/2 -volt flashlight Over 10 minutes recording on a 10" record at dual speed- battery, or three penlight cells connect- 4% min. at single speed. ed in series, furnish the bias for the High fidelity modulator tube. The primary of a mid- record player get push -pull pentode output transformer is used for modulation, and is con- Uses professional nected as a 2 -to -1 autotransformer. recorder Better results were obtained with this An auxiliary P.A. arrangement than with the B- supply amplifier connected at the center tap and a 3A4 Ready to operate with spk. crystal mil:. . plate at each end of the winding. Ideal for music lessons, parties, circuit Now-record and play back on this amazing your child's cute sayings- The d.p.s.t. toggle switch shown in that can be heard. and CASE 55*49" instrument any sound PORTABLE EXTRA FOR the diagram was removed from this many that cannot - from a concert hall COMPLETE DETAILS DUAL SPEED transmitter when it was installed in the of heart. Simple symphony to the beat Your 40/e OFF ON RECORDING RECORDING BLANKS sailplane, because the transmitter was interchangeable capstans provide a choice 25% on C.O.D. Orders -Order From This Ad well of tape speeds for high fidelity. medium mounted in the turtleback, aft of three FREE CATALOG RC IMMEDIATE DELIVERY fidelity. or up to 8 hour voice recording. The the pilot. The toggle switch was located ideal recorder and playback unit for home, Como and Visit Our Sound Studio near the battery case and spring-loaded office, industry. and broadcast station. to off position. A cord was run to the Other standard and portable models of short- RISCO ELECTRONICS cockpit through a series of eyelets, to also available. Write AIM provide pull -to -talk operation. er playing duration WHOLESALE DISTRIBUTORS today for our free illustrated catalog featuring The 7 -mc crystal is mounted outside 25 Broadway, N. Y. 1, N. Y. our complete series of Magnetape Recorders West the case to facilitate changing crystals. and accessory equipment. The transmitter chassis and cover are Send 25c. in stamps or coin for A.C. Shaney's made of 1/32 -inch semihard aluminum, new booklet, "Elements of Magnetic Tape Re- 1 and the transmitter is completely en- and 999 Applications. Trndemo,k .cording - STAHL'S STAR STUDDED closed when the wrap- around cover is * * placed over the top, back, and bottom * SPECIAL * of the chassis and secured with screws. The front panel and two vertical sides of the transmitter chassis are bent out EASY TO LEARN CODE of one piece of aluminum 31/2 inches high and 131/4 inches long. The sides are It Is easy to learn or increase sped with an Instructograph Code Teacher. 3 inches deep and the front panel 71/4 Affords the Quickest and most practical method yet developed. For be- inches wide. Another piece of aluminum ginners or advanced students. Available tape's from beginner's 5 inch Cathode Ray, Type 5BP I tubes. 4 by 8 inches, with all edges bent down alphabet to typical messages on all Brand New. 1/2 inch, forms the horizontal portion of subjects. Speed range 5 to 40 WPM. In their original cartons; Always ready -no QRM. At this price every scope owner should the chassis, and, after bending, meas- ENDORSED BY THOUSANDS! buy a few, and keep in ures 7 x 3 inches. It is fastened to the hte Teacher front and sides by metal screws or small' literallyli ' take. theh place of aneper- reserve. How can you go ter- Instructor and ben anyone to hout fu wrong for only $1.95 bolts. The wrap- around cover which Sher n assistance.sssnc1e Thousandsu of auceesfUl ton have the System. Q se Prompt Delivery-Write Dept. RC-6 Write I tfonoday or convenient rental etd 25% deposit required on C.O.D. order Shipped F.O.B. New York. INSTRUCTOGRAPH COMPANY Min. Order 52.00 4701 Sheridan Rd., Dept RC. Chieti. 40. III. MICHAEL STAHL, INC. 39 VESEY ST. MIRACLE KIT VALUES! 2882 -3 -4 New York 7, N. Y. H03 OSCILLATORTOR Tel. WOrth 4- TUE KIT Hi -gain with microphone Jack d It parta Includ- ing hhes $2.95 10 WATT TUSE Hi.OAIN Separately Radio Top view of chassis shows tubes and battery. Including drilled chassis, hardware. soldermircuit it: Get Started in gram, info.. etc. Lees Tubes 56.93 back, of every sRSA TROUBLE 10 "HOWTO- DO -IT" BOOKS forms the top, and bottom the tee e trouble. All arts including rase. case, is made from an 8 x 101/2 -inch w tent leads. plug 2 y x 6' 3 $3.95 Gott s lid foundation In radit,L17. PHONO- AMPLIFIER KITS -ALL PARTS INCL. TUBES means of the. 10e timely test piece of 1/32 -inch aluminum. 3 Tube Kit $4.29 2 Tube Kit $2.95 Each clearly written, profusely Illus- Pwr trans. 1500v C.T.. 150ma, 6.3v 2.55, trated, contains over 15,000 swords. The placement of parts is not critical 6.3vv 1.6a 5v 3a; 115v 50 -60 rye. p1I.. 95.08 ea. You'll be amazed at the wealth of . 0.3v 6a. 7.000v insu 1. 1 Fil hooks. atExcellentró rnreeference -Ideal because of the low power. In the origi- so-e0saye. pr1. $2.29 N. for technical library. Your money Write for Usa of bargains in Radio and Electronic back if not satisfied. nal transmitter, a special effort was parts. Also free data, b designed by portion of ROST. O. made to construct the r.f. HERZOG. 5 BOOKS for 50c the transmitter in the smallest possible Oniversafgene a cop.., 10 BOOKS for $1.00 space to gain experience in miniature 365 Canal St.. New York 13 (Dept. C-R) Wenger 5.9642 Sent to You Postpaid construction. An eyebrow tweezer was Terms) No. Maim u. found to be much superior to long -nosed DOerie Short WWave ve Sea No. 6--How oinH F1ASN rNa,rVOLTAGE No. 2 -How To Make The With Radio pliers in small confined spaces. H Most Popular AII-Wave 1 No. 7 -How To Read Radio Taro that knob. Extinguish the neon Diagrams voltage dial. and 2 Tube Receivers Use caution in insulating the variable glow. Instantly read cif No. 3- Alternating Current No. S -Radie for Spinners MINI -IOUs model 400B measure. 65 for No. Electrical [s to 660 v. AC. Also DC. Tells AC or About aerials peNmentile condensers from the front panel, be- DC. Virtually burn -out proof. Guaran- No. 5- Beginners' Radio Die- No. 10- Television leads. cause they carry the full plate voltage teed for 10.000 hours. I2 test Remit by check or money letter If you A "must" in electrical and radio work. send ney order-registero of the transmitter. The r.f. coils are At dealers or postpaid $2.50. (C.O.D. i tr.r extra). PUBLICATIONS mounted directly on the condenser ter- RADIO minals. This is made possible by cutting .INDUSTRIAL DEYICES,INC..EDGEWATER 3,N .J. 25A West B'eiy. New York (7) RADIO -CRAFT for 4:M!4,nR+n!,rWO. ;(reto.-c..p.4*1.FM,W.A±7!Ww4

- A®atems I79 a 3% x 1% -inch opening in the horizontal portion of the chassis, immediately above the variable condensers. Radio - Television - Electronic Batteries are two 45 -volt Mini nax's for B- supply. Two 1% -volt batteries in Parts .& Equipment Specials 2 out of 3 series supply the 3 volts for th( fila- ments. TELEVISION -CATHODE RAY HIGH Tuning 10 VOLTAGE upon 2000 volt D.C. Power Supply Need It! To tune the rig, remove all tubes ex- Why bother with bulky and dangerous 60 cept the 3S4 oscillator. a 0-50 - cycle supplies or expensive R.F. power sup- Connect plies when you can purchase a complete 2000 ma meter in the B -plus battery lea l and volt D.C. unit (not a kit), ready to plug into ESPEY the 110 volt A.C. power line. The ridiculously 7ke Cadent- tune the oscillator plate circuit for mini- low / ai au/Ú price has been made possible by a fortu- mum current. The dip is usually about 1- nate purchase of high quality components. 2 These units are brand new, completely tested mils. The 3A4 doubler is placed in its and socket and plate circuit tuned to reso- guaranteed. Price $7.95 nance. The oscillator will plate circuit 4000-6000 VOLT TELEVISION need retuning at this time. It may be SUPPLY Similar to the unit above, but has a much found that best results are obtained in higher D.C. output voltage suitable for use with the new 7" and 10" television tubes. exciting the 3A4 doubler by coupling PRICE the grid condenser about two -:urns $12.50 down from the hot end of the tri-tet TELEVISION BOOSTER! plate coil. Increases signal strength to the television re- r ceiver 16 -18Db. Rejects unwanted off- channel Insert the modulator tube and connect interference. Simply installed by connecting the antenna. Tune all circuits for in series with antenna terminals of receiver, self- contained power supply. minimum total B- current. The dip i 3 the Three models available doubler plate will be about 4 mils -with- Model TVf .-Channels 1 thru 6 out the antenna connected, and I mil Model TVH- Channels 7 thru 13 Model FM ---88 -108 Mc (FM Band) loaded. Total current for the transmit- Available in Walnut or Mahogany finish According to the RMA, ter loaded is 40 to 45 mils. Do not at- Size 3" z 5" z 6" tempt to use 135 volts as the 3A4 Price $26.95 over 18 million consoles doubler will not modulate satisfactorily at this higher voltage. SPECIAL! were built before '44! Magnetic Recording Wire -1% hour spool of This transmitter has worked out 2 GE steel recording and playback wire $1.95 miles across the city with a wire sus- priced for quick sale That's right! The newest are four years old, and there are more than II million of pended in the radio shack. In the sail- PHOTO-ELECTRIC TUBE them that are ten ears old. the 18 plane, with the antenna attached to the GE Of type P123 sensitive gas phototube- suitable for million owners, 51%, top of the fin, it a of 5 miles regular and Invisible infra-red light. Has four prong or over 9 million has range rocket and Calcium light sensitive element. LIKE their when the sailplane is on the ground. In cabinets -in spite of the fact Price $2.95 that the vest majority of receivers are flight, communication has been main- Cathode -ray tube Mask and Mounting bracket for 5' hopelessly tubes. Excellent for use with 5- television sets or obsolete, lacking such present - tained with a ground crew in a car 65 oscilloscope. day essentiels as FM. miles away, and the transmitter was Price $0.25 Chrome panel escutcheon for above --4y' diameter Furthermore, over 90% of the console once heard 600 miles from Texas. opening-sultable for use with cathode -ray tubes a' round owners WANT FM, but less than At the 1947 National Soaring Contest dials. 6% HAVE Price $0.25 it. What a replacement market! in Texas, nine flights were made, mostly TELEVISION PICTURE TUBE -9 Inch eleetromag nett. type. This Is the MW22.2 tube used by GE In It was to fill this tremendous need over 100 miles, and one of 221 miles. On their television sets. Can be used In other sets de- that signed for electromagnetic deflection. Has standard ESPEY designed its line of top -quality cus- seven flights the ground crew was on tom -built hand at the time of landing. Many times Complete3 °feng bióe.with Instrvetion booklet $13.95 chassis, supplied complete and ready to operate in your customers' cabi- it was possible to guide them into the nets. A SCIENTIFICALLY DESIGNED PHONC SCRATCH FILTER For further details about the ESPEY re- Resonated at approximately 4500 cycles effectively placement chassis, and the opportunities redueing objectionable needle scratch without niter ing the brllllaney of reproduction. in the replacement industry, we urge you Contains s HI-12 SERIES resonated circuit. Tested to write today to Dept. by means of an audio oscillator and an oscilloscope C -6. to give 22 db. attenuation with very low signal loss. Attenuation may be regulated by means of a SPECIAL MINIATURE galn control. EASY TO ATTACH lust two wires to clip on. Compact. Price $1.65 "Established -1928" THREE TUBE PHONO AMPLIFIER Bottom view of transmitter. Crystal at right. An assembled unit ready for Installation using tone and volume control and six feet of rubber pasture chosen for landing, and land cord $Z 95 Do you ne (Not including Tubes) , W directly toward the trailer, stopping With Complete Set of Tubes $3.95 only a few feet away and in position for BINDING POSTS? PHONO OSCILLATOR The XL U CH POST with its Spring immediate disassembly. The ground Action s Constant Contact and Wireless phono oscillator transmits recording for quirk connection. crew was my wife and W5KUB of Crystal pick -ups or voice from carbon mike through Manufactured in All Aluminum Type M radio without wires. Can also be used as an intercomm at Wichita Falls. by using P.M. speaker as mike. Price Aluminumum Body. Bakelite Top Type r (excluding tubes) $2.95 at each. A number of radio amateurs were With Complete Set of Tubes Types CeNP. ALL BRASS- STAIN- 53.95 LESS STEEL SPRING St PIN. PROVEN reached during the flights. They were by 240 HR. SALT SPRAY TEST sa NON- CORROSIVE at Mk each. usually within 50 miles line -of- sight. SPECIAL! SPECIAL! Manufacturera and Dealers Liberal W5IZL of Electra, Texas, was especi- Mammoth assortment of radio and electronic Discounts parts, not lees than TEN POUNDS of new X. L. ally cooperative. She left her receiver transformers, chokes, RADIO LABORATORIES condensers, resistors, 420 West Chicago Ave., Chicago on our frequency at all times, and a switches, coils, wire, hardware, etc. A super - 10, III. huy for experimenten, service- short call would always find her ready men, and amateurs for only $1.25 to relay any message to contest head- All popular types of Satisfaction guaranteed on all merchandise. quarters. All prices F.O.B. New York City RADIO TUBES at the lowest ever offered Several sailplane pilots are licensed WRITE FOR CATALOGUE prices radio amateurs. Reception aloft is crys- 70% OFF at current list prices tal clear, and, as a 10 -meter transmit- RADIO DEALERS SUPPLY CO. (25% deposit required on C.O.D. orders) ting and receiving location, a sailplane 135 Liberty St. New York, N. Y. HARRIS SUPPLY CO. can best be described as terrific. 1336 W. Chase Ave. Chicago 26, Illinois 4 JUNE, 1948 Test Instruments 80 ECONOMY MULTIMETER WESTERN By HOMER L DAVIDSON THE small 0 -1 -ma meter used in this volt- ohmmeter is a 3 -inch Trip- ELECTRIC lett with an internal resistance of 27 BRAND NEW WATT -35 ohms. There are 4 d.c. voltage ranges:

Priced Far Below Wholesale Cost! Full frequency response Driver Unit complete with projector. Excellent for Concessions, Bell Parks, Mobile, P.A. Work, / Stock up now, Never again of- $ 2495 co.s. fared at this sensational price. (* N.r.e. LAMPS ELECTRONIC PHOTO FLASH EQUIP- Extra Heavy Duty Unit. MENT, THE FAMOUS "MODEL 1503" AIR- CRAFT FLASH UNIT. V. BOOSTER This powerful high quality equipment was T. made for the U. S. Aircorpa and will be Clarifies pictures. In- shipped to you brand new in original boxes. cr ignal strength. THE POWER SUPPLY Ghosts with Helps eliminate Is built Into a beautiful gray finished casa, and picture in- all connectors. relay control. 2 condensers each 2000 external Volts, 50 M.F.U. light output 110 Watt seconds, terference. Simply hook an be used with any 12 Watt battery as a profes- up in series with Tele- sional studio limb equipment. The power pack alone vision Antenna. No Pow- is worth more than the price we are asking for the complete unit. er supply required. THE FOUR HIGH SPEED FLASH TUBES Complete, self- suffi- are plastic sealed, unbreakable. 12 million peak cient, housed in an at- lumen light output for more than 15.000 flashes. Octal socket and phone tip form the "switch." IN ADDITION TO THIS WE SUPPLY: $995 tractive black crackle aluminum reflectors. transformer. connectors. con- finish metal case. necting cords, spare parte. diagram and instructions Attention DEALERS DISTRIBUTORS from 0-10 volts, 0-100 volts, 0 -500 uon how to use It for battery or on how to convert the - nit for 110 Volt A.C. Send for r list of many other Items, fir below volts, and the highest voltage range IT IS THE BEST VALUE IN WAR SURPLUS wholesale cost. on company letterhead. MATERIAL. All prices F.O.D. N.Y.C.. 25% Deposit. Bal. C.O.D. extends to 1,000 volts d.c. All the voltage- dropping resistors are plus or WHILE THEY LAST. $6800 PRICE complete .... minus 5% accurate and were selected MANUEL KLEIN with an ohmmeter from a number to get C I N EX, INC., Dept. CR 74 CORTLANDT STREET ones actually accurate to within 1 %. 165 WEST 46th ST. New York 19, N. Y. NEW YORK 7, NEW YORK 0 -INA + t 500K 400k 90K IOK WANTED- DC VOLTAGE WILL PAY s1.00 PER COPY for the following melee IKV 500V IOOV 10V OFFICIAL SHORTWAVE LISTENER MAGAZINE June -July 1935 April -May 1936 Fig. I -Fou voltage ranges are available. Copies must be In good condition. All the different voltage ranges, ohms, -Craft 25 West Broadway, New York 7. N.Y. Radio and current circuits are broken down into separate circuits for clear understanding while discussing them: the d.c. CHOCK voltage schematic circuit in Fig. 1; high NOW -AFTER SEVEN YEARS FULL and low ohms in Fig. 2; milliampere schematic circuit in Fig. 3. Fig 4 shows OF BUYS! & 25B8 TUBES the complete instrument. 12B8 The low -ohm scale is from 0 -5,000 Now Available - ohms. The low -ohm readings are well Composed of adapter, 1-6AT6 tube. 1-6BA6 scattered over the entire range. The tube, and 2 miniature sockets. The unit takes has proved very handy on less space than the original 12B8 or 25B8 tube, ohmmeter and the adapter base will fit in the 12B8 or 25B8 this range to test for shorted i.f. trans- socket perfectly. Nothing else to buy -unit is windings. The high ohmmeter complete. Just plug in and it 'works!! Sold on former Amoleurs money -back guarantee. range runs from 0- 500,000 ohms and Experimenters Industrials 't 12B8 or 25B8 unit, complete: $2.49 each can be extended with an external bat- Institutions 10 units for $22.50. tery. The only batteries used in this Government Seed 20% Dee.. Bal. C.O.D. -Min. Order 82.00. Agencies Writs far new tre. bargain WAN. small meter were 3 small flashlight cells which total 412 volts. RADIONIC EQUIPMENT COMPANY COMMERCIAL RADIO The range was extended from 36 Wattle Street Boston 8, Mass. current 170 NASSAU ST., NEW YORK 7, N.Y. a fnbune (batre Erman" 0 to 100 milliamperes by shunting Tel. WOth 7.0421 (able (HUMOR small resistance, R5, across the meter terminals so part of the current would RADIONIC EQUIPMENT CO.. Dept 106 TUBE SPECIALS be bypassed around the meter. This re- 170 Nassau Street. New York 7, N. Y. is bar- AC -DC Me -O0L60T. 35Z5GT, 128M. B7. Q7GT..$1.90 sistor, for a 27 -ohm, 0-1 ma. meter, Rend st once your free catalogs, supplements and Miniature Ate-50115 35W4. 12ATe. BAB. BR6.... 1.90 gain TWO JUMBO ASSORTMENTS * 0.2727 ohm. The small resistor was of rradiodrtmalc pans and equipment * 40 -55115. 20 -5010. 10 ea. 351.6. 12SA7. )17. Q7. 100 tubes. wound with 1 foot of No. 34 enameled 40 -35W4. 30- 501í5. 10 ea. 12AT8. BAI. BEE. 100 tubes. % RAMS Either of the above epeeists at only $34.00 wire wound over a -watt carbon re- Every tube new Md perfect. Guaranteed 100%. Selenium rectifiera 100MA -tor for $7.20 sistor. It is best to calibrate this P.O. BOX or STREMI' Postage arena C.O.D. colors seed ter : de :salt o,i resistor against an accurate milliam- TOWN STAT HALLMARK ELECTRONIC CORPORATION meter. L 592 Communipaw Ave. Jog%y City e, New Jry RADIO -CRAFT for 4 Test Instruments

To eliminate a wafer gang switch for changing the different ranges E. sim- "wit' o tÄ4 Pte-4)- ple 8-prong octal socket was used. The 948 Radoltzk RADIO PROFIT GUIDE male prong is a phone tip pushed into JUNE SPEC` RESISTOR KITS $1.45 the end of a polystyrene rod. These are 100 assorted carbon and CONDENSER KITS Ire wound resistors ... NI E5 NEW 6 ranges, and an a.c. voltage rangs was % to 10 watt. Wide 50 assorted paper and added later. This is range of values. All mica condensers ... all COMPLETE optional with the standard items. now . . . good value. constructor plenty if. as of space still Wireless Phono Oscillator $4.52 RADIO Operates as far as 100 t. from radio and can be used with automatic recur changer and plagen ... complete with 2 tuba all wired and tested. Diagram. PROFIT 0_IMA 1.04 00-1001IA - _ b GUIDE '111 -LOA

2K 21( 4.5V FREE NIA LOA

Fig. 2 -The meter is in low-ohms position. Mike and Phene Amen- Item $14.95 available in the small cabinet. Pin con- Phono Pre- This unit sold nections Ampl Ser $4.95 °omelets with are shown in Fig. 5. Pin No. 5 This nit is for newer transform- RADIO REPAIR PARTS TOOLS was left over for the added a.c. v3Itage G. F. Reluc- er, 3 tubes and tance type car- 3 controls . . SOUND SYSTEMS TUBES and the last pin left vacant for some tridge. Com- all wired and pletel wired. teeter!. Diagrams PHONO EQUIPMENT & SUPPLIES future test position. tested Supplied supplied. TEST INSTRUMENTS ETC. with diagram. a d tune GSM. A s.p. 3-position switch (top of case) Big, new ENLARGED complete catalog switches low ohms and milliamper:s and RADIO PARTS showing thousands of Radio Bargains G.E. Reluctance Cartridge. List ST.95 $4.54 sent to you immediately. Helpful, money- has one open position for other ranges. 4 or 5 PM Speakers 1.15 laving buying information. Send coupon 8 PM Speaker 1.55 today' After the small volt- ohmmeter has 5. 45D ohm dynamic Soh. with 50L8 output 1.95 been thoroughly inspected after wiring Selenium Rectifiera -100 Ma Famous Make .69 % meg. Volume Control and Sw. long shaft .35 BIG VALUES, LARGE STOCKS, and soldering all connections, the ohm- Ose. Coll 12SA7 .15 8 ft. line cord .13 FAST, DEPENDABLE SERVICE. meter range should be tested. First place Asiatic Crystal Pickups 1.89 Astatio Crystal Cartridge. I. -70A, L-28A, L-40 1.59 the small tip in the high -ohm jack and Alliance Motor and Turntable 2.50 FREE...SEND TODAY also insert a pair of test leads it their FAMOUS MAKE CONDENSERS RADOLEK CO., Dept. C -068 801 W. Randolph St.. 8. respective phone jacks. Rotate the 5,000 - 50a30 150V. ....$ .45 25.:ÁV. $ .29 Chicago Ill. ohm potentiometer clockwise, plac ng all 20:20. 150V .35 18. 450V. .39 Please send your Free Profit Guide Catalog and 20x20 (10). 150V 400V. or $00V. Per 10 regular Supplements. (25) .39 .01, .02. .05 5 .49 9:8, 450V. .49 .001, .002, .005 .. .49 Name 25. 25V. .29 .1 .59 Address i All prices F.O.B. N.Y.C. -On C.O.D. 25% Den. City 7. 0- ZOOMA THE ROSE COMPANY ,-.no.... State 88 West Broadway, Dept. (C) N.Y.7,N.Y. LOA 0 -I0OMA SAVE AT RADOLEK

Fig. 3 -The current range measures 0 -II ma. prods together will send the meter indicator to zero. With this type of circuit its resistance in the circuit, and touch the battery is in the circuit at all times the 2 leads together. The meter movement should read toward full scale. Re- adjust the meter zero potentiometer, RADIO until the meter reads full scale. Now AC IKV SOUN Dand TELEVISION touch the 2 test leads to a low -ohm re- MA LO 5099

sistance and notice the meter movement. NI 1009 The meter should not read full scale, as LEARN QUICKLY IN 10V THE GREAT resistance was placed in circuit. If at NO CONN SHOPS OF any time the zero adjusting potentiom- Fig. 5 -Pin connections for range selector. COYNE 0 -IMA and be must switched off when not in Get ready for a better job, bigger pay NOW In 1,011 use. This can be done with the milli- Radio. Cash in with "All- around' knowledge of ampere-low -ohm Radio-Sound-Television. Train on actual equip- MA_ ..LOA switch which is in the ment not by "Home-study". You learn quickest 55-SEE TEXT off COYNE because it's a real SHOP course! 4 position at middle position. Do not at i leave this switch on in either position RECT 4 G. I. APPROVED..also Finance Plan while checking d.c. voltages for the NON -VETERANS. Don't let lack of 500( IKV AC meter for cash hold you back. Islany earn while 10K MIL will burn out immediately. It is best to learning. FREE Employment Service to graduates. Get Hln switch the test leads of any multimeter facts today! to a voltage position immediately after 101( 10Y NC SEND COUPON FOR FREE BOOK e any resistance or current measurement. Send at once for Big Free Book on This will prevent many unhappy acci- Radio, Sound and Television, and facts dents. As shown on the meter face the about our Finance Plan. 21( SK MAIL THIS COUPON TODAY - - -- LI _. _.A1,, 4.5V + left -hand (red) test jack is positive. S.W. COOKS. Pras., Goya. ENwMcal end Radie Scheel 1(111 Whenever polarity is switched, the 2 SOO S. Pauuee St.. Dept. As -su, Chieage 12, W Fig. 4- Schematic of the complete instrument. test leads are reversed. The a.c. voltage Please send Big FREE Book and complete details range was added some time after the NAME eter will not adjust the meter move - meter was constructed. If the builder de- STREET raent to full scale, the flashligit cells sires it, the data is included in Fig. 4. CITY STATE must be replaced. Full -scale reading A half -wave miniature copper -oxide should be checked periodically. rectifier was used to rectify the a.c. TUBULAR ELECTROLYTICS To test the low -ohm scale, the switch voltage to be measured. Fresh stook Fully guaranteed pin was shifted to the milliampere and The parts and 20 mfd. ISO V. 10 for $1.79 material needed for the 20.20 mfd. 150 V. 10 for 2.49 low -ohm prong and the potentiometer meter are very small. The whole instru- e mfd. 450 V. 10 for 1.85 Postage extra. 25% desalt on COD. adjusted so movement reads ful scale. ment can be wired in a few hours. The Write for our free hernia lists featuring The milliampere -low-ohm switch is cabinet used for the original model "AMERICA'S BEST BUYS" turned to low ohms. Touching tae test measures only 4 x 5% POTTER RADIO CO. inches. 1312.1314 McGee St. Kansas City I. Me. JUNE, 1948 f?- I _ Communications

PREFERS SHORT WAVE SIGNAL Dear Editor: GENERATOR I have been following with great in- 0 terest the arguments in RADIO -CRAFT on 0 kt only FM vs. short wave. for It is true that at this time FM has a /Send 295 very high plane of programs, but I re- 456 KC - 465 KC - 600 KC - 1400 KC member when AM was the same way. COMPLETE WITH TUBES READY TO OPERATE FREE COMPLETE CRACKLE- FINISH CABINET Now listen to it! TWO OPEN CHANNELS FOR ADDITIONAL FREQS. INDIVIDUAL TRIMMERS FOR RECALIBRATION To me, international short wave has SHIELDED OUTPUT LEAD BULLETIN FULLY GUARANTEED -FULL INSTRUCTIONS proven that it can present good dra- matic, musical, and public service fea- Sent you every month. Its FM TUNER KIT One tube experimental FM tuner. Amazing $295 tures consistently. One merely has to crammed full of real buys. performance. 111 With tube, punched A post cord with your I as and full i truet l.. tune in any daytime AM broadcast to name and address brings find out what has driven me to short- PRE -AMPLIFIER for GE it to you. You can't allot d $475 wave my opinion, Reluctance pickup complote programa. In FM will to miss its bargains. Mail r "3 PHONO-AMP. become the same as AM. your cord today. Complete with Tubes S e ONLY I can get the best music over short wave and it is music cannot be VALUE PRICE LEADERS PHONO -USC. that and Wireless Type-Mike 5 4g matched by our own ultra -commercial, or Phono Imp. Comp. THAT CANNOT BE MATCHED top -heavy system. WRITE FOR LITCRATUR" JOHN R. GATES, E CONSTANT E LEC TRI C New London, Conn. V Its tnoettin T 11 .li '1 N t // 1 m adp. (How about the noise, interference, t "y7 Our w° !',` ë < b, and heterodynes of the shortwave .r notlontis10"'"°"""b' Sots.- OPPORTUNITY AD-LETS ? 01 ädinav °, bands Editor) . - net b°g RSEQ° t s Advertisements to this section cost 25c a word for Whoit °h tong euh insertion. Name, sddrow and initials must be W conYl fall accompany ^ó °coloto +córe ywtK Included t the above rate. Cash should s eon all classified advertisements unless placed by an TRAINED MEN NEEDED No advertlaemont for eatil accredited advertlaing agency. of oP9'°"-f °v Ói FA ohm' less than ton words accepted. Tm percent discount Dear Editor: 100 six issues. twenty percent for twelve boues. Obiee- or misleading advertisements not accepted. Our experience has been that while SÓ0 M °hm. Per 10 $5.50 llmable 15M ohms Advortlsemmta for July, 1948. issue must reach w ° 24. 1948. thousands upon thousands of men have 1S Meg 35,00 not later than May ohm pssi. $ Radio -Craft 25 W. B'way New York 7. N. Y. SO M been trained in schools and the armed M Kn led 56W11<6, 39c eachlD°to' services, there is always a shortage of AMATEUR RADIO LICENSES. COMi'i.16TE CODE less radio ex- competent practical personnel when you 500 and theory preparation for passing amateur """1"s alelnatiom. lime study and resident couraea. American want to do anything serious in a com- Radio Institute. 101 West 63rd Street. Nev. York City. Beo our ad on pep 86. mercial way. For example, getting a RECtIF1ERS RADIOS, RECORD PLAYERS, TUBES. PARTS. SEND good FM repairman or television instal- SElEN1UMelves for free bargain Wt. Hallmark. 594 Uommunlpaw, Jersey lation and repairman is extremely diffi- °k City 4. New Jersey. l cult Every real good one rapidly mi- for ióÚ size 59c FTC.. FOR SALE. COOKSON. m RUUBB R TAMPS, grates into some venture where he can (,ist b1 Regula LANCASTER. ALLWINE & ROMMEL. 436 BOWEN more adequately use his ability. He then mil. size 79c7 Building, Washington 5, D.C. Registered Patent Attorneys. attempts to get novices to work for him. í2 ?5 Practice before United States Patent Office. Validity and Re20or list Infringement Investigations and Opinions. Booklet and Hence, there is a sad shortage of servic- form Evidenes of Conception" forwarded upon request. ing technicians for the FM and tele- MAGAZINES (BACK DATEDI- FOREIGN, DOMESTIC, vision business. O5N° arts. Books. booklets. ubscripUoa. Din-ups, etc. Cata- $ log 1De (refunded). Cicerone's. 863 First Am, New The complexities of shooting trouble ¿V E °FUonóS ESof 100r "1 York 17. N. Y. our Cott' 53' G and SFh«k Y through involved circuits require ex- PHONOGRAPH RECORDS 20e. CATALOGUE. PARA- SuPPIy Roti^ perience and what t;m;ted d AG5 (go- 1 .9 mount, KQ -818 East Market, Wilkes-Barre. Plena training beyond the t AmP public has been educated to pay for. We 1 pG1/ 3AG101B1ow 40 TYPES OF ELECTRICAL INBTRU- 2 z. WB REPAIR ALL 3AG checkers and analysera. Haaelton Instrument SFEb manta, tube are observing in television transmitting Co. Meter Laboratory). 140 Liberty Street, New AmP (Electric SFE A 3AG10 $1.9 York, N. Y. Telepitone- RArclay 7-4239. equipment that the maintenance man 3AG15 $1,60 of such is SFE9AmP YOU CAN ACCURATELY ALIGN SUPERHETERODYNE transmitting equipment in- sa. la receiver. without signal generata. Complete instructions deed difficult to train and expensive to ,FE. 20 AmP. tlot Assorted 31. Moneyback guarantee. Chu. Gates, Pecos 2. Texas. keep. An ordinary camera chain main- OuontNy Pnce RADIOMEN. SERVICEh4EN, BEGINNERS - MAKE tenance man has to be far better trained ore money. eas117. Quickly. $250 weekly possible. We and have show you ho. Information free. Merit Products. 216 -30L far more basic ability than the 132nd Avenue, Springfield Gardens 13. New York. master trouble shooter of an entire voice 4's broadcasting station. Indeed, they are BUILD YOUR OWN PRECISION VOIJT- OHM -CAPAC- Ity meter. Complete set of plans 8.50. Bradshaw Imtru- like the difference between the complex- at 73G .outOFf! ments, 348 Livingston St., Brooklyn 17. N. Y. ities of a giant airliner and the com- td oar - parative simplicities of a cub plane. t"'", 1507.4 ENGINEER, GRADUATE MECHANICAL. AUTOMO- fftubes.t you bilo- alrcrafL Age 44, veteran. Knowledge English. French. Radio, electronic and television arts them Gorman. Twenty years' experience. industrial. railroad-, mode road- A air-traffic field, public relations. radio. P. O. Bog move along in the laboratories at a tre- kno w N110 273, O.P.O. New York 1. t gor mendous speed. Technicians and engi- 'fad tai 9 of wrong WESTERN ELECTRIC CARRIER TELEPHONE AND neers who do not keep up with these Telegraph Equipment and Components. FRten, repeating rapid improvements fail financially coil, transformers. equalizers. Types CFI, CF2, R, C, and and ORDER INSTRUCTIONS other carrier equipment. Telephone and telegraph repeat- move into other professions. The tech- Minimum order- S2.CO. 25% de on. Box No. RC -A8, Radio- Craft. 25 West Broadway. New nical world belongs to the persistent and posit with order required for oll York 7, New Yak. C.O.D. shipments. Be sure to include aggressive. DEMAND THIS sufficient postage- excess will be 26 YEARS' EXPERIENCE RADIO REPAIRING AT The more you can do to help show the SEAL OF QUALITY refunded. Orders received without guar fingertips. I've perfected simple system you m postage will be follow step by step. No formulas or calculation.. Cuts widespread need for competence both shipped or express collect. All prices repair time to minimum. Total price $2.00 postpaid COD. Moneyback guarantee. Rtes Radio. 14816 -7 Grand- on the part of the old and new techni- F.O.B. Detroit. river. Detroit 27. Sfiehlgan. 4 1 cians, the better. Further than that, there should be some discussion of the IV-UM./ SUPPLY & ANSWERS TO QUIZ ON PAGE 61 words, "engineer" and "technician." A 1. ; 2. (a) ; 3. (b) ; 4. (c) ; camera maintenance technician has ENGINEERING (a, c) CO., Inc. 5. (b) ; 6. (all) ; 7. (b) ; 8. (c) ; 9. (b) ; actually to know more engineering than 125 SEEDON AVE. DETROIT I, MICH. 10. (a, c). many a competent voice radio engineer. RADIO -CRAFT for Communications

It is time that those of us who pioneer in these arts give attention to the mean- TECHNICAL KOS ing of these names. The engineer of 20 years ago in radio would not even be a OIL -FILLED TRANSMITTING competent technician today. CONDENSERS MICAS U. A. SANABRIA, PRESIDENT, .05 MIT 1000Y $0.35 30.0 90VAC $1.40 AMERICAN TELEVISION, INC., .05 800V .14 30.0 330VAC 3.75 .leres the .1 2500V .75 000025 2500V .15 1 7500V 1.85 00005 2100V .15 Chicago, Illinois 2x.1 7000V 4.10 .13 .12 15000V 7.96 00005 5000V .85 .25 1000V .35 000067 2500V .20 WANTS ESPERANTO TAUGHT .25 4000V 2.15 00007 2500V .20 KFProts .25 6000V 3.75 00025 2500V .25 10r.25 00025 V .83 more Dear Editor: d °000VBII 1.28 0005 QV .25 .5 0H2 6050V .85 day/ I have just read your editorial," Radio .5 °8(10ÓV .7Ó 5000V .B5 .75 400V .30 0001 250017 23 in the Next War." I taught electronics .85 800V .35 0011 5000V .85 i.0 1000V 002 1.200V .20 at the Army Air Force Radio School 2.0 .20 002 at Truax Field, Madison, Wisconsin, 2.0 0025 300ÓV .65 2.0 1000V .60 00275 for three years, so I think I have some 600V .60 2500V .30 Here's one of the finest business ó 1000v 1.00 600ós opportunities understanding of the importance of 5.0 220VAC ..66 250°00V .355 in years. You can 6.0 800V .70 :óós 1, .V. .15 radio in war. According to the Gallup 6.0 1000V cash in on the fact that people like poll, 65% of the American people favor 8.0 650V 1 855 ,ó°006 82ÓÓÓV .05 8.0 1000V 1.75 radio with their meals. That's why 10.0 .oÓ18 V. making the U.N. into "a more p.3rfect 800V 1.00 1z0Óí .15 Tradio- ette -a small, compact coin - union," and only some 13% are opposed. TUBES -CHOKE operated radio designed for res- A uslion of nations would be so strong 8176 METAL $0.89 12K8 METAL .29 taurant and tavern booths-has that any country which did not belong 100MA -10H, 250 OHM 1.59 become so nationally would never dare to attack, and, I be- POTS: 20K- 50K -100K $0.19 popular. Plays POTS: DUAL-1 MEG, % MEG, 15 minutes for 10c. lieve, would'eventually join. Texas, for "250K -50K" .30 example, might have continued is an SHIELDED WIRE #22 50 Ft. for .65 RESISTOR KIT ASSORTED 14,11W Small Thousands of high - independent country, but it saw a great 100 for 1.49 yield locations are advantage in joining the Union. BATHTUB KIT 3x 1 5 06 ETC. Investment available if you get In forming a federal union, the 10 for .58 in on the ground Boor. CONDENSER KIT .01,.00001....100 for 2.99 Only a small invest- United States had one great advantage MICAS .01, .002, .005, ETC. All Values .08 ment needed to operate this lucrative full or part time business. Tradio is which the world does not now have -a 01 150V PAPER (MIDGET) ....60 for 1.00 the nation's leading manufacturer of common language. This is where radio 0.1 600V PAPER 8 for 1.00 coin-operated radios. can do a great work for world peace. $2.00 sin. order F.O.B., N.Y.C. Add mistime 50% deposit. balance C.O.D. with ell orders. For Complete Details .. . Let radio back up its endorsement of Nanufa Curers Inquiries Invited. Send for Flyer. Esperanto. One can learn to read Es- Prices are subject to change without notice. Contact Us Today peranto in one hour because it is in WRITE Dept. U.6 essence a code. In six months, with lessons of one hour a day, any person can TECHNICAL RADIO PARTS CO. St. Dept. 7, learn to speak the language excellently. 266 Greenwich RC -1 N.Y. N.Y. TRADIO, Inc. NEWRJERSEY If we want peace, we must do two jobs: make the U.N. a more Ierfect union, and adopt a common language. GLENN R. TURF ER, NEW INDOOR TELEVISION ANTENNA Madison, Wisconsin ELIMINATES REFLECTIONS (The Editor of RADIO -CRAFT many years ago tried for many months over broadcast station WRNY, then in New York, and through one of his former -VISIBEAM- radio magazines, to sell Esperanto to For Use With All Television Receivers. Ideal for radio people. The effort was kept up for Hotels and Apartments. Compact-I2r" Diameter over a year but the response was so -Table Lamp Six.. Made of Polished Lucite. so low is Tunes to all channels. poor and the interest that it THERE IS NO LANDLORD OR INSTALLATION felt an artificial language will probably PROBLEM WHERE THE VISIBEAM IS USED. never succeed on this planet. -Editor) AFRAID TO ADMIT FAILURE RETAILS AT $, 695 Dear Editor: At Your Dealers I agree that it is unfair to plant a defect in a radio. This procedure is not MFG. by BURNETT SERVICE CO. a true test of the serviceman's ability, PAT. APP. 178 W. 168 ST., NEW YORK 52, N. Y. but it may indicate the extent of his honesty. There is no harm in admitting that occasionally problems cannot be solved immediately or at all. I'm an electrical engineer employed by a construction company. Despite my DTEL6TRPíZID experience, there are times when problems that I cannot handle confront me. Rather than make the situation worse, Atlantic City's Hotel of Distinction. I seek assistance, or permit someone The Ideal Hotel for Rest and Relaxation with more experience than myself to Beautiful Rooms Sah Water Baths Glass take over. inclosed Sun Porches Open Sun Decks Many radio servicemen, though, will atop Delightful Cuisine Garage on take a set and "botch it up" rather than premise. Open All Year. say to the customer, "I'm sorry. but I can't seem to find the defect." FIESTA GRILL FAMOUS FOR FINE FOODS DANIEL FEERST, Exclusive Penna. Ave. and Boardwalk Elmhurst, L. I. JUNE, 1948 CIIIII III II IlicntilNlS 841 SERVICE CHARGES TOO LOW ADDED VALUE AT Dear Editor: TOM ALLEN'S I am a radio technician, and I have also worked for a wholesale radio parts NO EXTRA COST house. I've spoken to well over 200 serv- RADIO SPECIALS icemen and found that their problems Many Others Not Listed another R C P first are all about the same. The radio technician's main problem a RADIO ALTIMETER is not overcharging, but how to get decent fee for his services. People seem Transmitter Receiver RT7 /APN1- complete with 14 tubes; 418 to 456 meg. 27v dyna- to think that anybody in the radio re- motor. Certified by CAA: cost $11 e95 pair business is working just to get ex- Govt., $2,000. Bargain perience. I think that the radio repair business kind of organi- BC -456B is sadly in need of some zation so that servicemen can get to- MODULATOR UNIT, new complete with tubes, 8 relays; parts worth more $3.95 gether on fees that are fair to customers than our low price of W 77 and themselves. Manufacturers and jobbers should RADIO RECEIVER BC -1023A help out with a program to tell the pub- Ultra High Frequency, covering 62 to 80Mc lic that radio servicing is a business, ramie. An extremely sensitive relay, works FM Signal Generator Model 720A Complete with 4 tubes; not a hobby, and requires an experi- on 4/10 of mil. 9.1 - 10.7 - 88 - 108 mc. 1251-17, 6S @7, 6SC7, 6U6TG. $3.95 enced serviceman plus expensive equip- Brand New ment. Shock Mts. and instruction book included. only $19.91 WILLIAM A. GREEN, R. C. P. scores another first with this new low - Farmington, Mo. BC cost accurate, pocket size FM Signal Generator I -733D Start cashing in now on the rich FM business- SUGGESTS RADIO GUILD tubes, 6 xtals, not by investing 100 dollars -or even 50--but with SUPERHET RECEIVER-10 FM 6 selector relays; operates on any one of the only $19.95. Order this extra profit -building Dear Editor: 6 xtal controlled frequencies ; from 108.8 to Signal Generator from your R. C. P. jobber today. - I there should be a National 110.3Mc. Can be easily converted to 2 meter Only $19.95 for an acculléte instrument that per believe barn or mobile telephone band. Gives both mite you to align and service FM receivers. Radio Service Guild with local chapters. visual or aural indications of position of air. Complete with tubes reedy to operate All members would pay an annual fee. craft in respect to the runway. Pocket size 3- x r 23: 10.95 Completely shielded and Isolated from Bee membership in the New IN. for axed fre- Servicemen seeking Calibration, accurate within guild would be required to pass an ex- Individual trimmers' foorr'renilbretlee AIRCRAFT RECEIVER Equipped with shielded output lead amination, critical enough to distinguish Many other outstanding features, too. If your him as a reliable and competent serv- R5 /ARN -7 15 tube set. 4 bands 100 -1750 con- Easily converted to Home Broadcast. local jobber can't supply Your needs, use examina- KC. venient coupon below. iceman. After he passes the 115v -400 cycle Power Supply Shock Mts. tion, he would be allowed to advertise and schematic included. $9.35 Lees Tube. ALSO MODEL 710 FOR AM Small- -.olnpaat--no- his membership in the guild. curate. Its the Ideal Job for -on-the-soot" alleein,. As much of the dues received as pos- 15 tubes for above $10.50 trouble -shooting, estimating and repairs. Flied frequencies: 1500 and 550 Its: 456 and 465 ke. Safe sible would go into advertising to infor AC and DC operation. Pocket aloe r a 6' Complete with tubes. output able, eta-, ready te form the public that guild members are TUBE KITS operate at the remarkably low price of $17.951 tops in their profession and honest in Comes in complete sets Send for R. C. P.'s complete new catalog of econ- their charges. omy-priced. quality -built precision instruments. In case of any dispute, the customer Each set $10.50 Before you buy any instrument-see R. C. P. first! It's best for every test. would submit his complaint to the guild SCR 269 -BC 433 which would appoint a board of mem- R5A /ARN 7- R5 /ARN7 If the RADIO CITY PRODUCTS CO..INC. bers to investigate the complaint. serviceman is found to be at fault, he TUBES would be given an opportunity either be 65C7 $1.10 6B8 88e to rectify the error or suspended $1.13 6F6 60e RADIO CITY PRODUCTS COMPANY. INC. from the guild. 6N7 York I. N. Y. 75c 2051 80e Dept. RC6, 152 W. 25th St., New would show the honesty 6K7 GENTLEMEN: This system 6L7 $1.00 5Z4 90c Please rush the folloelne information to me: and progressiveness of the industry. and 710. 6]5 68e ( ) Descriptive bulletin on Model 720A JOHN W. RITENOUR, ( ) Catalog No. 129 of complete R. C. P. Une. ( ) Name and address of nearest R. C. P. Jobber. Norfolk, Virginia FIELD TELEPHONE Name BRITISH REPAIR PROBLEMS W E and Kellogg Addrou Dear Editor: EE S-4 -5 and 8 with ringer and generator. French typehandaet and carrying case. $9.95 City Zone.... Stau I think radio servicing is harder here Guaranteed perfect working order... in England than in the United States. THE Only in one case in a hundred is a set RECEIVERS COUPON-OF- -MONTH a year or so old. More often, it is SRAM, 35Z5GT or 35W4....10 for $3.90 only /CRWSenst2 High quency TURES -STD. AN TUBES -STD. BRAND 12SQ7 or 125T6....10 for .90 at least 10 years old. In fact, the aver- 6 Tub es -2 U Ve Re lFreays. TUBES-STD. RRAND 501.60T or 50115...10 for 5.90 $6.50 SAPPHIRE PHONO NEEDLES (LIM $2.50)...10 for 8.90 age is about 12 to 15 years. BRAND NEW STO. BRAND Vol. Controls -.n Meg. W.SW..10 for .40 age AN /CRW2A High Frequency STD. RAND -40.40 MFD 150V 10 for 5.40 -.005 or .01 MFD The main snags are conversions, for 5 Tubes -3 Sensitive Relays. 9Y PASS CONDENSERS for 6.90 BRAND NEW 6.50 0o0Y example, 6M to 6A8, 42 to 6F6. These tubes and dynamotor. Combination Kit-All Above Items-Only $37.50 Both complete with AT ONCE normal conversions, but there are so Used for controlling purposes. WITH THIS COUPON -ORDER are RADIOS -4 tube Superhet. (Nat. Known) 11.95 other types that a serv- RADIOS -5 tube Superhet. (Nat. Known) 13.95 many more of ANTENNA WIRE Write for Monthly Coupon. and Bulletin ice bill is often about $15. No wonder On reel, 300 ft. braided copper. $2.50 RADIO DISTRIBUTING CO. PASADENA 1$, CAL people complain! BRAND NEW. Each Here the dud serviceman is in his POLICE CONVERTERS FOR CAR RADIOS element and the reputable repairman Can be attachod to any car radio. Does na affect re- Quantity Discounts reptlon standard broadcast band. MODEL 100 -It has the task of reservicing his job, cor- Write for Ith died condensers. coven 1800 to 2800 kilocycles. Prompt Delivery -Write Dept. RC6 clue ono tube recting bad conversions, and resoldering 25^,6 Deposit Required on C.O.D. Orden List prie, $19.95 in end, the customer Shipped F.O.B. New York Minimum Order $2.00 Model 800 -11 Super sensitive. Covers 1500 to 3500 cold joints. And the kilo(yclee. Ilea twotubee, 1. ceptional distance range. blows up at the large bill, and will not List price T. ALLEN CO., INC. Jobben and Dealen wanted. let the serviceman explain. Write for folder 564 Atlantic Ave. Brooklyn 17 ABC RADIO LABORATORIES N. E. BAYLISS, Tel. TRiangle 5-8241 New York 3334 N. New J.,-.ey St. Indi.napolls, Ind. Birmingham, England RADIO -CRAFT for Co111WUUicntiollS 85 PREFERS ASSOCIATION SENCO Stimulates Summer Buying AMAZING -NEW Dear Editor: I agree that there are some chiselers With These Outstanding Savings! SILVER CONDUCTING PAINT in radio servicing, but I don't believe that licensing will eliminate the trouble. Standard Use the printed circuit technique to in:rease Brand the efficiency of electronic circuits while 5 really The state of California has a licensing AC PHONO decreasing the physical dimensions of your radio law, but there are as many sets. (Pure silver conductors make this porible). chiselers MOTOR AND This marvelous advance in radio construction was here as elsewhere. PICKUP developed during World War II and h now A state radio association of service- 60 available to you. cycles. 115 men would be volts. with Turn- See April 1948 issue of RADIO -CRAFT for better than any license. table. (brnplete FREE transmitter measuring 2" a 3 ". The association would investigate cus- I NEEDLE CUP $4.35 with motor and Introductory else baffle- only 51.00 posts aid, tomers' complaints; and when they pickup or sent C.O.D. plus postage. found an unfair serviceman, they could Regular t os. both -now only 53.00. LOOK AT THESE TUBE VALUES! close him up and refuse to let him oper- EVERY TUBE IN CARTON R.M.A. Special quotations on larger quantities. Lots os Lots of Complete instructions with each bottle. ate. In this way, servicemen would see 10 they are only Type Each Each TYPO Each Each ORDER NOW -A must for every up that hurting themselves OZ4 69c 59c 6U7G 35 25 to date experimenter when they try to put something over 1A3 45 39 6V5G 59 49 on customer. IA5GT /G 59 49 6V6GT /G 45 39 RADIONIC ASSOCIATES, Dept. PC -6 the IA7GT /G 55 45 6X5GT /G 49 39 95 Nassau Street New York 7, '1. Y. MARTIN ROTH, 1H5GT /G 59 49 7A4 53 43 1L4 49 45 7A7 59 49 Jackson, Calif. I LI14 69 59 7A8 58 48 N5 9 59 7B6 44 35 IN5GT /G 59 49 7F7 49 44 CORRECTION ISS 59 55 7N7 49 44 In the diagram of the Hi -Fi 35 -Watt 1T4 69 55 7X7 1115 36 30 (XXFM) 44 35 Amplifier on page 33 of the April issue, IV 45 39 7Y4 44 35 RADIO TUBES two .004 -µf capacitors shown con- 2A5 65 55 12A6 35 25 are 2A6 45 35 12A8GT 39 35 nected to pin No. 3 of the 6SN7. Only 2A7 49 39 I2AT6 50 45 For immediate shipment one should go to pin 2X2/879 35 29 I2BA6 50 45 this -the other 3A4 49 39 1213E6 50 45 R.M.A. Guaranteed goes to pin No. 6. 3S4 55 45 12J5GT 35 27 The plate load resistors of the 6SN7 5U4G 50 40 12J7GT 45 39 Below Distributor Costs 5W4GT /G 39 34 12K7GT 45 39 shown as 5,000 5X4G 39 35 Individually Sealed Cartons are ohms. They should 12K8Y 49 39 be 50,000 ohms. The bottom ends of the 5Y3G 42 37 12Q7GT 45 39 5Y3GT /G 40 33 12SA7GT/G 40 32 Type Price 220,000 -ohm resistor, the .008 -µf con- 5Y4G 40 37 12SF7 35 32 denser and the 2- megohm bass control, 5Z4 59 49 12SJ7GT 55 49 6K6GT .40 6M 50 45 I2SK7CT/G 45 35 in the grid circuit of the 6N7, should be 6A8GT 49 39 12SQ7GT /G 40 32 6K5GT .46 connected to the upper end of the 50,000 - 69 59 I2SR7 35 32 6AC7 /1852 65 60 14A7 65 55 6V6GT .46 ohm resistor from control to ground. 6AC7 /6AK7 89 79 1466 59 49 OAKS 74 69 24A 49 39 6SA7GT .46 6B7 55 49 25L6GT /G 49 39 The headings Ll, L2, etc., in the coil 6C4 29 25 25Z5 49 45 6SJ7GT .46 data table for the 1 -10 Meter Receiver 6C5GT 40 35 25Z6GT /G 45 39 6C5MG 89 79 26 49 39 6SK7GT .46 described on page 23 of the February 6C6 45 32 27 49 44 1948 issue are transposed. They should 6C8G 37 29 32L7GT 52 48 6SQ7GT .46 be 61)6 49 45 35/51 49 39 L2, Ll, L4 and L3 when reading 6F5 55 45 3SL6GT /G 45 39 6X5GT .40 from left to right. 6F6GT 45 39 35W4 43 40 6H6GT /G 4.5 39 35Y4 43 40 12SA7GT .46 6J5GT/G 45 39 35Z3 44 35 The negative side of the filter con- 6J6 59 49 35Z5GT /G 43 39 12SQ7GT .46 densers in the 3 -Way Portable, page 42 MGT 42 38 36 49 39 6K6GT /G 45 39 39/44 35 29 12SK7GT .46 of the February issue, should be con- 6K7G 50 41 41 49 45 nected to the fused side of the a.c. line. 6K7GT /G 39 47 49 39 12SJ7GT .46 6K8G 55 49 50A5 60 55 We thank Mr. Joseph Montgomery of 6L6G 79 69 SOBS 42 32 35L6GT .40 West Newton, Penna., for calling this to 6Q7GT 47 39 50L6GT 50 45 SRI 55 45 56 65 45 35Z5GT .32 our attention. 6R7GT 59 49 57 45 39 6SA7 49 39 58 45 39 50L6GT .46 6SA7GT /G 44 37 75 50 39 687 49 45 76 49 45 10% DISCOUNT ON LOTS OF 50 OR M1RE Rabic( ZEfjírtp-gibe pains Zito 6SG7 44 39 77 35 27 80 40 38 25% Deposit Required-Be/wee C.O.D. 6SH7GT 40 32 31n errnsbatk Aìublitationd 68J7GT 44 37 83V 79 69 2% discount allowed on C.O.D.'s. 6SK7GT /G 49 39 85 49 45 6SL7GT 49 99V 35 25 HUGO GERNSBACK 47 99X 35 25 RAVAC ELECTRONICS CORP. 6SN7GT 49 47 117Z6GT /G 89 76 MAIL ORDER DIVISION Founder 6SQ7GT /G 44 37 182B 99 89 6SD7 49 39 Modern Electric, 1909 1231 39 29 432 -4th Avenue New York 16, 'i. Y. 6U6 49 39 1644 39 29 Electrical Experimenter 1019 Radio News 1919 POPULAR BRAND VOLUME CONTROLS Science & Invention 1920 SPEAKERS Popular Brand 3,4" Cono 4" Sq. Radler Craft 1929 shaft tapped with Frame ea $1.19 snit eh. Shari -Wave Craft 1930 4" P.M. Spkr ea. 1.19 25i),0o0 ohms Wireless Association of America 1908 5' P.M. Spkr ea. 1.15 7,00.510 ohms FREE CATALOG 5,4" ('one ev Sq. Frame ea. 1.55 2 mea. ohms SIMPLY SEND YOUR NAME AND AD- Some of the larger libraries In the country still hay 6" P.M. Spkr ea. 1.53 NEW conies of ELECTRICAL EXPERIMENTER on file for R- P.M. Spkr ea. 2.75 each DRESS AND RECEIVE FREE OUR nterested readers. 12 P.M. Spkr ea. 4.95 39c 1948 CATALOG. HUNDREDS OF BIG From THE ELECTRICAL EXPERIMENT- RADIO PARTS VALUES. 829 PUSH PULL TWIN -UNIT $1,49 ER, June 1914. Roam Power Amplifier Tube ea. AMERICAN SALES CO . I BRAND NEW WILLARD #27 -2 2 VOLT STORAGE 1811 47TH ILL. The "E e c t r o" Detectaphone and W. ST.. CHICAGO. BATTERY AND 2 VOLT VIBRATOR Radio Amplifier by H. Winfield Secor Used In General Electric model 55530 charge A PACK Wireless Receivers by H. J. Lucas portables. Suitable for all farm radio sets. Individually CLEARANCE ON TEST EQUIPMEII'.T BOTH FOR $2.69 Supreme 543 -S Multimeters (5000 %p.vJ 114.95 A High Amperage Key by Alvin E. Battery alone $1.79 Vibrator alone 99e Howlett- Packard Audio Oscillators (Rag. 3125) 69.95 Spencer 6 Volt Auto Vibrators, 4 Prong $1.09 EACH Radio City F'M Signal Generators (Model 720) 17.95 Meissner Signal Calibrators (Used/ (Reg. $77.17) 29.95 The Wireless Phone Record 25 °o deposit on all orders, balance C D.. Iteadrite Panel Meters (0 -200 Milliamperes)... .79 F.O.B. New York Triumph 5000 ohm per volt Multitesten A Simple "Quenched" Spark Gap (Like new) 14.95 PreNdon 920 Tube and Bet Tester (Used) Wireless Joins two Universities (Beg. $82.54) 59.50 20% Deposit -Balance C.O.D. Artificial Radio Grounds SENCO RADIO, Inc. Send for our latest bulletin. Radiophonie Apparatus 73 West Broadway, N T. 7, N Y REMER RADIO COMPANY TELEPHONE 5904 S. PRINCETON CHICAGO 25. ILLINOIS Radio Transmitting Problems BEEKMAN 3.6498

UNE, 1 948 86 RODIO SCHOOL DIRECTORY WANTED: Men and Women to Fill TOP RADIO JOBS PRACTICAL TECHNICAL TRAINING in AM- FM- Television If you are looking for aver with a futuro, why not Jolti Ne hundreds tK graduates from the Don Martin School of Radio arts now successfully employed ln the SPECIALIZE in 6 months to 3 years radio Industry. The demand L great for guandod radio personnel in AM-FM-Television. Train now to be an announcer. script writer, disk Jockey, news- Train in Electronics, Radio, Electricity for a substan- castor. or radio engineer. Complete day and Digla citases . . the latest equipment. Free placement COURSES tial career in industry-or a business of your own. service. Approved for veteran. Write for free booklet. SERVICE Prepare in one year to be a Technician-or in two Don Martin School of Radio Arts 6 to 12 Months Electricity additional years secure a Bachelor of Science Degree 1655 North Cherokee St. Hollywood 28, Calif. Welding in Electrical Engineering with major in Electronics. Refrigeration Heating More than 35,000 former students in industries the TECHNICIAN world over. 1,538 students now enrolled from 48 I to 2 Years states and 13 overseas countries. Faculty of 72 spe- Electricity RADIO ENGINEERING Radio cialists. Write for catalog and Personal Guidance Electronics Questionnaire -also mention course in which you are FM-Television- Broadcast Refrigeration, Heating Pollee Radio, Marine Radio. Radio Servicing. Asia - and Air Conditioning interested. tim Radio and Ultra High mobile applications . Thorough training in all brancha of Radio and llec- PROFESSIONAL ironia. Modell laboratories and equipment Old es acre 3 Years Terms start JULY, September, January tabliahed school. Ample housing facilities. 7 Electrical Engineering campus. Small classes. enrollments limited. Our graduates are in demand. Write for catalog. Bachelor of Science MMILWAUKEE-06t Veterana Degree Approved for Major in Machinery or 5CNmL of ENGINEERING VALPARAISO TECHNICAL INSTITUTE Electronics A TECHNICAL INSTITUTE Dept. C VALPARAISO, INDIANA Dept. RC 648 North Broadway, Milwaukee, Wis. THIS COUPON MAY PROVE TELEVISION TO BE THE KEY TO YOUR RADIO F M PRACTICAL TRAINING SUCCESS IN ELECTRONICS LATEST EQUIPMENT RADIO SMALL CLASSES MELVILLE RADIO INSTITUTE VISITORS WELCOME The Progressive Radio School OPPORTUNITIES Gotham Radio Institute Managed by Radio Men WRCI SPECIALIZED TRAINING- the "tratn. 3534 BROADWAY (cor. 145th St.) Increase one's Approved for Veterans tcensed by the N. Y. State Board of Education Ino- with -.-purpose° -DOES ean- WA 6 -0902 tse power. For example, well -paying positions of ENROLLMENT RECOGNIZED BY INDUSTRY IMMEDIATE responsibility now held by WRCI graduates In. APPROVED VETERANS FOR elude: CORRESPONDENCE COURSES IN ",./ e BROADCAST ENGINEER-OPERATORS RADIO0ndELECTRICAL ENGINEERING CUT IT OUTI FILI IT OUTI MAIL IT GOTI NOWI (AM & FM stations) - e broadcast ELECTRICAL ENGINEERING :°,te Kaié v mis ñel. Prepare you ses t Low Colt. for soeur futur.. Modem MELVILLE RADIO INSTITUTE RC FLIGHT RADIO OFFICERS 9 Implined yon. demand quickly. I e gain an. our. In die. Melville Bldg., 15 W. 46th St., N. Y. 19, N. Y. (transoceanic airlines) RADÌO EBGINEERÌÑO led man I ark. Trams you to be super.. InI vacuum- needed badly. Diploma Send ene without obligation information about robe technician. Servicemen I RADIO -TELEVISION completlon d your intensive courses, o for Pen 'Co Sgend. of - SERVICING TECHNICIANS fo I t. Co. s, Rodio Technician WAITS e p t f$15 / RADIO SERVICE SHOP OWNERS Lincoln Engineering School. Boa 931l -C -112. Lincoln 2. Neer. Rodio & Television ServTtingl g' Radio Communications e COMMERCIAL RADIO OPERATORS Fundamental Rodio Mathemet?, e (police, CAA, airlines) RADIO COURSES / RADIO OPERATING CODE My Name MERCHANT MARINE RADIO SERVICING - ELECTRONICS e F.M. TELEVISION RADIO OFFICERS Address / REFRIGERATION SERVICING With this proved record of successful training and persona l Counselling Services for Veterans placement. WRCI othre you. too. the best type of Write for Catalog ami Picture Brochure PRACTICAL training -under the supervision of / radio and television specialist,. Approved for Y.M.C.A. TRADE A TECHNICAL SCHOOLS/ / York City e veteran training. Nell- veterans accepted. Send for 7 W. sato Street New `------free illustrated Booklet "F "-no obligation of course, / irA CAREER e WESTERN RADIO WITH A FUTURE! / e COMMUNICATIONS INSTITUTE E`.EVItiIll\ 341 West 18 St., Los Angeles 15, California e "key" man. Learn how to rad and telegraph Stow won SINIW ROINIWl1 n5OIT MUT ININO MOMI0IW Be ea. Rea In code by and radio. Commerce needs thousands of 11.%11111 SER.'14'E 8c IIEP.t11t for Jobs. Good Pay, adventure, in- menteresting ork. Learn at home quickly F. M. .S; TELEVISION thmfltr famous Candler System. Qua TRANSMITTER Ify for Amateur or relal LI- COURSES LEARN RADIO! en Wrt forFREE BOOK. r;a lev r.0 C LICENSES S CANDLER SYSTEM CO. RADIO TEIHNOLOGI- IN ONLY 10 MONTHS Dept. 3 -0. Boa928, Denver 1, Colo.. V.S.A. a11NINn . 1.11010011 Inmuto ctatsO soawan Mm MSTYiRpn PREPARE FOR A GOOD JOB! AVILASII UNOS! O. I. SILL COMMERCIAL OPERATOR (CODE) BROADCAST ENGINEER RADIO 1 1F.I,I SCHOOL OF IIANTY RADIO SERVICEMAN TECHNICIAN and RADIO SERVICE COURSES RADIO ELECTRONICS TELEVISION 105 EAST 13th STREET, NEW YORK 3, N. Y. DEPT. R Television Servicing -15 Months FM and TELEVISION MICERSMO Sr STATI Of NEW YORK INSTITUTE Veterana get $130.00 Equipment AMERICAN RADIO SEND FOR FREE LITERATURE 101 Wnt 63rd St., Now York 23. New York BALTIMORE TECHNICAL INSTITUTE Approved Under G! BW of Rights Licensed by New York Stute RCA INSTITUTES, Inc. -1425 Eutaw Place, Dept. C. Baltimore 17, Md.- Offer thorough training courses in all technical phases of SOUND RECORDING SCHOOL Hollywood Make Good in at Eleert$ Radio and Television A practical engineering course In Round Fundamentals. Home DAYS- EVENJNGS WEEKLY RATES Recording, and Round Tranamlaslm measurements; in Rare To I RADIO- TELEVISION a Direct Hollywood. Tele- RCA Inautsles I. approved laboratory containing transmiselm sets. aclllaton, VETERANS: aguare wave generator and intermodulattm analyzer, and ision, Radio sa Soundnerve-centertivitiea, « on. R.TA S 1 me- under G. I. Bill of Rights Proven end bated borne training. Ron st last --eaer to other equipment. you For Free Catalog Dept. RC -/a team, home In.tructIon that quickly qualifies ton Write Two complete recording studios aulmUeting bradons, steady good-pay Job. or your own Radio business. 10 big ILCA INSTITUTES, mottas picture and commercial pound recording. under kat of radio parte given t extra Narye. Cet full de- Inc the direction of H. M. Trentaine. talla t o ' Send postal forr FREE ROOK Row to Make .4 Service of Radio Corporation of America Good In Radio- Television." R -T-A APPROVED FOR VET- 3,0 WEST ITH NEW YORK 14. N. ERANS. STREET Y. HOLLYWOOD SOUND INSTITUTE, Inc. RADIO TRAININO ASSN OP AMERICA. Deot. RCF 1040-C Ne. Kenwsr Hollywood 27. Cala. 5.20 Hollywood led. Hollywood 25. Calif. RADIO -CRAFT for 41- '* Book Reviews- 187 FM TRANSMISSION AND RECEP- authoritative in much material written TION, by John F. Rider and Seymour D. since its publication, and there is little Uslan. Published by John F. Rider, Inc. doubt that it has had and will continue Here it is! Paper or cloth covers, 5% x 8% inches, have influence on - 409 pages. Price, paper $1.80, cloth to a powerful hearing $2.70. aid design. JUST PUBLISHED The basic principles of wide- and nar- WHAT ELECTRONICS DOES, by Vin row -band FM transmission and recep- Zeluff and John Markus. Published by tion, antennas, and operation and de- McGraw -Hill Book Co., Inc. Stiff cloth The Practical Aspect sign of FM equipment are covered in covers, 53/4 x 81/ inches; 306 pages. this book. Price $3.00. of the Future of Radio The book is divided into two parts. An interesting description of the The first covers theory of frequency and numerous industrial applications of elec- phase modulation, reactance tube mod- tronics, written for the general reader, ulators, a.f.c., frequency multiplication, this book gives a picture of the many TELEVISION & and design characteristics of several wonders that electronics is performing commercial FM transmitters. today. Commercial uses explained in- FM antennas, tuners, and receivers clude color matching, navigation for are discussed in the second part. Each ships and planes, fault- finding in metals, F -M RECEIVER stage in the FM receiver is compared to paint spraying, cooking and defrosting, its equivalent in an AM set. Four types as well as many others. a of FM detectors are discussed in detail, including comparison of all types. WORLD RADIO HANDBOOK FOR SERVICING LISTENERS, published and edited by O. MOST - OFTEN - NEEDED FM AND Lund Johansen, Pilestraede 32, Copen- by TELEVISION SERVICING INFOR- hagen, Denmark. Heavy paper covers, MATION (1947), Compiled by M. N. 6% x 8% inches, 96 pages. Price $1.30. MILTON S. KIVER Reitman, Published by Supreme Publi- This book is a serious attempt to corn - Registered Professional Engineer cations. Flexible fiber covers 8% x 11 pile an authentic list of tell shortwave inches, 192 pages. Price $2.00. broadcast stations of the world. Divided As every radio man knows, the limitless Prepared in the style familiar to into users of other continents and countries, it gives possibilities of radio in the fields of F -M books in the Most- Often- locations, call signs and frequencies as and Needed Diagrams series, this manual television broadcasting are no longer contains well as condensed program schedules of "just talk"-the future of radio has ar- servicing information on and shortwave stations. Included are the rived! With more and more F-M and tele- diagrams of approximately 80 FM and normal clock time of each country and vision sets on the market and in operation, television receivers made by 24 manu- announcements and interval signals of no student or service man can afford to be facturers. the chief broadcasters, also without the wealth of up- to- the -minute The servicing addresses information in this great new book. information is much of broadcast administrations or com- more detailed and complete than in a panies and names of leading personal- Written by the author of U.H.F. Simplified, similar edition on AM receivers. ::n al- ities. The shortwave listener will appre- F-M Simplified and Television Simplified, most all instances the servicing informa- ciate these additional aids to identifica- this simple, well- organized text makes crys- tion includes dial stringing diagrams, tion and verification. tal clear all types of servicing problems. voltage and tube location charts, oscillo- There are specific directions for installing In addition to shortwave broadcast- television receivers, and for diagnosing, graphic patterns available at test points, ers, long- and medium -wave and photographs of test patterns pro- European locating and repairing the common troubles stations are also listed. of F-M or television receivers. In addition, duced with the set in various stages of complete alignment and servicing instruc- misadjustment. TELEVISION ENCYCLOPEDIA, by tions.are given at each point of a logical Stanley Kempner. Fairchild Publishing step -by -step procedure. These are sum- HEARING AIDS, An Experin.ental Co, 5% x 8 inches, 415 pages. Price marized in Study in Design Objectives, by H. separate chapters (one for tele- Davis, $6.50. vision, one for F -M) so that explanations S. S. Stevens, R. H. Nichols Jr., C. V. There are three main divisions in this and instructions are fully coordinated. Hudgins, R. J. Marquis, G. E. Peterson work. The first, called and D. A. Ross. Published by Harvard "Milestones to The student or service man familiar with University Press. Flexible fiber covers Present -Day Television," is a 39 -page presentday A -M receivers easily under- with plastic spiral binding, 6 x 9 inches, chronological survey of the subject from stands every page of this book. Mathematics 197 pages. Price $5.00. 600 B.C. to 1947 A.D. The second, cov- is kept to a minimum -just enough to An account of a very complete :;et of ering 92 pages, is a 'biographical en- enable the service man to compute prop- experiments conducted to discover what cyclopedia of people who have contrib- erly the lengths of transmission lines and types of hearing aids are most suited uted to the development of the art. Most antennas. The book is profusely illustrated for the average hard -of-hearing person, of the rest of the book is devoted to a with photographs and schematic diagrams. whether individuals would profit by spe- vocabulary of special television terms, CONTENTS The Antenna System, Opera- tion and Installation; Televi- cially- fitted equipment, and the effects chiefly technical but containing also a sion Receiver Installation; Television Test Equip- of varying the apparatus design for the number of studio and commercial ex- ment; The Television Receiver, Operation and Servicing (4 chapters); Television Receiver Align- individual user. pressions. ment; Trouble Shooting. Television Receivers; This book has been referred -:o as A rather complete bibliography adds F-M Fundamentals; Commercial F -M Receiver Circuits: F -M Receiver Alignment; F -M Receiver to the value of the book. Servicing. EXAMINE TELEVISION 1948!! THIBOOK Train at an Institute that ploneered FREE! In TELEVISION TRAINING since 1935. RADIO 7 Morning Afternoon or Evening Ses- sions in laboratory and theoretical in- MAIL THIS COUPON struction, under guidance of experts. COURSES D. Van Nostrand Company. Ina. covering sll phases of Radio, Fre- Preparatory, Service, Broad- 250 Fourth Avenue, New York 3, N. Y. quency Modulation, Television lead to opportunities in Industry, Broad- cast, Television, Marine Op- Please send me a copy of TELEVISION and F -M casting or own Business. Licensed by ereting, Aeronautical, Fre- RECEIVER SERVICING for examination. Within lo days I will return the book to Ms or lead you N. Y. State. Approvid for Veterans. quency Modulation, Radar. $3.25 plus few seats postage. ENROLL NOW FOR NEW CLASSES Classes now forming for Visit, Write er Phone the summer term June 1. Entrance exam. May 17. Name RADIO- TELEVISION Veterans. Literature. COMMERCIAL RADIO INSTITUTE address INSTITUTE Bounded 1920) 38 West Biddle Street. Baltimore t, Nd. 480 Lexington Ave. N.Y. 17(46th IL) City State Plaza 9.4585 2 blocks from brand Central RC -June 1948 JUNE, 1948 88 Before you buy TELEVISION INDEX TO ADVERTISERS

See the DeWALD BT -100- ABC Radio Laboratory 84 Oelrich Publications 58 Tom Allen Corporation 84 Offenbach & Reimus Be Allied Radio Corporation 5 ()limits Manufacturing Company .... 75 By far the FINEST we've Almo Radio Company 60 Olson Radio Warehouse 55 American Sales Co. 85 Opportunity Adlets 82 been able to discover American Surplus Products 46 ANYWHERE Amperite Company 76 Poker Radio Company BI Amplifier Corporation of America 75, 78, 88 Precision Apparatus Company 69 Audel Publishers 71 Progressive Electronics Co. 50 Bell Telephone Labs. Inside Front Cover Radio Apparatus 72 Boland and Boyce, Inc. 16. 64 Radio City Products Co., Inc. 84 Bonafide Radio Company 67 Radio -Craft BO Brooks Radio Distributing Co. 73 Radio -Craft Library Series 61 Buffalo Radio Supply 56, 57 Radio Dealers Supply Company 79 Burnett Service Company 83 Radio Development & Sales Co. 88 Burstein -Applebee Co. 75 Radio Distributing Company 84 Capitol Radio Engineering Institute 2 Radio Kits Company 71 Certified Television Laboratories 69 Radionic Associates 85 Cinex Corporation 80 Radionic Equipment Company BO Cleveland Institute of Radio 15 Radio Publications 7f Collins Audio Products Co. 67 Radio Research Products 74 Colombo Trading Co., Inc. 71 Radio Supply & Engineering Co. B2 Commercial Radio 80 Radio Wire Television, Inc. 53 DeWALD BT -100 DIRECT VIEW Communications Equipment Co. 6 Radolek Company 81 10" TELEVISION RECEIVER Concord Radio Corporation 59 Ravac Company 85 Constant Electric , 82 Reiner Company 85 13 channels 52 sq. in. picture Coyne Electrical School 77, 81 Risco 78 6 simple controls Automatic Stabilizer Electronics Balanced Input Circuit DeForest's Training Institute 9 Edmund Salvage Company 51 Fine Hardwood Veneer Walnut Cabinet 251/4" x 19" x 15" Edwards FM Radio Corporation 58 RADIO SCHOOL DIRECTORY Electronic Corp. of America 49 Net price to Dealers only. (Pages 86-87) Espey Manufacturing Co., Inc. 79 Apply on Letterhead LIST S372.10 American Radio Institute Esse Radio Company 12, 13 Baltimore Technical Federated Purchaser 69 Institute Candler System Company General Cament Manufacturing Co. 69 Commercial Radio Institute General Electronic Distributing Co 41 Delehanty Institute General Test Equipment 69 Gotham Radio Institute Green Radio Distributor 72 Hollywood Sound Institute, Inc. Greylock Electronic Supply Co. 75 Lincoln Engineering School Hallicrafters Company 54 Don Martin School of Radio Arts Hallmark Electronic Corporation 80 Melville Radio Institute Harris Supply Company 79 Milwaukee School of Engineering The Heath Company 48 RCA Institutes Hotel Strand 83 Radio Television Institute Industrial Devices, Inc. 98 Radio Training Association of Americo Illinois Condenser Co. 73 Valparaiso Technical Institute Instructograph Company 78 Western Radio Communications Institute International Resistance Co. Back Cover YMCA Trade & Technical Schools Joyce Radio Distributing Co. 67

Manuel Klein Ind. Corp. . 80 Lafayette Radio 53 DeWALD B -612 Lear Radio, Inc. 65 The Rose Company 81 Leeds Radio Company 63 Howard W. Sams & Company. Inc II 'WIRELESS F.M. TUNER" Leotone Radio Corporation 59 Santo Radio, Inc. Be Simply plug in and play McGraw -Hill Book Company, Inc. 54 N. Silverstine e AC DC Operation No wiring to Radio McMurdo Silver Company 4 63 Sprayberry Academy of Radio 7 5 tube and rectifier Superhet P. R. Mallory & Company, Inc Inside Back Cover Supreme Publications 47 Balanced F.M. Detector Circuit Meter Master 74 Transvision 45 11" x x 74111" Walnut Cabinet 6" Metropolitan Electronic & Inst. Co. 74 Technical Radio Parts Company 83 LIST $39.95 Michael Stahl, Inc. 78 Tradio, Inc. 83 Mid -America Company 74 Universal General Corporation 78 Moss Electronic Distributing Co. 43 D. Van Nostrand Co.. Inc. 87 Murray Hill Books, Inc 73 Warren Distributors se

National Radio Institute 1 Watterson Sales Company 54 National Schools 3 Wright, Inc. 76 Niagara Radio Supply Company 14, 52 X.L. Radio Laboratories 79

AtP 70 e7AYFLR INVALUABLE! All Merchandise Brand New 10% DISCOUNT ON ORDERS OVER OF $10 -20% OVER $25 ELEMENTS SFr met. vol. controls with switch. 3^ shaft. .... 39 C.C. Plate Circuit Relay -10M ohms-used with MAGNETIC TAPE SOLES-Operates on 8Ma. S.P.D.T 95 OPERATES ON A SEAM OF LIGHT Photo -electric relay kit complete with ll parts in- RECORDING tubes, lay, sensitivity. control and assemblyeluding Instructions. ONLY SS.95 and 999 Gruen 2V? meter -0 -8ms. movement -sale marked 0.300 1 95 APPLICATIONS 'AVAILABLE Weston a476 -3' /z meter-0.8v. Le 395 FOR ONLY Weston #507-0-1.5 amps. R.F. -2% as- by A. C. SHANEY curacy to 65me. 425 B -504 "PERSONAL" 25c Villard-6V. 3 ll- plexlgiaes case-miniature DeWALD storage batteries 3í/y x1 Vs.a 2%"; shipped DC Contains schematic diagrams 1.95 AC,' and Battery Operation Fil tern 100 ma.. 150 ohms re 4 tubes and Selenium Rectifier chokes-1011y, 0 1.25 Westlghouse chokes -4Hy 90ma. 300 ohms Superhet circuit 5 "PM Alnico Speaker AMPLIFIER CORP. of AMERICA 0 69 Only 4" x 81/4" x Vis" n.. LIST $27.95 398 -10 Broadway New York 13, N. Y. G.E. Solenoid operated contactor 3tCR 2820 - controls 6 circuits -operates on 115v. 60 cycles - Riso available Battery 4 z 9. 15 amp. contacts double break each circuit Operated LIST $19.95 -G.E. catalog trio, $25.00. YOUR COST..5.95 t'.T.C. "5.6" Input Xmfr. line or mike to grid; ALSO HAVE ALL THE 1948 dcale?S price $3.25: YOUR COST 1 25 WE NEW Leach 6v D.C. flays-3 pole n.o. YOUR COST..1 25 Selenium Rectifies: full wave -- center tap -18V TEMPLE AND MINERVA LINES Radio, Television, Electronic 49 Kits, Parts, etc. LOWEST Rotary2Switch with knoh- A.H.&H. 5 pole on and 2 PRICES. Also War Surplus off; to amps s0 120V. 59 Dealers: Send for Catalog DIscount Sheets Send your Get on our mailing list Bargains. Get Your Copy Now. No COD.. .Include Postage....Mini mum order $2.00 SALES CO. WARREN DISTRIBUTORS 1+ OffENBAC1- & REIMUS RADIO DEVELOPMENT & 323 ATLANTIC AVE. BROOKLYN, N. Y. CATS ST.. SAN FRANCISCO 2, CAL 51458 Washington Street, Jamaica Plain 31, Mau. 372

Printed In the D. R. A. RADIO -CRAFT for JUNE, 1948 t(

EQUALLY MATCHED Split the reed assembly of a Mallory vibrator they are the best replacement vibrators down the middle and the two halves will for you to stock. accurately that no scale match each other so In addition to assured quality, Mallory made will register a significant difference. offers the most complete line in the busi- This precise distribution of weight is a major ness. Mallory standardization permits 12 factor in assuring accurate output, reliable basic vibrators to meet 90% of your re- operation and long life. placement requirements. But a complete line of 52 vibrators is available to meet Mallory Vibrators Make virtually every vibrator need. the Best Replacements Such careful manufacturing Mallory "2448" Vibrator Deal This deal gives you a handsome storage and display cabinet makes Mallory vibrators for your stock of vibrators, together with a selection of vibrators and buffer capacitors that will answer 75% of free of bounce and chatter your requirements. You pay only the service man's End dependable in starting. net price of 824.48 for the mix vibrators and twelve buffer More of them are used in capacitors. There is no charge for the attractive, convenient original equipment than all cainet.cabinet. Your Mallory distributor has them in stock for immediate delivery. The .ifallory Replos. meut t ibeotor other makes combined. Guide is free. The 1 ibroror Uma Book is $1.00 -from your d 'butor That's convincing proof or by mail. MORE MALLORY VIBRATORS ARE IN USE THAN ALL OTHER MAKES COMBINED

SWITCHES . . . RESISTORS . . . RECTIFIERS . . .

VIBRAPACK* POWER SUPPLIES . . . FILTERS

Reg. U. S. Pat. Off. APPROVED PRECISION PRODUCTS P. R. MALLORY & CO., Inc., INDIANAPOLIS 6, INDIANA ti

...... v, This New LIC JUNIOR Control

Cabinet Belongs on Your Bench

HERE'S WHAT YOU GET

IRC Control Resistance Purpose Type No. 5 013 -133 500,000 ohms A

1 D13.133% 500,000 ohms B

1 D13.137 1.0 meg. A 9 controls, switches and shafts Here's one selection of "hot- number" 1 013 -137X 1.0 meg. B 2.0 meg. A you'll use every day ! The new IRC Junior Control Cabinet contains 9 1 D13 -139 control, of the most -used '/, 1 and 2 meg. type D controls with the added adapt- Purpose: A -Tone or Audio Circuit B- Topped for tone compensation. ability of the rap -in shaft feature -plus 4 switches and 4 special shafts. SWITCHES This inexpensive assortment of popular controls will save you time 041 S.P.S.T. and money, and reduce your need for exact replacements. Factory- 042 D.P.S.T. packed in a handsome four drawer cabinet of sturdy cardboard. Cabinet SHAFTS 1 Type "A" double -Batted tap -in shaft is finish -..c1 in blue, yellow and silver with twelve individually attractively Included with each control -plus: inexpensive Control identified compartments. Order the new JUNIOR 3 Type "E" with universal knurl for special Cabinet from your IRC Distributor today. International Resistance type push on knobs. Company, 401 N. Broad Street, Philadelphia 8, Pennsylvania. In I Type "H" with universal groove for many Delco, RCA, Sears- Roebuck and Westing Canada: International Resistance Company, Ltd., Toronto, Licensee. house models.

n! t// f,1OtlR l r if 161- INTERNATIONAL ' ANCE COMPANY 'M 117urevcrthe Circuit sass YVl,\