Adio-Electronics in All Its Phases

1 HUGO GERNSBACK,Editor

Olt

JAPANESE RADAR SEE PAGE 4C'4

ADIO-ELECTRONICS IN ALL ITS PHASES

LA& CLEVELAND YELLOW CAB COMPANY Uses RAYTHEON TUBES in world's first taxicabs with two -way radio!

The eyes of the nation's transportation indus- If you are a radio service dealer, you, too, try are on Cleveland these days, for it is there should realize that Raytheon's combined pre- that the world's first taxicabs equipped with war and wartime tube experience will result in two -way radio are being demonstrated by the even better tubes for all uses. Keep an eye on Cleveland Yellow Cab Company. Raytheon ... and watch for a Raytheon mer- chandising program that will help you be more Officials say that dispatching has proved so successful, in the peacetime years ahead, than much more efficient that future fleets similarly you've ever been before ! equipped will eliminate millions of miles of wasteful "dead" cruising. And they also report Increased turnover and profits... easier stock control Raytheon High- Fidelity Tubes, used in better tubes at lower inventory cost ... these are that benefits which you may enjoy as a result of the both transmitter and receivers, provide clear, Raytheon standardized tube type program, which is dependable reception -even in the tunnels part of our continued planning for the future. I under Cleveland's Terminal Tower. Raytheon This application of Raytheon Tubes is just one Manufacturing Company of many being planned for the postwar period RADIO RECEIVING TUBE DIVISION by progressive manufacturers in the electron- Newton, Massachusetts - Los Angeles New York - Chicago - Atlanta ics field. RAYTHEON

All Four Divisions Have Been Awarded Army -Navy "E" With Stars ELECTRONIC AND RADIO TUBES

- I WILL TRAIN YOU TO START A SPARE TIME OR FULL TIME

1. E. SMITH, RADIO SERVICE BUSINESS PRESIDENT National Radio Institute 31st Year of Training )ten for Success in Radio WITHOUT CAPITAL The men at the right are just a few of many I have trained, at home in their spare time, to be Radio Technicians. They are now operating I Trained their own successful spare time or full time These Men You Build These and Many Radio businesses. Hundreds of other men I trained are holding good jobs in practically every branch of Radio, as Radio Technicians or Other Radio Circuits with Operators. Doesn't this PROVE that my "50-60 Method" of training can give you, in your spare time at home, BOTH a thorough knowledge of 6 Kits of Parts I Supply Radio principles and the PRACTICAL experi- t`eigi Lins ence you need to help you make more money tr nronyLIC It n_ twhetrmlnrEAñs a f rtu"o By the time you've conducted 60 sets of in the fast -growing Radio industry? f,iratningRED á Experiments with . Radio Parts I supply, Let me send you facts about rich opportuni- agro C1IFF7 rynIE, made Itu3e c: hundreds of measurements and ad- ties in the busy Radio field. See how knowing ewvule, justments, you'll have valuable PRACTI- Radio can give you security, a prosperous fu- CAL Radio experience for a good full or ture lead ... to jobs coming in Television and e T Pr my part -time Radio job! Electronics. Send the coupon NOW for FREE 64 -page illustrated book, "Win Rich Rewards leyomu,urZ Xerth if:gsrn ek in Radio." Read how N.R.I. trains you at home DaRlkno¢ oCatpnDtO4r In spare time. Read how you practice building, Qhat.7..w testing, repairing Radios with SIX BIG KITS of Radio parts I send as part of your Course. a "Ahout slx mo%th after Future for Trained Men Is Bright e In Radio, Television, Electronics , or l, w ^ro l The Radio Repair business is booming NOW. É°nmroÿet saó ñ 1ñ0 -NeDd dam,o There is good money fixing Radios in your spare reg 3 2or_aymTa.Ycirsandea time or own full time business. And trained Radio Technicians also find wide -open opportunities in Police, Aviation and Marine Radio, in Broadcasting, Radio Manufacturing, Public Address work, etc. Send for free book which pictures your present and future opportunities. I Trained Think of the boom coming when new Radios can be made! Think of the backlog of business These Men built up in all branches of Radio! And think of even greater opportunities when Television. FM, Electronics, can be offered to the public! Use only a few hours of your spare time each You build the week to get into Radio NOW. You may never SUPERHETERO- again Fee the time when it will be so easy and DYNE CIRCUIT profitable to started. Mail com- above containing get coupon for µtattoo °rktng In preselector oscillator - plete information. atoa hinny mixer -first detector, µelfo[ huslneaeWeenk. Many Beginners Soon Make SS, n ek You build MEASUR- i.f. stage, diode -de- $10 citexr 'lile X ° ING LNSTRUMENT tector-a.v.c. stage and a Week EXTRA In Spare Tinte , venue, SldtemylSNeb. above early in audio stage. It will The doy you enroll I start sending EXTRA MONEY Course, useful for bring in local and JOB Slll ?EiS to help you make EXTRA money fixing Radio work to pick up distant stations. Get Radios in time while learning. You LEARN the thrill of learning pare EXTRA spare time Radio principles from me a >^ In-grasp Lessons- s2arotaamon°°rtto P°IrrrodloyultPm money. It is vacu- at home evenings ta PRACTICE what you learn be building real R Ain ADerdeea, i°. um tube multimeter, spare time while you Circuits with the six kits of Radio parts I send -t -SU bt ea. M.tSMtI\ erogo measures A.C.. D.C. put the set through your knowledge to money while getting ' ER. JR R.F. volts, D.C. cur- fascinating testa! ready for cood full timeo Radio job. rents, resistance,, receiver output. Find Out What N.R.I. Can Do for YOU rro"41,71 3LtiL TITE COTTON for your YR1 E copy of my sa owknna Building the A. M. 64 -pago book. It's with farts about opportunities N'.R.f. workfo 00 paWerk mont packed ae g°e for 1y n, SIGNAL GENERA- for you. head the details abed m Course. See the NORyAY Iher N.R.l. TOR at right will give fascinating jobs Radio offers. See how you can train MILLFJta lleh+un, you valuable experi- at home. Read letters from men I trained, telling what XeiiO rodtoh're ence. Provides ampli- they are doing, earning. No obligation. Just MAIL tude- modulated sig. COTTON in an envelope or paste it at a penny postal. nals for test and ex- J. E. Smith. President. Dept. SEX. National Radio perimental purposes. Institute, Pioneer Nome Study Radio School. Wash- ington 9, D. C. SAMPLE LESSON FREE Rom I will send you a FREE Lesson, "Getting Ac- sOOD OR SAMPIEELEfCN/FREE quainted With Receiver Servicing," to show you how practical it is to train for Radioat homein spare J. E. SMITH, President, Dept. SEX' time. It's a valuable lesson. Study it -keep it -use National Radio IQnstitute, Washington 9, D. C. it- without obligation! Tells how Superheterodyne man and 64 -page book, I 11 al r.i rag me, n °f iiadto checked be. Circuits work, gives hints on -, . .i. will call. Pi, . , v .l Radio Service a Rusines. of My, C Aviation Radie Own Receiver Servicing, Locating C Operating Broadcasting Station. Service Technicians for Radio Defects, Repair of Loud- stores and Factories Army. Navy Radio Jobs C Operating police Radio Stations Spare Time Radio Servicing speaker, I.F. Transformer, Ship and Harbor Gang Tuning Condenser, Government Civilian Radio C Ourt.ting adio (If you have not decided which branch you prefer-mall coupon for etc. 31 Illustrations. facts to help you decide.)

Name Age y Radio Course Includes Address !SION ELECTRONICS Zone 4FR QUENCY MODULATION ity State .a

RADIO -CRAFT for MAY, 1945 4A7 CL * LAPEL * Crystal Microphone

the conversions to utilize AG transmission when Yyou voice Crystal Microphone Pperfected Will be prevalent military that circuits period. Check Public Address and electronic immediate post hone quality. in the Microphone of American is. advantage

. It is discernable

co Crystal Microphone Public Address

JOBBERS Get your name on the list now, to receive important announcements American C7 will make when the Crystal Microphone war time job is done. Public Address RC Home Recorder Crystal Microphone

1915 So. Western Avenue, Los Angeles 7, California

468 RADIO -CRAFT for MAY, 1945 {/nt e Jeff e ox e 1 ur rifi Cway i ` REALLY LEARN RADIO ELECTRONICS and TELEVISION

SPRAYBERRY RADIO TRAINING

ECHNIC AL íHNICEDCE

SKILLED tiI HANDS !UA TRAINED TfCNN/C /AN

There's only one sight way to learn Radio Electronics. you must HOW TO READ RADIO DIAGRAMS get it through simplified lesson study combined with actual "shop" AND SYMBOLS me practice under the personal guidance of a qualified Radio Teacher. a valuable new book which explains K AD MONEr In simple. non -technical English how to EL It's exactly this way that Sprayberry trains you . . .. supplping reed and understand any Radio Set Dia- real Radio parts for learn -by -doing experience right at home. gram. Provides the quick key to analy:ing TE learn your understanding is clear -cut, you any Radio circuit. Includes translations Thus, you faster, of all Radio symbols. Send for this N acquire the practical "know how" essential to a good -paying Radio FREE book now while supply lasts and job or a Radio business of your own. along with it I will send you another big FREE book describing my Radio - Electronic traininu. A Bright Future Now's the right time to start training. Because Radio is surging forward, expanding at a rapid pace . with the promise of spectacular opportunities in Television, Frequency Modulation, Industrial Electronics .. . in the vast Radio Service and Repair business. When you train with Sprayberry, you need no previous experience. The Course starts right at the beginning of Radio, even shows you how to make spare time profits while learning. SPRAYBERRY ACADEMY OF RADIO F. L. Sprayberry, Pres. I'II Show You a New, Fast Way to Test Room 2055 Pueblo, Colorado Radio Sets without Mfg. Equipment Please rush my FREE copies of "HOW TO MAKE MONEY IN The very same Radio parts I supply with your Course for gaining TELEVISION." and "HOW TO READ pre -experience in Radio work may be adapted through an exclusive RADIO, ELECTRONICS and Sprayberry wiring procedure to serve for complete, fast, accurate RADIO DIAGRAMS and SYMBOLS." Radio Receiver troubleshooting. Thus, you do not have one cent which only of outlay for manufactured Test Equipment. is not Name Age expensive but scarce. In every respect, my training is practical. complete .... tested and proved for results. It will give you the broad, fundamental principles so necessary as a background, no matter which branch of Radio you wish to specialize in. Address City State MAIL COUPON NOW ! Tear oft this coupon, mail in e 'elope or paste on penny postcard ,a RADIO -CRAFT for MAY, 1945 469

A RAID I11 Contents May, 1945 Volume XVI, No. 8 Editorial: Radar Possibilities by Hugo Gernsback 477 C KAI: Radio -Electronics Monthly Review 478 Postwar Citizens' Radio. by S. R. Winters 481 <.40 POPULAR LIECIRONICS ELECTRONICS Incorporat,ny SHORT WAVE CRAFT TELEVISION NEWS RADIO IF TELEVISION Klystron Circuits by Capt. Eugene E. Skinner 480 Radar Principles, Part II by R. L. Smith -Rose 484 MEMBER Future Aspects of Television, Part II by Dr. Lee DeForest 485 AUDIT BUREAU OF CIRCULATIONS Police Radio on V.H F. 487 1$ Electrostatic Modulator by R. S. Havenhill 505 HUGO GERNSBACK, Editor -in -Chief H. F. Heating at a Glance by William Lyon 510 FRED SHUNAMAN, Associate Editor I. QUEEN, Editorial Associate WAR -TIME RADIO ELMER FULLER, Shortwave Editor Electrons Train T. R. Jr. 486 A. PASCALE, Production Manager Aviators by Kennedy, Army Radio Communications 490 G. ALIQUO, Circulation Manager JOHN J. LAMSON, Advertising Director ALFRED STERN, Promotion Manager RADIO TRAINING

Amateurs and Postwar Radio by Raymond Lewis 483 IN THE NEXT ISSUE Speech Amplifiers, Part VIII by Robert F. Scott 491 Broadcast Equipment, Part VIII by Don C. Hoefler 495 Receiver for 32 -Volt Plants Television and the Amateurs TEST INSTRUMENTS A Home -built Code Recorder Ultra- High- Frequency Tuning Test Comparator by Wm. F. Frankart 496 Amplifiers Practical V.T.V.M. by Wm. B. Miller 497 Cathode -Coupled Better Signal Generator by L. Lane 522

Published by Radcraft Publications, Inc. SERVICING Publication Office: 29 Worthington Street. Springfield 3, Mass. Voltage Regulators by Jack King 489 Editorial and Advertising Offices: 25 West Broadway, Tel. RE2 -9690, New York 7. N. Y. Rapid Conversion by W. G. Eslick 492 Chicago Advertising Office: Radio-Craft, 520 North Michigan Avenue. Tel. Superior 7306, Chicago 11. III. Cleveland Advertising Office: 405 Erie Bldg.. CONSTRUCTION Cleveland, Ohio. Burdette Phillips, Manager. Tel. Main 9645. Capacitor and Resistor Codes by Stuart Distelhorst 493 Los Angeles Advertising Office: 606 South How to Repair Electric Clocks by Homer L. Davidson 518 Hill Street, Los Angeles 14, Calif. Ralph W. Harker, Manager. La Low- Voltage Receiver by Paul Abramson 528 New England Advertising Office: 411 Lafay- ette Street, Salem, Maas. Claude C. Smith. Manager. SOUND San Francisco Advertising Office: 582 Market St.. San Francisco 4, Calif. Ralph W. Harker, Phelan 488 Manager. Tel. Garfield 2481. Sound Units and Sound Ratings by T. H. RADIO -CRAFT is published monthly on the 25th of the month preceding that of date; subscription price is $2.50 per year in U. S. (In foreign countries. 75c additional per year DEPARTMENTS to cover postage; Canada. 50c additional.) Special rates for members of the Armed Forces World -Wide Station List by Elmer R. Fuller 500 by or F.P.O. in U. S., or those addressed A.P.O. 506 mail. $2.00. Entered at the post office at New Radio Electronic Devices Springfield as second -class matter under the Radio- Electronic Circuits 508 Act of March 3. 1879. All communications about subscriptions should be addressed to: Try This One! 512 Circulation Manager, Radio-Craft. 29 Worth- I. Queen 516 ington St., Springfield 3. Mass. Progress in Invention by Communications 532 ii Notice of CHANGE of ADDRESS should reach us at least one month in advance. When 111111111 I I11111111111111 N 1111111111111111111111111 1111 ii i 1111111111111111 I1 111111111111111 111111 il 111111 ordering a change, please furnish an address dl! IIII': II iIGIÍ'I IÍÍ ili!II111ÍIÍiV;11111 Ili ill II 1111111111 Illllllllllll I I I I I I I I I I N stencil impression from a recent wrapper if you can. Address changes cannot be made without the old address as well as the new. ON THE COVER

Foreign Agents The cover illustration this month is from Warner London-Atlas Publishing and Distributing It represents Co.. Ltd., 18 Bride Lane, Fleet St., London. Brothers' picture "Objective Burma." E.C. 4. Hollywood idea of Radar installations and prob- Melbourne -McGill's Agency, 179 Elizabeth the St.. Australia. ably does not resemble any "real or fictitious" s equipment used anywhere on earth. The cone - Text and illustrations of this magazine are shades for cathode - copyright and must not be reproducgl without shaped hoods are apparently Permission of the copyright ownere4 racks, antennas. Copyright, 1945, Radcraft Publications, Inc. ray tubes and the long directed 470 h

YOU NEED huIIic:riifirs EQUIPMENT in high frequency development work

Rail and motor lines, maritime services and universally expanding aviation are planning new or improved communications systems to keep up with the forward pace. In these and many other fields of science there is an urgent demand for the latest developments in very high frequency and ultra high frequency apparatus. In your work in these fields, look to Hallicrafters for advanced communications and electronics equipment.

X BUY AWAR - BOND TODAY! "ihe new Hallicrafters AM receiver. Model S \ /FM -36, de. signed for maximum performance on the very high frequencies. THE HALLICRAFTERS CO., MANUFACTURERS OF RADIO Provides continuous frequency coverage from 27.8 to 143 Mc. Covers old and proposed new FM bands. AND ELECTRONIC EQUIP!OANT, CHICAGO 16, U. S. A.

RADIO -CRAFT for MAY, 1945 471 SPRAGUE TRADING POST A FREE Buy - Exchange -Sell Service for Radio Men 1

WANTED-'4 or % hp. variable speed WILL TRADE -EC -3 In good condition motor. William Lo(strom. 1302 West 11111 for either SX -25 or SX -28, paying any Ave.. Valdosta. Ga. cash difference. Howard O. Whipple, 14 -23- 121 St., College Pt., L. I., N. Y. FOR SALE -Philro Na ORS voltohmmeter. ,p`rË'* Three Star F. Andreseik, 22 Portland Ave.. Clifton, WANTED -Superior No. 1240 tube tester, N. J. also Knight 7- or 14 -watt amplifier sys- .0( f1r.AVi tem. Cash. H. G. Radcliffe, 1013 High Performance! URGENTLY NEEDED- Multimetor tester .T.. Petersburg, Va. and signal generator. WIII buy any test equipment you havo for talo. Cash. To be TUBES TO TRADE -One each: 117Z6GT; Note that the Sprague Army -Navy E Flag now used for helping the boys In the Pacific. 1115GT 1N5GT//G; IT5GT; 5OL6GT: contains THREE stars. These stars, coupled with Onlls I. Bradford SI /e. 974- 00 -54. USNII, 35Z5GT: 12SK7GT: 12:íG7 GT: I2NQ7GT: the original flag presentation, means FOUR separate citations for Fire Station No. 3. 118NRIt Navy No. 10. 128A7GT; 56; 71; 78: 26. all new or prac- % F.1'.O.. San Francisco. Calif. tically new. Want late sig. generator or outstanding service in supplying Sprague Capacitors and Koolohm will trade tubes and pay difference for Resistors to match the exacting demands of the nation's armed WANTED -One or more of following tubes: SX -2S Super Skyrider. Allen Admire, Jr., forces. CAS: IA7; 1115: INS; CAR: 12SA7' 1343 W. 255 St.. Box 1268, Harbor City, 12SK7: 12507: 3516; 35Z5: 561.5; 80 andd Calif. Such a fact explains better than words why it has sometimes been 117517 -GT. Roger F. Cain, Savannah, Mo. impossible to meet all civilian needs for these products. But it WANTED Small VOM such as Triplett also shows beyond question of doubt that you can rely on Sprague FOR SALE -Rider's manuals. No. 666. Supreme. Precision or Phlira Cash. the utmost in service and through No. 12. all now, $150; Tatra No. 4, G. SamkMaky. 527 Bedford Are., Brooklyn. Capacitors and Koolohm Resistors for $7.50: OVeaton No. 663 analysers. $30; No. N. Y. dependability! 665. 150: three No. 301 meters. $7.50 es.; Supreme 339 deluxe analyser. $45; Supreme WANTED -Late emission type tube test- Ask for them by name. We'll appreciate ItI No. 333. S35: Supreme No. 520 universal er with Instructions, also 4- or 5 -tube small AC bridge. tests res., capacity. and in- table radio: 1A70 or OT tube. J. IL ductance. $50; Clough-Brengle O -C oscil- Sawyer, 2604 Holmes Ave., Springfield- Ill lator 55kc to 30mc. $35: VTVIM Sylvania WANTED -Any kind of test eqpt. for radio WANTED -Late N.11.1. or Sprayberry ra- designed. $35: Jewell analyser AC 4 ranges work. cash, also tubes dio course. complete. State year and price. WANTED- Hallierafter SX -24 or SX -25 or electrical Will pay to 160v DC to 600v Ma to 150, $20. Joe receiver. Sgt. and L C. Jones, 10 -C -1 Upshot. Flank Dirks, Hebron, Nebr. Anthony Brocato, Jr., 393 parts. Koneeny. 34'20 Holland Ara, Saginaw, F.A. Bit., HO. Btry., Drive. Wilmington, N. C. Mich. Camp Iliad, Texas. FOR SALE- 6VS. fies. 6RR. 6F5. 25A5. 6A5. FOR SALE OR TRADE -Sprague Deiuse WANTED -One Hammarlund HQ -120X or 5114. 6114. 5V4. 57A, 6117, 82, 84, WANTED -RCA -Rider ehanalyst 162 -C. lisllIerafter SX -28 In good condition, list 6N7. 1114. and many other new tubes. Also Tel -Ohmike Na TO-2, used only a few (lush for used one. or one that nests times, in original carton. Tubes price. Alfred Stewart, Ârapohoe. Nebr. one 12. Jensen P. Ms. Pk. SloDevitt Radio repairs. R'm. E. Selby. preferred 76I -7th St., S.E., as part payment such as 1A7, INS, 1115. Service. 17 Monument St., Charlestown, Washington 3. D.C. Mass. 3516. 501.6. 3525. 1177.6 and 12v types. FOR SALE -Triplett freepoint tester unit. IL O. Dozier. 1208 College Are.. Tifton. latest model, motel with adapters and WANTED -1, 2, or 3 of following lobes: Ga. sockets for all tubes. Want used CE Ex- URGENTLY NEEDED -Two 3523 and 1A7: 7A8; 251AGT: 2525; 35Z5(FT; ammeter made by Solar. Buford Brown, 50141 tubes. Also modem tube tester. 5OL6GT: 117Z6GT. C. B. Davis. 681 WANTED- Rallirraftor S -19g or SX -21 Box 307. Trion. Ga. Thomas Morris. 11.F. D. 3. Box 247. Delmar Ave., Atlanta. Ga. Charleston, W. Va. or National. Howard or Fhophone Na 1 to 6 receiver, 125 to $75 maximum. Also URGENTLY NEEDED- Echophone EC -I FOR SALE OR TRADE- Electronic con- port. amplifying record player. maximtun. in goal condition for soldier. Sammy's WANTED BY EXPERIMENTER -Coils: verter 32v DC to 110v AC, 100 watts. Want, $20. A. Carlson. Post Box 601, Lewistown. Radio Service, Rushville. Ill. condensers; mica. tubular. electrolytic and portable record player or 0.1. recording Mont. variable tubes and resistors. Andrew R. unit. Phillip R. Birches. Box 293, Ells- SALE OR TRADE -Dayrad tube checker Harrar. RD. No. 2, Birdsboro, Pa. worth, Kans. Perles 11. $10; Na 305 Radio City tube FOR SALE -Scott Phantom chassis In perfect condition. 19 tester. 115; 5 amp. TTiplelt meter. 13.75; FOR SALE -New tubes In cartons, 50% URGENTLY NEEDED -Good used Philter tubo. I6 -watts output. 0 -7.140 Weston voltmeter. $5: 008 -.1 -15 or list price: 1G-i. 1115, II'S. IRS. 155. other $200. Santee Radio Service, 165 W. 9$ or goal make signal generator. De- St.. New N. mid. Readeite capacity meter, $3; 25.000 IT4. 3Q5. 354. 6E6. 616, 6SA7, awl many scribe fully. W. M. Finley, Jr.. Norfolk, York. Y. alun meter. $1.75. Want Rider's manuals. others. Also new Bogen high fidelity sound Ark. tubes. or parts. Glenn Fessenden, Box 1006. system. complete with speakers and mike. WANTED channel D. Janien, 7149 Ardlelgh St., Philadel- -Superior analyzer and Giendlve. Mont. FOR SALE OR TRADE -Meter dials, sig. generator. lato model tube checker and pitla 19. Pa. multiple range volt. ohm. milliamperes. v.t. voltmeter. Rufus P. Voorhies, P.O. FOR SALE -F2 Atwater Kent dynamic Any size for large or small meters. Want Box 126. New Iberia, La. speaker: Knight power supply 350v, 65ms, WANTED -Two No. 47 tubes; also Infor- large 0 -1 mil or less meter, bellows camera, 2.5v fil. power transformer 295íT. 8.3r mation on 5076. 3516. 11726. and 6A7. enlarger and other photo eqpt. J. L. Oxygen, SI.. 110v primary 1927 Steinite 7 tube What hare yak? Norman C. Hassan. Black Pewaukee, Wisc. WANTED -5016; 357.5; 12337; Metal 614 receiver with speaker. Also want two No. 26 Point Rd., Seareboro, Me. or 'hat have you new or in good used tubes. Wayne harried. RD No. 1. Box 92. condition? Wearers Auto Electric. Red FOR SALE -Mallory vibrators: Type 4.4, Lodge. Mont. Cuyahoga Falls. Ohio. WANTED -A -1 78 rpm phono motor, 6v; F290, 32v; 271, 6v; and one very heavy preferably variable speed. Gene Shumway, duty 6r unit; also one 6v vibrator power WILL TRADE for press or reflex ramera: Box 485. Sterling, Kansas. transformer for pp. output tubes. All per- FOR SALE -Weston voltmeter Na 301 two G -E meters 2 and 3 amps; 2 Westing- fect. 18.50 for lot. P. A. Rosenblatt. P.O. Av d -c; Weston Thermo-galvanometer Na house meters 1.5 and IO amps; 3 -2. square URGENTLY NEEDED-Rider's manuals. Box 905. Iloboken, N. J. 425. Want Phtico or G -E record player, Triplette 100- 100 -200 mills: FTC trans- W. J. Mitchell, P.O. Box 483, Anoka, Fia. also 357.5; 3516 and 12K7 tubes. Frederic former See: Thordarson T- 115170: and FOR SALE -One Superior channel analyzer, Ir. Pecasa, 16 Tracy Ave., Batavia, N. T. and 1 tubes. Wm. H. 3- HY407, -807 FOR SALE OR EXCHANGE -1941 Radio new, has never been used, 130. Henry Brown. Jr.. 1003 Boss St.. Aliquippa, Pa. Circuit Manual thy "Radio-Craft"). in Schap'''. Box 62. Nuela. Colo. FOR SALE -Std. brands IC7 tubes, per- original carton; Supreme No. 35 tube test- fect substitutes for 12SK7's, 65c ea. pest - FOR SALE-Two JFAI 90 General Electric er, with octal adaptera: and Lifetime rib- FOR SALE push frequency sett, new. never used, -Philro 016 Dutton signal paid minimum quantity two. W.E. 21111 modulation bon mike with banquet stand. Want Su- generator, 115. Norman Berg. P.O. Bea (O 9 tubes. 2 limiters each. Receivers without 31.50 ea.; 104 -D W 35c ea. Ph. Itos- perior multi -meter No. 1250 anti sig. gen- 193, Hillsboro, Kans. hertt, P.O. Box 905- Hoboken, audio. Retail value $59.50 ea. K L. Co,. erator No. 1230 or equivalent. L. B. N. J. 2035 West Academy St., Winston Salem, Mundy, 700 Palace Blvd.. Clifton Forge. N. C. Va. WANTED-Cash for Hickok No. 2105 zero URGENTLY NEEDED -Late model sig. current voltmeter or any other good V -O -M generator, preferably Phlim Na 010 or with large meter. Don Y. Yen. Rockford. Triplett pocket sise V -O -M; and 501.5. SEND US YOUR OWN AD TODAY! Mich. 7016. 3516. 8A8. INS. IRS. and IA7 tubes. Fred Kati. 825 Ifagnolia Ave.. For over two years now, the Sprague Trading Post has been helping FOR EXCHANGE -National SW3 receiver Orlando. Fla. radio men get the with tubes and rolls leas power supply and materials they need or dispose of radio materials speaker for Rider's manuals Nos. 7 and A. they do not need. Literally thousands of transactions have been made Earle R. Drake, 790 (ohannet St.. Taun- WILL SWAP -R.C.P. No. 312 tube check- through this service. Hundreds of servicemen have expressed their ton. Mass. er and rash for Hickok 510 or 155 traceome. sincere ter. Peters Electric Co., Box 821. Clawson, appreciation of the help thus rendered. Mich. Send your own ad us FOR SALE OR TRADE -Searee tubes such to today. Write PLAINLY -hold it to 40 as 128017, 57A. 68317 8.17. etc. Write for words-or less-confine it to radio materials. If acceptable, we'll gladly list. S /Sgt. J. C. Davenport, 18025080, WILL TRADE -Large stamp collection in- run it FREE OF' CHARGE in the first available issue of one of the 2725 N. 15th A, Waco, Texas. cluding first day covers, censor corers, mint five radio magazines wherein the Trading Post appears every month. singles. name blocks of flags, etc.. for FOR SALE - OZ4 tubes In sealed cartons. rommunlcatlon receiver or recorder. J. HARRY KALKER, Sales Manager Wellington Radio Service, Marvin Wel- Wong, 970 S. San Pedro St., lots Angeles lington, Oswego Kansas. 15. Calif.

Dept. RC -55, SPRAGUE PRODUCTS CO., North Adams, Mass. Jobbing distributing organization for prcducts of the Sprague Electric Co. SPRAGUE CONDENSERS KOOLONM...... _...... RESISTORS Obviously, Sprague cannot assume aitresponsibility, or guarantee goods, services, etc., which might be exchanged through the above advertisemelltsi 472 RADIO -CRAFT for MAY, 1945 ELECTRONICS DeFOREST'S A-B-C WAY!

THE fast- moving Opportunity Field of Radio - Electronics needs many F trained men! Let DeFOREST'S show you how to get ready to take advantage e. 9 -r.-.4 of the breaks -the good jobs -the satis- 4.4 fying pay checks of today -and the bright postwar opportunities of tomorrow. Write for DeFOREST'S big, free book -"VICTORY FOR YOU" and col- orful kit supplement. Consider Radio's Many Fields See how you may cash in on a vast field that includes F.M. Radio, Communica- tion Radio, Electronics, Broadcast Radio, Aye Motion Picture Sound, Radio Sales and PRACTICAL EQUIPMENT Service a Radio business DOING" FROM -or of your own. A "LEARN -BY- experiments at home Radio- Electronic Quickly Start a Business of Your Own Make 133 interesting parts and assemblies. BIG KITS of Radio ... a Light Beam See how DeFOREST'S has helped many -from 8 Circuits that operate Telephone ... Radio Receiving one .. . Radio get their start in Radio- Electronics- build Wireless Scores projects.ro ects. "Electric Scores of other fascinating helped them to good pay jobs in one of "Electric Eye" Devices. our most promising industries- others INTERESTING, LOOSE -LEAF LESSONS-. to preferred military classifications with 90 modern, well - illustrated loose -leaf les- higher ratings, better pay. Helped others sons, prepared under the supervision of one of the to full or part time sales and service The Billion Dollar Radio- world s foremost Radio authorities, Dr. Lee De- businesses of their own. Electronic Industry, with Forest, often called "The father of Radio!" its Manufacturing, Servic- Employment ing, Broadcasting, Com- Service! munications. and many DeFOREST'S also provides an effective other promising fields, in- EMPLOYMENT vites your careful consid- SERVICE which has eration. See how DeFOR- long -established contacts with many em- EST'S. helps you prepare ployers who use DeFOREST'S trained for a good pay job, or a business of your own in one Radio -Electronic men. of America's most promising, interesting fields. Mail the coupon Now -Today! See how DeFOREST'S can help YOU get started toward this fascinating Deforest's Home Training offers instruc work by means of its effective "A -B -C" fion in Motion Picture Sound Equipment, P Training Method -in your spare time. FM Radio and Television. Residential See Rodio Circuits in Action VETERANS: Check coupon Training in modern Chicago laboratories Electrons on the March -w below for special information. Is also available. Write for details. this genuine DeVRY Projector USE "LEARN -BY- SEEING" MOVIES READ WHAT THESE MEN SAY ABOUT DeFOREST'S TRAINING with a genuine DeVRY 16mm. Movie "I have obtained employment with "I cannot impress too strongly on Projector and Films to help you learn the Mfg. Company. They speak anyone who may be considering taking Radio faster ... easier. See hidden highly of DeForest's students and state your course the value of both the train- Radio action come to life! Radio waves they have had excellent results with ing and the employment service that in motion Electrons on the march.. . your men whom they have employed." goes with it. This service is not merely - Clifford Taylor, Mass. an empty promise, but a truly con- E. B. DeVry, President "As a result of DeForest's Training. scientious effort that continues until its I am doing very well. If my income job of preparing you is done. " Philip DeFOREST'S TRAINING. INC. Cummins, New Jersey. - doesn't range between $50.00 and $75.00 2535 -41. N. Ashland Ave., Dept. RC -Bj per week, I figure something is wrong." Lyle Rielly, Wisconsin "I am amazed at the many subjects Chicago 14, Illinois, U.S.A. I have learned with DeForest's. I also Please send me your "But the credit must go to you and want to praise your motion picture "VICTORY FOR your employment service for placing lessons. It is truly amazing, how well YOU" book and KIT FOLDER, FREE. me in this job when I really needed the action of electricity is brought out. one. I,shall always be grateful for the I feel safe in saying that no book could Name... Age...... help and guidance given me by you ever establish effectively those princi- and DeForest's Training. Thanks a ples and actions so well in my mind," Address...... million." - Earl Eichelberger, Illinois. -Yale Schorr, Texas. City. State......

T R A I N I N G, INC. I O If under 16, check here for special information.

DE F O R E S CHICAGO 14, ILLINOIS 1 S T' , p If a veteran of World War II, check here. RADIO -CRAFT For MAY, 1945 473 We can all see with the naked eye that the lationship between management and labor. Payroll Savings Plan provides the most To working America the Payroll Savings stable method of war financing. Analyze it Plan offers many new and desirable oppor- under the X -ray of sound economics and tunities. Through this systematic "invest- other important advantages are evident. ment in victory," homes, education for A continuous check on inflation, the their children and nest eggs for their old Payroll Savings Plan helps American In- age are today within the reach of millions. dustry to build the economic stability upon The benefits of the Payroll Savings Plan which future profits depend. Billions of to both management and labor are national dollars, invested in War Bonds through benefits. Instilling the thrift principle in this greatest of all savings plans, represent the mind of the working men and women, a "high level" market for postwar products. the Payroll Savings Plan assures their Meanwhile, putting over Payroll Savings future security -and is a definite contribu- Plans together establishes a friendlier re- tion to the prosperity cf postwar America!

The Treasury Department acknowledges with appreciation the publication of this message by

RADIO -CRAFT

This is an official U.S. Treasury advertisement prepared under the auspices of Treasury Depart ent and War Advertising Council.

474 RADIO -CRAFT for MAY, 1945 LIANE MORE MONEY

OFT MESE 28/0 BaXS You men already in Radio know how great the demand is for trained, experienced servicemen, oper- Here's Just a Few of the In- ators and technicians. You know how fast the field teresting Facts you Learn is -FREE growing and how important it is to keep up with with the FREE MANUAL. _ developments F.M. Receivers, Electronics and - I. Routine for diagnosing Radio iH Television. You know, too, a fellow cannot learn Troubles. paAD10¡ too much about any industry for REAL SUCCESS. 2. Preliminary Inspection of Re- Whether you have experience or are merely INTER- ceivers. 3. How to Check Power Supply. ESTED in radio as an amateur, you must recog- 4. How to Identify Various Stages nize the WONDERFUL OPPORTUNITY right of Receiver. within your to cash in on natural abil- 5. How to Trace the Circuit sod grasp your Prepare Skeleton Diagram. ities. Make them pay dividends. Cet into the EX- 6. How to Test and Measure Volt- PERT RADIO SERVICE FIELD. Be an F.M. and ages. TELEVISION specialist -OWN A BUSINESS OF 7. How to Test Speaker in Audio YOUR OWN, you Stages. if prefer. Fill out and mail the 8. How to Test Detector, I.F., attx±t coupon below for all the details of our plan. R.F.. and Mixer Stages. was, vtm 9. Complete Reference Table for Q a l e k l y Locating Receiver Get the Latest Inside Information-Short Troubles. Cuts -Trade Secrets by

SHOP METHOD HOME TRAINING FROM A REAL ESTABLISHED RESIDENT SCHOOL Now the famous National Schools brings its exclusive Shop -Method of training right into your own home. You can learn the most up- to-date, approved projects, systems and circuits step by step in your spare time. Thjects, is is the sound practical training you want and need -the development of experienced instructors working with thousands of students right in shops. NEW F.M. broadcast studios and ex per i m e n t a l laboratories of NATIONAL SCHOOLS -one of the most advanced trade educational centers in the world. National Trained Men Now Making the Best Money in History The real value of National trainishows n the quirk progress up LEARN BY DOING job. our men make on the Incomes !Nat coed fantastic only snort time being re{ by National graduates. Work with Real And this - only a sample of what the future holds für Experimental Equipment the MAN WHO KNOIVO RADIO. F.I.F.C TRONICS. F.M.. TELEVISION and Furnished without Extra Cost allied subjects. National is proud of the progress s graduates are mak- as Part of Your National Training ing all over the world. Read the farts -the actual proof in the Experience is the beet teacher. You learn by books e send you FREE. experience with the exclusive National Shop - Send the Method of Home Training. In the course of your Coupon and Be Sure Of Your Success And Security After The War t study you actually build various types of receivers Do 't let your pc* t-wt it atol. i ii..us lag. Don't let YOUR future depend -a powerful superheterodyne, a signal generator, prove to on others. Build a career for yourself. Never in all history has the return- an audio oscillator and ing serviceman, or war worker been confronted with such a great future others -You make tests and yourself what if he reaches out and grasps It NOW. Here la a now world opening before conduct experiments that show you the why and you. Get ready now while you are still In uniform -while you are on your how of things. You YOU can do war Job. Then FOU can soon step into an essential, well paid position or, understand what makes the with little capital, HET INTO BUSINESS FOR YOURSELF. It Isn't a various elements of electronics operate because you in RADIO!,,: bit loo soon to start now. Radio men are vitally needed. Fill out and mall actually see them work for you. Not only do you the coupon immediately and examine the NATIONAL SHOP SIEPHOD gain marvelous experience by this method of learn- HOME TRAINING COURSE carefully, without obligation. ing but you receive valuable equipment you will use on the job in the practice of your profession as an electronics expert. Mail the coupon and learn what NATIONAL SCHOOLS this means to you. Los ANGELES 37, CALIFORNIA EST.190Li MAIL OPPORTUNITY COUPON FOR QUICK ACTION

tmon in envelope TREE LESSON /NCIIIPED National Schools, Dept. 5 -RC caráiste Examine the exclusive National Shop Method of Home Training. 4000 South Figueroa Street, Los Angeles 37, California. See for yourselfCow sound and you can practical it Is. Re convinced that learn Radio, Electronics. Television-quickly n easily in Mall me FREE the books tioned in your ad including a sample lesson of your course. your spare time. You cant tell until you trv. This trial is ABSOLUTELY I understandn salesman will call on me. FREE. Fill t the coupon Immediately while you are thinking about It without obligation. Mid drop It N the mall at once. Mall tho upon here for the beaks that tell you the complete to p AGE of the marvelous new system of training in Radio. Electronics and Tele- NAME vision. Learn the facts of this excltialve shop- method of home training. See for yourself! DECIDE FOR YOIIRSEI.F! This Is the MODERN SYSTEM OF TRAINING: it matches the rapid progress in Electronics. ÌC is ADDRESS TIME TESTE.D.attoo. National Schools hase been) training It that has haÌpeO tthrousandsi to more PAY and opportunity. STATE You we it to rotuself-your future-to read the book "Your Future in Include your sone number Radio. Electronics and Television" -FREE to you when you send in the coupon. MIN M --1=11 RA010 -CRAFT for MAY, 1945 475 SIL VANIA XEWS RADIO SERVICE EDITION

Published in the INICrIsis of Bell, r Sigbl and Sound 1''15 Sylvania Expands Service Aid with New Radio Tube OVANIA Substitution Manual Full Data Contained in New 20 page SERVICEMAN Bulletin Superseding Earlier Guides V

by FRANK FAX

Newest of Sylvania Electric's technical bulletins on Tube Substitutions is the 20 page "Aids To War -Time Servic- ing" that servicemen throughout the country are finding most helpful in these days of radio tube shortages. The manual is another Sylvania con- tribution to assist servicemen in meeting the present acute shortage of many tube types. In addition, it contains Recognizing, early in the war, the diffi- 6 -page bulletin containing information several charts of diagrams showing culties that would result from tube short- based in part upon the WPB civilian adaptor circuits commonly required. ages, Sylvania Electric immediately took radio tube program, permitting complete This bulletin is available free on re- steps to aid servicemen in tube substitu- presentation in one convenient folder. quest from your Sylvania distributor, tion problems. Early in 1942, Sylvania Now, newest and largest of these Serv- published -and distributed free to serviceman Service is a 20 -page or from Sylvania Electric Products charts manual icemen-a 4 -page bulletin, "Correlation entitled "Aids to War -Time Servicing" Inc., Emporium, Pa. of Tube Types for Substitution." presenting the latest in Sylvania Tube Substitution Charts and containing 4 MORE EXTENSIVE DATA full -page charts of 9 diagrams each de- This bulletin proved so helpful to serv- scribing adaptor circuits. icemen that Sylvania continued this service in the Technical Section of Sylvania CONSISTENT POLICY News, and then decided to re -issue the in- Publication of this book is the latest formation in more comprehensive form. step in Sylvania Electric's consistent An enlarged, more fully developed "Radio policy of assisting radio servicemen to Tube Substitution Charts for War -Time carry on their business efficiently and Servicing" appeared in 1943. This was a profitably. SYLVANIAS "ELECTRIC SYLVANIA ELECTRIC PRODUCTS INC., Emporium, Pa.

MAKERS OF RADIO TUBES; CATHODE RAY TUBES; ELECTRONIC DEVICES; FLUORESCENT LAMPS, FIXTURES, ACCESSORIES; INCANDESCENT LAMPS 476 RADIO -CRAFT for MAY, 1945 RADAR POSSIBILITIES ... Radar is bound to play a prominent radio role in the postwar period. There will be literally thousands of new peace -time applications ... . HUGO GERNSBACK

RADAR is not a new or wartime radio invention purposes if found necessary, practical, or convenient. -indeed it is older than radio itself, its instru- This also suggests many industrial uses in factories, mentalities antedating even early wireless. plants, mines, etc., where radar not only will save untold Actually it was Henrich Hertz, the illustrious dis- lives and accidents but also will speed up work. coverer of electro- magnetic waves, who was the first One of the important uses of radar in the future will one to experiment with microwaves during the 80's. He be in a rather unsuspected quarter. As aviation pro- refracted them through a pitch prism, just as we refract gresses, long distance travel is tending to move into the light rays through a glass prism. It is the same micro- higher strata of the earth's atmosphere. Now it so waves to which we have returned during the present happens, in the upper regions of the atmosphere (where World War, using them in modern radar. we are approaching a vacuum) space abounds in meteors Radar -which is nothing but a radio echo whereby and meteorites which move at the terrific speeds of microwaves are sent out in one direction and which between four and seven miles a second. This is a far bounce back from a solid medium or a water surface- greater speed than that at which the fastest bullets and has many uses besides the present war applications, projectiles move today. Should a small meteorite strike a whereby planes, ships, warships, etc., can be detected plane or rocket- machine, it would go through it with the at night and through fog; whereby airplane navigators same facility as a bullet cuts through butter. So far, can detect their objectives at night or during fog and engineers have not had to bother themselves much about bomb the object which they cannot see. meteorites for the reason that the earth's atmosphere For peace -time use the radar idea will find applica- protects our planes. Meteorites striking the upper re- tions which are not even dreamt of today. First and gions of the atmosphere immediately melt and volatilize. most important, saving human life through prevention The composition of these foreign bodies -of which of collisions is probably the most urgent need. Radar on actually several million strike the earth's atmosphere locomotives will prevent not only head -on collisions, but every hour is mostly iron mixed with some nickel and rear -end collisions with other trains as well. Fog, thick other metals. They may vary from the size of a pea weather and darkness, whether at night or in tunnels, to the size of a house and larger. do not interfere with radar. What is true of trains is Radar in the future will be able to anticipate strikes equally true for airplanes, which no longer will collide of such meteorites and the navigator will be able to with other planes in flight nor run into mountains at change his course so that the larger size ones will not great loss of life, as at present. Ships at sea will not strike the plane or flying machine. The danger to the collide either with other ships, nor will they run into machine only becomes acute once we start to fly through icebergs or other obstacles, including uncharted, newly - the upper regions of the earth and its extreme atten- made volcanic islands. Automobiles can be made prac- uated atmosphere. tically collision -proof because radar will stop head -on Another new use of radar has just been announced by and rear -end auto collisions. A driver who has gone to the Civil Aeronautic Administration to make postwar sleep will not crash into another car, if his own car has air travel safer than it is today. Radar is expected to been made collision -proof by means of radar instrumen- increase the safety factors of flying in fog, snow, rain, talities. It is possible even with the driver asleep to or when the ground is obscured by clouds. This is called brake his car automatically by a radar system in order "instrument weather" by pilots. to prevent crashes. These are only a few and the most The C.A.A. experimental station at Indianapolis is obvious uses of radar and any technician can let his working on the perfection of two radar devices, one for imagination run wild if he wishes to think up new ap- airport use and the ottler a collision warning device used plications on the radar principle. Anything that moves in the airplane itself. Almost ten carloads of radar anywhere may be radar equipped for safety or other equipment has been lent (Continued on page 507)

1911111111 ., ..

3Rabío Zfjírtp-Iitle Dear.5 Ago yn ótrnsbidc t]u6laanons FROM the May, 1910, issue of MODERN Wireless Lightning Protector, by Warren ELECrRTCS- "Special Wireless Issue ": HUGO GERNSBACK N. Crane. Bellini -Tosi Station at Boulogne, by A. C. Founder Tubular Variable Condenser. Marlowe. Modern Metrics 1908 Duplex Detector, by J. C. Berckman. Electrical Experimenter 1913 Directive Aerials, by George F. Worts. Radio News 1919 Universal Detector, by Thomas Durry. Radio Experiments. Science & Invention 1920 Telephone Radio -Craft 1929 Laboratory- Transmitter, by Harold S. Auxiliary Loose -Coupled Tuner, by Wal- Short-Wave Craft 1930 Nash. ter E. Keever. Wireless Association of America 1908 A New Receiving Circuit,. by Milton Wireless for Dispatching Trains. Goodman. A 100 -Mile Wireless Station Using the Experimental Wireless Telephone, by A Duplex Aerial, by Russel Rankin. Duplex Aerial, by Richard H. Foster. Moore Stuart. A Simple Sending Condenser, by Williams Transmitting Pictures. A Further Help to Tuning. F. Crosry. New Electrolytic Detector. Directive Aerials, by Bernadotte Ander- Wireless with a Static Machine, by New.Ascillograph. son. Moore Stuart. srwlnwummu9999n9uun1mulwnminunluulullwlmlul9uululolum9luiunluwuummmwuunmuuumnuumumlmwuminwwwuwwltmwlun1u1m1umnm91w1 ®9911mumnuull9wwwwww9mlwun uumuluuf.ruuuluR9lnlumuuw9m9 RADIO -CRAFT for MAY, 1945 477 -y

ALLOCATIONS for all the chief public and government radio services are to be complete by May first, according to reports from sources Radio -Electronics Close to the FCC. It is expected that by this time even the opposing proposals for FM assignments, Items which have been put forth with much vigor Interesting and some occasional heat, will have been reconciled, probably with the help of information on propagation conditions which may not be permitted to becoyte public during the war. The FCC expects to go into the matter ARADIO TUBE Task Committee SHORTAGES in radio equipment of clear channels for broadcast stations as has been created to advise on other than tubes may be alleviated soon as the more general allocations are methods for increasing production somewhat through surplusses not re- disposed of- probably early in the second of radio receiving tubes, the War quired by military orders, it was un- t:eck of \fay. Production Board announced last month. derstood from a WPB release last month. Requirements for 1945 are about 25 per Distributors were advised that lists of RUBBER curing methods which speed cent higher than the 12,000,000 a month available excess or surplus electronic ma- is process 17 times by the use of required in 1944, according to WPB. terials may be obtained at all \VPB re- electronics were revealed last month The members of the new \VPB task gional offices immediately upon publication by officials of the Firestone Tire and committee are Peter G. Noll of the Inter- each month. Materials in inventory after Rubber Co. national Union of United Automobile the expiration of a 45 day period become Vulcanization -the joining of sulphur and Workers of America (A.F.L.) and Elmer available for civilian supply, it was stated. rubber molecules -is accomplished through Chamberlain, Charles A. Rackliffe, Alfred Any distributor may request release of the application of heat. When steam is Stern, and Frances Saylor of the United excess material, and if not taken on rated used, the heat must soak in slowly from Electrical, Radio and Machine Workers of orders in the 45 day period, release is the outside. The thicker the product, the America (C.I.O.). usually approved. Due to the specialized longer time required for the heat to reach At the first meeting of the committee, needs of the the core. tropical Pacific theatre, military require- Harold Sharpe, assistant director of the ments will not fall Electronic equipment, on the other hand, radio and radar division of WPB, and off greatly it was stated. heats the entire product almost instan- William A. As transformers were reported as be- Major Gray, chief of the tube coming critical taneously throughout and brings it up to section of the radio and radar division, again, due largely to in- the required temperature in seconds or min- outlined future production requirements. creasing military demands, closer control by \VPB is anticipated, utes depending on size and thickness. The The WPB officials reported Army although available that the production capacity is believed product to be heated is placed between two and Navy are doing all they can to place greater than metal plates that are supplied high -fre- orders promptly military needs. as an aid to facilitating Aluminum phonograph records "out" quency alternating current by an electronic increased production this year. The com- are generator, and is raised in temperature by mittee expressed except for high rated orders, it was re- the view that existing ported, remaining supplies being available internal molecular friction. manufacturing facilities, if fully utilized, The company's foamed sponge rubber sufficient increase only to broadcasting stations making master - are to production to the records, and then only when filling such Foamex -was cured in 30 minutes by steam extent required, in spite of the fact that and in four minutes by electronics. After orders as would not interfere with military the lower schedules for 1944 were not quite and it is cured Foamex is dried with hot air. met. OWI requirements. It takes 16 hours to dry foamed sponge rubber with hot air alone, but if it is There is no immediate prospect, however, treated electronically for 30 seconds the it was pointed out, that the civilian tube ACANCY on the Federal Com- drying time is reduced to an hour. supply situation will improve materially. munications Commission has been Large hard rubber wheels can be cured Rather, it is expected to remain about the filled with the appointment of in 18 minutes with electronics, but if the same as in late 1944, approximately one and Charles R. Denny to the last un- job is done with steam it takes five hours. a half million tubes a month. filled post The nomination was greeted Actually the electronic treatment is applied Regarding the availability of tubes and with general satisfaction, as Denny is well only two minutes, then the rubber wheel electronic equipment following the end of known to Congress as Commission spokes- is placed in a steam mold for 18 minutes.to the European War, it was said that al- man at hearings of both the House of finish the cure and give it shape. Brake though certain military requirements may Representatives and the Senate in the last blocks are cured in seven hours by steam fall off, much of the electronic equipment two years. and in 48 minutes by electronic heat. used in Europe would either have to be Mr. Denny, a native of Baltimore, was A 20 per cent saving is achieved in the tropicalized -made moisture and fungus born in 1912, and is the youngest man ever curing time for garden implement tires and proof -or replaced by new equipment for appointed to the FCC. He is a graduate the figure is much greater with larger tires. use in the Pacific theater. In either event, of Amherst and the Harvard Law School, Elastic thread can be cured electronically it would appear a continued burden will and was chief of the Appellate section of in P/2 minutes, while 15 minutes are need- remain upon the manufacturers of military the Department of Justice Lands Division ed if steam is used. equipment. until 1942. Joining the FCC then as assistant general counsel, he succeeded general counsel Telford Taylor when the latter 1 went into the service late the same year.

ORECAST of a postwar radio market of 60,000,000 home radios -enough to Fkeep radio production at peak for six Checking adjustments years is made in the stockholders' quar- on the high- frequen- terly report of Westinghouse Electrical and cy rubber vulcanizer. Manufacturing Co., issued last month. A small tire, seen un- Five factors are enumerated that will der the disc -shaped affect the postwar market. They are: plate at right, is ur 1. Frequency Modulation (FM) radio will dergoing treatment. hasten total replacements by outmoding Note the shielding practically all sets now in use; 2. The screen around work will increase and directly above demand for radio-phonographs by the the apparatus. the size of the market increasing average sale; 3. Returning service men, establishing new homes, will represent a huge new market; 4. The surface has only been scratched in the market for extra sets to provide listening convenience throughout the home; 5. A steady growth in home television is anticipated. 47 RADIO -CRAFT for MAY, 1945 Monthly Review to the Technician_,

CONVERTERS to permit reception of TELEVISION for the postwar world FM signals on the new frequencies was demonstrated last month by the can be constructed for $8.85, it was Radio Corporation of America in a proved by experiments made last series of showings to press representa- month by the engineering department of tives staged in cooperation with the Na- the FCC. tional Broadcasting Co. Patterned along the design of remote - Featuring an image five times larger than control tuning devices and wireless record those of pre -war sets, the new receivers use players which can be used with a standard the Schmidt optical system with plastic broadcast receiver, the FCC converter can lenses (Radio- Craft, December, 1944) and be operated from any convenient location project a 16 x 21 -inch picture on a special in a room with the present receiver. If plastic screen. Two different optical prob- operated from an arm -chair, you can tune lems had to be overcome by special features stations in and out without touching your of the new translucent viewing screen. One a lazyman's main receiver, making it re- problem faced by the designers was a ten- Size of RCA's new screen may be seen above. mote control. dency which the screen would normally The converter was developed by the have to develop a "hot spot," resulting in a FCC as a result of protests from FM glare in the center and insufficient light in pleted. "Tear outs" and ragged edge effects broadcasters at recent hearings following other parts of the image. The other prob- would result. Preventing this form of dis- the publication of proposed frequency allo- lem was the need for distributing a major tortion, the new system regulates reception cations. portion of the transmitted light to the area in somewhat the same way that a fly -wheel These broadcasters declared that by mov- which the spectators would occupy in rela- regulates machinery. ing FM up in the spectrum, thousands of tion to the receiver. Brightness of the picture is largely due expensive receivers now in the hands of A new development is the automatic fre- to the new high- voltage cathode ray tube, listeners would become obsolete. The FCC which is far more effective while substan- has replied by offering this converter, that tially smaller and lighter than the pre -war is capable of converting an FM receiver direct- viewing tube. geared to the present 42 -50 megacycle Designed to operate at 27,000 volts- band where FM is now located, so that it nearly four times the voltage used in pre- can receive the 84 -102 megacycle band to war picture tubes-the new tubes produce which the FCC plans to move FM. a much brighter initial image. This high Any radio amateur or handyman can initial brilliance, in conjunction with the build one of these FM converters, which efficiency of the optical system, makes it is about the size of a cigar box, at a total possible to obtain from a tube with a face cost of $8.85 for parts that are now avail- diameter of only five inches a bright, clear able in radio stores. Commercial ready -built image on the screen that is more than five converters will also be available for about times as large as could be produced on a $11. No special knowledge is needed to pre -war direct- viewing tube with a face install one of these converters. The con- Aspherical Viewing Screen diameter of 12 inches. verter in no way affects the fidelity of tone Correcting r and the quality of reproduction of sound in Lens r DUPLICATING in three days a (Molded Plostiç`r the FM receiver. German vacuum tube, American sci- One of the converters demonstrated at entists made available to Yank Washington was a one- tuber, the other a Loudspeaker fighting forces strategic telephone three -tube device with power pack. Grille equipment abandoned by the Nazi armies It is believed that FM broadcasters may in their retreat in Belgium and France, take steps to make these converters avail- Kinescope said the Bell Laboratories Record last able to their listening audience at cost in (Receiving i Tube) month. the event that FM is shifted in the In retreat the Germans had left their spectrum. communications equipment substantially in- tact, except that they removed nearly all t r , the radio tubes. BROADCASTERS Isere called upon The Army turned a sample tube and the to take voluntary action against an problem over to an official of the Office of alarming trend toward excessive com- Scientific Research and Development. It mercialism, in a speech last month by wanted 1,000 duplicates at once. Rushed to Paul A. Porter, new head of the Fed- the United States, the tube was examined eral Communications Commission. by engineers of Bell Laboratories and the The FCC chairman warned that the Western Electric Company. Commission is considering new license re- Spherical Mirror The German tube was a cathode -type newal procedures which would require sta- pentode made by Siemens Halske. It was tion owners to show that operation of their Simplified view of the large screen receiver. different from any known American tube stations is actually in the public interest, not only in electrical characteristics and in as required by communications law. quency control, which discriminates be- cheater voltage but also in the dimensions "In cases," stated Mr. Porter, "where tween the transmitted synchronizing im- of the bulb and base and in the arrange- commercial opportunities have caused a pulse and any stray noise impulse, which ment of the pins which fit into the socket complete abandonment of other services otherwise might trigger the sawtooth wave base. Furthermore, as is common in Europe, which the broadcaster lias agreed to per- voltage prematurely, by fixing a time in- the bulb of the tube was sprayed with metal form. . . Are we of the commission to terval for the former and shutting out im- for purposes of electrostatic shielding. assume that the statutory standard of pub- pulses which do not arrive on schedule. Within three days eight replicas of the lic interest becomes a mere negative pre- Without some such control, noise inter- German tube were designed from avail- sumption and that so long as the licensee ference could throw the scanning beam in able parts used in American tubes, some violates none of the specific prohibitions the receiver out of synchronization with of which had to be adapted, and the tubes against obscenity, lotteries and the like, the the one in the transmitter, causing the were on their way to the battlefront in regulatory authority is not to inquire former to "black out" and return on some Europe. Within three weeks the entire further ?" lines of the picture before they were corn- 1,000 tubes were delivered. RADIO -CRAFT for MAY, I945 479 Klystron circuits

"Tube of the Future" as Oscillator and Amplifier

By CAPTAIN EUGENE E. SKINNER'

the October, 1944, issue of Radio -Craft, ant applications. Its widest use is as an the author published an article on the oscillator, but it is also widely used as an Klystron, "Tube of the Future," in amplifier, and can be applied as a detector, which the operation of the tube was modulator, mixer, or frequency multiplier. explained. A reference to that or any similar The basic Klystron oscillator circuit con- article will refresh the reader's memory of sists of the Klystron itself, a power supply, these basic fundamentals. and an antenna (if radiation is desired), In using the Klystron, it should be re- together with the necessary connecting membered that the positive side of the cables. There is no connection to the input antenna seal of the tube, and the output B+ is connected through a coaxial cable to the antenna, which is normally a dipole type. COAXIAL Courtesy Sperry Gyroscope Co The is grounded to the metal shell B+ Cut -away shows Klystron's internal construc TRAN5M/I! /ON of the tube, and the B- is connected to tion, co -ax leads and vernier tuning screw LINE the cathode. This is the oscillator in its simplest form, and as such is a transmitter within itself. In this basic form, the power frequencies requires different physical is not very great, but when the pertinent methods. facts are considered, it is realized that not The Klystron will stop oscillating if it is a great deal of power is needed. For ex- overloaded. In connecting the feedback to ample, for the range of frequencies for the Klystron for an oscillator, a short which Klystrons are needed, it is a simple coaxial cable is used. The total phase shift FIG.! matter to make a very highly directional must be 2aN radians, where N is any B FIL. antenna, so that practically all of the power number except zero. There are several radiated is beamed right where it is de- factors which cause phase shifts, but this BASIC KLYSTRON OSCILLATOR CIRCUIT sired to send it. In the second place, due coaxial cable can be cut to the proper to the very small bending effects in the length to allow sufficiently for them and voltage supply is grounded, and that the ultra -high- frequencies, the range of the attain the necessary 2aN radians. high negative voltage is connected to the transmitter is, for all practical purposes, When the Klystron is used as an ampli- cathode. All the transformers and the power limited to the line -of -sight distance. Figure fier, the signal voltage is applied to the supply must be insulated for this high 1 shows this basic oscillator circuit. with buncher by means of the buncher antenna voltage, which is usually in the vicinity of the connections to the power supply and seal. The output is taken from the catcher 3,000 volts, and the usual safety precau- antenna. cavity by means of another antenna seal. tions should be taken as for any high The power supply must be well regulated, The function as an amplifier is accom- voltage equipment. For this voltage, a as the tube will not maintain a stable fre- plished when, in addition to the external typical Klystron may deliver an output quency if the voltage is not stable. Also, source of power of the proper frequency of about 10 watts. One of Sperry's Klys- there are limitations in the voltages which fed to the buncher, the situation is such trons is rated at 20 watts. may be used, as the tube will oscillate for Ná3 Although tuning may be accomplished a given adjustment only voltages. TRANS! at certain TIME in number ways, the Klystron lends This limitation is due to the PHASE a of transit time DELAY OUTPUT itself particularly to a simple mechanical characteristics of the tube. Except for these method. A vernier tuning knob, as 'shown two points, the tubes act much the same as in the photograph, gives a frequency ordinary triodes. This tube acts as an am- TRIODE CIRCUIT EQUIVALENT TO KLYSTRON AMPLIFIER change of 1.35 megacycles for each turn plifier, and any amplifier will oscillate if of the knob. This vernier tuning mechan- it has sufficient gain and enough output that more energy is delivered to the catcher ism operates on a micrometer principle, energy is returned to the input to over- from the electron stream than is needed and operates a wedge which mechanically come the losses. An equivalent triode os- to drive the buncher. Efficiencies of about varies the distance between the buncher cillator circuit is shown in Fig: 2. 15% as power amplifiers, and voltage and catcher grids by changing the overall amplification of about 20 are possible. It length of one of the three tuning struts LS! is obvious that the operation of the tube used with each cavity, which operate as an amplifier is radically different from against a center ring midway between the OUTPUT the conventional vacuum tube amplifiers. two resonators, strengthening the anode end COOPING The equivalent amplifier circuit is shown 1 and the cathode end away from the center, in Fig. 3. changing the distance between the buncher In this circuit, the input is coupled into and catcher grids. The end plates are the grid through the inductive coupling normally kept firmly against these struts TRIODE CIRCUIT EQUIVALENT TO KLYSTRON OSCILLATOR from some external source. No coupling by tension springs. A second widely used is used between the input and output cir- method of adjusting the frequency is that As can be readily seen, the resonant cuits, all of the output being fed to some of changing the volume of the resonant portion of the equivalent circuit is com- other point by another inductive coupling. cavities by inserting adjustable metal plugs posed of a coil -and -condenser combination The output of the tube and the output in the side. A combination of this and the which is the equivalent of the walls and coupling are separated as in the oscillator previously described method will give a pair of grids of the buncher cavity. The equivalent circuit by a transit time phase very satisfactory range of frequencies for added block in the equivalent circuit repre- delay. most purposes. sents a circuit which would be necessary Some Klystrons are provided with a grid Input and output connections, and con- to introduce the transit time phase delay, between the catcher and collector which nections between the two cavities are made but which would not affect the circuit as makes possible the use of the tube as a through "antenna seals," which are the an oscillator. The output of the equivalent detector. This grid is slightly positive so terminals for coaxial cables, and are con- circuit is another coil which is the equival- that when no excitation is applied to the nected to single loops inside the cavities, ent of the coaxial cable coupling of the buncher, most of the electrons emerging giving inductive coupling with the flux buncher cavity. The feedback is accom- from the catcher reach the collector. When inside. plished by an inductive connection in both the buncher is excited, the field builds up Like the ordinary vacuum tubes, the cases -by a few twisted wires in the in the catcher, and slows down some of Klystron lends itself to a number of differ- equivalent circuit, and by a coaxial cable in the electrons so that the collector current 'Headquarters, Army Air Forme Training Aids the Klystron -but by inductive coupling, is reduced. By adjusting the bias of this Division. nevertheless, even though the difference in (Continued on page 513) 480 RADIO -CRAFT for MAY, 1945 Postwar Citizens' Radio Microwave Transmitter -Receivers Will Invade Our Private Lives

WHEN the dogs of war have been By S. R. WINTERS purposes. Anyway, this citizens' radiocom- quelled, swords may not be con- munication hand will be available to taxi- verted to plowshares but the cabs, delivery vehicles, such as laundry and "walkie- talkie" and "h an die- bread trucks, and similar mobile units, in talkie," as symbols of compact combination zon of actual accomplishment, the war - addition to service as incidental communi- radio transmitters and receivers, will switch converted walkie-talkie will contact a cation between fixed points. uses with ease flipping to peace -time the of physician from a central exchange while Common carrier operation in the citizens' a coin. These vest -pocket editions of radio he is en route by automobile to a patient's radiocommunication too numerous to be channel of frequencies will have applications home; the farmer's wife who formerly will not be permitted by the computed, too flexible to be defined. Commission; summoned her husband to the noon -day no fee can be charged for the sending of On the basis of recent hearings (extend- meal with a clanging dinner bell will call messages and no charge made for the use ing over a period of weeks) before the him on 460 megacycles ; hunters exploring of licensed facilities. Thus the service will Federal Communications Commission there the far reaches of forests or swamps, in be for the private use of the person licensed is a 200 -page report, amassed by 231 radio search of wild game and fish, will be in and he will be governed by the regulations technicians -a forecast of things to come contact by radio with a central hunting and of the Communications Commission. The in radio and electronics. Dryly labelled fishing lodge; department stores, dairies, 460 -470 band allocated to the public is said "Docket No. 6651," it may become as laundries and similar business concerns will to be admirably adapted to short range famous for its implications upon the radio communicate directly by radio with their communication, requiring only feeble power. structure of the future as was infamous delivery trucks en route; city firemen will However, the government rules are suffi- the "little black bag" in the Government's employ the throat microphone, now used ciently flexible to allow the use of "booster" Teapot Dome oil scandal. This bulging, by aviation pilots in detecting speech by or automatic relays. The low -power trans- brown radio volume is a blueprint of to- the quivering of the throat; and cowboys mitters will not utilize extremely high morrow's radio. Not only has the Fed- on our western plains will carry vest -pocket antennas, but increased transmitting power eral Communications Commission turned editions of radios to communicate with will be permissible in remote rural areas, prophet, with an unbridled imagination, home or ranch. where interference is absent. but within a single volume it has pieced The Federal Communications Commis- together, in jigsaw puzzle fashion, a com- sion has assigned separate bands of fre- Flexible, too, is the design of the com- pendium of radio's varied services, such as: quencies for urban and rural transit radio bination transmitter and receiver, although citizen radiocommunication service, theatre contacts. These voice channels may be used its weight will be kept to a minimum and television, centercasting, general mobile for communicating with city or inter -city preferably mounted in a suitcase. A broad- radio service, facsimile broadcast service, buses, trucks, taxicabs, etc. Such radio cast receiving unit, an alarm outfit, or a motion picture radio stations, geophysical services may assume the pattern of a com- remote control system may be incorporated service, or radio prospecting, radio for mon carrier or on a private basis using with the transmitter in the suitcase, variable electric, gas, water and steam utilities, the limited frequencies allotted for such (Continued on Ne.rt Page) police radio service, limited private radiotelephone service, taxicab radio service, and bus, railroad and highway radio services.

RADIO FOR THE CITIZENS Of these allocations of frequencies to various categories of non -governmental services, in the spectrum from 10 to 30,000,000 kilocycles, there is none so new and none so challenging to the imagination as the projected "Citizens Radiocommuni- cation Service." Without the usual demands for frequency assignments in an already overcrowded spectrum, the Federal Com- munications Commission did the startling thing of voluntarily allocating the band from 460 to 470 megacycles to a multitude of private uses of radio, just over the postwar horizon. It was a generous gesture of recognition of "walkie- talkie's" war con- tribution. This government move was as if to say to all light -weight, portable, short - range types of radio, "You have performed admirably on the battlefronts -now the doors swing wide for peace -time opportunity of performance." Instead of the proverbial sky or Heaviside layer being the limit, the Commission asserts that the possible uses of low -power, portable transceivers are as broad as the imagination of the public itself, and its adaptation is cir- cumscribed only by the ingenuity of radio manufacturers in devising equipment to meet the varied applications. The vision of a Jules Verne or a Hugo Gernsback alone could match the Federal Communications Commission in lifting the veil of the future-forecasting the startling civilian uses of the war's walkie-talkie, the airplane pilot's throat microphone and the vest radio with wrist microphone, earphones under cap, and transmitter in special pock- The postwar mother has her master unit right beside her in the kitchen, thus keeping watch ets. Not visionary, but just over the hod- over children in the nursery and communicating with others at camp or husband in the fields. RADIO -CRAFT for MAY. 1945 481 ¡Continued from previous page) ment in going to or from a conflagration, as the particular needs may dictate. Fol- the Federal Communications Commission lowing the policy of the service to radio has tentatively assigned 15 radio channels amateurs, the Commission will not assign for governing the movement of trucks and individual channels within the allotted other mobile units, as well as firemen, while band. The use of simple circuits, already the latter are working in burning buildings known to the radio art, will mean that both or areas. A home fire is burning somewhere transmitters and receivers will be tunable in this country every one and one -half min- over most of the 460- 470 -megacycle range- utes and, startlingly enough, a fire fans out emitting sufficiently sharp signals to pre- to 50 times from its incipient stage within vent any possible interference. eight minutes. Thus, it is significant that This new public radio service is designed 92 cities with populations exceeding 100,000, to serve the greatest possible number of and 890 cities with populations ranging users, hampered by only a few requirements between 10,000 and 100,000 persons, have of the Communications Act, and a mini- indicated to the Federal Communications mum of traffic rules need be imposed. No Commission their intentions to adopt radio technical knowledge is required to par- as an agency to combat fires. In addition ticipate in the "Citizens Radiocommunica- to the fixed radio stations required in each tions Service," and the operator's license of these municipalities, it is estimated that takes the simple form of a small card, 128,000 mobile fire department units will remaining in force for a five -year period. be equipped with radio equipment soon after The particular licensees are not cloaked the cessation of hostilities. By their very with immunity from interference; they The FCC has issued permits for the opera- numbers, Citizen Radios will make have no vestment in any frequency or chan- tion of eight fixed radio stations, 175 and reliable communi- nel- instead, it is a mutual opportunity to portable and portable- mobile stations by share this new band with others. Radio cation possible in transportation companies. These stations time technicians assume that the 10,000 kilocycle are in operation in Chicago, of emer- Cleveland, De- gency or width of the hand is ample for its purpose. troit, Fort Wayne, Philadelphia, St. Louis, disaster. Seattle, Washington, Columbus, Spokane, "VOTES BY RADIO" TURNED DOWN terns as an agency to conserve life and Pittsburgh, Boston and New York City. property, when the invisible waves are the As a parallel to the Crosley and other Stations in Chicago, Cleveland, Detroit, only medium of communication between popular polls by sampling the opinions of New York, Philadelphia, St. Louis and studios and locations far removed from select individuals, the so-called "Center - Boston are employed exclusively in con- what we of the city call civilization. casting" (See "Votes by Radio," Radio nection with transit operations in the re- With the stringency of gasoline rationing Craft, March, 1945) as "a means of radio spective cities; in the other cities mentioned unrelaxed, the proposal to use radio in dis- voting or polling" was refused the requested above, the radio stations are used jointly patching Cleveland's 430 assignment for taxicabs augurs radio frequencies. Nonethe- with local power companies. Twenty other a trend rather than accents an example. less novel as an offshoot of radio develop- transit companies have indicated their in- These cabs are now ments being dispatched by in the immediate post -war period, tentions of building radio stations as soon wire lines, but by way of the ether the the system and instruments involve the use as the equipment is available. driver, immediately preceding the discharge of a graphic recording device, named the FOR HIGHWAY MAINTENANCE of a passenger, would report to headquar- "audimeter." It is at present installed in ters his home radio cab number and the location at receiving sets, supposedly rep- Highway maintenance departments are which he was or would be available. His resenting a cross -section of homes, deter- also utilizing the facilities in speeding up car would mined then remain at the designated by a sampling procedure based on the prosecution of work incidental to road location until otherwise instructed by radia data obtainable from the Bureau of Census upkeep. Excepting the California Division In this manner, taxicab "cruising" of U. S. Department would the of Commerce. The of Highways (which operates a chain of be sharply curtailed and the ordinary mile- listening record appears on a continuously special emergency radio stations comprising age of Cleveland's 430 taxicabs reduced moving wax -coated tape, indicating with 23 fixed stations and 36 mobile units), all from 4,000,000 to 3,000,000 miles. precision the day, hour, and minute that a of the highway maintenance agencies use Electronics, radio just a continuing process in particular receiver was switched on, radio jointly with state police forces. The the unfolding of the broad aspects of radio, each and all stations intercepted, the num- Michigan State Highway Department, op- also ber minutes will afford limitless vistas in the post- of of listening to each station, erating a ferry service across the Straits war world. Tiny electronic devices will the amount of dial twisting, and just when of Mackinac, is authorized to operate five avert automobile and airplane collisions; the receiver was turned off. Possessing such ship radio stations and two limited govern- traffic signals within data, company motor cars and the sponsoring "Centercast- ment coastal harbor stations. planes will glow as red and green warning ing" is able to determine the number of A "Motion Picture Station" is operated signals. Even the dashboard instruments minutes listened to each program. Cur- as an intermittent service. It functions for will function electronically ; rently, service has electric eyes this been sold to 40 communication purposes in conjunction will automatically turn on auto headlights clients, including the broadcasting networks, with the filming of moving pictures. Studios as commercial darkness blankets the arteries of com- advertisers, and advertising employ radiotelephone signals between merce; tourists traveling from New York agents. headquarters in Hollywood and film col- City to California Realizing radio will transfer the respon- that affords the only onies on remote locations, aboard ships, or sibility of guiding the steering wheel over speedy avenue of communication for the in isolated, rugged areas. Infrequently, to operation and a photoelectric cell which will scan a control of fire -fighting equip- radio may be used by motion picture con- white line on the highway -and follow it unerringly. Such are the vistas of radio and electronics -just beyond the horizon- when the fierce dogs of war bark no longer.

Less than one out of every twenty U. S. radio-listener families -or less than 2% of the American public -can be reached regularly by Axis propaganda, even if all shortwave receivers were capable of receiving enemy programs. This fact was learned from a recent survey of radio listeners conducted by Sylvania. The survey revealed that about 52 out of every 100 sets now in use may be tuned to short-waves although 37% of them are never used for short -wave reception. Even among the short -wave listeners more than half said they listen rarely or occasionally and only ten percent said they listened frequently. Evidently Americans have little or no interest in what the axis broadcasters If is doubtful whether this is within the scope of Citizens' Radio or will need a commercial have to -say and so much if not all of the license. In any case, radio will be widely used for office-mobile unit communications. enemy radio propaganda falls on deaf ears. 482 RADIO -CRAFT for MAY, 1945 ' ° _ N'CCG8 1 l' zssU vJ"p° iáWb ÈS.( Amateurs and , 1Y5KiM Postwar Radio By RAYMOND LEWIS

WHEREVER amateurs gather, there is talk about post -war plans. The war is far from won, but this can't dampen the ardor of the dyed -in- the -wool hams. In all these bull sessions though, there is a new fellow to be considered ... the man who since the war, first learned about amateur radio. Above -Simple low -power phone and CW These willing converts picked up some station. At left -Final stage of a medium - knowledge from the jargon of the boys who power station. Note QSL cards from all knew the game "when." All the rest they parts of the world. know about amateur radio is what they have read in publications which say very little outlined in the recent FCC allocations, is about ham radio as we knew it. Once encouraging, but by no means final. After brought up to date, these men and women the United States decides what it will do, can become a part of a hobby which is a The station licenses may be different when it must go into an international conference. wonderful world of science and make -be- the FCC starts to hand them out again. The Amateur ranks are going to increase by lieve. The more people who have post -war old system was to give the three -letter al- many thousands. The failure to recognize ideas, the better off we all will be. phabetical combination that was next on the this with adequate frequency allocations is list in your district. (The United States was unfortunate in light of the war-time con- LICENSES ARE REQUIRED divided into nine districts.) In some of them tributions of the amateur. We hear the old Tu be a real amateur you need a license. they had just about exhausted all possible line about how the amateur will make out Licensing requirements were then, as they combinations, which lends credence to the -developing new methods of overcoming still are, Class B to operate CW on all rumor that some change may be made in QRM, etc. But, if they gave us another bands and phone on all bands except 75 me- future licensing. If you happen to live in few hundred kilocycles, we could put that ters and 20 meters. The Class A license is Florida, a 4th district state, you might end many more men to work on the solution. obtainable after holding the Class B for a up with a call such as W4RLW. It was There will be plenty of QRM for everyone ! year and grants the privilege of working once considered stylish to request special In the interim, some of the commercial sta- phone on these two additional bands. The combinations, but that went out many years tions could start to share frequencies and Class C license permits the saine operation ago when the licenses started to run into the alternate in wearing out each other's V as the Class B. The only difference is that tens of thousands. A simple little thing like wheels. the Class C is a special affair created for a call has a lot of angles . . does it have those individuals who live too far away a good swing on a bug; is it adaptable to SPACE FOR THE STATION from an FCC examining center to take the some catchy slogan for phone . . but don't Regardless of the frequencies, you will tests in person. It is still possible to obtain even give it a second thought because it's need a place to set up a station. Those fortu- an amateur operators license, although sta- your baby from then on. nate enough to have an entire room can tion licenses will not be issued until after spread out at will. If you are limited in the war. The Army and Navy take cogniz- NEWCOMER HAS AN ADVANTAGE space it will require more imagination, but ance of the knowledge required to get the The war -born amateur has an advantage a complete station can be set up in half a amateur ticket, making it a highly desirable over the old- timer. He is starting from closet. One important thing to keep in mind war -time project. scratch. There are no boxes of junk which is safety -first! Working around radio in- must be used. All inhibitions are off and volves voltages which are dangerous. You the sky is the limit ! The biggest pitfall may be competent in handling them at all to beware of is the mad urge to get going times ; let's hope so. Every precaution must in the greatest hurry. That invites haywire, be taken to protect others who might come which somehow or other never gets cleaned in contact with the equipment. Interlocks, up. There is no reason why this should overload relays, screen, guards, fuses . . . happen to the newcomer who has already in fact every conceivable safety device obtained a background in radio. Starting a should be incorporated in the well designed ham station should be done in a logical ham shack. Better be safe than sorry! sequence of steps. The first move, which The receiver you make or purchase should is highly recommended, is to survey the be your most careful investment. Transmit- antenna situation. You may be undecided ters come and go, but it generally remains as to what frequency you will start out on. a fixture over a period of years. A survey If you have a rough idea whether it is taken before the war showed that the ma- going to be the VHF's or the medium fre- jority of amateurs had purchased a com- quencies, plans can be made accordingly. A mercially- manufactured receiver. Few hams good skywire is just as important for re- were equipped to do the precision job of ceiving as transmitting, so the effort of building one at as reasonable a price. In doing a first -class job will not be wasted. either case, bear in mind that a good re- Apartment house tenants should not be ceiver is more important than a lot of money discouraged since some of the finest ham spent on a high -power transmitter. It is an work has been done from such locations. old adage in ham radio that you can't work Wherever practical, use a directional array. what you can't hear. All the features are There is nothing like a beam to put your desirable, including a crystal filter, noise signal where you want it, while causing limiter, AVC, etc., but they may be limited your fellow hams considerably less inter- by your pocketbook or experience in build- ference. ing. For ultra -high frequency operation All amateurs are in the predicament of most commercial receivers were very ex- not knowing exactly what frequencies will pensive. Home built sets covering the high - Amateur Radio CT2BP, located at Horta in be available after the war. It is possible frequency ranges above 5 meters were more fhe Azores Islands. Transmitter at left -Amer- that 160 meters will not be returned to the commolithan manufactured receivers. ican receiver built into wall at right. hams. The possible creation of new bands, as (Continued on page 529)

RADIO -CRAFT for MAY, I 945 483 RADAR PRINCIPLES Part II- Historical Development of Radiolocation By R. L. SMITH -ROSE, D.Sc., Ph.D., M.I.E.E., F.I.R.E."

THE first applications of radio waves the region, which later became known as In the years following the dates men- for determining the distance of a re- the ionosphere. tioned above, a considerable amount of reflecting surface were devoted to demon- This was the first classical example of search work was devoted to the develop- strating the existence of the Heaviside the use of frequency -modulated radio waves ment and use of methods of determining layer as a portion of the upper atmosphere, for determining the existence and location the height of the reflecting layers of the now known as the ionosphere, which is of a reflecting layer which had hitherto ionosphere, using both the frequency - responsible for the transmission of waves remained undetected by any direct experi- change and pulse -modulation methods. A around the earth. After many years of ment. We may therefore say that the direct comparison of the two methods speculation with a variety of indirect ex- Heaviside layer was the first object to be showed that they gave substantially the perimental evidence, the first direct demon- detected by radiolocation experiments. same result in height determination; and stration of the existence of the ionosphere Shortly after the first of the above in a paper published in 1931, E. V. Apple- as a reflecting region was provided by Dr. measurements were made, G. Breit and ton and G. Builder described certain im- (now Sir Edward) Appleton and M. A. F. M. A. Tuve began some tests in the United portant improvements in sending and re- Barnett at the end of 1924 and during 1925. States of America, using interrupted con- cording technique which demonstrated the tinuous waves which were the equivalent of pulses of continuous waves about 1 G G lal millisecond in duration and with a recurrence frequency of 500 per second. At the receiving station a high -speed oscillograph vW wWNMNAPV\A+nhUnA.NArmN.MwJJWWnnN was used to record the incoming signals and permit the examination of their wave -form. s In July, 1925, experiments were made over IDb a distance of 7 miles using wave lengths of G .F, IG F, 71 and 42 metres, and it was observed that the received pulses nominally of square

Tl wave -form, were distorted by the attach- 1R ment of humps, sometimes in duplicate. er: These humps clearly indicated the arrival of a second wave- train, or echo, by an Fig. 7-How height of ionosphere is checked. indirect path; and from a measurement of With the cooperation of the British its time retardation in relation to the orig- Broadcasting Corporation the wave length inal hump due to the direct or ground of the Bournemouth broadcasting station wave, the path difference of the two sets of waves could was varied over the range 385 to 395 be determined. (See Fig. 7.) te) In one of metres over a period of from 10 to 30 their publications, Breit and seconds, and the strength of the resulting Tuve remark that their experiments on signals at Oxford, about 100 miles distant, the above lines arose out of some work was measured. It was found that as the being carried out at the time on another wave length was varied, the received signal method proposed by W. E. G. Swann and passed through a series of interference J. G. Frayne. It is also of interest to re- maxima and minima, indicating that the mark here that a United States patent was issued to H. Löwy on an application signal was the result of two sets of waves Fig. Records of ground pulses and tim- filed in July, 1923, for a radio -frequency 8(a)- arriving by different paths; one set of ing oscillations. (b) -Same, with returned ech- counterpart of Fizeau's method of de- waves was transmitted along the ground, oes. (c) -Same, photo of C -R screen pattern. while the other arrived termining the distance of a reflector, to by an indirect path which after reflection from a layer. After veri- reference has already been made. In fying that this patent Löwy describes an electronic advantages and illustrated the possibilities the paths were in the same switch vertical plane, a measurement of the num- used for alternately keying a trans- of the pulse method, in so far as the sig- ber of interference fringes caused by a mitter and receiver, so that the latter is nals arriving at the receiver due to the known change in wave length gave a meas- only in a sensitive condition after the pulse ground wave and successive reflected echoes ure of the height of the reflecting layer in or train of waves has been emitted by the could be separately received and recorded. transmitter. It is not known whether At the sending station a tube oscillator 'National Physical Laboratory. this device was put to any practical use. (Continued on page 524)

mummmmmmumummmmmummi:u = OUR COVER FEATURE "JAPANESE RADAR" = HE Japanese radar, which appears on our front cover this month, is a sequence from the 1/ Warner Brothers' film Objective Burma. This elaborate radar installation was located in the Northern part of Burma and a United States Task Force was charged with eliminating it. In the movie this mission was successfully completed and the installation blown up. This fanciful radar, cooked up by the Hollywood technicians, looks most impressive in the motion picture and is supposed to let the public in on the sacrosanct wonders of radar-still suppressed by the Allied military authorities. This particular Japanese radar installation was manned by two operators and was a revolving affair, the entire framework, transmitter, receiver, and operators rotating continuously. Spectacular as it appears in the motion picture, modern radar installations do not look anything like this. Indeed, most modern installations are quite compact, probably not too many of the cumbersome revolving types being in existence today. Nevertheless, the radar principle of transmitting microwaves, which are then reflected back to the operators, is correctly pictured for a not too technical public consumption. Needless to say, the Hollywood technicians could reasonably well have shown a modern radar installation atet really appears, but in this they were prevented by military censorship. c mmnuumnmmmnmmnuummmmuni mmunummmn, uuininummuuuuinmunuunuumnnnunmmi oummni nninunnmmnmmunmminu,ummn, imuii!lvaimia;:um purimunmmuunmumnummmum unmmnnmmnmmm milmommuu mmuum un lluccnmmM 484 RADIO -CRAFT for MAY, 1945 Future Aspects of Television Part II -Will We Have "Live" or "Canned" Television?

EMPHATICALLY it behooves the By DR. LEE DEFOREST "Those two prize parasites- spot -an- television set manufacturers to step nouncements and hitch -hikes-have no place to the front now and lift from the urge that Dad buy one of these skybuggies in visual broadcasting. For nothing will let shoulders of the courageous telecaster next summer. A commercial made so innoc- the air out of the tires of the new industry the prolonged and ever -increasing financial uous, so interesting that it is actually more more promptly than a spewing of spot - burden. He will do this, not in the spirit entertaining than many a spectacle or play. announcements. The 'station-break com- of generous self -sacrifice, or camaraderie - For here is reality, real life directly ap- mercial' in an unashamed violation of the but because his eventual profits will enor- plicable to your own. sponsor's trusteeship. The spot advertiser mously outdistance those to be reasonably For television offers the advertiser so demands audience attention, but gives noth- expected from the old sales plan. rich a medium for telling his tale that no ing in return. He's a chiseler. His message If the set manufacturers, ALL of the embellishment, no nauseating repetitions are is a barnacle, sucking its hold on the pro- set manufacturers, without a single daring needed -nor tolerable. \Vhat takes a minute grams which precede and follow it. The exception, refuse to rent, we shall see, I by microphone can here be seen in a flash spot must go." greatly fear, an exceedingly slow growth of light. The smart advertisers will sense There will be small dissent, on any hand, of television. After the first flash of nov- this. Effective use of television adver- to Mr. Lee's views ; at least at present when elty wears off, those who have purchased tising means a maximum economy of the our television babe is so spotlessly pure. Let the cheap, small -picture receiver, will lose viewer's time, a minimum drain on his in- us hope that as the child grows to adoles- their initial interest. Eye -strain and the total terest. The smart sponsor will soon sense cence it may be induced, or constrained, to inadequacy of such pictures will not be that in television he has at his careful dis- avoid the previous sins which the - author long endured. posal the most potent salesman in all history here outlines, so nauseatingly apparent to From these small pictures, moreover, -radio or print are not in its class. But, as every radio listener throughout the land television will receive a black eye. Invited RobcrtLee says in his excellent book, "Tele- today. who miniscule neighbors have viewed the vision : The Revolution ": But to return now to our television pro- show won't be inclined at once to rush to "Cheap, lazy advertising methods will be gram. It has been on for a delightful hour. the nearest sales office for duplicate sets. the kiss of death to television. Sound radio Another 15 minute drama followed a rollick- And the yen to sign for the purchase of a has proved a hardy specimen despite a ing comedy. \\re have had a fleeting glimpse respectable projection screen instrument scrofula of spot-announcements and day- of how entertaining and pleasantly educa- won't. be too compelling either, not only time- serial beri -beri. It has survived these tional it may be made. There was not a fault from the large cost involved but because all too frequent fits of commercial nausea, in the acting, a single slip in the dialogue - the tiny pictures they have seen can give occasionally to say something fine and decent every element of the entire program was in them only a wholly inadequate conception and worthwhile. And these occasional flash- its exact place, the continuity perfect. Doubt- of what television in their own hone might es of genuineness, out of a welter of sordid less many hours of painstaking rehearsal be. commercialism, seem to justify the system, were required to insure its 100 percent per- Consequences : A very slowly growing although we may pray nightly for the fection. Such rehearsals now, are genuinely television audience, a tendency on part of growth of a more -than -microscopic com- expensive. Good actors such as these are the watchfully waiting would -be sponsor to mercial conscience. not picked up at a town hall meeting; their hold off from buying expensive time at telecasting studio; a resultant inclination by the station's backer to retrench on that program budget; further deterioration in public interest, fewer sales, lessened total hours of viewing. Result : general television stag- nation -which would be little less than a national calamity. No -this magnificent instrumentality roust go forward, full speed ahead. And it is up to the manufacturers of television receivers to take the required step to insure that television shall go forward fast, and continue to grow fast -not flash, falter, and finally deteriorate. You must not sit advertisingly by and complacently expect the brave broadcaster to shoulder all the load. He can't do it, he won't do it, not for long : not if you won't take a little risk to swiftly speed the day of millions of screen sets in nightly employment. Rentals will do just this. Mr. Manufacturer, the destiny of Amer- ican Television is in your hands. You may Authorities by no means agree that "canned (movie) shows" are equal to spot television. rest assured that the Telecaster men will In the above drawing, the artist compares "live" and "canned" versions of the same action. do their full share. Now let's assume that all this has been "Television, on the other hand, is not so salaries may total several thousand dollars. done. John Q. Millions have signed three - robust a youngster as his radio brother. What a shame that all this effort, all this month rental contracts, at $2 per week, plus Video is much more sensitive. Sight audi- cost, is solely for a fleeting hour, finished a $20 fee for antenna and installation. They, ences give much more attention than listen- now ! family and neighbors, sit expectantly before ers to sound alone. Impressions reaching These plays can't be repeated, not in this a translux screen 24 by 32 inches in size. eye and car simultaneously impinge Inure community. Lacking a perfect chain hook- Appear in smooth succession a parade of dominantly on the consciousness than what up this troupe of actors must now spend a glamor girls, some singing; beautiful music comes only from a loud -speaker. Most radio day or two rehearsing their next show, or accompaniment. Then a 15- minute playlet listeners have developed a cerebral relay, be transported to another distant studio for involving 4 or 6 characters, all but the vil- which automatically clicks off the attention a repeat, and then on to another -old time lain good looking, he handsome; a humor- when a commercial becomes boring. Not so trouping, or stock company stuff. But our ous ending. (Television must abound in television. The viewer must give most of audience won't be satisfied in seeing the laughs, be rich in humor, not cheesecake.) his consciousness to the tele- screen ; moronic same group week after week as in stock, Next an entrancing travelog, entertaining commercialism will make him leave his re- nor can the same group appear oftener and instructive. Followed by a trip through ceiver in disgust. It is apparent that video than once or twice a week, due to re- a helicopter factory, the main features of broadcasting has a digestive track which hearsal -time demands. Hence in each tele- that craft illustrated, its mode of flight cannot stomach a plethora of cheap ads. vision studio three or four groups of good lucidly explained, ending with an irresistible Television will gag on Wheatsy- Flakes. (Continued on page 509) RADIO -CRAFT for MAY, 1945 485 Instruction on the Flight Engineer's Panel. The Flight Trainer as viewed from the rear. Instructor sits here and manipulates "Crab." Electrons Train Aviators Here is the story of the Navy's new operational Flight Trainer, which, it is reported on good authority, can make a 5 -man crew for a PBM in something like 15 to 20 hours of instruction. Technical information on the trainer is now largely a military secret. Someday this will be released and those interested in such things can see just how this new marvel of electronic science operates.

HE roar of mighty motors slugged By T. R. KENNEDY, JR. ary -no lives lost, no equipment smashed into our ears. Small points of light on by inexperienced men, and millions of dol- the flight -control panels cast an eerie lars and much time saved. glow over a dozen or more electric me- Magically, somehow, we were actually "in The demonstration had to be on Sunday ters. Except for the faint gleam the cabin the air." Every human sense told us so, because the Navy's training schedule was was dark. even though the 10-ton mockup of the big so full. Arriving at the base, our party "Steady as you go," a soft voice said, PBM -3 of the Navy's Atlantic air transport was soon being divided into flight "crews" through the "intercom" system earphones service-the first "operational flight train- of 5 persons. Each crew was to be "given we wore. "Give her a little more gas - er" off the production line and now being the works"-just like regulars undergoing you're off the ground now." seen and operated for the first time by out- training. "God," exclaimed a girl just behind the siders; into which our party of newspaper pilot's chair, incredulously, "he said we're men and women had climbed a few moments AS BIG AS A HOUSE in the air." before -was as earth -bound as so much sol- The Navy's big PBM flight trainer is.;' The air -speed indicator climbed rapidly id concrete. housed in a building as big as the average from 140 miles an hour to 210. A slight We were, in fact, taking part in a unique 5 -room metropolitan apartment. It has wiggle of the machine indicated bumpy demonstration to show exactly how the everything for flight except wings and atmosphere, heightening the illusion. Tug- Navy now trains its 5 -man PBM crews wheels. Its construction required more than ging at the controls, we "saw" the airplane without sending them off the ground in an a year by experts trained in a half -score come hack to even keel. actual plane. Results have been revolution- of arts and crafts. The scene of its birth was a score or more of workshop -rooms in the Bell Telephone Laboratories, New York. The operational flight trainer was a brain child, of course, before it became a ma- .4 chine. It originated in the United States Navy's Bureau of Aeronautics special devices division, headed by Captain Luis de Florez. Into its actual creation went more than 20,000 manhours of drafting, which resulted in more than 500 separate drawings comprising some 15,000 square feet of paper prints. Fifty complete sets of specifications were written up before one was adopted. The work went forward at the Bell Labor- ...-- 4 atories under the direction of project engi- l_ neer R. C. Davis. Head of the work in the t actual development was E. J. Kane. 1',0 `r' 1 ;1' " Before beginning the actual development 1 f 7:,(%!,- . _ work, however, it was found necessary for all the laboratory men to become familiar '7 FT* with the principles of aerodynamics. Then they spent many hours deriving scores of special equations covering all the phases 4IrM1:: 4."001., of actual flight, which in turn had to be resolved into practicable electrical circuits. The job was a huge one, but a simplifying factor was in their favor-the huge mockup "A "- Instructor's control desk. "8"-Electrical computing apparatus. "C" -The trainer. (Continued on page 534) 486 RADIO -CRAFT for MAY. 1945 Photo I -The 250 -watt 118.55 Mc. Motorola transmitter. Lt. Ben Denby, at left of rack is using handset for monitoring during adjustment.

Photo 2- Mobile transceiver. The small converter unit is the little boa on the sidewall at left. Photo 3- Aerial on the Dade County Cocr.house is used for both transmitting and receiving. POLICE RADIO ON V. H. F. Tests On 118.55 Mc Show Advantages Over Lower Frequencies COMMUNICATION on 118.55 Mc. has 1. On this frequency there is no skip ramps of various construction, under metal - proved to have a number of advan- interference apparent though over 40 relay roofed structures, inside wood, metal and tages for two -way police radiotele- stations in the United States operate otf concrete buildings fifteen miles from the phone service. A series of tests have 118.55 megacycles. No bursts of any nature main station, and also under power lines and been conducted in Miami, Florida, by Lieu- have occurred which would interfere with transformer banks ; in fact, anywhere and tenant Ben Denby of the Police Radio- the operations or open the squelch. everywhere it was thought interference telephone service, using equipment designed 2. Excellent operating efficiency is ob- might result. In no case were there inter- and manufactured by the Galvin Manu- tained with the 23 inch antenna. This length ruptions or loss of signal strength and oper- facturing (Motorola Radio) Corporation, also obviates the hitherto encountered di,- ations were considered 100% satisfactory. Chicago. The purpose of the experiments advantages of using the long length antenna 4. The signals definitely fade out at a was an attempt to overcome the difficulties for detective cruisers. There is no notice- certain distance depending on the power in two and three -way radiotelephone sys- able difference in either roof -top or side - and antenna elevation. tems that have confronted practically every top mounted antennas for reception up to 5. Satisfactory car -to -car transmission is police department throughout the, country 20 miles except that the side top antenna is provided up to five miles though up to using AM in the usual channels, or FM in less efficient for car -to -car talk and tends to eighteen miles has been obtained on level the 30-40 megacycle channel. exert a directional effect after two and one ground. These common difficulties are briefly: half miles. 6. Any operational changes that may have A. Long range skip interference from dis- 3. Though there were always several been created by the weather, hurricanes or , tant stations. dead spots when operating on AM in 2442 other elements in Miami are not apparent B. The presence of static, both elemental kilocycles or on FM when in the 30 to 40 in any of the tests or recordings made. and from human sources. megacycle hand, none were encountered in Lieutenant Denby is still conducting his C. Too long a length for the antennas on the 118 megacycle spectrum. Mobile units experiments but has already reported to the the mobile units. In many cases, this were located in and between steel buildings, FCC: "After actually seeing the operation necessitated the omission of two -way in basements of reenforced concrete and as well as conducting these tests, we feel radio for detective cruisers in order to steel structures, in office buildings. under (Continued on page 513) avoid the conspicuous appearance of the usual transmitting antenna. When Lieutenant Denby first declared his intention to utilize the 118 megacycle frequency, many electronic engineers were skeptical. Several predicted it couldn't be done. The waves would bounce off everything they touched. But from their long and successful experience with automatic relay stations in the 118 megacycle spectrum, Motorola Radio engineers took up the cudgels and designed and provided enough units to equip seven Miami patrol cars with mobile transceivers and one central control and one remote control station. Both mobile and fixed station transmitters were of 15 watts power. The antenna for the central station was located on a telephone pole. After the preliminary tests showed successful results, in Novem- ber 1944, the antenna was shifted to the top of the Dade County Courthouse, 345.9 feet above sea level. The 15 watt fixed transmitter was discarded and a newly designed transmitter of 250 watts was installed. Here are the results of the exhaustive tests taken, operating on a twenty -four hour Courtesy Calvin Mfg. Co. basis and in every kind of Miami weather. The transmitter used in the 118.55 Mc. tests. A photograph of the set is seen at left, above. RADIO -CRAFT for MAY, 1945 487 Sound Units and Sound Ratings

By T. H. PHELAN'

THE basic unit applied to sound equip- decibel. The term "V ,U." is used only when ment such as Microphones, Amplifiers, measurements are made with a meter hav- and Loud -speakers is the Deci-Bel. ing the accepted electrical and dynamic Since this is fundamental let us study characteristics defined by the volume unit its origin and value. In the early 1920's and standards. Use of this unit also denotes before, losses or gains in telephone circuits, that all readings are referred to the zero attenuators and amplifiers were expressed V.U. basis of one milliwatt of power in a in miles of standard cable. As telephone 600 -ohm circuit. facilities expanded it was found that meas- From the above it can be seen that all urements in terms of miles of standard cable three units, "T.U.", "db ", and "V.U." are was impractical. A new standard called numerically equal. the Transmission Unit, "T.U." was adopted Thus far our discussion of the various in 1924. This unit approximately equalled units has only been concerned with the microphone the attenuation of one mile of standard purely electrical phases of the db. Each Speaker calibration. Note how is swung to measure angular cable but had an absolute value. One "T.U." basic sound system has two electro -sound sound distribution. P, E, transducers, one at the beginning of the = 10 log - or 20 log -, where Ps and P, system and one at the end. At the begin- reference level is used in expressing sound P, E, ning, a microphone is used to change the levels produced by a loud -speaker system. or Es and E, are the jnput and output power sound waves or energy into electrical waves The electrical equivalent of this sound pres- or voltages of the system or amplifier under or energy. At the end of the system a loud- sure zero line is 10-'8 watts per square cen- consideration. speaker is used to change electrical energy timeter. A new standard called the "Bel" was into sound energy. Since we are changing A few typical sound levels will illustrate adopted in 1929, as a tribute to Alexander types of energy, these units must be rated the magnitude of this zero sound level. The Graham Bell. This is equivalent to ten in a manner which will permit simple cal- background sound level is approximately Transmission Units. For practical applica- culations of the overall sound system. 35 -40 db above zero level in the average tions it is too large a unit and one called living room of a suburban house. Ordi- the decibel (db) was adopted for general ZERO REFERENCE LEVEL nary conversations in the room would raise use. The value of one db is equal to a The basic judge of sound is the human the sound level to a magnitude approximate- Transmission Unit. This today remains ear. It was logically decided to correlate ly 60 db above the zero. A sound about 130 our basic unit of Transmission measure- the reference "zero level" point for sound db above zero level would be so loud as to ments. computations with the characteristics of the cause a sensation of pain. Due to confusion between the major average ear. Tests have been conducted The minimum difference in levels which broadcasting companies and the telephone which show that the threshold of hearing can be detected by a person under ideal con - company in the measurement of levels and corresponds to a pressure of .0002 dynes per ditions'is one db. Under average conditions checking of "Program Peaks," a new unit square centimeter. This reference point has the level difference must be 3 db to become of measurement called the Volume Unit, been established as the "zero" level for noticeable. The sound level must be in- "V.U. ", was adopted in the year 1939. Nu- sound measurements or computations. In- creased approximately 10 db before it merically one volume unit is equal to one creases in sound pressure above this point sounds twice as loud to the ear. *Assistant Audio and Video Facilities Engineer are expressed in db computed by using the We must remember that doubling the National Broadcasting Company. formula previously mentioned. The same power output of a sound system only increases the level 3 db and that if we wish to make it sound twice as loud we must increase the power by 10 db or ten times. Now let us take the equipment which makes up a typical sound system and see how these ratings utilize the standard units discussed so far. The microphone is the first unit in the system and must be rated on a sound pressure input and an electrical output. A typical rating for a higis fidelity microphone would be a sound pressure of 10 dynes per square cm. which will produce an output level of -55 db below a standard zero level of 1 milliwatt. The sound pressure of 10 dynes per square cm. is equivalent to a sound level approximately 95 db above the zero sound level. The second unit in the system is the amplifier. Its amplification characteristics may be expressed in db of power gain or voltage gain. Because voltage gain expressed in db is the most convenient to measure and utilize in calculations, there is a trend to rate the gain of amplifiers on this basis. The last link in our system is the loudspeaker. This is the point at which we convert electrical into sound energy. The efficiency and distribution characteristics will determine how much sound energy results from a given electrical input. The most useful type of rating on this unit is one which Photos Courtesy RCA shows the electrical input in watts required Signal generator and measuring equipment used for calibrating speakers and microphones (Continued on page 515) 488 RADIO -CRAFT for MAY. 1945 VOLTAGE REGULATORS

GOOD voltage regulation is impor- By JACK KING High- resistance supplies may be used tant in many radio circuits. A radio with devices which draw very little current. transmitter's frequency may shift By having more than 90% of the total if the plate supply voltage swings. Energy from this condenser is then re- circuit resistance in R. (Fig. 1) any change Changes in voltage may cause instability turned to the circuit. Electrons flow from in the load impedance can only have a 10% and oscillation in some receiving circuits. that condenser into the tube (the load re- effect on the circuit as a whole. A few types of electronic instruments resistance), tending to maintain the output quire supply voltages fixed as closely to voltage constant in value and thus serving the predetermined value as human in- as a voltage regulator. Ordinarily, we don't genuity. can achieve. This voltage regula- think of a condenser as a voltage regulator; tion may be attained in three chief ways: yet, in reality, it may act as one. By using by careful attention to apparatus used in large values of C and L, not only the A.C. construction of power supplies; by use of ripple can be reduced in compliance with special voltage regulating and ballast tubes; the radio law and F.C.C. regulations, the B+ and by the use of special power supplies voltage regulation can be improved, aiding with built -in circuits which act to oppose in getting a "clean" note in radio code and neutralize any tendencies to change in transmission. R the supply voltage. The circuit of Fig. 2 may be simplified A basic diagram of a source coupled to for our purpose into the circuit of Fig. 3. a load is shown in Fig. 1. If the source re- If a steady current is bled through R, due to the presence of Rb a steady voltage drop In some communities trouble may be ex- R. will be developed across R., tending to maintain the output perienced due to excessive line voltage at voltage constant, since certain times of the day. Tubes may fail ER that output voltage is always equal to the in the receiver prematurely t'-- internal source potential minus the or may even voltage be burned out. By putting a resistance in Ei drop in the internal resistance R.. Then, if series with load the line, a measure of protec- the resistance swings between rea- tion may be gained. ER ER sonable As the line voltage rises L-Ei' limits above and below some nor- and the circuit mal resting value, percentage current tends to rise, the the change increased current flow through the series in current through and voltage across R. protective FIG.I will relatively resistance develops an increased be smaller. voltage drop which subtracts from the line In Fig. 2, a bleeder resistance Rb is sistance is kept very Inv, the voltage regu- voltage applied to give the receiver work- connected across the output filter condenser ing voltage. A special form of this regulation will be good. With an incorrectly and helps not only to stabilize the output chosen source resistance, varying the load voltage but lator is the "ballast resistor." This is con- also allows charges to leak structed to work on a critical point of its resistance between two limits above and off the condensers when the transmitter below the resting value will mean an ab- not temperature -resistance curve. If current is in operation, an important safety through it increases slightly its resistance normally large swing in the current through feature in high- voltage equipment. The R. (internal resistance). The varying cur- rises greatly, thus holding down the volt- same circuit may be used with a voltage age supplied to the load. rent flowing through R. will produce a vari- regulator tube. The tube acts to maintain able voltage drop across the source resist- a constant voltage across the load. The A more refined device is that of Fig. 5, ance. Since the output voltage is equal to regulator resistance is Rb and the load which may be a part of an industrial con- the internal voltage minus the drop in the is RL. trol. A saturable reactor T is used. A bias internal resistance, it will fluctuate too potential E, is applied to the grid of a much. If R, is very low in value, clearly control tube, and a certain amount of plate the variation in potential across it will be current, determined by the tube design, the low and the output voltage will be quite bias, load impedance, plate potential, etc., steady for reasonable changes in load re- flows through the winding L,. The mag- sistance. This points to the desirability of netic flux due to this D.C. current circu- low- resistance chokes and transformer lates in the core of the saturable reactor windings in power supplies. transformer T. As long as this plate cur- Voltage regulation may also be tied in rent does not become too large, saturation with the storage of energy in a reactance. and decreasing of primary inductance In some radio receivers, a shunt resist- the In a radio transmitter with the key open, of L, does not take place. When the line the load resistance connected ance is used for voltage stabilization potential E rises, an increased to the power of a tube. A typical signal voltage supply in effect. is made much higher in the screen grid potential at the line frequency is applied through I.F. stage is shown in Fig. 4. Again the ohmic value and the load is de- condenser C, to the grid of the control current Fig. 3 We substitute tube, creased. Referring to Fig. 2, the circuit basic circuit of applies. R for Rb and R, for R.. When the control grid of the tube (nearest the cathode) is made highly negative due to automatic volume control bias potential, the screen grid current decreases and there is a reduction in the voltage drop across R,. A reduced drop across R, would mean an increased screen grid potential at resonance. Rise in the screen potential is limited by the action of R,. As the voltage across R, rises, the current through it tends to rise. This increased current flowing in R, and current through the choke may be low R, will tend to produce an increased voltage in value with the key open. The output drop in R which works against any rise which is so biased that any increase in voltage across B plus and B minus is then in voltage on the screen, providing a stabili- signal voltage due to E will cause a linear high, and the filter condensers are charged zing action. rise in the current through the plate circuit up to high values of potential and store The series resistance of a supply may and L,. With increased D.C. current in L energy. be made either very high or very low to the core flux rises and the core approaches When the key is pressed, a load is put secure a stabilized output voltage. In both saturation, causing a decrease in the ef- on the supply and the output voltage tends cases, what is sought is a stabilization of fective inductance of L, and the impedance to drop. The choke's resistance causes the voltage across the element in series of L,. We have, in effect, a variable im- power dissipation and reduction of output with the load circuit in order to obtain a pedance comected across the load. Decreas- voltage. As the output voltage drops with stabilized output voltage, since the output ing the value of the impedance reduces the increased load, it becomes lower than the voltage is the internal source voltage minus load voltage and increasing it causes the potential of the output filter condenser. the drop in the internal resistance. (Continued on page 521) RADIO -CRAFT for MAY. 1945 489 LpÓ

RADIO RELAY SET AN-TRC RADIO TERMINAL SET -4 AN -TRC -3 RADIO TERMINAL SET AN-TRC -3 ea M, a 0 P. w I&'' . u eao / Ape / ,s: 4 1.. iA ENGLAND ARMY 10' TORWART) FRANCE NN .0f; 7;

How the relay link sets were employed in the Normandy invasion. The central relay station is two terminal sets placed back -to -back. Army Radio Communications I- THOUGH the Army's basic policy range beyond the distance range of an indi- up purposes within the system. Each radio considers wire to be the primary vidual radio set. set is equipped with filters to confine the means of communication, and radio It is used in conjunction with the Army's order channel to the band 200 to 3000 cy- the secondary means, the very na- telephone "spiral- four" carrier cable sys- cles and prevent mutual interference with ture of this war with its highly mobile tem which provides the practicable terminal the carrier frequency channels. Ringing forces deployed throughout the world has equipment whereby a radio circuit can be over the individual telephone channels is ac- placed ever increasing emphasis upon radio integrated with the wire circuit, or substi- complished from field telephones or switch- as the primary means for communications tuted therefor, in whole or in part, as the boards by the use of voice frequency ringers with highly mobile elements such as air- necessity dictates. which provide a 1000 -cycle tone modulated craft, tanks, amphibious vehicles and as- Fig. 1 shows a simplified functional dia- by the 20 -cycle telephone ringer. sault troops, or across enemy held territory gram of a complete multichannel VHF ra- Tone teletype channels may be provided and over water and terrain inaccessible to dio relay communication system. The tele- over any one telephone channel by the con- wire line construction. Radio must provide phone and telegraph terminal equipment nection of the Telegraph Terminal CF -2 a degree of service comparable to that of CF -1 and CF -2 is common to both the radio thereto. Additional teletype channels may be a wire facility, including when necessary, system and the "spiral- four" wire system. applied in like manner to other telephone the capability of being tied in with existing The radio terminal set is connected to its channels. Facsimile service may be obtained wire circuits to form one system giving the associated telephone terminal by "spiral - by the use of Facsimile Equipment RC-120 same grade of service as the wire system. four" cable up to approximately 15 miles on any one or more of the telephone chan- One of the outstanding developments of in length, one pair of the cable being used nels. is pair this war in Military Communications the for transmitting and the other for re- The principal of the radio Army's VRF Radio Relay System which ceiving. The radio relay sets comprising in characteristics receiver and transmitter are: (1) a horizon- provides a true integration of wire and radio effect two radio terminal sets connected tal three -element antenna array comprising a single system may back -to are substituted for circuits into or be -back the tele- a driven dipole fed by a 50 -ohm flexible used as a separate system in much the same phone repeaters of a wire system. Duplex solid dielectric coaxial transmission line and manner as the wire circuits. operation is achieved by the use of separate parasitically excited reflector and director heart is receiving and transmitting frequencies The of this system the broad at dipoles, all adjustable in length to the op- band FM radio set, designated AN /TRC -1 each radio set. erating frequency and supported on a mast developed by the Camp Coles Signal Labor- Four telephone channels, each approxi- head by a 40 sectional steel tube 2800 cycles wide, an -foot mast; atory of the Signal Corps Ground Signal mately within audio (2) a 2500-watt, 115 -volt, 60- cycle, gaso- Agency with the collaboration of the Link frequency band of 200 to 12,000 cycles line engine driven generator. Radio Corporation. This set is capable of are obtained from the Telephone Terminal operation either as a terminal of a radio CF -1. Channel 1, operating at voice fre- A 250 -watt radio frequency amplifier is circuit or as an automatic radio relay set quencies, is normally used as an order chan- available as auxiliary equipment for use between the two terminals of a radio circuit nel for intercommunication between termi- with the 50 -watt radio transmitter to in- in extending the overall communication nals and relay sets for supervision and line- (Continued on page 520)

A TERMINAL RADIO RELAY STATION (AUTOMAT /C) B TERMINAL r Ft - -,f2r TfLfPN HE, C"/ z.u TEL '® TRA NI REC. TRANI TELETYPE WRITER ArBI A roB AroB ; WRITER

CHAN.2 i (CARRI 2 7E[f©FI TELEPNONE ORDER IORDER WRITER I TELETYPE. CHAN I (MAMI WRITER CNAN3 F4i 12 (CARR) 7ElE©CA f; WRITER REC. - TRANI REC. BroA B roi B roA , CHAN4 CHA/t4 (ARRI RADIOJET M INAI RADIOIETM /NAL L (CARR) TELFTTYYPE , TELEPHONE RAD O RELAY JETT L® TELEPHONE L WRITER rFLEÇRAPN TEL i i JTELETrPF. TERMINAL TERMINAL TE (PHONE 7FLf0RAPN WRITER TERMINAL TERiC/NAL Fig. I -A typical army network, in which wire lines, carrier channels and VHF radio circuits ere combined in a large multi -channel system. 490 RADIO -CRAFT for MAY, 1945 SPEECH AMPLIFIERS Part VIII -Tone Compensators Using Tuned Circuits

THE tone controls previously discussed By ROBERT F. SCOTT be controlled by the presence of variable are inexpensive and simple to apply to resistances in each of the tank circuits. For almost any piece of audio equipment impedance becomes equal to R1.. The value maximum boosting of the resonant fre- and may be utilized in very compactly of R determines the sharpness and magni- quency, the impedance of the circuit must built pieces of apparatus. It may be well tude of the resonant peak voltage. be higher than the value of the plate load to remember that the non -resonant circuit If RI. is considerably smaller than R. resistor. may be made to boost or suppress some and r, in parallel The series resonant network consists of portion of the audio spectrum but in no R, X r, a condenser and inductance connected in instance of boosting is it possible to exceed series. The impedance is at its minimum the value of amplification at the middle R. -F r, value at resonance. As in the parallel tuned frequencies. the increase in amplification at resonance circuit, the sharpness of the circuit depends We are aware that when all factors are will be appreciable, hence this circuit is most on the network's "Q". Such a circuit may constant, the amplification of a vacuum efficient when applied to high mu triodes and be applied to the plate load resistor of a tube amplifier varies directly as its plate pentodes. tube to compensate for the apparent low - load impedance. We can see that it is de- Fig. 2 shows a circuit which may he em- and high- frequency losses when the radio sirable to have some scheme by which the ployed to gain complete control of the fre- or amplifier is being operated at low volume. impedance may be made to increase with quency response characteristics of an am- An application of this principle is shown in the frequency. This may be accomplished plifier stage. Thus it is possible to compen- Fig. 3. The plate load resistor is in the by the use of tuned circuits properly placed sate for deficiencies in the response of a form of a potentiometer with its movable in the plate load. mike, pickup, speaker or specific acoustic arm connected to the series -tuned network. It is common knowledge that a parallel or conditions whichare unwanted. This circuit This is tuned to the middle of the audio series tuned circuit may be made to accept has been found to give a wider range of range, 1,000 cycles, and due to attenuation or reject the frequency to which it is boosting and control than is possible with at this frequency, the highs and lows will resonant. It is this factor which makes it some of the commercial types of tuned net- be apparently boosted. The degree of at- applicable to tone control circuits. Unlike work controls. tenuation will depend upon the setting of non -resonant circuits, it is possible to in- This circuit is fundamentally the same as the arm on the plate resistor. crease the gain at middle frequencies if it is Fig. 1. In this circuit, there are three The series -tuned circuit may also be com- desirable. tuned networks. Two of these networks bined with inverse feed -back for tone con- In the resonant circuits, there are three resonate on the high- frequency end of the trol as shown in the fundamental circuit as constants for each particular frequency. audio range and the amplification at these shown in Fig. 4. We know that if a portion These are capacitance, inductance and re- frequencies is fairly constant up to 15,000 of the output voltage of an amplifier stage sistance. The latter is equal to the D.C. cycles. The remaining network is tuned to a is fed back to the input in proper phase resistance at audio and low radio frequen- frequency of 60 cycles and when a low "Q" relationship, the original signal voltage will cies but increases far above the D.C. value choke is employed, the curve will be suf- be reduced at the frequency of the feed -back at ultra -high frequencies. The inductance ficiently broad to bring up the response to voltage. In Fig. 4, the feed -back voltage is and leads of the circuit will be the only as low as 15 cycles. The values of the con- taken from the plate circuit and fed back factors to introduce appreciable resistance stants in these circuits are shown in the to the cathode circuit. The amount of feed - in the circuit. drawings. The sharpness of response may (Continued on page 523) Parallel and series circuits have characteristics which are entirely opposite but each has specific advantages for certain applications. The series-tuned circuit is characterized by maximum current and minimum impedance at the resonant frequency. The magnitude of the current in the circuit is controlled by the value of the resistance. The parallel -tuned circuit presents maximum impedance and voltage at the specific frequency to which it is resonant. This type of circuit is most commonly encountered in practice and will be discussed first, since it is probably the most easily recognized of the resonant circuits. 1.0003 The voltage across such circuits is proportional to the impedance (E =IZ), C=.02 hence it is desirable to have a high ratio 20,000 o of inductance to capacitance (a high RL o value of L and a low value of C). d'O Fig. 1 illustrates how a parallel -tuned net- Lo work may be connected in the plate circuit .00015 of an amplifier tube to increase the amplification at the resonant frequency of the 20,000 network. At a frequency which makes the (C reactances of L and C equal, the impedance 115 will be very high. Since this impedance is in et 10,000 .05 series with the plate load resistor, RL, the total plate load impedance may be considered as equal to RL + R2 + (XL -Xc)2 I( where XL =6.2832XfXL .0008 ; 62832 =2 pi i ó o X. = 1 0 Ñ

6.2832 X fXC Bi- '1;-r003 O At frequencies removed from resonance, the effective impedance of the network is reduced to such an extent that the plate load

RADIO -CRAFT for MAY. 1945 491 RAPID CONVERSION Battery Receivers Can Be Changed Over Quickly and Profitably

By W. G. ESLICK

MANY radio shops have on their shelves used (By changing the oscillator coil we audio must be high -gain, so we choose a number of the older types of battery can use a 6SA7). We consider the 7A8 and a diode- triode with a gain of 100. sets. These can't be sold because they use 6D8 too valuable as replacements for the If the set used a magnetic speaker, we so much battery power, and batteries are 12SA7 to use in this work. The 6K8 works, must junk it. If a PM was used we may really hard to get! Due to the present but with less gain than the above, and we have to change output transformers if it scarcity of radios, they can now be sold don't want to lose any gain. would make a bad mismatch or if its re- if converted into fairly good A.C. -D.C. sets, Regardless of the original circuit, we sistance is so high as to cause a bad voltage and will convert a liability into a profit for use a 75, 6Q7, 6SQ7 or a 7C6 as diode drop to the 25L6 plate. If it becomes neces- the store. detector, AVC and first audio. For our sary to install a speaker, use a dynamic We rebuild quite a few, mostly for out- power amplifier we use a 25L6. A 43 or a type with a field of not more than 450 ohms. side stores. As they furnish all the neces- 25A6 gives about .9 watt output, while the This saves buying a filter choke. sary parts, our labor runs from $7.50 to 251.6 gives a little more than 2 watts, a $15.00 per set, and it doesn't take as long worthwhile difference. as one might think to convert a receiver. For the rectifier, a 2525, a 2526 or even As an example, we rebuilt an Airline Model two or three 76's tied together, enough to 67 -377 in 4% hours today. It used (original supply about 90 to 100 volts on the screen setup) a 1C7, four 1H4's, a 1D5 and a of the 25L6 with the set full on, through a 1E5. In the new hookup, it has a 6A8, 6K7, filter choke or field of about 450 ohms. 6Q7, 25L6 and 25Z6. There are other choices of tubes and cir- The later sets using octal 2 -volt tubes cuits, and other ideas (such as a separate are easier to work on and generally give oscillator) but remember, we must rebuild better results than the older ones with 30's these sets quickly, have a decent radio and Fig. 2 -A conversion which uses the II7P7 and associated 2 -volt types. use a minimum of parts new or used, if we First must on we decide what tubes to are to make any profit. One of the stores Now we are ready to change the set. use. For the R.F. stage (if any) we have buys sets for $15 to $20, spends about as First, cut the rivets holding the sockets of the choice of 6D6, 78, 6K7, 6SK7, and much more for labor and parts and still the old -type tubes and install new sockets 39/44 (I have never tried the latter). For makes a good profit on the sets. to fit the desired tubes. If the set used octal the converter a 6A7, 6A8 or 7A8 can be Another point to remember is that the sockets (and all contacts are on them) they are O.K. (Some sockets didn't have any contacts for the number 8 pin on octal sockets.) After the new sockets are in, take the wires off the old sockets and solder them onto the new ones. This saves time checking wiring. As a rule, we can use a uniform circuit on all sets. (See Fig. 1.) There may be some special reason for departing from this in special cases, however. We use a 300 - to 500 -ohm resistor by- passed with a .05 mfd. condenser for the bias resistor of the 6A8 and 6K7 cathodes, which are hooked together. If the set has more than one R.F. stage or I.F. stage, then we use a 300 -ohm resistor in each tube. For the diode and 1st A.F. we usually ground the cathode and use a 5- to 15- megohm resistor or a bias cell in the grid circuit. For the 25L6, a 150 -ohm 5 -watt resistor and 25 -mfd., 25 -volt condenser supply the bias. The filaments are wired in series, with the 6A8 wired to the 6Q7 and the other end of the 6Q7 filament going to ground. We The original Airline 67 -377 which was made info the satisfactory A.C.-D.C. model below like to keep these filaments as near ground as possible. We use a line cord, but a ballast tube can be used. An experimenter 6A8 converting a set for his own use may use a 110-volt light bulb of correct wattage. Don't forget to use a condenser (.001 to .006 capacity) from the 25L6 plate to prevent audio howls and squeals. A .01 -mfd.' VJ condenser from the rectifier plates to O ground will prevent tunable and other hum. 25 R 25. We use the chassis as a return "ground" for all circuits. When doing this, use a 2MFG 50 .01 condenser in series with the antenna 15t1tyea, bp1 .05 lead and paste a label on the set warning i6+Mw.JA./J./t against using a ground. Pilot lights and tone controls are a matter of taste and may 2523 li RTC AC-ac be adapted to the particular set. os Y-r----+ If oscillation occurs, isolate the B -plus leads to each individual plate circuit .., 20-,.. through a 1,000- to 2,500-ohm resistor and , by -pass with a 0.1 -mfd. condenser. We have ALL OROONOS TO CNA551$ ONLY never run into serious oscillation trouble yet, but keep our fingers crossed. Fig 1-Standard 6 -volt tubes and a few circuit changes make the Airline an electric set (Continued on tage 507) 492 RADIO -CRAFT for MAY 1945 1 Capacitor and Resistor God es By STUART DISTELHORST Lt first three dots give the first three significant figures of the capacitance in micro - A -D are ceramic, E -H L microfarads and the fourth dot, directly mica, and I, J. ceramic below the third, the number of additional capacitors. K to O, zeros. The fifth dot indicates the tolerance 7i > - -_...==--_.. are carbon resistors. in capacitance and the sixth, the working :ioïr.W voltage. This code also differs from the previously described basic code in that a lYMIENENEY19111l111111ETIN body -color voltage dot indicates a minimum D.C. working voltage of at least 500- volts. EXAMPLE: A capacitor of 0.006 - ONLY occasionally do smaller capaci- (number -of- zeros) dot. The color of the plus -or -minus per tolerance to tolerances be- rnf (6,000 -mmf) ten tors and resistors have their nu- dot corresponds cent. 800 -volts D.C. working voltage, is 1 cent and 20 per merical values marked, stamped, or tween plus -or -minus per marked as follows: blue T6), black printed on them. The trend toward cent. Gold and silver are added to the basic (0), code indicate tolerances of approxi- black (0), brown (one additional zero), reduction in size and weight of these indi- color to silver (10%), and gray (800 -v) in that 5 10 cent, respect- vidual components themselves, as well as mately per cent and per order. the operating units into which they are ively. Thus, either green or gold may be assembled, has resulted in capacitors and used to indicate a tolerance of 5 per cent. TABLE II. RMA SIX -DOT COLOR CODE resistors of such microscopic size that cod- Similarly black. normally indicating zero, goo- First and Third Fourth Filth Sixth ing systems have had to be adopted to and the leaving of this dot blank so that Color Dot Dot Dot Dot Dot Dot provide a continuously legible indication it appears the same color as the body of Black 0 0 0 none of their electrical values. Several codes are the capacitor, both indicate the highest tol- Brown I 1 1 0 1% 100-v Red 2 2 00 2% 200-v in current use and it is of this erance: plus -or -minus 20 per cent.' the purpose Orange 3 3 :3 000 3% 300-v article to clarify the minor differences be- The voltage dot, when used, is located Yellow 4 4 4 0.000 47 400-v tween the various codes. All of these codes above or below the first capacitance -value Green 5 5 5 00,000 5% 500-v denote the direct - Blue 6 6 6 000.000 6 600-v are based on separate colors representing dot. The various colors Violet 7 7 7 0.000.000 7% 700-v each of the individual ten digits as follows: current working voltage. When no color Gray 8 8 8 00.000,000 8% 800-v is indicated, the voltage rating may be as White 9 9 9 000.000.000 9% 900-v of of the Gold divide by 10 5% 1,000 -v 0 -black 5 -green low as 300- volts. Omission both Silver divide by 100 10% 2.000 -v 1 -brown 6-blue auxiliary dots is made for capacitors hav- (body) 20ó'û 500-v 2-red 7- violet ing maximum tolerance and a D.C. working 3- orange 8 -gray voltage rating which is the lowest used for *not used. 4- yellow 9- white that type and size of capacitor. AMERICAN WAR STANDARD CODE Gold and sometimes used to TABLE I. BASIC THREE-DOT COLOR CODE. silver are First Second Third Toler- Volt - The AWS code for molded mica capaci- indicate decimal multipliers of one -tenth and Color Dot Dot Dot ana yo tors, like the RMA code, makes use of six one -hundredth of the values indicated by Black o n none 20% colored dots but with somewhat different the non -metallic colors, as well as Brown I 1 0 1% 100 approxi- Red 2 2 00 2% 200 significance. The first four dots give the mate tolerances of five per cent and ten per Orange 000 3% 300 capacitance in micromicrofarads in the cent of rated electrical values. Additional Yellow 4 4 0.000 4% 400 same manner: first significant figure, sec- specific values to these metallic Green .5 5 00.000 5% 500 are assigned Blue 6 000.000 0% 000 ond significant figure, third significant fig- colors by the various color coding systems. Violet 7 7 0.000,000 7% 700 ure, and the number of zeros. Like the Gray 8 8 00.000,000 8% 800 RMA code, the fourth dot is lofted under BASIC THREE -DOT COLOR CODE White 9 0 000.000.000 9% 900 Gold divide by 10 5% 1.000 the third or last dot in the top row. Cur- The basis of the three -dot color code for Silver divide by 100. 10% 2.000 rently none of the capacitors standardized mica capacitors is a series of three colored (body) 20% (lowest) under the AWS code requires more than dots which indicate the capacitance in *not used. two significant digits to specify its capaci- micromicrofarads (mmf)*. Auxiliary col- tance. Therefore, the first dot is always ored dots are sometimes added to indicate RMA CODE FOR MiCA CAPACITORS black on all molded mica capacitors marked the voltage rating, temperature coefficient, The l- iA code uses six colored dots with the AWS code; the two necessary and tolerance in percent of rated capaci- with an arrow to show the sequence. Great significant figures are given by the second tance. An arrow or other device is ordi- er accuracy can be obtained than that pro- and third dots. As a result, the black first narily molded or stamped on the case of vided by the basic color code because the (Continued on following page) the capacitor to indicate the sequence in which the dots are to be read. The first two dots show the first two significant figures DOT DOT DOT VOLTAGE NO in of the capacitance uucronsicrofarads, I 2 3 RATING COLOR TOLERANCE while the third dot indicates the number of zeros to be added. A gold or silver third dot indicates that the mmf -value shown by the first two dots is to be divided by 10 or 100, respectively. EXAMPLE: A 0.006 -mf (6,000 - OR mmf) capacitor is marked by three dots in sequence as follows: blue (6), black (0), and red (00). The dot indicating tolerance, when used, is usually located above or below the third VOLTAGE NO TOLERANCE *Reference: Graphical Symbols for Telephone, DOT DOT DOT Telegraph, and Radio Uses, approved October 24. RATING COLOR I 2 3 1944. by American Standards Association: Microfarads-mf See Table I. M icrom icrof a rads -m m f Basic 3 -dot color code provides working voltage and tolerance indications. 493 RADIO -CRAFT for MAY, I 9 4 5 dot becomes an important feature or identi- AWS PAPER CAPACITOR CODE significant figures plus the number of addi- fication symbol for a molded mica capacitor Fixed paper -dielectric capacitors of the tional zeros in the usual fashion. The ca- marked according to the AVIS code. home -receiver replacement type have their pacitance tolerance, in per cent of rated values on DOT DOT DOT printed them together with an capacitance for capacitors of greater than indication as to which lead is connected to 10 -mmf or tenths of a micromicrofarad for I 2 3 the outer foil and, therefore, might best be capacitors of less than 10 -mmf, is indicated grounded. No color coding of capacitance by the last dot. values is used with capacitors of this type. EXAMPLE: A 30 -mmf plus -or- o \\ \' The AWS code for molded paper ca- minus 5% capacitor with a temperature pacitors, like the code for mica capacitors, coefficient of 80 parts per million per de- t>o bihKLl' NRltl uses six colored dots -together with an gree Centigrade would be marked as fol- arrow to indicate the proper sequence. Units lows : end band or dot, red (80 parts/ marked according to this system can be million /C °) ; second color, orange (3) ; identified readily by the fact that the first third color, black (0) ; fourth color, .TT? and fifth dots arc always silver. The second black (no additional zeros) ; and fifth color, green (plus -or -minus 5 %). DOT DOT DOT DOT DOT DOT The symbol (negative) indicates that the capacitance 6 5 4 I 2 3 varies inversely with tempera- RMA six -dot code, explained in Tabla II. ture. The temperature coefficient is expressed in micromicrofarads per micro- EXAMPLES: A 0.00012 -mf (120 - farad per degree Centigrade. Some capaci- mmf) capacitor is marked, to indicate tors are marked with a numeral instead its value, as follows: black (0), brown of a color code. For example, N -930 repre- (1), red (2), and brown (one addi- Ldhlütl=, Kl.b4L' sents a negative temperature coefficient of tional zero). 0.00003 -tnmf /mmf /C . A 0.0091 -mf (9,100 mmf) capacitor is marked as follows: black (0), white FIXED RESISTORS (9), brown (1), and red (00). Small fixed resistors, of both composi- Note that in,each instance the first dot DOT DOT DOT tion and wire- wound types, are frequently is black (0). 6 5 4 marked with colored bands and dots to in- The fifth dot in the AWS color code dicate the resistance and tolerance. An indicates the capacitance tolerance in per AWS paper capacitor code. First and fifth RMA and a AWS color code are both in cent of rated capacitance as previously de. dots are always silver, sixth black or brown. general use. The two codes are not identical scribed. The sixth dot, introducing a new in all particulars but are similar in many factor, denotes characteristics of design and third dots give the first and second respects. In all cases the various. color com- involving Q- factors, temperature coeffi- significant figures while the fourth indi- binations of body, ends, bands, or dots cients, maximum drift limitations, and pro - cates the number of additional zeros to give indicate the resistance in ohms to two sig- auction test requirements. the capacitance in micromicrofarads. The nificant figures, the number of additional It will be noted that this color code does sixth dot shows whether the capacitor has zeros, and the per cent tolerance in re- not include the voltage rating. This is con- a maximum operating temperature from sistance. sidered unnecessary since, with few excep- minus -67° to plus -167° (brown) or plus - tions, all capacitors marked with the AWS 185° (black). No indication of working voltage is given DOT DOT DO T by this color code. However, all AWS 9 2 molded paper capacitors have D.C. working f al voltages between 300 -v and 800 -v. The lower rating applies to units with high - capacitance ratings and the higher voltage TIP DOT DOT DOT DOT rating applies to units with low- capacitance I 2 3 4 htl:NGl'. NAME. ratings. The RMA code for tubular ceramic capacitors. TUBULAR CERAMIC CAPACITORS The first method makes use of four col- Tubular ceramic dielectric capacitors ored bands, starting at one end of the unit, may be marked according to either an to show resistance and tolerance. The bands, DOT DOT DOT AWS or an RMA color code. The tem- reading from the colored end, indicate (1) 6 5 4 perature coefficient is indicated by the color first significant figure, (2) second signifi- of the band or dot at one end of the unit. cant figure, (3) number of additional zeros, AWS code. First dot is always black. Fourth Capacitance in micromicrofarads is shown and (4) per cent tolerance. The body color and sixth dots are explained in Table III. by the first three succeeding dots to two (Continued on page 497) color code are rated at 500 D.C. working volts. The exceptions, all of which are rated at 300 -v, are (1) AWS type CM35 capacitors with capacitances of 6,800 -mmf, 7,500 - SIGNIFICANT FIGURES: SIGNIFICANT FIGURES: mmf, and 8,200 -mmf; and (2) AWS type FIRST SECOND BODY FIRST (BODY) SECOND CM40 capacitors with capacitances of 9,100 - mmf and 10,000 -mmf. TABLE III. AWS SIX -DOT COLOR CODE FOR MICA CAPACITORS 1st 2nd 3rd 4th 5th Color Dot Dot Dot Dot Dot Sixth Dot Black 0 0 0 none 20% No specified qualities. DEC MAL TOLERANCE TOLERANCE DECIMAL Brown 1 1 0 Specified "Q ". MOLT PLIER MULTIPLIER Red * 2 2 00 2iú Temperature coefficient: plus -or-minus A BI 200 parts /million /C °. Orange * 3 3 000 Temperature coefficient: plus -or-minus 100 parts /million /C °. SIGNIFICANT FIGURES: SIGNIFICANT FIGURES: Yellow 4 4 * Temperature coeffi- FIRST (BODY) SECOND FIRST (BODY) SECOND cient: O to plus 100 parts /million /C °. Green 5 5 * Temperature coefficient: 0 to plus 50 parts /million /C °. Blue G G * * Temperature coefficient: O to minus 50 parts /million /C.° Violet * 7 7 * TOLERANCE * 8 8 DECIMAL TOLERANCE DECIMAL Gray l MULTIPLIER White 9 9 * MULTIPLIER Gold * divide 5% B2 133 by 10 Silver * divide 10% by 100 Resistance markings as used by both RMA and AWS codes. Note that body color is not part *not used. of the code in A -in the others, body color is one of the significant figures. 494 RADIO -CRAFT for MAY, 1945

L. BROADCAST EQUIPMENT Part VIII -CLASS -C AMPLIFIERS

By DON C. HOEFLER*

THE Class C amplifier is used almost For unmodulated exclusively in broadcast transmitter ap- Class C R.F. stages, plications because of the numerous ad- the bias should be vantages which it offers. It may be used about twice cut -off. as a linear power amplifier, a modulated In plate -modulated R.F. amplifier, or as a frequency multiplier Class C stages, the (harmonic generator). However, operation value of grid bias must be confined to the R.F. stages since should be somewhat relatively high excitation voltages are re- greater than cut -off quired and the output wave -form exhibits at the highest plate a high degree of distortion. It differs from voltage encountered. other tuned amplifiers in that it operates Experience has with a grid bias which is appreciably greater shown that a desira- than (1% to 4 times) the cut -off value. ble value is about The Class C amplifier has exceptionally three times cut -off. high efficiency, as a result of the fact that For purposes of econ- plate current flows only when the instant- omy and good regu- aneous voltage drop across the tube is low; lation, grid -leak bias i.e., the plate current is zero when no al- is often employed. Photo Courtrsy Western Electric ternating grid voltage is applied, and plate This has a particular current flows during much less than one- advantage in plate - The power amplifier of Radio WLAC, employing Doherty circuit. half of each cycle when a signal voltage is modulated Class C applied. These very short pulses of plate amplifiers, as it ma- current exhibit several important character- terially reduces the high grid current and The Doherty circuit provides a plate istics ; as the pulses become shorter : (1) driving power which are required because of power efficiency of 60 to 65 %. To under- Efficiency becomes greater; (2) Input pow- over -saturation at normal plate voltages. stand its basic principle of operation, we er and consequently the output power be- Then without modulation a small degree of may draw an analog by reference to an comes less; (3) Harmonic components of increase in grid current will add to the bias electric power system. If we have a genera- the plate current become greater. and thereby lower the undesirably high tor delivering electric power into its load This last factor enables the circuit to be positive grid swing. When the plate voltage under conditions of maximum efficiency and designed as a frequency multiplier, for con- increases due to a positive modulation peak. additional voltage is required, we can mere- siderable output may be obtained from suit- the grid current lessens, reducing the bias ly insert another generator in series with able tubes at several integral multiples of and increasing the positive grid swing. For the first at the times that additional output the excitation frequency. This is accom- this reason experiment has proved that bet- is needed. While it is not possible to oper- plished simply by tuning the output tank ter modulation is obtained with grid -leak ate vacuum tubes directly in this manner, circuit to the desired harmonic frequency. bias than with fixed bias. the Doherty circuit permits exactly the it Thus can be readily understood that Grid -leak bias when used alone has a dis- same effect to be accomplished by connecting the output wave -form of a Class C amplifier advantage in that it disappears with the the tubes in parallel and causing their out- loss of excitation. Therefore, regardless of puts to be in series. feo ao. the source of Class C bias employed, a re- This may be understood by reference to G10 Gtt/fR sistance in series Fig. 1. The excitation voltage E. divides CIRCl/IT LyRr/i/fR with the cathode should F^o. always be provided to safeguard against into two parallel branches. In the upper sec- the complete loss of bias. Then as long as tion, the voltage undergoes a phase shift of plate current flows a minimum safe value -90° in the grid circuit before it is im- of self- biasing is provided. If the indepen- pressed upon the control grid of the carrier dent bias should fail and this cathode re- amplifier tube. The voltage is then amplified sistor were not provided, the plate current and further shifted 180' as it passes through would immediately rise to dangerously high the tube. The output voltage then goes proportions, possibly causing irreparable through the impedance-inverting network damage to the tube. where its phase is again retarded 90 °. Thus the resultant voltage has rotated 360° and is in phase with the exciting voltage. THE DOHERTY AMPLIFIER In the lower branch of the circuit. the The high -efficiency linear power amplifier signal E. is shifted -90° in the phase - is a result of efforts of W. H. Doherty, of shift network, -90° in the grid circuit, and the Bell Telephone Laboratories, to reduce 180° in the peak amplifier tube, whence it the expense of operating power for the also emerges in phase with E. and coin - ILC. amplitude-modulated stages of broadcast bines additivcly at Eo. This apparently brings us right back where we started. but Fig. I -The Doha ty high -efficiency amplifier. transmitters, particularly of 5000 watts and over. Maximum efficiency is obtained from not without accomplishing our original pur- any vacuum -tube power amplifier only when pose. The carrier amplifier is so adjusted is very complex and contains large harmonic the tube is delivering the maximum possible that it is approximately fully loaded when components. Nevertheless, the output volt- R.F. voltage into its load. However, since no modulation is applied. Thus the plate age may very nearly approach the sine -wave this maximum voltage is delivered only dur- current can follow the negative nuxlula- condition, due to the "flywheel effect" of a ing infrequent and momentary peaks of tion peaks, but cannot follow the positive properly -designed tank circuit, as previously amplitude modulation, and the unmodulated alterations due to saturation. The peak am- explained in the discussion of the Class B carrier voltage is but one -half of this maxi- plifier is so biased that it does not begin circuit. Under this condition, the output mum value, the average plate power ef- delivering power until the excitation exceeds voltage is 180° out of phase with the excit- ficiency of such stages ranges from 30 to the unmodulated value. Thus its plate curing voltage. 35%. When considering the entire system rent is capable of following the positive modulation alternations but not the negative *Broadcast Engineer. ex -W2XMN (F.M.). Al- from power mains to output tank, the over- pine. N. J. all efficiency may range from 20 to 25 %. (Continued on page 517) RADIO -CRAFT for MAY, 1946 495 Test Comparator A High -Speed Checker for Production By WM. F. FRANKART

THE Comparators described below were very thin sheet of mica between wires, then designed for use in factory production covered with mica and clamped in a folded The Comparator. Connection to components testing. Because of their speed of op- half -inch square piece of 20 -gage sheet being tested are made by posts at upper right. eration they will be found excellently metal. The unit, which has a resistance of adapted to such work. For the small labora- .0625 ohm, was then hard -wax impregnated. without retuning the circuit, or resonating tory or service shop they may be calibrated The Comparator was built on a 10 x 17 within a certain fixed tolerance -within a to serve a number of purposes, such as "Q" x 3 -inch chassis, with stages isolated by certain number of degrees on the C, dial - meter or signal generator. proper shielding and circuit insulation. As are then acceptable. One of the units is a variable- frequency may be seen in the photograph, ordinary Sixty -cycle modulation is incorporated, device for checking radio- frequency coils numbered dials were used, the author plot- and the instrument may be used as a signal and all types of condensers. The second is a ting curves against the dial readings. There generator by connecting a 100 -mmf capaci- "production type" adaption of the first. The are five curves for the oscillator and two tor in series with the "LO" terminal of LX third is designed for checking iron -core for the investigation capacitor, C,-one for as the output lead, and the "LO" terminal components such as audio transformers, a single section in the circuit and another of CX as the ground lead. power transformers, chokes and filters. for both sections connected in parallel. This Used in production, they can save many connection is made by means of the binding PUSH BUTTON COMPARATOR man -hours of test time. For the smaller posts on top of the cabinet, as may be seen The second unit is composed of a triode producer or serviceman, the three pieces in the schematic. in a Pierce oscillator coupled through a crys- compose almost a small laboratory and will Dials should be of the vernier type and tal filter unit to the same general circuits answer many problems in which accurate preferably of large size. Four inches should described above (6N7 cathode follower, checking has been unattainable because of be the minimum for easy reading and a etc.) This instrument uses twelve crystals, the high cost of such equipment. higher degree of. accuracy and "reseta- As can be seen in Fig. 1, the first instru- bility." ment is a grounded -plate Hartley oscillator The constructor may calibrate this equip- using a 6SJ7 tube, with a 6N7 -G (elements ment to an accurate degree and thereby have paralleled) as a cathode follower. The a very reliable and useful instrument. With vacuum -tube voltmeter section employs a the investigation capacitor calibrated, meas- 6F5 and a 200 -micro-ampere D.C. meter. urements of R.F. inductance and capacitance The 6F5 is operated at reduced filament may readily be made. Calibration of the voltage to eliminate instability. Low loss oscillator makes the device a signal gener- construction is used throughout. The instru- ator and frequency meter. For direct com- Fig. 2- Push -button Comparator. Six crys- ment was built up around a Miller T -550 parison tests, however, such calibration is tals are switched into each position shown. coil kit that covers fróm 50 Kc. to 20 Mc. not necessary. in five switching positions. While there is six in the oscillator and six in the filter cir- still a lot to be desired in this kit, it is COMPARISON TESTS cuit. The Oscillator Crystal and the cor- low- priced and readily available. I:.F. coils under investigation are simply responding filter crystal is selected by push- The constructor should take care to see connected across terminals "LX" and reson- button. The reader may wonder why the that no coupling other than that brought ated with C, till the maximum deflection of filter is necessary. It is to eliminate har- about by condenser C, occurs between the the meter is obtained. The indication on the monic output or rather input to the cathode oscillator and the cathode follower and V.T.V.M. will then indicate whether the follower stage. It was also necessary to take V.T.V.M. stages. This may be checked by "Q" is above or below that of the coil used excitation from the grid of the Pierce resonating a high "Q" coil, then disconnect- for a standard. oscillator rather than the plate circuit. The ing C, from the oscillator and grounding To check a capacity, a coil is first placed capacitor used for excitation control in the the 6N7 -G grids. If a reading is still ob- across the terminals LX and resonated by oscillator is a rather good by -pass to ground tamed, better by- passing of circuits is in means of C,. The condenser to be measured for the harmonic energy. The frequencies order, or better shielding between the oscil- is placed across terminals C. and condenser used were 455 Kc., 600 Kc., 1000 Kc., 1500 lator and other stages. Since, due to the C. again turned to resonance. If C, is cali- Kc., 3 Mc., 6 Mc. The two low- frequency impracticability of specifying a standard set brated in capacity, the capacity of the un- of parts, no layout will be given, these pre- known condenser is the difference between cautions may vary with individual instru- the capacities at the two settings. For com- ments. parison only, as in production tests, it is One component of a very special nature only necessary to turn C. to a minimum or is the non -inductive resistor R,,. This was other convenient setting and resonate the made from a one -half -inch piece of ni- coil with a standard condenser across the chrome wire folded back on itself with a CX terminals. Other condensers resonating Fig. 3 -A Comparator for audio frequencies.

T330 Ri 6SJ7-OT LO N1+ crystals are of the "GT" cut type and the 6N7-bT(t,aourJ cxo- high frequency crystals the "AT' cut type. cawrno Ru LX NW,.nJ Filter Crystal A,, is approximately 15 -2111D¡.-:- \ LX maniuk1 Fig. I- Diagram of mmf higher in frequency than the oscillator the Comparator shows crystal A2. few hard-to-get parts. The main advantage of the crystal con- R6 co Circuit is simple but trolled Comparator is with large production extreme care in selec- runs of either transmitters or receivers. tion of materials and Usually a limited number of coils and con- construction is re- densers are under investigation and an acquired. to prevent curate knowledge of frequency is necessary. leakage which would AUDIO COMPARATOR RIO cause indications to become unreliable. The third unit, illustrated in Fig. 3, is built around the typical "RC" type audio R9 R7 oscillator. The Hewlett- Packard type 200B with a power amplifier added may be used. (Continued on page 499)

496 RADIO -CRAFT for MAY. 1945 PRACTICAL V T.UM.

By WM. B. MILLER

THE following is a description of a resistor in series will produce the required When this operation is complete. the thoroughly practical vacuum tube volt- drop. other ranges will depend for their accuracy meter. The design is the result of much The only critical wiring is the input grid on the precision of the multiplying resistors. experimenting. A bridge circuit is used circuit ; the 3 meg. resistor should be Precision resistors are extremely hard to with feedback for stability. mounted right at the socket and as short a In the original model a 6SN7 twin triode wire as possible used to connect to the arm was used, which is the same as two 6J5's. of the switch. The test prod and lead Almost any triode with a separate cathode should be shielded right up to the switch. will serva. It was found that increased Outside of these everything else is straight- sensitivity resulted from the use of power forward and the other leads may be cabled tubes such as 6V6's and 6K6's connected for neatness. as triodes. Two volts full scale .was all CALIBRATING THE METER that was wanted, so a 6SN7 and a 500 microamp meter were used. Before attempting calibration the current A voltage- egulated power pack is necessary. through the VR tube must be set. if one More sensitivity may be obtained from is used. This is done by opening the wire the circuit being described by substituting from pin No. 2 on the VR socket to ground obtain now, so part of each range section a 5000 -ohm resistor in place of the 24,000 and inserting a milliammeter (50 Ma. may be made variable for adjustment. If one from P.2 to ground. This reduces the range). this is done adjust each range for full scale Remove the 6SN7 and turn on the power, reading, starting with the 10 volt position then adjust the variable 5,000 ohm resistor and working up to the 1000 volt. Repeat the IMEG 3ME0 150a4 until the current through the VR tube is operation at least once as the total resistance 10.000 from the prod to ground is just as important .5W 2. well within its operating range, preferably 80.000 about 20 Ma. Now the 6SN7 may be re- as the resistance between taps. Twenty per- 10. 400,000 placed and allowed to warm up. The voltage cent of cadi range made adjustable will 5o. allow plenty of variation, if good carbon 500.000 regulator tube will hold the plate voltage soo. at 150 volts, plus or minus 1 volt, and will resistors are used. 1 MEG When all the resistances have been set, a 200. take care of normal line fluctuations. 341E0 The only way to calibrate a meter of drop of Duco cement on the potentiometer 500. 5MEG any kind is to have some kind of a standard shafts right at the bushings will hold them r000v Ó a from unintentional shifting, P.2, being the 20.000 for comparison; either known voltage or a meter of known accuracy. The first opera- Zero Adjustment, is on the front panel as ET,'" tion after the tubes have warmed for about it should be checked each time the meter twenty minutes and the meter has been is put into use. P.1, the 2-volt adjustment. is chassis and be sealed after The balanced electronic voltmeter circuit. exactly zeroed by means of P2, is to adjust on the should for the basic 2 volt range. Set the range being set. It is only necessary to check switch to the first position and apply a small each range at full scale as the meter is feedback, however, and the meter loses voltage, starting with about 1 volt. Grad- linear. If 1 or 2 watt resistors are used for some of its stability. Those lucky enough ually increase until a full 2 volts is applied. the voltage divider they will have no to possess a more sensitive meter, can use Watch the meter needle as the voltage is noticeable variation with temperature and 6V6's in this circuit and get full scale de- applied- increasing the resistance of P.1 if will only change because of aging. One watt flection with a small fraction of a volt. it tends to go off scale. With the 2 volts resistors may also be used at all other points There is one important thing to remember feeding in, vary P.1 until precisely full scale not otherwise marked on the schematic. if other tubes are substituted, and that is is registered on the meter. Now remove the The writer is experimenting with a recti- they must be operated on the straight por- external voltage and recheck the pointer fier for the same meter to allow the reading tion of their Eg -Ip curves. If this precau- for zero position. If it has shifted reset it of A.C. voltages and will pass the information is not observed the meter deflections and repeat the full scale adjustment. , tion along as soon as it is complete. will not be linear.

..,1 i mm.7 smr: .. .:1.;11111 The operation of the circuit is as follows: ,1111111'1,,,I,1,11.4111111.1', ri n°.. n .nunm,nnm,,, ,;:u1n,nunmm11nnnie1u1nimunnmrnmiimnnnunnurunn.wwuwrmw1nnmininnn P2, the 500 ohm potentiometer in the CODES cathode circuit, is the balancing control. CAPACITOR AND RESISTOR By varying this the cathode currents may (Continued from paw 404) be exactly balanced so that the meter pointer rests at zero. plays no part in indicating resistance or EXAMPLE: A 5,600 -ohni When a voltage is applied to the grid of tolerance but is used to indicate the type minus 10% resistor would be marked the active triode the balance is upset, be- of resistor unit. Under the RMA code, a in either of two ways : cause more current then flow in the will black body is frequently used to indicate (A) First band, green (5) ; second cathode circuit of this tube, creating a dif- an uninsulated composition unit, while a hand, blue (6) ; third band. red (00) ; ference in potential between the two cath- tan, olive, or white body usually indicates fourth band, silver (plus -or -minus odes which, of course, is registered on the a -wound The code specifies 10 %). meter. wire unit. AWS that an uninsulated unit have a black or (B) Left end. silver (plus -or -minus In constructing the meter almost any lay- white body unless the body is a part of the 10%) ; body, green (5) ; right end. out that fits an available chassis and cabinet color coding. The body of an insulated unit blue (6) ; central band or dot, red (00). will do. Where the meter is to be used near may be any color other than black although strong external fields which might influence TABLE VI. COLOR CODE FOR SMALL FIXED a natural tan is preferred. When there is RESISTORS. it, a grounded metal cabinet should be used. a resistor doubt as to whether particular First band Second band Third band Fourth bald The plate and cathode resistors should be is composition or wire- wound, it is well to end tm end fairly well matched so that the zero balance remember that any resistor of 100 ohms or Color body riant center** potentiometer will not lose its range of Black 0 0 none less is most likely wire -wound and that it Brown 1 I 0 control. is probably wound inductively. Red 2 2 00 Filtering of the plate voltage is Several variations of this method are in Orange 3 3 000 supply Yellow 4 4 0.000 of very minor importance. Any small choke use. With all these, however, the interpre- Green 5 5 00.000 or wire wound resistor will do in comhina- tation of the code is practically the same: Blue 6 6 000,000 Violet 7 7 0.000,000 tion with a pair of 4 mfd. electrolytics. left end (dot facing, leads downward) or Gray S 8 00.000.000 Regulation, however, is highly desirable. If narrower end stripe, tolerance; body, first White 9 9 000,000.000 a VR tube is not to be had though, a large significant figure; right end. second signifi- Gold divide by 10 5% band, Silver divide by 100 bleeder current will help. Longer tube life cant figure; and the central dot or (body) u 10% will be realized if the heater voltage is number of additional zeros needed to com- reduced about ten percent; a 2 -ohm, S watt plete the indication. *not used. RADIO -CRAFT for MAY. 1945 497 IMPROVED TUBES NEEDED FOR INDUSTRY, CONTROL LET THIS TEACHER" Quality of electron tubes in many delicate "AUTOMATIC control applications-especially in aircraft and tanks where vibration is a decisive fac- show you exactly how to repair over tor-is much more important than in the home radio, where large tolerances from optimum characteristics are permitted. This point was brought out in a report by Lt. R. J. Colin, Jr., in a paper read at the annual meeting of the Society of Automotive 4800 RADIO MODELS Engineers held early this year. "The critics of electronic controls for aircraft," he said, "question their reliability without expensive test equipment ! perhaps more than anything else. They feel that a vacuum tube is a very temperamental and mysterious device -at any rate a thing not to be depended upon. Fortunately we SAVE TIME -SAVE MONEY! now have sufficient field experience- partic- ularly in the European theater of war -to Girardi's RADIO TROUBLESHOOTER'S Reports from HANDBOOK is the ideal manual to show you answer such criticism. this exactly how to quickly repair radios at home in theater have demonstrated that such con- spare time -quickly and without a lot of vious pre- trols are practical and reliable. We must experience or costly test equipment. It am- not forget of these controls is tains MORE THAN 4 POUNDS OF FACTUAL. that this test time -saving, money -making repair data for re- under actual battle conditions. In the matter pairing all models and makes of radios better. of altitude and low temperatures alone, faster and more profitably than you may have thought possible! electronic controls are getting many hours of flight tests which would have been im- NOT A "STUDY" ROOK practical to obtain before the war began. RADIO TROUBLESHOOTER'S HANDBOOK "It should be emphasized that the grade can easily pay for itself the first time you use it. You'don't have to study it. Simply look up of vacuum tubes used in these controls are the make, model, and trouble symptom of the the ordinary commercial receiving tube Radio you want to repair and go to work. No types. When it is possible for tubes designed lost time! Clear instructions tell exactly what the trouble is likely to be- EXACTLY how to to be used in ordinary home radio receivers fix it. Actually, this big 744 -page manual -size to make a reasonably good performance HANDBOOK brings you factual, specific repair record, tubes of the highest possible quality data for the common troubles that occur in practically every radio in use today -for over would leave little to be desired. 4900 most popular models of Home and Auto- "The possibility of making a vacuum radio receivers and Automatic Record Changers tube as reliable as other apparatus com- of 202 manufacturers! In addition, there are hundreds of pages of helpful repair charts, tube ponents for a given life span is not some- charts, data on tuning alignment, transformer thing to be hoped for. It can be done and troubles, tube and parts substitution, etc.. etc. - has been done. There are at least two pro- all for only $5 ($6.60 foreign) on an UNRE- SERVED 5 -DAY MONEY - ducers in the United States of high quality BACK GUARANTEE! tubes of this nature. The essential difference between high quality tubes and ordinary "garden varieties" is the care exercised Get a Complete RADIO -ELECTRONIC in their construction, selection of materials, pumping and de- gassing thoroughness, mechanical tolerances, and general ruggedness. Therefore it can, I believe it can, be con- SERVICE EDUCATION chided that the electrical components (including tubes), going into an electronic con- AT HOME- WITHOUT AN INSTRUCTOR trol are actually the factors which would put a certain electronic control in either the first or second reliability classification." TEST INSTRUMENTS TROUBLESHOOTING - The foregoing is important as pointing REPAIR A. A. Ghirardi'a big 1300 -page MODERN RADIO SERVICING is the finest, most com- out that the present success of electronics plete instruction book on Radio- Electronic service work for is being achieved with equipment not yet either the novice or the professional Radio -Electronic service- thoroughly adapted to the work which must man -bar none! Read from the beginning, it is a COM- be done. In the Electronic Age, we will PLETE COURSE IN SERVICING by the most modern have tubes built especially for the job in methods. Used for reference, it is an invaluable means of which they are used-long -life filaments brushing up on any servicing problems that puzzle you. be 24 hours per Gives complete information on all essential service instru- for tubes which must "on" ment types; how they work (with wiring diagrams), when day, vibration -proof tubes for applications and why to use them; how to build your own; preliminary involving rough treatment, and many other trouble checks; circuit and parts analysis; parts repair, variations, such as constant- frequency de- replacement, substitution; ob- sign features for certain types of intrusion scure radio troubles; aligning alarms and wide -range temperature char- and neutralizing; interference acteristics for gas rectifiers used in some reduction - and hundreds of kinds of equipment. Technical other subjects including How to Division, MURRAY HILL BOOKS. Ina Start and Operate a Successful The electron tube, regarded by many as Dept. RC -55. 232 Madison Ave., New York 16, N. Y. Radio- Electronic Service Busi- a finished product, may still be in its in- . Enclosed find S for books checke,!.or n send C.O.D. (in ness. 706 fancy! U.F.A. only) for this amount plus postage. If not fully satisfactory. self -testing review I return Inc books at the and of a da;n and receive MY questions help you check your money hack progress EVERY STEP OF MODERN RADIO SERVICING C: RADIO TROUBLESHOOTER'S SS (53.30 foreign) HANDBOOK SS (S5.50 foreign) THE WAY. Only $5 complete PALEY GERMAN RADIO HEAD L Special MONEYSAVINO COMBINATION ($5.50 foreign). Both big books for only 59.50 Control of entertainment in occupied ($lO.SO foreign) MONEY- SAVING OFFER! Germany is to be in the hands of Col. Wil- liam S. Paley, well -known in American Name While or write the present limited supply is under- (Please print plainly) lasts you can get BOTH big radio and former head of CBS. It books -radio's most famous com- stood that his duties, while primarily con- Address plete Modern Service library total- cerned with radio, will also extend over ing over LOSO pages -at a bargain and other forms of enter- combination price. See coupon. moving pictures City and Dist. No. mte tainment. received his commission 5 full days. Money re- Col. Paley, who for two months ago, was expected to start his "BORROW"THESE BOOKS funded if you don't like them! new job at once.

498 RADIO -CRAFT for MAY, 1945 .. , .. and be world w ill unsurpassed eVer+ts of unsure the future instruments' petrolo built" seen on beauty. value and Television Receivers ' Rodio < Word gvtomou. odvc} Receivers p and ohe electronic Chongers,

ON Detroit' ION AN [/\Q)J CORPORAT KEEP division pETROIA p1TERNATtONAMichigan Detroit 9,

w.. w,.cs ...ew r.a.Mr r.we..

RADIO -CRAFT for MAY, 1945 sol HOW THE N. U. EQUIPMENT PLAN HELPED SERVICE DEALERS PROSPER I

Here's a typical example of how service dealers obtained the test equipment they needed through National Union deals. This N. U. plan was OK'd 60,000 times by radio service dealers - and helped make servicing more profitable for thousands!

tFRTA /NLYJOE,P/CK 0VE011TOhhHf NU. EQ(//PMEN7 ENCYCIOPED/ AND ea TELL YOU HOW rO{ CAN 6ET /T"

'YHA 5 ASV- /UST SIGN THIS AGREEMENT ID USE ND PRODUCTS AND LEAVEA TESTER Wilt I "' DEPOSIT, THE \ EA70NCEuYOU

' : `, "DO / NAVE TO BUY ALOT ' OfN.UORDDUCTSR/6/? ' = AWAY AND l4'NEN09/ ( °/' 6ET MY DEPOS/7 . / ; / ( BAC/Y CALLED FOR ON7NE \ \ CONTRACT YOU OFT O YOUR DEOOJ/l BAC/( AS A MERCHANDISE %...0 REDIT"" -- OK PAL SERVICE /T'S A DFAIfR DEAL

NATIONAL UNION

Bulbs ransmining, Cathode Ray, Receiving, Special Purpose Tubes Condensers Volume Controh Photo Electric Cells Panel Lonips Flashlight

502 RADIO -CRAFT for MAY, 1945 WHAT PEOPLE WANT IN !OSTWAR RADIO AM RICAN families will buy 100,- ,000 radios within the first five nda.rd és:l[ll(Ú!/ or six ears after total victory, according .% J to a s rvey just completed by Sylvania. . Two-th rds of the current population will As a ,//ud9/ a order t e first new sets on the market - prefera ly combination radio -phonograph ivenlu,v models. More people say they will pay an additional $75 for television than will spend $10 extra for FM. (Frequency Modula- tion), but if FM doesn't dig a hole in their pockets any deeper than $5 they say they want it almost to a man ; demand as many gadgets as they can get, insist on short wave although they seldom use it on thei present sets. The survey, which was conducted by one of the country's leading market research organizations, was notable in its covera of the small city and town areas, which epresent so important a part of Americ 's buying public. The 1,000,000 radio homes in the country no have an average of 1.54 sets per home and not only has there been a steady increase in the number of people owning a radio but an equal growth in the number of families owning two or more sets is indicated. In the past, radio buyers displayed little loyalty to the brand of radio already owned. Illustrating this, sixty -three per cent of the families who own three sets admitted ELECTRONIC that all three were different brands. While the average set is turned over every seven years, half the radios now in operation are between four and eleven aga years old and their owners have little to say against them. Only five per cent expressed any real dissatisfaction. Frequency Modulation will be a big RADIO SERVICE selling Iffactor, with over ninety percent of the people looking forward to it. A small group would be willing to pay $30 extra for FM, half those interviewed would pay erfonemt an additional $10, but the majority of listen- Á11,tf4ipès uóe 9nd ers would prefer to pay only about $5 for the clearer reception possible with FM. Serf Tester Provided that telecasting stations are HICKOK Instruments have long within range, and program quality is ac- in ceptable, the public think they will buy been known as the ultimate fifteen million television sets at $75 over scientific development. Illustrated the usual cost of a radio set. Survey results show that at present only a little here are but 4 of our 36 leaders in over tl ee per cent of the people will pay the Radio Service field. Thousands $300 a d under thirty per cent want to see tel vision programs if it adds $125 to of Radio Service men have preferred $200 t the cost of the set. Horn radio owners are divided almost HICKOK Instruments because of equally among those who have short wave their unusual accuracy and de- faciliti s and those who do not. Even those ho have short wave and don't use pendability. HICKOK pioneered it will -ant it on their new sets. At pres- in Dynamic Mutual Conductance ent onl about 5% of U.S. radio families slgnat Generators listen o short wave programs regularly. Tube Testing Equipment. In the Pus button tuning is fairly popular. Of th 31% that have it, three -quarters field of Signal Generators, Traceo- like it, the rest report unsatisfactory serv- meters, Vacuum tube Voltmeters, ice, w ich indicates, according to Syl- vania, a need for considerable improvement. Oscillographs, Zero Current Testers, Asked what they like about their sets, Volt- ohm -milliam- meters and owners had this to say, in the order mentioned: Tone and reception is good on over Industrial Analyzers the name 75% f the sets, half the owners are excellence. pleas with the models and styles, like HICKOK is assurance of the to ing, get good distant reception, get good N lume, little static. As oon as radios become available, THE HICKOK ELECTRICAL over tN enty million families will buy new ones. ver 46% say they want Radio-Phono INSTRUMENT COMPANY models the majority preferring console 10531 Dupont Ave., Cleveland 8, Ohio styles. The figures show a trend toward one ba is model for each home and additional mall sets in other rooms- kitchen, bedroo , playroom and the like. RADIO -CRAFT for MAY. 1945 503 NEW EDITION j ads TELEVISION NOW RE AND ELECTRONICS 5 -PHOTO

O t fGí

oto

1 101 c tsCwPnE PÑ0t05 c9) a5 GNARts 00 ADDA & 0,á00D ,AG 38 BIG CHAPTERS c p- Easy to Read -Easy to Grasp -Easy to Apply t.51 A home -study course-especially well 1O Ap organized. The style is so interesting 'K E MR. you will read along without effort, INF O hardly realizing that you are actually studying and taking in vital informa- ON tion. Audels Radiomans Guide gives ;_=. ai you just the right amount of mathe- It gives usable formyou matics required to cope with radio pointers on radio, problems successfully. You can solve, including frequency modula- with the aid of this extraordinary book, tion, television, practically etc. Also valuable inside information QAND A everyradioprob- for Aviators, Ma- lem that comes rines, Commercial up. At your fin- Operators and UNIQUE Technicians, Serv- ger tips is a icemen a n d Stu- QUESTION complete index dents. and for instant use. ANSWER sto METHOD

c sh Highly Endorsed e ce ,b t' 1. ` #. m § 0 .4.01o , `` ' 1001 RADIO FACTS AND FIGURES . #1 A Complete Library In One Book AÚ0& e e Se a ásU s 40. 1 AUDELS RADIOMANS GUIDE gives authentic Princi- ,,4 , ples and Practices in Construction, t`i Operation, Service 9 ter.1eos and Repairs. Covers clearly and concisely radio fund*. tb menials -Ohm's Law- Physics of sound as related to ;v radio science-Measuring instruments -Power supply i Resistors - - Inductors - Condensers - Transformers and . examples- Broadcasting stations-Radio Telephony -Re- Sc ceivers- Diagrams -Construction- Control Systems - s Loudspeakers - Antennas - AutoRadio - Phonograph Pick-ups- Public Address Systems -Aircraft and Marine Radio - Radio Compass - Beacons - Automatic Radio Alarms-Short Wave-Coil Calculations- Testing-Cath- ode Ray Oscillographs - Static Eliminations - Trouble Pointers - Underwriter's standards -Units and tables. REVIEW QUESTIONS -READY Reference Index.

RADIO -CRAFT for MAY, 1945 TEST COMPARATOR 496 ) ALL THE SCIENCE OF BASIC The gcucratu to a linear standard (LiTC) output transformer and connected tó the typical circuits. This unit has been of particular advantage in checking audio transformer tol- RADIO -ELECTRONICS erances and audio oscillation transformers for frequency range. It is also used to check filter chokes and will check all types of laminated iron core components. Numerous one big uses in other kill, of course, present themselves to the constructor.

Parts List LI- Miller T-550 Coil Kit 60 Kc. to 20 Mc. 5 bands 3'/2 Ib. book C1-366 mmf. 2 section low loes capacitor C2 -100 mmf. silver mica capacitor CS -500 mmL silver mica capacitor C4 -Same as CI WRITTEN FOR BEGINNERS C5-.O1 mfd. midget mica C6--Same as C5 C7 -Same as C5 C8 -Same as C5 C9 -Same as C5 CIO-Same as C5 TRAIN NOW FOR THE BEST C11 -.25 mfd. 600 V. oil paper C12 Same as C5 C13-Same as C6 OF ALL POST -WAR JOBS! C14-4. mfd. 600 V. oil filter capacitor C15-4. mfd. 600 V. oil filter capacitor A. A. Ghirardi's famous 372 -page lb. Cl6-Same as C3 RADIO V1 -6N7G PHYSICS COURSE book with its V2-6F6 500 illustrations and 856 self -testing review VS -83 V. questions can teach you basic Radio -Elec- V4 -6SJ7GT 36 tronics from "scratch " -quicker, easier, and PL -Mazda No. 46 6 -8 V. .25A TI -Pri and Sec both 116 V. (Commonly used as at far less cost than you may have thought AC -DC receiver isolation transformer) COURSES IN ONE possible! This ONE BIG BOOK (which is T2 P -6011 -Stancor II this big book were broken into actually 36 Courses in One) has given more R1- 40,000 ohms 10 -watt wire -wound monthly Iessons and sold as R2- 50.000 ohm pot. wire wound (Hi-current you'd regard it as a beginners their start in this fascinating field type) bargain at SSO or morel In this than any other book or course ever pub- R3 -10 megohms 2 watt convenientt book lished! 60,000 10 watt wire -wound yoyou get it Also, it is used by more U. S. Army R4- ohms for only 11.5-500 ohms pot. 3 watt Signal Corps, Navy, and civilian schools and R6 -2000 ohms 2 watt for more home study than any other book of R7- 25,000 ohms 2 watt its on R8- 15.000 ohms 2 watt type the market! 119-1. ohm ID watt wire-wound COMPLETE Nothing is omitted, nothing condensed. RIO -100 megohms (10 -10 meg. 4 -watt in series) Ell-Special .0625 ohms non -inductive Everything is fully explained and made as Meter-Weston 301. 0 -200 Microampere D.C. This is only a fraction of what RADIO easy as A -B -C. Ask any radio-electronic C11-160 ohm 76 Ma. filter choke PHYSICS COURSE brings you: First, over man! You'll be amazed how quickly RADIO (Metal chassis and cabinet) 300 pages devoted to a vitally important PHYSICS COURSE will help you master foundation in Basic Electricity . all made simple as A -13-C by clear explana- subjects that other courses make seem very tions and over 150 illustrations; also broad- complicated. And you'll be even more casting ; Sound, Speech, Music: Radio trans- amazed to find that it gives you a COM- mission ; Broadcasting stations; Receiving units; Vacuum tube theory, characteris- PLETE basic training -ALL YOU NEED tics, construction. action ; Detection : R -F easier, better, and faster -at a total cost amplification ; Audio amplification ; Super- of only $5 complete. Send coupon today. heterodyne receivers; Tuning coils ; Loud- speakers! Microphones; Power Supply Examine this truly great book for 5 days - units; Auto Radios Aircraft Radio; Pho- we guarantee to refund every nograph pickups and amplifiers; Public ad- cent of your money if not dress systems; short wave characteristics and equipment; Photoelectric cells; Tele- more than satisfied! vision ; Sound movies ;- and many other subjects and chapters:

"THE ELECTROLYTIC CAPACITOR"

An Important New Book on a Little -Known Subject Complete modern Probably no Radio-Electronic component is more vitally data on Electrolytic important than the Electrolytic Capacitor -and this new Capacitors in one book by Alexander M. Georgiev, who has devoted more authentic volume. than 15 years to electrolytic capacitor research and development, answers all the many questions engineers, servicemen and others have been asking about the various types of electrolytic capacitors ... their con- Technical Division. MURRAY HILL BOOKS. INC. struction, characteristics, advan- Dept. RC -55, 232 Madison Ave., New York I6. N. Y. tages, applications. measurement, 7) Enclosed find $1 ($5.50 foreign) for Ohirerdl's RADIO PHYs', testing, defects, etc., etc. Tells cOtnlSH book: or O send U.O.D. (In U.S.A. only) for this s une when and where to use electro- plus postage. If not fully satisfactory I may return It at the end lytics in preference to non -elec- of 5 days and have my money refunded. trolytic types; relative merits of O Check here for Oeorglev's "THE ELECTROLYTIC "wets" versus "drys "; applica- CAPACITOR" book. $3 ($3.30 foreign). tions at low and high voltages and frequencies: a-e or pulsat- Name ing d-c, ambient conditions, etc., etc. The most important book ever written on this vital sub- .sidras ject 1 Only $3 complete. C'ourhsy Mack Molding Co. City and Dist. No. State Cousin to Alec Electron and the Erg twins, Reddy Kilowatt represents the idea of electricity for 200 power companies. Reddy is a 5 -DAY MONEY -BACK GUARANTEE bright red celluloid figure, five inches tall. RADIO -CRAFT for MAY, I945 499 World -Wide Station List Edited by ELMER R. FULLER

MR. FULLER is busy this month on a existing Station List. He has therefore been reorganization of the World -Wide unable to spend time on the air, picking up Station List which he hopes will help to the weaker and more elusive shortwave give a better service and quicker and more broadcasters. For this reason it has been accurate reports. This has involved a great impossible for him to prepare his usual deal of work in typing up an index -card monthly report on reception conditions and system which will speed up both incorpora- stations heard. The usual report will appear tion of new reports and corrections to the next month. All schedules are E.W.T.

Frei. Statlen Location and Schedule Free. Station Location and Schedule Freq. StatlOn Location and Schedule

11.040 CSW6 LISBON. PORTUGAL: Brazilian lean beam. 5:50 pm to midnight. 11.880 IRR ROSARIO. ARGENTINA: heard at beam, DEL to DA. AZORES: 11.770 KCBF LOS ANGELES, CALIFORNIA: South 8:30 pro. 11.000 P DEL GADA. AZ heard American beam, 5 to 8:30 pm; 8:45 11.885 MOSCOW, U.S.S.R.: 6:45 to 7:25 pm. - at 2:45 pm. to 11:45 pm. 11.890 KNB- A SAN FRANCISCO. CALIFORNIA; 11.115 RICH LUXEMBOURG; heard with Army 11.775 GENEV1A45SWITZpERLAND: 4 to 4:30 Fast Indies beam 11 pm to 4:45 am. hour for New York. - lan: 11.890 KNBX SAN FRANCISCO, CALIFORNIA: 11.145 WCBN NEW YORK CITY: European beam. 11.780 GVU LONDON. ENGLAND. South American beam. 7 to 9:30 1KAR. FRENC 11.780 PANAMA CITY. PANAMA: evenings: pm;; 9:15 to 11:05 pm. 11.405 -- DAKAR. FRENCH WEST AFRICA; t IMPS afternoons. 11.893 WRCA NEW YORK CITY: Brazilian beam. 2.45 to 4:55 pm. 11.785 FZ1 BRAZZAVILLE, FRENCH WEST 6:45 to 7:15 am: European beam. 11.616 COK HAVANA, CUBA; noon to lo AFRICA: about 3 pm. 1:15 to 4:45 pm

11.645 BELGI AN NAL RADIO: - 11.785 BELGIAN NATIONAL RADIO; heard 11.887 1VU3 TOKYO. JAPAN; 6:15 to 8:15 pm. n about 8:30. at 8:30 to 7 pm; 9 to 9:15 pm. 11.900 XGOY CHUNGKING, CHINA: Allied Forces 11.680 CMCY HAVANA. UBA: hear) at 17 am. 11.790 WRUW BOSTON. MASSACHUSETTS: Euro- In the Far East. 8 to 9 pm: Asia. 11.680 GRO LONDON, Middle Near East. pean Imam 1 :3o to 6 ppm. Australia, New Zealand beam. 6 to 4 am; Middle Fast. nowt to 11.790 WRUS BOSTON, MASSACHUSETTS: North 6:30 am; Bast Kuria beam. 6:30 to 9:45 pm. African barn, 6:30 am to 5 pm; 7 am; Japan beam, 7 to 7:30 am. 11.690 XORS SHANGHAI, CHINA: 11:15 am to 515 to 7:15 pm. 11.900 WGEX SCHENECTADY. NEW YORK; Euro- 1RLI pm. 11.790 KGEX SAN D FRANCISCO. CALIFORNIA; pean beam. 1:30 to 4 pm. 11.695 -- BERLIN, GERMANY: Amor. East Indies beam. 5:15 to 6:45 pm. 11.900 CXAIO MONTEVIDEO, URUGUAY; heard at iD beam, 7:15 to 9:45 am.m. 11.800 MOSCOW. U.S.S.R.; heard at 7:25 R:IS pm. 11.700 GVW LONDON, ENGLAND¡ Africa. 11:30 11.930 GVX LONDON, ENGLAND: North Amer- am to 5 pm. 11.800 GWM LONDON. ENGLAND. ica. 6:15 to 8 am; 2:30 to 5:15 11.700 PRLB RIO DE JANEIRO, BRAZIL. 11.800 121 TOKYO. JAPAN; heard at 1:45 pm. pm; PaeiRe, midnight to 4 am; 11. OS SBP STOCKHOLM. SWEDEN. 11.820 GSM LONDON, ENGLAND: Pacia°. 1:45 India. 10:30 am to 12:30 PM. 11.705 MONTEVIDEO, URUGUAY; heard at to 6 am. 11.940 MOSCOW. U.S.S.R.; 8:18 to 8:50 pm. 8 11.826 WCRC NEW YORK CITY; European beam, 11.950 - MEXICO CITY. MEXICO; beard eve - - Dm. 11.705 'V ERCH EKES. CANADA; 11 am to 7 to 11:1-, am. - ne,. CBFY 11.830 WCRC NEW YORK CITY- Brazilian beam. 11.955 GYY LONDON. ENGLAND. 11.710 WLWS2 CINCINNATI. OHIO; South Amer- 11:45 am to 12:45 pm: European 11.970 BRAZZAVILLE, FRENCH WEST ican beam. 6 to 8:15 pm:,8:30 to beam, 1 to 5:30 pm; South American AFRICA; noon to 8:50 pm; 1 to 10:30 pm. beare, 0 pm to midnight. 2:30 am. 11.710 WLWK CINCINNATI, OHIO; South Amer- 11.840 VLC4 MELBOURNE. AUSTRALIA; 9:45 to 11.995 LISBON. PORTUGAL: heard about ican beam. 6:45 to 8:15 am: Eu- 111:45 pm. 8:30 am. ropean beam. 8:30 am to 5:30 pm. 11.840 SINGAPORE. STRAITS SETTLE- 12.040 GRV LONDON, ENGLAND; Australia. 1:45 11.710 VLG3 MELBOURNE, AUSTRALIA: 1:15 to MENT; Itadio Shown" heard at ton r 1:45 m. 7 12.070 CSW LISBON. PORTUGAL: heard 2:30 to 11.718 CR7BH MARQUIS. MOZAMBIQUE. 11.840 GWQ LONtDON. ENGLAND. 4 pm. 11.720 PRLB RIO DE JANEIRO. BRAZIL: 9:35 to 11.847 WGEA SCHENECTADY. NEW YORK: Eu- 12.095 GRF LONDON. ENGLAND: Near East. 10:45 pm; off Sundays. ropean beam. 6:30 am to 4:45 pm: noon to 1:15 pm; Italy, 6 am to 11.720 CKRX WINNIPEG. CANADA. Brazilian beam. S to 11:30 pm. 11.725 JVW3 TOKYO, JAPAN; heard at 2 pm. 11.847 XMHA SHANGHAI. CHINA: 9 to 10 am. 12.110 HI3X CIUDAD TRUJILLO. DOMINICAN 11.730 WRUL BOSTON. MASSACHUSETTS: Euro- 11.850 CEI185 SANTIAGO. CHILE: heard at 1:30 REPUBLIC: noon to 6 pm. pean beam. 6:30 to 8 am: 10:30 am 12.115 ZNR ADEN. ARABIA: 11:15 am to 1:15 to 6 pm: Mexican beam. 9:30 to 11.855 HAVANA. CUBA: enings. Pm Ia IIY. 9:15 am; 2 to 8:30 am; Caribbean 11.860 GSE LONDON. ENGLAND: Africa. 11:15 12.120 DZE BERLIN, GERMANY African service. beam, 6:15 to 7:15 pm. am to 2:45 pm: Routh America. 4 11 am to 5:30 pm; Brazilian sombre. 11.730 GVV LONDON. ENGLAND. to 10:15 pm; Mediterranean. 5 am 5:50 pm to midnight. 11.740 COCY HAVANA. CUBA; afternoons. to 3:45 pm. 12.175 MOSCOW, U.S.S.R.: 11:10 to 11:20 11.750 GSD LONDON. ENGLAND: South Amer- 11.870 WNBI NEW YORK CITY: South American aM. ica. 5:15 to 10:15 pm: Africa. 1 to beam. 7:30 pm to midnight. 12.190 LSN3 BUENOS AIRES, ARGENTINA; 7 :15 4 am: 5 to 11:15 am: 11:30 to 4:30 11.870 WOOW NEW YORK CITY: European beam. PM. pm. 6:30 am to 3 pm. 12.235 TFJ REYKJAVIK, ICELAND; Saturday.. 11.760 BERLIN. GERMANY: evenings. 11.870 KW1X SAN FRANCISCO, CALIFORNIA: 10 to 10:30 pm. 11.765 - ALGIERS; beard at 9:30 am and 1 New Guinea beam. 4:15 to 5:45 pm. 12.265 MOSCOW, U.S.S.R.: 11:10 to 11:20 - 11.880 VLR3 MELBOURNE. AUSTRALIA: 9:45 pm am. 11.770 DID BERLIN. GERMANY; North Amer- to 3:45 am. 12.270 HAVANA, CUBA; evening.. 12.445 -HC18 QUITO. ECUADOR; evenings. 12.967 WLWR2 CINCINNATI, OHIO; European beam, 7amta5:30 DM. 13.000 HDD QUITO, ECUADOR; 3:45 to 4:30 am. 13.022 WLWLI ' CINCINNATI, OHIO; North African RADIO beam, 6:30 to 8:15 am: 9 to 9:45 CABINLT5 am; 2:45 to 3:15 pm: 3:30 to 7 pm. 13.050 WNBI NEW YORK CITY: European beam. 6:30 am to 3:30 pm. 13.050 KNBA SAN FRANCISCO, CALIFORNIA: Fast Indic. beam. 1 to 3:45 pm 9:20 to 11:15 pm: Oriental beam, 4 to 6:45 pm; 7 to 9:05 pm. 14.540 PARIS. FRANCE; with Army - Hour for 14.560 WNRX NEW YORK CITY: European beam, 6 30 am to 4:30 pm. 14.800 WQV NEW YORK CITY. 14.950 PARIS, FRANCE: "Station Pared': - calls NBC and CBS with press reports. 15.000 WWV WASHINGTON. D. C.: U. S. Bureau of &rtdards: frequency. time and musical pitch: broadcasts continuously day and night. 15.060 GWG LONDON, ENGLAND. 15.070 GWC LONDON. ENGLAND. 15.105 TOKYO. JAPAN: heard at 9:30 pm. 15.110 - MOSCOW. ; 9:15 pm and - 11:15 pm; Sá5 to 5 : 15.110 DJL BERLIN,- GERMANY: African service. 11:10 am to 3 pm. 15.110 HCJB QUITO. ECUADOR: 430 to 6:30 pm. 15.120 DKSA "DEUTSCHER KURZWELLEN SENDER ATLANTIK." location not' disclosed; early evenings. 15.120 :RCA SAN FRANCISCO. CALIFORNIA; awaiian 11 pm. 15.130 KGEX SAN FRANCISCO,E beaCALIFORNIA;

15.130 NGEI SAN FRANCISCO, CALIFORNIA; beam, 5 to

15.130 WRUL BOSTON.. MASSOACHUSET Mex- Suggested by: ican to S: BERLIN. GERMANY. W. F. Onder, Kemmswick, Mo. 15.130 DXR7 "If the price is the same. I'll take this one." (Continued on page 527) 500 RADIO -CRAFT for MAY. 1945 Electrostatic Modulator By R. S. HAVENHILL Fig. I -The contact apparatus. Fig. 2- Electrostatic modulator. AT the June Meeting* of the High amplifier and measured on an output meter. In conclusion, the authors state that with Polymer Division of the American If a loud -speaker is used in the output the new apparatus, preliminary data indi- Physical Society at Rochester, circuit, the electrical charge on the speci- cate that both reinforcement and vulcani- New York, Messrs. R. S. Haven - men can be heard as a 300 -cycle hum. If a zation of rubber are electrical in nature and hill, H. C. O'Brien, and J. J. Rankin of the cathode -ray Oscillograph is used the support the formulation of an "Electrostatic Research Laboratories of The St. Joseph charge appears as a 300 -cycle wave. Contact Potential Theory of Reinforce- Lead Company described a new electronic The greater the charge, the greater ment." apparatus for measuring the electrical the amplitude of the resulting wave. By charges present on all substances such as the use of this apparatus in place of con- air, water, dust, paper, cloth, rubber, syn- ventional electrometers, electroscopes and thetic rubber, etc. high -gain D.C. vacuum -tube amplifiers, in- AUDIO AND THE EARS The authors state that not only can these stability and charge leakage in the grid electrical charges, which they term con- circuit are eliminated. A special form of AUDIO quality may reside in the ear tact potentials, be measured, seen on an this device, in conjunction with a mirror of the listener to a far greater extent oscillograph or heard in a loud -speaker, surfaced metal plunger reference electrode than has hitherto been suspected, according system (See. Fig. 1) for contacting the to F. Y. Gates, acoustical consultant at sample was used to measure the contact KSL, Salt Lake City. RUBBER STEEL TEST SPECIMEN-. potential of various rubber and GR -S syn- A series of tests, made with a standard thetic rubber compounds. Western Electric audiometer on 44 mem- LOWER LUCITE CHARGE PLATE A photograph and line drawing of the bers of the studio staff, revealed some Electrostatic Modulator are shown in Figs. startling facts. Of the 44 tested, only 23 GRID PLATE- FAN BLADE 2 and 3. In measuring the charge, it is not were "normal," or possessed of average necessary to contact the upper electrode hearing in both ears. Six were subnormal plate on the modulator ; in fact, the charge in both ears; six were sub-normal in one PLU G FOR on a lucite rod be ear. Eight were abnormal (in sense CONNECTIO N No.20 GAGE can detected at a distance the of TO STEEL OX of 15 feet from having more acute hearing AUDIO AMPLIFIE R the apparatus. The mi- than average) nute charge brought about by touching a in one ear ; and one was abnormal in both piece of rubber with the finger can also ears. This was based on an acuity not in be measured. excess of 20 decibels from normal average. The schematic diagram of the audio am- These differences in hearing have a BRACKETS FOR INDUCTION MOTOR plifier is shown in Fig. 4, along with parts direct and marked effect in radio produc- SUPPORTING MOTOR 110V -GOCVCLE values. It will be noted that the amplifier tion. The person whose hearing was ab- W000 BASE - , follows more or less standard P.A. System normal in both ears, for example, was a practice -is in fact an excellent P.A.- ampli- stenographer, noted for friendly but per- fier Fig. 3 -Plan of the electrostatic modulator. if the input is modified for mike or sistent "beefing" about the station's sound phone. A 6J7 completely shielded high - effects. They didn't sound real to her, gain input stage feeds into a 6N7 dual she but they have found a correlation of them tri- maintained. Her audiogram showed ode which acts as a second audio and phase that her acuity was unusually high, making with the tensile strength on both natural inverter. The and synthetic rubber compounds. grid circuit of the second her a natural for a technician. Today she audio is provided with a selector switch works in KSL's sound effects department, so that DESCRIPTION OF APPARATUS various values of grid resistance doing a bang -up job because she has much can be switched in. This .takes care of a keener ears than the average person. In this apparatus, which the authors call wide range of input an "Electrostatic Modulator," the electro- voltages and still ob- One of the station's producers frequently tains nearly full scale deflection on the clashed static lines of force established between output meter for with a control operator over the all ranges. placement of microphones in regard to the charged specimen and the grid of an The output stage consists audio frequency amplifier are or modu- of two 6L6 the violin section. of the orchestra. Their cut beam -power tubes operating in push -pull. lated at audio frequency by a motor driven The audiograms showed that the producer was fan output meter consists of a 1 Ma meter subnormal in hearing in higher frequencies, blade. The resultant alternating current and 6H6 tube rectifier. voltage is amplified and measured on a whereas the operator's hearing was ab- This amplifier was made to have a linear meter in the output circuit. In other words, response gormal in the higher frequencies. Thus, the D.C. electrostatic so that the output meter readings when the E string of the violin was barely charge on a charged would be proportional to body is converted into an alternating cur- the input voltages audible to the producer, it was unbearably and electrostatic charges on the test speci- harsh rent voltage which is amplified by an A.C. mens. The to the operator. Shown their audio- approximate gain of the ampli- grams, the pair were able to adjust to See Journal of Applied Physla, November. fier is 110 DB and it has a power output 1944, page their known strengths and weaknesses in 731. of around 20 watts. hearing. Another producer was shown to have decidedly subnormal hearing in certain frequencies. Knowing this helps him do better work-he now defers to an assistant Fig. 4 - The special in achieving microphone balance. amplifier. Input cir- All in all, two members of the KSL staff were cuit uses bias cell and transferred to entirely new duties as a result of Mr. Gates' study, while five must be completely key men improved their work by learning shielded. Any good to compensate for auditory irregularities. amplifier may be A slight, but very real, improvement in the adapted for this work. quality of the station's output is the result of the series of tests, which was originally undertaken as pure research. It may well be that certain radio "faults" can be traced to the listener rather than to the receiver! RADIO -CRAFT for MAY, 1945 806 New Radio Electronic Devices

LOU D- SPEAKER which assures positive contact giving interpolation values on terms of absolute pressure in very minimum of con- lines 500 ohms microns. The gauge is supplied University Laboratories, Inc. with the other than (from tact resistance. The contact gap 5 to 10,000 ohms at 6 milliwatts with a special Leeds and North- New York, N. Y. is .040 -inch on each contact; zero level). Test leads supplied. rup Micromax Strip Chart Re- THE AA -7 has a super -power therefore, the total contact ga, Dimensions, 5Yz inch x 394 inch corder calibrated directly in mi- audio capacity of 200 watts which breaks the circuit is .080". x 3% inch approximately. - crons. and is designed with 250 cycle The Grayhill Snapit Switch Radio-Cra f t The type "S" recorder for ul- low frequency cutoff for crisp employs a snap action principle tra vacuum contains two ranges clarity in voice projection. The which assures fast make and H -F CONDENSERS break as well as a contact pres- projection range of this speaker General Electric Co. is over 1% miles. sure of approximately 35 grams, making the switch practical for Schenectady, N. Y. use on D.C. current. ALINE of high- frequency The Snapit Switch operates on paper-dielectric capacitors, a .0625-inch movement of the available in ratings of 5000 to push button and carries a cur- 20,000 volts D.C., 0.01 micro- rent rating of 10 amperes at 115 farad, has been announced. De- volts A.C., and 2 amperes at 115 volts D.C. It is general practice on D.C. current to increase the D.C. current rating with a de- -0-500 microns for pressures crease in the voltage. Radio above 1 micron, and utilizing the Craft No. 500 thermal gauge in this range and an industrial type ionization gauge for the range MULTIMETER 0 to 0.4 microns. Accurate read- Weston Electrical Inst. Corp. ings may be obtained down to for corn- Projector is reflexed Newark, New Jersey 10 -s mm Hg. (.001 micron). pactibility and mounts a battery The type "S" instrument also of 7 Model PAH hermetically THE Model 695 Type I1, an veloped primarily for grid and features a safety circuit which sealed, shock and blast proof extremely compact portable turn on instrument, is plate -blocking service in the makes it impossible to driver units. UNIVERSITY test essentially a the ionization gauge until a vac- rubber damped rim construction rectifier type voltmeter which electronic- oscillator circuits of high- frequency induction -heating uum of 1 micron has been reach- effectively eliminates all trace of ed. Average life of ionization mechanical or acoustic resonance equipments, they can also be used to advantage in other high - gauge is 3000 hours. -Radio and rattle even at full power. Craft Construction is rugged, though frequency oscillator circuits of a similar nature. relatively light- weight, with TRANSFORMER swivel mounting bracket for The internal kraft -paper and easy handling and rapid orienta- aluminum -foil assemblies, corn - Electronic Components Co. tion. Projector may be subjected pactly arranged and thoroughly Los Angeles, Calif. to continuous severe atmospheric impregnated with a low -loss ANEW development in exposure -waterproof protective liquid dielectric, are hermetically transformers with self - coating and hermetic sealing as- sealed in rectangular metallic aligning, detachable mounting sure unaffected performance. cases. The size of the case cover studs allows an actual tolerance Perfectly adapted to marine or and the over -all dimensions of in mounting dimension that can bulkhead mounting where the capacitor is reduced by use exceed one-quarter inch and rugged dependability is a pre- of a single insulated terminal, eliminates rejects due to bad requisite. provided with a threaded termi- threads, leaks around studs, bent The AA -7 has many other nal stud. For the other terminal, or broken studs or changes in applications for the commercial a stud is provided for connection length specifications. and sports field, besides its war- to the case cover. A simple clip arrangement, time use. Installations in sta- The units are supplied with stamped from heavy gauge steel, diums, race -tracks, ball parks, removable footed -type brackets, cadmium plated, prevents the shipyards, freight yards, air- which provide for a firm four - stud from turning while it per- ports, fire departments, etc., will point mounting in any position. mits centering in two directions. find this AA -7 perfectly fitted to provides readings in decibels as The 20,000 -volt rating is avail- The stud can be moved (not their needs.- Radio -Craft well as in volts. Thus it is ideal able in two designs-one in a bent) in four directions to align for power level measurements plain case, And the other with with irregularly spaced holes and SNAP ACTION SWITCH in all types of sound -equipment cooling .fins to permit a higher is replaceable in the field with and in radio receivers -as well current -carrying capacity.-Ra- any round head machine screw Grayhill as A.C. voltage measurements dio-Craft Chicago, Illinois available. Radio Craft from 2 to 200 volts full scale. THE phenolic body of the A medium speed instrument PRESSURE GAUGES switch is round and measures with moderately damped move- Precision Scientific Co. only 74-inch in diameter by 1h" ment, Model 695 has a constant Chicago, Illinois high, measured from the top of impedance of 20,000 ohms. When the push- button to the end of the connected across any sound line, TI i E type "MR" instrument solder lugs. The switch is ranges can be shifted continually with a range of 0 -500 microns mounted by a 44-32 bushing, without varying line impedance. utilizes the new Televac No. 500 7/16" long and held securely by Eleven db ranges are provided, Thermal Gauge with specially two mounting nuts. from -4 to +36 db at zero on treated elements. Features of The fixed contacts are of fine the db scale. Seven a -c ranges latter include coated filaments silver overlay on phosphor from 2 to 200 volts also are to prevent "off calibration" pe- bronze. These contacts are available. riods due t ) water, oil vapor threaded and arc held securely A self- contained condenser, or other contaminating vapors, in place, the electrical connection available through a separate pin - increased sensitivity gained being made by brass screws jack is provided for blocking through use of two filaments in which also hold and secure the any D.C. component. The instru- both standard and variable tubes two solder lugs. The moving ment is calibrated for 500 -ohm of the vacuum gauge, all gauges contact which bridges the two lines with a zero level of 6 milli- are interchangeable without re- fixed contacts is also fine silver watts or 1.732 volts. Each in- calibration, and the user is as- overlay on phosphor bronze, strument is supplied with a chart sured of duplicate readings in 506 RADIO -CRAFT for MAY, 1945 RADAR POSSIBILITIES to the C.A.A. for this research. Cd«uee Poc&t-Se At airports the radar tower control will permit the tower operators to see on a screen the actual position of any and all aircraft within a radius of about 25 miles. This immediately detects any hazardous condition that might occur because of a pilot's error or a mechanical failure in the radio landing system. The radar operator can then adjust the controls of all out - bound traffic at a fog bound airfield, because CONTINUITY he will have complete knowledge of the exact position of all planes. The only way in which this can be done today is for a ground operator to determine the position TESTING of planes near his field by position reports radioed in by pilots. Now only one such report can be handled at a time and the distance estimates are not always accurate. The collision warning device is mounted right on the instrument panel of the plane. Here the radar screen will be of immense WESTON value. It will report to the pilot his own position in the air relative to other planes MODEL 689 as well as obstacles in his path, such as radio towers, beacons, water towers, and other objects that may be hidden from actual eyesight. OHMMETER With the collision radar instruments, pilots will find it easy to maintain proper distances from other aircraft while climbing to their assigned altitudes, or descending to an airport for landing. The complete Pocket -size but with typical WESTON de- landing approach will be handled by the pendability and ruggedness, Model 689 pilot while the control tower acts as a Ohmmeters are unequalled for checking monitoring agent through its radar screen. by resistance and continuity This will speed up landing and take -offs circuits in thick weather. method. Available in two types ... type lE with double range of 0 -5,000 ohms and eelalg1d111111g1a111a1111111111111I111111111IIC 0- 50,000 ohms, and type IF with double RAPID CONVERSION range of 0 -10 and 0 -1000 ohms ... ideal Cuntin u-d froh rage 4921 for motor maintenance. Entirely self- contained. Order through your local Much has Deco said about the recent Weston representative, or direct from . battery and portable radios using the 1.4- Weston Electrical Instrument Corporation, volt tubes. A word of caution on these sets. 618 Frelinghuysen Ave., Newark 5, N. J. We have used 10 -watt filament dropping resistors and had trouble. We now use 20- w'atters. The trouble was that the filaments would drop to about 1 volt after a few days' operation. Another method of hooking 1.4 -volt tubes WESTON l g& on bigger sets or portables is to use a 117L7/117M7 or a 117P7 and use a 450 -ohm filter choke in the filter section. Wire the tube filaments in order, from cathode of the beam -power pentode section to grouted through a 100 -mfd., 25 -volt condenser. Con- nect the tubes up in the order shown in Fig. 2. A system usable with a 25Z5 or 25Z6, 35Z5, 45Z3 or similar tube is shown in Fig. 3, which also shows the important bias arrangement. If tubes are not biased correctly the set will not work or will be inoperative. We use AVC on the 1A7, but LEARN BUILD YOUR OWN! the I.F. grid return goes to the negative or It's Easy positive filament of the tube, whichever RApiOsii,EL,NDISYSTE MS,ETC. and Fun gives the most volume. The INS may he *FAS7JREEZER very critical. We found sets getting locals N "Learn by Doing" Every amateur will be proud to iIO 12 -WEEKS Training bunt! tilla modern household only. Changing the grid return to its plus necessity. It Molt takes a few IN COYNE SHOPS time to or minus filament prong -either direct or Train now for a good boors of your spare We have fKcditle, build, and operates elect rire l l'; through a 500,000 -ohm resistor by- passed to job and a peace -tine for men with phys- on any voltage. 'l'here's fun di future in Radio -Elec- ical di.ilitiee. If blltlding and profit In using r I.!s ground -would bring a physical the sets to normal tronics. have handy Invzer. Haven 1111 tu 71, , . Free employment dyouisabilitr r y operation. service after graduation. Earn kind check heren NO EXPERT _p 4I.341:. while you learn. If short of n mil with KNOWLEDGE NEEDED This outline cannot go into coupon. detail on the money I'll finance your training ()llr plans are simple and easy to Inllew and this A or 12 many modifications necessary or desirable Send coupon today roe al details. _ cubic fout. size can be built of new Or I ed party. Ma 1 Si bill, cheek or money order for corn plots hp anti catalog. for the various types of radios brought in N.C.Lwla, Pr+a s my FO, e e c d ea Pl: School Dept. 55-14.s 500 S. Paulin.. St.. Chicago 12. III LEJAY MFG., 4S6 LeJay Bldg., Minneapolis g, Minn. for conversion, but it is hoped that it may Send f ree lieuS and details of Pay-Alt rCraduation"plm act as a guide to profitable set conversions, NAME that will make both the serviceman and the ADDRESS BUY WAR BONDS owner happy. CITY STATE

RADIO -CRAFT for MAY, I 9 4 5 507 Radio -Electronic Circuits

value is good for comprr i,ln AUDIO OSCILLATOR and vice -versa for expansion. Figure 5 The screen voltage has been found very critical and no This compact oscillator may changes whatsoever should be be used for A.F. generator pur- contemplated in these circuits or poses. It fits into a 4 x 4 x 6-inch in the audio filter components. cabinet. No danger of grounds The 100,000 -ohm series resistor or shocks exists, and very little in the output can be changed heat is generated as compared to alter frequency response, but to A.C.-D.C. sets. A voltage - was found best in my case. doubling circuit supplies about The input should not be too 20 volts to the oscillator tube. high for good fidelity. Output This is ample for fone use. from a record player or the sec- A small Figure I grid condenser helps ond detector of a receiver is give a pure note. Different tones about right. It is possible to are provided for by the use of MALODYNE RADIO "EXPRESSORr" obtain 30 to 40 DB change, and several values of condensers in that is plenty deviation from Figure I Figure 3 a switching arrangement. Note normal. DON LANGBELL, I have searched for some time that only low voltage filter con- With tubes and parts so Edmonton, Canada. densers are required by the 6H6 scarce, maximum use must be for a simple volume expander - compressor which would be ef- doubling circuit. made of each. Being unable to fective and not use a 6L7 which SPACE -CHARGE SET DORIS G. VINEY, purchase tubes for my portable, Glace Bay, Nova tends to be noisy and requires a Figure 4 Scotia. I decided to make a very small lot of parts. I wanted to use the set with maximum output. Two compressor for making tran- Good volume on all local stations is had from receiver dual triodes give me a four - scriptions, the expander being this which fits in a box 4 x 5 x 2. tube set result. more or less incidental. Either a 6P7G or 6F7 may be Note that the input is fed to the Plug -in coils are used, the screen grid, and that the control tuning condenser being 360 grid is used as a space -charge MMF. I am driving a 5 -inch element. speaker with too much volume. Two regular flashlight cells The set includes a stage of R.F., form the "A battery, and 3 penlight detector, A.F. and half -wave cells are used for the Figure "B ". The grid 5 power rectifier. If anyone can coil has 95 turns 1/" diameter, the tickler 35 improve on it, I would like to turns wound just above. I use a know. 365 Mmfd. trimmer (mica) 35 -WATT AMPLIFIER ALBERT MALINICIC, with one plate removed. Figura San Diego, Calif. 6 JIM BROPHY, This extremely Chicago, 35, Ill. compact and high- powered amplifier is suit- Figure 3 able for dancing, skating rinks SIGNAL TRACER and auditorium use. It has an Figure 2 used, the triode section being excellent frequency character- used to obtain signal voltage for istic to well over 8000 cycles. This circuit has been in use rectification. The .005 condenser Low -note response is also excel- for the past five years and has blocks the input signal from the lent. given an excellent account of D.C. bias. A small value is best itself. The output consists of two here, ta prevent distortion. 6L6 tubes in class AB, for The 6Q7 is used as the prod, When the DPDT switch is added volume and being completely the phase in- shielded but thrown upwards, the signal is verter uses two 6C8 tubes. Ele- for an A.F. and an R.F. bind- expanded; downwards, it is Figure 4 ments of each are paralleled ing post. is for The tube connected compressed. Filter values are added output. For home use in- to the A.F. amplifier (last two such that the compressor takes (The space- charge principle, put No. 2 is used, input No. 1 tubes) by about 3 feet of 3- hold almost immediately and re- in which the grid nearest the for an auditorium. No trans- wire cable which includes the leases gradually, while the ex- cathode is kept at a positive formers are required for high filament and plate voltage leads. pander acts more slowly. The voltage to increase space cur- impedance inputs. An ordinary Either a meter (plug -in) or the output control acts as master rent, was one of the oldest ef- push -pull output transformer speaker may be used at the out- gain. fects used in screen -grid tubes, may be substituted for the one put. The 5000 -ohm cathode circuit but has dropped into obscurity. shown. PVT. J. LEONARD KING ;, control is required for proper It is well worth some experi- Oceanside, Calif. operation of the pentode. A low GEO. CAMERON TREMBLAY, mentation.-Editor) Chaplcau, Canada. Figure 2 Figure 6 AF 3-4 FEET OF 2OR3- `JACK FOR PHONO INPUT OUTPUT T SPKR WIRE SHIELD CABLE 607 5PS.T . 6C5 A 6F6 \'R )

R JACK FOR AUDIO OUTPUT NEitet RF

- SHIELD AC 7 CABLE i I SW N 1T RF -TO DIODES AUDIO POT. 05 00025 AF RF 1t 508 RADIO -CRAFT for MAY, 945 !fl'.Ilno FUTURE ASPECTS OF TELEVISION IIsFREE!/IsNEP/i (C utrliuur'd Ir'o rays 485)

actors arc on the payroll continually -expense tripled, quadrupled. All this spells, if not bankruptcy at least dis ouragingly di- minutive profits for the tele- producer, and this multiplied by the hundreds of television CONCORD transmitters in operation throughout the nation. The solution to this problem is simple. It BUYING -GUIDE is "Transcription," that savior of so many radio broadcasters. Here our transcription is on picture film, 16 and 35 millimeter. The and REVISED LISTINGS contented audience didn't know it. They may have assumed that the actors they be- held were at that very instant performing before the iconoscope in the KWAD television studio. (Just as at last night's movie theater they all supposed those beautifully gowned stars and satellites were actually on Iadio the stage behind the picture screen!) But they had enjoyed that movie immensely, notwithstanding, and will go to another tomorrow night. The bogyman "Immediacy" is simply silly. We have long ago learned that screen entertainment can be every whit as good as a Parts stage performance -that a good screen play with top actors is miles ahead of one poorly HUNDREDS presented by mediocre players on the Just published! Concord's great, new theatre stage. And in television there can- OF PARTS LIKE THESE 68 -page Buying -Guide and latest 1945 not be a stage substitute. The show must Revised Listings of standard lines of be on a screen. The argument for Imme- -Many Available Condensers, Transformers, Resistors, diacy is therefore 100% eyewash. Misquot- Tubes, Test Equipment, Repair and Re- ing Shakespeare : "The Film's the thing, to Without Priority placement Parts, Tools, and hundreds show before the public or the king." The of other essential items. Page after page film will prove the salvation of television. of top-quality radio and electronic parts, It will enable it to pay its producers. It will and a special 16 -page Bargain Section avoid long, letter perfect, rehearsals. All offering hundreds of hard -to -get parts the refinements, the script -perusals, the cuts, at important savings. Mail the coupon the re- shots, the desired sequences, the in- now for your FREE copy, Use it to get stant flash to distant locales, the ingenious what you need -and get it fast -from ways for best telling of a story which the AUTO -LITE RELAY MIDGET POWER Solenoid relay similar to TRANSFORMER Concord. movie industry has been learning through 40 relays on autos with push- Fri. 117 volts, 60 cycles. years, is now at television's disposal. It is button starters. 8.5 to 14 Secondary 6.3 volts @ .5 Quick Shipment from CONCORD inconceivable that Television will fail to volts D.C., with heavy amps., 150 volts 14 150 CHICAGO or ATLANTA take full advantage double make contacts. M. A., 50 volts ß 65 M. A. of this knowledge, this 3$íse x 3!IS Size3t1/ e3 "x Concord carries vast stocks. Concord art, this film. 2 1/4". A14516. 21/2". A5959. ships to you at once from the nearest Then vanishes, together with a whole Spdally priced. $1.19 Your cost, shipping warehouse, CHICAGO or mare's nest of small crowded studio tech- ATLANTA. Concord invites you to nique, lighting, and camera difficulties -the consult our technical experts on special greatest bug -a -boo of them all -the yet non- 0,.. .,,.N,,.,ee,,. requirements. Concord can expedite existent, still unsolved television chain any "essential" order and speed action. broadcasting-whether by airplane- messed- Concord now serves the United States up aerial links, or by continental coaxials, Government, Institutions, Industry - burdensomely heavy financially. 6" PM SPEAKER TAPPED RESISTOR and can serve YOU, whether you want The solution is ridiculously simple -the Ideal for ACDC radios, Vitreous resistor, 90 wo"s, one part or a hundred. Telephone, wire, nation -wide P. A., and Intercom re- 6.4 ohms resistance tapped television hook -up is by the In or write your needs. And rush this cou- tin -can placements. 20steps of.32 carrier, and express. 5B700 0 $1x98 ohms ea. 58197. pon for the new 68 -page Buying -Guide. Scoff as you well may. Mr. Executive. Your cost, Your cost, each, 89c It's FREE. Time, and Old Man Profit -and -Loss will soon show who is right ! CONCORD RADIO CORP. Television with full natural color within two years after the end of World War II L'alayelie Pak& atp was offered as a possibility by Clyde M. NOOK-UP WIRE CHICAGO 7, ILL. ATLANTA 3, GA. Hunt, chief engineer of \\'TOP, in a talk g 20 solid rubber covered. 901 W. Jackson Blvd. 265 Peachtree Street last month. Red or yellow. 100.ft. coils. Specify "One or two years will be required for color. Your cost, engineers to prove by field tests the results each 49c , , FREE BOOK! of their laboratory work," the veteran radio NaiteetOonT engineer declared, "and for the television Concord Radio Corp. t1C0AA industry to convert manpower and materials 901 W. Jackson Blvd., Dest. RC -55,0 Ta from war work to the peace -time pleasure Chicago 7, Illinois of turning out your television receiver." Please RUSH FREE copy of CONCORD'S new 68 -pge Television transmissions in full color were Buying -Guide and Revised w pioneered by D,0 the Columbia Broadcasting KURMAN RELAY Listings, Just off the press. ^0 System in 1940, he said, AUDIO REACTOR and only the advent Type 223C34. S.P.D.T. con. Sealed. .15 Hy at O. D.C. Name of the war, which threw the nation's radio tact,. 2.5 v. D.C., 8 MA, 300 current. Con 2" e 2" s 2 1/2" research and manufacturing facilities into ohm coil. 584020. with 4^,,; 10. inserts. Address military channels, Specially 535010.n has delayed its normal priced .... 2.50 Your cost, $2 95 City State expansion. L

RADIO -CRAFT for MAY, 1945 509 H. F. HEATING AT A GLANCE Millions of dollars invested in H -F Heating give ample testi- mony for the future of the art. Industry and the home offer expanding postwar markets for the apparatus. By WILLIAM LYON

SEALING HEATING PLASTIC SEALING RADIO TUBE- PACKAGES PREFORMS GL ASS To GLASS BOMBARDING

THE art of Radiothermics is divided into two branches: Induction and Capacitative Heating. Induction Heating works at a much lower frequency than that usually employed in a capacitative rig: a wide range casually between 20 and 500 kc. It has reached a point of successful application during years of development the metal industries. Highly skilled labor isn't required to operate the equipment. Workers can be quite readily trained. In the accompanying illustrations stippled areas within MELTING METAL the field of the coils show the sections being heat -treated. CRUCIBLE 13E. Hardening metals is accomplished with speed and uni- rr WON'T formity. Gears and modern cylinder walls are two of the most glowing examples. Annealing and normalizing is ac- LONG, NOW complished in a fraction of the previously required time. All such applications as well as brazing and soldering have been put on the production line. They pass through the magic coil and, presto, the job is done! And melting metal is Soon, yes and probably sooner, almost as simple as flowing water. you'll see those "New Item" Aerovox Bombarding radio tubes is one of the oldest Induction cartons back on your jobber's Heating accomplishments. Intricate glass products reached shelves. There'll be many new items, the production line through the same process. Imagine an internally water- cooled radio tube being turned out by the ANNEAL /NQ new developments, new refinements older methods! The cost would be prohibitive. in Aerovox capacitors because of Fairly small portable rigs are used for metallurgical AND NORMALIZING war -time experience. And of course analysis and laboratory experiments. there'll be the good old standbys Capacitative Heating is also called Dielectric Heating because, unlike Induction Heating, its application is to again -types Uncle Sam rounded up non- conductive material. The frequency range is higher for the urgent needs of our fighting and greater than that employed in Induction Heating. men. The subject to be heated is placed between the two plates of a condenser. This is admirably illustrated in the accompanying sketch heating plastic preforms. While on the subject of plastics it is worthy of note that High Frequency Heat- Yes, it won't be long now. The mo- ing will "iron the bugs out" of future Bakelite radio cabinets. ment Uncle Sam releases the gigantic These housings have always been held to a wall thickness METALLURGICAL Aerovox production facilities, you of one -eighth of an inch because of curing difficulties. ANALYSIS can begin counting once more on just Strengthening ribs are rarely over one quarter of an inch thick and at these particular points you will invariably dis- the types you need in place of war- cover distortion in the walls. time "Victory" substitutes. Future plastic cabinets will have walls one quarter of an inch thick with ribs and bosses from fifty percent to double this thickness. Capacitative Heating will be responsible for Consult Our Jobber . . - the uniformity and strength. Almost any amount of heat at very high frequency can be applied when necessary for high speed of production, or Meanwhile, consult our local jobber necessary long, or short, curing time. about your immediate and future The illustrations showing package scaling and the de- requirements. Ask for latest catalog hydrating of chemicals will be (Continued on following page) BRAZING -or write us direct: AND SOLDERING

INDIVIDUALLY TESTED

AERO`.0X CORP., NEW BEDFORD. MASS., U. S. A. SEAL /NQ BONDINq WOOD DEHYDRATING HARDENING In Canada: AEROVOX CANADA LTD . HAMILTON. ONT. QLASSToMETAL ToW000o.QMETAL CHEMICALS METALS Wort: 13E.AOSr.,NEw Yon 16,N.Y. Cable: 'ARAB'

510 RADIO -CRAFT for MAY, 1945 (Continued front previous page) will be cooked in a matter of seconds with understandable from the foregoing. Bond- all of the major food values retained. ing wood and pressure glueing are especially In tomorrow's world the Electronics and important in the aviation industry. Further Radio Serviceman will have an ever ex- examples could be given in catalogue form. panding field in both the home and in- The field is enormous! dustry. Radio -Craft intends to run an article U. H. F. RADIO... Not the least engaging of future de- on an experimental 1 -Kw Capacitative velopments will be the application of Capac- Heater, with constants and constructional explained in itative Heating to the home kitchen. Meals information, in an early issue. ONE TEST YOUR SPARK PL UGS ELECTRONICALLY SIMPLE BOOK THE important role of the spark plug in each spark plug will be fired 100 times per without mathematics the performance of automobile and air- second for a six cylinder engine. The volt- craft engines makes desirable a simple and age in the transformer will rise to a maxi- Here is the key that opens the quick method of spark plug testing. Such mum just prior to firing, so that the door to a complete and profitable an instrument should determine at once oscilloscope beam will be deflected verti- understanding of UHF Radio -so the quality of all the plugs without neces- cally and drop sharply as each spark gap effectively and widely used in war sity for their removal from the engine. breaks down. The sawtooth horizontal de- and destined to play so mighty a Several methods for checking have been flection will have a frequency of 100 cycles part in America's peace-time de- made available recently. One originated by per second. velopments. Walter van B. Roberts of Princeton, N. J., A typical pattern is shown. Note that is especially simple and effective. an instantaneous picture of all spark plugs EASY TO UNDERSTAND Connections are illustrated in the sche- is obtainable at once, so that the perform- This masterfully prepared book matic. In series with the battery are the ance of each may be inspected. The se- takes the mystery out of UHF breaker points (shown as a switch) and a quence of firing is known and it only re- Radio. By simple steps, in plain ransfermer primary. A high voltage is in- mains to determine where the cycle begins. English, it proceeds from ordinary duced into the secondary and led through For this purpose any spark plug may be radio circuits to a thorough un- the distributor arm to the various cylinders momentarily shorted out while noting derstanding of the principles and o successively fire the corresponding spark which of the peaks is affected. applications of ultra -high fre- lu nne of which is shown . With little experience, the mechanic can quency radio. The author explains tell at a glance which, if any, plug needs it in person -to- person style. You'll replacement. The instrument should find be amazed at how easy it is to 2j wide use in airports, garages and manu- understand and to remember. facturing plants. s7 6 A new relay designed to respond to change in frequency has been developed by RADIO HORIZONTAL 'Westinghouse. It uses a single electro- U.H.F. DEFLECTION magnet and has two balanced circuits ar- CONTROL FMNAGENERATO.. ranged so that a small change in power factor makes large changes in current. SIMPLIFIED \Vhen two parts of a power system joined by Milton S. Kiver by a tie line are separated by lass of the Associate Instructor - connecting line, one section may not have U. S. Army Air Forces -Radio sufficient generating capacity to carry its Formerly Instructor in Radio, loads. The frequency will begin to fall off, Illinois Institute of Technology. perhaps so rapidly and to such an extent HUNDREDS OF ILLUSTRATIONS that the two systems cannot be resyn- chronized until perhaps a great deal of Hundreds of illustrations show every detail and aid in the A voltage divider across the primary important load has been dumped. To de- amazing clarity of the book. picks off a suitable voltage. This is applied crease the amount of load dropped and to Questions on salient points and to both sets of deflecting plates of the do it on a preselected basis instead of in chapter summaries fix the know- oscilloscope. In addition, the horizontal the heat of an emergency, is the function ledge in your mind. plates are influenced by a deflection control of the new relay. generator connected in series. The fre- Relays were built for this purpose be- COMPLETE ... PRACTICAL... USABLE quency of the latter is adjusted to the nth fore, but they have been much Covers Magnetron Oscillator, The complexed, Klystron, Transmission lines at the sub -multiple of the breaker point frequency, entailing the balancing of two opposing UHFs, Wave Guides, Cavity Reso- where n is the number of cylinders in the torques (i.e., two electromagnets) on a nators, UHF Antennas, UHF Meas- particular engine. single disc. The new relay is far superior urements, Wave Propagation -each As a numerical example, if the breaker in being independent of ambient temperature explained thoroughly and from the point frequency is 600 sparks per second, and in the degree of fineness of adjustment. practical, usable standpoint. SEND NO MONEY SERVICE PROBLEMS ON THE GYROPILOT American industry offers great rewards, now and post -war, to the man Repairs on the Sperry who knows UHF Radio. Fit yourself electronic gyropilots in to go places and do things with the use on the European knowledge this great book gives. battlefronts have been SEND FOR IT TODAY! FREE speeded up S00 per cent EXAMINATION. No obligation. by a testing panel recently developed by the company's engineers. -- MAIL THIS COUPON - -, The complete panel is composed of six com- D. VAN NOSTRAND CO. ponents, each for use in 250 Fourth Ave.. New York 3, N. Y. making a particular test. Send me "UHF Radio Simplified ". Within By turning up the analyzer 10 days I will either return the book or send and amplifier switch in you $3.25 plus a few cents postage. (If you one of these components, send remittance of $3.25 with this coupon the Army's pilot repair we will pay the postage. Same return privi- technician can get an lege, refund guaranteed. accurate check on an instrument's electrical system. Likewise, he tan Name..._ ...... _.._ check for breaks or PLEASE PRINT short circuits in the wiring by switching on to a City continuity test panel, while a vertical gyro Zone No .Stosse.. analyzer checks the gyro (if you know it) operation. A turn indicator tester has also been incorporated in the panel. O¡liciol U.S. Army Photo J RADIO -CRAFT for MAY, 1945 51I TRY THIS ONE!

EXPERIMENTAL KIT PHONO PICKUP (Figure I) Radio -Craft wants original kinks from its readers, and will (Figure 4) award a seven -month subscription for each one published. In looking By combining on one chassis To be accepted, ideas must be new and useful. Send your through my Radio - Craft file the other day I came a power supply with a number pet short -cut or new idea in today! of commonly used parts, a uni- across an article, "MOVING versal experimental unit results COIL PHONO PICKUP." and an unlimited number of ex- I used a discarded volt-am- periments may be made. "Vari- receiver, it is connected to the used also. The core is cut or one meter, sometimes used in auto able" points of a number of fun- 2 megohm resistor. side is removed, and the wind- ignition work. The stylus of an damental circuits are brought Among uses of this unit are: ings left on. Both windings may old phonograph reproducer is out to tip jacks and binding R.F. amplifier, audio amplifier, be connected together for added bound and cemented to the posts. It also includes its own R.F. oscillator, signal tracer and impedance, but is not necessary, meter pointer, after aligning soldering iron and testing olitfit! all -wave receiver. it being possible to use a trans- the stylus pivot point with the Since parts wear out quicker E. E. YOUNGKIN, former with a burned out pri- axis of the moving coil of the from handling than from use, Altoona, Pa. mary by connecting secondary meter. One or more rubber this unit conserves them. alone. bands hold the stylus in the neu- The sketch shows the general BATTERY CHARGER Windings are not shown in tral position (vertical). As idea. dimensions the diagram for the sake of sim- shown, a bracket is used to sup- No or parts list (Figure 2) is given since the experimenter plicity. The armature is of soft port the pickup weight without will have some of his own ideas You don't need expensive ap- iron to prevent its maintaining binding the meter coil pivots. to add. paratus to charge your storage magnetism. "C" is a copper STYLUS BONDED TO METER POINTER The writer prefers a chassis battery. You only need a 6 amp. rivet. Space between armature RUBBER DAN resembling an inverted table. charger bulb and a resistance. and core should he small for The legs are cut long enough to The latter may be a 600-watt higher efficiency. The armature clear everything mounted on top, cone heating element with one- could conveniently be one of the so that the unit may be turned half the resistance wire removed laminations cut out to proper upside down, stood on end or and the remainder stretched to size and shape. The optional side without danger of damage. fit the cone form. This arrange- spring "S" may be from an old A wooden frame with masonite ment produces a 5 amp. charge tire valve or dial spring. or plywood top will be found rate. If the entire resistance The upright for the pivot may convenient. Metal is impractical unit is used the charging rate also be made up from an old because of the number of bind- will be about 2 amps. An inex- lamination. ing posts and tip jacks to be pensive ammeter may be insert- The diagram shows the in- amour used. ed at A to indicate charging sertion of this unit into the plate FRONT 5101 The soldering iron is made rate. circuit of a tube. Other specifi- (Figure 4) from a tube base (4 prong) with cations are shown in the accompanying figures. The leads from the meter leads s o l der ed to filament /ITK A.G coil are brought out to the pri- prongs. One lead terminates in ;E.-L. 6 P JTORAGE BATTERY A Ford ignition coil secondary might be used with a few modi- mary of a suitable transformer a clip, the other in a metal tube which may be used as counter- which holds a flashlight cell T ` fications in design. GILES M. CRABTREE, balance for the pickup. A voice - carbon. To use merely remove 6A.UR CNARGER BULA coil -to -grid or a ribbon mike the 80 (thus automatically cut- Peoria, Ill. (Figure 2) transformer may be used. ting off . high voltage during E. E. YouNGKIN, soldering) and insert above tube OLD RECORDS Altoona, Pa. base into socket. To operate: connect clip C to one cell of the battery and as I some The second filter choke can be soon as the bulb filament glows, have very fine old disconnected and a speaker field records over 20 years old which DIAL POINTERS insert plug P into a 110 volt out- Necessity was the mother of plugged in. Also the filter con- let. When rectification starts I wanted to play in my record invention in my case. . . . I densers can be taken out of the remove Heat changer. Because they did not circuit and used with test leads clip. produced by have the spiral cut in them at needed a dial pointer on the rectification maintains the ac- end of a % -inch shaft to hold to check another set. tion. the end, I was unable to use these By suitable plug -in, phones or old records. it removably in place, so I HAROLD E. BULMORE, By soldered the pointer to a metal speaker may be used or the am- Nezcfane, Y. cutting a spiral in them plifier changed from resistance N. with a pair of calipers, sharp- tube grid clip and slipped it on to transformer coupling. Re- ened at one end, I am now able the shaft. This fits tightly and sistor "ST" is used for signal RELAYS to play them just as well as the is still removable. ones. Another type of pointer is tracer work. (Figure 3) new Don't use thick rec- Leads from the plug -in coil ords or you will wreck the rec- one which slides on the shaft socket permit hooking up a This substitute for a high- ord. player. This applies only to with a knob in front. This re- number of circuits. For audio, resistance relay uses a core those old records that are of the quires the circular type of clip. the 500,000 -ohm resistor is from an old audio transform- same thickness as the modern The pointer is fastened to the grounded directly. The con- er or filter choke- with the core ones. clip and slipped on the shaft. denser across it is .0005 mfd. cut as shown in the dotted lines. L. S. SEAMAN, JAY J. LUCAS, For use as a signal tracer or Earphone pole pieces might be, Camas, Wash. Robins Field, Ga.

Fig I, below-The multi -use test layout. Fig. 3, right -Relay made from junkbox parts. BALANCING WEIGHT ( SOLDER) SOLDER LOCK NUT TO LOOP CLIP 7'0 rAP LOOP PIVOT ARMATURE ` _ 0 0 OLA METAL UPRIGHT POSTBINDING WOOD WOOD I BASE SOLDER UPRIGHT - CENTER FL-0 PUNCH DENT -DRILL

O CARBON RP? BEND INSULATED !/ "DING POSTS ARMATURE HERE T ON O PLAN GINOING Mfrs O rePJACKS as SOLDER/NQ UNIT

512 RADIO -CRAFT for MAY, 1945 POLICE RADIO ON V. H. F. (Continued from page 487) PORTABLE POWER PROBLEMS ununnumum:uuurtnnum;rnuoca; rum; uaimmonmimmmnnnmunoominmai ,.,ra i that a frequency in this particular section would be far superior and more easily controlled from an interference standpoint THIS MONTH -FISHER CARBANALYZER (from other stations) than any other frequency made available for experimental or operational use for law enforcement." Previous tests of the use of the 118 Mc. spectrum for two-way radiotelephone communications between a central control station and roving mobile units have also been conducted in Chicago and in Cleveland, Ohio. In Chicago, with a central control station located at the plant of the Galvin Manu- facturing (Motorola Radio) Corporation, and a remote control station, over two miles away in the Graemere Hotel, two -way radiotelephone communication was successfully maintained between three mobile units operating on the North, South and West sides as well as in Chicago's Loop Talk -back was clear and intelligible up to distances of twenty miles. At no time, regardless of the location of the roving mobile unit, were any of the difficulties encountered that were so common on the 30- 40 megacycle band. Car -to-car was clear up to five miles and reception faded, station-to- car, after twenty -five miles.

TIME -SAVING carbon content analyses of steel samples -from molten metal to report-take only five minutes with the portable, battery-powered Carbanalyzer, produced by the Fisher Scientific Company. Leading steel firms employing open hearth or electric furnaces quickly make carbon deter- minations of each batch, achieving close control of quality.

CARBANALYZER, powered by Burgess Industrial Batteries, operates over a range of .05% to l.50X carbon content and is sensitive to a change of ± .005%. The power requirements of Converter which picks up 118 -Me signals and modern control and test instruments are fully met by feeds into a receiver in the 30-40 Mc band. Burgess Industrial Batteries -the standard of quality for all commercial uses. The types you require may not be In Cleveland, 15 -watt mobile units were immediately available today since industrial battery produc- installed in part of the Yellow Cab Com- tion is greatly reduced by urgent war needs. pany fleet with a 15 -watt transmitter located to downtown Cleveland. Here also the same Burgess Battery Company, Freeport, Illinois successful reception and transmission were obtained with distances covered comparable SUPPORT THE 7TH! BUY YOUR SHARE TODAY! to the power used and the height of the antenna. The tests in Cleveland are still continuing but closely conform to those made in both Chicago and Miami. From the above the following conclusion i BURGESS BATTERIES may be made. The use of the 118 -Mc. spectrum for 1 I cu mummnmmmmunummumimmnnmmnmmuminomm moirai mmmommmmnmmmummnnmmammumnmmmnummnmwmununmoummmmoun immual_Ag_o operated two -way mobile radiotelephone systems is practical, efficient and more sat- KLYSTRON CIRCUITS (Continued from page 480) isfactory than on any other wave length mmIInnnmimmimnnnnnnuuunmunnnnnnnmmimimemmmnmmmmununumMO so far used. It is further concluded that the grid, the current can be made to increase Lion. Most methods give a combination of results of these successful experiments have when the buncher is excited. If the de- amplitude and frequency modulation from opened up a whole new series of hitherto tector grid is sufficiently negative, no elec- which either type may be "extracted" by unused wave lengths for two -way radiotele- trons reach the collector plate at all, and using combinations of modulations by phone service available for police and fire if it is sufficiently positive, practically all acceleration voltage and beam current in departments, public utilities, industrial con- of them may do so. proper proportions and phases. cerns, trucking fleets and others desiring Mixing may be accomplished by intro- By tuning the buncher to one frequency, such service. ducing a signal to one of the resonators and the catcher to a harmonic, a fre- and connecting a local oscillator to another, quency multiplier is had in which the if high intermediate frequencies are used. efficiency decreases to 48% at the 20th Single resonator mixing may be accom- harmonic relative to an assumed 100% for The year 1945 has been declared the plished if the intermediate frequency is the first harmonic. twenty -fifth anniversary of broadcasting by narrower than the bandwidth permitted by More material is becoming available the National Association of Broadcasters. the Q of the tube. concerning these important tubes, and when Special programs and series will be broad- Klystrons may be modulated in three they are more available, their versatility cast during the year, to observe the anni- different manners- amplitude modulation, will make them very important for count- versary. frequency modulation, and phase modula- less applications.

RADIO -CRAFT for MAY I945 513 See Either or Both of These 2 New Books FREE ELECTRICIANS HANDBOOK ELECTRONICS

Here's a BRAND NEW. up to the minute ElectriciansBand- book. A book electrical workers need for reference on the job. Over 5,000 electrical facts- wiring diagrams -essential elec. trical formulas- latest code rules,tables, charts, and wirinif methods. Includes In- dustrial Electronics data. A practical book every electrical worker can use every day. Pocket size, flexible leatherette cover to stand every day usage. Electricians Handbook See this book FREE for 7 days. Its a book electricians have been Operator's is at beside the five -foot p.._i waiting for -360 pages Mein picture shows the model propeller. position "A" "chuckfull" of VALUABLE model. The insert is a top view which gives a more complete picture of the operation. ELECTRICAL DATA that can kb earn it's small cost many times over. Price $2.76, payable after Cs 7 days' FREE inspection. t ELECTRONICS Electron Robot Makes Propellers GET The QUICK Way PAY A GIGANTIC electronic "pantograph" THESE get and operates to shape ship propellers, with NOW and in the futurecytou of A steel finger mov- BOOKS should know ELECTRONICS. a 700% saving time. It is the big pay field for Elec- ing lightly over a wood or plaster model trical workers. Coyne's new 7 DAYS 400 page book - just off the guides the huge cutting arms. which shape >, press lsespeclallywrite the propeller. to its curves, this FREE l ten for busy Owing Cis wh o npcpractical work formerly could not be fully auto- I LrP^' "on the job" simplified electronic information. This is no tezl matic, and a great deal of time -consuming hook - it's a practical book written hand work was necessary. Two weeks was for practical men. Electricians should find this book a "GO L DM I N E" of the normal time for finishing a large pro- EASY TO FOLLOW electronic data. peller. Now it can be done in two days. Priced at only $s 96- payable after 7 days' FREE inspection. The apparatus may be seen clearly in the photographs. The model is mounted ÿ;l Send No Money horizontally on a disc between the two rk columns. Fingers contact its surface. These See both of these books FREE for 7 days. tlere's my offer. I'll send either affect a sensitive instrument, called by or both books to you for 7 days' inspection at my expense. If you de- Westinghouse a "Silverstat," which regu- cide you don't want the books, send lates the speed of the electric motors. These them back and you owe nothing; if you keep either or both you can outlined motors then drive the cutting tools. the coupon. Don't delay- SUI'PLY LIMITED dun The regulate the motors in to paper restrictions send that coupon NOW electrons - such a way as to produce a variation of their speed and to make them operate either forward or in reverse. This causes N.C. LEWIS, President the cutting tool to move in exact propor- 1 500 S. Pauline Street. Dept. 55.T1, I CHICAGO ta, ILLINOIS tion to the movement of the tracer finger,

Send me the books checked y free duplicating the motion to within one -one- trial. I'll either retors them inbe14'7.-y.;-", pay fo Westinghouse Photos them according to the plan l select asouthned here hundredth of an inch of the correct con- tour. 1.Q. Propeller is shaped by large cutting burrs. O c.7e+re $2.75 after 7 day H FREE examination. Electronics for Electricians Radiomen O1 Vol. Price f4 9t afterr 7 days Free amination $ SPECIALPAYMENT PLAN If you keep both books you can send $2.00 in ARMED FORCES TRAIN POSTWAR TECHNICIANS 7 $7.70 is paid. I days and pay $2 monthly until STAFFS for postwar television and FM ditions of Pacific war, where they were NAME stations will be available from the ranks compelled on occasion to take over "un- ADDRESS- of army- and navy -trained technicians, de- workable" equipment and make it operate CITY 2ons____STA7E. clared Commander William C. Eddy, U. S. efficiently, the trainee -technicians emerged O If books sent C.O.D. -you pay port. over and ñ çew.antprice re Navy (retired) at the recent Television victorious tropical deterioration Same 1W ásatisfiction guarantee. Broadcasters Association conference. lack of parts in every case. Such training is Their intensive course of training has ideal for men who will have to face new given these men a complete theoretical problems in a new technique. grounding, and they have been put to work It is the responsibility of television and on apparatus which works on the same related branches of the radio industry, principles as television equipment. This warned Commander Eddy, to provide op- combination of intensive theoretical and ex- portunities for the utilization of this talent tensive practical training has produced men at the end of the war, to the'mutual bene- who have seldom been stumped, said Com- fit of the industry and the ex- servicemen mander Eddy. Even under the difficult con- concerned. 514 RADIO -CRAFT for MAY, 1945 SOUND UNITS AND SOUND RIDER VOLUME XIV COVERS 1941 -42 RECEIVERS RATINGS (con/mu/fed jrwn page 488) stuimmumummumusimmonommmommummainonemnia,. .,,._ to produce sound levels in db at fixed distances from the speaker. The sound levels are referred to the standard zero db sound level. One thing which must be kept continually in mind when referring to sound and electrical db is the reference level. Both are computed using the same basic formula but their zero levels, .0002 dynes per square cm. for sound and 1 milliwatt in 600 ohms for electrical energy, are different. A TYPICAL EXAMPLE To illustrate how these various ratings may be correlated in a sound system let us consider an example.

1 have always had a warm temporaries who just couldn't take íf Fig. Points measurement in a system I- of spot for "Duffy's Tavern" any longer. The trouble is that our because the first program serviceman hasn't heard that Rider Referring to Figure 1 we see the elements ® of a complete sound system. Assume we carried was its first spon- Manual Vol. XIV covering 1941 -42 re. wish to pick up sound on the high fidelity sored broadcast. Ah, I was young, ceivers has been published. So, he is microphone and reproduce it over the loud- strong -and what a tone I had in those wasting a lot of time trying to diag- speaker with a sound level of 100 db. at a days. nose the ills of 1941 and 1942 sets point 30 feet ahead of the speaker. We know Today, however, after the beating when the servicing data in Volume XIV that this particular microphone produces an I've taken during the past few years - could lead him right to the causes of output level at the point A of -55 db. below well, as "Archic's" song suggests "Leave the troubles -and quickly. Us Foce It." I'm in bad shape. I ought to If your jobber is out of Volume XIV the zero level of 1 milliwatt. The standard other number please bear with microphone is to a preamplifier be in the radio repair shop this very or any connected paper restrictions, you know. having a voltage gain of 25 db. Thus with minute, along with many of my con. him. WPB the input voltage level to this preamplifier of -55 db. and a voltage gain of 25 db. we have an output level of -30 db. at the point B. The volume control is the type RIDER MANUALS 114 VOLUMES) The Meter at Work which offers no loss when turned full -on Volumes XIV to VII .. 12.50 each volume An elementary tent on meters ... 2.00 but to allow a range for normal operation Volume VI 950 The Oscillator at Work How to use. test and repair 2.50 we must turn it to a point where the voltage Abridged Manuals 1 to V (I vol.) 15.00 loss is 25 db. Thus at the point C we again Automatic Record Changers Vacuum Tube Voltmeters tc,h theory and 2 50 have a level of -55 db. Our next amplifier, and Recorders 7.50 practice Automatic Frequency Control Systems commonly called the "Voltage Amplifier," OTHER RIDER BOOKS YOU NEED -also automatic tuning systems . .. . 1.25 has a voltage gain of 55 db. Thus at the The Cathode Ray Tube at Work A -C Colculotion Charts output of this amplifier (Point D) the Accepted authority on subject 4 00 Two lo live times os last as slide rule . . . 7.50 Voltage level is "0" db. One of the given Frequency Modulation Hour -A- Day -with -Rider Series . requirements is that we produce a sound Gives principles of FM rodio . . 2.00 - "Alternating in Rodeo Reccl.ers by Signal Tracing On Currents "- level of +100 db. 30 feet from the loud- Servicing On "Resonance S Alignment speaker at Point F. The amount of electri- Basic Method of rodio servicing 4 00 On "Automatic Volume Cc,.'- - cal energy necessary at the voice coil of the Servicing Superheterodynes 2 00 On "C .0 VoIroge 1.25 each loudspeaker (Point E) to produce this sound level will depend on the design of the JOHN F.RIDER PUBLISHER, INC. 404 FOURTH AVE.,N.Y. I6, N.Y. speaker used. Escort Dndvon: RoderIrJeroatronPl CorP. 13 E. 401h Street New York City CaLie AR LAB This information is obtainable from the manufacturer in the form of tables giving the wattage required for a given sound level [U copt,ok/e at a specified distance from the speaker in the presence of a given amount of background noise. RIDER MANUALS IN 14 VOLUMES For the example we choose a loudspeaker with a voice coil impedance of ten ohms and voltage at our Power Amplifier input. We Thus our Power Amplifier is required a requirement of ten watts input to produce 40 necessary sound output. now have the voltage input to our Power to have a voltage gain of db. to supply the Our Power Amplifier .78 output. Amplifier must therefore produce ten E _ and the voltage output the needed watts E 10. All have been on the 10 = of our calculations in this -ohm circuit. This is because law we basis of voltage. common From Ohm's calculate that the CALCULATING THE GAIN it is more practical to measure voltages at voltage at the amplifier output is Our output circuit is a 10 -ohm impedance. different points in a sound system than E = VP.XR Therefore we will insert an imaginary trans- power at the same points. Only at the Power or E = 10 Volts at Point E. At the input former to make it possible to measure the Amplifier output was it necessary to con- to our Power Amplifier we have a voltage output voltage across a 600 -ohm- impedance sider actual power and this in turn was level of 0 db. Our standard reference level like the input. See Fig. 2. Since the voltage converted to equivalent volts for further is one milliwatt in 600 ohms. From Ohms ratio in a transformer is equal to the square calculations. law E = VPXR = V.001 X 600 =.78 root of the impedance ratio, 600-10 or 60 -1, The basic sound level of .0002 dynes per volts. This voltage E = .78 is the actual the primary voltage is the square root of square cm is an accepted standard while 60, or roughly 77.5 volts. its electrical counterpart, 1 milliwatt in 600 TURNSM4770 7.75J 77.5 ohms, has not been universally recognized. 20,08,, a-7.5 The decibel rating is then 20 log -. If equipment ratings are based on other 20,o9,,O+4046 ,p o EI(7n-10`s .78 reference levels, care must be exercised in For practical purposes it is convenient to computations. It is hoped that eventually round this off to 78/.78,\ or 100. Since the all other zero levels except 1 milliwatt in logarithm of 100 is 2, the decibel rating is 600 ohms will be discarded in the interests Fig. 2 -Gain calculations for an amplifier. 20 x 2, or 40 decibels. of standardization. RADIO -CRAFT for MAY, 1945 515 Progress In Invention Conducted by I. QUEEN

OVERLOAD PROTECTION U.H.F. F.M. DETECTOR Patent No. 2364.136 Patent No. 2.367.764 DELAYS are often used for protection of vacuum optical characteristic, of ultra -high fret tube circuits, but they have the disadvantage THEquencies are made use of by Warren R. Ferris of throwing the circuit out of operation even on in his invention relating to FM signal reception. slight, temporary overload. G. L. Graveson of Amityville, N. Y.. and C. R. Keith of Maplewood. N. J., have developed a method using a ther- O ZONES OF MAXIMUM mistor, which operates only when the tube plates FIELD STRENGTH WITH SELECTIVITY (CHANGE reach a temperature. is espe- predetermined It WITH FREQUENCY) cially useful in connection with such circuits as a ZONES OF ZERO FIELD class -C oscillators. STRENGTH The thermistor (T) resistance varies with tem- a ZONES OF MAXIMUM perature. It is placed in shunt with a leg of a INCOMING FIELD STRENGTH BUT phase -shifting bridge, and is positioned adjacent PLANE NO SELECTIVITY WAVES 100 to the tube plates. Radiation from the latter NOT CHANGE WITH causes an out -of -phase voltage to be applied to FREQUENCY) the rectifier grids, decreasing the voltage output. .)q)9) As soon as normal conditions return, the grids RECEIVER are in phase with the plates (of the rectifier 10,000 PARTS immediately tubes) and a normal voltage output is again available on priorities. available.

Incoming waves strike a metal baille containing slits. Their width may be equal to the wave SAME-DAY SERVICE length of the signals and their spacing several times greater. As a result of spreading. cylindri- Trained expeditors fill your cal waves are formed beyond the baffle, resulting in weakening and strengthening of energy at order the day we receive it. different points, as shown. Positions of maximum and minimum strength will vary with the frequency. The system is described as it would be used SINCE 1922 we have been with waves in the order of one centimeter long. but is adaptable to longer or shorter waves. known as reliable and A dipole is placed at a point of maximum responsible jobbers, wholesalers signal at a frequency representing maximum F.M. deviation. Then as the signal varies in fre- and manufacturers, of radio quency each side of the carrier, received signal amplitude changes and may be detected by any and electronic equipment. U.H.F. means. A large number of slits and dipoles may be used to increase sensitivity to the extent desired. Warren R. Ferris, East Orange, New Jersm SENSITOMETRY assignor to Radio Corporation of America. Patent No. 2.361.447 photographic work and film recording film TWO WAY AMPLIFIER INemulsions are compared and studied by means ire of densitometers. This circuit plots an H & D Patent No. 2,366.011 Wu) curve directly on an oscilloscope screen per- two -way transmission must take place mitting rapid determination of film characteris- WHEREas in long distance telephony. special precau- tics. It is the invention of Judd O. Baker, Med- tions must be taken to avoid feedback and oscilla- ford Ickes, N. J. lac The film is secured on a drum D inside of Wlevision 13, YORK which is mounted a photocell. One film edge A NEW -5 I. a 13 be AYE. Din N. overhangs so that light from bulb may 100 SIXTH NEWARK. focussed upon it. On the same shaft is mounted MASS. BOBION, the movable contact of a potentiometer P (see illustration) . The photocell output (determined by the film transmission) is amplified and connected to the oscilloscope vertical plates, while the potentiom- The WORLD'S LARGEST eter output goes to the horizontal plates. horizontal beam displacement (sweep) is linear RADIO SUPPLY HOUSE and depends upon the potentiometer arm, while the vertical displacement corresponds to the film transmission. As the motor rotates a density urve is traced out by the electron beam on the tube screen.

Originators and Peacetime )larkeietrs tion because of interaction. H. L. Donaldson of Chicago has a simple solution to this problem. of the celebrated I MOTOR A super -audible oscillation alternately biases L J each of the two amplifiers shown. In other words. channel 1 operates while Channel 2 is cut off during one alternation of the 20.000 cycle oscillation, and vice versa during the next alternation. Thus no feedback can occur. The high frequency jc/'a4'e//e hWiö does not interfere with the audio frequencies being transmitted. While intended for telephone use. in the man- Frite today for our bargain ner of the familiar two-way repeaters. this circuit might well be adapted to a line or carrier office flyers and special bulletins. intercommunication system.

516 RADIO -CRAFT for MAY, 1945 BROADCAST EQUIPMENT G -E UNIMETER... mlmlimdf...... peaks, due to cut -off. The result is that both THE UM -4 is an invaluable instrument for service work. Not tubes work at a much greater proportion of is radio industrial their ratings, with increased efficiency due only it useful in common and applications, but to full -load operation. also for the higher voltages employed in cathode -ray tube work and This cannot be accomplished merely by the very high voltages encountered in television. Special jumbo connecting the tubes in parallel and apply- ing unequal values of bias, because the out- prods are provided for protection on high voltage work. Two-tone put of the peak tube would not combine scales permit quick and accurate readings. Write: Electronics in proper proportion with that of the car- Department, General Electric, Schenectady 5, N. Y. rier tube. By means of Doherty's ingenious circuit, the combination does become addi- Electronic Measuring Instruments tive. Distortion in this system is rather high, but by the use of inverse feedback it is possible to meet all the requirements of high -fidelity broadcasting. GENERAL 3 ELECTRIC Today's broadcast engineer has many opportunities to encounter this circuit, as it has been incorporated in all Western Elec- tric broadcast transmitters of 1000, 5000 and 50,000 -watts power since 1938. A modified form of negative feedback as applied to broadcast transmitters permits a high- fidelity modulation envelope by reducing audio distortion and noise created within the transmitting equipment. Hum and noise may be reduced to as low as 65 db below the 100% modulation level (even with A.C. on all filaments) a value which is 15 to 25 db better than the FCC standards of good broadcast engineering practice. Harmonic distortion may also be kept well within the FCC minimum, usually to around 2 or 3% at 100% modulation. The application of degenerative feedback to broadcast transmitters is similar in principle to its application in audio amplifiers. It is well known that if a portion of the output signal of an amplifier is returned to the input and combined with it in reverse phase, the gain of the stage is reduced. Furthermore, if the feed -back signal contains distortion and noise com- AVAILABLE NOW! ponents not present at the input, it will FOR tend to cancel such noise and distortion, DEALERS & SERVICEMEN provided that it reenters the circuit very nearly 180° out of phase with the input IMMEDIATE SHIPMENT signal. FROM STOCK! One means of accomplishing this in radio- No Priority Needed for telephone transmitters is to apply the feedback signal to a linear rectifier designed Dealers and Servicemen for minimum phase shift, thereby devel- PROVIDES EASY ACCESS TO COM- oping an audio signal which is an exact reproduction of the modulation envelope. PONENT PARTS ... FINGER -TIP This is then introduced into the first speech CONTROL amplifier in the same way as any other The new Acro Chassi= Cradle has been audio -frequency feedback. designed and built to help busy industries smooth out production. simplify and speed When operating a transmitter in this assembly and inspection. and hasten de- manner, it must be borne in mind that the liveries of their products. It will definitely effect important economies in time. mate- gain of the audio system is reduced by rial and man- ACRO CHASSIS CRADLE the amount of degeneration used. Thus if power. One the feedback is lost, the faders must be example of how the Cradle is used WITH STANDARD CLAMPS to great advantage is illustrated at left. $4.95 readjusted to prevent overloading. Photo shows the Cradle holding an elec- STRAIGHT CLAMPS for sub- panels and An alternative feedback arrangement trical assembly in an easy -to- get -at posi- other flat pieces :-These clamps also enable which is applicable only to unmodulated tion for quick inspection or repair. An you to use your cradle for a reel. $2.50 per amplifiers consists of merely coupling the component parts and connections can be pair. Additional STANDARD CLAMPS checked without danger of damaging tubs, $2.50 per pair. output and input tuned circuits in such a coila and other delicate parts, as so fre- manner as to cause degeneration. The main quently occurs by dropping and bumping RIGID CONSTRUCTION object in this case is the reduction of in- during More ordinary handling. than that, The Acro Chassis Cradle Is made of cadmium plated nate noise, as no modulation is present. units can be assembled much more rapid- steel and White metal and consists of the support- In either case, when the voltage ly and with greater accuracy with the ing legs and locking clamps that hold the wank In fed back new Cradle, because it allows workers to a viselike grip. Adjusts to any position by anger. to the input is some value other than 180° use both hands, and permits them to po- tip control and is equipped with an automatic stop. out of phase with the input, less cancella- sition the working area to their convenience. Its rimple. sturdy construction assures ye:u- .n trouble -free service ... Obtain at least me of t - tion of noise and distortion will result. This Work can be rotated and locked in posi- hscost units at once.o Don't wait -act now -Send is particularly true when the phase shift is tion by a "flick" of the finger. your order today! less than 90° or more than 270° ; and when the phase difference is near 0° or 360 °, stabilizing circuits are required SERVICE CO. to prevent RADIO ELECTRIC Phone: - strong oscillations in the entire transmitter. OF PENNSYLVANIA Neutralization is our next topic for dis- LOMBARD 6177 cussion, to be followed by a consideration N.W. COR. 7th & ARCH STS. LOMBARD 1951 of modulation equipment. PHILADELPHIA 6. PENNA. RADIO -CRAFT for MAY. 1945 517 How to Repair Electric Clocks

By HOMER L. DAVIDSON

WITH a few inexpensive tools, the points are the only needs. The most fre- average radio serviceman can re- quent repair on electric clocks is the 110 pair most of the electric clocks volt A.C. power cord. This generally breaks brought into the shop. Practically at the male plug or where it enters the all of these clocks are based on the syn- case, resulting in a sharp bend. If by visual chronous motor. The non- seifstarting motor inspection the cord shows no sign of weak- requires a twist of the wrist to give it the ness, we can place a metal screwdriver on starting torque. They will then run until the lamination near the rotating armature. the current goes off and will not start A small vibration should be felt if the again but will heat up and hum. The most A.C. is getting to the field coil. expensive clocks have a starting winding If by chance the A.C. power cord is which consists of two copper "shading good, the trouble must lie in the connec- rings" located in the leg of the iron laminations from cord to field or an open field tion. These type of motors generally con- coil. tain a sealed unit. The field coil can be checked for con- The sealed unit should be sent in to the tinuity in the same manner. An open clock manufacturing company to be re- solenoid is generally caused by excessive paired. The oil in this unit may run out heating. The solenoid should always be during the summer months and sometimes will chill and pack during cold weather. When shipping this scaled unit to the manufacturer, be sure and give all model numbers, voltage numbers and correct frequency (60, 50 or 25 cycles) and address. In handling the elaborate clock cases, the repairman should be very careful to prevent scratches and marring of surfaces. THAT GIVES YOU - Especially great care should be exercised where the clock is built in grandfather - clock cases, lighthouses, statues and models, reer y tiring! ships and chimes, etc. The latter generally triggers a striking arm upon long -tone * Design proven by over S years production of thousands of this chimes which ring the half- and full -hour model. periods. A -A.C. terminals. B -Field coil. C -Alarm * Operation as simple as ABC. Mul- It is best to have at hand two small striker reed. D -Alarm release. F -Bell. tisection push -button switches do screwdrivers, side cutters, long nose pliers, all work. Simply "follow the ar- soldering iron and a few inexpensive test- rows" for tube checking. No ers. A continuity tester will check the field removed from the lamination assembly be- roaming test leads for the multi - is removed from the meter. or transformer winding, alarm solenoid and fore the brown paper A.C. line cord. This simple tester is shown windings. All of the turns are uncoiled un- * Open face wide cal. 4i/a -inch is found. connection is rugged meter in Fig. L It is always handy to have a til the open The built especially ter If this tester -500 microampere sen- small ohmmeter around for the above soldered, taped and rewound again. these sitivity. checks also. windings are burned, they should be re- * Each AC and DC range individu- wound with new wire of the same size. If ally calibrated. TROUBLE ANALYSIS the solenoid sets up a magnetic field, we suspect the sealed unit shown in Fig. Professional appearance. Solid following trouble should then golden oak carrying case. The indications 2 (if it is a selfstarting clock). It could be tested as follows: Guaranteed Rectifier. also be the rotating armature in the non - 1- Visual indications. selfstarting clock. 2- Magnetic field check. A common fault is bad bearings on each SPECIFICATIONS 3-A.C. cord inspections. end of the revolving armature. In the MICROAMPERES: 4- Sealed unit and bearings. cheaper clocks, these are nothing more than 0.500 Actually the first thing we notice about bakelite bearings which are molded in the DC MILLIAMPERES: 0.2.5. 10.50 -250 the clock is that it isn't running and our case. These bearings cannot be replaced. DC AMPERES eyes quickly check over the assembly. You The clock is so cheap that repairs would 0.1.10 will usually find that small simple repairs cost score than it is worth. The better - DC VOLTS -1000 OHMS PER VOLT: such as frayed cords, broken cord connec- built clocks have metal bearings and should 0. 5.25100. 250 -SOO- 1000 -2S00 tions, plug connections, and poor contact be worked on by the jeweler only. AC VOLTS 0.510. 50.250.1000 OUTPUT VOLTS: clock checking. Fig. Circuit of standard electric 0 -5- 10.50- 250.1000 Fig. I -All that is needed for electric 2- alarm solenoid. Fig. Timing action for alarm. OHMMETER: alarm clock. Fig. 3 -Clock with separate 4- 0.200.2000. 20.000 OHMS 0.2.20 MEOOHMS BATTERY TEST: Check Dry "A' and B" Pa BELL TRIER© DrPotle BELL FIELD ALARM SW CONDENSER CHECK: COIL Electrolytics checked on English Readln Scala at Rated voltages of 25.50.100 200. 250 -300.450 volts. ALARM TUBE TESTER: 414( j11-` pp.. Emission type with noise test. floating filaments. easy chart operation. Checks ti al Ìy rt POWER SUPPLY: 115 volts 60 cycle. Special voltage and frequency upon request. REED FAITENED TO FRAME

VIBRATING REED ALA MO PREiNE a eQ SUPREME INSTRUMENTS CORP. COPPER To CHECK at : Greenwood. Mìsr.. U.S.A. SEALED UNIT STRIPS J CIRCUIT LAM/NATIONS 518 RADIO -CRAFT for MAY, 1945 (Continued from previous page) ALARM CONTROL HALLICRAFTERS * HALLICRAFTERII The most common alarm controls are shown in Figs. 2 and 4. There are also alarms which have a separate solenoid for magnetic vibrations. This type is shown in RECEIVER HEADQUARTERS Fig. 3. The vibrating reed in Figs. 2 and 4 is attracted to the laminations by the clock's own field winding. When the alarm Ot the AtlOn lever is pulled out and the revolving notched cam has pulled around to the BEFORE the war Bob Henry served the amateurs correct hour, the vibrating reed will start as the world's largest distributor of communications striking against a metal bell or clock flanged frame. receivers. These reeds arc insulated from the fixed Now Henry Radio is Hallicrafters receiver head- lamination with small strips of aluminum quarters for the Nation at war. Hallicrafters Re- or copper. Another of is type alarm shown ceivers can be supplied on AA -1 priority. I can in Fig. 3, where a solenoid is closed circuit usually supply SX28As at $223.00, S -39s at $110.00, by a switch rotary on a geared shaft of SX -25s at $94.50, PM the clock. The switch will close at the and -23 speakers at $15.00 at alarm hour. This type of solenoid hooks once. It takes longer to supply other models. directly across the 110 volt A.C. line. An COMPLETE advantage of this type alarm over the Soon, it is hoped, non -priority orders can be filled others is that it is much louder. STOCKS and Bob Henry can become again Hallicrafters I have in stock some headquarters for the nation at peace. The vibrating tapper is checked by visual Hallicrafters receivers inspection of the rotating cam. Look for available for imme- I have stores at Butler, Missouri, and at 2335 West- diate delivery on bent parts. The solenoid alarm can be pri- wood Blvd., Los Angeles 25, Calif. checked in the very same manner as the ority and the follow- field coil. Besides checking solenoid con- ing parts without priority: meter rectifiers Your orders und in. tinuity, the switch contacts should be $1.95, transmitting checked and cleaned. These contacts will tubes, transformers, quiries are invited. sometimes arc and burn off due to dirty resistors, condensers, contacts. Be sure and wipe off all excess panels, headsets, etc. dirt and grease found on the inside of the Your orders and in- Bob Henry, W9ARA clock movements and case. Do not oil un- quiries invited. less necessary, then use a very fine grade HENRY RADIO SHOPS of oil. Never use oil on the clock jewel bearings. Take it to the jeweler! Butler, Mo. and Los Angeles, 25, Calif. With a little judgment and care, electric clocks can be repaired very satisfactorily. "WORLD'S LARGEST DISTRIBUTOR OF COMMUNICATIONS REOIIVIIIN Their mechanisms are extremely simple, and technique and tools are identical with those used in radio receiver repair. * * * * * * * * * * * FIX ANY RADIO

Find radio faults with a new simplified method. Repair radios in minutes instead of hours. Revolutionary, different Comparison technique permits you to do expert work almost immediately. Most Developed by repairs can be made M. N. Beitman, without test equipment. Simple point- radio engineer, teacher,author, NEW This newly developed to- point, cross -reference, circuit sug- & serviceman. method tells you how to gestions locate faults quickly and 1945 EDITION locate the source of trouble in any radio easily. You may try this unique plan 3 COMPLETE PLAN REPAIR ANY RADIO IN MINUTES without equipment. Make without risk or obligation. Learn time- saving trouble- shoot- needed tests, measure vol - r I$150 ing age, trace the signal, by short-cuts; find any radio fault using only a 5c resistor, TRIAL ORDER COUPON with ease. Follow the tests shown small condenser, and a crys- on 24 large circuit blueprints. Over tal detector. Inject signals 1,000 practical repair hints. Hun- without any signal generator. Test parts by the new dreds of simplified tests using a 5c Comparison method. Test Supreme Publications resistor and any filter condenser. tubes without equipment. Introductory material for beginners Repair any radio expertly Pl 9LIgHfRt Of IiAni[r P.Oi)Kt. \IAI AL°. AND DLGItA?f and to serve following illustrated, simpli- as review for expe- fied plans. Improve your ra- 9 S. Kedzie Ave. 12, rienced radio men. Several chapters dio servicing ability. Data Ch ;cago Illinois on test equipment. Complete plan on all sets, portables, AC- Ship postpaid the new oomplete Simplified Radio Servicing manual for 10 days' in manual form, 64 job- sheets, data DC, FM, recorders, inter- examination. I am enclosing 31.50, full price I muse be entirety satisfied or you on all tubes, size: 81/2 x 11 inches. coms, P.A. Examine and will refund my teal remittance. apply the plan for 10 days Sold on no risk trial. Money -back without obligation or risk. NAME: guarantee. Use coupon to order m Send coupon today ADDHESS: RADIO -CRAFT for MAY, 1945 519 ..,.i...rAlllü:aal!I:ICII:'.I:;P:7:::1 ïl;::;::.;IiIII;IIJII ARMY RADIO COMMUNICATIONS Train Now fora More Secure Future in crease signal strength over unusually berg work vi tcicphoue, kit. type and telegraph or noisy transmission paths, where high circuits covering an area in Europe equiv- power is advantageous. alent in size to that from New York to Radio-Electronics On the second day after the initial land- Chicago and from Detroit to Atlanta. ing on the Normandy coast, the cross -chan- Through this integration, the radio systems Engineering nel circuit illustrated above began operation, became vital links in the network in pro- providing initially facsimile transmission of viding primary circuits under enemy fire air reconnaisancc information on military which took prohibitive toll of lives and ma- objectives from a Tactical Air Command terial during attempted wire installations, Headquarters to the invasion forces. Shortly or over terrain impassable to wire lines; thereafter full multichannel telephone and and also emergency circuits in the event of teletype facilities were provided from Cen- traffic overloads or failures of other facili- tral Headquarters in England to the field ties. commanders of the First U. S. Army in In citing the importance of this equipment France. Following these outstanding uses as an emergency facility during a failure other armies, as they became operational of the main cable system across France as a on the continent, extended similar multi- result of combat operations, the Chief Sig- channel radio facilities to their Corps, from nal Officer, Major General W. Rumbough, their Corps to Divisions and between Corps European Theater of Operations, stated, "In within each army. The Air Forces likewise spite of this very serious cable interruption, linked their base command establishments and I do not think any single trouble could There's No Priority by means of similar radio circuits providing have been worse, we handled 2709 messages the establishment of equivalent wire cir- -, that is nearly 2 messages per minute cuits. throughout the 24 hours." On A As the Armed Forces progressed across The logistical advantages accruing from France additional radio relay facilities were the use of radio relay communication sys- established for both tactical requirements tem over the "spiral- four" cable system, as BETTER Job! in the forward areas, and for administrative illustrated in Fig. 2, have been the principal purposes in the rear Communication Zone. factors through which this type of equip- ADD CREI Technical Training to With the installation of additional cross- ment has achieved its favorable reception Your Practical Experience -THEN channel facilities, and of wire lines and and praise in relieving transportation, instal- Get That BETTER Radio Job other radio circuits on the continent, the lation and maintenance problems. Greatly You Want! radio relay systems became part of a com- expanded commercial use of the principles pletely integrated and comprehensive net- for post-war applications are indicated. CREI home -study training in practical radio s engineering enables you to go after -and CALMfRC#ATLirS I get the better jobs that mean something in n CF-3 /\4 TELEPNAtf INGRAM ? radio. There's no priority on success -but moo* r,` CABLE the better jobs are "rationed" to those men TERM /N& TERMINAL TERMINAL 25 MI. Y7 25 MI Y7 25 N1. 25 MI. -0 who have the necessary technical ability. CF-I CF -f CF-2 Jobs that provide security -jobs that will Sx Sx Si Sx ix x mean something long after "tomorrow" has come and gone be won and held on L. -must WIRE COMMUNICATION ability. The men who will retain the im- FACSIMILE FACSIMILE portant radio -electronics engineering posi- EQUIPMENT r- SYSTEM EQUIPMENT tions after the war is over are those men RC -120 RC-120 whose positions are essential-whose abili- _ ties are specialized. ------RAO/OTERM/NAL- SITS ANT*C7 More than 10,000 professional radiomen ¡RADIO RIMY JETI AN-1ICe1 2 2 have for CREI home courses HfORAIN 7FLfPMONI / 7F11GRAPH enrolled study D3 in Practical Radio -Electronics Engineering. TfRAWGL TfRM/NAl TERMINAL 3 Today, hundreds of ambitious men, just like D4 CFI CF/ CF -2 yourself, are taking our specialized spare - D-- time training to give them the technical skill to supplement their present ability . to earn a better living . and to create a FAI/MILI RADIO COMMUNICATION fACt/MILE secure place for themselves in the great IQLIPMENT SYSTEM EQUIPMENT postwar world of radio and electronics. RC-120 RC-120 Don't say YOU haven't the time. CREI courses are designed to be suited in the most Fig. 2- Comparison, wire and VHF communication facilities, U.S. Army multi -channel systems. crowded schedules. You can study a few hours a week without interfering with your WIRE COMMUNICATION SYSTEM required for a system length of 100 miles in average terrain. Indicated number of present work. So, write for all the facts I. Approximately 94 ship -tons of equipment now this is radio relay sets may be reduced, or system -for the time to make sure that a length 100 your preparation for post -war success shall required for fixed system of length may be increased without additional miles. not be "too little, too late!" equipment, when radio sets are installed on materials 2. Requires large force of men and high elevations which afford long transmis- WRITE FOR NEW, FREE 36 -PAGE BOOKLET installation and maintenance. for sion paths (without greatly exceeding line - If you hey* had professional or 3. Subject to interruption from enemy action. amateur radio experienee want of- sight) between stations. and equipment failure, and electrical interfer- to make more money -let us help 2. Installed, operated and maintained by a you qualify for a better radio lob. number of points along ence at an infinite small force of men without special equip- TELL US ABOUT YOURSELF. so cable route. we can Intelligently plan a course ment or materials. 4. Not for transmission over large beet milted fer your needs.- PLEASE suitable 3. Subject to interruption from enemy action, controlled by STATE BRIEFLY YOUR BACK- bodies of water or territory equipment failure and radio interference GROUND OF EXPERIENCE. ED- the enemy. UCATION AND PRESENT POSI- at 5 points only. TION. 4. Well adopted for transmission over reason- RADIO COMMUNICATION SYSTEM ably large bodies of water or portions of CAPITOL RADIO 1. Approximately 25 ship -tons of equipment territory controlled by the enemy. ENGINEERING INSTITUTE FOUR HUNDRED FM APPLICATIONS EXPECTED Home Study Coursrs in Practical Radio - merciai FM, 1200 Standard broadcast and Kieetronics Engineering for Profes- FM Broadcast station applications sional Self-Improvement reached the total of 353 last month, says 450 non -commercial FM applications in the Dept. RC -5, 3224- 16th St., N. W. Miles Loucks of Frequency Modulation first year, the commission is asking an Broadcasters. increase of 10 employees in the broadcast WASHINGTON 10, D. C. The FCC expects a flood of applications division of the engineering department, Contractors to U.S. Navy -U.S. Coast Guard materials and three in the accounting department and 14 -- Canadian Broadcasting Corp.-Producers of as soon as the war ban on Well-trained Technical Radiomen for Industry manpower is lifted. Estimating 1200 cont- in the law department. 620 RADIO -CRAFT for MAY, 1945 Wlklglllllllll! IIIIIiGI :iII:C:CiFIL'!E!4111!'i.^,I. 111111: J:: I: IllIi :II:IIII:':':II!'Il " "IJC6:'. ".'. "IIIJI ".:111'1111 VOLTAGE REGULATORS (Continued front pays 489)

aaIIIIIIssaiIIIIIIIItssiIIIIInsflIIIIIIIIIIIIIIIIIIIIIIl111111issiI1snitsisi111111nsit111 load voltage to rise. By suitably choosing PARTs operating parameters the circuit conditions Apo can be set. Tube and Circuit A different form of control action is used Reference Book NITS ° in Fig. 6. A D.C. potential is applied to AVAILABLE NOW ! -:Ma Here's a handy reference the grid of the tube. If the output voltage hr.-:° hook that meets the de- of If you are a radio repairman you can buy radio mand for simple, easy the supply rises, there will be a tendency parts with Priority AA -3 -V3 according to CMP _.. to understand data on for the grid to go more positive. When this Regulation 9 -A. Schools, institution, and indi- subst ant ion of radio happens, an increased amount of current vidual account, -see tie first for your electronic tubes. Contains valuable needs. Experimenters write to Leo, W9GFQ, for á5í`9 technical information on tends ¡ to flow in the plate circuit of the complete information on bow to buy hard -to-get ìa - I tubes and circuits. It's tube and through the cathode resistance. radio repair part,. it "_731iviP.`f a guide you'll refer to tone awl again. Send for your copy today! Any increase in the voltage drop across Only 10c postpaid. R, will tend to reduce the current SEND FOR OUR plate LATEST FLYER since, with increased drop across R the Tube- Bas e TODAY! Calculator Our new flyer Is full of merchandise you've been Only 25c trying to get. Stooks won't last forever. Write today. Here's just the calculator you've been look- Forty pages of hard -to -get ing foil Tells you quickly, tube character- parts not available else- istics that enable you to substitute available where. Choekful of items tubes for those hard to get. Only 25c. We pay such u meters, multi -test- shipping expense. ers, mikes, pickups, speakers, wire, etc. All in stock Radio Reference Map -15c for Immediate delivery to Time zones, ama- the radio repair men. teur zones, short wave stations. QUICK SERVICE Other valuable In- formation. Print- Yeirf quick service from the heart of the na- ed in colors; size tion. We're all set to give you that "same day's 3k x 4k ft. It's grid is made more negative with respec service"-we've remodeled our store, doubled our yours! Send 15e shelf space and increased our stock many times. to help with to the cathode. Accordingly, a certain We want you to know that we are doing every- packing and mail- amount of degenerative action and stabili- thing possible to bring you the best in radio parts ing. zation may be expected. In effect we have and equipment. WE SPECIALIZE We have made available thousands of items to IN a shunt resistance across the output of the thousand, of new customers in spite of existing HALLICRAFTERS B supply, between the B plus and B minus shortages. REMEM- Service men all owl the world are learning terminals, consisting of the tube's plate - BER! all merchan- that the name " 1lallicnfters" stands for cathode resistance in series with R3. Some- dise in our latest quality in radio equipment. For many years flyer is available to we have been one of the country's largest dis- what better regulation may be obtained by you repair men. If tributors of Ilallicrafters- "the radio man's substituting a special bias battery for R you are new in the radio." We have Itallicrafters available for thus maintaining constant voltage between business, send us Immediate delivery on priority. For full pu- your order. Enjoy tieulars, write is today. grid and negative terminal. our quick personal A completely electronic voltage regulator service. is shown in Fig. 7. The voltage -regulator tube of Fig. 6 is used in conjunction with another, VT which acts as a variable re- r - - sistor. The action is the same as Fig. 6, as far as the voltage-regulator tube, VT,, Wholesale Radio Laboratories 8C-6 744 %Vest Broadway is concerned and may be substituted for it Connell Bluffs. Iowa. at the points X and Y. An increase of out- nSend your reference Book "Tubes and put voltage increases the voltage on the Circuits." Here's my 10e. grid of VT, thereby increasing its plate You bet I want a Tube-Base Calculator. current. This current is drawn from the 25e Is enclosed. output voltage terminal through the half - LiShip me your radio map. 15e 1s enclosed megohm resistor between grid and cathode for packaging and mailing. Send your free flyer of hard -to -get radio of VT,, increasing the voltage drop across parts. it and proportionately dropping the grid voltage of VT,. This reduces current Name through that tube and increases the voltage Address drop across it, effectively reducing the out- 744 WEST BROADWAY Town State put voltage. VT, is an electronically vari- I am pan amateur; p experimenter; able resistor. COUNCIL BLUFFS, IA. El service man. A neon -tube, N, or a battery may be used to maintain the cathode voltage at a predetermined level above ground. The serted half-megohm and the grid attached to its movable resistor between it and the arm. Thus the output voltage may be ad- rectifier output causes the tube to remain justed "struck" at within certain limits. all times, thus avoiding oscil- This type of voltage regulator has been lator action sometimes experienced otherwise. widely used by experimenters. For voltages in the order required for receiver -type Instead of connecting the control -tube Radionic's Catalog No. 26 apparatus, the constants shown in the figure lists hard -to -get radio parts! Nelps grid to a fixed point on the resistor net- are correct. VT, may be you fill your radio and electronic work as in one or two 2A3's Fig. 6, a potentiometer is in- or other heavy -current low- resistance needs. All parts are available far tri- immediate shipment All are highest VT-I t odes, and VT, a 6J7 or equivalent. The quality. All are exceptional values, neon tube N is usually of the small 1 -watt SEND TODAY FOR YOUR or 2 -watt type, the kind with no built -in FREE COPY TO Dept. SE resistor. A voltage of approximately 60 is i maintained across it. Necessity for special voltage regulation systems is confined to circuits or devices in which voltage must be kept within very 10,000 narrow limits. For most work, careful attention to keeping the source resistance low, by using large transformers, filter Photocells now protect the housewife's Y chokes and condensers, as described in the preserves, inspecting glass jars and bottles earlier part of this article, will be sufficient. for cracks which might spoil the contents. RADIO -CRAFT for MAY, I945 621 Better Signal Generator One Central By L. LANE*

T,IE competition for signal generators Range Turns Diameter Length constructed by readers (in the October, 9-30 Mc. 3 r " 1944, issue) interested me greatly. I 3-9 Mc. 12 %" 1" Source FOR may offer one comment re the winning 1-3 Mc. 60 1" 2" entry. It might he overlooked that although a transformer is used, it is necessary to The above calculations were based on the Some/daft, cot take the usual A.C.-D.C. precautions, that .0005 condenser and ranges will be slightly the screened box must be isolated and that different with an American .00035 variable. if half the transformer primary should For the broadcast and intermediate fre- become shorted a high filament voltage will quencies, plenty of universal -wound coils RADIO and be impressed. are available from old receivers, and will For five years I have been employed be practically pre -calibrated. Plate coils in a radio factory doing war work, putting should have approximately one -quarter the ELECTRONICS in nearly 60 hours a week plus one night number of turns given above, though this of 12 hours on fireguard duties, which time number may be exceeded for the high I have utilized to build several instruments, frequencies. one of which was a signal generator. Design For audio oscillator I used a small inter - was governed by components I had from stage 1 -3 transformer parallel -fed to triode before the war or what I court construct section of 61(8. Checking with an oscillo- LOUT myself. scope, almost perfect wave form was found First I rewound an old small power at 400 cycles with depth of 30%. The S10CKS transformer for a secondary 120 -120 volts attenuator was governed by values on hand 4!ttte A at center -tapped and a 6-volt, 2-amp. winding and works quite well. for a 6X5 rectifier and 32 mfd. condenser. The whole instrument was built in three COMPLETE Main input chokes were universal wound decks, allowing coils and attenuator to be FREE on 1 -inch forms and condensers were all triple shielded, and the rest double. All Helpful SERVICE mounted in small steel box. hot wires were also shielded, complete BUYING R.F. coils were calculated and checked dimensions being 12 inches high, 7 wide' GUIDE on a Q bridge using Litz wire, except for and 5 deep. the two high - frequency coils dried and The large 180° plastic dial had a 3 -1 Centralized here are impregnated with coil dope. With the aid reduction drive, pointer being a piece of today's largest and of the oscillator now built on a small chassis scrap plastic with hair line. Calibration REPAIR and most complete stocks and mounting a small tuning condenser and was accomplished by beating with a stand- REPLACEMENT electronic voltmeter, I now wound the feed- ard signal generator and all -wave receiver, under one roof. Over back windings. To keep good wave form PARTS 10,000 items from all also with a 100 -Kc. crystal oscillator locked I aimed for 30 volt output from grid coil. AVAILABLE leading manufacturers in with a 50 -Kc. oscillator which I built. I for the Armed I found that a series condenser helped had to borrow the crystal, as they are not without priority maintain oscillations on the higher fre- obtainable except for industrial use. Graphs Forces, Radio Train- now had ing, Laboratories, In- quencies. I complete coverage presented no difficulty since the calibration from 90 Kc. to 30 Mc. follows a gentle curve except at extreme dustry, Service Replacements. Our experi- not fortunate to enced staff simplifies procurement-expe- Constructors enough minimum. I have now had the dial engraved have access to coil- measuring equipment directly in frequencies. dites delivery. from may use windings I.F. transformers, Your issue first I and short -wave coils may October was the one R. F. Resonance broadcast which had seen in years, although I had been a and Coil Winding be available to them or may wind their may regular reader in former times, and it seems CALCULATOR own. The following approximate data better than ever. We have nothing like it be useful as a guide: No. 37 -955 in this country. I am an ex -New Postpaid 2Se York *London. England. radio serviceman. 6 Radio Books for 7Sc Dictionary of Ra- Rodio Doto Hand - r dio Terms. book. seem OUTPUT 1 I No. 37.751 IV( No. 37 -754 25c 1 01101. LOW Five bands are cov- I Radio Circuit Rodio Builders I Handbook. Handbook. ered by Mr. Lane's 0001 R.r 100e No. 37 -753 O( No. 37 -750 -1t F 1000 1000 1000 l i O( generator. A construc- g Rodio Formulas & Simplified Radie tor satisfied with less Dota Book. Servicing. range could make one $ $ No. 37 -752 l Oc No. 37.755 10C with fewer coils. The All Six Books No. 37- 799..... 75c escellent attenuator is -o o- Write /or Quantity Prices worthy of special note. L., is Feedback prevented CHOKE a aTTENUATOR by the transformer and e.--GL-ILAMENTS the two choke coils. 02 zoo

CHOKE ALLIED RADIO CORP., Dept. 2 -E-6 838 W. Jackson Blvd., Chicago 7. III. Please send following books (...c enclosed) FREE 87 -750 37 -752 37 -754 Guide 37 -751 87.753 37 -755 AUDIO AND VIDEO ON ONE CARRIER Calculator No. 37 -799 (All 6 Books) The first broadcast application of the a quality which will set the standard for Name principle of sending sight and sound signals broad -hand, fine screen television of the frequency in- highest quality. Address on the same carrier will be corporated in a new television transmitter The carrier frequency will lie between City State to he produced by the Federal Telephone 450 and 500 mc. and the video frequency and Radio Corporation for the Columbia band will be 10 mc. The transmitter will Broadcasting System. The transmitter will be installed on the Chrysler Tower in New ALLIED RADIO permit a high degree of definition or sharp- York City, and will broadcast programs ness in black and white and in full color, originating in the studios of WCBW. 522 RADIO -CRAFT for MAY, 1945 amo mfnmlmmulmumman.._. SPEECH AMPLIFIERS (Continued from page 491)

Blmmimluss mmiti minim s i iii mnnnnunennnnm minimum miu i back voltage is limited by the value of Rt. By inserting a tuned network in the feedback line we will have a high impedance at TOUGIB all frequencies removed from resonance. This causes the non -resonant frequencies to appear as a voltage drop across the impedance and R, in parallel. This voltage is in opposition to the signal voltage and the gain is reduced. At the resonant frequency, the impedance is low and the voltage is by- passed to ground. There is no degenerative action, therefore the gain is boosted at the resonant frequency. Figs. 5 and 6 are applications of the fundamental circuit. The former named Cinaudagraph Speakers are made circuit functions in the same manner as dis- to take the tough raps. This is the for cussed Fig. 4. Fig. 5 is somewhat sim- built -in result of better manufac- ilar in its operation. In this case the tuned circuits are placed in the grid lead of one turing experience. Look at the of the amplifier stages. All frequencies record of achievement and you'll which are removed from the resonant fre- put Cinaudagraph Speakers at the quency will have their amplification reduced through the medium of inverse feed- top of your list. back. At the resonant frequency of the Watch Cinaudagraph tuned networks, the impedance will become Speakers After Victory! very low and the voltage fed back at these frequencies will be by- passed to ground without any appreciable voltage drop which would tend to neutralize the input signal voltage. When attempting to apply these circuits to present -day equipment, it may be somewhat difficult to obtain the correct value of Cinaudagraph Speakers, Inc. inductance called for by the diagram or 3911 S. Mrthigan Ave., Chicago from calculations. happens be If this to Expert Div., 13 E. 40th St.. Now Tora 16, N. Y. the case, it is well to remember that old audio transformers, high resistance speaker fields and small A.C.-D.C. chokes will APeIIa GneA e79h6CL1[P/d in all "lie 9l'ozl.d .. often do excellent jobs. It is somewhat difficult to even estimate the inductance of a coil or choke without OPPORTUNITY AD-LETS employing laboratory equipment which is "WONDER" Advertisements in this section cost 20 cents a word unavailable to the average experimenter for each insertion. Name, address and initials must be included at the anne rate. Cash should accom- but in these circuits, the cut-and -try method pany classified ttaunless placed ELECTRIC BUTTON anaaccredited ccred advertising No advertisementt will give excellent result if the builder has for less than ten words accepted. Ten percent dis- 5lunt Interesting electrical a - a little patience. After using one of these paratus discovered. Make count six lams, twenty percent for twelve issues. Objectionable or misleading advertisements not ac- tone -control circuits in the speech amplifier Det.etlphone. Transmit u voice' roirlmusiceto distant cepted. Advertisements for June. 1945. issue must hundreds fascinating experiments. reach us not later than April 28, 1945. section of your amplifier or radio, you will ó tiItnecanb c on ed In sde o lceeSnySnd button and free 5.000 f begin to wonder how any one is able to booklet withw 50 rImentxr'.l SPECIAL Radio -Craft 25 W. B'way New York 7, N. Y. OFFER button. and booklets mint postpaid for 65. appreciate the beauty of recorded music Write now without some means of balancing the re- BUCK MFG. COMPANY Nash Aurora. 011901. BUILD RADIO. COMPLETE RIT WITH TUBES. sponse curve to suit the listening taste of 510.95. details. Radio, 9418b Avenue "A' , Brooklyn, N. Y. USED CORRESPONDENCE COURSER AND TECHNI- the audience. Many headaches and hours cal Books Bought. Sold. Rented. Catalog Free. Educa- spent computing reactances, resonant fre- RECORDING tional Exchange. Henager, Alabama. MACHINE CORRESPONDENCE COURSES AND SELF- INSTRUC- quencies and other values may be saved if llon hooks. slightly used. Sold. Rented. Exchanged. AB the builder has available one of the React- REPAIR SERVICE mbieds. Satisfaction guaranteed. Cash paid for used coursa. Complete Information and 92 -page Illustrated bu- ance Slide Rules which may be obtained We aro specialists In sales and service of gain catalog Free. Write -NELSON COMPANY, Dept. AMPLIFIERS, RECORDING MACHINES. 2 -39. Chicago 4. from your local radio supply dealer or from Also PLAYBACKS and RECORD CHANGERS. LARGE AND VARIES) STOCK OF PANE'. MEIFE]1R one of the leading manufacturers of micro- design and build equipment to Your epedllca- tlona. bane -Write your and multi -range meters. Panel meters 3Sí -Inch round phones and pickups. Wirel' problem. war-standard. Specify ranges you want and ask far quotation. Many D.C. instruments without priority. Good STUDIO SERVICE CO. supply of critical types on priority. HATAY AND YOUNG. Hartford, Connecticut. Division of LERRIS INDUSTRIES MtIJFITESTER FOR SALE. BRAND NEW 119.75. OR- 242 West 49th St. New York 10, N. Y. der Today. Omaha Radio Products CO.. 368 Saunders- NEW TRANSMITTERS SOON Kennedy Bldg.. Omaha. Nebr. RADIO .PUBES. PARTS. CONDENSERS. FREE BAR- Transmitters may become available as a BUILD YOUR OWN MULTI- TESTER gain lists. Pater. 1314 McGee. Kansas City. Mo. result of the war's end in Europe. A sub- MAGAZINES (BACK DATED) -FOREIGN, DOMESTIC. COMPLETE KIT OF PARTS á14.95 arta. Boda. booklet,. subscriptions. pin -ups. etc. Cata- stantial number, ranging from 1 Kw. to 50 Matched variable condensers and coils for log 10c (refunded). Cicerone's, 863 First Ave.. New York 17. N. Y. Kw. in power may be on the market for the T.R.F. or Superheterodyne, $1.50 per set. 150 volt present or prospective station owner, accord- Dual 20 Mfd: condensers, 35c each. UNIVERSAL RADIO TOOLS -DANDY 16 PIECE SET: ing to a report last month by John Creutz of Midget Pliers, Diagonal Cutters, Fear Midget End RADIO COMPANY Wrenches. Needlenese Pliers. Screw Holder. Six Punches the Radio and Radar Division, WPB. Most and Chisel, hound File, Midget Crescent Wrench. $14.85. 120 Cedar Street New York. N. Y. Remit with order. Immediate Shipment Overnight by Air of the equipment will be sold as surplus to Anywhere. P.S.A. Universal Tool Company, 1321 property but some of it, including high - Grand RC. Kansas City. Slp. power transmitters still in the process of Radio Servicemen: I HAVE A FEW AC METERS. WAIT METERS, MILLI- manufacture, will be completed to fill long- RADIO PARTS -TUBES amp Meters, Belays. Details. Radio. 301 Baynes SC. BARGAIN PRICES -NO PRIORITIES Buffalo 13. N. Y. standing non -military orders. The bulk of KING P.M. SPEAKERS. Or S inch 61.19 KING 450 OHM SPEAKERS, 4 or 6 Inch 1.49 HARDWARE AND RADIO ATT.-CONTAINS 1000 broadcast equipment in use by the military FILTER COND.. 20 -20 MM. 150 V. .39 6V PASS COND.. .01, .02. 05, 1, 600 V .07 items for repairing and experimenting -bolts. screws, is unsuitable for commercial broadcast op- VOL. CONT.. 5 Mao., W. SW., Tap. 3^ Shaft. .55 nuts, speed nuts, washers. rivets. spacer.', springs, studs, erations, A.C. CORD AND PLUG SET. 6 Ft .29 eyelets. oaten, loge, brackets. angles. etc., pieces bake- although a considerable part of it RESISTOR K1T-50 Aas'td, 1/3 to 1 Watt .99 Ate. fiber, formica. mica, myealex. rubber. bimetal. Also may be utilized for federal, state and local Write Today for Bargain Bulletin coils. sockets, condensers, resistor.. rheostats, ele. $2.00 RADIO DISTRIBUTING CO.. Pasadena 18, Calif. per kit. Sent C.O.D. RADLOCO, 1110 B Marshall Bldg.. government needs. Cleveland. O. RADIO -CRAFT for MAY, 1945 523 '' ' Itrit!,:CiR!!'I" IIII:I^II!!'I"'P^I!'IIIIIP":IIIIIIIIIIIIIIIII!II!PII'.IIIIIIIIIIIIIIIIIIIIIIIIIIIIIYI111114 DEALERS RADAR PRINCIPLES Continued frone pug; 484)

arraugelnent was used in the well -known "l he pulse -geucratiug oscillator, and the " squegging" condition to produce trains of cathode -ray tube and linear time -base com- oscillations or pulses of a duration of about bination so described by Appleton and 100 microseconds, spaced in time 0.02 second Builder in 1931, formed the basis of the apart; i.e., at a recurrence frequency of technique used some four years later in 50 per second. This type of oscillator had the first Radar experiments on aircraft been used previously to give a linear time detection conducted in this country. base for cathode -ray oscillographic de- lineation of wave -form by E. V. Appleton, AIRCRAFT HEIGHT INDICATORS R. A. Watson Watt, and J. F. Herd, and had While scientific research on methods of its application to ionospheric recording exploring the ionosphere was being con- been by Appleton in 1928. suggested on the lines described above, a Since the time of transit of the waves to ducted ionosphere back corresponding technique was being de- the E region of the and veloped concurrently and on very similar again is of the order of 0.002 second, it is lines in- type for the purpose of producing an clear that using pulses of the just strument for indicating the height of an described, first the ground -wave pulse will in flight above the ground. For before the of the first aircraft be all over arrival example, in 1928 J. O. Bentley described echo, is ample in- and secondly, that there a method in which frequency -modulated terval between successive ground -wave waves are radiated towards the from pulses to receive and record one or more earth and sub- a transmitter on the aircraft. A receiver, echoes. For visually observing, on receives waves photographing, nature of the also the aircraft, the sequently the reflection from and - signals, cathode oscillograph after the ground corn received a -ray bines them with those received direct from was used, with a time -base provided from the differing using a squegging transmitter, the latter waves a similar basic circuit slightly in frequency due to the time of oscillator, the stroke -frequency of the time - with the pulse re- travel of the waves to the ground and back doll base being synchronized again. The frequency of the beats in the currence frequency of the sender, so that a receiver resulting from two sets . stationary image on the oscillograph screen the of /ii. waves is thus a measure of the height of was produced showing the ground wave received. the aircraft above the ground beneath. as and any echo waves distinct from its altitude above sea -level, The type of result obtained is shown in tir44**- igaY! which is what is indicated by the type of Fig. 8 (a), (b) and (c) which are repro- upon barometric pres- referred to above, altimeter dependent duced from the paper sure. and are specimens of the actual records This instrumental technique was later Appleton and Builder in 1931. Let reprocess obtained by improved by L. Espenschied in 1930, and Fig. 8 (a) shows the ground -wave pulses Fig. culminated in a commercial pattern of received without echoes, while 8 (b) indicator" produced by your dead of a single echo signal "terrain clearance shows the presence the Bell Telephone Laboratories in 1938. reflection from F1 layer. In this after the The delay in the successful pro- case the time interval can be measured in apparent an duction of this instrument was due to the terms of the trace of alternating current heights in much 1115 per second shown fact that the question are of frequency cycles smaller than those involved in ionospheric below the signal record. Fig. 8 (c) is a RADIO TUBES on research, and that therefore the echo-time snap photograph of the echo pattern the intervals be measured are correspond- cathode -ray tube, showing the ground wave to NEW Scientific Process ingly less; e.g., 10 microseconds for about G and the F region echo delineated on a ft. of in 5,000 An illustrated description this time-base, which this case corresponds method of echo sounding for aircraft was of 12 milliseconds. This REACTIVATES THORIUM to a period about given in Radio -Craft for January, 1939. was probably the first published picture of CONNECTS OPEN FILAMENTS what is seen on the screen of the cathode - The pulse modulation method of alti- ray tube of a sending and receiving system tude determination in aircraft is clearly CLEARS SHORTS and used for determining range by measuring applicable, provided that the pulse lengths MICROPHONICS the time delay of the echo signal relative are reduced sufficiently to discriminate the to that of the ground or direct path signal. echoes arriving at a much shorter time delay (NOT the old "flash" trick) than is the case of the ionospheric work. A WAVE TRANSFORMER Such a system was, in fact, described by I Mar the Submarine Signal Company to June, 1933. Here the scheme proposed for MINIMUM ORDER 6 TUBES measuring distances used pulses of electric waves, in association with a means of re- SEND NO ceiving the reflected echoes, and determining the time interval between the emitted CASH and received pulses with the aid of a 0 EA. cathode -ray tube and synchronized time - C. O. D. Price approved base. by s O.P.A. In December, 1931, the British Post ONLY I colt & 3 -Q5 $1.00 Office observed the effects of reflection of waves from aircraft in the course of some 30 -Day Guarantee radio communication tests being conducted Every tube fully tested in . r on a wave length of 5 metres over a path checkers & sets before playing 12 miles long. Extracts from the station log show that on various occasions the received signal was subject to a beat type of variation, which was not only audible but Send itemized list with order was detectable on the volume indicator of Make sure glass, base & prongs are in- the receiver. The amplitude of the beat varied from about ± % db. up to 10 db. on tact ... flashed, exploded or open ca- some occasions, and at all times when this thodes REJECTED and NOT RETURNED iK.1NK gFAVEN occurred an aircraft was found to be flying in the neighborhood at various dis- 2% miles and at heights up as RADIO TUBE SERVICE CO. INC. tances up to Suggested by to 500 feet. The period of the beats varied 6805 20th Avenue. Brooklyn 4. N.Y. Albert A. Mueller, Sioux Falls, S. D. from 5 to 15 per second; and this is to be 524 RADIO -CRAFT for MAY, 1945 compared with the calculated value of 11 per second for an aircraft flying directly towards the receiving aerial at a speed of 60 m.p.h. This experience was confirmed by further observations made in America in 1932 by engineers of the Bell Telephone Laboratories ELECTRICITY in the course of an investigation of the mode of propagation of radio waves in the range of wave lengths between 4.7 and 5.7 pp ot Arctic) and metres. In a paper describing this work by Messrs. C. R. Englund, A. B. Crawford and W. W. Mumford, and published in March, L.IQettoniC %Cat/0/ 1933, it is stated that an aircraft flying about 1,500 ft. overhead r1ll and approximately along the line joining transmitter and receiver, ONAN ELECTRIC GENERATING Models range from a noticeable flutter of about four cycles per second was produced PLANTS supply reliable, economical 850 to 35,000 watts. in the low- frequency detector meter of the receiver. When obser- electric service for electronics appli- A.C. types from 115 vations were carried out in the neighborhood of an airport, it cations as well as for scores of gen to 660 volts; 50. 60, was noticed that near -by aircraft produced field strength variations eral uses. 180 cycles, single or tip to 2 db. in amplitude. Similar reradiation was noticed at Driven by Onan -built, 4-cycle gasoline three -phase; 400, 500, various subsequent times, occasionally when the aircraft was engines, these power units are of and 800 cycle, single invisible. single -unit, compact design and sturdy phase; also special It was thus clearly established, over ten years ago, that radio construction. Suitable for mobile, sta.' frequencies. waves reflected from aircraft in flight could he detected with tionary or emergency service. D.C. types range suitable receiving equipment on the ground; and it now remained from 6 to 4000 volts. to be seen whether this principle could be applied to the develop- Dual voltage types ment of a technique for the defection and location of aircraft at available. Write for ranges and under conditions of practical utility as an aid to engineering assist- navigation in peacetime and as a defensive weapon in war. This ance or detailed lit- important, and by no means easy, step was accomplished by a erature. small group of scientists working under the direction of Mr. (now Sir Robert) Watson Watt, who was at the time Super- Over 250,000 intendent of the Radio Department of the National Physical In service Laboratory, incorporating the Radio Research Station at Slough where the initial experiments in the radio location of artificial objects in this country were conducted. Watson in Watt, association with the late J. F. Herd, had also Model Shows devised the original form of visual direction finder, using twin is from WIC balanced amplifiers and a cathode -ray indicator. series, 2 and After some preliminary experiments, J -KW, 60-ey- members' of the staff cle, 115 volt; under Watson Watt's supervision established a new "ionospheric" powered b y exploring station on the East Coast of England, at which were water - cooled installed for 2- cylinder en- the, those days, high -power pulse transmitters made gine. at Slough, together with suitable receivers and appropriate aerial systems and goniometers for determining the direction of arrival of the echo waves, both in azimuth and elevation, scattered back to the receiver from the aircraft which was illuminated, as it were, by the flood- lighting effect of the radiation from the 2415 Royalston Ave., transmitter. D. W. ONAN & SONS Minneapolis 5, Mina The members of that small band of scientists and technical assistants will well remember the thrill of seeing for the first time a clear image on the cathode -ray tube EPAIRS WITH THESE G -C AIDS! due to an aircraft which was so far away as to be invisible to the naked eye; the distance of the pip along the base line gave the range of the aircraft while its bearing and elevation were obtainable by turning the knobs of the goniometers. Much hard work and not a little ingenuity were still required to convert the technique from an experiment in the hands of scien- FREE tists to a working system which could be STEEL ;ski used and maintained by this miscellaneous CABINET type of personnel which was at that time G -C NE-0-LITE provided by the Service design. departments for G -C DIAL BELT KITS New improved this new "side -line" of radio communica- hundreds of ways. replacement woven Useful tion or signalling. It was not long, however, Exact AC and DC lines, and well fabric belts. Easy to install Tests before war was declared, before GC AUTOMATIC polarity, fuses, etc. more one no stretching -no ad- DC than Service station was in opera- fit WIRE STRIPPER afford to be tion, and justments -a perfect You can't the plotting of the tracks of insulation from all types all - Kits with Strips job instant- without this handy various aircraft, some on their legitimate everytime. of .ire. Does the o oe 300 perfectly. ideal shooter. civil or military 25, 50, 100, 200 ly. easily. electricians purpose trouble duties, and others whose tool fr radio me business was perhaps less innocent, was a belts. and sound men. n matter of daily routine. Jobber From Your Radio Parts WORK IN OTHER COUNTRIES Order FOR G -C PRODUCTS An indication of the trend of thought ALWAYS ASK and activities in other countries in the years before the outbreak of the present war can be gained from a perusal of one or two GENERAL CEMENT MFG. CO.1 publications which are available. Reference ROCKFORD, ILLINOIS has already been made to the patent taken out in U.S.A. by H. Löwy; but the main development in America seems to have funken Company filed a patent in 1935, published in September, 1935, a two -page taken place partly in the Service research disclosing an arrangement similar to the set of illustrations descriptive of the air- institutions, and partly at the Bell Tele- frequency- change method used by Apple- craft detection arrangements alleged to be phone Laboratories. The latter organiza- ton, with the modification also suggested by under development by the Telefunken Com- tion, after developing the aircraft altimeter, Appleton that, while the carrier frequency pany. An interesting feature of this pic- demonstrated the use of this instrument in remained unaltered, the frequency of the torial display was the reference to the use a modified form to the detection of ships modulation was varied, while the number of wave lengths in the band 5 to 15 cm. and over short distances. With regard to the of interference fringes was counted at the of magnetron valves with permanent mag- Continent, it is to be noted that the Tele- receiver. The American journal Electronics (Continued on following page) RADIO -CRAFT for MAY, 1945 525 (Continued from previous page) nets developed specially for wave lengths rFOR SALEN of about 10 cm. An alternative scheme was also described by the Telefunken Com- HARD -TO -GET ITEMS ALLEN pany in 1937, which utilized two beams of All items are brand new, except where Indicated. ALL transmitted waves to produce a stationary in PERFECT WORKING ORDER. In any cases. the parts alone total more than the price we re interference asking. Satisfaction guano teed or your money back. pattern, the disturbance of ORDER FROM THIS PAGE. Use our amont coupon. which by an object moving across it was Include suficient extra remittance ffor parcel st otherwise order is express collect.llect. Any detected at the receiver. excess will be refunded. All C.O.D. shients require Key Kifs deposit. No C.O.D. shipments on orders for les. duct35.00. accompanies de- duct scount.) Send moneyy o iAndch FRENCH AND ITALIAN APPARATUS U. S. stamps. No C. O. O.' to foreign coure tries. Key Assortments to fit Hex - Socket In Italy, E. Montu described a twin Screws in the range of sizes the radio rotating aerial arrangement for locating aircraft in bearing and elevation, and the ULTRA MAGNET LIFTS MORE THAN 20 TIMES mechanic needs for everyday work. patent specification of this arrangement was ITS OWN WEIGHT published in this country in December, LITTLE GIANT MAGNET Lifts 5 Ins. easily. Welgn. 4 1936. About three years later U. Tiberio Made of ALNICO Pew high-magnetic rel. (',.mplet with keeper. Wold' published the first part of a comprehensive 'Ìmost powerful net a made. iu a erimenter' and hobbyist will paper, discussing various aspects of the And hundreds of ex u . for this high qualityrla." permanent magnet. radiolocatiott of ships and aircraft, in the Meaeures 11/2 Ship. Wt. 0,4 u>.. ,k Italian periodical Alta Frcquensa: the later ITEM NO. 159 $1.50 YOUR PRICE TT parts of the paper were apparently with- held from publication after the outbreak GENUINE MICROPHONE TRANSMITTERS These are regular "bte- of the war. An interesting development in phono transmitters'. of the on France was the fitting of the steamship telephones. uTakken from la Normandie with an iceberg detector, which large tarn ten,ll overstock. these O offer o was described and illustrated in Wireless Opportunityruityt n to obtain S plendid unit for little World for June 26, 1936. This equipment moo than the price usual- comprised a transmitter and receiver !rot Icrsophoneebultovltl operating on a 16 and The mateur. expert. wave length of cm. Mutter and telephone nie. chanic will find varietyariety mounted in the fore part of the ship. The of uses Pie these transmitting and, receiving aerials were of microphones. They work the dipole be used on P.A. Systems oice11Usnsmi.,ion:: type and mounted in parabolic tan will With reflectors, 75 cm. in diameter and installed t.i.p tone receivers (radioÌ eadphon do) KEY SET No.603: This canvas partitioned bag at a distance of 6 metres apart; this ar- n os-utes o.houee orrs frm-i-farman 'pho a lims.ear Trill can use them to talk thrnugl, your o raaio, or contains 11 hexagonal keys which fit all ea led dictaphone Irk -use units for listening to short arm rangement provided a beam having a width in distant room or building. The tel.. screws from and including No. 10 up to and in- of ± 10 deg. at half amplitude, and the Phóorations. mechanic will find them useful replacements On battery -operated rural telephone lines. cluding 11/4" diameter set screws. List price 81.75. THESE ARE GENUINE TRANSMITTERS. MADE BY reflectors could be rotated automatically KELLOGG. W ELECTRIC AND STROMBERG. through an arc of 40 deg. When the re- e AmarkablandA eevalue. one sledom ofered thm times. SNP. Wt. 1 lb. ceiver indicated the arrival of a signal from ITEM NO. 160 the transmitter after reflection from a dis- YOUR PRICE $1.50 tant object, the two parts of the equipment AMAZING BLACK LIGHT!! could be manually and accurately trained Powerful 250-Was Ultra-VIo1N Sour. - The best nd mast p etleal on this object, the distance of which Source of ultra- violet lisht for could general e wrimental and enter. be tainment use. Makes all fluores- then calculated from the directions of cent suhatace hrllliantly lumi- nescent. No traneformers of any the transmitted and arriving waves. In this kind needed. Fits any manner amp e. de with special it was claimed that a coastline filter glass permitting only ultra. could be located at a distance 20 violet e to through. of km., rings t beautiful opalescent hue. types ma- and large ships were detected at ranges up terial.. Swell for amateureur 7 playa. tc., obtain to about km. unique lighting effects. Bulb Such was the state of affairs abroad as a Ib. IT[ BNOO. e7 $2.45 judged by the sparse published information YOUR PRIGS L available. As to what was the actual state METER of affairs at the outbreak of the war in WATTHOUR Completely overhauledov rhau led Europe must remain a matter of specula- nDadfor mt Indce. 60 2dlta.Wr ia tion at the present time; but many readers volt. ÄC. circuit. Servicemen We It will look forward with interest to the time n their shops to check when more facts may be disclosed, and soldering irons. etc. Keeps JUNIOR. KEY KIT No. 604: Seven short- Costs down. If dismantled . the progress of the Radar technique con- te parts Moms would arm Allen Keys are included in this strong leather- bring the price. The l,ó. ette envelope. They St the hex holes of sizes Nos. ducted by the various belligerent nations orate gear train could no nines ious kinds. 8 1/2 ", 1 may be described and compared. of rvs 10 Vie, VW and /z" set screws and Simple to Install: a wine Nos. 4, 5, 6, 8. 10, also I/4" and s /1s" cap screws. (The above article was reprinted by spe- from the e d B wine to m load. Sturdily cons deep. In beng metal . List price 80.50. cial permission of Wireless World, London, ati,- alga. Sr..- wide. S- deep. Westinghouse. O. E. Pt. Wayne. sangemo or other available make. Bhp. England.) a m .. w KEY ISLAND ITEM NO. 33 YOUR PRICE $5.95 This handy key set con- $3.00 FOR YOUR CARTOON LIMITED QUANTITIES! tains 14 keys bttingallsizes IDEAS PROMPT SHIPMENTS! of set screws It's Easy to Order-Clip Coupon -Order from u to and in- RADIO -CRAFT, as you will have noticed, This Page -No Catalog Bent. cluding 11/2": MAIL TODAY cap screws up prints a number of radio cartoons, which -NOW! to 1 "; shoul- we intend to keep on publishing every (See corresponding Ad Page 533) der screws to month indefinitely. We invite our readers t BM 1" and pipe HUDSON SPECIALTIES CO. plugs to 1'. to contribute to this feature by sending in Container is their ideas of humorous radio ideas which 40 West Broadway. Dept. RC -545. New York 7. N.Y. cirMvcled below of m. Item. I'm plainly label- can be used in cartoon form. It is not ordering. full It e numbsof s ed to show lude hipping charge./ ii enclosed (NO O.O.D. necessary that you draw a sketch, but you ORDERS UNLESS ACCOMPANIED WITH A DEPOSIT./ the correct 120% size key to may do so if you so desire. ran uiredldship ordo C.O.D. for balance. . use with each FOR LESS U. 9. ,tamps. screw. No. RADIO -CRAFT will pay $3.00 for each DñDE ó STH:eNi 55.00 (New 615; list original idea submitted and accepted. Circle Item No. wanted: 33 87 159 180 price 82.35. We cannot return ideas to this department nor can we enter into correspondence Name Ash for complete listings of Allen Hollow in connection Screw Assortments and Key Kits. with them. Checks are payable on acceptance. tddros Address inquiries and orders to Dept. E, Please Print Clearly Address all enfries to RADIO CAR- TOONS, e/o RADIO -CRAFT, 25 West THE ALLEN MFG. CO., city State Broadway, New York 7, N. Y. Send remittance by check. etnmoe or money ord rl HARTFORD 1, CONN., U. S. A. register letter It you semi rash o stein..

526 RADIO -CRAFT for MAY, 1945 WORLD -WIDE STATION LIST

15.140 GSF LONDON, ENGLAND: Australia, 7:95 tu 10 am; Near East. 1:45 am to 1:15 pm; India. 7:95 to 11:15 am. 15.150 WRCA NEW YORK CITY: Brazilian beam, 5 to 7:45 pm. 15.150 WNBI NEW YORK CITY: European beam, 9 to 11:30 am; South American beam. 11:45 am to 3:30 pro. PROVIDE DELAYS RANGING 15.150 KNBC SAN FRANCISCO. CALIFORNIA; East Indies beam. 9:20 to 11:15 pm. 15.155 SRI STOCKHOLM, SWEDEN; 11 to 11:55 FROM 1 TO 120 SECONDS 15.160 JZK TOKYO. JAPAN; heard at 8:30 pm. 15.170 TGWA GUATEMALA CITY. GUATEMALA; daytime transmissions. 15.180 GSO LONDON, Other important features include: ENGLAND; Pacific. 6 to - 8 am; South America. 12:15 to 3:45 pm: India, 2 to 4 am. 15.190 CBFZ MONTREAL. CANADA. 1. Compensated for ambient temperature 15.190 WOOC NEW YORK CITY; European beam, changes from to 110 °F. 6:30 alla to 3 pm. -40° 15.190 KROJ LOS ANGELES. CALIFORNIA; New Guinea beam. 4 to 5:95 pm. 2. Contact ratings up to 115V-10a AC. 15.200 DID BERLIN. GERMANY. 15.200 WLWSI CINCINNATI, OHIO: South Amer- ican beam. 8:45 to 10:15 am; 6 to 3. Hermetically sealed - not affected, by al- 8:15 pm. 15.200 WLWL2 CINCINNATI. OHIO: South African titude, moisture or other climate changes .._e beam. noon to 2:30 pm. 15.210 KGEX SAN FRANCISCO. CALIFORNIA: Explosion -proof. Fast Indies beam. 7 to 11:15 pm. 15.210 WBO8 BOSTON. MASSACHUSETTS; Euro- 4. Octal radio base for easy replacement. peon beam. 7 am to 2:15 pm. 15.210 MOSCOW. U.S.S.R.: 6:45 to 7:25 pm. 15.225 -JTL3 TOKYO. JAPAN; 6:15 to 8:15 5. inexpensive. pm. Compact, light, rugged, 15.230 VLG6 MELBOURNE, AUSTRALIA. 15.230 WLWL2 CINCINNATI, OHIO: Central Africa with beam, noon to 2:30 pm; North 6. Circuits available: SPST Normally Open; African beam. 2:45 to 4:45 pm. porcelain 15.230 MOSCOW. U.S.S.R.; 6:45 to 7:25 pm. SPST Normally Closed. 15.240 KNBC SAN FRANCISCO. CALIFORNIA; heater Oriental beam, 4 to 6:45 pm; 7 to WHAT'S YOUR PROBLEM' Send for "Spe- 9:05 pm: East Indies beam. 9:20 to 11:15 pm. cial Problem Sheet" and Descriptive 15.250 WLWK CINCINNATI. OHIO' South Amer- ican beam. 6 to 8:15 pm. Bulletin. 15.250 WLWO CINCINNATI. OHIO; European beam. 8:30 am t 3:45 pm. 15.260 GS' LONDON. ENGLAND: Africa. 11:30 561 BROADWY am to 5 pm. 15.270 WCBX NEW YORK CITY: European beam. AMPERITE CO e NEW YORK 12, AY. 6:30 am to 4:45 pm. 15.270 KCBA LOS ANGELES. CALIFORNIA: South In Canada: Atlas Rodio Corp., Ltd. with heater wound American beam. 5 to 8:30 pm. 15.280 DIG BERLIN. GERMANY: Eastern cerv- 560 King St. W., Toronto directly on blade ice. 8 m to noon. 15.290 KWIX SAN FRANCISCO, CALIFORNIA; Oriental beam. 6 to 11 pm. 15.300 MANILA. PHILIPPINES. 15.300 -GWR LONDON. ENGLAND; South Amer- ica. to 7:15 am. 15.310 GSP LONON. ENGLAND: North Amer- ica. 7:15 am to 5 p m; Africa. 2 17.800 KRHO HONOLULU. HAWAII; Chinese -Japa- 4 to am. ntue beam. 7 pm to 2:45 am. 15.315 VLC4 MELBOURNE. AUSTRALIA; North 17.810 GSV LONDON. ENGLAND: Australia. 6 American beam, 9:45 to 11 pm. to 10 am; Africa. 5 to 11:15 am; Hard to get Radio Parts 15.315 VLQ3 SYDNEY. AUSTRALIA; 12:45 to India. 3 to 10 am. 1:45 a 17.820 APH ALLIED HEADQUARTERS IN 15.325 .11.P2 TOKYO. JAPAN; 11:30 pm to 12:30 ITALY: heard mornings with press rePorts for New York. 600 VOLT CONDENSERS 15.330 WGEO SCHENECTADY. NEW YORK; Eu- 17.830 WCBN NEW YORK CITY: European beam. ropean beam. 6:30 to 9:30 am: 9:45 6:30 ant to 1:15 pm. I Sprague - Solar - Aerovox) to 11 am: 11:15 am to 12:30 pm; 17.830 KROX SAN FRANCISCO. CALIFORNIA: 12:45 to 3:95 pm. .00025 Mfd. 12 100 Mid. 25 V. .51 Hawaiian beam, 5 to 6:45 pm; .001 12 10 50 V. .33 15.330 MTCY HSING KING. MANCHUKUO: beam. " last Philippine 7 to 11 pm .002 12 20 " 150 V. .45 heard at 1 to 3 am; Japanese con- 17.850 DJH BERLIN. GERMANY; South American .005 12 20.20 " 150 V. .78 trolled. beam. , :15 to 10:30 am. .01 12 50 " 150 V. .66 15.340 BERLIN. GERMANY; mornings. 17.870 GRP LONDON. ENGLAND: Africa. 11:30 15.340 KNBI SAN FRANCISCO. .02 12 20 " 250 V. .60 CALIFORNIA: am to 1 pm. .05 15 10 " 450 V. .51 Smith American beam. 11 am to 6:30 17.880 WGEX SCHENECTADY, NEW YORK: Eu- .1 IB 10-10 450 V. .84 pm: 7 to 9:30 pm. " pCINNATI .25 r' 27 40 " 450 V. 1.05 15.350 WRUW BOSTON. MASSACHUSETTS: Carib- 17.955 WLWL1 CIN OHIO: North African bean , 6:15 to 7:15 pm. beam, 6:30 to 8:15 a South 15.350 WRUA BOSTON. MASSACHUSETTS: Eu- African beam, 10 to 11,45 1 am; noon Volt Solar 6:30 to 2:30 pm; European beam. 9 to 1600 Buffers- 15.360 SINGAPORE. TRAITS SETTLE- 9:45 am. .01 ... .27 .05 ... .33 .005 ... .27 - MENT: "Radio Shoran." .02 .27 18.025 GRP LONDON. ENGLAND. ... .27 .007 .. 15.375 GRE LONDON. ENGLAND. 18.080 GVO LONDON. ENGLAND; South Amer- 15.420 6WD LONDON. ENGLAND; Philmore Headphones Double (2000 Ohms Imp.) 1.95 Pacific, 4:95 ica. 7 to 8 am: 10 to 11:15 am; I -Watt Starkpole Resistors, 10 Ohms to 30 Moos. .12 tu f am. 12:45 to 1:45 15.430 MANILA. pm. Wire wound Vol. Controls. 2 Ohms to ION .60 PHILIPPINES: used call 18.135 YDA BATAVIA, JAVA (NETHERLANDS OZ4 Tubes (Limit 0 Ea) .90 - C1RN under Japanese R at pm; not EAST INDIES). since Americans. 18.160 WNRA NEW YORK CITY: European beam. .411 orders must be accompa- 15.435 OWE LONDO ENGLANDt: DMiddle East. 9:30 am to pm. m 18.180 WLWS2 CINCINNATI, OHIO: South Amer- nied with L -26.5 Certification. 15.450 GRD LONDON ENGLAND; Africa. 11:30 ican beam. 8:95 to 10:15 am; 11:95 am to am to 3:30 pm. BAKERSFIELD RADIO SUPPLY 15.460 KKR LOCATION UNKNOWN: heard point- 21.470 GSA LONDON. ENGLAND: Africa. 7:95 to-point with New York. to 11 ani. 15.505 1)irision of Poston Radio CMAS HAVANA. CUBA: 7:45 to 8:30 pm. 21.530 GS) LONDON. ENGLAND. 15.595 FZI BRAZZAVILLE. FRENCH WEST 21.550 GST LONDON. ENGLAND. 2808 CHESTER AVE. AFRICA; 11:45 to 12,55 pm. 21.610 SAN FRANCISCO. 15.620 KNBX CALIFORNIA; BAKERSFIELD, CALIF. VRRG JAMAICA. BRITISam WEST INDIES. South American beam. 11 am to 6:30 pm. 15.810 LSL3 BUENOS' AIRES, ARGENTINA 21.640 GRZ LONDON. ENGLAND. heard inge. 21.675 GYR LONDON. ENGLAND; India. 5 to 15.820 PARIS. FRANCE: "Station Paree"; 7:20 pm. PATENTS -TRADE MARKS call CBS and NBC for press reports 21.710 GVS LONDON. ENGLAND. and relay broadcasts from European 21.750 GVT LONDON. ENGLAND. Booklet concerning Inventions & Patents r theatre. 25.750 GSQ LONDON. ENGLAND. Form "Evidence of Conception" with in- 17.445 HVJ VATICAN CITY; heard at 11 am. 26.100 GSK LONDON. ENGLAND. 17.700 GVP LONDON. ENGLAND. 26.400 GSR LONDON. ENGLAND. structions for use and "Schedule of 17.715 GRA LONDON, ENGLAND. 26.550 GSS LONDON. ENGLAND. Government and Attorneys Fee." -Free 17.730 GVQ LONDON. ENGLAND: Near East. LANCASTER. ALLWINE & ROMMEL 7:30 to 11,15 Registered Patent Attorneys 17.750 WRUW BOSTON. MASSACHUSETTS: Cen- tral American beam, 8:30 to 10:15 436 Bowen Bldg. Washington 5, D. C. am: 7,30 to 9:15 pm; European beam. 10:30 am to 1:15 pm. 17.760 KWID SAN FRANCISCO. CALIFORNIA: A magnetic method of separating pure American 17.760 KWIX SAN 11iFRANCISCO8m CALIFORNIA: iron particles from those containing carbon Radio South =Attention Servicemen- American beam. 10 am to 4 has been patented by Prof. John Wulff of pn1. Many hard to get items. 17.760 KROJ LOS ANGELES, CALIFORNIA; New Harvard. Send post card for new price list. 17.780 WNBI NEW tnYORKntCITYt: South pAmerican Iron containing carbon becomes much less Dram. n to 7:15 pm magnetic at a certain critical temperature JOHN A. COX 17.780 WRCA NEW YORK CITY: European beam. 7 :30 am to 1 pm. than pure iron. Iron powder is therefore WHOLESALE RADIO SUPPLIES 17.790 GSG LONDON. ENGLAND. flowed -7th Street, Parkersburg, Va. 17.810 WLWO CINCINNATI. OHIO: South American over a magnetic separator, the pure 557 W. beam, 6 to 6:45 pm. iron sticking and the other falling off.

RADIO -CRAFT for MAY, 1945 527 LOW-VOLTAGE RECEIVER

By PAUL ABRAMSON

THE regenerative grid -leak detector control is turned on full. Due to this fact, followed by several stages of amplifi- we may use the regeneration control as a RADIO cation has long been the standby of volume control without any difficulty. "hams" and experimenters.. It involves It is possible that the use of inductances a minimum of expense and knowledge to instead of resistors in the plate circuits PARTS build and when properly operated gives would give even louder signals, but in this results comparable in sensitivity and se- case it was not necessary. The network in AND SOUND EQUIPMENT' lectivity with many superhets. In addition the plate circuit of the 6SJ7 is for tone to this, it has been found that the values compensation. The coils L1 and 12 were of the components are not at all critical, an ordinary broadcast plug -in coil to start Hookup wire -short lengths - so that good operation is obtained under with, though with the 140 -mmf. condenser 69e pound a wide range of values. Hookup and Push -hack wire- assort- the whole broadcast band could not be ed colors- rubber, cotton and plastic The requirements of this type of a re- covered. A 365 -mmf. condenser would be cover -89c per 100, -10 assorted ceiver call for some type of a remote cut-off necessary for that. As voltage was reduced, 100' rolls 57.80 high gain pentode, a high -gain voltage it was necessary to add turns to the 20 Mfd 150 V Tubular condensers 37c amplifier, and a power output tube. The 20 -20 Mfd 150 V Tubular tickler to increase regeneration. In winding condensera 60c combination which was most preferred up one's own coils, it would be correct to start 20 -30 Mfd 150 V Tubular until several years ago, was the "57," "56," with about 90 or 100 turns of No. 28 enamel condensers 69c and "2A5." Later, the 6 volt filament equiv- 4" ElectroDynamic Spkrs 450 on a 1% -inch form, with 30 turns of smaller ohm 51.68 alent of these tubes such as the "6D6," wire as the first approximation, on the 0 ElectroDynamic Spkrs 450 "76," and "42" became common. tickler. The deciding factor was voltage ohm 1.86 6" ElectroDynamic Spkrs 450 Recently, I became interested in trying ratio to the tube elements rather than ohm 2.58 this type of circuit on new type tubes and tickler adjustments, which were not de- 5" 6 Volt Auto Speakers 1.68 consequently re- designed it for a "6AC7" cisive. The 0.5 megohm potentiometer, for 7" 6 Volt Auto Speakers 1.59 grid leak regenerative detector, a "6SJ7" example, was one necessary modification of 8" 6 Volt Auto Speakers 1.59 6a9" 6 Volt Oval Auto Speakers 1.59 amplifier, and a "6L6" power stage. The the standard circuit. 10 Watt Wire Wound Resistors, results, using an orthodox circuit and a Further experimentation with the re- all values 24e 250 -volt plate supply, were extremely good, ceiver brought out several other interesting Write for latest bulletin listing hun- the output being considerably more than facts. It was found that operation is satis- dreds of items available for imme- necessary for a 12 -inch P.M. speaker. factory on 12 volts plate voltage if a small diate shipment. This set is operated in the same manner 3 -inch speaker is used. Furthermore, using as all others of its type. A common diffi- only 6 volts we obtained good results with culty, lack of regeneration, is usually cor- headphones. SOUND rected by reversing the tickler .winding on Since the gain of the "6AC7" detector - LIFETIME EQUIPMENT CO. the tuning coil. In tuning, it was found amplifier is very great, the circuit was the trimmer condenser exerts a con- P.O. BOX 834 TOLEDO 1 oN,0,l1.5.g. that changed slightly and the "6SJ7" tube elim- siderable influence and should be readjusted inated entirely. The output of the "6AC7" for maximum selectivity, especially when was coupled directly to the grid of the changing from a low- frequency station at "6L6" through a condenser, thus by- passing approximately 600 Kc. to one at 1600 Kc. the "6SJ7." The voltage, however, in this case, had to be raised to 45 in order to OPERATION ON 18 VOLTS obtain sufficient output to drive the 12- This receiver was built in a school lab- inch speaker. oratory and was used for instruction. Due to a shortage of power supplies, it was de- ADAPTED TO PORTABLE USE cided to run the set on batteries. Three 45 -volt "B" batteries in series produced It is my opinion that a circuit such as results comparable to the power -supply described here may be designed for portable arrangement. This interested us in examin- use, and would provide an extremely light ing the effect of low plate voltage. Reducing and compact receiver with as great an out- the voltage in steps and redesigning the put as desired. Low- current -drain heater circuit, especially the regeneration, brought tubes, of course, would have to replace the us to the circuit shown in the diagram. tubes used here. This set is now under With this set -up, and on an 18 -volt battery, construction and will be described as soon the receiver was operating as well as ever, as satisfactory operation is obtained. blasting the 12 -inch speaker. The principal A circuit of this nature very well illus- ss\ changes made to allow the receiver to op- trates the versatility of modern vacuum YOU SAVE OVER A erate on the very low voltage were elim- tubes. The tubes used, especially the "6L6," DOLLAR ON 300 FT. ination of most of the regeneration control were designed for use with plate voltages OF CORD, AND YOU circuit, the cathode bias resistor and the of at least 100 volts. Since we find that 18 GET THE HANDY PLUS volts on the plate produces characteristics CORD-HOLDER FREE condenser in the "6SJ7" stage, and the POSTAGE screen dropping resistor in the "6L6." which are useful in modern radio circuits Includes 100 ft. of pre- One of the characteristics of this set many new applications should be developed stretched Special Thin Cord, fiberglas core: lust operated on low voltage is that it will not for these tubes, particularly in portable right for most small sets. 100 k. of pre-stretched go into oscillation when the regeneration apparatus. Standard Cord. fiberglas core: finest quality. 100 ft. of Medium Cord, recommended for larger table models and consoles. With this assortment you can replace Cord on practically any set made since 1934. The 0.5- megohm regeneration control, plate resistor of Mae Radio ZOaaeleoecoe 150,000 ohms and 500 73-D Mill St., Akron, Ohlo mmf by -pass condenser were found to Please send me the Thrifty Cord Rack with 300 give best regenera- h. of Cord in three sizes. l enclose $4.87 plus 13c tion at low voltages. postage. The number of tickler turns remained ap- NAME proximately the same as with high voltage ADDRESS applied to the plates

528 RADIO -CRAFT for ImNlumonumummmummmnnnnmunimm nnmmmmnmmmmnmmumlmmmnnmmommmmmumlminmummminnnu mmmmummmmummmemmnmmnmmnnnnmmnmim AMATEURS AND POSTWAR RADIO (Continued from page 483) uunnnunnuunnnunnuennumnnnmennugmnunmm18mngmnnnnnnnn6nnnnn111811 nnnnnnnumngmnuunnnnmmIIun66nn9mummmmMmmnuunnnnmmmmmmmnmu Favorite of professionals complete help to amateurs- WHAT KIND OF TRANSMITTER? fens, in case the little woman doesn't see and beginners. The transmitter should be the third item eye to eye with your absorption in the acquired. The post -war period is going to hobby. One of the easiest methods of over- The MASTER offer so many wonderful gadgets that it is coming this obstacle was becoming quite Rerés Quality equipment going to where popular prior to the war. Many of the boys mounted on a 24" r 20!k' be'a problem to start. Al- Masonite board: Crystal. most all the hams have their own individual started to train the XYL. (Ex- young -lady, clear strong plastic mechan- ideas about the best way to do it. There are or wife.) Combination man -and -wife sta- ical square, 4 scales. 8th All e- and 16th In.: protractor full no fixed rules. The FCC regulations are ex- tions were quite commonplace, and will ebanical in dnwiag. degree graduation; nine tremely flexible, requiring observation of increase greatly the future, due to the layouts cutout circles 1/16' to power and frequency laws principally. Build number of women with radio training ob- Sketching $' dia. tained during the war. d. with the best components available! There Adjustable self -alignment metal Equipment leck, In any peel. is nothing to prevent you from putting a Not all of ham radio is experimenting [fen. A:curate, useful. Guaranteed crystal oscillator on the air, and gradually or chewing the fat. almost as adrertbsed. On every band Get your order In right NOW! Sup - adding stages. pWrite anpad faxt. The results which are readily there were networks extending from coast for circular. obtained with low power are amazing . . . to coast and to most of the American pos- RANDOLPH RADIO STORES provided a is Dept. F good antenna set -up available. sessions. 609 W. Randolph St.. It doesn't hurt to mention the friendly con- Chicago 6, Ill. troversy between phone and CW men, be- THE TRAFFIC NETWORKS cause sooner or later someone brings it up. Do you need A fellow should enjoy both types of com- These networks handled traffic, free of munications. charge. The only stipulation was that it BINDING POSTS? must not be commercial traffic. Because radio is IThe XL POSH POT with Ice SprinE Ham far more than slapping to- Constant Contact an gether a station. No words can adequately these services are free, handling or delivery quickn connection, was not guaranteed. The pleasure that comes Manufactured In All Aluminum Type M describe the thrill from contacts on a at 12e trans- from helping has each. mitter built in a basement shop. When some others developed a code Aluminum Body. Bakelite Top Type SI of ethics which seldom saw non -delivery at 1Sc each. friend standing across the lawn with a RF of Types CP or HP. ALL BRASS-STAIN. messages. Emergency networks manned by LESS STEEL SPRING A PIN. PROVEN measuring device tells you that the signal eP AY TEST as NON. amateurs are playing an important war- CORROSIVE240 im atALLTe drops to zero off the ends of the rotary Manufacturers and Dealers Liberal beam, you'll know that Marconi is watching time job in the WERS. In almost every na- Discounts out for his laurels. QSL cards are also a tional disaster, it was local hams who were X. L. RADIO LABORATORIES part of amateur radio. They are printed able to first establish communications and 420 West Chicago Ave., Chicago IO. III. verification cards exchanged with a station, play a vital part in emergency work. Our confirming a contact. Individual stations use country was dotted with emergency coordi- different designs, each trying to have the nators, assistants, and a trained pool of men best looking one. ready to serve at an instant's notice. The technical achievements of the amateurs are CONTESTS AND MEETINGS unsurpassed by any group of people in the On the air there are all kinds of special world. amateur activities to be enjoyed. Such an Their service to humanity in times of event is the Sweepstakes Contest. The idea need closely rivals their contributions in is to have as many contacts with as many the art of radio. The technical proficiency different stations as possible in a given it has afforded the armed services, the gi- time limit. There is also the DX contest gantic radio industry which was largely sup - to see who can work the most countries ported by amateurs ; and the hours of en- and foreign stations. If you are not inter- joyment it has brought thousands, makes ested in that sort of thing, you can go right amateur radio a unique hobby. After the war TO YOUR on testing and experimenting. You'll get to it may serve a new purpose, as an instru- HARDEST PROBLEMS know many amateurs at the "hamfests" ment of good will among nations. Those that are held all over the country in peace- who plan on entering this wonderful hobby 1178 I liustrations time. Technical talks, open house discussion, must remember they are assuming the re- 1000 Pages good food and fun make them something sponsibility of keeping ham radio great. It 130 Tables - 105 Graphs to be looked forward to. is a big order, but now is the time to start Being a ham has a lot of good points, thinking about it. Come on in ... the wa- GET THE ANSWERS NOW! many of which you will need in self -deter's fine! Rem. In one big volume, you'll find all the time saving answers to your radio problems . . . and time saved is MONEY EARNED. Written I easily understood language, yet accurate enough for an engineer. Completely revised and cross indexed for quick 1f reference, this handy reference book for your tough lobs coven radio transmission and reception, nubile r address &eaten.. television, photocells and data on their important parts. It's a hook you'll ADIOS use. And . . . It's only $5.00 ANOTHER TIME SAVING BOOK! FL.ECTRICAT. AND RADIO DICTIONARY. Over 9800 definitions of technical words and terms used In all brioche. of radio and electricity. 900 Pages -550 Illustrations $2.50 GATEWAY PUBLISHING COMPANY 53 W. Jackson -Dept. RC -5 Chicago 4. III. Clip This Coupon NOW Send rne the new Drake Cyclopedia r IMMEDIATELY. And the 300 Page Radio Dictionary.

Name Address City State .... - -IA 1C - BROADCAST stations have lost 30% of their personnel to the armed forces, according to Broadcasting Yearbook. Nearly 8,000 Suggested by: men and women, representing 900 stations, E. M. Pave, Vicksburg, Mise. are in the forces. Only six stations report "I don't know whet beech combing's come to!" no personnel with the armed services. RADIO -CRAFT for MAY. 1945 529 FIELD SERVICE ENGINEERS

For Domestic and Foreign Service ELECTRONIC ENGINEERS! Must possess good knowledge of Radio War - Winners Today, Post - War Builders Tomorrow! Essential workers need release. Leaders in NATIONAL UNION RADIO CORPORATION'S staff of engineer,. scientists and technicians have brought us far out in front in the electronics indu, - try. We have a research laboratory and two manufacturing plants in Newark, N. J.. HAZELTINE and a manufacturing plant near Philadelphia, Pa. We invite you to consider your opportunities with us for professional advancement, stimulating, friendly associa- CORPORATION tion,. and a future with pronti.e. 58 -25 Little Neck Parkway Little Neck, Long Island NATIONAL UNION NEEDS:

SENIOR TUBE ENGINEERS: These men NIUST have actual experience with radio tube manufacture. The pay and opportunities are commensurate with your ability. RADIO STATION COMMERCIAL ENGINEERS: Engineers interested in developing electronic tube applications, who may represent us among radio manufacturers upon occasion. TECHNICIANS

QUALITY CONTROL MEN AND WOMEN : Here you need an interest in the practical application of statistical and /or engineering procedures to man, MEN AND WOMEN factory processes. for Point -to -Point International Men TEST EQUIPMENT ENGINEERS: experienced with meters or electronic Radio- Telegraph Stations in the test equipment to work either as TEST EQUIPMENT DESIGN ENGI- NEERS or as MEASUREMENT LABORATORY ENGINEERS. United States. JUNIOR ENGINEERS -MEN AND WOMEN: Do you have a college degree Applicants must possess FCC in Physics, Electrical Engineering, Chemical Engineering, Mechanical Engi- radio -telegraph commercial li- neering, Mathematics or Chemistry? This company offers an opportunity for young, ambitious graduates to assume responsibilities and to exercise initiative. cense, and ability to copy Inter- national Morse code at about FOREMEN AND ASSISTANT FOREMEN: Men experienced in radio or radio tube manufacture to supervise exhaust, stem or grid operations. 20 wpm. TECHNICIANS, CIRCUIT MEN: Have you been a radio ham, or have you WMC rules observed. built or repaired radios? Have you studied radio in the Services? We need men who can read circuit diagrams and do wiring and construction. Apply weekdays except Satur- days between IO am and 3 pm WOMEN! or write PERSONNEL DEPARTMENT We have a number of fine young ,;omen e,! iineers with us now. We need More. If you have a degree in Electrical Engineering, Chemical Engineering, Mechanical Engineering. Physics, Chemistry or Mathe- RCA COMMUNICATIONS, Inc. matics and are seeking career opportunities, investigate. 64 BROAD STREET NEW YORK 4, N. Y. If you have thorough training in your field, as evidenced by job experience in radio or allied industries, or by a college degree -if you have ambition, initiative and resourcefulness -if you have the ability to inspire your co- workers, then . . . A RADIO CONVENTION? Phone or Write Education by air suffered a setback due DR. L. GRANT HECTOR to the ban oit unnecessary travel, Dr. I. Director o/ Engineering Keith Tyler, director of the Institute and of radio education at Ohio State University, announced last month. The possibility remains that the Institute may use radio to NATIONAL UNION RADIO CORPORATION circumvent the disability. Said Dr. Tyler : "It was deemed inad- Plane Sr. at Raymond Blvd. Newark 2, New visable to continue with the 'Institute this Jersey year in view of the Office of Defense Trans- WMC RULES OBSERVED portation's suggested national ban on large conferences and conventions. "However, there will be an 'institute' in 1945. We are studying the possibility of a closed circuit broadcast, with prominent men WANTED ELECTRICAL and RADIO ENGINEERS and women in commercial radio, the armed RADIO LICENSED AMATEURS forces, government and education taking thoroughly familiar with all types of parts. tubes. RADIO TECHNICIANS is out, meters. test equipment, receivers. transmitters, etc. part. Whether or not this plan carried Permanent position: excellent salary: splendid op For Design, Development and Production Work. the annual Institute yearbook will be pub- portunity for some one residing in metropolitan Post -war Opportunity. Also Openings for tvle- New York area. chanical Draftsmen, Junior and Senior Designers. lished and will contain the views of qualified experts in the United States and Canada on SUN RADIO & ELECTRONICS CO. ALLEN D. CARDWELL MFG. CORP. 212 Fulton Street New York 7. N. Y. 81 Prospect St. Brooklyn problems of radio in the war and post -war period." 530 RADIO -CRAFT for MAY, 1945 WSB) Atlanta, Georgia, and W4XCT of A WAR PRODUCTION JOB Chatanooga, Tennessee. The skypieces undergoing trial include biconical horn radia- TODAY MAKES WAY FOR tors, vertically polarized antennas and A PEACE JOB TOMORROW stacked corner reflector types. II Earlier protests against the change in the FM band are decreasing in number and volume as the probable advantages of the EXPERIMENTS WITH FM new spectrum are becoming better understood. Latest to suport the FCC allocation FM broadcasters are at present under- was William J. Halligan, president of Hal - Wanted taking, with the help of the FCC's Engi- licrafters Co., Chicago, who last month neering Department, the widest series of commended the FCC on its proposal to transmission tests so far attempted. Reason move FM to the 84 -102 me band. Police for the experiments is the proposed new and amateur experiences in the 30 -60 me ENGINEERS spectrum between 84 and 102 megacycles, area show long-distance interference, he concerning which much more should be said. FM above 80 me will assure the public known. high fidelity service Radio a free from static and Long -distance interference between pres- man -made disturbance, and from any dan- Electrical ent FM stations, while not common, was ger of interference from a distant FM frequent enough to cause some apprehen- transmitter on the same frequency, he as- Electronic sion as to conditions should hundreds of serted. stations get on the air in the United States. Mr. Halligan discounted the economic Mechanical "Bursts" were another form of interference phase as "not too serious ", contending only which might conceivably be troublesome a comparatively few transmitters operate in "Factory Planning with a greatly increased number of stations. the 42-50 me band. For this reason, the proposed new alloca- Materials Handling tions are in the neighborhood of 90 megacycles. While it is anticipated that little Manufacturing Planning interference trouble will be experienced in SOUND IN AN ENVELOPE those regions, other transmission characteristics of the region are not well known. PLASTIC records used in a new electronic Work in connection with the manufac- dictation device are so thin and flexible ture of a wide variety of new and ad- Among the stations taking part in the may experimental that they be folded and mailed without vanced types of communications equip. work are WMFM and damage. The records are seven inches in ment and special electronic products. W9XJC of Milwaukee, who are working diameter and carry fifteen minutes of re- with "booster" stations scattered near the cording on each side. These "sound in an edge of the service Apply (or write), giving area. KLZ of Denver envelope" discs, as the manufacturer calls is another station experimenting with boost- full qualifications, fo: the mailable recordings, can even be written ers in areas of low signal strength. on with a pencil without harming the sound R.L.D., EMPLOYMENT DEPT. New types of antennas are being tested track. by four stations, WHDH -WIMXR of Bos- It is possible that the postwar office may ton, WEOA, WGBF and W9XEV of have an electronic dictating machine and a Western Electric Co. Evansville, Indiana, W4XAJ (operated by good phonograph instead of a stenographer. 100 CENTRAL AV., KEARNY, N.J. *Also: C.A.L. Locust St., Haverhill, Mass.

Applicants must comply with WMC regulations

WANTED PUT YOUR HOBBY TO WORK Is radio, mechanics or electricity your TRANSFORMER & hobby, or are you interested in becoming a draftsman or engineer? Would you like SMALL ELECTRIC to work at it in the engineering laboratory of a long- established, growing com- MOTOR MEN pany, having postwarprod ucts with established markets ? We have openings for ENGINEERS persons with such aptitudes to assist our DESIGNERS developmental engineers. Formal scientific education is not a requirement. Our DRAFTSMEN company is located in a small, friendly city TECHNICIANS in the heart of Connecticut. It is large enough to offer good opportunity for advancement... not so large that individual For war time and post -war design and development of intricate, specialized, ability is overlooked. Write me about hermetically sealed transformers, a n d your qualifications and salary require- special purpose fractional h.p. motors. ments. Your letter will be treated with Write, giving details about age, ex- complete confidence. perience, past salaries to William R. Curtiss, Chief Engineer SPERRY Connecticut Telephone & Electric Division GREAT AMERICAN INDUSTRIES, INC. GYROSCOPE COMPANY, INC. RESEARCH LABORATORIES 99 Britannia St. Meriden, Conn. STEWART AVE. AND CLINTON RD. GARDEN CITY, NEW YORK

RADIO -CRAFT for MAY, 1945 531 Just O11' Press! Communications THE BLUE BOOK LICENSES -BUT WHAT KIND ARE REQUIRED? Dear Editor: like and stays done. His comebacks are nil. Supplement No. 3 Many of our Radio -Craft correspondents On the other hand, the poorest man I ever seem to feel that a license and a college had was a graduate E.E.R.E. of one of to the education are necessary for proper repair- the largest schools in the East. He knew ing. I don't believe a college education is his higher mathematics all right. He could "RADIO TUBE SUBSTITUTION necessary, and I don't believe a license is read a slide rule faster than most folks necessary or even advisable. We have far can read a newspaper. In fact, he spent and CHANGE -OVER MANUAL" too many laws and too much local inter- about two-thirds of his time using said ference and too many taxes already. But slide rule trying to show us what dopes Price .. Mlle if some of these folks feel that a license most of our R.C.A. and Philco engineers is absolutely necessary and an examination really were, what cheap material they used, should be given, WHAT kind of an ex- how poor their cabinets were, and so forth. Preceding Issues amination should it be? In the meantime, half his jobs were come- From some statements made by said backs. Radio Tube Substitution a n d correspondents, they would force repair- Now, don't misunderstand me. I am in Change -Over Manual" a man be an in order favor of education and I believe any good (Code: Black) to engineer to earn a $1.00 living. May I ask what higher mathe- workman will study constantly in order to Supplement No. I (Code: Yellow) .50 matics and physics have to do with repair- improve his standards of work. The point ing radio sets or television, or vacuum I am illustrating is that my best man Supplement No. 2 (Code: Green) .50 sweepers or any other electrical appliance? could not pass an examination such as most Contain .Absolutely nothing. folks apparently feel should be given a 10 Substitutes for 12SA7 I maintain a good radio man should be repairman. And my poorest man could pass 7 Substitutes for 12A8 a first class mechanic and not an engineer. this same examination very easily. And he If he is able to handle ordinary mathe- still wouldn't be worth a damn to anyone, 14 Substitutes for 50L6 mathics, can read schematics, can follow license or no license. 11 Substitutes for 35Z5 manufacturers' instructions to the letter, So, if an examination and license (by the 9 Substitutes for 1217 and knows an instrument from a soldering way, almost every city makes you pay a and many others iron, his only other requirements should be: business license now) are still to be required, 1. He must be honest. WHAT KIND of an examination See Your Parts Jobber or 2. He must be absolutely reliable. and WHAT KIND of a license? write to 3. He must be a good mechanic. JACK GEIER, 4. He must like this work better than Northridge, Calif. OELRICH PUBLICATIONS any other kind of work. No licensing or will (It would seem that a repairman who 1627 So. Keeler Ave. Chicago 23, III. form of taxing guarantee the above, in the remotest degree. can turn out work like that described above would be able to pass any reasonable ex- To illustrate: amination, eighth -grade education or no My best repairman was never able to eighth -grade education. Few indeed are the LAKE complete the eighth grade. He works rapid- servicemen who have no comebacks. - Radio Cabinets & Parts ly and accurately. His work is workman- Editor)

FOX -HOLE RADIOS AND METAL -FILM DETECTORS

Dear Editor: crystal proper will rectify as well, and in As an interested reader of your Elec- some instances better than the crystal. For trical and Radio publications for the past simplicity, sensitiveness, such sulphide - twenty-five years, the recent articles, Hugo coated metals in contact with various Gernsback's "40 Years of Home Radio" metal* especially aluminum, far exceeds Portable Phonograph case, of sturdy durable plywood. acid, metal, or n handsome brown leatherette finish. Inside dimen- and the "Fox -hole Emergency Receiver" the crystal combinations of sions 161/2' long, 14" wide. 91/2' high. Rae blank reminded me of some very interesting ex- olden days. motor board As Illustrated aboro, ape- daily priced at $6.95 periments I stumbled on many years ago Joseph D. Amorose of Richmond, Va., Also blank cabinets of walnut r t and the surprising results attained from in a letter to Radio -Craft, Jan 1945, corn - owbla stable speaker opening onleft frni,t aide: (Note: 7 has renter speaker grill.,' contact detectors as described in the articles menting on experiments with the Fox -hole 31 - Bya L x SW H x 4' $1.95 above. receiver, states "I found I could bring in #2 -10 /a' L x 8' H x S' $2.75 as -I3%' L x 7W H x 81/4' $3.25 I discovered that the sweat of the hands music with just a catwhisker lighting s7 -10/i L x r H z Wß $2.50 touching the crystal cup holder." Here Mr. ir8 -ir L x 9' H z WA" $4.50 in contact with the various metals com- a'9 -21' L x 9V H x 10,/e $5.50 Amorose had accidentally discovered the lble Cabinets prising experimental crystal receivers had iIrBlonrin Ivory color and Swedish t Moton.iñtfvaia given them rectification qualities. rectifying properties of sweat corroded sur- fur prices. faces as above. He further states that two POWER TRANSFORMERS Brass or plated balls, crystal cups, etc., clips in would also of such spring light contact amp. would act as rectifiers if a trace rectify such as a crystal. SO Wiillr PO er T s loaners $2.45 corrosion was present. It was reasoned that The experiments as above may be of amp. it must be the high sulphur content of b Pnwe: T:a°',ö mér>, $2.65 value of budding radio enthusiasts of the the body acids that caused such corroded crystal set stage and many happy hours A 1 types of radio parts available in today ' surfaces to act as a rectifier. Various metals, can be obtained at . of experimenting can be enjoyed with these Lake's ney- saving price as silver, brass, copper, etc., were Write For Our Free, New Illustrated Catalog: such sulphide detectors in combination with immerged in a concoction of Sulphur Flow- various metals, also crystals included. LAKE RADIO SALES CO. ers and Lard for 24 hours, forming a light 615 W. Randolph Street, Dept. C, Chicago 6. III. In closing, may I give my deepest appre- sulphide film on their surfaces. ciation and praise for your splendid maga- All were converted into super- sensitive zines and to Mr. Gernsback for his many radio detectors, in contact with untreated encouraging editorials. I only sigh for the %d 7,46.6iay similar metals, especially aluminum. Direct good old experimental days. However, a World's Largest Manufacturer of contact with sulphur fumes will convert a great deal of satisfaction can be obtained Wireless Telegraphic Apparatus metal, its corroded surface of sulphide thumbing through the old faded copies cor ,aur,ST forming a perfect detector. cherished in the attic relics of by-gone McElroy Manufacturing Corp. A treated copper wire laid across the days. aluminum plates of a tuning condenser of R. F. DILLIMORE, 82 Brooklloe Arene 'costa', Massachusetts most any crystal set in substitution of the New Westminster, B. C. 532 RADIO -CRAFT for MAY, 1945 MORE VIEWS ON LICENSES rFOR SALE Dear Editor: RADOFK HARD -TO -GET ITEMS Why should radiomen be licensed, all radio establishments are required to have - All Items are brand new except where Indicated. ALL In PERFECT WORKING ORDER. In many oases. a city license to do business. the parts alone total more than the price asking. Satisfaction guaranteed or your money back. The so- called screw driver man has seen ORDER FROM THIS PAGE. Use our convenient coupon. his day, for the present and future radios Include sufficient extra remittance for parcel post charges. otherwise order i sent collect. Any are too complicated for his screw driver. will be refunded. All C.O.D. shipments require 20% deposit. No C.O.D. Shipment, on orders for less Let us forget him for a while and strive than 5.00. If full remittance order de- duct 2% dcount. Send m oey o certifiedrobed check, to build up our standard of living and put Large slacks Osta,S the finest and most or new U. S. tamp.. No C. O. D.. to cours tries.. our occupation in the professional class, complete selections of all available item, where it should be. at lowest prevailing prices. Thousands of THE MAGIC ELECTRIC WELDER It's not the screw driver man who held active buyers depend on us for their entire Radio repair and replacement requirements. Hare Is one the radio serviceman down, it's the service- most compact. f Ule Because we understand service problems, anal we have man himself, the majority of servicemen. er Anyone every order is expedited for delivery in for shop. They don't know what the word coopera- farm and home re- double quick time. Everything we do is p I e. WELD . tion means, they refuse to work together, BRAZES, SOLDERS. planned for convenience and satisfaction to CUTS they are jealous of each other; each one ANYONE CAN TAOP. our customen. You will find it profitable to . he knows more I' Repairs thinks than the other make Rodolek your buying headquarters. aluminum. brass. cop- fellow. As long as these conditions exist, per. bronze, with pow- their fate is sealed. er L me d FREE BUYING GUIDES e). It has become absolutely necessary that lode. (Really two welders in Carbons. fuie . mask Included. Just plug It electric out- the serviceman educate himself in the art B. f existing renditions we beep our let. 110 volte AC or DC. For hobbyistlit any e u atonal. of cooperating with his fellow -man. If we caslornen right up to the minute on oval. CET 600M. This able merchandise by releasing wpplemenN set quicklyyNteches youAwelding. o perate- continue to operate and work as individuals, rrout BC an hour. COMPLETE SAFETY Is assured. NO frequently instead of sending our regular ums. with this outlet. SET COME) COMPLETE-noth- we can hope for no better conditions; they ing else- to buy. Big Profit Guide ed the American probably can get much worse, and prob- liftman Kodak Co.. Bell ratories. etc.ISBRAND once a year. Send NEW OUTFIT. Guaranteed for one year. ably will, when the hundreds of new manu- Simple Instructions wins each Set. A the coupon now ITEM NO. 158 $19.95T facturers get in the fight after the war YOUR PRICE to get these free and with the thousands of ex- soldier radio- Buying Guide Sup- WESTERN ELECTRIC BREAST MIKE men return to enter the service business. plements as they fine air- arc craft carbon microphone.icrophone.. It weighs The manufacturers, jobbers and distribu- only 1 lb. cons with brlaethlate tors learned years ago that cooperation and has swivel-ccan ing sdiu turent so that It sticking together was their only salvation. adjusted to env desire Bition.b FAST SERVICE! dera woven t n one How does the serviceman expect to main- around e the RADOLEK CO., Dept. 102 around chest. n Straps can he tain a fair standard of living, or build up C. an 601 W. Randolph St., Chicago 6, III. Ingenious arrangeme his occupation, without the benefit of asso- This cellent mike be fl.e.. Iced lttl suyleg guide Supple,eeII adapted for home broadcasting or ciation or cooperation? communication Systeme. By NAME dismountingbreastplate. It can be If the servicemen were organized or had teed se desk ADM" rpitelem with e -foot an association backing them like the manu- ward and hard rubber plug. Finished In aherm alse,l iste. n atable. facturers and distributors have, they could THIS o IS A BRAND NEW MIKE. IT HAS NEVI- it ORDER FROM RADOLEK REEK SOLD AT SUCH A LOW PRICE BEFORE. ((ties. control the distributors, manufacturers and WAL LIST PRICE 815.00. Shipping weight. 2 lbs. even the driver Our Headphones are used ITEM NO. 132 screw man. YOUR PRICE $2.55 by the United States, Ca- I wonder how many times each service- nadian, New Zealand and POWERFUL ALL -PURPOSE INDUCTION man has worried and cursed over a two- South African Govern- MOTOR by-four midget, that should have never ments as well as other IDEAL FOR EXPERIMENTERS -101 USED been made? How many times has he Governments not directly Sturdily constructed to preciMUn searched for an outlaw schematic not to in the war. stanaanl,, this self-starting shaded A.C. Induction motor be found. Distributors have not all been leu' number en.. gr ÌElTim. playing fair with the servicemen; some #aadsat loDvicCreg ees.ourto Inlata Electric Fan, Electric Chimes. are now selling critical tubes and batteries Window Displays. Photocell Control to non -service Scientifically Devices, Electric Vi , Small organizations, what is the guilt on. Heavy bar mag. #aadivattati Mini Pumps. Mechanical Mod. serviceman to do about these conditions, neta In- Siren.. and other applies. creasetheir effi- Folder R5 illustrates lWe.ions. he can do nothing as long as he works ciency. Consumes about tts of rugged, unusually sensi- Power treed of am on alone, REMEMBER, ISOLATION AL- r.p.m. when geared down, this tive, dependable Cannon -Ball Headsets. sturdy unit will oper- MOST PROVED DISASTROUS FOR ate 18-Ineh turntable loaded Write wan y POWERI THE UNITED STATES. I enelon." Se high l by 2N wid IIV deep: C. F. CANNON COMPANY has convenient mounting studs: shaft laEctnase long Let us get an association or organization Y. runs In self-aligning SPRINGWATER, N. er7ectaining bearinng..rDeasiggned I110.2Ó as strong as the strongest, fight together, Shp. WI. 2 lb.. tiGlees. A..C'. only. work together and rise together; in this YOUR PRICE way and this way only, will the serviceman ever be placed in the professional class LIMITED QUANTITIES! and receive the remuneration due them. PROMPT SHIPMENTS! I am trying to organize an association of servicemen in South Georgia, and would "LEARN BY DOING" IN We Euy to order -CUD Coupon -Order from COYNE SHOPS like to hear from anyone interested, we Electricity offers you neportonitiee for MIN Page Catalog Sent. the bent jobs today- with enreal peace -No plan a meeting in the near future, to work real machinery. Earnowhileylearning.oRI'ght 1 out MAIL TODAY -NOW the details and form some plan of I'm offering extra training in In- dnowustrlalElectronics at nn extra cost. (See corresponding ad paga 526) operation and would like to have a big lifetime employment service alter graduation.duation. Get ell- around practiiccal mm at Coyne in attendance. eahofor Ing.gMSSSeoupon Free BOOR. We have !twiÌni.n HUDSON SPECIALTIES CO. G. E. RENFROE, for men with physical maabinue,.lf you have. ph ',Plea di.- whiney of any kind check coupon below for details. 40 West Broadway, Dept. RC -5.45, New York 7, N.Y. Thonlarville, Ga. I have circled below the items N. C. Lewis. President, COYNE ELECTRICAL SCHOOL number of the l'in SOO S. Pauline St.. Dept. 55.78, Chicago 12. Illinois ordering. My full remlltance of no. Send tree book and all detall,. Send physical disability plan. elude &hipping charges) le lod. (NO C.O.D. ORDERS UNLESS ACCOMPANIED e.eWITH A DEPOSIT.) NO TUBE DUPLICATION! NAME OR my deposit of is enclosed (20, ADDRESS hip order C.O.D. for balance. NO C.O.D. ORD!red).ER FOR LESS THAN 55.00. (New U. S. stamps. Dear Editor: CITY it /NE ST:tTh. check or y order accepted.( Circle Item No. wanted 147 152 15e How about a little propaganda against duplication of tubes having similar elec- Guaranteed Rebuilt Radio Name trical characteristics but slight physical differences? The number of types a service- VIBRATORS Ada re so man should carry in stock, if he could get -Sí00 ea. Please Print Clearly them, is beyond reason. Send old vibrator. For very prompt delivery, enclose remittance and return postage. We City State Well, cheerio for now. rebuild any make or kind of vibrator. Send Sena remittance by check. stamps or money orlon GAULT your old vibrator to register letter if you send cash Rame.. WOl E. F., BEST VIBRATOR CO.. Box 5802 -2. Cleveland I. O. Be R.C.A.F. Overseas. RADIO -CRAFT for MAY, 1945 533 New Direct -Coupled FM - AM ELECTRONS TRAIN AVIATORS JHOP/G .l6 4dtIP4 (Continued frum page 486) AMPLIFIER MANUAL Aerovox Corp. 510 unmmnnminumnmmmmmn iu u munnmommimuswunminimmun uummuma Allen Manufacturing Co. 526 Allied Radio Corporation 522 By A. C. SHANEY would not have to fly. An actual pilot, American Microphone Co. 468 Engineer. Amplifier Co. of America ex- Chief perience taught, gained little information Amperite Co. 527 Amplifier Co. of America 534 about his ship from the "feel" of a heavy Audel & Co., Theo. 504 airplane in flight. This was a further sim- Bakersfield Radio Supply 527 plification. However, other factors had to Best Vibrator Co. 533 be reckoned with -"loading," the "angle of Buck Manufacturing Co 523 attack" of wings against air, the block of Burgess Battery Co. 513 air in which the plane was flying. Finally, Buratein-Applebee Co. 634 all of this mass of aerodynamical- electrical Cannon Co., C. F. 533 Capitol Radio Eng. Institute 520 information was put into the form of cir- Cardwell Mfg. Corp., Allen D. 530 cuit information, and the experimenters Cinaudagraph Speakers, Inc. 523 were ready to build the first trainer. Concord Radio Corporation 509 To make sure that the mockup trainer Cox, John A. 527 would "act" just like a real in Coyne Electrical School ....507, 514, 533 PBM the DeForest's Training, Inc. 473 air, duplicate motion- picture films were Gateway Publishing Co. 529 made at intervals of one second of the General Cement Mfg. Co. 525 real instruments pf a real PBM in the air General Electric Co 517 and the instruments of the trainer on the Great American Industries, Inc. 531 ground. Hallicrafters Co., Inc. 471 Hazeltine Corporation 530 The noise of an actual ship was recorded Henry Radio Shops 519 in the air under varying engine speeds and Hickok Elec. Inst. Co. 503 For the Layman, Serviceman loads, and duplicated in the trainer, not Hudson Specialties Co. 526, 533 Recordist and Engineer with whirring motors, but with a sound- International Detrola Corp. 501 Regardleas of whether you are Interested in the finest film feeding a amplifier Lake Radio Sales Co. 532 of reproduction. high fidelity recording. track large and bat- typo phonograph & sound -on -film applications. FM or Aar program. you tery of loudspeakers. This was coupled Lancaster, Allwine Rommel 527 will lied invaluable information in this practical handbook. LeJay Mfg. Co. 507 of coupled am- to the speed -control circuit of the mockup Written by the leading exponent direct- Lifetime Sound Equipment Co. 528 plifiers who has spent more than 10 years improving and engine. perfecting the famous Loftin-While circuit. McElroy, T. R. 532 Explains the theory and practical Standard controls were set up in the train- McGraw -Hill Book Co. 535 application of: er (photo 134131). Once in the gigantic in- Maedel Publishing House 535 Variable Speed NonOverloading Push -Pull Expansion strument, seated in pilot's or co- pilot's seats, Mallory & Co., Inc., P. R. NonFrequency Discriminating Scratch Suppression at real radio equipment, Inside Back Cover Push -Pull Balanced Direct -Coupled Amplification peering through the Meissner rushPoil High-Frequency Equalization ground speed and drift indicator, or just Mfg. Co. 537 PushPull Low - Frequency Equalization National Radio Institute 467 Push -Pull Volume Corn ion looking on from the navigator's position Automatic Volume Limitation National Schools 475 Automatic Volume Control with earphone "intercom" carrying messages National Union Radio Corp.....502, 530 Calibrated V. U. Indicator back and forth, the illusion of actual flying Oelrich Publications 632 Audi. Spectrum Control Remote Control Was so realistic that experienced flyers were Olson Radio Warehouse 528 If you are Interested in the latest audio development.. dumbfounded. Onan & Sons, D. W. 525 you can't afford to be without this complete compilation Opportunity Adlets 523 of authentic articles on Direct- Coupled Amplifiers. 99 Panoramic Radio Corp. 538 pagos 8%' x 11 ". Over 100 diagrams and Illustrations. CONVERTING A CRITIC Priced to Cower Cost of Personnel Help Wanted 530, 531 Printing and Mailing 25C One day, shortly after the first trainer Send U. S. S la ,nps or Coi,, was received, an officer fresh from 500,000 miles of flight in all theaters of war arrived AMPLIFIER CO. of AMERICA to inspect the mockup. He, frankly, was RADIO SCHOOL DIRECTORY 396 BROADWAY NEW YORK, N. Y. skeptical, and said so. No one, he went on, could teach a PBM flight crew to operate Page 536 together without actual air experience. He would prove it. Quietly, he was asked if American Radio Institute NATION -WIDE he wouldn't like to try it out before mak- Candler System MAIL ORDER ing his report. Capitol Radio Engineering Institute Radio Institute DISTRIBUTORS Into the mockup he went. The ground Commercial Lincoln Engineering School SINCE 1928 crew exchanged significant glances. This skeptic from the front would be convinced. Melville Radio School Actually, severe flight conditions can be RCA Institutes manufactured by the mockup control room in a room adjoining the actual trainer. Seated at a desk, with duplicates of the trainer's instruments before him, the flight - RCA Communications 530 control can create severe icing conditions, Radio Distributing 523 strong headwinds, cause one or both of the Radio Electric Service 517 Radio Kits 528 Oil trainer's "engines" to quit, cause fouled Radio & Technical Division or fuel pipes, increase oil or cylinder-head Murray Hill Book Co. 498, 499 DEVICES temperatures, shift the center of gravity, and Radio Tube Service Co. 524 a number of other things. The idea behind Radio Wire Television, Inc. 516 this is to see how the pilot will react to Radionic Equipment Co. 521 Company 533 TRADE ... INDUSTRY... the unusual conditions. The control man Radolek sitting quietly at his desk sees all and Randolph Radio 529 Raytheon Mfg. Co. ..Inside Front Cover COMMUNICATION... knows all. By moving a dial or two he can Rider Publisher, Inc., John F. 515 "throw the plane into a nose dive" and Sperry Gyroscope, Inc. 531 PUBLIC UTILITY... cause a technical "crash." The instruments Sprague Products Co. 472 AND before him tell instantly what the pilot is Sprayberry Academy of Radio 469 VOCATIONAL doing, and how well, to right the trouble. Studio Service Co. 523 Sun Radio & Electronics Co. 530 EXPERIMENTAL On the table top is a mercator chart. Supreme Instruments Corp. 518 Atop this chart is an electrical "frog" that Supreme Publications 519 APPLICATIONS moves about in exact accordance with the Sylvania Electric Co. 476 theoretical flight of the trainer. The navy Triplett Elec. Instrument Co. Back Cover man from the front, with 500,000 miles of Van Nostrand Co., D. 511 flying experience, wasn't aware that he was Western Electric Co. 531 BURSTEIN-APPLEBEE CO; Co. 507 to be- given the "works." But twenty mm- Weston Elec. Instrument 1012 -14 McGEE ST. Wholesale Radio Laboratories 521 utes later he signalled he had enough. The X-L Radio Labs. 529 KANSAS CITY 6, MISSOURI control -room man had all but "crashed" the expert flyer, who emerged from the mockup 534 RADIO -CRAFT for MAY, 1945 with perspiration dripping from his chin, Others are assigned to the radio equipment, his shirt wet, completely spent, and - the navigator's table, the drift indicators, NOW -A REALLY HIGH-POWERED fully convinced. "I'm cured,' he said, the gun position, and so on. The headgear - "what a machine that is I" is strapped on over cars and mouth, as a The Navy got the first trainer late last voice over the intercom asks you if everyone year, but now seven or eight more are in- is ready. Radio Engineering stalled and doing an unequalled job in the "Ever been in one of these ships before ?" creation of flight crews at Banana River, the voice asks. Everyone replies "no." The Fla., Corpus Christi, Texas. Others are in voice calmly asks the pilot and co-pilot to Library operation or are on the way to all theaters "take hold of that lever tinder your seats of war, according to latest information. and move forward as far as you can." This When a crew takes an actual plane up advances the seats so the pilot and co -pilot it is responsible for about $500,000 worth can easily reach all the controls. of equipment and the lives of ten or more "All right, let's go," the voice orders. men. All the crew must know their jobs, "There is no danger, just do as I say," he goes on. "Throttle," voice. each other's abilities and shortcomings, and orders the NOTE: We step on a pedal and idling motors must be able -collectively -to meet a great The Library comprises a selection spring into life. The airspeed indicator of books culled from leading M. variety of emergencies with instant action. Grow -Hill publications in the ra In flight, when a mistake is made, it is shows a slow rise of speed. "Taxi to posi- i dio field. generally too late to remedy the situation. tion on runway No. 1," the radio man relays, especially selected by radio specialists of Mc- A crash often results. Now the old method after receiving the instructions from Graw -Hill publications of assembling promising crews and trying the "operator" in another room, who is to give mat complete, dependable coverage of them out in the air is superseded by the directing the take -off. Flux -gate compass facts needed by all whose fields are grounded on swings around as the turn is accomplished, radio fundamentals electronic method. When mistakes are made available at a special price and terms in the trainer, they do not result in loss of and we are on the runway, ready to go. "Give her the the flight commander THESE books cover circuit phenomena, tube the- equipment and lives. The flight- control man, gas," ory, networks, measurements, and other sub- speaking a word or two through the mockup orders, as we press down on the pedal and jects -give specialized treatments of all fields of intercom system, merely say's: "OK, boys, motor sounds roar. Airspeed indicators practical design and application. They are books show 120 miles per hour. "Tail up," says of recognized position in the literature -books you you are theoretically dead. Come down here be voice. move will refer to and referred to often. If you and I'll tell you what's the matter." Then, the We the elevator control - are a practical designer, researcher or engineer in a matter of minutes, they are briefed the ship seems to respond instantly with in any field based on radio, you want these books something indicates we for the help they give in hundreds of problems again and on a new trial. that are level. whole field of radio engineering. "More gas," orders the voice. The speed throughout the Good flying weather, moreover, cannot climbs to 180 miles. There is no sensation. 5YOLUM ES, 3319 PAGES, 2289 ILLUSTRATIONS always be had for the wishing, and the train- t. Eastman's FUNDAMENTALS OF VACUUM TUBES "We are off the ground," the voice advises. Terman's RADIO ENGINEERING ing must go on. With the PBM trainer it "More gas." We are now doing 200. A I. Everitt's COMMUNICATION ENGINEERING can go on in rain or shine, and the only slight waver of the "lever" indicator shows 4. Hand's HIGH FREQUENCY MEASUREMENTS equipment expended is s. Henney's RADIO ENGINEERING HANDBOOK the electric current us that we are indeed "airborne." The waver nay.. Easy terms. Special price required to operate the trainer. this r less than bookse ' Add the,. is corrected. The height indicator reads 500 standard works tto your library now; pay small Mutably Installments, while you us, the boks. feet, then 600, then 800, then 1000, then 1500 HOW 10 DAYS' FREE EXAMINATION-SEND COUPON A TRIAL RUN FEELS feet, which has been given us as our cruis- When one enter, the one -story building ing elevation until further orders. What a that houses the trainer he finds himself in McGraw -Hill Book Co., 711 W. 12nd SI. New York 11 sensation I A motor wavers a bit and we Send me Radio Engineering Library, 5 vols.. for 10 a bare room with a desk and a dozen days' examination on 1. UO days I will mad chairs. get a new thrill. The operator "on the centsmourn postage. MI This is where the crews are instructed for $2 00 paid. postpaid. We payypoet. ground" gave us that one by moving a E on orders accompanied by itsaac* of ant lap flight, e t.) or briefed. An instructor explains dial a wee bit -caused a bit of bumpy air. tarlm: what is ahead. To the right is a door from He gives us a new one by Name behind which stopping one mo- comes the staccato drum of tor entirely, then causing it to catch again powerful Address motors. You enter that fateful and go on with a steady purr. What a ma- door, finally, after a bedraggled crew chine-all man made, electronically con- City and Mate emerges, and are on your own. Steep steps trolled ! We have a difficult time believing carry the visitor to the cockpit. Seats are we are not in the air. Company seen ahead, as one goes through what seems The soft voice goes on, bidding us turn Position RCS,15 to be a real airplane. You are strapped into "north -north east," for "fifteen miles or so." one of them, the co-pilot into the other. Then another turn and we are soon back over the Patuxent Base, maneuvering for a A FIXED RESISTANCE landing. We come in, finally, a beautiful three -point landing, taxi up to the starter's MATHEMATICS booth, shut off the roaring engines and step out -surprised to find ourselves in the sawn building from which we started our flight. "God," said our girl passenger again, "I'm a little light- headed -get that way FOR RADIO often in a train but flying is worse." Every- Two volumes, prepared for home study. one smiles, a little weakly, to be sure, for Book I (314 pp.) covers the algebra, all of us feel the relief that comes after arithmetic, and geometry; Book II (329 an ordeal. pp.) covers the advanced algebra, trigo- THE ROOMFUL OF SECRECY nometry, and complex numbers neces- Back in the operators flight-control "tow- sary to read technical books and articles er" again we look over the equipment used on radio. to create the hazards of "synthetic" training. The flight man explains how the MAEDEL PUBLISHING HOUSE Room 117 "crab" followed our "flight" and points out 593 East 38 Street, Brooklyn, New York RINGS that we received a rating of 80 per cent for Send me MATHEMATICS FOR RADIO AND our job. Inside I enclose WATC S the crab are several electric COMMUNICATION as checked below. motors that cause it to move in exact ac- payment therefor with the understanding that I may return the book(s) within 5 days in good cordance with the movement of the controls condition and my money will be refunded. in the mockup. "See that little jagged bit of line in red ink ?" he asked. "That came when I gave Name you the bit of motor trouble. You see, I HIIIIIIIIIfI knew not only just what you were doing, Address but exactly how well you did it; that is, how quickly and accurately you responded to correct the conditions I interposed. This permits us to weed out the men who are Book I at $3.75 plus Cc postage BEAJEtj, O Book I I at 54.00 plus 6c postage slow at such things, who are then given El Books 1 and 11 at 57.75 postage prepaid Suggested by: E. R. Lacing, Weston, Mo. (Continued on following page) Foreign and Canadian prices 25c per volume nigher RADIO -CRAFT for MAY, 1945 535 brains as the operational flight trainer-one in New York and another in London, with DIRECTORY the respective yacht skippers operating the RADIO, SCUOOL controls, which had been pre -set to simulate all the conditions of wind and wave. The skippers then might pit their skill against PREPARE NOW FOR POST -WAR RADIO AND ELECTRONICS each other electronically by moving a series MAKE a place for yourself in a new world of radio and electronics -a world in which of dials designed to tack, run before the revolutionary electronic developments will require highly specialized technical wind, round a buoy, jockey for position knowledge. Take a good course now to fit yourself for a good paying job. The training and a dozen or so other things in the you need can be supplied by one of the schools advertised in this publication. science of yacht racing. Radio engineers, however, would have to retire to their laboratories for another year RADIO INSTITUTES to resolve the proper kind of areodynamical ELECTRONICS Offer thorough training equations and translate them into the ele- Intensive training in courses in all technical phases of ments of wind, wave and tide. Airline, Merchant Marine, Radio and Television Press Communications, DAYS -EVENINGS WEEKLY RATES Television. Co- MUSIC BY TELEVISION! Electronics. VETERANS: RCA institutes is approved educational. FREE booklet. under B. I. Bill of Rights The first part of Dmitri Shostakovich's VETERANS: For Free Catalog Write Dept. RC.4S for FREE copy. G.I. latest musical score -a composition Request RCA INSTITUTES, Inc. and cello entitled "Trio" bill of rights A Radio Corporation of America Servire piano, violin - "A Radio School managed by radio men." 75 VARICK STREET NEW YORK 13. N. Y. has been flashed to New York directly from 45 W. 45th St., Dept. RC, New York 19. N.Y. Moscow by radiophoto over the circuit of RADIO INSTITUTE Inc. prior its MELVILLE LEs Courses In RCA Communications, to Correspondence American premiere. Hurdling wartime com- RADIO ELECTRICAL ENGINEERING munication obstacles, the transmission is ELECTRICAL ENGINEERING;;i "w;ä; the first of its kind involving a major mu- trial field. prepare yourself. at Low Cost. for the speeding of future. Modern. ainlined. quickly.F sical work and presages yous n e under. and RADIO ENGINEERING eaddrcae.pnnw.electr .work. compositions by the world's great musicians Learn to he a Telegraph Traina you to be sup.eeryñeeded lee an real vacuum tute from one continent to another by radio- Radio Operator. Thousands of technician. Servicemen badly. Diploma comple- tion. Tuition S15. eeither course. peewee men needed Intensely interest- Pet conies school catalogs.aloymnpan. student photo as soon as completed. Work pay. Learn at ing -good ah>eIr. complete details. SENI NOW! home or wherever you are. uuiekly, F R E E In actual transmission time, it took twen- easily, with the famous Candler LINCOLN ENGINEERING SCHOOL L°rohe,3iféé3 ty -four minutes for the first page of the Code Speed System. Rook of particulars Free. Candler System Co., Dept. 3E, Boa 928. Denver I. Colo. latest score to come from Moscow over the COMMERCIAL RADIO INSTITUTE RCA receiving radiophoto machine. To f a- A radio training center for cilitate handling, the photograph of the RADIO twenty -jour years. composition was sent an four sections of Courses Qualifying for six by eight inches each, and these were Service Technician Laboratory Technician RESIDENT COURSES ONLY cut into a mosaic of standard musical page (Electroni< Television) Communications Operator Pre -induction. Broadcast, Service. Aeronautical. Tele- for positive print. Register Now for New Classes Starting 1st Monday of vision and Sistine telegraphy classes now forming tot size the each Month. Day and Evening Classes. June 18. Literature upon request. Veteran training. Consideration Given To Veterans Eli goals For Training Home Study Course In Mathematics H -F TRANSMITTING TUBE AMERICANICAN RADIO INSTITUTE Dept. C. 38 West Biddle St., Baltimore 1, Md. 101 West 63rd St.. New York 33. N. Y. * BUY AN NGINEERING & SERVICING Training Veterans Under "G.1." Bill Prepare n w for profitable ENTER ANY TI M E. Renldence coolher, classes In R * EXTRA rA0TaIONvsnclan.iiolengintrrinic and Sv W rf te f or FREE Boo klet p itol Radie Engineering Institute Dept. RC.S. 3224 With Street, N. W.. W as h,na' fo n 10. * WAR BOND (Continued from previous page) dred thyratrons and a score of motors intensive training to eliminate the fault." whirl into action. The sound is something "Is that all there is to the trainer ?" we like the chirping of frogs on a summer ask, incredulously. ?By no means," said the night. The blinking thyratrons add to the operator. "Just go into that door at your illusion. left and see what makes the whole thing The electrical brain can do a score of tick." things at once. It can integrate simultan- Inside we found a mammoth series of eously as many as a dozen trying flight seven electrical panels about eight feet high. conditions and come up with the answers Little lights seemed to blink in the semi - in a matter of seconds. Quicker than the darkness. They were thyratrons,well -known human eye or brain, the thyratrons turn on gas -filled bulbs that have the useful purpose motors to just the correct speed to simulate of controlling the flow of large electric cur- electrically one law of aerodynamics or a rents when a control- circuit is energized. dozen if need be. Motors, nearly 100 of them, either hummed Such an electronic calculator, with dif- with activity or otherwise, in response to ferent electrical constants interposed, can do the thyratrons. This was the really secret a number of jobs. For instance, it might part of the operational flight trainer, the be arranged to predict the operation of a "brain" by which its mysterious properties new airship before a single model is con- are controlled in response to the movement structed, and do it solely from blueprints of gadgets in the mockup or control desk. of the device. It might design a new loco- Behind the mysterious panels the blinking motive, a new automobile engine, or a new thyratrons and rotating motors translated washing machine. It might even be a boon into actuality in an electric circuit every- for international yacht racers. Alfred Van- thing that the engineers foreordained in derbilt and a foremost British yachtsman, months of experimental work in the Bell for instance, might run off a race with as Laboratories. much assurance of success for the best sail- Move a control in the mockup or control ing master as if their vessels were compet- desk and a thyratron blinks, a motor speeds ing within sight of each other just outside up or diminishes its rotations per second in New York Harbor or off the Isle of Wight. terms of some law of aerodynamics, and They might do this, even though neither some condition of actual flight is satisfied. had a vessel in the water, and had never Encounter "trying conditions" of headwinds, seen each other across the 3000 or so miles An interesting- looking tube, the new Eimac motor temperature, oil feed, icing of wings of the Atlantic. All that would be required 4 -2I5A, a power tetrodo. Two tubes can put and a dozen other such things and a hun- would be the creation of two such electrical out as much as 750 watts in the VHF region. 536 Printed t etc U.S.A. RA DIO -CRAFT for MAY, 1945 MT. CARMEL HAS

AN EYE TO THE FUTURE

"Personnel" is an outmoded word in the little city of Mt. Carmel, Ill. Why? Because it has been replaced by "precision -el," a word that more aptly describes the men and women whose skills and enthusiasm produce Meissner precision -built products for a world at war and who will soon help rebuild a world at peace. He has mastered his craft. Each movement of his sure, deft hands adds Meissner quality to the precision electronic equipment he builds. Dedicated to the armed forces today, tomorrow his skills will mean Meissner precision -built products for you. Jog 1=1rC. S ' o1 T. 3r # ,

A scene "Behind the Front." Skilled Meissner workers are turning out vital electronic war equipment. Their "know-how" means dependable weap- ons for our boys at the front now - it will mean better performance for you in tomorrow's products.

"SW Up" Old Receivers! These Meissner Ferrocart I. F. input and output transformers are getting top results in stepping up performance of old worn receivers. Special powdered iron core permits higher "Q" with a resultant increase in selectivity and gain, now available for frequency range 12 7 -206. Ask for numbers 16 -5728 input, 16 -5730 output. List $2.20 each.

They live in the future! Through their hands pass the work of Meissner's "precision -el," embodied in Meissner pre- 111881ER cision -built electronic equipment now going to our armed MANUFACTURING COMPANY MT. CARMEL, ILL forces. Many of the parts they now handle as part of their daily routine will mean new comforts in postwar living. ADVANCED ELECTRONIC RESEARCH AND MANUFACTURE Export Division: 25 Warren St., New York; Cable: Simontrice RADIO -CRAFT for MAY, 1945 537 FASCINATING, NEW BOOK FOR AMATEUR RADIO OPERATORS!

From One Ham to Another"

Packed full of brand new information on amateur radio operation! Shows how you can solve many of your problems! Completely explains, in your own language, the PANORAMIC Technique, and what if will mean to you when you get back to your rig!

"From One Ham fo Another" fells you how to get the most out of your rig. It shows you how you can have even more satisfactory OSO's with your friends all over the world. In detail if describes the problems that confront amateur radio operators ...and proposes solutions. For example, after you have read "From One Ham to Another," you will know how to reduce the number of missed signals, how to determine quickly

11 which frequencies are free, how to step up your efficiency. Simple and pleasant to read, "From One Ham to Another" is written for the ham in terms you use. And you will be amused by the clever cartoons that illustrate it throughout. You will want to file and keep "From One Ham to Another" for the new ideas it pro- To obtain your free copy of "FROM vides. You will learn about the role that the ONE HAM TO ANOTHER," just send us PANADAPTOR will play in future ham opera- a card with your name, address, and s/ tions. You'll be thrilled by the stories of war -

call letters if you have them. If you - time applications of this technique. Send for are now connected with radio in your free copy today! some way, we should like to know "Frew Ono Ham to Another" discusses such subjects as: She name of the organization with which you are affiliated, Watching for CQ's and the type of work you Answers to CQ's Operation of nets do. EVEN IF YOU ARE NOT Choosing a spot in the band for your xmfr YOU ARE WELCOME A HAM, Helping your brother ham TO THIS PANORAMIC BOOK Reading signal strength Logging the frequencies of your friends And many other topics of great Interest

ROZO CORPORATION 242.250 WEST S5'" ST../1«, 6.4/S7..4?

538 RADIO -CRAFT for MAY. 1945 Program A New aization 5t and a of Mallory Here's Typical MALLORY Standardization!

12 VIBRATORS MEET 90% OF YOUR REPLACEMENT NEEDS .65 VIBRATORS REPLACE

101 DIFFERENT TYPES

Score another bull's eye for the Mallory program available. Because of the reduction in the number of standardization! Now the entire line of Mallory of vibrators, your distributor will stock fewer vibrators has been simplified so that replacements types -and more units of each ! Delivery will be can be made more easily and quickly -with a tremendously speeded up. really streamlined stock to select from! Yes, the replacement problem has been changed This streamlining imposes no penalties. It means and simplified -but Mallory quality remains the that the new list of 65 Mallory vibrators will same! Mallory precision vibrators, backed by answer the needs that formerly required 101 years of outstanding performance, still offer the different types. Even more important, 90% of dependability, the long life and the trouble -free your replacement requirements can now be met with service that you and your customers expect from us. only 12 vibrators! Order them from your Mallory distributor. Ask Not least of the advantages of the new set-up is the him, too, for your copy of the new Mallory Vibrator fact that Mallory vibrators will be more readily Standardization Folder.

P. R. MALLORY & CO., Inc., INDIANAPOLIS 6, INDIANA

PF VIBRATBRAP SERS More than VOLUME CONTROLS SWITCHES RESISTORS FILTERS RECTIFIERS POWER SUPPLIES ys MALLORY ON APPROVED ALSO MALLORY "TROPICAL." DRY BATTERIES, ORIGINALLY INSIST DEVELOPED BY MALLORY FOR THE U. S. ARMY SIGNAL It PRECISION PRODUCTS CORPS, NOT PRESENTLY AVAILABLE FOR CIVILIAN USE. Trodemert EVERYDAY IS WASHDAY AT TripleU The special equipment and solutions with which jewels are washed are minor parts of the Triplett method of manufacturing fine electrical measuring instruments but they are significant. They typify the dozens of out -of -sight Extra Precautions that assure your permanent satisfaction with Triplett Instruments. These Extra Care provisions are routine in Triplett plants but through them Triplett maintains in mass production the hand -made quality of fine instruments.

Extra Care in our work puts Extra Value in your Triplett Instrument. Triplett ELECTRICAL INSTRUMENT CO. BLUFFTON, 01110