Aid 10 Ironies'

AID 10 IRONIES'

APRIL 1949

312k-

u S and LATEST IN RADIO MONEY BACK GUARANTEE-We believe units offered for sale by mail order should be sold only on a "Money- Back -If- Not -Satisfied" basis. We carefully check the design, calibration and value of all items advertised by us and unhesitatingly offer all merchandise subject to a return for credit or refund. You, the customer, are the sole judge as to value of the item or items you have purchased. j1 rasa - FOR FM -AM TELEVISION BUILD YOUR OWN SIGNAL TRACER and SAVE!! Increasing production of F.M. and Television Receivers means more complex Receivers. Now more than ever this time -saving method of quickly and easily localizing the exact cause of trouble becomes the "must" method. Since 1939 when we first introduced our CHANNEL ANALYZER we have worked continuously developing and improving the "short -cut" method of Receiver servicing. The Only Signa! Tracer in the Low Price Range Including BOTH METER AND SPEAKER!! FEATURES: * Comparative intensity of the signal is read directly on the meter -quality of the signal is heard in the speaker. * Simple to operate-only one connecting cable -no tuning controls. * Highly sensitive -uses an improved vacuum -tube voltmeter circuit. * Tube and resistor capacity network are built into the detector probe. * Built -in high gain amplifier- Alnico V speaker. * Completely portable- weighs 8 pounds- measures 61/." x 61/2" x 9 ". MODEL CA -12 Kit includes ALL PARTS assembled and (We can supply the Model CA -12 completely ready for wiring, circuit diagram and detailed operating wired, ready- to operate -$29.25.) data for the completed instrument.

THE NEW MODEL 670 The New Model 770 - An Accurate Pocket-Size SUPER METER VOLT-OHM MILLIAMMETER SUPER METER. A Combination (Sensitivity: 1000 ohms per volt) VOLT - OHM - MILLIAMMETER Features: plus CAPACITY REACTANCE, Compact -measures 3%" x 6%s" x 214 ". INDUCTANCE and DECIBEL Uses latest design 2% accurate 1 Mil. MEASUREMENTS. D'Arsonval type meter. Same zero ad- D.C. VOLTS: 0 to 75/15/75/150/750/ justment holds for both resistance ranges. 1:00/7500. A.C. VOLTS: 0 to 15/30/ It is not necessary to readjust when 150/300/1500/3000 Volts. O U T P U T switching from one resistance range to VOLTS: 0 to 15/30/150/300/1500 /3000. another. This is an important timesav- D.C. CURRENT: 0 to 1.5/15/150 me.: 0 to 1.5 Amps. RESISTANCE: 0 to 5011/ ing feature never before included in a 100.000 ohms. 0 lo 10 Megohnls. CA V.O.M. in this price range. Housed in PACITY: .001 to .2 Mfd.. .1 to 4 Mid. round- cornered, molded case. Beautiful ((plenty test for electrolvtles.I REACT- black etched panel. Depressed letters ANCE: 700 to 27.000 Ohms; 13.000 Ohms filled with permanent white, insures long. to 3 Mcgohms. life even with INDUCTANCE: constant use. 1.75 to 70 Henries: 35 Specifications: 6 A.C. VOLTAGE RANGES: to 8.1100 licorice. 0- 15/30/150/300/1500 /3000 soils. DECIBELS: -10 to +18. +10 to +38. 6 D.C. VOLTAGE RANGES: 0-7;4/15/75/ +311 In +58. 150 /750/1500 volts. 4 D.C. The model 070 comes housed In a rugged. CURRENT RANGES: 0- 114/15/150 srackieTni steel eat,. Me. 0 -I V4 Amps. 2 RESISTANCE Anet complete with test RANGES: 0 -500 Ohms. 0 -1 -g $2840 Megolim . leads and sreti In- The structions. Size 5Vs" x Mdelo 770 comes complete with l co 7l x 3 ". NET lotteries. /x' lends and all operating Instructions. 390NET THE NEW MODEL 777 The Model 88 -A COMBINATION 20,000 OHMS PER VOLT!! SIGNAL GENERATOR A TUBE & SET TESTER SIGNDNAL TRACER Tube Tester Specifications: ',Frequency * Tests all tubes including New Miniatures, etc. Also Pilot Lights. Range: 150 Kilo- * Tests by the well -established emission method for tube quality, cycles to 60 Megacycles. ',The directly read on the scale of the R.F. Signal Frequency is kept meter. * New type line voltage. completely constant at all out- V.O.M. Specifications: put levels. ',Modulation is ac- D.C. VOLTS: (at 20.000 Ohms complished by Grid -blocking ac- Per Volt). 0 to 7.5/15/75/150/750 / 1.500 Volts. tion which is equally effective for alignment of amplitude and A.C. VOLTS: lAt 10.000 Ohms frequency modulation as well Per Volt). 0 to 15/30/150/300/ as 1.500/3.000 Volts. for television receivers. ', R.F. ob- tainable separately or modu- D.C. CURRENT: 0 to 1.5/15/ 150 Ma. 0 to 1.5 Amperes. lated by the Audio Frequency. RESISTANCE: 0 to 5.000/.50.- 000 /500.000 Ohms. 0 to 50 Meg- Signal Tracer Specifieatlons: ohms. Uses the new Sylvania 1534 Ger- Model 777 operates 90 -120 tnonlum crystal ])lode which com- alts SO eCe)., A.C. ',Housed bined with a reslelonee-copaclty net- beautiful band . rubbed Cabinet. Complete with test mad., tube., work provides a fre- Charts and eG quency mice of 300 per"nn in true cycles to 50 Megacycles. 85 size- lx" $5d J.7 $ bons. 9NET The Model 88 comes complete with all test leads and operating NET instructions. ONLY 2 20t'4 DEPOSIT REQUIRED ON ALL C.O.D. ORDERS

PARK PLNC, GENERAL ELECTRONIC DISTRIBUTING CO. NEW Y RK 798 3

You Practice COMMUNICATIONS You Practice Radio SERVICING As part ofmynew Com- As part of my Servicing I Send You Parts To Build- munications Course I On This Modern Radio You Course, I send you the speaker, send you parts to tubes. chassis, transformer, build your own Trans- loop antenna. EVERYTHING This Equipment mitter. Conduct actual Build With Parts I Send you need to build this modern procedure demanded Radio Receiver that brings in of Broadcast Station local and distant stations. You Operators, practice use it to con - many interesting ex- duct many periments and tests. tests and ex- learn how to put a periments. ,transmitter on the air. NEW

Learn Servicing or Communications

by Practicing in SpareTïme

YOU BUILD 'with MANY KITS OF this Tester as 1..1 PARTS I Send of my Servicing Course. It Want a good -pay Job in the fast- growing Radio soon helps you earn Si, It0 and and Television industries or to be boss of your own more a week EXTRA MONEY tiring money- making Radio and Television shop? I've nelghnors' Radios in spare time while Iearning. trained hundreds of men with no previous experience to be Radio technicians. I can do the same for YOU BUILD thi, Power Pack as YOU BUILD this Superheterodyne yon' Or now, for the first lime, enroll in my new part of my new Communi- Receiver Circuit and pros. t i cal course in Radio-Television Comm urli- cations Course. Use it to conduct Frequency cationa -learn to be a Broadcasting and Communica- conduct tions technician. You learn Radio and Television fascinating Modulation experi- principles from experiments with fre- ments clear, illustrated lessons. You get and many practical Radio experience with MANY KITS OF quency am- other teats PARTS I SEND in my train -at -home method. AU plifiers and as part of equipment yours to keep. multipliera, my Ser- MAKE EXTRA MONEY b u f f e r vicing IN SPARE TIME I. E. IMR6, PreIdM As part of my Radio stages, etc. Count. Nalsul Wie Imiltrlr Servicing Course, I send JC EXTRA MONEY booklets, starting the day you enroll. Use your know -how to make $5, $10 and more a week EXTRA YOU BUILD this YOU BUILD this MONEY fixing Radios in spare time while training. The next step Signal Generator as Wavemeter as part is your own Radio shop or a good -pay Radio servicing job. Or, if you part of my Servic- of my new Commu- prefer, get Into Government, Police Aviation or Marine Radio, Broad- ing Course for more nications Course. casting, Radio Manufacturing or Public Address Work. valuable VETERANS Use it with Oscil- experience. lator you also build BRIGHT FUTURE IN TELEVISION It provides ampli- Think of the present and future opportunities In GET THIS that furnishes basic Television the fast -growing tude- modulated sig- power to transmit- field. New stations are going on the air every month. . nals for many inter- ter and determines Television manufacturers are producing over 100,000 sets a month. It's a fast- growing field and the man who knows esting tests and TRAINING transmitter fre- be In Television will experiments. quency. demand. WITHOUT COST GET ACTUAL LESSON AND BOOK FREE Send now for my special DOUBLE FREE lesson OFFER. Get actual UNDER on Radio Repairing short -cute absolutely free. Also get G. I. BILL 64-page book "HOW TO BE A SUCCESS IN RADIO -TELEVISION -ELECTRONICS." See how quickly, easily you can start. J. E. MAIL COUPON SMITH, President, Dept.9D%, National Radio Institute, Pioneer Home Study Radio School, Washington 9, D. C. I TRAINED THESE MEN AT HOME Coed,Argo* -FREE Good Job In Makes Extra Cash Operates Own Radio Station In Spara Time Radio Business MR. J. E. SMITH, President, Dept sox "Am Chief Engi- -, "Earned enough "Now have two National Radio Institute, Washington 9, D. C. neer of Station legare rash time Radio shops ser- Mail me WORD, In to pay for my vicing about 200 FREE Sample Lesson and 64 -page of book about how to win success in Radio and .`.. chute four .course by time I sets a month. men. Owe all I know ahont graduated. NRI Television-Electronics. (No salesman will call. training Have largest service es- Please Radio to NRI." -CLYDE is tops) " -ALEXANDER tablishment In Southeast write plainly.) J. BURDETTE, Spartan- K I S H , Carteret, New Missouri." - A R L E Y burg, South Carolina. Jersey. STUDYVIN, DeSoto, Mo. Name.. Age_. MAIL COUPON! FIND OUT ABOUT THIS Address

City . Zone State TESTED WAY TO BETTER PAY D Oak II Vgtad/ APPROVED FOR TIAININ9 ORDER L L BILL J 4

Hugo Gernsback, Editor -in -Chief Fred Shunaman, Managing Editor HAD 10 - M. Harvey Gernsback, Consulting Editor Robert F. Scott, W2PWG, Technical Editor An Efficient Low -Cost ELECTRON KS R. H. Dorf, W2OMI, Associate Editor I. Queen, W2OUX, Editorial Associate Replacement Speaker formerly RADIO -CRAFT Angie Pascale, Production Manager In corporati no Elmer Fuller, Shortwave Editor SHORT WAVE CRAFTS TELEVISION NEWS Wm. Lyon McLaughlin, RADIO 5. TELEVISION Tech. Illustration Director Trademark rogó stared V. S. Patent Office G. Aliquo, Circulation Manager Charles K. Brett, 177,000 C O P I E S National Advertising Director O F T H I S I S S U E John J. Lamson, D I S T R I B U T E D New York Advertising Director Alfred Stern, Promotion Manager Contents April. 1949

Editorial (Page 19) lelevision By- t'roducts by Hugo Gernsback 19 Radio Science (Pages 20 -23) Improved Electrets (Cover Feature) by E. D. Padgett 20 TRU -SONIC Electronics (Pages 24 -30) Model P -52FR Microwaves, Part I by C. W. Palmer 24 Oscillator Circuits as Used in Industry by Ed Bukstein 27 Diathermy Generator by H. L. Bumbaugh 29 Co- Spiral Speaker Television (Pages 31 -35) Subdues deficiencies both in set itself Cinema Television by E. Aisberg 31 and in source material. Built with the M. 32 Antennas for Television, Part IV by Edward Noll and Matt Mandl same precision limits and same engi- Magnetic TV Enlarger by Mohammed Ulysses Fips, I.R.E. 34 neering skill found in all Tru -Sonic units. Broadcasting and Communications (Pages 36 -38) Full 15 watts of power handling ca- Telephone Lines in Broadcasting by Leigh L. Kimball 36 pacity. 15" seamless molded curvilinear Audio (Pages 38 -42) cone of new design. Two acoustic sec- Quality Disc Recorder by Richard H. Dorf 38 tions, one designed for reproducing Audio Impedance Matching by Walther Richter 41 lowest boss, and one section for extended Useful 10 -Watt Amplifier by W. D. Hayes, W6MNU 42 high tones. Reproducing range is 40 to 14,000 cycles! (flot ± 5 db 70 -7000 cps). Amateur (Pages 43 -45) Bandswitching Exciter by Bob White 43 Powerful Alnico 5 Magnet. Greatest electro- acoustic transfer efficiency and Servicing (Pages 46 -49) widest range of any speaker utilizing I is by John T. Frye 46 Fundamentals of Radio Servicing, Part Ill -What Induction?.... voice coil. 90 Degrees of high frequency Guy S. Cornish 48 Sound Can Make Money for You by dispersion List Price $80.00 Theory and Design (Pages 50 -51) (Normal trade discounts) Transmission Lines by Robert C. Paine 50 Construction (Pages 52 -54) A- Battery Eliminator by Ryland Hobson 52 20 -Meter Vacation Converter by P. F. Egerton, Jr. 54 Test Instruments (Pages 55 -56) Ohmmeter Reads to 300 Megohms by John T. Bailey 55 Foreign News (Pages 68 -69) European Report by Major Ralph W. Hallows 68 FM (Pages 74 -84) "Back Porch" Booster Brings up FM Signals by James C. Drake 74 FM Station List 78 Departments The Radio Month 10 New Patents 72 Radio Business 16 People 85 New Devices 58 Technotes 87 TRU -SONIC Radio -Electronic Circuits 60 Miscellany 89 Model P -S2A Question Box 66 Communications 95 Try This One 71 Book Reviews 97 Coaxial Speaker

ON THE COVER: Miss Mary Jane Padgett checks the charge on an electret. Combined in a single assembly are a Kodochrome by Avery Slack. Low -Frequency unit of the cone type, a High- Frequency unit of the multicellu- lar type and the Dividing- Network. Ideal RADIO- ELECTRONICS, April, 1949, Volume XX, No 7. Published monthly. Publication Office: Erie Ave., for AM and FM reception, broadcast F to t: Streets, l'tu ladelpt as 31, l'a. Littered as second class Mattel Seplamuer 2 -i. 1948, at me post office at t'hilmielphia, l'a.. under the Act of Starch 3. 1879. SUBSCRIPTION RATES: In U. S. and Canada- In U. S. station monitoring, and sound- motion- possessions. Mexico. South and Central American countrlee. $3.50; $6.00 for two years: $8.00 for three years: single copies 30e. All other foreign countries $4.50 year. $8.00 for two years. $11.00 for three years. Allow one picture reproduction. List Price $205.00 month for change of address. When ordering a ,lunge please furnish an address stencil impression from a recent wrapper. (Normal trade discounts.) RADCRAFT PUBLICATIONS, INC. lingo Gemshack. Pres.; M. Haney Gernsback. Vice -Pres.; O. Aliquo. Sec'y. Contents Copyright, 1949. by Radcraft Publications. Inc. Text and illustrations must not be reproduced without Write for Circular 252 illustrating and de- permission of copyright OWners. scribing the complete Tru -Sonic line of EDITORIAL and ADVERTISING OFFICES, 25 West Broadway, New York 7, N. Y. Tel. REctor 1-9690. BRANCH ADVERTISING OFFICES: Chicago: 308 W. Washington Street. Telephone RAndolph 6 -7363. Detroit: Frank Holstein, Speaker Systems for Theaters and Homes. Boom 402. Lexington Bldg., 2970 West Grand Blvd. Telephone TRlnily 1 -7026. Los Angeles: Ralph W. Harker, 606 South Hill St. Tel. Tucker 1793. San Francisco: Ralph W. Harker. 582 Market St. Tel. Garfield 1 -2481. FOREIGN AGENTS: Great Britain: Atlas Publishing and Distributing Co.. Ltd., 18 Bride Lane, Fleet St.. Lon- don };.C.4 Australia: MrCill'a Agency. 179 Elizabeth Street. Melbourne. France: Rrentano's. 37 Avenue de l'Opera, Parie 2e. Holland: Trilect mn, llremsteedsche. Dreef 124 Ileemstede. Greece: International Book A: News Agency. 17 Amerikte Street. Athena. So. Africa: Central News Agency. Ltd.. Cor. ltiaslk & Commissioner Sts.. Johannesburg; 112 Long Street, Capetown; 369 Smith Street, Durban. Natal. Universal Rook Agency. 70 Harrison Street. Johannes- STEPHENS burg. Middle East: Steimotzky Middle East Agency. .lane Road. .Jerusalem. Indie: Such Gupta (Distributors) Co., Armita Basar Patrika Lt.. 14 Ananda Chatterlee lane, Calcutta. Broadway News Centre, Post Bag 05557, Dadar. Bombay V14. K. L. Kannappa Modeller. 30 General Patters Road, Mount Road, Madras 2. Pakistan: Paradise Book MFG. CORP. Stall, Opp. Ilegal Cinema. I'reedy Sl.. Karachi 3. 8538 Warner Drive Editorial and Executive Offices: MEMBER AUDIT BUREAU OF CIRCULATION Culver City Calif. ABC 25 West Broadway, New York 7, N. Y.

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APRIL. 1949 8

REG. $27.50 LIST 12 INCH COAXIAL ONLY HALLICRAFTERS il N M SPEAKER $10m 11 -TUBE FM -AM CUSTOM REC. .7 ..I * BRAND NEW * FACTORY CARTONED * BUILT IN CHASSIS III MATCHING NETWORK I $11001 ed by one of America's finest speaker builders. VALUE for fidelity selling M °GEE'S This speaker incoorporated In radios in 11-TUBE FM /AM ATUE FM /AM $5950 500.ÁInicbracket. MODEL SALE PRICE t 84 agn ta PM for tttealowdnlgeeand2- MODEL 5.56..959.50 5.59..539.95 V The pass axially built -In 3- Alnico tweeter. high Model 9 -56 Hallicrafter, high fidelity. 11 tube AM.FM Radio receiver chassis for custom pot Installations. Receives standard broadcast 540 to 1700 KC and 88 to 108 MC. Automatic 8 ohm output transformerthewill hook in place ofany home Phono connection on rear voice coil). 2 wires frequency control on FM, holds the receiver in perfect tune. radio speaker, as have an 8 ohm Only to connect will of Chassie. Full range tone control with base boost. Push -pull 8K8 Tubes In audio system. handle 18 tts .ey response. 50 to 15.000 CPS. This co -axial PM speaker Frequency response essentially far. from 50 to 14.000 CPS. Wide vision accurately should buy an ordinary speaker. when we offer you the speaker of calibrated slide rule dial, with pre.$ lection on broadcast bend. Output transformer matches for $33.uSyu. 500 ohm line. 4 Antenna terminals: two for AM and two for FM. This is the finest type Stock NO. CH -12%- Weight e lbs. 510.95. 2 for 520.95. home radio that know oftoday. Better get your order In early. Designed to be used In radios ystppurcBhOase00 use DELUXE MODEL 12 INCH COAXIAL P.M. SPEAKER $12.95 this hassis` $I 1Ó.ÓÓR However8400.00 nables treofer` these same basic design as the model CN -12X. described above. carton. S -58 Halllenften Ch Is, complete with tubes and operation in- 12" co-axial No. CR13%. The to voice but furnished with 0.8 os. magnet i the 12" woofer. Frequency response. 40 to 15,000 strucStions, at only 859.50. less speaker. Spe her matching Transformer 500 OHM %. Weight 9 lbs. coil 251bs. S -58's with coaxial PM speaker. Pick your ModelllCR -13X 512.95. 12 `for a$2 95Y b l2. 0nextr. [heig,ht uylyour tchingg S-511 tubes. 500 ohms line Aorspeakerschassis, ubes, 500crOhm"to "lineed matching traie transformer. High fidelity 12 coaxial PM former and 15° King Co -AX PM eaker: REGULAR speaker: Model CR.I3X. All for only 571.95. model S-1p X. This is an ideal hination for the recreation room, having both heavy $60.00 LIST SPEAKER $2495 5 -5e Nellie ra /ten AM-FM is, with base andexcellent high frequency response. 15 INCH COAXIAL tubes, 500 ohm to line matching trans- of former and our 12. 12 co. Alnico V PM All for the price only $51.95. *CURVED MOLDED CONE *21.5 02. MAGNET *OUR FINEST SPEAKER University THE KING COAX. A 21.5 oz. 15 inii, Alnico V PM speaker with a built-in high frequency rqe Thi co bin-efuncy FM. folded dipole antenna, with 80 feet of awcur Will respond to from 50 to 12.000 cycles. This le ruggedly built speaker with then equipped with 5 foot vr. piece molded cone. Built -In high pass filter. Just hook to any 8 ohm frequency response..All for only $03.50. mast. °$4.49. extras output. Built by the maker of our ever popular 12 Inch coax model 4.12X. Weight 22 lbs. Model 5.59 Nallicrafters, high fidelity. 8 tube FM -AM radio chassis, for custom Installa- This ker has a retail list of over $80.00. We offer you our 5. 15x15 -inch coax for tion. Size 12 x 71" 9-. An excellently engineered hassis for radio sen of the only $24.95. 930b broadcast to 700 kc ratedcalideReceivesdl Variable tone n Frequencync1SI response 60 to 14 000 CPS. LIST BK8 audio yystemm.y Output transformer matches 500 ohm line. A terrific value REGULAR $35.00 only $39.95. Priced comple tubes, but less speaker. Brand new factory ear - tatoned.Welght 18 lbs. Net S39.95.With Line to voice cou matching transformer $2.50. extra. Price complete. 8 -59, line transformer, ou Cn -12X. 12" coaxial PM speaker: tel for "JUKE BOX" 15 INCH $995 the Scoop [Tice of 549.95. P.M. SPEAKER SALE PRICE BUY COMPLETE FACTORY ENGINEERED KITS AT McGEE CONE HAS NEW MOLDED DELUXE 5 -TUBE 4 -TUBE T.R.F. KIT A carload purchase, from a number one builder of fine PM only enables prieceta ne.Owith 8l ohmpvaice AC -DC KIT for New one molded cone. voice BARGAIN $695 cou. 12 . Alnico V °magnet. will take 1 att. average SPECIAL and 25 you want Speaker woof the OUR $995 5buy tills model. Is ithot a doubt the most peaker LEADER for the money that is available today. Include postage for 11 lbs. Stock No. 15 -KR. Net price $9.95. dtsand beginners.g ëetafisten ry parurnhed o Made from Detrela Components build this kit. Including tubes diagram and A full size 5 -tube superhet radio kit housed photos. Has Alnico V PM speaker and tubes. KINGJUKE 50 -WATT 15 INCH P.M. SPEAKER SCOOP PRICE $16.95 13-in 12SK7. 12547. 5085 d 35W4. Plastie front. Lighted slide arullee dial. Incorporates cabinet with airplane dial. Receives broad- of juke astandard 2 gang perhet circuit. LOOP a 35x ease. The most effciently de- cast 550 800 easiest Will` ta15-LS-Thets peak dio nd aattspeaverage. with ntnna. ready punched chassis, etc. This is adio .1e.41.. signed watts input to give the another one our line radio KittKit Model of production kits. Weight 8 ins. a inary Lspeaker. Has 1/2" ohm voihceecoil and molded e pitwiceet cone. Design d Nt $6.95. retail for 550.00. Include postage for 18 lbs. Stock No. 15.1.9. Net price $14.95. MIRAS, for °12p8E6.f 1:AT6. 1005 and 3SW4. 2 $32.95. instructions are 1nt 11-TUBE eluded.. 5 dynamic spaeaker. broad. RADIO KIT cast 550 to 1850 kc. Weight 9 lbs. 50 WATT 12 INCH P.M. SPEAKER SCOOP PRICE $14.95 2 -BAND Model A30-12. 50 wattay super heavy padane" speaker. 1 Vse 8 ohm Kit Medal TF -6C. Net $9.95. treated voice coil and on Y t half ac Haspot, bolt os. V magnet. Frame Is of heavy construction with metal poteit r. soured 2Ìn .vAllnico enamel. This speaker is the best lue possible today. Efficiency Portable Player KIT Scoop $9.95 silver-grey speakers. Is two to three times that of ordinary Especially recommended for all public Deno . portable electronic $1695 address systems and high quality home audio systems. Will handle 35 watts with ease lengths of time. Its tai value record player k,t ,o ,lelute 50 watts peak for short Is $50.00. But, by our large n,l case Includes ll Purchase, speakerpp with parts partsand dia. Kit Model AC -AK6. A c,tnplele kit of parts. merchandisse1eThis . t Is the latest pfroductioon. Model Á5 0. Weighte15s lbs. SÚ.93,$14.95, Xram. (conies complete w'i toll tubes antid ready assts 2 for $29.00. grey leatereue portable to build a lime B.'u'll Le r ch tran 1110 cahillrt:, rying case selfstartlne 'dio. We fun,isb ,very pleee s well plum,' motor- pickup. 5" l,1ntM diaknun and photo. Chassis size lax 100 MINIATURE CARTONED TUBES $29.95 speaker aal all neerasaryPM 0 -inch lighted slide rule dial. Be. Part to sill 701.7 :m,Il- ndcast and foreign short w ,O MALLORY CONDENSER SALE 250,000 Tubes for fast sale. Tremendous Stock Na. ('K.I. Net IO lid MC, 3 kgang tuning condenser, lire - Value. Tubes up to Hat. 100 Cartoned selection , n both nt'6 Output and branded $3.00 i`ri.. 59.95. N- ,Meat This EVERY COND. GUARANTEED 1 YEAR fiyvac Miniature Tubes for k:t goes together like a manufactured i,'a . ' $29.95. Over a million sold. Guaranteed full Sale r. intended use rdo replacement. rt ALUMINUM CAN 340 Each In smaller quantities. 12 -WATT AMP. r ed , me libe i fur 10 Ibo. yodel AlAK1. Net $16.95 '.e SCREW MFG. IRS 12BA8 125%7 6AÚ6 ótFs KIT, described above. SAVE HALF 174 I28ES 19TS 6816 SAUT $10.95 yyyroouicalready have the small rta bes IUS 35W4 ISSUE 6846 GUM KIT MODEL AC.12. 12 watt amplifier kit. for receiver you Save half on these genuine Mallory Aluminum is parts onconstruction. amely the punched can upright screw mounting. Fresh stock. 3A4 SOBS 12BF6 68E6 (Miry Ideal for high quality record Player as ell dial assembly, condenser public address eO rding amplifier. gang, IF coils. Ose. one guarantee. 155 3585 11723 SATE and BF coils, band switch. diagram and S213 8 mfd. 50V. 1-x23/4" 49c Matched component parts, ready punched This is without a doubt the brat RS215 12 mfd. 50V. 1.8244 3V4 12ÁT7 6A6G 6E4 pan. One control fade. from phono phon.lue o microphone. Gain enough or in the V.S. today. Include postage q'I hs3-__. Sac 304 12AU7 ESNS GALS thassis for crystal for 9 lbs. Model DRKS. Net $6.95. 83282 888°1mfd 44504.12 dynamic microphone. o Kit A5K -7. A complete Kit on same chassis 354 12 BA7 6 %4 SAOS for volt AC 00cycle operation. a AC-A103.AC -AB. but ix an Priced complete with tubes: 2-OVO. 8SN7. w 8 Tube AC -DC circuit MALLORY Popular GT Tubes. individually cartoned and 68H7 and rectifier. Diagrams d photos push-pull 251.8 Output tubes. Other spec. AC -AKB. Include postage for branded acs. $35.00 per hundred. 39c furnished. Kit AC-12. Net $10.95. 12- 14 EVERYDAY Each in smallerH1á quantities. speaker lin. Net 510.95. microphoneSand extra. REPLACEMENTS evo 6x5 85147 128F7 12557 stand $4.95 6507 The above AC -12 amplifier wired and 'tested THEATRE lessff 85N7 6507 Ins 12.F7 ready to operate net 514.95. Specify Sback 45. ude GCS SY3 251.6 535 691.7 No. AC.1125. 12 -Inch Al nico V PM speaker QUALITY with metal tabs for rtlstly°ardor SeS 6K7 7OL7 55.95 extra. Crystal mike and desk stand chassis mounting. Fresh stock, nes year 6SJ7 352$ $4.95. guarantee. ° 1248 5Y3 184 12S17 AMPLIFIER ST505 8 mfd. 4504. a/4.421/2" 39v 6K6 12K8 65FS ST597 16 mfd. 450V. 1x22aa/n 39c 658 1948 MODEL -MIKE- BROADCASTER KIT ST598 20 mfd. 4504. 1x2°/ 44r 1258 6SA7 1246 BO 2X599 30 mfd. 50V, lry3 x- 49c ONLY $7.95 $75.00 Value bk 289 39 e 2N509 20x20 mfd. 150V. - T.V. SALVAGE $2.95 214518 858 mfd. 4504. lleggiVe 49c WIRED AND ONLY 25558 30,130 mfd. 150V. 1.42j/.. 44c Buy this sight nse Television Salvage 3N533 30430 mfd. 150V. 20x25V 34c Scoop. Over Resister molded. 848 mfd. 208254. Chassis 150 TESTED 35579 54c plastic. and rimle Condensen. No °Coils. 17 Tube Octal kets, 2 F.P. Condensen. Broadcasts 800 to 1500 35584 Bx8x3 mfd. 4504. 1411- 2ska ßßc a up built 45718 8x8 mfd. 450V. 10x10 254. parts. KC from either s9c tear fors theñat 317Fz Net epehyono- 3/4 2.95. Weight 12 oradynamic mile. Makes with paper any radio receiver a P.A. Complete 1-, sail rue -fidelity audio ampU- Insulatingt Ctubes.°Ltseparate sectionss ith or recording amplifier. 1k1t000c from a AUTOMATIC CHANGERS $12.95 system, record player lu . Bur PPIn of these at over ives broadcast quality. Has fader control cycles. LInputls flor crystal mike ha f off. Fresh stock, a year guarantee. Record a regular oraGeneralaand st3 39t from mike to record simulating TCS45 20x20 mfd. 150V. 1-x2 12 nc h or 21,-1100 Óh uomaicl y. broadcast station. is electrrick ariable- arluctañ a TCS47 30x30 mfd. 1504. 1x2 44e Base 13/x14. LDiight weight crystal 2- 12SJ7 ad 35W4 tubes. tone controls and fader controll.p. Merit high TC848 40440 mfd. 1504. 1.52 " 49t ppsin a changer. Net Priced with tubes and connecting Instrvc- fidelity TCS52 10x10 mfd. 250V. l-x2 SSc $IÌ2.93,rtwo for°$35.00.'" Works , 0. 250 ande500teoohm Complete 20x20 mfd. -. Stewart Warner with Permanent Needle. Cextra. DgCrryyel Model with miniature tubes. (P 6 BAPSyS ; n tout - mike and s tdo $4.95 7 TCS71 45O. 1- x2AM.9 - 49e Size Webster for kk°truly a de-luxe mike -phono oscillator. TCS74 15x15 mfd. 450V. 1x2 690 Dual Speed 95ndel 240.5.00. prreh TCS7S 20x20 mfd. 450Vi"x3t 05e Size 12x13 1/2. Net 529.25. DE-2X Wired and ME 15R naety$24.95. Lachassis.ired andntested Mallon, TCD dual with common neg and sttedd. Broadcastsdch from 18ÓÓ to $34.95. Speakers recommended. Alter 15- for any crystal pick-ups. A new. power- inch model 603E. Net $63.00. Our 15 -inch TCDSS 20x20 mfd. 2504. 1'x2 34c COMPLETE fgainfulul circuit has variable sin control. Priced King coaxial regular $02.50 list net 524.95. TCDS2 10x10 mfd. 250V. 1x2- 29e with 2 rtDea and connecting Our 12.inch coaxial model CR -13X 512.95. TCD85 20420 mfd. IV,nv. 1 ^43- 34c INTERCOM atr uctione 53.95 ODD ABOVE MALLORY ELECTRO YTICS B AND $11.95 CRYSTAL CARTRIDGES 6 -VOLT TAKE 10% DISCOUNT Artie MLP1 cartridge used in Webster POWER SUPPLY McGrade Intercom.Master aand d y original equipment SCOOP $2.95 MALLORY BY- PASSES iand sub -station. housed changers.hanggee with needles 51.49. n small matching wal- MLP -2 Improvement over the MLP -l. lr/ Volt -90 Volt Vibrator DONT PASS UP THESE . bete, 5Ló x 7 xa34 Inches. Has quiet type QT needle. Scoop price, Power Supply- Makes I f4 GENUINE MALLORY Slnutoping frontfor desk all installations. S1.9S. tand- portable radios works on TusutacS AT 50 Standard L -40. 1..28. cartridges. old O volt storage FireiaSuub- statiion may be °usinterconnectingto lys. Complete with rest clip. Each $1.79: battery. Has PRICES UNEQUALLED du 10 prong pacalk plp . W r feet from Cation. These units are new 10 for 515.00. $10.00. S e I $ug 2o9 5rth. 800 Volt type TP -Wax filled. and factory cartoned. Complete with tubes. Annie L -70. L-75. cartridges or equal. Each, Stock No. VT. lbs. .004 .008 Se Each. Made to retail at $29.95. A lucky purchase 51.79: 10 for $15.00. X Weight 6 .ióó for2s. 4s08 enables us to offer these to you: for Only Anatole ñe2 -A or equal volt output. B eldon =100 Watt Soldering Mallory-1800 Volt Buffers .002 .02 .04 511.95. postage for 8 lbs. Stock used in long players, etc.. $1.79; Iron for radio set bile. Worth .05. 15e Each. 10 for 51.29. No. MG -2S. 10 for 6ne 53.05. Sale Price 51.95.

T "" Ad. Privet F. o. e. Koda SEND 25% DEPOSIT- BALANCE C.O.D. °'d"25% DepmTfrom with C.O.D. order include McGEE RADIO COMPANY ra.taga with f°" remittance. 1227 McGEE ST., KANSAS CITY, MISSOURI RADIO- ELECTRONICS for 00 QQQQ

Increase Your Technical Skill and Your Income

with CREI Spare -Time Training at home . a e

' YOU'RE satisfied with your present job -and so wrapped up Here's what Student Roeschke says of CREI: "This course of in its routine that you don't look beyond today -then CREI study has been very beneficial to me, not only because it has added can't help you. But if you're an ambitious radio technician who alot to my technical knowledge alone, but has enabled me to realizes that better jobs go to melt with technical education, then obtain several increases in income during the past two years." CREI has an educational program for you. Whether your interest service its 22 years of background in and activity are in manufactur- CREI places at your broadcasting, television, servicing, radio -electronic instruction- It is an ing or you the way" home study and residence any other branch of electronics, can "go all that takes you through introductory, with CREI. Accredited Technical Institute basic principles to advanced work, and on to specialized fields of capabilities permit. Add CREI technical education to your present radio experi- radio -electronics as your ence, and you can become worthy of a better job with bigger pay Send for, and read, the new CREI catalog and course outline. checks. You can't ignore your need for more technical education, It explains the sound up- grading program, the thoroughly proven because the radio -electronics industry is moving ahead so fast, courses, and what CREI can do for you. It gives you a good that more technical knowledge is necessary if you want a better idea of how practical and easy -to- understand CREI courses are, position -and larger pay checks. You need to fortify yourself and shows you why so many thousands have benefited by CREI with additional study if you are to meet the challenge of expanding enrollment since 1927. fields -and the job competition created by wartime advancements. VETERANS! CREI TRAINING AVAILABLE UNDER G. I. BILL

If you have had professional or amateur radio experience and want to make more money, let ua prove to you we have the training you need to FREE BOOKLET qualify for a better radio job. To help us answer MAIL COUPON FOR intelligently your inquiry -please elate briefly your background of experience, education and present position. CAPITOL RADIO ENGINEERING INSTITUTE 16th & Park Road, N. W., Dept. use. Washington 10, D. C.

Gentlemen : Please send your free booklet, Your Future in the New World of Electronics," together with full details of your home -study training. I am attaching a brief resume of my Capitol Radio experience, education and present position. Check field of greatest interest: PRACTICAL RADIO -ELECTRONICS PRACTICAL TELEVISION Engineering Institute BROADCASTING AERONAUTICAL RAD10 ENGINEERING RECEIVER SERYICIND An Accredited Technical Institute NAME --- STREET Dept. 14íA 16th and Park Road, N. W., Washington 10, D. C. CITY ZONE STATE

I AM ENTITLED TO TRAINING LINDER C. I. RILL. BranchOffices: New York (7) 1 70 Broadway Son Francisco (2) 760 Market St. APRIL, 1949 101 The Radio Month ,1Ific,t "Flip -Up" TV ANTENNA the revolutionary PRE -ASSEMBLED, PRE -WIRED TV ANTENNA that gives Su- perior Performance on ALL CHANNELS -yet COSTS YOU ONLY I/2 the price of equivalent antennas!

Pre.wired, reedy for use.

Connes with% Guy Ring end wire Rotatable New multiple recorder may make music and entertainment available on tape as it is on discs. Base TAPE RECORDINGS are duplicated vania at a special meeting held for the by a new multiple recorder paralleling purpose February 14. The presentation the disc -pressing process, developed by was made at a luncheon held at the G11 The Minnesota Mining and Manufac- William Penn Hotel in Harrisburg, to turing Company, makers of Scotch re- James M. Skinner, Jr., Philco's vice - cording tape. The firm announced last president in charge of service and PRE -ASSEMBLED, ready for use. month that the machine would repro- parts, by Leonard Helk, president of the Radio Technicians As- Just "flip -up" (like an umbrella) and duce 48 hours of recorded material on Lackawanna tape in one hour. The master tape is sociation. install. played through a playback head and The award was made in recognition done by Philco in estab- PRE -WIRED -just connect your the impulses are fed to recording heads of the work to lishing training courses in television lead -in to the two terminals. through which tapes are running several other reels simultaneously. All repair and maintenance. The meeting RECEIVES ALL CHANNELS tapes are driven by a common capstan was addressed by Mr. Skinner and by to maintain perfect speed accuracy. Dave Krantz, chairman of FRSAP, and ALL -DIRECTIONAL; can be ori- Either single -track (ordinary) or dou- briefly by delegates from neighboring of radio press, and ented for the weakest station in an area ble -track tapes can be duplicated. The states, editors the (see on Magnetape Twin - representatives of Philco. More than 40 with assurance that all other channels latter story Trax, October 1948 issue, page 42) run persons, some from points as far dis- will be brought in equally well. in one direction using half the tape tant as New York City and Indianap- cere- EXTREMELY SENSITIVE. Unusual width, then in the other using the re- olis, attended the presentation maining portion of the tape. Forty -eight mony. high gain on upper channels. Ideal for of these running at 33/4 inches per sec- fringe areas. ond can be turned out in an hour, each TOWN MEETING of Radio Techni- containing an hour -long program. At cians, the fifth and last in the current $695 NET series, will take place on April 11, 12, PRICE: 71/2 inches per second, 32 can be dupli- and 13 in the Ashland Boulevard Audi- Completely assembled with rotatable base, 7 -ft. cated in an hour, each with an hour's mast, guy ring and guy wire. program material. torium, Chicago, Harry A. Egle, Town Additional 7 -ft. masts, to build antenna up to 19 Meetings chairman for the Radio Parts ft., of small extra cost. ANNUAL AWARD to "the organiza- Industry Coordinating Committee, an- ADDITIONAL Superior Features of the tion or individual who has done the most nounced last month. For the first time, "Flip -Up" Antenna for the radio service technician during each technician attending will be given Upper and lower bonds completely wired. Elimi- the year" was made to the Philco Cor- a "Certificate of Leadership in Tele- nates need for two separate antenna installa- and hang- tions for the high and low TV bands; therefore, poration by the Federation of Radio vision" suitable for framing no coupling losses. Servicemen's Associations of Pennsyl- ing in the shop. RUGGED CONSTRUCTION: Most of the antenna has been designed of non -conducting material which prevents possible grounding and reduction of signal strength. It has unusually high mechanical strength and is extremely rigid when installed. Guy ring and guy wires provided for added rigidity. Additional 7 -lt. extension masts can be furnished to increase height to total of 19 ft. -and REMEMBER. "Flip -Up" COSTS ABOUT Vs the price of equivalent antennas!

All prices fair traded . All prices 5% higher west of the Mississippi River. See your local Transvision Outlet, or for further information write to: TRANSVISION, INC.DELT. NEW ROCHELLE, N. Y. uth.r Tranarision News on Page 61 Leonard Halle, left, presents plaque to James M. Skinner, Jr., right, Philco vice -president. RADIO -ELECTRONICS for The Radio Month U.H.F. TV experiments will be carried on by WQAN, Scranton, Pa., WCFI, Pawtucket, R. I., and WPTZ, Philadel- NOTICE phia, Pa., if construction permits asked Beginning with the May issue the of the FCC last month are granted. The term "serviceman," which we have stations propose to operate experimental used for 20 years, will be discontin- transmitters to check the propagation ued. Instead the new and better term characteristics of "upstairs" television. TECHNICIAN CLOSE -SPACED TRIODE is the will be used. name given to a new u.h.f. tube an- The new term is coming into corn- nounced last month by Bell Telephone mon use throughout the entire radio Laboratories. The name is derived from trade and is in keeping with the growing importance of the service- the extremely small spacing -about one - se technician. When radio was young fifth the diameter of a human hair - almost anyone with a smattering of Y between grid and cathode. The small rodio could service a receiver. Now- spacing reduces electron transit time, adays the increasing complexity of making for better performance at ex- radio receivers - and particularly tremely high frequencies. It is only television receivers-is such that only about one -sixth that found in any pre- a qualified technician can do justice vious triode. The tube's grid wires, to such receivers. This condition will . continue in the future. The Editors á COLORED RECORDS will be offered by RCA Victor, the company announced last month. All the new 45- r.p.m. discs (see page 12, March issue) will be color - coded to indicate the type of music. Ruby red will be used for serious music, midnight blue for semi -classical, black for popular, yellow for children's, green for Western, blue for international, and cerise for folk music. íü%Gf!%C RADAR played a dual role last month in an accident at sea. The radar indicator aboard the Coast Guard icebreaker FREE 1949 Eastwind showed that a ship was close by but the master did not believe the CATALO G indication. The Eastwind collided with the Gulf stream, a tanker, in a pre -dawn fog, because the radar was ignored. Re- ceiving an SOS from the stricken ship, ALL MERCHANDISE AVAILABLE ON Captain Frank G. Boyer of the Suzanne, 14 miles away, picked it up on his radar, WARDS MONTHLY PAYMENT PLAN which guided him to the scene. This Supplement to Wards Electronic Equipment Catalog contains nationally Photo and cutaway drawing of new u.h.f. tube. known test instruments for the radio serviceman. Has everything from pocket - .0003 inch in diameter, are spaced .001 inch apart; winding them is one of the size meters to large oscillographs, in- most delicate operations ever attempted cluding new models for servicing FM, vacuum -tube construction. in AM and television equipment. The tube will be used as an amplifier, modulator, oscillator, and frequency Also features high quality Sound Sys- multiplier in microwave relays. It is tems at greatly reduced prices, tele- expected to make the relays capable of handling more frequency channels. vision sets and accessories, amateur Another new development of Bell Lab- gear, and high fidelity radio components. is two- stream oratories the amplifier. Mail coupon for your free Catalog. This is a traveling -wave tube with two electron streams instead of one. A _-__------stream of slow electrons takes power RE from a stream of fast electrons, and an MONTGOMERY WARD- Chicago, - impressed wave becomes stronger as it Baltimore, Albany, St. Paul, Denver, no travels down the tube. There are Kansas City, Portland, Oakland, Ft. Worth. resonant circuits; the tube is simply a Raytheon Photo wave transmission path which can am- Please send free 1999 Supplement to Wards plify over a range of 1,000 mc. Capt. Boyer of the Suzanne scans radar 'scope. Electronic Equipment Catalog.

Name MainnallMMINNININ (Please PRINT plainly) al*is: . v Address

City Two -stream amplifier is a modified traveling -wave tube with a bandpass of over 1,000 mc. State APRIL, 1949 12

leaticl¢it 5"OSCILLOSCOPE KIT ?e4ta/eea Instant switching to plates or amplifier from front panel. Sweep generator supplying variable sweep 15 cycles to 30,000 cycles. All controls on front panel. Cased electrostoticly shielded 110 V. 60 cycle power transformer. AC test voltage on front panel. External synchronization post on front panel. Deflection sensitivity .65 V. per inch full gain. Frequency response ± 20% from 50 cycles to 50 Kc. Input impedance 1 Megohm and SO MMF. The Heathkit 5" Oscilloscope fulfills every servicing need. The husky cased power transformer supplies 1 100 Volts negative and 350 Volts positive. Tubes supplied are two 1949 MODEL 6SJ7 amplifiers, 884 sweep generator, two 5Y3 rectifiers, and 5BP1 CR tube. Grey qeciritiegr VACUUM TUBE crackle aluminum cabinet and beautiful grey and maroon panel. Chassis especially designed for easy assembly. KIT An oscilloscope provides endless sources $3gsó VOLTMETER of experimentation in radio, electronics, medicine and scientific research. Detailed instructions make assembly fun nom:., 9e+ateal:ed and instructive. Shipping Wt., 24 lbs. Express only. ELSE TO BUY New 200 ua Meter. 24 Ranges. New Accessory H.V. Probe makes AND Heathkit a kilovoltmeter. (Extra) ?tea, eaddeiít SIGNAL TRACER New A ry RF Probe extends range to 100 megacycles. (Extra) UNIVERSAL TEST SPEAKER KIT A new Model V -2 Heathkit VTVM with The popular Heathkit signal tracer has now new 200 microampere meter, four ad- been combined with a universal test speaker ditional ranges - full scale linear ranges at no increase in price. The same high on both AC and DC of 0-3 V., 10 V., quality tracer follows signal from antenna 30 V., 100 V., 300 V. and 1,000 V. to speaker - locates intermittents - de- Accessory probe listed elsewhere in ad fective parts quicker - saves valuable serv- extends voltage range to 3.000 and 10,000 ice time - gives greater income per service volts D.C. New model has greater sen- hour. Works equally well on broadcast - sitivity, stability and accuracy - still the FM or TV receivers. The test speaker has highest quality features - shatterproof assortment of switching ranges to match plastic full view meter face - automatic push pull or single output impedance. Also PA systems meter protection, push pull electronic tests microphones, pickups - $1q5° V. voltmeter circuit, linear scales - db. - comes complete - cabinet - 110 60 scale - ohmmeter measures 1/10 ohm cycle power transformer - cubes, test probe, ELSE TO BUY all parts and detailed instructions for as- to 1 billion ohms with internal battery - e44K9 isolated DC test prod for dynamic meas- sembly and use. Shipping Wt., 8 lbs. urements - 11 megohm input resistance on DC - AC uses electronic rectification with 6H6 tube: All these features and s eat`tie ELECTRONIC SWITCH KIT still the amazing price of only 524.50. t Comes complete with cabinet - panel - three tubes - new Mallory DOUBLES THE UTILITY OF ANY SCOPE switches - test prods and leads, 1% ceramic divider resistors and all An electronic switch used with any other parts. Complete instruction manual for assembly and use. Better oscilloscope provides two separately start your laboratory with this precision instrument. Ship. Wt., 8 lbs. controllable traces on the screen. Each trace is controlled independently and the position of the traces may be varied. The input and output traces of an amplifier may be observed one beside the other or one directly over 'e¢e% the other illustrating perfectly any change occurring in the amplifier. Dis- tortion - phase shift and other de- fects show up instantly, 110 Volt 60 RF SIGNAL cycle transformer ca-..rated. Uses 5 tubes (1 6X5, 2 6SN7's, 2 6SJ7's). Has individual gain controls, position- GENERATOR KIT ing control, and coarse and fine sweep. ing rate controls. The cabinet and panel match all ocher Heathkits. Every part supplied including detailed in- $345° $195? structions for assembly and use. Ship- ping Wt., 11 lbs.

3 -TUBE ALL WAVE ELSE TO BUY ,Cgeide R A D I O K I T An ideal way to learn radio. needs Heathkit fulfills every This kit is complete Every shop a good signal generator. The ready to assemble, with tubes Kc. to megacycles with and all other parts. servicing need, fundamentals from 150 30 Operates from 110 V. AC. Simple, strong harmonics over 100 megacycles covering the new television clear detailed instructions make this a good radio FM 110 V. 60 cycle transformer operated power supply. training course. and bands. Covers regular broadcasts and short wave bands. 400 cycle audio available for modulation or audio testing. Uses Plug -in coils. Regenerative circuit. Operates loud 6SN7 as RF oscillator and audio amplifier. Complete kit has every speaker. Shipping Wt., 3 lbs. part necessary and detailed blueprints and instructions enable the builder to assemble it in a few hours. Large easy to read calibration. HS30 Headphones per set $1.00 Convenient size 9" x 6" x 43/4 ". Shipping Wt., 41/2 lbs. 2½" Permanent Magnet Loudspeaker 1.95 Mahogany Cabinet 2.95

.. a BENTON HARBOR 20, MICHIGAN

RADIO -ELECTRONICS for 13

Hearbkri tech/from: ra!brarin /or Crobdcskerrrr,sr Hearbkri Condng ariee GOO, r raParity bridge o/ R°dio 1 % acrarary.

eeettitkie- TELEVISION ALIGNMENT GENERATOR KIT

Everything you want in a television alignment generator. A wide band sweep generator covering all FM and TV frequencies -a marker indicator - AM modulation for RF alignment - variable calibrated sweep width 0 -30 Mc. - mechanical driven inductive sweep. Husky 110 V. 60 cycle power transformer operated - step type output attenuator with 10.000 to 1 range - high output on all ranges - band switching for each range - vernier driven main calibrated dial with over 45 inches of calibrations - vernier driven calibrated indicator marker tuning. Large grey crackle cabinet 16 -1/8" x 10 -5/8" x 7-3/16". Phase control for single trace adjustment. Uses four high frequency triodes plus 5Y3 rectifier - split stator tuning condensers for greater efficiency and accuracy at high frequencies - this Heathkit is complete and adequate for every alignment need and is supplied with every part - cabinet - calibrated panel - all coils and condensers wound, calibrated and adjusted. Tubes, transformer, test leads - every part with instruction manual for assembly and use. Actually three instruments in one - TV sweep generator - TV AM generator and TV marker indicator. Also covers FM band. Deliveries start early in $395° March. Order early.

110 V. A.C. MILITARY RECEIVER Veatfizit SINE SQUARE WAVE POWER SUPPLY KIT AND Ideal way to convert military sets. 110 V. 60 CONDENSER CHECKER KIT AUDIO GENERATOR KIT cy. transformer operated. Supplies 24 volts for filament - no wiring changes inside radio. Also supplies 250 V. A95? D.C. plate voltage at $345? 50-60 MA. Connections itaftsurg tI direct to dynamotor in- itoitGOLg put. Complete with all ELSE TO BUY parts and detailed in- ELSE TO BUY S5.95 structions. Ship. Wt., 6 pounds. 7eae7ea Experimenters and servicemen working with a Bridge type circuit Power factor scale square wave for first the time invariably wonder 110 V. A.C. TRANSMITTER Magic eye indicator Measures resistance why it was not introduced before. charac- The 110 V transformer Measures leakage teristics of an amplifier can be determined POWER SUPPLY KIT in operated Checks paper -mica- seconds compared to hours For several of tedious BC -645, 223, All scales on panel electrolytic. plotting using older methods. Stage by stage, 522, 274N's, etc. amplifier testing is as easy as signal tracing. Ideal for powering Checks all types of condensers, paper -mica- The low distortion ( less than 1%) and linear military transmitters. electrolytic- ceramic over a range of .00001 MFD output ( ± one db.) make this Heathkit equal Supplies 500 to 600 to 1000 MFD. All on readable scales that are or superior to factory built equipment selling for volts at 150 to 200 read direct from the panel. NO CHARTS OR three or four times its price. The circuit is the MA place, 6.3 C.T. at MULTIPLIERS NECESSARY. A condenser popular RC tuning circuit using a four gang 4 Amps., 6.3 at 4 checker anyone can read without a college variable condenser. Three ranges 20 -200, 200- Amps., and 12 V. at education. A leakage test and polarizing voltage 2,000, 2,000- 20,000 cycles are provided by 4 Amps. Can be com- for 20 to 500 volts provided. Measures power selector switch. Either sine or square waves bined to supply 3-6- factor of electrolytic between 0% and 50%. instantly available at slide switch. All com- 9-12 or 24 volts at 4 amperes. Kit sup- 110 V. 60 cycle transformer operated complete ponents arc of highest quality, cased 110 V. plied complete with husky 110 V. 60 with rectifier and magic eye tubes, cabinet, cali- 60 cycle power transformer, Mallory F.P. filter cycle power transformer, 5U4 rectifier. brated panel, test leads and all other parts. condensers, 5 tubes, calibrated 2 color panel, oil filled condensers, cased choke, punched Clear detailed instructions for assembly and grey crackle aluminum cabinet. The detailed chassis, and all other parts, including use. Why guess at the quality and capacity of instructions make assembly an interesting and detailed instructions. Complete - nothing a condenser when you can know for less than a instructive few hours. Shipping Wt., 13 lbs. else to buy Shipping Wt., 22 lbs. twenty dollar bill. Shipping Wt., 7 lbs.

>. > t .j9 e e e BENTON HARBOR 20, MICHIGAN ` 3 APRIL, 1949 l4

BC 746 TUNING UNIT NO. 257. Plug in transmitter NMN look tuning unit from army Walkie Tolkio. Contains antenna and I POWER TRANSFORMER Streclais tank coils, tuning condenser, NO. 226. Primary 117V. 60 cycle. I transmitting and receiving crystals. Ideal transmitter founda- ,e. Secondaries supply 746 V.CT at 220 ' MA, 6.3V. at 4.5 A., and 5V. at 4A. tion. Shipping Wgt. 1 Each tit Will handle 13 tube radio receivers. lb. $1.00 is limited, (Same as above except trans- Supply order early. Ship- mitter PEIO1C BC645 POWER SUPPLY ping Weight 11 lbs. each. crystal in 80 meter ama- NO. 273. Complete power supply teur band 52.50 each) . . for BC 645. Operates from 12 $3.95 3 for $9.95 24 Volts. Supplies both AC and DC T30 THROAT MICROPHONE 410 required. Shipping NO. 258. Makes excellent contact Wgt. 13 lbs. Each $3.95 T32 TABLE microphone for musical mat,- MICROPHONE ment or vibration pick -up. Ship- DM 35 12 VOLT DYNAMOTOR NO. 210. One of the Army's best. ping Wgt. 1 Ib. 51.00 each NO. 274. New input 12 Volt at 18.7 Built by Kellogg, ideal for factory Extension cord with switch for Amperes. call system, public address, amateur Supplies 675V at 275 MA above S .50 each or 1/2 above voltage from 6 volts. Ex- use. Brand new in original cartons. cellent for auto use. Ship. Add postage for 5 lbs. $2.95L 7 BM MU Mt NEI n1=1 ping Wgt. 11 lbs. Each $7.50 MINIATURE ELECTRIC MOTOR BC731 CONTROL BOX 01/ONINIMMII=- NO. - 211. Tiny Delco motor only 1" x with Weston Model 476 AC Voltmeter -- 1t/4 "x2" 10,000 RPM. Operates from HOME WORKSHOP GRINDER KIT 6 NO. 208. Excellent buy in motor control to 24 V. Excellent for mod- NO. 230. Easily assembled 110V box. Site B "x10 "x51/2".Contains Wes. els. Add postage for 1 lb. L AC or DC ball bearing fully en- $2. 957J ton 0 -150V. AC 31/2" voltmeter, motor closed motor from Army surplus starting switch, 28 Rises all 30 Amp dynamotor. Purchaser to make OUTPUT TRANSFORMER 110V. and 8 fuse holders. Fuses d holders alone worth the price. simple changes and shaft exten- NO. 227. Push 95 pull 6V6's to 6 - 8 ohm Shipping Weight 18 lbs. sions, detailed instructions and all excellent 7J parts supplied. Motor approxi- I chacoilracteristics,. 3 for mately 5,000 R.P.M. Ideal for $1.95 METER SPECIAL tool -post grinder, flexible shaft I RCA SATURABLE REACTOR TRANSFORMER NO. 237. Brand new Delur Model tool, model drill press, saw. Ship- $3.95 246. New RCA No. CKV30531 AC 312 0 -800 M.A. D.C. Square ping Weight 3" 0 -10 6 lbs. INO.current 750 MA DC rrent 2 Amperes. M.A. basic meter with built in Rated 1.75 henries. Ship - shunt. Probably the best buy ever I ping wgt. 4 lbs. Each $1.00 offered in a surplus meter.d.2 Shipping Weight 1 lb. $2.95 COLLINS AUTOTUNE CONTROL HEAD 12.6V POWER TRANSFORMER NO. 278. Brand new controls used NO. 247. New cased 110 V 60 cy. on the ART /13, 100 -® Watt, Trans- v Power Transformer. Supplies 440V CI. `- - - - mitter. Types 7, 8, 10, and 11 avail- at 60 MA, 6.3V at 2A. and 12.6V at HEARING AID HEADPHONES able. Get a spare while available `uad 1 Amp. Excellent for military sets. NO. 216. The Army's best - eliminate flat as new cost is over 522.00 each. Shipping Wght. ears and outside noise. Complete with Shipping Wgt. 3 lbs. Price any type 6 lbs. Each. $1.951 transformer for co e on from low to (mention when high impedance. With cord and plug ordering). Each RCA INPUT TRANSFORMER complete. I NO. 248. Heavy duty RCA No CKV- Aid postage for 1 lb. $1.00 300 MA SELENIUM RECTIFIERS 30529. Input has primaries 600 to 200 I and 25 ohms secondary 250,000 ohms ß.4I NO. 209. Rated 300 MA of 36 BC 451 CONTROL BOX Volts, complete with mounting C.T. Shipping Wgt. dr T AA 12 lbs. Each NO. 236. Control box for 274N brackets. Shipping transmitters. Contains proper c.v. Wgt. 1 lb. 3 FOR $1.00 FEDERAL POWER TRANSFORMER I voice switch, 4 channel switch, NO. 252. New cased 110V 60 cy. power switch, mike jack and tele- 1N90 FEED THROUGH INSULATOR Power Transformer. Supplies 480V CT I graph key. NO. 276. Heavy duty feed at 50 MA and 6.3 V at 2.1 Amps. A Add postage for 2 lbs. 51.95 through, 2" diameter 4' long, beautiful transformer. Ship- complete with brass hard- ping Wgt. 4 lbs. Each $1.50 100 MA FILTER CHOKE ware d gasket. Shipping 1.5 in Wgt. 2 No. 641. Heavy henry choke drawn steel case, resist- 2 FOR $1.00 MILITARY POWER TRANSFORMERS 50 ohm NO. 229. Convert your military re- once, conservatively rated at 100 ceivers without rewiring the filament. MA. Shipping Wt. 1 lb. 50c 1N86 STRAIN INSULATOR "A type supplies 500 VCT at 50 MA, 0 , 5V. at 2A. and at FILAMENT TRANSFORMER NO. 277. Husky army type 11/4" 24V. 1/2 A. "B" type supplies 500 VCT at 50 MA, diameter, 51/4" long. Brown 5V. No. 922. 220V. 60 cy. primary sup at 2A. and 12V. at 1 Amp. State plies 12.6V. at 3.5 Amps, 15.6V at porcelain. Shipping 4 whether A or B type desired. 1 Wgt. 4 lbs. 4 FOR $1.00 $2.95 Amp. Supplies 6.3 at 3.5 Amps Shipping Weight 4 lbs. f 2.95 and 7.8V. at 1. Amp from 110V. Shipping Wt. 8 lbs. $1.50 G.E. BC 306 ANTENNA WALKIE TALKIE TRANSFORMER No. 744. Carbon microphone input PANEL METER TUNING UNIT transformer and to output head- Burlington 0 -300 VAC Meter NO. 231. Matches any aerial to 150 phone transformer, all in one case, I IF Watt transmitter, used on BC 375. Brand excellent for building your own. No. 290. Model 32XA 31/2" round new. Add postage AC Voltmeter 0 -300 VAC full scale. $25 Shipping Wt. 1 Ib. 4 for $1.00 for 20 lbs. L . 97 Scale also calibrated 0.600V. Bakelite I LOW PASS FILTER UNIT case. A beautiful meter in original I No. 637. 3000 cycle cutoff consists carton. Shipping Wt. $3.95 of 3 inductances and 4 capacitors G. E. 1,000 001.T 350 MA network, 500 ohms in and out. DRIVER TRANSFORMER Excellent for clipping oll frequen. No. 651. Couples 3000 ohm plate DYNAMOTOR cies above 3000 cycles. Drawn steel to push pull parallel grids hermeti- NO. 213. An ideal dynamotor for cose, shipping Wt. 5 lbs. $2.50 cally sealed. Ship. Wt. 1 lb. $1.00 mobile operation in taxicabs, police 0 cars, sound systems and amateur sta- `----_-----s and. MODULATION TRANSFORMER OUTPUT tions. Supplies above voltage from 12 FM PUSH BUTTON TUNER No. 745. Companion transformer Volts or 500V. at 350 MA from 6 NO. Volts. Complete with starting relay, 224. Brand new ten push but - to above driver. A push pull output, ton tuning assembly from Army to 5.95 and fuses. New. Our Dynamotor A. FM 3000 ohms 3.2 ohm voice coil, or I . eiver. Contains 4 gang 100 MMF to 1250 ohms at 80 MA.. A high Shipping Weight 72 lbs. silver plated tuning conden- quality cased unit. Shipping Wt. _ - - - _ M. set. Add postage for 10 lbs. $2 . EACH 2 pounds. $1.00 GIVE PART NUMBER AND POS

e W 1 T O W HOW TO ORDER E G H SHOWN. ORDERSS USNCDREIR TSf20.0 0 ... W W I L L STAGE C. O.-Dí- COMP,cVIVY ... BENTON HARBOR IO, MICHIGAN RADIO -ELECTRONICS for .r-r.__...... T..._ ...... , . 15 itea' s{eattle t :t'' FM TUNER KIT HEATHKITS re aid ACCESSORIES Vie/agar ELSE$295o TO BUY CABINET EXTRA CHECKER KIT A truly fine FM Tuner with the coils ready TUBE óSt4 wound, all alignment completed - all that is necessary is wiring and it's ready to play eatcviced V. - uses super regenerative circuit - 110 individually. 60 cycle transformer operated two gang each clement - 1. Measures roller than. tuning condenser -slide rule calibrated 2. Has gear driven instructions switching for speed. dial - two tubes - complete 3. Has lever voltages. including pictorial enable even beginners range 4. Complete elementlament to build successfully.Shippmg Wt. 4 pounds. 5. Checks every lever switches. Beautiful mahogany cabinet for FM 6. Uses latest type full view meter. beautiful shatterproof Tuner (shown above) extra $3.75 7. Uses "x4" complete. 8. Loge size 11 "x14 you want. realizectthat this res features and you will sireeathkitobsolescence. aseallmThet qualityern Check the beauty -P The high Speed simplicityty- beautiful e power transformer - each gged of tthter - measures oesizeb 110 V.0 cycle complete- parts - ofw 60 ower meter of best controls -9 fast action gearfete typees- Centralab f future ear finest Mallorybtslfory qckly typet cube ction cha all rays including. and set ruf and soofroller ckets locate time. sec ssa brass Bears to q valuable service driven nollcr chart minimum and saves the Heathkit necessary time to of tube elements, k_r switching cuts matter what arrangement element check. No your qualityC SHIPPING open handles r Heathkit the switching saves yit. rrder today.c self thattHeath again better build it now. WT. 15 LBS. today. See yO in a few weeks - char[ ready for itself cabinet - et ecwit will all F arts this tube detail stutructions - - ComPlea with to wire up and operate. VA< eeetetlect Iteweativeet BATTERY OPERATED VACUUM TUBE BATTERY ELIMINATOR KIT VOLTMETER KIT Now a bench 6 Volt power supply kit The famous Heathkit VTVM now in for all auto radio testing. Supplies 5 - battery operated type. Use it anywhere 7t/2 Volts at 10 Amperes continuous or - carry it out for work on auto aircraft boats any 15 Amperes intermittent. A well filtered radios - - - place where 110 V. house current is rugged power supply uses heavy duty not available - instant warmup - selenium rectifier, choke input filter turn the switch and it's ready to with 4,000 MFD of electrolytic filter. operate. Same quality features, six linear D.C. ranges 0.3V.-10V.-30V.- 0.15 Volt meter indicates output. Out- 100V.- 300V.- 1000V. High voltage put variable in eight steps. Excellent for extended to 10,000 Volts with probe demonstrating auto radios. Ideal for listed below. Large 200 microampere meter with shatterproof plastic face. servicing can be lowered to find - Ohmmeter measures from 1 /10 ohm sticky vibrators or stepped up to equiva- to one billion ohms with internal lent of generator overload - easily con- battery. 11 megohm input resistance on DC. AC is copper oxide rectifier in less than two hours. Com- structed type with ranges as above except no plete in every respect. $34 :° 3 Volt range. Complete with all parts, SHIPPING WT. 12 LBS. cabinet, 2 color panel, tubes, batteries. $225.° ELSE TO BUY test prods and detailed instruction SHIPPING WT. 18 LBS. i¿etlGcy 72otlel g ELSE TO BUY manual.

S H I P V I A 71e4' ñeatlrkll TOOL KIT BLANK _Parcel Post Now a complete tool ORDER _Express kit to assemble your HEATH COMPANY _Freight Heathkit. Consists of BENTON HARBOR, _Best Way Krauter diagonal cut- ters and pointed nose MICHIGAN assembly pliers, Xce. Inc screwdriver, 60 Gunn Watt 110 V. soldering iron and supply of solder. Shipping Wt., 2 lbs. Complete kit. 55.95

RF Crystal Teti Prase Kit No. 309. Kit to assemble RF probe extends VTVM range to 100 MC. Complete with IN 4 crystal. Shipping we ght, 1 lb. $6.50

0,000 V H.V. Tett Praha Kit No. 310. Extends ange of any 11 meg. ohm VTVM to 3,000 nd 10,000 Volt ranges. A necessity for tele- Enclosed for-lbs. Please Ship C.O.D.... Postage vision. Ship. wt., 1 lb. Money Order for $4.50 Enclosed ind Check ...

a . . BENTON HARBOR 10, 16 Radio Business General Electric Tube Division, Sche- RCA Engineer Products Department's nectady, New York, has developed a new engineer, RALPH V. LITTLE, JR., outlined `IT'S UP TO US! metal television picture tube which of- recently the progress in the develop- IYes, that's our favorite expression here at SENCO fers more viewing area in low -priced ment of television equipment for mo- RADIO. We know that "it's up to us" to provide TV sets. The tube has a diameter tion- picture )ou with to a prices, high quality merchandise, fast of 8% theatres. Isort, ce! Why not try us out now and see for inches, but will cost no more to build In an address before the winter meet- ourself 7 than a 7 -inch tube such as is used now ing of the American Institute of Elec- TUBES! in lower -cost sets; it will give 50% more trical Engineers at the Staler Hotel, All Banc New! R. M. A. Gwren'ee! picture. New York, Mr. Immeda,e Deaver t! a w .p Carlene. Little disclosed, "Two of Lots of basic systems of large-screen television 10 lo are being studied by RCA the Type Each Each Type Each Each Garod Electronics Corp., Brooklyn, in at present OZ4 69c 59c 6U5/6G5 69c S9c an effort to protect patent rights pend- time. One is the direct projection sys- 1A3 45 39 6U6GT 40 29 tem under which high -brillance IASGT 59 49 6Ú7G 35 25 ing on its new Tele -Zoom television re- kine- 1C5GT 69 59 6V5GT 59 49 ceivers, is utilizing every legal means scope images are projected by a highly 1C7G 64 58 6V6GT /G 45 39 reflective optical system upon special 105G 67 60 6W4GT 69 59 to prevent unlawful infringement, ac- 107G 69 59 6X5G1/G 49 39 cording to a statement issued by LEON- screens; the other an intermediate film 1F7 79 69 6Y60 71 63 ARD ASHBACH, system, using standard motion -picture ILC6 69 59 7A4 53 43 president of the com- 1LD5 69 59 7A7 59 49 pany. Provisions are being made, how- projection technique after television 11H4 69 59 766 49 44 images have been photographed on mo- 1LN5 69 59 71;7 49 44 ever, to permit competitive manufac- 1L4 ' 49 45 788 69 59 turers to make use of the development. tion-picture film and suitably processed. IP5 59 49 7C5 55 49 "At the present time," he said, "the 1R4 69 59 7C6 49 44 185 55 49 7117 49 44 problem of the engineer is to develop 155 58 48 7N7 49 44 Radio Manufacturers Association re- kinescopes capable of handling greater 1T4 69 55 797 69 59 ports that more than 975,000 television ITSGT 59 49 7671XXFM) 44 35 beam currents and operating at higher 1U4 49 39 7Y4 44 35 receivers were produced during 1948, potentials in an effort to increase the 1V 45 39 12A 79 69 bringing the postwar total TV set pro- 2A7 32 25 12A6 29 25 light output, while at the same time 2E5 89 79 12A8GT 35 28 duction to at least 1,160,000. An addi- developing smaller, less costly reflective 2X2/879 35 29 12AT7 69 59 tional 25,000 to 30,000 unassembled TV 3A4 49 39 12AU6 65 55 optical systems and directional screens 387/1291 59 49 12AV6 49 39 set kits were reported to have been with increased light gain." 395 55 49 128A6 50 45 manufactured last year. 354 55 45 12H6 39 34 Commenting on the performance of 3V4 79 69 12J7GT 45 .<9 With set manufacturers applying an the two systems, Mr. Little said, "The 5U4G 50 40 12K8Y 35 2S increasingly large share of their manu- 5W4GT 39 34 12 7GT 45 39 capabilities of the projection system are SY3G 42 37 12SA7GT/G 40 32 facturing facilities to television, par- equal to the best studio television equip- MGT 'G 40 33 12SFSGT 40 32 ticularly during the second half of 1948, ment, SY4G 39 32 12SJ7GT 55 49 but, of course, any deterioration 5Z3 59 49 12SK7GT/G 45 35 production of radio receivers last year of the signal between the camera and 5Z4 59 49 12SL7GT 49 43 declined about 20% under the all-time the projector 6A3 69 59 12SN7GT 49 43 causes an inferior picture 6A4 79 69 12597GT/G 40 32 peak reached by the industry in 1947. on the screen. Experience has shown 6A7 5.) 45 12SR7 35 32 Last year's output of radios, however, that large- screen images produced by 64135 '6N5 99 89 7223 55 49 was second in 6AC5 69 59 14A7 65 5S the highest the industry's both the direct and intermediate sys- 6AC7:'1852 79 69 1486 59 49 history. tems are entirely acceptable to critical 6AH6 49 39 1497 65 55 Total 6A L7 69 59 19111 89 79 industry production of radio audiences. The equipment and tech- 6AN5 65 5S 24A 49 39 sets in 1948 was estimated by RMA at niques of operation will 6AT6 49 39 25L6GT 55 45 continue to be 684G 89 79 25Z5 49 45 more than 16,000,000 of which RMA improved." 6BA6 49 39 25Z6GT/G 45 39 member companies manufactured 13,- 66E6 49 38 26 32 25 265,793. In 1947 the entire industry's 6BG6G 99 89 27 45 35 Scott Radio Laboratories of Chicago is 6BH6 79 69 32L7GT 52 48 production of radio sets exceeded 20,- demonstrating a new record player 6BJ6 59 49 35L6GT/G 45 39 000,000. TV set production by RMA ca- 6C4 29 25 35W4 43 40 pable of playing all three of the current 6C5GT 40 35 35Z5GT/G 43 39 member companies reached a new high types of records. The machine 6D6 49 45 35Z6G 43 39 of 161,179 in December, only 17,500 can be 6F5GT 55 45 35/51 42 37 set for three speeds, 78, 33%, and 45 6F6GT 45 39 36 35 29 sets under the entire output of televi- r.p.m. 6F7/VT70 39 29 39/44 25 19 sion receivers in 1947. 6G6G 59 49 43 54 47 6H6GT/G 43 36 45 49 39 RMA member companies reported 6J7GT 42 38 45Z5 59 49 manufacturing 866,832 TV sets in 1948 Garod Electronics Corp. president LEON- 6K6GT/G 45 46 59 49 39 ARD 6K7G 50 41 47 49 39 as compared with 178,571 in 1947 and ASHBACH announces the formation 6K7GT/G 49 39 50 1.49 99 6,476 in 1946. Production by non -mem- of a new company to be known as Garod 6K8 69 59 SOL6GT SO 45 e 615G 69 59 56 55 45 ber manufacturers brought the total Electronics, Ltd. of Canada, with a plant 6N4 49 38 57 45 39 TV set output in 1948 to more than located in the Small Arms Building at 6P5GT 55 49 58 45 39 65A7GT/G 44 37 75 59 49 975,000. Long Beach, Ontario, a suburb of To- 6507 49 39 76 49 45 Something more than 200,000,000 ra- ronto, for the manufacture and distri- SSH7GT 40 32 77 35 27 * 1SK7GT/G 49 39 78 49 39 dio receiving tubes were sold in 1948 by bution in the Dominion of Canada of the 6SL7GT 49 47 80 40 38 RMA member companies. Tube sales complete line of radios and television 6SN7GT 49 47 81 1.49 99 6507GT/G 44 37 84/6Z4 49 39 during last year totalled 204,720,378, an receivers now manufactured by Garod. 6SR7 41 36 85 49 45 increase of more than 5,000,000 over the Mr. Ashbach stated that manufactur- 6557 59 49 99V 35 25 199.533,827 in 1947. facilities 65V7 55 49 99X 35 25 tubes sold ing for the new organization 6T8 89 79 117Z6GTïG 79 69 Sales of receiving tubes in December are now completed and the company is OIL FILLED CONDENSERS also increased considerably over Decem- already producing Garod receivers for Standard Brand- Uprinhf Type. ber, 1947, but fell below the November, the Canadian market. Mr. Ashbach St. nd -Off Insulafo's. 6 Mfd. 600 VDC 69r 1948, sales, RMA said. December sales further commented, "It may be surpris- B Mfd. 600 VDC 79, totalled 19,270,164 compared with 16,- ing to the industry that this new com- 10 Mfd. 600 VDC 89, 8 Mfd. 1000 VDC $1.90 511,408 in December, 1947, and 21,118,- pany will produce television sets in Write for our FREE catalool 874 in November, 1948. Canada when it is well known that Can- /rlet"NUM ORDr°1 52.50 A breakdown of RMA member com- ada, at least at the moment, does not WHEN ORDERING -Send 25% deposit for al' C.O.D. shipments. Include sufficient postage -es pany sales in 1948 showed 146,162,214 have any facilities or television stations. cross will be refunded. Orders without postage tube; sold for new sets; 47,056,521 for However, our receivers have been engi- will be shipped express collect. All prices F.O.B Ne'. York City. replacements; 10,686,769 for export; neered to such a sensitivity point that and 814,874 sold to government agen- Buffalo and Cleveland can be picked up cies. December sales included 14,721,114 throughout the Toronto area with such &ENCO RADJOIN C. tubes sold for new sets; 3,440,437 for clarity that a substantial market ob- Dept. G. 73 West Broadway 1,048,760 for New York 7, N. Y. Tel. BEekman 3.649" replacements; export; and viously exists in Canada for the recep------59,853 sold to government agencies. tion of U. S. television broadcasts." RADIO- ELECTRONICS for 17

SCURLOCK'S RADIO SHOP Here's what ELECTRICAL APPLIANCES -- HARDWARE EVERYTNINO PERTAININO TO RADIO BUMITON, ALABAMA radio men September 18, 1948 say about Advertising Department Sylvania Electric Products Inc. Emporium, Pa.

Gentlemen:

In 1937 when we started our radio repair business, we used personal postal cards to get our name before our prospective customer.. For a beginner, this kind of advertising seemed a little more than we could pay, although it did won- ders for our business.

We are happy that the service industry has a great company behind us with national advertising and personal postal cards. During your first co-ordinated advertising campaign we bought 1200 cards and mailed them to our customers according to Sylvania's specifications. The results were so effective that we are going to use the campaign again. We want to see if the campaign is really responsible for the extra business we are enjoying.

The "funny cards ", as our customers cell them, are even responsible for payment of some of our past due accounts. Our radio sales are up. We are making allowance for old radios which our customers get out for us to repair after receiving our atomic reminder card.

We want to personally thank Sylvania for taking an interest in us and !riving us this low cost, yet effective, advertising.

RADIO AND TELEVISION SERVICE Like these service dealers you EXPORT ISERVICE ON ALL MAKER Ca can increase your business LOS Aama.ce. CA.. Sylvania's May, June, July and August campaigns November 1, 1948 are ready for you. Here's what you receive: Advertising Department 4 Postal Card Mailings -one for each month. Sylvania Electric Products Inc. 4 Window Displays -one for each month. Emporium, Pa. 4 Window Streamers - one for each month. Gentlemen: 8 Newspaper Ad Mats -two for each month. Radio Spot Announcements -several for each month. I would like this opportunity to tell you how much the Syl- vania co- ordinated advertising campaign has helped my business. Send for full details now! Remember, you pay only the postage on the government postal cards Although I have used direct mail postal card. in the past for soliciting new business, the tie -in with national advertising offered you mail. Sylvania supplies everything else free! in the Sylvania campaign was responsible for an extraordinary return. The response I have had from your campaign bee been truly amazing.

As an example, I mailed 1000 postal cards in May at a cost to ae of $10.00. To date this investment has brought a return of $352.19. During June, July and August I mailed another 1000 cards each month at a total cost of $30.00. To date the return from this investment bas SYLVANIA amounted to $760.46.

You will note that for a total investment of $40.00 I have, to date, enjoyed an increase in business amounting to 21,112.65 -- all from new customer.. I can safely say that there is still more Imeinees to come from these carde in future months. ELEHRICFLUORESCENT RADIO TUBES; CATHODE RAY TUBES; ELECTRONIC DEVICES; I mailed another 1000 cards to m' prospect list of 12,964 LAMPS, FIXTURES, WIRING DEVICES; PHOTOLAMPS ; LIGHT BULBS same. during October and November. I also expect to mail another 1000 cards during December. r Speaking for myself, I mould certainly like to see this cam- Sylvania Electric Products Inc. paign become a regular shot in the ere' at least twice a year. It will Advertising Department, R -1704 do much to help businese'in the spring and early fall when business is Emporium, Pa. usually slow. Gentlemen: Send full information on your May, June, July and Dealer Many thanks and best wishes. August Service Campaigns. Name Eery truly yours NIKE'S RADIO SERVICE Company By ///LLf /i'ms.oaer Address NScheelMe:a"an City lone ..,..,...... _ We 1811 vmel. trt - ...LI" ,s. Srfröttra. sel Itsrlo TV., 4 State

APRIL, 1949 18

Get Your FCC Ticket Which Jobs worth Better Pay $3,000 to $7,500

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I can train you to pass your FCC License Exams in a few short weeks if you've had y practical radio experience -amateur. Army, a N ny, radio servicing. or other. My time - proven plan can help you, too. on the road to success. License Let me send you FREE the entire story Just fill out the coupon and mall it. I will send FREE you. tree of charge, a copy of "How to Pass FCC Tells where to apply for and take FCC examina- License Exams," plus a sample FCC -type Exam, tions, location of examining offices, scope of knowl- and the amazing new booklet. Money Making edge required, approved way to prepare for FCC FCC License Information." Exams your Edw. H. Gaillard examinations, positive method of checking Vice President knowledge before taking the examinations.

Add Technical Training to Your Get This Amazing New Booklet Practical Experience & Get Your t, TELLS OF THOUSANDS OF BRAND-NEW. BETTER -PAYING err RADIO JOBS NOW OPEN TO FCC LICENSE HOLDERS 2. TELLS HOW YOU WILL BENEFIT BY HOLDING AN FCC COM- COMMERCIAL MERCIAL LICENSE. 3. TELLS HOW YOU CAN GET YOUR FCC COMMERCIAL RADIO RADIO OPERATOR OPERATOR LICENSE IN A FEW SHORT WEEKS -EASILY AND LICENSE QUICKLY, BY USING CIRE SIMPLIFIED TRAINING AND COACHING AT HOME IN YOUR SPARE TIME. a Few Short Weeks... 4. TELLS OF HUNDREDS OF OUR SUCCESSFUL STUDENTS WHO in NOW HAVE LICENSES AND NEW, SETTERPAYING JOBS. S. TELLS HOW WE PREPARE YOU TO PASS THE NEW FCC EASY if you use CIRE Simplified Training COMMERCIAL LICENSE EXAMINATIONS, WHICH NOW It's INCLUDE FM AND TELEVISION. and Coaching AT HOME in SPARE TIME 6, TELLS HOW WE GUARANTEE TO TRAIN AND COACH YOU UNTIL YOU GET YOUR LICENSE. PAYING. and quickly and be 7. TELLS HOW WE HELP YOU TO GET A BETTER Get your license easily LICENSED JOB, WITH OUR FREE AND EXCLUSIVE SERVICE, ready for the $3000 to $7500 jobs that are WHICH PREPARES YOUR EMPLOYMENT APPLICATION FOR holders. CIRE MAILING TO HUNDREDS OF EMPLOYERS. INCLUDING FM. now open to ticket RADIO course AM AND TELEVISION BROADCAST STATIONS. training is the only planned MANUFACTURERS, POLICE RADIO STATIONS, AND RADIO. of coaching and training that leads EQUIPPED TAXI, BUS AND PUBLIC UTILITY COMPANIES directly to an FCC license.

Your FCC ticket is always recognized in all radio fields FREE Send Coupon Now! as proof of your technical ability CLEVELAND INSTITUTE OF RADIO ELECTRONICS D .w RC -4 4900 Euclid Building, Cleveland 3, Ohio (Address to Desk No. to avoid delay) CIRE Find FCC License Pays Off in few short weeks by training Graduates I a I want to know how can get my FCC ticket time. Send me your amazing new FREE booklet "Money license has helped at home in spare "I now hold ticket Number P -10 -3787, and holding the Information," as well os a FREE sample FCC type exam dreamed of having. Yes, thanks Making FCC License me to obtain the type of job I've always and FREE booklet, "How to Pass FCC License Examinations" (does not cover CAA as Radio Maintenance Technician, to CIRE, I om now working for exams for amateur License) I am deeply grateful." at a far better salary than I've ever had before. Student No. 3319N12 Name .. 4. next I was signed license P -2 -11188 on Novemer The day "1 was issued radio operating, on board o tanker as Radio Operator- Purser. Besides which is all over -time and brings my monthly Address - - I handle the payrol's etc., No. 2355N12 pay up to between $400 and $650." Student Zone State CLEVELAND INSTITUTE OF RADIO ELECTRONICS City 3, Ohio Veterans check for enrollment information under G.I. Bill Desk RC -4 4900 Euclid Bldg., Cleveland NO -NO SALESMEN APPROVED FOR VETERAN TRAINING UNDER THE OBLIGATION "G.I. BILL OF RIGHTS" RADIO -ELECTRONICS fo Editorial

TELEVISION

. . . By-products sometimes constitute the

only profit of large corporations . . .

By HUGO GERNSBACK

HE radio industry has consistently missed the boat Never underestimate the influence of our youngsters -they in certain by- products on which it should have have usually an active say when a television set is bought, cashed in. nowadays. A good television gadget may influence them Ever since the earliest days of the art, outsiders strongly. who had no connection with the trade cashed in- Soon all television manufacturers will have to com- first on wireless, later on radio, and now on television. pete actively when the present boom has spent itself. For some foolish reason the established radio interests We can imagine all sorts of little gadgets that can have always thought it beneath their dignity to help pop- be made for a few cents, either to be given away or ularize radio. sold at cost by the manufacturer. All of these gadgets It would seem that others, par- would, of course, be in the shape ticularly the toy trade, have reaped and form of a brand television re- a harvest on items that rightfully ceiver, making in this manner a belong to the radio industry. permanent advertisement at an ex- During the early twenties when ceedingly low cost. the first radio boom started, hun- Such items too are kept for years. dreds of radio gadgets were sold in Savings banks for children, jew- toy, novelty, and department stores elry boxes for young girls- dozens all over the country. Only a pitiful of others instantly come to mind. few ever originated within the There is a long list of similar ar- radio industry itself. ticles that can readily be made to be With the present popularity of used as ashtrays, stamp boxes, television -which is sweeping the match boxes, ink sets, paper country - nothing is being done weights, nail boxes, puzzles, etc. either by the transmitting broadcast interests or the These items can be made in plastic, metal, or a combina- television set manufacturers to reap permanent good tion of both. They can be produced at low cost. will for themselves. Soon the country will again be The television broadcasters likewise can cash in on the flooded with hundreds of television gadgets, games, vogue of some particular feature that is timely. toys, and novelties without benefit to the industry. To mention only one, a miniature plastic articulated On this page we show a single example of an exceed- Howdy Doody can be manufactured probably for less ingly well- engineered miniature "television set." This is than one cent and given to the youngsters or sent to a replica of an RCA televiser and is currently mer- them in exchange for some box top. In this case the chandised by the Ralston Breakfast Food interests. It sponsor would, of course, foot the bill. is certain that several million of these little television The test pattern which is being broadcast by various gadget sets will be sold this year. It is a smart piece of stations lends itself particularly well for an ashtray - advertising for the RCA people, and is the first instance the pattern being embossed in plastic inside the tray. we have seen in years where some benefit accrues to the All these ideas can be hugely beneficial to the indus- radio industry from such an effort. try. But, the industry must work fast and it must be To get the set, you send 20 cents, plus an Instant up on its toes. Ralston box top, to the cereal company, and you receive We recently consulted a number of toy manufac- your television set, plus a musical ring. The little set, turers. All of them seem to have planned some kind of which measures only 7/s x 13/8 inches, is made of brown a television toy. By the middle of this year dozens of plastic, and with it come five 3/46 -inch circular films such toys will be on the market. Yet all of them will be which are inserted by way of a brass-back closure plate. sold without the television industry getting any direct The circular film's edge extends a bit beyond the set benefit. and can thus be rotated. A strong glass lens is molded There is truly a huge market for television by -prod- into the plastic case, and you look through it against ucts forming at present. The industry should cash in on the light to see various scenes. it immediately. APRIL, 1949 20I leadio Science Cover Feature

the Plect.et looks Tike. Improved ELECTRETS

By EDWARD PADGETT INTERESTING op ities for the electronics reses lie in the development of oved electrets. An New compounds produce elec- electret fixture of certain di- electri als which has been cooled trets with better stability t cation in a strong electric field. room temperature one electret sur- and higher surface charge .4 face has a negative electric charge and the other surface is charged positively. If the electret is covered with a metal - foil "keeper," these electric charges do not decay appreciably with the passage of time. The first workers to make electrets were Mototaro Eguchi of the Higher Naval College of Tokyo and Andrew Gemant of England and the United States, who repeated Eguchi's experiments some years later. Victor Laugh- ter published the first photographs of electrets in this hemisphere (RADIO - CRAFT, May, 1948). Andrew Gemant holds British patents in which electrets are used in experimental electrometers and transformers. The Japanese, however, were the first to find extensive practical uses` for the electret. Micro- phones captured from the Japanese during the war used electrets to furnish polarizing voltages. Scientists report that Carnauba wax (which comes from a Brazilian palm tree) is an essential ingredient in the preparation of wax electrets. Carnauba wax is a unique mixture of high-melting- point esters. (Esters -as well as water -are formed when organic acids and alcohols react. They are somewhat like salts, but react more slowly than salts.) The best grade of the wax is No. 1 yellow, or No. 1 North Country Carnauba wax. It is hard, brittle, and cracks easily. This cracking may be eliminated by adding suitable extenders such as par- affin wax to the Carnauba. Experiments performed by the writer The author's sister engaged in removing from the mold o new electret just out of the oven. at New York University indicate that RADIO -ELECTRONICS for Radio Science I21

HEATING ELEMENT TO TOP SCREWS AT LEFT HAND SIDE OF OVEN 5/8 i 29/32

9/16

O 4 -40 SCREWS e ® NUTS ON

1WALLLS o o BINDING POST

HEATING ELEMENT WIRE I FROM SCREWS ON BOTTOM RIGHT HAND SIDE DIMENSIONS IN INCHES OF OVEN 4 3/4

Diagram of heating wires shown in the photo. electret properties are associated with the polar groups (i.e., -OH, -COOH) that occur in certain substances. Para- ffin waxes contain no polar groups and, in themselves, do not form electrets. Carnauba wax contains polar groups and forms electrets. Early workers made electrets from a mixture of Carnauba wax, rosin, and beeswax. This mixture is not satisfactory for several reasons. For instance, beeswax is relatively soft and so complex, physically and chemically, that it is difficult to study. Rosin is unstable, is subject to decomposition by light, and precipitates out of the wax mixture. The writer has made electrets of better stability, and with higher surface Insulation in the author's oven allowed studies of prolonged cooling effects. charge, from equal parts of Carnauba dielectrics mentioned; metal foil (.001 - stores). Transite can be cut with a wax and Hercules hydrogenated rosin inch thick) ; a high -voltage power sup- small, heavy- bladed hacksaw. The (Staybelite resin). Hydrogenation of ply; a metallic mold (really a parallel - Transite slabs are held together with rosin eliminates the difficulties men- plate disc capacitor) to hold the molten brass 4 -40 machine screws and home- tioned above. Splendid semiplastic elec- dielectric; and an oven to house the made brass brackets (right angles). trets can be made from 45% Carnauba mold. An oven is used because controlled One of the photographs shows an oven wax, 45% hydrogenated rosin, and 10% cooling of the dielectric makes better lined with flake asbestos. The lining ethyl cellulose. electrets. From 1 to 2 hours is the best gave sufficient insulation to study pro- cooling time for the mixtures described. longed cooling of the dielectric. The Electret- making apparatus An insulated oven can be made from asbestos is not necessary. For preparing satisfactory electrets sheets of %- inch -thick Transite (ob- A suitable oven for electret making the following items are necessary: the tainable from lumber yards or hardware is shown in Fig 1. The inside dimensions 3 1/e I 4 3/4 3 In -.I VARMC 0 -200.0 THERMOMETER THROUGH CORK IN LID rV3RET of ` IITFrYK .-4D BRASSMKH.SCREWS MOUNTED ON 3. /B I I OVEN WALLS To SUPPORT HEATING u ELEMENT 3/8 Snt.l NICHE. BINDING POSTS FOR VARIAC 8-I W-3 /e TO SUPPLE AC TO 11 1" OVEN HEATING 3/8 ELEMENT

3 /4"ANGLE BRASS I- I -.I l 2-3/B T .030 THICK it)

%r INTERNAL LEADS L CLIPS 6.3/4 TO ATTACH TO MOLD $ e- HIGH VOLTAGE - ' BINDING POSTS FOR T/ I AC TO OVEN EATING `' 7POS Hv I al A ELEMENT NV BINDING POSTS

CIE Do

RED UP i , , BLACK I

CAP I I

I{ I 1

MATERIAL FOR WALLS.LID AND BASE : TRANSIT E

DIMESIONSIN INCHES 3 I/8 fa-- 4-3/4 C 3 I/8

Fig. I -Top and side views of an oven suitable for making electrets.

APRIL, 1949 221 Sadie Science

voltage power supply used to apply a Lift the lid off the oven. Pour the strong electric field to the dielectric in Carnauba wax -hydrogenated rosin mix- the mold. Notice the warning not to ture, previously heated to 110 degrees ground the chassis. The General Radio C in a beaker for one half hour to drive 200 -B Variac permits control of the out- out moisture, into the mold through a put from about 500 to 10,000 volts (no small Pyrex funnel. Stop pouring when 'load). High -voltage connectors and the molten mass is just deep enough to cable must be used for the output circuit. touch the upper electrode. Replace the A 0 -200 microammeter in series with oven lid and, when the thermometer ten % -watt resistors totaling 50 meg- again reads 100 degrees C, turn off the ohms is placed across the output termi- heating element. nals. This shows the voltage applic3 to Disconnect the V5 -M -T Variac from the dielectric in the mold. A cheap its terminals on the oven. Attach the multitester meter (0 -1 ma) with a Ma- high -voltage cables from the power sup- ampere miniature fuse in the high -volt- ply to the colored high -voltage terminals age leads shows the current that flows on the oven. When the thermometer through the dielectric. falls to 90 degrees C, turn up the 200 - B Variac in the power supply until How to make electrets approximately 3,000 volts is applied to Fig. 2- Transite stand holds the mold, covered with tinfoil. Stand is placed in the oven. The mold, with a 4 -mm distance be- the mold. For a 4 -mm distance between tween electrodes, is placed on the Trans- mold electrodes the field strength will be 7,500 volts per centimeter. Depend- oven 4 x 4 x 6 inches. of the cavity are ing on the purity and the nature of the Two colored binding posts for applica- VIVAC 5A ' HEATER SW dielectric, the current through the molt- tion of high voltages to the mold are walls. From en mixture will be from about 400 to mounted in opposite oven 1,000 microamperes. This current de- il7V PL lengths of No. 18 hook- R these posts short VA IA C the dielectric solidifies, read- with small clips creases as up wire terminated ing approximately zero at room tern - pass into the oven cavity. Connecting perature. the clips to the mold permits applica- At room turn the 200 -B field di- temperature tion of the high -voltage to the 879/ n Varac to zero and turn off the power electric inside. 2X2 117VPL - - supply. Wait least one minute before M at One of the remaining oven walls con- (2) 2.SV/2A disconnecting the high-voltage leads at posts for 0-IMA tains two nickel -plated binding the power -supply terminals on the pan- the heating element of No. 28 Nichrome ülw 0 -200C THERMO.IN LID / If el. Be careful to avoid shocks during wire (4.25 ohms per foot). The element this procedure; a shock from charged may contain from 25 to 50 feet of re- IPS 4 -µf condensers can be fatal. sistance wire, depending on the number Next, disconnect the mold from its of screws in the oven walls. Two rows the oven and take the stand in leads inside of staggered holes are drilled each and mold from the oven. Unscrew the wall. Machine screws and nuts are in- x top electrode and remove it from the serted, the nuts facing into the cavity. With the fingers lift the foil con- 2 0 2W stand. Start at one nickel binding post and 1 DO NOT GND CHASSIS taining the electret from the lower wind the Nichrome wire in zig -zag fash- Fig. 3 -Power supply furnishes high voltage. electrode. Brush off loose flakes of di- ion over the screws on the inside cavity. electric. Fold the edges of the foil up Terminate the wire at the other nickel ite stand and inserted in the oven. Clip over the electret until it is completely binding post. Washers prevent cutting covered by foil. The foil acts as a the Nichrome wire when tightening the the high -potential leads inside the oven to the mold elements. The V5 -M-T Vari- keeper and has the same function as the nuts to hold the wire in place. Com- keeper on a magnet. Completed electrets mercial a.c. is applied to the heating ac is attached to the heating -element terminals, and the oven is heated to must be kept wrapped in foil and stored element through a General Radio V5 -M- in a closed dessicator or fruit jar which T Variac. Oven temperatures are read 100 degrees C. contains about 1/a ounce of CaCl2 or from a thermometer (0 to 200 degrees other dessicant. C) mounted in a cork in the oven lid. Simply lift off the lid to remove it from Measuring the surface charge the oven. In the lab thermocouples and a The surface charges on electrets are Leeds and Northrup recording potenti- measured with an electrometer -an in- ometer were used to obtain temperature strument for measuring potential dif- readings. ference or indicating the presence of The mold which holds the dielectric electricity. The gold -leaf electroscope is a parallel -plate capacitor. The lower is one type of electrometer. The Linde- electrode is a circular, rimmed brass mann electrometer, used by this writer, cup with an inside diameter of 40 mm and an inside depth of 13 mm. Cup walls are 1.6 mm thick. The top electrode is a flat brass disc 25 mm in diameter and FARADAY CAGE 2 mm thick, silver -soldered to a brass LINDEMANN E ECT ROMETER RING STAND, rod 14 inch in diameter and 1/ inches 0-.0,001 long. Both electrodes are lined with AND CLAMP .001 -inch aluminum foil. The rod of the upper electrode is screwed to a bakelite THREAD insulator attached to a Transite stand (see Fig. 2). A slit in the back of the stand allows adjustment of the vertical distance between electrodes. The Trans - I _ CAGE ADDS CAPACITY TO SYSTEM ite stand is 43/4 inches high and 2% WEIGHT inches wide, and fits nicely into the oven ELECTRET IN MEASURING CAPACITOR cavity. Fig. 3 shows the circuit of the high- Electrometer is observed through microscope. Fig. 4- Schematic of the electrometer setup. RADIO -ELECTRONICS for Science Radio 123

is a metal box which contains four con- tory ring stand and moving the weight circuit capacitance, and causes an elec- ducting plates. Opposite plates are con- by hand permits adjustment of the dis- trometer deflection. The sign of the nected internally to form two pairs of tance between plates of Cm. induced charges is opposite that of the quadrants. A conducting needle, hang- A Faraday cage is connected to the charges on the electret. Then bring a ing from a fiber inside the box, completes high side of the electrometer measuring charged rubber or glass rod near the this capacitor -type measuring instru- circuit. The dotted capacitor in the Faraday cage. When the electrometer ment. Connect the needle to one pair of drawing shows that the cage adds ca- shows a decreased deflection, it indi- pacitance to the circuit. The Faraday cates the sign of the net electret charge ,r-DENSITY OF SURFACE CHARGE efu per cm2 +5 cage is a metal cookie can with the lac- is the same as that on the charged rod. +4 quer removed. Its use will be apparent A charged rubber rod (negative) al- +3 in a moment. ways causes a decreased electrometer +2 The total capacitance of the measur- deflection, showing that the net electret +I ing system, with maximum distance be- charge is negative. This is based on the tween plates of Cm, is measured by the principle that unlike charges attract. substitution method. For a 50-µµf value To find the actual magnitude of -2 of C the total capacitance was 61 µµf. charge on an electret surface the meas- -3 uring capacitor Cm (Fig. The 4) is used. -4 electret's charge Place an electret on the bottom plate of s The observed growth of charge on Cm. With the measuring system short - 1 2 4 5 10 8 9 II 12 electret surfaces follows the exponen- circuited, lower the top plate of Cm T ME IN WE KS-. until it touches the Fig. 5-A graph of surface- charge growth. electret surface. Then remove the short circuit. Raise quadrants (see Fig. A. potential 4). dif- the top plate of Cm to the top ference applied to the quadrants charges of the the plastic mount. Raising Cm causes work electrometer (regarded as a capa- to be done and induces citor) and deflects the electrometer a charge on the top plate of Cm. The sign at the in-. needle. The deflection is proportional to the duced charge is opposite to that on the square of the applied potential dif- electret The ference. Thus batteries surface. work done charges of known e.m.f. the measuring system capacitance and can be attached to the quadrants (electrometer terminals) deflects the electrometer needle. The de- to calibrate the flection is noted, and the corresponding electrometer measuring circuit. Graphs potential difference read from a cali- of electrometer deflection versus poten- bration curve. tial difference can be drawn for various To obtain the total charge on the values of C. C is a small mica capacitor electret surface the relation Q that can be placed across =CV the electrome- is used. The total capacitance is ter to increase the total capacitance of C the measuring known. Since 0.9 X capacitance, in system. Consequently, microfarads equals centimeters when an electret is placed the of ca- in measur- pacitance, and practical volts (p.d.) ing capacitor Cm, the deflection corre- divided by 300 equals sponds to a known potential difference statvolts, the total charge Q on the surface on a calibration curve. The deflection is is obtained in statcoulombs. The density of Et ECTRET ON PLASTIC STICK MICROSCOPE Fig. 7- Lifting electret from Faraday cage. re surface charge is Q /A,, which is stat- tial curve predicted by E. P. Adams of coulombs per square centimeter. A. is FARADAY CAGE v Princeton University. The time required the electret area. Reversing the electret for the charges to reach maximum in Cm, and repeating the procedure values is from 2 to 4 months. The gives the density of surface charge for growth of charge for one of the author's the other electret surface. electrets is shown in Fig. 5. This graph For these surface -charge measure-

ANN [ -i , ELECTROMETERELECTR Fig. 6 -Setup for finding electret polarity. observed through a microscope and measured in terms of the units on an arbitrary scale in the microscope eye- piece. A photograph shows a closeup view of the electrometer and the microscope. The measuring capacitor Cm (Fig. 4) is a modified N -10 Hammerlund capacitor. The capacitor plates are The electret is mounted on a plastic handle so that it need not be touched with the hands. taken off the original insulator and cut shows a reversal in the sign of the ments the electrets were mounted as down to a radius of 20 mm with a lathe. charge on each surface as time passes. shown in the photographs on plastic This makes the area of each plate the Also, this graph shows that the sign of handles, to prevent the observer from same as that of an electret. Then the the net charge of Carnauba wax elec- becoming charged and to make it un- plates are mounted on a plastic stand trets is negative. necessary to touch the electret at any 2 inches high. Disregarding the thick- To find the sign of the net charge on time. nesses of the base and top arm of the an electret the Faraday cage (see Fig. Eguchi and Gemant found the rela- plastic mount, the maximum distance 6 and the cover picture) is used. Insert tive density of surface charge, under between plates will be 1', inches. the electret in the Faraday cage, first ideal laboratory conditions, to be A ap- thin brass strap 3 inches long by short- circuiting the measuring circuit proximately 6 statcoulombs per square % inch wide is soldered to the top plate with a small piece of wire in an insu- centimeter. To find the magnitude of of Cm. The strap slides up and down lated handle (pigtail in cover photo). surface charge for practical purposes through a slit in the top arm of the Then remove the short-circuit and lift this writer used the above method and mount. A silk thread is attached to the the electret from the cage as shown in depending on the type of electret, found free end of the strap. The other end of Fig. 7. The work done in lifting the that the density of surface charge va- the thread is tied to a weight (a heavy electret from the cage induces charges ried from 0.25 to 4.00 statcoulombs per nut). Looping the thread over a labora- on the sides of the cage, charges the square centimeter. APRIL, 1949 Electronics 24 I

OVS

s- be tra g aes coo o 'Ore leaves radio ilote tiside

WittedPEa0M G. ßy . P

quartz rods. As a matter of fact wave - guides can be made of solid dielectric rods. The waves will follow along just means of restricting ultra- high -fre- as the light waves do in the lucite rod. N ove9Mdes quency waves within its walls so that The losses are higher than in hollow they may be transferred from one place metallic waveguides, however, which WAVEGUIDES and wave - to another. explains why dielectric rods are seldom guide techniques have devel- Waveguides are used mostly for con- used.) oped so rapidly as a result of ducting the waves generated by a u.h.f. Propagation in wave guides wartime use in radar, point - oscillator to the antenna, for conducting to -point communication, and other ul- the waves picked up at a receiving an- So much for a general explanation of tra- high- frequency radio systems that tenna to the converter or detector, and what constitutes a waveguide. To un- the average radioman has not had time for mixing or combining several u.h.f. derstand how high- frequency radio to acquaint himself with their princi- waves. Waveguides also provide a con- waves travel in a guide, let's look at ples, understand their advantages in venient method for measurement of fre- Fig. 1. This picture is familiar to most u.h.f. applications, or to learn how to quency, power, and similar character- radiomen and is often used to explain use them. Technical publications have istics in the u.h.f. spectrum. dx transmission. A few miles above the devoted considerable space to waveguide Waveguides may be rectangular, cir- earth's surface, there are accumulations techniques during the past year or two, cular, or oval, though most of the pres- or layers of ionized air or gases that but usually in language which presup- ent -day applications use the rectangular act as a reflecting plate or mirror, poses some familiarity with the subject guide because it has been found easier bouncing the waves back toward the and considerable engineering training. to fabricate than the other two shapes. earth s surface, where they are again It is important that the practical ra- Losses in waveguides are relatively T dioman get a thorough understanding low since the waves bounce off or are of waveguides and their use. With color reflected by the inner metallic walls of television in the offing, and with ham the guide but otherwise travel much radio (particularly narrow -band FM) the same as radio waves in free space. REFLECTION OF WAVE FROM INNER WALL OF looking to higher frequencies in the The guides may be bent around corners, WAVE GUIDE u.h.f. spectrum, "radio plumbing" (as carrying the waves with them. (The ac- Fig. 2 -The waves bounce off the metal walls. the guides are affectionately called) will tion here is similar to the transmission become increasingly common in the next of light waves through lucite or fused reflected by the surface of the earth. few years. Thus the waves are bounced back and First of all, what is a waveguide and forth to appear in receiving antennas how does it differ from the parallel -wire REFLETI NG LAYERS OF IONIZED GASES thousands of miles away from the trans- and co -axial transmission lines that mitter. have become second nature to the ham In a like manner, the u.h.f. waves and the television and FM experimen- bounce back and forth from opposite ter? It is a simple hollow tube, usually NMITTER sides of the waveguide as shown in Fig. made of metal, having no central con- 'EARTH'S SURFACE 2. The only restriction is that distance than a half -wave- ductor or wire. It is essentially a Fig. I -The oldest and best -known woveguide. A must be greater RADIO -ELECTRONICS for Electronics 25

We present here the first article of a series on microwave propagation and waveguide equipment. Since waveguides are the only practical means for propagating and controlling waves across a wide hand of frequencies in what is becoming a highly important part of the radio spectrum, the up -to -date radioman must master waveguide technique:

ength or the waves bounce back and illustrated in simplified form in Fig. 4. PROBE CO -A% CONDUCTOR forth from directly opposite points and Similarly, in a waveguide, electrostat- STATIC FIELD MAxl do not advance through the guide. The ic and magnetic fields are built up due frequency at which A is half a wave- to the propagation of r.f. current. These T d length is known as the cutoff frequency can be seen for one mode or orientation of the guide. of fields, called the TEN mode, in a 1 i Waveguide action cannot be fully un- rectangular waveguide in Fig. 5 -a. The B +l CO-AX CONDUCTOR '- B - MAGNETIC derstood in terms of transmission -line magnetic lines of force can be likened FIELD 'MAXI theory, though there are some similari- to whirlpools when looking down on the Fig. 6-Getting energy in and ouf of guides. ties between them. Waveguides must top of the waveguide. These whirlpools Microwave testing equipment is usu- be approached from the viewpoint of travel down the tube in the direction of radiation of electromagnetic waves in- propagation. ally arranged so that the coupling de- The electrostatic lines of vice can be shifted by means of a slot stead of that of conduction. longitudinally However, since most radiomen are cut in a length of wave- familiar to some extent TOP VEW guide. This allows the energy distribu- with transmis- tion to be examined sion lines, they provide -off continuously along a jumping MAGNETIC FIELD a f-ù + + + +4_t t ±t_3 the guide. There is it point of maximum point. Let us examine Fig. 3 -a. This iftt t4 shows energy, reversed in polarity from the a section of two -wire transmis- previous maximum, half -wave sion line with a quarter -wave stub at each 151DE VIEW I point. This provides a convenient means across it. The open ends - of a quarter of measuring wavelength or frequency wave stub present high impedance 1 ELECTROSTATIC FIELD a 111111111 iliiflii and also standing-wave which will across the line and do not short f ratio, circuit be discussed in detail in a later article. it. As a result, the addition of the stub has very little effect on radio currents Waveguide dimensions flowing in the transmission line. Now if RF VOLTAGE A given size waveguide can carry we add an infinite number of quarter - ALONG WAVEGUIDE wave stubs, as in Fig. u.h.f currents of any frequency higher 3 -b, we will have than a continuous rectangular pipe (3 -c) or cutoff, but there is one optimum frequency that is carried best by a one type of waveguide. In this guide, Fig. Energy in 5- a rectangular waveguide. given size of guide. For this reason the MULTIPLE INFINITE NUMBER OF radio industry has endeavored to stand- SHORTING BAR SHORTING BAR STORTI BARS force are at right angles to the mag- ardize on the smallest number of sizes I /4h netic ones and are shown in the side consistent with good performance. In view of the waveguide in Fig. 5 -b. The the following list, dimensions are in corresponding instantaneous r.f. poten- inches and frequency in megacycles: %MISSION LINE tial along the guide is shown at c. There are numerous modes, identified A dimen- B dimen- Cutoff Wall a by the letters TM for transverse mag- sion sion freq. thickness Fig. 3-How a waveguide might have evolved. netic and the letters TE for transverse 3 1% 2,080 .080 electrostatic modes, one of the most 2 1 3,155 .064 dimension A must be least - at a half commonly used one being the TEol. 1% % 4,305 .064 wavelength but may be larger. (If it The subscripts refer to the number of 11/4 % 5,265 .064 were smaller, the waves would be be- waves which travel down the guide at 1 1,ße 6,772 .064 low the cutoff frequency of the wave- one time. A TE02 wave, for example, in guide.) % 9,495 .064 would have two waves traveling down 1/4 1/4 14,060 .040 In considering the transmission of the waveguide side by side, much as if 11f.í2 350 20,935 .031 r.f. energy in waveguides, a new term, a vertical partition were running down mode, has been applied. If we examine the center. A diagram of the TEN mode Above 20,000 me it has become the a cross section of co -axial transmission is given in the article Microwaveguides practice to use solid coin -silver wave- line, where there is a central conduct- in last December's issue. The question guides or, in some cases, laminated ing wire surrounded by a metal tube or of modes will be covered in shield greater de- guides, because of the difficulty of man- but insulated from it, we find tail in a future article. ufacturing hollow guides of constant that there are two fields, a magnetic The modes are determined or selected size. The tentative outside dimensions INNER CONDUCTOR by the type and placement of the coup- of these are as follows: ling device from the source of r.f. en- ELECTROS1X11C FIELD OUTER CONDUCTOR ergy. Usually r.f. power is introduced A dimen B dimen- Range OR SHIELD into or extracted from a waveguide by sion sion (mc) , means of a quarter -wave dipole, probe, (inches) . (inches) MAGNETIC FIELD or coupling loop. Two of these are 0.42 0 .17 18,000 -26,000 shown in Fig. 6. In the case of the TEol 0.34 0 .17 22,000- 33,000 CROSS SECTION OF CO -AXIAL %MISSION LINE mode the probe is introduced at the cen- 0.28 0 .14 26,000-40,000 Fig. 4- Energy in co -axial transmission line. ter of the A dimension and at a point of 0.224 0 .112 33,000- 50,000 maximum electrostatic field. When a 0.188 0. 094 40,000 -60,000 field and an electrostatic field, resulting loop is used, it must be introduced in 0.148 0. 074 50,000- 75,000 from the conduction of r.f. current the B dimension at a point where the 0.122 0 .061 60,000- 90,000 through the transmission line. This is magnetic field is greatest. (Continued on following page) APRIL, 1949 261 Electronics

Because of size and construction lim- cutting a slot approximately a quarter - itations, waveguides are not practical wavelength deep in the junction plate for frequencies higher than about 100,- of one of the pieces of waveguide, an 000 mc or lower than 3,000 mc. An idea r.f. choke is created at the junction (see of the relative efficiency of a given size Fig. 3 -a) ; it effectively prevents high - frequency leakage. See Fig. 11. A straight junction is always butted f1` against a choke or slotted junction in Ile, joining waveguide units. From the few examples given above it can be seen that you can do anything II . with waveguides that can be done with The standing -wave detector, a device for ex- the old familiar coils, capacitors, and ploring energy distribution in a waveguide. I1 SLOT F1. 1/4)1 DEEP CIRCULAR II. By moving the closed ends, the guide i'. can be tuned. LIE 064WAVEGUDE -ended or closed sections of mop,. T 01 Open HI ' waveguide can be used for switching NM u.h.f. currents from one waveguide path WAVEGUIDE r 'I`WAVEGUIDE to another, without actually closing off CHOKE JUNCTION ORDINARY JUNCTION RI, the undesired path mechanically. Fig. I Fig. I quarter -wave stub (slot in this section of waveguide I-A 10 shows a small case) is an efficient radio -frequency choke. Y Z and a short Ni ,. with two paths and u1 section U arranged with a me- transmission lines. The only difference closed IIILIE chanical flap that provides a short cir- is in the mechanical form of the wave- I 06 cuit at point A. When A is shorted, guide circuits. In further articles of this L point X is effectively a solid wall and series, the use of waveguides as induc- 5 r.f. current can pass only through path tors, capacitors, and attenuators will be Y. When the short at A is removed, cur- described. Setups for measuring fre- TMEN rent can pass both Y and Z paths. Many quency, generating power, and measur- ,,, varied switching arrangements have ing standing-wave ratio will be shown, B500 7500 e500 9500 10,500 11,500 12 500 been devised following this general and the discussion of basic waveguide FRED MC theory will be continued. Fig. 7- Attenuation as cutoff is approached. scheme. (Our next installment will discuss guide for a wide frequency spectrum some of the things mentioned above in can be seen in Fig. 7. Here, attenuation greater detail, paying special attention in decibels per foot of a piece of 1 x to standing waves and the standing - '/z -inch waveguide is shown at various ! i C I /4À wave ratio, waveguide tuning, and frequencies. The low- frequency cutoff resonant cavities, and will introduce at aboutt 6,700 mc is quite evident in the 1_'jß I -1/411 some simple waveguide circuits.) greatly increased loss as this frequency (r -A--41 is approached. Fig. 9 -The waveguide section may be made to act like an inductor or capacitor by mak- Special waveguide devices ing it less or more than a quarter wave long. Just as at lower frequencies, special See RADIO -ELECTRONICS, Dec. 1948, p. 24. devices for introducing inductance, ca- Impedance matching, usually done pacitance, and resistance are available with transformers on lower frequencies, for waveguides, though they differ in is accomplished in waveguides with shape and use from the familiar coils, shorting stubs. For instance in match- capacitors, and resistors. For example, ing a waveguide section to a length of waveguide fixed or variable resistors in co -axial line, the characteristic impe- practice are strips of resistance mate- dance of the waveguide is higher than rial introduced longitudinally in the that of the co -axial line. The impedances are matched by introducing metal plates PARTITION OF RESISTANCE stubs. They reduce the MATERIAL OR METAL called matching opening in the guide and reduce its impedance to match the co -axial line, which is coupled by means of a loop or LE OT IN WAVEGUIDE TO ALLOW ATTENUATOR TO BE dipole to the waveguide. INSERTED When two lengths of waveguide are Fig. 8-Variable resistor, waveguide style. coupled together, there is danger of u.h.f. at the junc- guide as shown in Fig. 8. The further leakage of the current into the waveguide the resistor strip is tion, with resulting loss in efficiency. By lowered, the greater the attenuation. By U adding a driving mechanism, we have a variable attenuator which can be cali- 4- CLOSED END A brated. 4-- OPTIONAL SHORT AT THIS POINT A section of waveguide can be used 3/0 as a tuned circuit or as a transformer, 1/2 II displaying both inductance and capacitance or, to be more exact, inductive and z.- 4-SOURCE OF RF POWER reactance. In Fig. 9 the u.h.f. capacitive I/4A voltage is introduced at point X. If the -wave A terminating section, or piece of waveguide C dimensions are a quarter each, 1 with an attenuating strip which presents to reflections will occur and reinforce the Y the waves the waveguides characteristic im- voltage at X. (Dimensions C may also Fig. 10 -Right -angle stubs may make a point pedance, terminating the line without caus- be multiples of a quarter -wavelength.) in the waveguide impassable to radio waves. ing reflections or setting up standing waves. RADIO- ELECTRONICS for Electronics 27 Oscillator Circuits as Used in Industry

By ED BUKSTEIN*

IN addition to their usual signal -gen- and the metal vane between the tracks, this oscillator, the grid -to- ground ca- erating function, oscillator circuits arrival of the car at a given point on the pacitance is so altered that oscillation are suitable for a wide variety of tracks would operate the relay. ceases. As in the previous case, when control applications. For example, Another variation of the same basic the oscillation stops, no bias is devel- starting or stopping oscillation may principle is the protective meter. Coils oped and the plate current increases to cause a relay to operate and to control Ll and L2 are made compact and are a value sufficient to close the relay. an external circuit. For this purpose mounted on the face of the meter as To eliminate the necessity of touch- the oscillator is a sensitive and reliable shown in Fig 2. A small aluminum slug ing a grid, the grid is connected to a control. is attached to the pointer. As the meter large metal plate. Contact with this Fig. 1 illustrates the operating prin- reading increases to a predetermined plate will cause the relay to operate. ciple of one type of control oscillator. value, the aluminum slug passes be- The circuit may be made sufficiently The circuit is simple, oscillation result- tween the coils and the relay closes, pre- sensitive so that direct contact with the ing from the energy fed back from Ll venting a voltage or current from ris- plate is not necessary, the approach of to L2. When the circuit is in oscillation, ing above a certain level. The coils may a person or object being sufficient to the plate current of the tube is at mini- be made movable to permit setting at trigger the circuit. The metal plate may mum and the relay is open. The reason any desired level. be a metal door or a large plate fastened for this is that during oscillation grid The oscillator shown in Fig. 1 could to a door; the circuit will indicate the current flows and produces a bias vol- also be adapted to assembly -line prob- approach of anyone toward the door. In tage across the grid resistor. The nega- lems such as detecting metal particles - o tive grid voltage limits the plate cur- in packaged foods passing on a con- rent. veyor belt. Operation of the relay would e+ energize a reject mechanism to remove t_, the objectionable item from the con- METAL PLATE RELAM R+ veyor belt automatically. RELAY In other applications, it may be desirable to have the relay normally closed LI so that it will open upon the insertion of the metal vane. This may be accom- METAL VANE NM-. plished by providing some other form of feedback and reversing coil L1 so that its feedback is degenerative. Under Fig. 3 -The simplest capacity -operated relay. Lz these conditions, oscillation is prevented by the degenerative feedback until the other cases, the doorknob itself or the metal vane is inserted. The metal vane handle of any cabinet or compartment reduces the degenerative feedback, al- door may be used as the metal plate. Fig. 1-Vane stops oscillation -relay closes. lows the circuit to oscillate, and causes The system may be used to protect a the relay to open. bank vault or safe, in the latter case If, for any reason, oscillation ceases, the safe itself being used as the metal no bias voltage is developed, the plate plate. current increases, and relay closes. For Another possible use of the circuit instance, if a metal vane is brought into is for counting, for instance, the number the space between L1 and L2, feedback of automobiles passing over a bridge. is reduced to a point where oscillation The automobile's approach to a metal stops. In short, insertion of the metal plate initiates circuit action. The relay vane causes the relay to operate. is replaced by an electromechanical One application for this circuit is counter with numbered disks. The same leveling elevators at floor levels. An os- system could be used to count objects cillator is mounted at each floor, and the passing down an assembly line. metal vane is attached to the bottom of The circuit is also adaptable for the the elevator platform. The electrical Fig. 2 -The vane circuit adapted to a meter. protection of power- machine operators. connections to the elevator door are The metal plate is located so that the made so that the door cannot be opened Another form of control oscillator is operator's hand, if in a dangerous po- until the oscillator relay is closed; that the capacitance- operated relay often sition, will prevent the machine from is, until the elevator is properly leveled. used as an alarm to indicate the ap- operating. A similar arrangement might be used proach of a person or object. Here again One system of remote control involves with railroad cars. With the oscillator the circuit consists of an oscillator con- the use of carrier -current transmission. mounted on the underside of the car taining a relay in its plate circuit (Fig. An impulse of r.f. energy is transmitted 3). over the power lines. Somewhere else Northwestern Vocational Institute. If a finger is touched to the grid of in the same building or vicinity a re- APRIL, 1949 28 Electronics ceiver connected to the same power lines passing the material between rollers and tuned to the same frequency picks mechanically coupled to the plates. A up the signal and operates a relay. This mechanical gain resulting from lever method of remote control is illustrated action will cause a small movement of in Fig. 4. When the transmitter is the rollers to produce a relatively large turned on by a key or push- button, a movement of the plates. pulse of r.f. energy is transmitted The same circuit may be used also through the power lines. At the other as a humidity gauge. In this applica- end of the system, the pulse is picked tion, the two plates are connected to up by the receiver whose output oper- Fig. 5- Typical receiver (above) and trans- opposite ends of a stretched fiber. ates a relay. mitter (below) for power -line control circuits. Changes in the air's moisture content Suitable transmitter and receiver cir- cause the fiber to expand or contract cuits are shown in Fig. 5. The trans- and consequently vary the frequency of mitter is a conventional oscillator. For oscillation. convenience and simplicity, no rectifier The oscillator shown in Fig. 6 is often is used, the oscillator operating directly RFC used in conjunction with a fixed oscil- from the a.c. line. When the switch is lator as shown in Fig. 7. The fixed oscil- closed, the circuit oscillates and feeds lator and the variable one both feed r.f. energy into the line. into a mixer circuit to produce an audio The receiver also is small and simple. beat note. Any variation of plate spac- A series- resonant L -C circuit tuned to ing produces a change in the audio note the frequency of the transmitter picks in the loudspeaker, giving an aural in- up the signal from the power lines. The dication. two plates, one of which is free to move. signal voltage developed across C causes B+ ionization in the 0A4 -G gas tube. The As the plates become farther separated, the capacitance is decreased and the PLATE POWER LINES frequency of oscillation increases. Con- /MOVABLE L RCVR I versely, as the plates move closer to- ^^1111 T - fWVi gether, the frequency decreases. This RF IMPULSE oscillator may be used as a highly sen- Fig. 4 -Power lines carry control impulses. sitive electronic micrometer for accurate thickness measurements, the thick- resultant increase of plate current ness of a material placed between the closes the relay. This system is satis- two plates determining the frequency of Fig. 6-An oscillator used for measurement. factory for a wide variety of remote oscillation. Thus, oscillator frequency MOVABLE PLATE VAR. IREO control uses. becomes a function of material thick- C Use of the oscillator for measurement ness. OSC. is demonstrated by the circuit of Fig. The plates may also be moved by the AF AMPL 6. The frequency of the signal is de- changing thickness of a belt of manu- termined by the L and C of the tuned factured material as it passes between FIXED OSC. circuit. The capacitor is made up of them. Sensitivity may be increased by Fig. 7- Measuring circuit with aural output.

FOR SAFER ANTENNA INSTALLATIONS The rapid increase in the use of tele- is used for lead -in, suitable protection fire department or where liable to vision receivers has brought a flood of will be provided by grounding the ex- crosses with electric power lines. Some inquiries as to the relative fire and life terior metal sheath. fears have been expressed as to the pos- hazards of television sets, and as to Where the antenna is mounted on a sibility of shock hazard on contact with their proper installation and the in- metal pole or tower, the pole or tower an antenna or lead -in, because of the stallation of their antenna systems. should be properly grounded. Opinions high voltage used in the receiver, but Since television operates on essential- vary as to the size of the grounding these fears are groundless if the re- ly a line -of -sight basis, proper reception conductor, but it should preferably be ceiver is properly designed. usually necessitates an exterior anten- at least a No. 6 or 8 A.W.G., connected It is generally considered that a tele- na and as the distance from the tele- to a suitable ground such as an under- vision receiver has a greater inherent vision transmitter increases, the an- ground water pipe, and if the building fire hazard than a conventional radio tenna must of necessity extend higher is equipped with a lightning rod sys- receiver, because of its greater current in elevation. This increases somewhat tem, should be properly bonded to this consumption, a greater number of heat the possibility of damage by lightning, system. producing components and the higher and, as the antenna is usually mounted The type of lead -in commonly used voltage used. Particular care should be on a pole or tower on the roof, there is is the polyethylene ribbon type. Al- taken that the natural ventilation built a possibility that, unless properly in- though this material burns much like into the set is not obstructed or re- stalled and supported, the system may rubber, and falls in flaming drops, its duced by location or blanketing. Televi- fall in high winds, dropping across use for this purpose is not considered sion sets should not be left turned on power lines or injuring persons or particularly hazardous. Recent improve- while unattended. property. ments of the polyethylene lead -in, al- Television sets of several manufac- The National Electrical Code, in Ar- though still flammable, have eliminated turers have been listed by Under- ticle 810, contains provisions covering the flaming drops. The co -axial cable writers' Laboratories, Inc., as having radio receiving aerials, but these pro- lead -in is generally considered the best been acceptably designed and con- visions were designed primarily to from the fire hazard viewpoint, but is structed with respect to the fire and life cover conventional radio installations considerably more expensive and has hazard. Prospective purchasers should and do not appear adequate for the spe- operational disadvantages. assure themselves that the set they cial conditions of television.... Arrest- Considerable care should be given to contemplate purchasing is listed by the ers for ordinary radio aerials are not the mechanical stability of the antenna Laboratories. suitable for television, but proper ar- and its support. Where located on the (The report quoted above was Special resters are available. These arresters roofs of buildings the antenna and sup- Interest Bulletin No. 875 issued by the should be placed on each conductor of a porting guys should not be so located National Board of Fire Underwriters, ribbon -type lead-in. If a co -axial cable as to interfere with operations of the New York, N. Y. Editor) RADIO- ELECTRONICS for Electronics 29 Diathermy Generator

Any experienced radio constructor can build a serviceable diathermy machine

By H. L. BUMBAUGH

THE diathermy equipment shown a pickup coil L2 mounted co- axially with Front -panel photo shows the control markings. on these pages has been in use the plate coil and a series variable tun- several years. It has proven powering capacitor. With increasing capac- Many of the parts required for the ful enough and free from "bugs." itance this capacitor causes the pad oscillator will be found in the junk -box. No repairs or adjustments have ever circuit to approach but never attain The pads or other applicators will prob- been necessary, mostly due to the fact resonance with the plate circuit. This ably have to be purchased from a manu- that all components operate with large permits loading the oscillator adequate- facturer of physical therapy apparatus. safety factors. ly but cannot make it unstable due to Tubes equivalent in power rating to The application of high- frequency al- reduced excitation resulting from a too 838's may also be used if proper grid ternating currents to body tissues has heavily loaded plate circuit. bias is applied and other operating re- long been considered of great therapeu- The degree of heat furnished is con- quirements are met. Gammatron 54's tic value. The equipment, however, is trolled by the grid-bias setting of the have been used with considerable suc- relatively costly. With this fact in mind 4- position bias switch and of the pad - cess, and the initial cost is quite low. the author set out to design and build a circuit variable capacitor. (Continued on following page) modern diathermy oscillator and to present information about it in such form that any amateur, serviceman, or other technically qualified person might easily duplicate the device. A word of caution should be given. All apparatus of this nature comes under the regulations of the Federal Com- munications Commission and must be constructed and operated strictly in accordance with those regulations. The equipment described here does comply. Medical men consulted expressed the opinion that a raw a.c. wave places considerably more strain on the body tissues and nerves than the relatively smoother wave from a rectifier with a small amount of filtering and that the rectified waveform gives greater heating effect for any given power output. Since a rectified output means length- ened tube life, a reduction in interference, and generally better all- around conditions a rectified setup using 866 tubes was decided on. Considering the nature of the requirements and the probability of operation by technically unskilled persons, it was deemed advisable to provide for at least 200 watts of power. The oscillator chosen was a push -pull type using 838 tubes. Other tubes of equivalent power rating may, of course, be substituted. The circuit diagram appears on the next page. The oscillator must operate at one of the frequencies designated for diathermy by the FCC; in our case the 13,560 -kc band was chosen. The oscillator should not deviate from this center frequency by more than 6.78 kc, which is a reasonable stability requirement. As will be seen from Fig. 1, the circuit for the applicator pads consists of The equipment is mounted on two decks inside the cabinet. R.f. section is on fop. APRIL, 1.949 30I Electronics

In Fig. 1 it will be noted that two on the capacitor dial. While the milliam- Each pad is a flat grid of small -mesh switches are required to put the device meter will not show as great changes in wire cemented or molded between two in operation. The oN position of these readings with rotation of the variable layers of rubber, with a stranded con- switches is indicated by a red and a pad- circuit capacitor as it will between ductor soldered to the wire mesh, the green bullseye behind which small night successive points on the POWER switch, conductor being housed in rubber tub- light assemblies have been placed. The a neon bulb held near one of the pads ing. In use, the pads are placed on each TREATMENT switch cannot connect the will show a considerable variation in side of the body or the member to be primary of the power transformer to r.f. energy output through the range of treated. the line unless the WARM UP switch has the capacitor. When the coil is used, it is wound connected the filament transformers. The cabinet for the equipment may around the member or coiled upon it. This is to prevent application of plate either be purchased or made by the con- Distributed capacitance completes the voltage with no filament voltage; the structor. We were unable to find a "patient circuit." filaments should be heated for a short ready -made cabinet which met our re- A word of caution is in order here time before applying high voltage. Op- quirements, so we built one, 21 inches concerning any metal objects in the field erators should be thoroughly instructed high, 18 inches wide, and 16 inches deep of either the pads or the coil. Any piece in this routine. out of 3 -ply veneer. The sloping panel of metal -no matter what size-will To apply the output of the equipment on which all the controls are mounted have induced in it currents which may to a patient, plug the machine into a was made of tempered Presdwood and heat the metal to a very high tempera- convenient 117 -volt a.c. outlet. Insert after several coats of shellac was fin- ture and may cause painful burns or the banana plugs on the ends of the pad ished off with three coats of black perhaps ruin clothing. Always make leads into the large jacks on the lower - enamel, dressed down with steel wool, sure no metal objects of any kind are in right -hand corner of the control panel and a final coat of wax applied. The the field of the applicator. (see photo). Turn on the WARM UP cabinet proper was given three coats of Diathermy can be extremely danger- switch which applies filament voltage an orchid gray enamel. ous. Treatments must be administered and turns on the green pilot light. After Four large -wheel casters and a metal only by a qualified physician who is a couple of minutes -having arranged handle on each side of the cabinet make familiar with diathermy techniques. the pads on the patient as explained it easy to move the equipment from When constructon is finished, the os- later - close the TREATMENT switch place to place. cillator should be set on the operating which applies power, lights the red Figure 2 shows how the pad circuit frequency of 13,560 kc by means of an pilot light, and begins the treatment. terminates on the control panel in two r.f. oscillator, a calibrated communica- Coarse adjustment of the treatment large jacks which accommodate large tions receiver, or other available means. intensity is obtained by adjusting the banana plugs on the end of the pad Once set it will require no further at- POWER switch in the lower -left -hand leads. tention. As a final precaution a check corner of the control panel. Fine grada- The high -voltage transformer is an should be made to see that the operation tions are obtained by varying the set- old instrument transformer obtained of the device in no way interferes with ting of the pad- circuit variable capaci- from the local power company's salvage any established service, such as radio tor (the wheel in the lower center shop. It furnishes 1,000 volts each side or television. Should any such inter- section of the control panel). In the of the center tap. Such transformers ference show up, the usual amateur majority of cases a maximum meter are ideally suited for this use as they remedies may be applied. reading will occur at or near full scale are very small and yet have adequate (Interference from diathermy equip- power capacity. Any local power com- ment has troubled many users of radio 838(2) pany should be able to furnish an ob- 250 r equipment for a number of years. The solete one a very reasonable price. PAD 50MM/SPLIT-SUTOR at FCC, after considerable study, assigned ) 7 Of course, any other transformer giving L2_ß -LI three bands of frequencies for dia- s0m 1,000 volts each side of center and hav- SPLIT-STATOR thermy equipment. These bands were al- ing a power capacity of 200 or 300 located in portions of the radio- frequen- watts may be used equally well. cy spectrum where 300MA they are least likely Any value between 4 and 12 henries to interfere with broadcast or vital will do for the filter choke. It should communication services. The center fre- have a PAO current- carrying capacity of quencies of the bands are 13,560, 27,120, about 300 ma. and 40,680 kilocycles. The frequency The line filter chokes shown in the tolerances of these bands are 6.78, 162.0, 0-300MA 117 -volt supply line are air -wound 1% and 20.0 kilocycles respectively. There inches in diameter to a length of 2% is no limit to the radiation of the funda- inches with 14 turns of No. 18 IOV/7,5A enameled mental so long as it is within the pre- wire. There are two windings, inter - scribed bands. The harmonic radiation WARM UP SW wound with each other. One winding is o shall not exceed 25 µv per meter at a shunted with a 100 -guf variable capaci- distance of 1,000 feet. tor which can be tuned to give greatest If such equipment interferes with GREENN R t.L ---- trap effect. Because of the unity coup- 12 Ifl: OIL operation of nearby broadcast or tele- A 300MA ling between the two windings, the one vision receivers, wave traps and tuned MEE MEN 2.SV/10A capacitor serves to tune both windings. stubs may effect a cure. If your equip- The 838 plate coil Ll is 17 turns of ment does interfere with the neighbors No. 8 enameled wire air -wound 2% radio, it is advisable to have a radio inches in diameter to a length of 4 service technician take the necessary inches. L2, the pad pickup coil, is 22 remedial steps.-Editor) turns of No. 10 enameled wound to a diameter of 11/2 inches in two sections MATERIALS FOR DIATHERMY GENERATOR of 10 turns each, spaced the diameter Resistors: 2- 15,000, 2- 25,000 ohms 25 watts. of the wire, the two sections being Capacitors: 6- .002µf, I -kv, mica; 1- I -0, I -kv, oil - filled; 2- 50µµf, split- stator, I-250µµf, variable, y4- spaced 2 inches apart by partially inch plate spacing. H straightening out two of the center Tubes: 2-838, 2- 866/866A. Switches: 2- s.p.s.t. toggle, 1-single-circuit, 4 -posi- turns. L3 is 25 turns of No. 10 enameled, fion rotary. 11/2 inches in daimeter, air- wound, 3 Transformers and choke: 1 -2.5 -volt, 10- ampere, 1-10-volt, 7.5- ampere filament transformers; 1-2,000- inches long. volt, 300 -ma, center -tapped high -voltage transformer; LINE FILTERS SEE EAT SA FUSE MAC The builder has the option of using 1 -12- henry, 300 -ma filter choke. Miscellaneous: I-2.5 -mh, 300 -ma r.f. choke; l-0- either pads or a coil for applying r.f. to 300-ma d.c. meter; sockets for 838's and 866's; 2-117 - CAPACITORS C .002 / IAv the patient. Either form may be ob- volt pilot-lamppilot -lamp assemblies, one with green, one with red jewel; I fuse and holder; 2 -diathermy Fig. I- Schematic of the diathermy generator. tained from the larger supply houses. application pads; cabinet; necessary hardware, RADIO -ELECTRONICS for Television I31

IN October, 1948, an international con- gress on the relations between television and the cinema was held in Cinema Television Paris. The chief subject was television, a new technique which lends itself to discussion more readily than the By E. AISBERG* moving picture art in which practically everything is already standardized. A number of very interesting ideas were brought forth. Incontrovertibly, television has benefited by numerous ideas gained from the technique of the movies. Especially in the television studio has the new art profited from the experience gained. in moving -picture photography. Whether lighting, "panning," mixing, or fading, the technique is that of the cinema studio. The regular special effects of movie - camera technique are more or less successfully reproduced in television. The technicians who transmit images through space draw without shame upon the immense treasure accumulated by the specialists of the transmission of images through film. Finally-and more immediately and directly- television fills a good part of its programs with the help of moving - picture films. At least this is the case in France where the relations between the cinematographic industry and the of- ficial television services are excellent. The producers of films realize (with a more keen intelligence than was ex- from competing with pected) that, far A French television truck equipped for outside news pickup and microwave transmission. the movie producers, television offers excellent advertising to their films. This is why the antennas of Télévision Fran- All these qualities of television give in staging required to make corrections çaise transmit feature films, documen- rise to the belief that in the future the unnecessary. taries, and newsreels every week. television camera will be substituted for In the case of newsreels, it is again If television benefits from the services the standard moving -picture camera useful to register them with the aid of offered it by the cinema, it may, in re- now used. The pictures will be taken a television camera and to transmit turn, pay its debt in a most striking with one or several television cameras, them by shortwave to a central recep- manner. One can foresee what an im- operating under the best possible con- tion point where they may be filmed. mense contribution television may make ditions. The images when registered Further, they may be relayed from the to the motion- picture art. For example, will be transmitted on co -axial cables, reception point to moving -picture the- the television camera offers several in the form of video frequencies, to a aters equipped for large- screen projec- points of superiority over that of the central reception point where they will tion television. In this manner, the cinema : be projected upon the screen of a tele- event may be viewed by moving -picture 1. Its sensitivity is notably greater vision receiving tube, from which they spectators at the time it takes place. than that of the most sensitive emul- will be finally registered on film. Simultaneously it can be preserved in sions. The slow -electron orthicon tube The director can control the images celluloid for the thousands of other permits taking pictures in twilight on a television screen which will indi- spectators who will view it with a cer- and even by the light of a candle - cate to him exactly how the images are tain displacement in time. Thus, after something impossible even with the being registered on the film. He can having received essential help from the fastest panchromatic films. thus make any necessary corrections moving -picture art, television may in 2. In a television camera it is pos- with the receiver controls, at the same its turn lend its assistance to the adult sible, by purely electric controls, to time giving instructions for the changes techniques of the cinema. modify, not only the mean brilliance of the images, but also their gamma y,MIKES is to say, the degree con- -that of TELEVISION TRUCK TV CAMERAS trast. In film, the gamma of a given SCENE BEING zto FILMED emulsion handled with a given devel- RECEPTION CENTER oper is constant. FILMING TELEVISION T I 3. An electronic finder, consisting GLASS PARTITION S U D O O r NEWSREELS of a viewing tube, permits viewing GENERA,. CONTROL CONSOLE MIZROWAVE )(MISSION SOUND IMAGE the image at the instant it is being 0óö0 CONTROLS RAPID FIL CONTPO,.S taken. On the other hand, the optical O O {\000 DELIVERY finders of moving -picture cameras in- form the operator only incompletely. 4. By using several cameras simul- RESULT NNT-T77MAGE taneously it is possible to take advan- U¡ o V b tage of all the of mixing, the tricks FARTdA FILMING & MOVIE HOUSE SOUND MIRING J passage by fading from one scene to i NOT FOR TV CA EPA FOR FINAL EQUIPPED another, without resorting to the FILMING t. ICMd1G ROOM MOVIE HOUSE WITH LARGE SCREEN FOP IELEaSION artifices of the cutting room. EDITOR: Tonte La Radio, Paris, France. How television may be used in film studios Television and microwaves speed newsreels APRIL. 1949 321 Television Antennas For Television*

Part IV- Excellent reception may be had By EDWARD from the simple dipole provided it is M. NOLL and made and matched to the line correctly MATT MANDLt

ASIMPLE antenna properly cut, Antenna equivalent circuit screen of the television receiver af- positioned, oriented, and The simple half -wave antenna opened fected? Was the change for a given test matched will equal or surpass and fed at the center (Fig. 1 -a) acts as so small as to be insignificant, or was it in performance many of the a resonant worthy of serious consideration because elaborate series circuit, consisting in arrays now so prevalent. effect of an inductor and capacitor plus of its effect on performance ?" Elaborate antennas do give additional resistive 1 In making the checks on different gain a component (Fig. -b). This and noise rejection, but the an- is similar to the tuned types of antennas, accuracy and uni- tenna type is not circuit with the only important which the radio serviceman is familiar. formity were obtained by positioning factor in reception. Thus, each antenna in a space loop of the There the antenna has a specific resist- are many locations in which a ance and reactance. is same station. One hundred feet of 300 - very basic antenna with its It the resistive simplicity, component which is matched to the ohm transmission line was used between ease of erection, and lower cost will transmission line to convey antenna and receiver. Much of the reserve. The simple maximum antenna is much signal along the line to the receiver in- search was made at a test site near easier to support and it can be mounted put. The net reactance increases as the Trenton, N. J., using the signals from high and clear-an increase in antenna signal departs from the resonant fre- the three Philadelphia television sta- height being more effective than the ad- quency and introduces mismatch and tions approximately 30 air -line miles dition of an element. loss, limiting the bandwidth of the an- from Trenton. Thus the checks were tenna. Because bandwidth is an im- made near the fringe area of the sta- portant consideration in television due tions, where antenna performance is of to the broad band of frequencies which great significance. At the same time must be received, the ideal television RCVR antenna is one with a rather low Q, that TERMMATION is, a high ratio of resistance to either inductive or capacitive reactance at resonance. This can be obtained by using an antenna with a relatively large surface area or effective surface area Fig. I- Actual and equivalent dipole circuits. (antenna with a number of fanned elements) . For A series resonant circuit also has optimum performance from any resonant type of antenna these points must be characteristics at harmonic frequencies. For this reason an antenna considered: MISMATCHED made TO 1. Correct antenna matching. To ob- can also be sensitive on harmon- 300n LINE tain maximum transfer of ically related frequencies. For example, signal, it is an vitally important that the, antenna a half -wavelength long and transmission fed line match the receiver input, for it is at the center at a current maximum this point from which reflections might can also have sensitivity at the third start. Antenna match to transmission and higher odd harmonics (Fig. 2). It becomes a three -half -wavelength an- line and correct 3 transmission -line length tenna Fig. -Two ways of matching to 300 -ohm line. (or addition of lengthening stub) can at the third harmonic, and point of feed is again a current maximum. give considerable improvement to weak long -range checks were made on the stations, regardless of the type of an- Experimental procedure New York stations approximately 60 tenna used. Use a low -loss line, remem- air -line miles from Trenton. Special bering that the longer it is, the greater Extensive tests on both simple and elaborate antennas were undertaken checks were also made in many other the attenuation. If any mismatch should areas to verify results obtained at the be present, it will be aggravated by ad- major test site. ditional length. CURRENT MAX FUNDAMENTAL In testing antenna performance, a 2. Antenna positioning and orienta- folded dipole was used as a standard tion. Ideal performance of any antenna antenna because it conveniently matches system can be expected only if that an- HALF-WAVE line, DIPOLE a 300 -ohm which in turn matches tenna is oriented and positioned to ob- the 300-ohm input of television re- 3RD HARMONIC tain peak signal from the weakest sta- FEED POINT ceivers. tions. Fig. 2- Reason for third- harmonic reception. Simple dipole antenna From a forthcoming book: "Reference Guide for A simple dipole (Fig. 3) proved us- Television Antennas." with these considerations in mind. In able at this distance when mismatched t Television Instructors- Technical Institute, the tests, the paramount factor was al- to a 300 -ohm line. Height of antenna, Temple University. ways "How was the picture on the orientation, and positioning in a space RADIO- ELECTRONICS for Television 33

loop were of major importance, proving a dipole was cut for channel 3 and a lapsible mast is the ideal tool for locat- more effective in bettering antenna sys- quarter -wave matching section was also ing the loops for all signals to be re- tem performance than the addition of a cut to match this antenna to a 300 -ohm ceived. It is shown in Fig. 4. This an- reflector or stacking antenna elements. line. Reception was appreciably im- tenna, although it certainly cannot give Of course, the erection of a higher -gain proved on channel 3. The signal was no good performance on the low -band sta- antenna at this optimum position re- poorer on channel 6 than with the same tions, does give a positive indication of sulted in a further improvement, but dipole mismatched to a 300 -ohm line. space loops on all channels. Light in not so much. On channel 10 there was a perceptible weight and easy to handle, it can be held improvement compared to the same at a level which approximates the dipole previously mismatched to a 300 - height of the antenna to be installed for ohm line. Obviously, then, a matching the customer. section in conjunction with the dipole The antenna is made very simply as will improve performance on a weak can be seen in Fig. 5. It consists of the station without detracting from the sig- folded dipole attached directly to the á nal of a stronger station. top section of tlae mast without any in- It is, of course, possible to match a sulation. This can be done if the mast simple dipole to a co -axial line; but as is joined to the antenna at the éxact attenuation of co -ax cable line is con- center of the unbroken side of the s siderable and it does not match stand- folded dipole since this point is a volt- ard receiver inputs, a definitely weaker age node or ground point. A small signal results. metal standoff is used to hold the antenna away from the mast. The radio- Harmonic relations man can build it in a few minutes with A dipole or folded -dipole antenna cut no difficulty. for a specific channel has a certain bandwidth and has appreciable sensitiv- Antenna dimension table ity at odd harmonics. For example, a To assist the serviceman in choosing folded dipole cut for channel 3 gave sat- correct antenna dimensions, Table I is isfactory performance on channel 6. On very helpful. Antenna lengths given channel 10 which is approximately the have been corrected for end effects (ca- third harmonic of channel 3, sensitivity pacitive loading at the ends of the an- was excellent, in fact, equal to that tenna), and quarter- wavelength match- which could be obtained from a folded ing sections have been shortened in dipole cut for channel 10. Thus it seems accordance with the velocity constant Fig. 4 -Hand -held antenna used for testing. sensible and possible in most locations of the usual 150 -ohm ribbon line. to cut a single antenna for some point To help in choosing a low-band an- As the diameter of the dipole ele- tenna which will have good pickup on ments was increased, not only was there the high-band channels because of har- increase in signal strength, TABLE I a perceptible Folded di monic relations, the chart also indicates but also an increase in bandwidth. This Pole (ful Length (in nch n 1/4-wave those high -band channels which have a made the dipole antenna cut for the Chan- Channel e h half he ¡ harmonic nel Limits ON) of dipole folding/ action hannela; harmonic relation to a low -band channel. lower- channel stations quite effective The third harmonic is the only harmonic A minimum 2 54 -60 48.6 207 40 7 for the high -band stations. which is significant because other har- 60 44 181 36 8,9,10 recommended diameter for a dipole ele- 3 -66 monics fall outside the TV channels. ment is icy inch. 4 66 -72 40 166 33 11,12,13 As an example, a dipole for channel A mismatched to a 5 76-82 35 145 29 dipole antenna 3, with a % -inch separation at the 300 -ohm line gave inferior performance 6 82 -88 32.6 134 27 center where transmission line is at- on all channels compared to a folded 7 174 -180 15.6 64.7 12.9 tached, would have an over -all length 12.5 dipole. However, with a quarter -wave 8 180 -186 15.1 62.6 of 88.5 inches. According to the last -ohm 12.1 matching section between the 73 9 186 -192 14.6 60.6 column, this antenna would also be ef- -198 14.2 58.7 11.7 dipole and the 300 -ohm line, the signal 10 192 fective on channels 8, 9, and 10. strength came up to a level not much 11 198 -204 13.8 57 11.4 In the next article performance com- different from that delivered by the 12 204 -210 13.4 55.3 11.1 parisons will be given for various an- standard folded dipole. 13 210 -216 13 53.8 10.8 tennas with respect to propagation The matching section consists of quar- low have same characteristics, including the use of ter- wavelength of line attached be- in the band and that reflectors and directors. tween antenna and transmission line. antenna perform very well on the high - In calculating the necessary impe- frequency channels. dance Z,,, of the line used for the match- An antenna cut for any of the high - ing section, band channels, however, will give defi- Z,,, R,Z nitely inferior performance on the low - where R. is the antenna's radiation frequency channels. In most localities, resistance and Z is the impedance of therefore, a very simple antenna will the main transmission line. Thus, to suffice for reception of all stations if match a 73 -ohm dipole to a 300 -ohm the antenna is properly cut and posi- line requires a quarter -wave section of tioned for best performance on the 150 -ohm line. Its length should be Weakest station. Performance can be slightly shorter than a quarter -wave in further improved for the weak station free space; it is found by multiplying by adjusting the length of the transmis- the free -space figure by the velocity con- sion line, or by the use of a stub across stant of the 150 -ohm line, usually avail- the antenna input terminals. able from the manufacturer. The mismatched dipole does have a Space loop check low Q and therefore a broad bandwidth. A simple folded dipole can be used to However, it was found that that is not locate the space loops of the stations to always desirable. It is often helpful to be received. Most TV antennas and their be able to improve sensitivity on one or masts are too cumbersome to carry more stations at a sacrifice in band- around a roof. A simple channel 13 width. For example, in a specific check folded dipole mounted on a light col- Fig. 5- Close -up shows construction details. APRIL, 1949 ;. \ \17, I f ///' ." "' 1 :.'/ !' .= ; .. \ T -.a+' -`_- _. . \\t' /' _.. ;e

s 'Y,ti+... tt. ,.,,... .. ,. -,. _ _,; L

."014 tt';;_fl bepU}),iehe d-*d e:. _-

1 y ob a d a e d d s . t vision` to ggoing fú blastsWithout' wasting any words whatsoever he took Sensational new in- tube, and if now the image could be en- two Alnico bar magnets each about four larged to any desired size at low cost, inches long and began waving them at vention enlarges im- the television images of each of the receivers. We noticed that each image age over 250% .. . was influenced profoundly by the powerful magnets. By manipulating the two magnets the image was either drawn been made. He urged us earnestly to out-or by reversing the polarity of give the matter serious thought because the magnets -the image was com- he was certain that the effect would pressed. In other words, the picture was have practical uses in the future. enlarged in the one case, reduced in s the other. (You can try this pretty ex- The idea which the Chief had demon- periment yourself by getting a pair of strated to us fascinated me irresistibly. permanent Alnico magnets.) I kept thinking and dreaming about it The Chief then explained to us that for days. Finally an idea crystallized, the action of the magnetic field merely and I immediately started to work on it influenced the electronic beam of the with my usual enthusiasm. cathode -ray tube, to create this effect. One of television's great troubles -it A number of photographs showing seemed to me-is that the price of tele- the action were then taken. To the best vision receivers is out of all proportion. of my knowledge it is the first time that The way we are going, it will take sev- photographs showing this phenomenon eral decades before everyone in Amer- ica has a television receiver. To solve *Inane Radio Electronics this price bottleneck would be the most

E ements of magnetic enlarger: I- electromagnetic coils; 2- inside of ground glass coated with fluorescent paint; 3- enlarger case; 4 -6X5 rectifier; 5- rheostat; 6 -plug.

television certainly would have arrived in earnest. I immediately started building an experimental device which I call The Magnetic TV Enlarger. It is shown here in several illustrations. First we require an electromagnetic field built in the form of a rectangular electromagnet with four field coils. These coils are energized from the 117 - volt a.c. line. A rectifier tube (or selenium rectifier) is used to obtain the necessary direct current. A rheostat in the circuit regulates the flow of current. The magnetic field should be roughly the size of the cathode -ray tube. I intended to use my enlarger with the smallest television receiver made: the Pilot, which uses a 3 -inch tube. I then constructed a box of wood, at the other side of which there was a ground- Holding a pair of permanent magnets on both sides of the screen elongates the picture. glass plate. As a fluorescent or phos- RADIO -ELECTRONICS for Television 135

The three photos show what happens when magnets are held in various positions around a TV screen. Any set owner can try this for himself. phorus coating was necessary for the is completely and 100% electronic. has been able to project an electron picture, I coated the mat side of the The thing that pleased me most about beam any distance outside a glass 8x10 -inch glass with fluorescent paint my development was that the cost is cathode -ray tube. Hence, your enlarger obtained from a luminous paint company. very small. I built the entire enlarger in this form cannot operate. So, the next for less than $3.00. time you build one of your fool contrap- RECT 4 MAGNET COILS tions be sure you think it all 6X5 We can enlarge a 3 -inch cathode -ray- through 00000 tube picture to a 10 -inch image, or 7- carefully before building models." inch tube image to a 20 -inch picture, With that the Chief threw my mag- 0 "1.1IIIII etc., at an exceedingly low cost. netic enlarger into his waste basket. He Once the television manufacturers then gave me a not too friendly push 0 11 LINE CORD IITVAC B e have adopted my the and slammed the door behind me. RES 0000`ß enlarger, cost of TV receivers will drop sensationally. As I sailed into the outer office I collided with the opposite wall on which How line current is rectified for the coils. The next morning I went to see the a Chief and excitedly told him what I had. large calendar was hanging. As I hit it When we energize the electromag- He looked the enlarger over with a puz- I was also forcibly struck by the date. nets, the image is enlarged in propor- zled mien and then wanted to know if I It read tion to the strength of the magnetic had tried it out. I said no, not yet, be- April 1 field. The electron beam now strikes the cause I did not have a television set at glass, coated with its active film. home. So I thought it might be an ex- Inasmuch as the glass measures 8x10 cellent idea if we tried it out on the inches, the image from the 3 -inch cath- Chief's office receiver. ode -ray tube is enlarged nearly 300% The Boss lit a huge fresh cigar and on the glass screen. started to look over my enlarger with Theoretically, if the magnetic field is a somewhat quizzical look on his face. LUMINOUS COATING ENLARGED IMAGE ON SCREEN "Fips, my boy," said the big Chief, Io" "you certainly have something here. Your busy little brain must have been working overtime. Let's see it work!" I turned on the set, plugged in my

MAGNETIC magnetic enlarger, and then adjusted LENS the rheostat to bring it up to the proper SYSTEM field strength. The Chief was sitting IRON CORE nearby puffing away on his big cigar with a curious smile upon his face. The , INTENSE IMAGE ON END OF CR TUBE set took a long time to warm up. Once I took off the enlarger to see if there was an image on the 3 -inch tube. There was. However, for some reason or other the (TELEVISION FIX TUBE 10 -inch screen did not light up. Was it possible that there was a break somewhere in the circuit? I carefully went over the connections, all of which seemed O.K. There was something wrong somewhere, which I could A photo of the finished magnetic TV enlarger. not grasp immediately. I was now exud- Beam deflected ing perspiration all over the place, by coils covers area of glass. when out of the vacuum -like silence the scornful voice of the Chief rang out correctly proport'oned and carefully with metallic harshness. adjusted as to strength, there should "Well, Fips, you pulled another not be any distortion whatsoever. The boner, and I know exactly where it is. reason for this is that the enlargement Your enlarger should work perfectly is proportional at all points. except for one minor point: Just how do Mark well that there is no aberration the electrons from the cathode -ray tube as when an image is enlarged by a lens. get to your glass plate? With the magnetic enlarger you view "With the power which you have- the image on a perfectly plane surface s 3 -inch cathode -ray tube -you cannot and consequently there can be no dis- project an electron beam out in the air tortion whatsoever. Most important, so that it will strike your prepared with the magnetic enlarger we do not glass plate several inches away. Other- enlarge the image optically; the effect wise, your device is fine. So far no one The enlarged 3" picture measures 8 r 10 inches. APRIL. 1949 Broadcasting and Communications Telephone Lines in Broadcasting

Part I- Frequency response measurement and equalization of program lines

By LEIGH L. KIMBALL*

THE telephone line is still the major link between the broadcast studio, the remote pickup point, and the transmitter located outside the city. Relay transmitters and portable recorders despite all their recent developments are still a long way from supplanting the telephone line because of the latter's simplicity, relatively low cost, and ready availability from the various telephone systems throughout the country. Today, telephone lines go to almost every point of interest-net- working even small communities in amazing detail -so that it is usually no problem for the telephone companies to supply wire facilities to broadcast stations quickly, efficiently, reliably, and Courtesy National Broadcasting Co. inexpensively, with a minimum amount of bother to the broadcaster. But the Election -night state of NBC's patch board shows importance of telephone lines to broadcasting. problems confronting the broadcast engineer are what to expect from his lines cies. There are several methods of com- convenient reading on a standard vol- in the way of performance and how to pensating for or equalizing the high - ume indicator (VI) in its output circuit. use telephone facilities most efficiently. frequency drop; one of these is to add A dummy load R, equal to the ampli- Telephone lines have two main uses series inductance at intervals along the fier's output impedance (usually 600 in broadcasting: program transmission line. The telephone companies make ohms) should be provided, as the VI is from remote pickup point to studio, wide use of this series loading, both in a high- impedance device (7,500 ohms from studio to transmitter, and from inteacity voice circuits and intercity for the NAB standard VU meter) and long lines. But procedure is studio to the long-lines exchange for that usually RI /2 too complicated for radio circuits which network operations; and program -co- VAR. RECEIVING ordination communication by means of may be used for relatively short periods FRED. PROGRAM LINE PROGRAM the program pair itself or by means of of time. The more common practice is o5C. AMPLIFIER a private line (PL) direct to the remote to supply the line without loading and R ¡/2- - -- point,, intended primarily for telephone use equalizing equipment at the ter - Fig. 2- Simpler response measurement hookup communication. Long- distance intercity minations. facilities should not be left out of a list Frequency response of nonloaded 0 lines is determined mainly by of major uses, but in most cases the line length RELATIVE only part of such circuits over which and the gauge of the wires used. The RESPONSE 5 the broadcast engineer has any direct heavier the gauge, the better the high - OB control is the local loop to the long -lines frequency response. As line length increases, it becomes more difficult to to exchange. Therefore, this article will 40 70100 200 400 700 KC 2 4 7 10 20 concern itself strictly with the relative- transmit high frequencies. The response GPS ly short telephone lines referred to as may be calculated in advance; but, since Fig. 3- Correct and incorrect measurements. local loops. the total line may include several differ- The most important technical charac- ent wire gauges, it is usually much will not load the amplifier correctly. teristics of a telephone line are frequen- simpler to measure it. The measurement If the arrangement in Fig. 1 is too cy response, loss, and noise. is a problem in itself. bulky for portable work, another ar- In general, it is best to test a line rangement requiring only an oscillator Frequency- response measurement with the amplifiers that will be used for (shown in Fig. 2) is equally good if the program purposes. The input level to internal impedance of the sending am- At audio frequencies telephone lines the sending amplifier should be held plifier is known. In the diagram R, is are mainly capacitive, which, along constant as frequency is varied. A the internal impedance of the sending with typ- copper and insulation losses, re- ical arrangement is shown in Fig. 1. amplifier normally used at the line induces their efficiency at higher frequen- The receiving amplifier may simply be put. Chief Engineer, WASH -FM. connected to the line and adjusted for a This is the arrangement agreed upon by the major networks and the A. T. & T. When only an oscillator is avail- SENDING RECEIVING VAR. FREO.OSC. PROGRAM LINE response meas- PROGRAM AMPL PROGRAM AMPL. able for line frequency- IE urement, it should be adhered to strict-

CADS H -PAD ly. Putting the voltmeter or VI (used

Fig. I -Setup for measuring frequency response of phone line. VI's are volume indicators. to see that oscillator output is held con- RADIO -ELECTRONICS for Broadcasting and Commuldcntions 37

stant) directly across the line terminals of the program amplifier should be quencies due to reflection from the mis- at the sending end can result in serious known. Measuring it is simple. matched termination. This system is errors, since the test generator's effec- Referring to Fig. 5: used for longer lines than method 1 ; tive internal impedance becomes zero it will equalize lines up to about 10 miles rather than simulating that of the am- E -E, R , and in length. Method 2 is: plifier to be used for transmitting pro- R +R, 1. Set the parallel resonant circuit grams. An indication of the possible R(E, (L, and C,) to a frequency slightly error is shown in Fig. 3 for an actual R -E ) higher than the maximum desired. case on a short loop. The solid curve E. 2. With the equalizer in the circuit shows the line to be actually very poor "E, is measured by the a.c. v.t.v.m. when and R, at zero resistance, send a when used with a 600 -ohm amplifier, R is disconnected from the circuit and tone reference from the test oscil- although, when measured incorrectly an audio tone is applied to the input of lator at the highest frequency de- (dashed line) it looks very good. the amplifier; E is the a.c. voltage sired and note the VI reading at The reason for the series resistors is across the output terminals when R is the receiving end. that an audio amplifier is actually a connected ; and R is a resistance com- 3. Shift the oscillator to a low fre- constant -voltage generator with an in- parable to R,. R must be small enough quency (50 or 100 cycles) main- ternal resistance of R as shown in Fig. to give a substantial difference between taining the same output level as 4. The constant voltage E can be con- E, and E , yet large enough not to cause before, and increase the resistance distortion in the output stage of the of R. until the same VI reading is amplifier. A workable value usually is obtained as before. 600 ohms. 4. Make a complete frequency run The procedure is valid only if the out- and take care of any touch -up ad- Fig. 4 -Audio amplifier output, equivalent. put impedance of the amplifier is con- justments necessary to get a flat stant and resistive over the audio range. response over the desired range. sidered as the microphone output volt- This is usually true of a high -quality The maximum variation can usu- age (amplified by a constant factor) broadcast amplifier; but, if there is any ally be held to ±1 db. which, of course, is independent of con- doubt, R, can be measured at several Various combinations of methods 1 ditions in the output circuit. Therefore, frequencies. If there is appreciable vari- and 2 may be used. One of these, method when E is constant, the amplifier output ation in R,, the line must be equalized 3 is recommended for especially long voltage E. depends only on the internal and tested in accordance with Fig. 1. lines where good frequency response resistance of the generator, and on the with low noise level is important. load impedance at any frequency. This Equalization Two effects which may cause irregu- is true of an amplifier, and the condition Two principal methods of local -loop lar frequency response cannot be re- equalization are commonly employed. moved by these equalization procedures. They are shown in Fig. 6. Method 1 The first and most serious is a series simply makes use of the transformed loading coil in the line. The telephone input and output impedances of the company may sometimes overlook one Fig. 5- Internal impedance measurement rig. line amplifiers to provide a heavy (150 - of these inductances which they use to ohm) resistive loading to shunt out the equalize voice circuits and unintention- is duplicated, for all practical purposes, effects of line capacitance. This extends ally leave it in the line. The symptoms by the arrangement in Fig. 2 where R, the high-frequency response in much are unmistakable -no reasonable amount is split into two parts for the sake of the same manner as is sometimes used of equalizing work will extend the fre- line balance. The internal voltage of the in audio amplifiers. Method 1 can be quency range much higher than 4 kc. generator is held constant manually, used to equalize lines of the following Fig. 7 is a typical response curve. by adjusting the gain control at each maximum lengths and wire gauges to frequency for constant reading on the about 8000 cycles. If 15 -kc equalization VI across the output. is desired the lengths should be scaled down. 0 Internal impedance Wire Gauge Length (miles) The internal impedance of a commer- 16 5 cial broadcast amplifier may or may not 19 2.3 be equal to its rated output impedance. 22 1.5 For instance, the 600 -ohm output of a The equalizing procedure for method popular line amplifier was found to have 1 is a simple frequency- response check. 65 ohms internal impedance due to in- Method 2 makes use of a variable - verse feedback over the last two stages. impedance leg at the receiving end that This is desirable, as the low internal actually mismatches the line at the low impedance helps to equalize the line. frequencies but has little effect at high 20 40 70 loo 200 400 700 INC 2 4 7 But if line frequency- response meas- frequencies. Correct equalization is CPS urements are to be made in accordance obtained when the line loss at high Fig. 7- Effect of loading coils in the line. with Fig. 2, the true internal impedance frequencies equals the loss at low fre- The second common cause of irregu-

METHOD I larity is an impedance discontinuity J an/ l along the line resulting from the use of -. AMPLIFIER 4 600a 7111 + --150n. PROGRAM LINE 150n - C) 600n AMPLIFIER different cable gauges in the loop make- up or from branch circuits which are METHOD 2 tied on at some point. The principal result is a bumpy response curve. The AMPUTIER PROGRAM LINE AMPLIFIER effects of different cable gauges in the line are usually small. However, the results of branch circuits may be more serious, especially since an untermi- nated branch is very suceptible to cross- METHOD 3 talk interference from adjacent cable PROGRAM LINE 130443 II pairs. 14- (The concluding part of this article, which will appear in an early issue, will discuss line loss, noise, correct ter- Fig. 6- Several methods of equalizing the frequency response of program telephone lines. mination, and maintenance.) APRIL, 1949 381

Recording components or

FOR the large number o /.+ is found on most records. As a thusiasts who are not satis suit, any good playback system ad- ordinary -quality recorders, he justed for ordinary records will give a portable system which is capable top results with records made with this of making records comparable in qual- al volt- amplifier. ity to the best commercial jobs. Besides age amp is a little The equalizer circuit used to obtain giving the recordist the benefits of high more than necessary, as a matter of the curve consists of Rl and Cl in com- fidelity, the system is compact, versatile fact.) The 6N7 is a self -balancing phase bination with R2. The network, though enough for PA work, and suitable for inverter, and the output stage is a pair extremely simple, cannot be arrived at record listening at home. The three of push -pull 2A3's. (6B4's -with the by ear. In building the amplifier, the functions- recording, PA or monitor- necessary filament- and bias-voltage constructor should not vary the values ing, and record playing -are selected changes -might be more available to- of the equalizer circuit, no matter what by a novel "gearshift" switch on the day. The 2A3's were on hand when the changes he may want to make in other side of the amplifier. unit was built.) sections of the amplifier. The amplifier is designed for use with A crystal cutter, the Brush RC -20, is the audio control console described on Equalization used because it gives the best results page 34 of the February issue of RADIO - Of the two unusual features in the for the least amount of money as far ELECTRONICS. However, any other pre- amplifier, the more important for re- as fidelity is concerned. Because a crys- amplifier could be used, or additional cording purposes is the carefully cal- tal cutter is a constant- amplitude de- voltage amplifiers could be added to the culated equalization. As the writer has vice, a resistor must be placed in series recording amplifier itself. When used previously pointed out (Practical Disc with it to obtain the modified- constant- with the console, the entire recording Recording, Gernsback Library, No. 39), velocity characteristic usual in phono- records. system is portable in two parts: the con- there must be a certain amount of pre - graph sole is fastened to the power supply emphasis in the high- frequency range Fig. 3 is a diagram of the components with thumbscrews and carried by means during recording so that signal -to -noise on the motor board. The amplifier out- of the handle on the console top; and ratio will be high in playback. As a put is fed from the 2A3 plates through the recorder case, containing amplifier practical matter, too, the record -play- 0.5 -sf blocking capacitors (Fig. 1) to and turntable assembly, is carried by ing systems owned by most people have the cutter jack. The cutter plug (Fig. its handle. While the combination is a drop in the high range, making pre - 3) is plugged into this jack to carry neither as light nor as small as many emphasis necessary to restore fidelity. audio to the cutter. R3 is the necessary commercial portable recorders, the re- The only standard for pre -emphasis series resistor. sults it gives and the versatility it of- in the recording field is the so- called fers are well worth the added size. NAB curve, which results in a boost of The "gear shift" Fig. 1 is a schematic diagram of the 16 db at 10,000 cycles. Most phonograph The second interesting feature of the recording amplifier. The output of the records have frequency curves some- system is the switching arrangement. console which feeds it is zero db in 500 where between the NAB standard and The amplifier can be used, not only for ohms, which results in 1.73 volts. Rather a characteristic with slightly less boost. recording, but also for listening. A 3 -po- than use an expensive (and hum- sensi- Fig. 2 shows the response of this am- sition, 6- circuit rotary switch S1 (Fig. tive) transformer at the input of the plifier with the switch in the recording 1) selects any of three functions: In recording amplifier, the 6C5 input grid position. The boost is 2.5 db less than position 1, output is fed to the cutter; resistor is a 500 -ohm potentiometer. the NAB prescribes at 10,000 cycles, in position 2, output is fed through a This terminates the 500 -ohm line from giving a very close approximation to high -fidelity transformer to the speak- RADIO -ELECTRONICS for Audio 139

er; and, in position 3, output is also fed JI RECORDING VOL CONT JI- 500o LINE FROM CONSOLE J2-XTAL PICKUP JACK SI -A to the speaker, but the input circuit is R4 SI -a transferred from the regular line to a J2 3o ''SDADJ 8C5r21 8N7 2A3r21 crystal pickup mounted on the motor a ó board. SI-b 3 10 WATTS EQUAL TO 2 OF VOICE RS 500 SI -d As the under -chassis photograph q o1 COIL shows, S1 is mounted lengthwise on the 2_ I j sKJ 2 chassis. Long switch supports allow the PLAYBACK two wafers to be placed reasonably close VOL CONT to the circuits they control so that ac- 2.2K IIG SPKR cidental feedback is not likely and long leads are unnecessary. B 450v +125v

The photograph of the main case 150K 50 shows how the amplifier is mounted so that only the dust cover shows. If the SI-a b- c -d -e -f GANGED POSITION I - RECORD + 360V knob controlling S1 were at the end of 2 - PLAYBACK 3 -%TAL PICKUP Fig.! the chassis, it would be inconvenient to s1 5 a turn. Therefore a metal shaft coupler SI- CUTTER was attached to the shaft in place of a TRANSMISSION I DB 1

knob. One of its screws was removed SI -+ and a long rod, the end of which was +15 EMI threaded, was screwed in its place. This arms .-2 $ DO NOT GOO +10 rod 30 (it can be seen at the right of the PWR CABLE amplifier) controls the switch very +5 much like an automobile gear -shift lev- 2A3FILS I.! er. Pull it toward you and record; leave o

it at center and listen to the output of 5 the console; push it to the rear and 60 00 100 200 300 400 600 800 IK 2K 3K 4K SK 6K SK 10K use the built -in crystal pickup. FREQUENCY IN CYCLES 6.3V FILS4 . PWR PLUG Two volume controls R4 and R5 are Fig.2 switched the amplifier input. is at R4 Fig. I- Complete circuit of the recording amplifier. Fig. 2- Equalized frequency response. mounted at the left end of the chassis and has no knob. Once set for the proper recording level, it is thereafter left Making the case cover is lowered, the edges of the motor alone. R5 is mounted on the chassis, an The construction of the case is shown board keep the sides of the cover ex- in line. extension shaft projecting through the in detail in Fig. 5. These dimensions will actly The dust cover. The control knob seen atop do for almost 12 -inch photograph shows how the com- any recording mounted the amplifier is used to control volume mechanism. The one shown in the photo ponents are on the motor board. Mountings are not given in the when listening. The crystal pickup has is a prewar Rek -O -Cut. An overhead - its own volume control, as Fig. 3 shows. lathe mechanism almost always gives -c Sl switches the equalizer. When it superior results to a swinging -arm unit, BRUSH RC-20 XTAL CUTTER TO CUTTER JACK R3/42K is not in the circuit, in position 2, the and the case cover is high enough to ac- oJ amplifier output to the speaker is flat commodate most lathes. - o within 2 db from 50 to 15,000 cycles. It The amplifier is set in the rear of the R6 is switched in when the crystal pickup case. Holes are drilled into the amplifier is used because it has almost exactly chassis through the 1 x 1 cross -member 500K s JO-IMA the correct high boost to give a good METER RECT on the floor of the case. The chassis TOSPKRJACK TOSPKR` crystal pickup the right correction for holes are tapped so that a machine o-ro standard records. screw can be passed through each hole The power supply (Fig. 4), a stand- in the wood to hold the amplifier in ard job with plenty of filtering, is built place. Similar holes for additional sup- on a separate chassis 14 x 6 x 2% inches porting screws are made through the TO xTAL PU JACK 500K o _ e with a standard amplifier dust cover. rear of the case into the amplifier. The 1 -V Separation of the power amplifier chassis is 5 inches deep, and supply from VOL COOT TOÑE CONT XTAL PU both recording amplifier and console the space allowed is 5% inches. Its width (which it also supplies) keeps hum is 10 inches, allowing space for plugs on down to the irreducible minimum. Octal either side. 117V AC SW TURNTABLE MOTOR tube sockets mounted on the rear apron The 1 x 1 motor -board supports are accommodate plugs and cables to carry flush with the top of the sides. The mo- power to amplifier and console. tor board is placed (and fastened with Fig. 3 shows how the components edge screws) on top of these; it is, thus, Fig. 3 -Components mounted on the motor mounted on the recorder motor board above the sides of the case. When the board. are connected. The rectifier and milli - ammeter provide an additional check volume on being fed to the cutter, al- 5.3V 5T4 TO REC AMPL

though the decibel meter mounted on I g 3° f 1211/100MA o0Q /* the console should be used mainly; the 360%. 375V 4 a + 65. milliammeter will give false readings, o o e B 8 5K 251/ since it is preceded by high -boost equal- 375V w PL 450V 450v ization. It is, however, a positive indi- Ì 16 16 cator which will show at once any mis- Sv takes or faults in switching or connections. If the meter 40 150 kicks, the cutter is 2.5V almost certainly receiving audio. R6, TO CONSOLE an adjustable meter multiplier, is mounted on the motor board underneath B00/25W the turntable and has no knob. When it is once set, tampering is not likely. Fig. 4-The power supply. A 25,000 -ohm, 25 -watt bleeder can be added for better regulation. APRIL, 1949 401 Audio drawing because they will depend on closed case was up -ended and balanced using the recorder. These are setting the particular recording mechanism on a sharp -edged support to find the R4 and R6 for the correct recording used. Two 5 -inch speakers were on hand center of balance. The balance point was level. when the recorder was built, so they marked, and the handle placed there. Feed a 200 -cycle tone through the were placed in the cover. For better re- Keeping in mind the fact that the am- console and adjust the volume control sults, an external high -quality speaker plifier and mechanism are heavy and may be plugged into the speaker jack that either can easily be damaged if mounted on the right rear of the motor dropped, be sure to make all wood joints board. in the case firm and strong. The original The cover is fastened to the case with job was done by a cabinetmaker, who loose -pin hinges, similar to those used rabbeted the joints and used the strong- on portable typewriters, so that the est possible glue. Heavier stock would cover can be removed entirely. Trunk also provide insurance against accidents catches (large ones) fasten the front but might add too much to the weight. for carrying. A heavy leather handle The mechanism and pickup must be attached to the front of the cover must fastened down tightly for carrying. The be positioned so that the weight will be photo reveals the angle brackets and evenly distributed. After assembly, the thumbscrews used for the cutter. The method will vary, of course, with different mechanisms, but the only require- 153/4 ment is that nothing must be allowed The amplifier chassis without its dust cover. to move. An ordinary alligator clip screwed to the motor board keeps the pickup in place. Clip brackets in the 15.1/2' top of the cover carry stylus containers. MOTOR BOARD PARTIAL VIEW and cleats carry cables. A photogra- 22 pher's telescopic tripod is carried, too, SPNR HOLE SIZE AS REQUIRED as a microphone stand. There is always a thread -removal .. LOOSE PIN HINGES problem with disc recorders. It is solved in this unit with an Audiodisc Chip \ Chaser, which is a felt "brush" fastened to hinged supports. The device is sold with a heavy metal base and is usually MAIN CASE just placed next to the turntable. To make the chaser part of the assembly, AMPLIFIER 22- the base was removed and the vertical 16.1/2 COMPARTMENT support screwed to a small angle brack- The power supply uses two big, heavy chokes. MATERIAL:1 /2- PLYWOOD et fastened to the motor board. EXCEPT AS NOTED A -11f1' 8-3PLY Adjusting the system on the console so the decibel meter reads 0 -HOLES FOR FASTENING AMPLIFIER zero. Adjust R4 so a vacuum -tube There are only two adjustments to be that voltmeter (a good nonelectronic volt- Fg. 5 -How to make amplifier- recorder case. made in the electrical system before meter could be used) connected directly across the cutter reads between 90 and 100 volts. Never disturb R4 again. Make a mark on the milliammeter on the motor board at about the 0.6 -ma point. Then adjust R6 until the meter needle is at the mark. When recording, do not depend on the milliammeter to read correct level, since high frequencies will not register correctly (due to the equalization).

MATERIALS FOR RECORDER Resistors: 1- 2,200, 2- 3,300, I- 39,000, I- 42,000, 2- 47,000, I- 100,000 5- 270,000, 1- 300,000 ohms, 1/2 watt; I-8G0, 1 -5,óO0 ohms, 25 watts; I- 150,000 ohms, SO watts, adjustable; 2- 500, 3- 500,000 -ohm paten tiometers; I -10 -watt resistor equal to impedance of voice coil.

Capacitors: 1 -330 ulaf, mica; I -.01, 4-0.1, 2-0.5 'f, 600 volts, paper; I -25 uf, 25 volts, 1-40 uf, 150

volts, 4-8, 1 -16 uf, 450 volts, electrolytic. Transformers and chokes: I- power, 750 volts center-tapped, 100 ma, 6.3 volts, 4 amperes, 5 volts, 3 amperes, 2.5 volts, 8 amperes; 1- output, 5,000 -ohm push -pull plates to voice coil, IS watts, 100ma primary; 2 -12 -h, 100 -mo filter chokes. Tubes: 2 -6C5, 1-6147, 2 -2A3, I -514. Switches: I- 3- position, 6- circuit, rotary, with long- est ovailable indexing assembly; 2- s.p.s.t. toggle, I- d.p.s.t. toggle. Connectors: 5- single- circuit, non -shorting phone jacks; I- 2- circuit phone jack (for PL -68 -type plug); 3- single- circuit phone plugs; I-2-circuit phone plug (PL -68); 2 -octal tube sockets; I -cable -end octal mote plug; 1-chassis-mounting, unpolari:ed mole 117 -volt plug. Recording comp ts: I- turntable; I -Brush RC -20 crystal cutter; I- crystal pickup. Miscellaneous: I -meter rectifier 1 -0-1 -ma d.c. meter; 1-6 -volt pilot light assembly; 4- octal, 2-4- prong tube sockets; I- threaded rod and shaft Amplifier (above) and power supply (below). Notice the long switch assembly. coupler for "gear shift "; wood for case (see Fig. 5); loud-speaker(s); loose -pin hinges; trunk catches; knobs, hardware, etc. RADIO -ELECTRONICS for Audio I41 Audio Impedance Matching

Part II-Data on how to match several speakers to an amplifier, each powered as desired and all impedances correctly r matched to the output of the amplifier By WALTHER RICHTER*

_ IN the first installment (February regard to damping? Whatever the in- one -half of its own resistance, is look- issue) of this article we showed ternal resistance of the amplifier, it will ing back into a resistance almost twice why amplifier load and internal im- certainly appear smaller to a 500 -ohm its size! pedances are important in transfer - load than to a 125 -ohm load. If it hap- ing power to the speaker and in speaker pens to be an amplifier with a triode in No build -out resistors damping. The practical application of the output stage, the internal resistance By trying to be too smart, we could the principles presented is best illus- (as seen at the transformer secondary) do even worse! We might reason, for trated with the aid of a few examples. can be expected to be around 60 ohms. instance, that for an amplifier to oper- Suppose we are given an amplifier With a load of 500 ohms looking back ate most efficiently on the 20 -ohm tap, rated at 30 watts, and that the output at 60 ohms, the damping will be con- the load connected to this tap should be transformer is provided with 20- and siderably better than with a 125 -ohm 20 ohms; and since we have only a 125 -ohm taps. The statement that the load; and this connection will there- 6 -ohm speaker, we might have the amplifier will deliver 30 watts permits fore actually give better results than bright idea of placing 14 ohms in series us to calculate the maximum voltage the 125 -ohm load -provided the ampli- with it to bring the total up to 20. To and current values of the two taps. fier is truly capable of 30 watts output. be sure, this gets our 6 watts to the Applying one or both of the formulas Now suppose that, instead of a speak- speaker, but 14 watts of audio power in P = E2/R and P = I2R, we find that er of 500 ohms, we have one with a the 14 -ohm resistor are thrown away for a single load of 125 ohms, if oper- resistance of 6 ohms and capable of and do us no good whatsoever. More ated from the corresponding tap, a volt- handling 6 watts of power. (To use a important, the total resistance in the age of 61.2 and a current of 0.49.ampere 30 -watt amplifier to drive a 6 -watt voice -coil circuit is now equal to the will result in 30 watts; on the 20 -ohm speaker seems ridiculous, but let us as- internal resistance of the generator tap, 24.5 volts and 1.22 amperes will sume that the two pieces of equipment (which was already too high on the result in 30 watts. These, then, are the were inherited from two different un- 20-ohm tap) plus the 14 ohms of series voltage and current values which must cles.) To obtain 6 watts in a 6-ohm load llstance. not be exceeded. requires 6 volts at 1 ampere. The 24.5 In this case, we should use, a match- Suppose, now, that we want to oper- volts and 1.22 amperes which can be ing transformer, which will make the ate a 500 -ohm speaker from the ampli- obtained from the 20-ohm tap are in 6-ohm speaker appear as either 20 ohms fier, and that the speaker is rated at excess of the current and voltage rat- (if we wish to connect it to the 20 -ohm 10 watts. Should we use a matching ings of the 6 -ohm speaker, and we could tap) or as 125 ohms (if that is where transformer? connect the speaker to this tap. we wish to connect it). The design and To obtain 10 watts in a resistance of But how does this circuit arrange- construction of a matching transformer 500 ohms, 70.7 volts are needed; the ment look with regard to damping? to take care of a relatively small mis- current will be 0.14 ampere. If we con- Again we do not know the internal re- match, such as perhaps 4 to 1, is not nect the loudspeaker directly to the sistance of the amplifier ; but if it is a very difficult and can usually be accom- 125 -ohm tap, we cannot quite reach the triode amplifier, the internal resistance plished by utilizing the core of an old full 10 watts without exceeding the at the 20 -ohm tap will look like ap- audio transformer. Such a design will voltage limit of the amplifier although proximately 10 ohms. To connect a 6- be discussed in a future article. Match- we will be below the maximum rating ohm speaker to a generator with an ing transformers can be purchased for as far as current goes. internal resistance of 10 ohms is not a all common impedances. How will this arrangement be with very satisfactory arrangement, since the voice coil, instead of looking back A multiple speaker problem Engineering and Development Dept., Allis-Chalmer Mfg. Co. into a resistance equal to approximately Suppose we have an amplifier rated at 30 watts, with an output transformer having 500 -, 16 -, and 6 -ohm We 5004, taps. 164, wish to operate a 500 -ohm, 10 -watt loudspeaker, a 20 -ohm, 20 -watt speaker, 0: 64, and four 6 -ohm, 4 -watt speakers. The - COMMON full power which all the speakers can take is 46 watts, which exceeds the 30W AMPL 6 rating of the amplifier. First, therefore, 12.65n u 53.4n 2140n 5004, we must decide how the available 30 e°0 1W watts are to be distributed. M ° II 6n One could argue that the wattage al- lotted to each speaker should simply be n 5045 of its maximum. This solution is not necessarily the best one. One of the speakers may be considerably more efficient than the others. Or the speakers Fig. I- Simple calculations were used in matching these six loudspeakers to the amplifier. may be serving different rooms which APRIL, 1949 42J audio require different amounts of output. er. The transformer primary must the power to be drawn by each speaker, After the best judgment has been form a load which will consume 7 watts we can find the impedance necessary at used in distributing available power, it when 122.5 volts is placed across it. each matching transformer primary. probably will still be necessary to insert Substituting 122.5 volts and 7 watts in Transposing the formula P = E "/R attenuators in some of the speaker the formula P = E2 /R, and solving for to solve for R (R = E2 /P), substituting lines. However, any audio disappearing R (R = E2 /P), gives us a value of 2,140 122.5 for E and, successively, 7, 9, and in an attenuator is a total loss, so it is ohms. This apparent mismatch is in the 14 for P, we find that the primary of well worth while to try to make the right direction, since the internal im- distribution as close as possible to the pedance of the amplifier looks smaller R. INTERNAL IMPEDANCE OF AMPLIFIER required conditions. to a 2,140 -ohm than to a 500 -ohm load. Suppose now that with the amplifier By the same reasoning, we find that ¡.0572A iA735A 1.u42A wide open delivering 30 watts (See Fig. to consume 9 watts the 16 -ohm speaker ¡2140 '1870 1070 1 tgW 1) the 6 -ohm speakers are each to re- must look to the 16 -ohm tap like a load "7W 14W ceive 3.5 watts; the 20-ohm speaker, 9 of 53.4 ohms. The four 6 -ohm speakers I watts; and the 500 -ohm speaker, 7 watts. together, to consume a total of 14 watts, LOW AMPJ None of the speakers can be con- must look to the 6 -ohm tap like a load 500k 30 WATTS NET nected directly to any of the available of 12.85 ohms. The 6 -ohm speakers may dB s 500k OUTPUT TERMINALS transformer taps; the 500 -ohm speaker be connected either in series or in Hg. Matching with 3 output transformers. cannot even be connected to the 600 -ohm parallel; whatever the resultant com- 2- tap, since with this connection alone bined impedance is, the matching trans- the 500 -ohm matching transformer the amplifier would be fully loaded. If former must make it look to the ampli- must have an impedance of 2,140 ohms; additional loads are to be placed on the fier like 12.85 ohms. Assuming that we that of the 16 -ohm transformer, 1,670 other taps, the current taken from the choose the series connection, the impe- ohms; and the transformer for the four 500 -ohm tap must be reduced; which dance ratio must be 24 to 12.85. 6 -ohm speakers, 1,070 ohms. Fig. 2 means that the load resistance con- It is not necessary to have a multitap shows the resistance, current, and nected to this tap must be increased. output transformer. Suppose the trans- power values. Resistors have been If a single 500 -ohm load were con- former has only one output impedance, drawn in place of the transformer pri- nected to the 500 -ohm tap and the am- 500 ohms. The primaries of all three maries to accentuate the circuit's sim- plifier were delivering 30 watts, 122.5 matching transformers, when paral- ilarity to an ordinary resistor network. volts would have to be delivered by this leled across this 500 -ohm output, must It is not usually easy to find match- tap: E = VPR. Since we have decided result in 500 ohms, and each must draw ing transformers with the correct val- that only 7 watts is to go to the 500 - the required power. Since the voltage ues. The next article of this series will ohm speaker, a matching transformer available at the 500 -ohm output is demonstrate the simplicity of making must be used between tap and speak- known (122.5) and we have decided on transformers to fit the job.

Useful 10 -Watt Amplifier

by W. D. HAYES, W6MNU

ONE of the most useful pieces of half. This provides a very simple and Across the front are the microphone equipment for the radio build- effective mixing arrangement. Trans- gain control on the extreme left, fol- er and experimer:ter is a former coupling is employed both in the lowed by the phono gain control, the simple, medium -powered au- input and output of the push -pull 6V6- pilot light, and the on -off switch. dio amplifier -free of bugs and flexi- GT's, and output impedances of 4, 8 ble with regard to input require- and 16 ohms are available. MATERIALS FOR AMPLIFIER ments. Such an amplifier can be used The amplifier and its power supply Rest I-470-ohm, 2 -watt; I -1,000 -ohm, 1- in conjunction with an ri. tuner to are built on an aluminum chassis 6% 2,200 -ohm, I -watt; I -3,300 -ohm, 2- 33,000 -ohm, 3- 330,000 -ohm I -470,000 -ohm, I- I- megohm, y, -watt; make a complete receiver. It makes an inches wide, 10% inches long, and 2 2 -500,000 -ohm potentiometers. inches excellent phono amplifier for use with deep. There is ample room be- Capacitors: I- .03 -0, 3- 0.I -µf, 400 -volt, paper; either ordinary records or special low the chassis for the few parts re- 2- 20 -0, 450 -volt, I -8-pf, 450 -volt, I-50 -0, 25 -volt, sound -effect records for home movie pro- quired. To reduce the possibility of hum, electrolytic. ductions. It can act as the principal unit the power transformer is mounted at Transformen: I- power, 600 -volt, center -tapped, 55 -ma, 5 -volt, 2- amperes, 6.3 -volt, 2.7- amperes; I- of a small public address system with right angles to the two audio trans- interstcge, 1:3 turns ratio; I- output, 8,000 -ohm, push - either phonograph or microphone input. formers. Across the rear of the chassis pull, to voice coil. The amplifier described provides 10 from left to right are the microphone Tubes: I- 6S17 -GT, I -4SN7 -GT, 2 -6V6 -GT, I-80. watts output from a pair of push -pull jack, the two sets of phono input ter- Miscellaneous: I -2- ampere fuse and holder assem- 6V6 -GT's, and has sufficient gain to give minals, the speaker socket, the fuse bly; 1- s.p.s.t. toggle switch; 4-octal, I-4-prong tube sockets; 1-51/2 s 101= s 2 -inch chassis; necessary full output from any high-impedance holder, and the 117 -volt line cord. hardware. microphone. Provision is made for two phonograph pickups so that sound effects can be faded in and out in case the amplifier is used with home movies. If two phonos are used. each must have a volume control. Two gain controls are incorporated in the amplifier itself, one in the microphone channel, and one in the phono channel. The microphone signal is amplified by a 6SJ7 -GT pentode, which is resistance - coupled to one half of a 6SN7 -GT. The other half of the 6SN7-GT cathode - 8SJ7-ST 6SN7-GT couples the phono channel into the first 117 M -a11/L M RADIO -ELECTRONICS for Amateur 43 Bandswitching Exciter

By BOB WHITE

must be connected to the tuning controls Sera na, rEP through insulated couplings. The two variable 25 -µµf coupling capacitors must also be thoroughly insulated with steatite, lucite, or a similar good high - frequency insulating material. sf It is probably best to wire the power supply first. Of particular interest in this section is the relay system. The send -receive switch for the entire transmitter should be connected across terminals A and C to energize the 120 -volt BAND relay coil. Terminals B and C should be SWITCH connected to the coils of the other trans- S3 mitter relays (final amplifier relay, modulator relay, antenna relay, etc.). Terminals D and E are to be connected to the receiver's standby terminals to silence it automatically during trans- S2 KEY 16CrNf mission. PILOT BUFFÎR PLATE CRYSTAL LI NE TUNING One set of contacts on the relay con- LAMP SW ITCH FUSE 350 µµf 1501.41f trols the high -voltage supply. When the CRYSTAL- OSCILLATOR DOUBLER PLATE TUNING coil is energized, high voltage is sup- PLATE TUNING AND S6 plied to all stages. The cathodes of the 6L6 doubler and 807 are returned to The exciter is fully described in the photographs. Here is the 7 x 13 -inch front panel. the negative connection of the power supply through a set of relay contacts ABAND -SWITCHING exciter is Because the rotors and frames of the and the keying jack. a necessity in the amateur sta- oscillator and first doubler plate-tuning Switch S1 connects high voltage to all tion which operates on more capacitors are connected directly to the stages with the relay in receive posi- than one band. This exciter positive side of the high- voltage supply, tion. Only the oscillator functions, be- will operate with a crystal of any fre- the capacitors must be insulated from cause the cathode contacts of the relay quency from 80 to 10 meters, though the chassis and panel. Stand -off insula- remain open. There are many advan- only a single set of low- frequency crys- tors or small insulating boards of suit- tages in having the oscillator operative tals is needed for operation on 80, 40, able plastic are satisfactory. The shafts during the receiving period. The oper- 20, 15, and 10. It can be used with doubler stages for operation additional FLÓE S0 on v.h.f. bands which are not integral ST.: OUTPUT ! / SHIELD 3000 v multiples of the lower amateur frequen- -47411. cies. There is a send -receive relay and a keying system. OUTPUT 2 The exciter has three stages: a 3.45 - 30-mc, bandswitching, harmonic- gener- ating crystal oscillator; an 11 -33 -mc and a 3.45-33 - TI bandswitching doubler; 25µ1f mc bandswitching buffer or doubler. A L3 power supply is included. The pictures will be of much greater 350 f assistance in constructing the exciter 56 than any description that could be writ- 6L6 3942W ten; however, a few suggestions are in- OSCI LLATOR cluded on some of the less obvious de- ANO CH. tails. 807 The chassis is 17 x 13 x 2 inches and Li the dimensions of the front panel (a standard relay -rack panel can be used) 16o) kf are 11 x 19 inches. The panel should be securely fastened to the chassis, and a shield panel should be erected from front to rear between the 807 plate circuit and the other plate circuits. The parts should be arranged for short, direct leads. All grounds of each stage 6L6 DOUBLER o -Soma i50p.}lf 54 L2 should be made to a single point on the METER chassis, and each grounding point should be returned directly to the negative terminal of the power supply. This top view shows positions of all components. Power supply is mounted on same chassis. APRIL, 1949 44I Amateur

r EXTERNAL EXCITATION L2 is constructed with the same wire 50'ur/3KI V ss OUT I and form as Ll. From the Plate end of RFC SEE TEXT to 3 5 EXTRA COIL the coil tap 1, there are 1% spaced 56 25ruf 3912W i 40 0 13o turns and from tap 1 to tap 2 there are OUT 2 3/z turns. The length of the wire con- ap LI #I80 2o- necting switch to coil affects tuning. 6L63 Nur I 53 2 r The two -position switch S4 is a small 3 5 2 roller -leaf microswitch. The small non-

1XTAL .005 metallic roller of the switch rests - IKV against the outer rotor plate of the tun- .005 which .06 69 ing capacitor, can be rotated .5 20K 06 .005.,. 6.26/2W IKV through 360 degrees. When the capaci- /.0001 is 180 60MA MICA tor rotated degrees from mini- r+ mum p^, I° S2 to maximum capacitance, the w 0 -50 A `-'PL 2(SMH 300/SW 250/IOW slight pressure exerted on the roller by the rotor plate is sufficient to hold the switch closed in position 1. When the SPRING 6N /200MÁ KEY 6.3V PL 13+350V capacitor is turned through the remain- } =r 000 - ing 180 degrees, the rotor plate does not 1T 500V T20 touch the roller and the switch is re- 514 ;_~ 1 10K /T5W ADJ AT leased to position 2. Two frequency = _30 200V ranges are thus covered and the entire -14004 360 degrees of rotation are utilized. VIVAC Switch S5 in position 3 connects the E 807 grid to a terminal for external ex- D citation; in position 2 it connects the CAPACITORS 600V UNLESS NOTED output of the 6L6 oscillator stage to the RESISTORS 112W ^ - 807, bypassing the 6L6 doubler; and in position 1 it connects the output of the oscillator to the doubler A B C and the doubler A -C TO SEND-RECEIVE SW; B -C TO OTHER RELAYS; D-E TO RCVR DISABLING CIRCUIT to the 807. No. 12 or 14 wire is recommended for the wiring of this switch The schematic. Switch 55 permits bypassing the 6L6 doubler or using external excitation. and the other r.f. circuits. The two 25- Ind variable coupling capacitors are ator can check his frequency for inter- ing two narrow strips of lucite to the adjusted to give adequate excitation on ference. Because the oscillator frequen- windings. all positions of S5 and at all frequencies. cy can be varied approximately 1 kc The 6L6 doubler stage is the third The best position was found to be with by the plate tuning circuit if the oscil- section to be wired. The plate of this the plates about half meshed. lator is operated on the fundamental stage should never be tuned to the fre- The fourth and last division of the frequency of the crystal it is possible to quency of the grid signal because this exciter to be wired is the 807 stage. This adjust the transmitting frequency ex- may result in parasitic oscillation. The can be operated as either a straight actly. circuit tunes from 11.0 to 19.5 mc with amplifier or a doubler because of the The bleeder resistor with the variable S4 in position 2 and 18.8 to 33.0 me in special precautions taken in its con- tap cannot be adjusted until all stages position 1. struction. The plate circuit is shielded are completed. The tap on the resistor should be set for approximately 200 volts. The 6L6 oscillator may be wired next. The purpose of the toggle switch S2 is to short -circuit the choke and capacitor when the oscillator plate circuit is to be tuned to the same frequency as the crystal. Closing the switch reduces the crystal current to a safe value. The pilot lamp connected in series with the crystal serves as a current indicator and provides some protection. L1, S3, and the 350 -uuf variable capacitor are the oscillator plate- tuning circuit. Position 1 of the switch covers 3.45 to 7.5 me; position 2, 6.00 to 13.5 mc; and position 3, 13 to 30 mc. Ll was wound with No. 12 enameled wire on a 1% -inch cylindrical form. From tap 1 to tap 2 there are 9 close -wound turns; from tap 2 to tap 3 there are 7 close - wound turns; and from tap 3 to the B- plus end there are 2% spaced turns. The coil should be fastened to its switch S with the form still in place. The form can be removed after the end leads have been soldered. The tap connections should be soldered with special '\ FILTER care to see that the adjacent turns are CONDENSERS not short -circuited. The oscillator should be tested and the coil spacing adjusted for the correct coverage. The turns can then be held rigidly in place by cement- This view of the output end shows construction and layout of the 807 stage excellently. RADIO -ELECTRONICS for Amateur I43

METER Next, plug in a crystal and turn switch S5 to position 2 so that the oscillator S6 807 S4 I L2 6L6 output excites the 807. Set the oscillator bandswitch S3 to the position that includes the fundamental, second-harmonic, or third -harmonic frequency of the crystal. Remember to closè switch S2 for operation on the fundamental crystal frequency. Adjust the oscillator L3- tuning capacitor for an increase in the 807 screen current; the oscillator stage is then approximately adjusted. '60 1.1µf If the 6L6 doubler is to be used, S5 OUTPUT should next be set to position 1. Band - 005 switch S4 and the doubler tuning capa- 1000 V citor should be set for twice the output frequency of the oscillator stage. When the doubler plate circuit is tuned to resonance, the meter reading will rise. The plate circuit of the 807 can then be resonated either to the fundamental or a harmonic by turning switch S6 to the correct position and tuning the capacitor. The screen current will increase still more when the 807 tank is ad- FILTER SHIELD 5T4 RELAY POWER justed. As a last step, the getting of all CONDç N. CORD SEO, LE 40S the tuning condensers should be touched up to produce maximum screen current. Rear of the chassis. A small shield separates the output stage from the rest of the exciter. MATERIALS FOR EXCITER from the oscillator and doubler stages rection. The coupling link for the 11.9 - Resistors: I -6,200 ohms, I watt; 1 -39, 1-620, 1- 6,200, 1- 20,000 ohms, 2 watts; 1 -300 ohms, S watts; by the shield placed on the chassis (see 33-mc plate coil must be spaced about I -250 ohms, IO watts; I- 10,000 ohms, 75 watts, photos). The 807 is enclosed in a metal % inch from the winding. This output adjustable. Capacitors: I -100 put 1 -.001 pf, 2 -.005 pf, mica; can as a further precaution. A 39 -ohm, system is suitable for link coupling; I-50 ppf, 1 -.005 pf, 3,000 volts, mica; 5-.06. 3-0.1, 2 -watt carbon resistor with a choke in co -axial cable between the exciter and 1 -0.5, 1-4 pf, 600 volts, paper; 1 -20, 1-30 pf, 450 volts, electrolytic; 2 -25, I -150, 1 -160, 1 -350 put, parallel is also used to suppress para- the transmitter is recommended. variable. sitic oscillation. The choke consists of One 0 -50 -ma meter in the screen lead Transferrers and chokes: I -power transformer, B00 volts, center -tapped 6.3 volts, 3 amperes, S volts, 2 20 turns of No. 26 d.c.c. wire wound of the 807 serves for adjusting the en- amperes; 1--(1-h, 200 -ma filter choke; 4- 2.5 -mh r.f. around the carbon resistor. tire exciter. With no excitation applied chokes. Switches: 3- s.p.s.t. toggle; 1-1-circuit 3. position, The rotor and frame of the 807 plate to the 807 grid, screen current is prac- 1-1-circuit, 5- position, 1-2- circuit, 3- position rotary; tuning are grounded directly tically zero. It is increased when excita- 1-s.p.d.f. micro -switch with insulated roller actuat- capacitor ing arm. to the chassis. The .005 -pf plate bypass tion is applied, and further increased Tubes: l-ST4, 2-61.6, 1-807. capacitor should be mounted as close to when the 807 tank is tuned to resonance. Miscellaneous: I -117 -volt a.c. relay, 3 -pole, double. throw contacts; 1- 0.50-ma meter; 1- closed- circuit so is the tuning capacitor as practicable The procedure for tuning similar phone jack; 1-6.3 -volt pilot assembly; 1 -17 it 13 s that short, direct leads to the coil and for all bands. First, turn the exciter on 2 -inch chassis; I -11 it 19 -inch rack panel; necessary insulators, binding posts, shield metal, insulated tuning capacitor are possible. Coil L3 and energize the send- receive relay. couplings, hardware. consists of two windings; positions 1 and 2 on the bandswitch S6 tune 3.45 to 6.30 and 6.20 to 12.0 mc, respectively. 5T4 Positions 3 and 4 tune 11.9 to 20.0 and FILTER CONDENSERS FUSE (F) 18.0 to 33.0 mc. Position 5 is for an of extra coil any desired range. - /4\ --...... The windings were made in much the same way as the coils previously discussed. The low- frequency coil consists 4, of 11 close -wound turns from the B -plus 6 pf end to tap 2 and 19Y2 turns from tap 2 IOK /75W- -T to tap 1. The bottom coil, wound with 6.2K /Iw the same size form and wire, consists of 250n /I0w 2 spaced turns from B -plus to tap 4 A01 pf 3 from 4 to 3. and spaced turns tap tap 05N.f 2 5mh Two output systems are shown. The .005 N f 25 yHf first employs a 50-µµf coupling capacitor connected to the 807 tank circuit. 6L6 This is suitable for connection directly 2.5mh OSCILLATOR f 06rf to the grid circuit of the next trans- 6 2K/2W -620r/2w mitter stage, which must be located 201I5,y2w near the exciter. 005pf 25rnh The second output system employs a 06µf pair of series -connected coupling coils 2 5mh placed at the B -plus ends of the two PILOT tuning -coil windings. Each coupling LAMP coil is composed of approximately 2 FUSE turns of No. 12 enameled wire. They are alike except they are wound in LINE KEY S t. PILOT 55 S2 10Óµµf CRYSTAL that SWI -CH LAMP 300n/5W opposite directions with a continuous SEND -RECEIVE RELAY length of wire which forms a figure -8 6L6 DOUBLER because of the reverse in winding di- The underchassis view. Most of the important components ore identified in the call -outs. APRIL, 1949 Servicing 461 Fundamentals of Radio Servicing

Part III- What Is Induction? By JOHN T. FRYE

HAVE you sat in a hotel lobby the current is flowing; then the fingers er lines of force that issue from one where all was quiet until a cute will be pointing in the direction in end of the coil, return outside to the blonde got up from where she which the magnetic lines of force en- opposite end, and then pass through had been sitting unnoticed be- circle the wire. the center of the coil. hind a potted palm and glided across (Radiomen used to go along with Ben 2. Between the adjacent turns, the the floor? If you have, you may have Franklin's original mistake and pretend opposite -going lines of force buck each noticed -if you were not too busy the current flows from positive to nega- other and so cancel. watching the blonde-that there was tive-although we know .that just the 3. The new magnetic field is most something about the girl in motion that opposite is true. They, of course had to intense inside the coil where all of the seemed to exert a magnetic effect on use the right hand.) lines of force are crowded together. every masculine head in the lobby. Increasing and decreasing the cur- 4. The coil has a N and a S pole just Well, what this blonde has, our friend rent while moving the compass needles as does a bar magnet, and reversing the the little electron has, too; for as soon to different distances from the wire will direction of current through the coil as an electron starts to move, it is sur- show that the strength of the magnetic causes these poles to exchange places. rounded by a magnetic field. Let me re- field is related to the amount of current 5. Since the individual fields of all the peat this, for it is one of the most im- flowing. It is easy to see why. More cur- turns of wire are added together to pro- portant facts in radio: an electron in rent means that more electrons are duce the field of the coil, it follows motion is surrounded by a magnetic moving, and the total magnetic field that the more turns of wire there are, field. about the wire is simply the sum of the stronger will be the magnetic field The magnetic field surrounding a the magnetic fields of the individual of the coil. Also, since the strength of single hustling electron is too small to electrons that are passing through the the field of each individual turn depends be easily measured with crude instru- wire. upon the amount of current flowing ment;, but when a few million of them through it, so does the strength of the cavort along through a wire carrying The inductor field of the coil as a whole depend on the current. a substantial direct current, it is easy Suppose we wind our length of wire field gen- to observe the total magnetic into a coil. What happens to the mag- 1 wire car- erated. Fig. shows a vertical netic field about the wire? Fig. 2, showing two adjacent turns of such a coil with an exaggerated separation between the turns, gives the answer. For one thing, we see that as the magnetic lines of force continue their dog- chasing -his- tail routine about the wire of each loop, all of these lines pass through the center of the loop, and as they do so, they Fig. 2 -The fields help or hinder each other. are all traveling in the same direction. This is true for all the turns of the If a bar of iron is thrust through the coil: when the lines of force are at the center of our coil, the magnetic field is "most inside" point of the coil, they are greatly increased. The reason is that a all traveling in the same direction. A magnetic line of force feels about iron half -turn later, when each circling line the way a cat feels about catnip. It Fig. I -The field around an electric current. of force is at its greatest distance from just loves to wriggle through that soft rying such a current, with four com- the center of the coil, it is traveling in iron, and it will endure a great deal of passes grouped around the wire. Since exactly the opposite direction; and that crowding to be permitted to do so. In a magnetic field is the only force that means that all of the lines of force are fact, a coil with an iron core will ac- affects a compass needle, and since lines doing so. Between turns, though, the commodate several hundred times as of magnetic force enter the S pole of lines of force of two side -by -side turns many lines of force as will the same the compass needle and leave by the are traveling in opposite directions. coil carrying the same current with N pole, we can see that the magnetic When we reflect that these magnetic only air in its center. The more lines of field about the wire consists of circu- lines of force are true forces and can force there are, the stronger is the lating concentric lines of force. Revers- be added when they are working to- magnetic field. ing the direction of the current causes gether, we come to the following con- the needles to reverse their positions, clusions about a coil of wire carrying Magnetism creates current indicating the truth of the left -hand a direct current: One of the nicest things about the rule for wires: 1. The circulating lines of force about study of electricity is that it is such a Grasp the wire with the left hand so the wire add together inside and out- vice versa business: There are so many that the thumb points in the direction side the coil to produce new and strong- statements in this subject to which you RADIO -ELECTRONICS for Scrrici.s 14?'

can add, "And so is the opposite true." of the coil wire, and then the magnetic rent passing through it -that always An example is our statement about the field ceases to expand. It just hovers tries to preserve the status quo -is moving electron creating a magnetic out there in the vicinity of the coil with- called inductance. The unit of measure- field. If a conductor is cut by the lines out either increasing or decreasing. ment of how much of this property a of force of a magnetic field, an e.m.f. Since the lines of force are no longer circuit element has is the henry. When is set up in the conductor which causes moving and cutting the turns of the a current change of 1 ampere per sec- electrons to move, or current to flow. coil, there is no more back- e.m.f. ond in a circuit produces an induced When we speak of the conductor be- Now let us quickly open the switch. e.m.f. of 1 volt, the circuit is said to ing "cut by lines of force," we mean Instantly the ammeter falls to zero, but have an inductance of 1 henry. If 2 that either the conductor or the lines of a split- second later the lamp flashes volts are produced, the inductance is 2 force must be moving. A wire moved very brightly and then goes out. Where henries, etc. Smaller units are the milli- between the poles of a horseshoe mag- did this lamp- flashing voltage -obvi- henry (one thousandth of a henry) and net, a bar magnet thrust into a coil, or ously higher than our battery voltage - the microhenry (one millionth of a a wire placed so as to intercept the ex- come from? How could current continue henry). panding and contracting lines of force to flow through the lamp after the bat- Inductors are often used in radio that surround another wire through tery had been cut off? Gremlins? work, but they are usually called by which a current of varying intensity is No, the answer lies in what happened some other name. For example, we have flowing all fulfill this requirement. Re- to that hovering magnetic field when we filter and audio chokes which consist of member, though, that either the field or opened the switch. Since this cut off the many turns of wire on iron cores and the conductor has to hold still while the sustaining current, we simply knocked may have inductances from 1 to 100 other moves through it-or else one has the props from under that field, and it henries. R.f. chokes have fewer turns of to be zigging when the other is zagging. did the only thing it could do: collapsed. wire with an air core, and they vary The intensity of the e.m.f. "induced" As the field contracted, the lines of force by this action depends upon how many whizzed through the coil turns faster lines of force are cut in how short a than a small boy going through his yard 1 time. This means that a strong magnetic gate at curfew time; and the speed with field with many lines of force and a which these lines of force intercepted very rapid movement of either those the wires accounts for the fact that high lines of force or the conductor will pro- e.m.f.- higher than the battery voltage Fig. 3 -Setup to demonstrate self- induction. duce a high voltage. -was set up in the coil. You remember that the e.m.f. gen- from a few microhenries to 100 milli - Self- induction erated by the expanding magnetic field henries. was of such polarity as to resist the Inductance is chiefly concerned with And now we to - are ready meet self voltage of the battery. As might be sus- with induction, which is coils, and anything having to do just about as bull- pected, the voltage induced by the headed and conservative a col- coils is of major importance in radio. quality as lapsing field is of opposite polarity and This business of is you will find anywhere, inside magnetic induction electric- tries to keep the current flowing after the key to what goes on ity or out! It simply cannot bear understanding a the battery has been cut off. After in many of the parts you find in any change. Take the case of Fig. 3. Here doing all it could to prevent the not, we have current radio receiver. Do therefore, dis- a battery connected across an from starting to flow in the first place, miss it as not being of practical value. iron -core coil of many turns. A lamp now the self- inductance does all it can A knowledge of induction is that lights on volt- magnetic barely the battery to prevent that current from stopping! as in understanding radio as age is coil, and a practical across the switch and This property of a coil or wire that the knowledge of the alphabet is in an ammeter are in series with it and the tends battery. to prevent any change in the cur- learning to read. When we close the switch, the light glows dimly; but the hand of the current- indicating meter rises quite slowly to a maximum reading. Why so slowly? We know that electrons move with the speed of light. Why are the little cusses apparently dragging their feet just because there is a coil in the circuit? Well, when the current started to flow through the coil, a magnetic field started to build up around that coil. As the lines of force of this expanding field cut the turns of the coil, an e.m.f. was induced in those windings that had a polarity opposite to the voltage applied by the battery. This "bucking" voltage was very nearly equal to the battery voltage. However, as the induced bucking voltage or back- e.m.f. approached the battery voltage, it slowed down the increasing current from the battery. This in turn slowed down the expansion of the magnetic field that was producing the bucking voltage. As you can see, this gives the battery voltage the whip -hand: if the induced e.m.f. could rise to the value of the battery voltage, it would stop the current flow; and this would spell its own doom. The net result is that the battery steadily wins the tug of war, but it takes time. Eventually the current rises to the maximum amount the battery can push through the resistance This group of high- frequency (r.f.) inductors includes both transformers and chokes. APRIL, 1949 Servicing 418 l

Sound Can Make Money For You

By GUY S. CORNISH drawings and file them in a fold or he syste/; shóì ld-bé called for and de- future use. The amplifiers used in hound livered by the people renting it, saving motion -picture equipment ;aì d- 'electilic he serviceman's time. Those renting

guitars are checked in the 31ìne -Me the equipment should be told that they EVERY radio servicerna inter -. .as those used in public- address sy4,ten>`s. will be held responsible or an damä ested in making li.ien' honey. ome repairmen have added thejseri- due to_ misuse: Probably -` the móst obvious way is icing of hearing aids to their line. Then -i To assist the serviceman in getting to get more radios to fix -and ittlë units are nothing more than -mini- this business, here are some sugges- dd a few more hours`to_thep s n tu e audio amplifiers using special tions: Contact church groups, lodges, ay's 24. But there is at least one ,o h u Servicing, as a:rule, amounts to clubs, schools, business organizations, a y : that is, specializing in sound n hing more than replacing batteries and civic associations, 'n addition repairing and explain to to radios._As a^ánd tubes, but should circuit trouble them that you are in a position to fur- atter oillfact, some radiomen have develop it can be located by standard nish public -address equipment for their one so vie ll1 lvith audio that thè`-have\ checking methods. meetings at a reasonable rental rate for lmost'éompletelii forsaken receiver re -`J pair! an evening. If booked for several eve- f Rental of sound equipment nings, say once a week or once a month, Nodou t'the most popular piece of you can quote a special price. If any sound equipment\.in use is today the In addition to servicing audio devices, are lukewarm to your proposition, offer ismall portab e pùblic- address system, the serviceman often finds a good profit them a demonstration at no charge. consisting of it a4idio amplifier,'óne or in keeping an amplifier or two on hand Another wo speakers, a icrophone, and the ne- to sound unit that is fast be- rent out. Without a doubt one of the coming popular is the applause meter. cessary cóiiñ ting cables The circuit in best sound units for rental is the small he audio a ifier does not differ This consists of a sound pickup such as n great- portable public-address system; the ra- a good microphone housed ly from that used in larger console dioman or a specially the should build or purchase one for speaker, a high -gain audio amplifier, `adios. There may stage or two this should bg'a purpose. It consist of a 10- and a special decibel meter with a ore of amplificatio to increase the or 20 -watt amplifier, two speakers, mi- scale ver -all gain, but the radioman, with crophone, stand, of either 100 or 1,000 divisions. This and the necessary con- unit can be purchased complete or can is knowledge o radio circuits, should necting cables. The equipment must be ave no difficult' in be constructed from readily available checking the unit. reasonably light, for portability, and all parts. It is used to register ,Infuádditionco public-address, is controls should be the intensity there plainly marked. If of the applause given any tlhel fhìeico nrunicating used in is in contestant in system the radioman located a community local amateur contests like. ctoribs hools, and offices, which is where the use of such equipment is not and the re than a small audio ampli- common, he should set it up without o.,,hg A complete sound service eejo fining a speaker. The speaker charge, as a demonstration. After peo- a microphone when the lever ple have become accustomed to the use The radioman who wishes to realize s pre <

by a complete sound service is back- Permanent installations Be sure that no cables lie on the ground or dinner music, soft music Before setting up an indoor system, ground where someone may trip and played while crowds are assembling or make sure the available voltage and fall over them. Such accidents some- while dinner is being served. The vol- current are correct for the equipment. times result in expensive lawsuits. Do ume must be kept low enough not to in- Ordinary PA systems are designed for not permit anyone, especially children, terfere with conversation, and is usual- 110 -120 volts a.c. at 60 cycles, and in to play with the equipment. It is better ly slow or waltz music. Another type of most locations the current in the build- to delegate one man to make the an- popular service is playing band records ing will be correct. However, there are nouncements, thus assuring better han- at political rallies, sporting events, still some buildings with their own gen- dling of the microphone. If wires are fairs, and festivals. erating plant supplying d.c. at 110 volts. hung overhead, they should never be The safest thing is to consult the cus- stretched too tight; if the span is long,

POLES todian of the building. a rope should be stretched and the ca- The radioman will not have much bles hung from the rope. Very little choice as to where he places the micro- trouble will be experienced in outdoor PlcnuP phone, as the position is established by hookups if ordinary precautions are the location of the stage or platform. taken. STANDARD PHONE RCVR AM The amplifier should not be placed too

E RE NOT" PHONE RCVP far from the microphone, and if possi- Sales make profits, too AL. ble, close to an electric outlet. The radioman may find that when If a close -talking microphone is used rentals become too frequent, schools, and the amplifier gain is not advanced dance halls, and so on may decide to too far, the speaker placement is not purchase their own equipment and have critical. But where the gain is advanced it permanently installed. Here the ra- to increase the amplification, a serious dioman can enter the sales field and problem may develop. If the sound work on a commission basis. waves from the speakers strike the mi- Fig. I- Headphone makes telephone pickup. S crophone directly, feedback will result. IÌ L.---,11111111 III III 1 11111 111111111111111 11 Drawings of several small halls are 111111111 I There are times when a large gather- shown in Fig. 2 with properly placed 111111111 i lilt .I1111 111111111111111111 ing desires to hear a special program speakers. P.]I I II11111 s un11l III11111 11111 from a radio station. The radioman can `SEATS 111u11 IIII.II easily arrange to rebroadcast the pro- Outside installations 1 1111 1111 111111111 t SE ATS i up a M.: MIRE . gram over the public- address system. It Setting public- address system to 111111111 IIIIIIII 11111111 can be done by connecting one side of a make announcements at picnics, sport- ts, I11111111 11'I `I 11111111 S: SPRR .03 -µf capacitor to the grid circuit of ing events, and other outdoor gather- s 11 1111111 the output tube of a good a.c. receiver. ings is, as a rule, somewhat simpler Fig. 2- Placing speakers in vari- shaped halls. The other side of the capacitor is con- than inside installations in small halls. nected to the center conductor of a mi- Outdoors there are seldom reflections He should contact several distributors crophone cable and the outer shield of and feedback. The first thing is to see of sound equipment, get their prices and the cable is connected to the radio if the current and voltage are correct sales information, and call on these chassis. The cable should be several feet for the system used. Be sure you plug prospective customers. He should quote long and supplied with a phone plug on in near the main line and not at the prices and cost of installation; and, if the other end to fit the phonograph in- end of a string of lights where the volt- he makes a sale, the agreement should put jack on the amplifier. age drop may be excessive. be made in writing to avoid any misun- A telephone pickup often comes in The speakers should be hung higher derstanding. After the installation the handy and can be easily made. It is an than the heads of the people and 40 or radioman can suggest a maintenance induction device. No connection must 50 feet from the microphone. If the contract, in which he will make regular ever be made to any telephone equip- speakers are not weatherproof, covers inspection trips to check tubes, micro- ment. The pickup is made from a two - made of thin rubber cloth or cellophane phone cables, and all connections, and pole telephone receiver, or better still, should be carried and slipped over the keep the equipment free from corrosion one of the early magnetic loudspeaker speakers in case of rain. and dust. units. The diaphragm of the receiver is removed and the space inside the receiver is filled with melted sealing wax (see Fig. 1) to a point level with the pole pieces. This acts as a protection for the coils. The receiver is equipped with a length of microphone cable ter - m urinated by a phone plug to fit the phonograph input jack on the amplifier. By placing a telephone receiver on this pickup and rotating it to find the best position, any telephone conversation can be amplified so that a crowd of any size can hear it. In some of the rural or smaller communities, playing phonograph records through the public -address system provides excellent music for dancing. Even in the larger and more populated sections, dances are sometimes given outdoors at lawn parties and playgrounds, and here the amplified music can be heard better than music from a live band. If good dance records are selected, the dancers will prefer the music to that of the smaller and less experienced orchestras. The author's workbench holds a large assortment of instruments for servicing sound devices. APRIL, 1949 Theory 8111Il Ilcsilln 501 Transmission Lines

The quarter -wave section -how its impedance-inverting

qualities are used to make it a matching transformer,

By ROBERT C. PAINE an insulator, or to balance junctions of unlike lines

BEFORE radio communication went er (determined by the diameter and The 9-section transformer wires) is 150 ohms. The to its present high frequencies we spacing of its As of Q- section impedance the folded dipole con- an example the used used to think of a transformer as of by amateurs, take a half -wave dipole of of wire wound together nected to one end of the transformer is two coils '72 ohms impedance to be to a The of the coupled on an air or iron core. But at the higher 300 ohms. ratio, therefore, 600 wires impedance -ohm line of parallel supported frequencies used today, a transformer antenna to the transformer on insulating spreaders. The required is 2. the reciprocal of 2 is '/s, the can be just a pair of heavy conductors Since impedance of the Q- section equals (a section of transmission line or co- impedance at the other end of the trans- axial cable). This is the quarter -wave former is one -half Zn,: 150/2, or 75 V72 X 600 = 208 ohms. Two '/z -inch- diameter tubes spaced 11/2 inches be- or Q- section, as it is used ohms. A 75 -ohm line can be connected transformer tween centers would give this imped- by hams. to this 75 -ohm impedance, the net effect being to match the 75-ohm line to the ance, as calculated by the formula for 300 -ohm antenna. This use of the Q- impedance of parallel conductors given section is common in FM and TV prac- in the December installment of this tice when the receiver input is designed series. This Q- section is shown in Fig. 2. to match a 75 -ohm line. On co -axial lines at ultra -high frequen- The radioman often has to find the cies the quarter -wave transformer may -wave be in the form of a sleeve over the 4 correct impedance of a quarter Z0,75.n 1 transformer to match two known im- center conductor. Fig. 3 shows the end of a co -axial line with such a sleeve Zn, ISOn pedances. If the input or line impedance imped- is called Z,,, that of the quarter -wave transformer. The characteristic ance of the co -axial line depends on the Z1 FOLDED DIPOLE 300n matching transformer Z,,,, and the load impedance ZL, the formula is: ratio D/d of the inside diameter of the outer sheath to the outside diameter of Z,,, = v ZoZL the conductor. Then the imped- In words, simply multiply the in- center other ance of the line can be decreased for put and load impedances together and the last quarter -wavelength by making v 1 take the square root (the geometric the inner conductor larger (d') to form a quarter -wave transformer. This sleeve Fig. I -A quarter -wave matching transformer. forms a section of lower impedance than the rest of the line. The first two articles in this series The quarter -wave transformer is a (December, 1948, and February, 1949) quarter -wavelength only at a given described several uses of transmission - frequency and functions properly only line sections for impedance matching. in a relatively narrow band near this The quarter -wave transformer converts frequency. To pass a wider band the the ratio between the impedance con- transformer may consist of a series of nected to one end and its own impedance two or more sections in graduated im- to the reciprocal of this ratio at the Fig. 3 -A co -axial quarter -wave section. pedance steps. The more steps used, the other end of the transformer. Fig. 1 is an example. The characteristic impedance Z,,, of the quarter -wave transform- mean of the two values) for the impedance of section. 1 1 the matching ZO.son Zo',54n Since the characteristic impedance of Z0", 64n Z1, /On a line is usually nearly pure resistance, the quarter -wave transformer can match it only to a load that is also pure resistance. The impedance of any kind Fig. 4- Sample wide -band matching section. of load as seen at the points in the 600n (2,,, 206n standing wave (see earlier articles in this series) where the voltage is at a wider the band transmitted. The author 11 ZL,7ZnM minimum (node) or maximum (anti - has shown elsewhere' how to compute node or loop) is pure resistance. If the these steps logarithmically. Fig. 4 4 load happens to be reactive and not pure shows a two -step multiple transformer resistance, the transformer should be for connecting a 50-ohm line to a 70- located at one of these points. At a ohm load. This two- section transformer voltage antinode the resistance equals practically eliminates standing waves the standing wave ratio times the char- in the range 70 to 110 mc. (s.w.r. = acteristic impedance, or s.w.r. X Z0. At 1.03). If a single- section transformer a voltage node the resistance equals were substituted the s.w.r. would be Fig. 2 -The Q- section is well known to hams. Zo /s.w.r. 1.13 in this range. RADIO -ELECTRONICS for Theory and Ilesia kl

Insulators and bazookas monic while freely passing the funda- to feed a dipole from If the quarter -wave section is short - mental. a co-axial line. This circuited at one end it shows an infinite The co -axial type of line is essentially is shown in Fig. 8. impedance at the other end (for an unbalanced to ground. If it is directly Here the bazooka is 1, ideal, no -loss line). Actually the input connected to the balanced parallel type reversed and the out- impedance can be made very high, as of line or to a balanced load, unbalanced er surface of the explained in the second of this series of currents flow along its outer surface, sleeve itself radiates articles, making it possible to use such resulting in undesired radiation or pick- and becomes the low- a section as a metallic support or "in- up of interference. To avoid this con- er half of a dipole of sulator" for an ultra- high- frequency dition, special transformers known as which d (connected line or antenna2. bazookas are used. to the center conduc- One type of bazooka is shown in Fig. tor) is the upper 7. A sleeve a quarter -wave long is half. The inverted placed over the end of the cable. One quarter -wave insula- end is closed and the other open. The tor separates, this ra- cable passes through the closed end, and diating surface from the outer sheath is soldered or other- the outer surface of wise secured to the bazooka sleeve. The the co -axial sheath sheath of the co -axial cable then forms and keeps an unbal- the inner Fig. 8-The bazooka - conductor of a co -axial line anced current from principle antenna. of which the sleeve is the outer con- appearing upon it. ductor. Since the sleeve is a quarter - It should be pointed out that in all wave long and it is shorted to the line of the above figures dimensions have sheath at one end, the impedance be- been purposely distorted to show more tween points a and b is high. The sleeve clearly the principles described. is effectively the grounded element; since the end of the actual line sheath References: Fig. 5- Showing how to use copper insulators. is separated from it by high impedance, it is effectively isolated Robert C. Paine, Broad Band Quarter -wave from ground Transformers Radio News (Radio -Electronic Fig. 5 shows two elements of a direc- and may be connected to one side of a Engineering Ed.) pg. 14, July, 1947. tional array of dipoles, with connecting balanced parallel -wire line. Robert C. Paine, Metallic Insulators for Broad - transmission line, supported by such A different form Band Transmission, Rodio News (Radio -Elec- of bazooka is used tronic Engineering Ed.) pg. 9 April, 1947. metallic insulators. Some radar systems use large arrays of these elements. The same principle is applied to co -axial lines at ultra -high frequencies to support the center conductor, as shown 30 -KV NEGATIVE VOLTMETER

The inverted -tetrode voltmeter, so 813's, 8OO1's, and similar tubes can be called because the functions of the grid used in adaptations of this circuit. It and plate are reversed, is designed to will be necessary to experiment with measure high negative voltages devel- the value of the cathode resistor to get - oped by low- current sources. This cir- the lowest usable grid- current plate - cuit, described in The Review of Scien- voltage relationship. The bucking volt- tific Instruments, measures up to 30,000 age must be adjusted to limit the cur- volts with an input impedance 10,- Fig. 6-The quarter -wave insulator in co -ax. of rent through the meter. 000,000 megohms. Its operation is based This v.t.v,m. is useful in measuring in Fig. 6. The supporting pillar is a on the fact that current flowing in a the output of voltage multipliers, ra- quarter- wavelength long, and is soldered positive grid circuit can be controlled dio-frequency and kick -back power sup- or otherwise solidly connected to the by the plate voltage. In this circuit, a plies, and other low- current high -volt- outside conductor. If a sleeve is used large change in plate voltage produces age sources of the types commonly used over the center conductor also, as shown, a small change in grid current when in cathode -ray and velocity -modulated a broader band of frequencies can be the grid voltage is held constant. The circuits. transmitted. voltage to be measured is applied be- 1 AQOM END tween the plate and ground -with the 4-125 A 2/4 OPEN ENO negative side connected to the plate. RC 15N /IOW CO-Ax The meter in the grid circuit measures PARALLEL UNE changes in grid current and may be calibrated in kilovolts. 5V/6.5A The screen grid is grounded to shield 3

the control grid from the plate and IMA Fig. 7- Bazooka between co -ax and line. thereby lower the transconductance of open the tube. R2, R3, R4, and R5 provide a R5 A. section of line a halfwave long bucking voltage to cancel the grid cur- RI R2 R3 15N /10W shows the same impedance at both ends. rent that flows through the meter with Thus if it is shorted at one end, it shows zero plate voltage. R2 zeros the meter. 7.56/5W 10012W 300/IW R4 zero impedance at the other end; or if Degeneration provided by the cath- 0C3/VR 105 it is open at one end, it shows infinite ode resistor RC improves the linearity impedance at the other (for a no -loss of the grid- current plate -voltage rela- C R line). The quarter -wave metallic in- tionship and further reduces - II SOMA the trans 5Y3-G sulator at twice the frequency for which conductance. RC is adjusted for full - it is intended is a half -wave section scale deflection 30 e-16/450V t and at kv. 470V 117V shorts the line. This frequency is the The 4 -125A is a transmitting -type SOMA AC second harmonic of the generated fre- tetrode with a 125 -watt plate dissipa- quency, so the quarter -wave section can tion rating. It handles positive plate also serve to suppress the second har- voltages up to 3,000 volts. HK257's, 5V/2A o PL APRIL, 1949 52I Construction

The laminations used for the transformer and choke were taken from old burned -out radio power transformers. The area of cross section (A in Fig. 1) is 3.375 square inches for the transformer and 3.28 (3%% approximately) square inches for the choke. Lamina- tions from two identical transformers were used for the power transformer and were stacked until the calculated area of cross section was obtained. (It is advisable to draw the transformer to full size and check the window space for the winding.) The first step in designing the transformer wás to calculate the power required from the secondary winding. The current for the secondary was set at a little more than was actually needed, and as there is a voltage drop across the dry -disc rectifier and choke, this, too, had to be taken into consideration. The maximum secondary voltage was therefore set at 16 volts and 10 amperes. Wattage was therefore 160. To determine the primary wattage, the formula, "primary wattage = total secondary wattage / efficiency expressed as a decimal," was used. The efficiency was assumed to be 90%, which, expressed as a decimal, becomes 0.9. When the known values are substituted, the formula becomes "primary wattage = 160/0.9 =178 watts." With the primary and secondary wattage known, the next step was to calculate the turns per volt for the primary winding. As the transformer used is of the shell type (see drawing) and is to be operated from 60 -cycle a.c., the formula, "turns per volt = 32 //Primary Wattage," was used. (If the transformer is to be of the core type A- Battery and the unit is to be operated from tiu cycle a.c., the formula, "turns per volt 42 //Primary Wattage," should be used.) By substituting the known values in the Eliminator becomes, "Turns per volt formula, it = 32/x178= 2.4 turns per volt" By 13.34 - RYLAND HOBSON for the primary. "Turns per volt" means that for each volt impressed across the primary winding, there must be 2.4 RADIO servicemen realize the ad- the power transformer. As is the case turns of wire. vantages a battery eliminator has wherever a transformer is used, a cer- The size of the core in square inches over the battery. At their best, tain amount of mathematics is in- was determined by the formula, "area storage batteries require a lot of volved. The simple formulas used here of cross section = voltage per turn x attention, are usually messy, and must are sufficiently accurate for all prac- 7.5." "Voltage per turn," as used in the be kept charged. The eliminator de- tical purposes. formula, is merely equal to 1 divided scribed in this article can be built for less than the cost of a good storage bat- 4-V2 A AREA OF tery, and because of variable output CROSS SECTION voltages, has many more applications. 2-1/4 Because most builders prefer to fol- i low their own design in respect to appearance, and because the constructional details can be clearly seen in the photographs, no plans are given for chassis, TE panel, or cabinet. The information in the schematic diagram will be enough 2-1/2 for the experienced builder; nor, with will less the help of this article, the 2-S/e I-I/4 45/e+5/9+I experienced builder have any difficulty 2-1/4 --I-I/243/4+lal/44/DINENSgNSININCHES in highly efficient battery building this Fig I- Transformer aminations are interleaved from opposite ends no stacked up as shown eliminator. (see any transformer). Choke laminations are all inserted from one end, with a gap between Special attention is given to winding them and the straight end pieces. A piece of fiber inserted in the gap keeps it constant. RADIO -ELECTRONICS for Construction 153

the primary switch in the t.ow position input filter was used, but a choke input and with a line voltage of 115 volts, filter gives good results. If a choke - without the transformer getting hot. input filter is chosen, a capacitor of not The number of turns for the second- less than 4,000 µf should be used. ary winding per volt output was cal- Eight 1,600 -µf, 12 -d.c.- working -volt culated a little high, to allow for resist- electrolytics were used in a series -par- ance drop and possible losses. Thus, we allel circuit so as to give a total of used 2.5 turns per volt. For every. turn 1,600 µf at 24 working volts each side per volt on the primary, there is 0.1 of the choke. more on the secondary (2.5-2.4 =0.1). With the eliminator connected to a No. 12 enameled wire was used to pure resistive load drawing 6 amperes wind the secondary. At 1,000 circular at 6 volts, there is no measurable a.c. mils per ampere, No. 12 will carry safe- in the output (measured with a v.t.v.m. ly 6 amperes or a little more. (Only 700 on the 3 -volt a.c. scale, and with a 'scope turned .06 Chassis -top view shows how parts are mounted. to full gain, volt root - mean- square per inch). With the above load connected to the output terminals, by the "turns per volt." Since the turns there is a measured d.é. drop across the per volt, as already calculated, is 2.4, choke of r volt (measured with a the volts per turn is equal to 1/2.4 =0.42 v.t.v.m. on the 3 -volt d.c. scale). approximately. Due to the core losses, As shown in the diagram, an am- etc., the rounded figure 0.42 can be out meter is used in the output to indicate to a little more than actually calculated. current drain. The ammeter was chosen We made 0.45 for convenience. it Area instead of a voltmeter because an ex- of cross section is then 0.45X7.5 =3.375 ternal ammeter is the most trouble- square inches. some meter to connect and because most To determine wire the size needed for radiomen do not have an ammeter in the primary winding, the formula, "cur- their volt- ohm -milliammeters. An am- rent watts volts," was used. The finished home -made transformer and choke. X / Since meter will, at times, indicate a defec- the primary wattage was found to be tive vibrator, is circular mils and capable of standing 178 and is to be connected to a 115 -volt per ampere is used by a heavy overloads. (maximum) lighting circuit, number of manufactures of radio re- the ap- From the secondary winding to the proximate current be 178/115 ceiver power transformers.) For the will =1.5 output terilninals, the eliminator is wired amperes. A conductor cross section first secondary tap, 15 turns of wire of with No. 12 enameled wire. The line 1,000 circular mils each ampere were used (2.5X6 =15). For the sec- for of cord is conventional, and is brought up current flowing through the primary ond tap, 5 turns were added to the first through tap (2.5X8 the chassis, directly under the winding was chosen. 1,000 circular mils =20). Another 5 turns were primary switch. added for the third tap (2.5X10 =25) ; SECONDARY PRIMARY There are a number of dry -disc rec- HARD 5UBBER END 5 turns were added the for fourth tap tifiers on the market from (2.5x12=30), the fifth tap which to (2.5x14= choose, but this eliminator was 35), and the sixth and last tap built (2.5x16 for a Mallory 1S16CB7J. Most dry-disc =40). The last tap is not used until the WINDOW SPACE rectifiers will stand severe intermittent rectifier ages and its efficiency decreases. I overloads, but should not be overloaded The maximum no -load a.c. voltage for constant duty. should not exceed 14.4 volts for the rectifier specified. The secondary has two layers of wire, a total of 40 turns and AWG MALIDRY 70151607J 3.37554.IN. N12665 ENNA / 7.26125 SO.IN. approximately 30 feet of wire. If the / .. / N12:67412 EMI HARD RUBBER window / ND% space of the transformer and ° ;+ 21 t choke will permit, a larger size wire -O" OMCCOREE 1/. ! O NNG well be // /// / // //i can used. O.BA j 1 1/2- No were 1 formulas used in designing ALL101I6000 the choke. Various charts, technical 12wV Fig. 2 -The transformer core drawn fo scale. 240T books, and so on were consulted, and NS LO the choke was wound on a trial basis. Dc OFF. per ampere =1.5 x1,000=1,500 circular Laminations 264T from two similar trans- MEDIUM 6V- IST -o mils. A wire table showed that No. 6V formers were also used in the choke 276T -20T-e 18 (A.W.G.) enameled 1GV 25T-e wire has a con- and stacked until the desired area of NIGH ductor cross section of about 1,600 cross I2V-30T 10 )-SHORTING SW section was obtained. (If the 14V-35T-* 10- 20 AMP circular mils, and it was chosen for the builder will use the same area of cross OF0F IBV-40T-o primary winding. The primary has 6 section as stated here, good results can NSWNON- SHORTING SW layers of wire, 46 turns per layer or a be expected.) Unlike transformers, the total of 276 turns -approximately 245 laminations of the choke should not be Fig. 3 -Complete schematic of the eliminator.' feet of wire (see Fig. 2). Insulating interleaved, but should be butted. As paper .008 inch thick was used between the choke is to carry mostly d.c., it Two all layers of wire. automobile radios (6 tubes each) should have an air gap in its core to have simultaneously been connected to As the line voltage in this area is not prevent magnetic saturation of the core the eliminator, drawing always 110, the was 10 amperes at primary tapped for by the heavy d.c. The effective air gap 5% volts, and both radios 100, (low) 110 operated in (medium), and 115 will be that of the sum of individual a normal manner. (high) volts. For the 100 -volt 240 tap, air gaps. The air gap was kept constant The d.c. voltage from the eliminator turns of wire were used (100X2.4= by a piece of insulating paper .008 inch will vary with load. The secondary 240) ; for the 110 volt tap, 24 turns were thick, and can be adjusted if need be. switch is calibrated with a load draw- added to the first tap (110X2.4 =264) ; Approximately 33 feet of No. 12 ing 5'/z amperes at 6 volts, and for the last tap (end starting at of winding), enameled wire was used to wind the the 8 -volt position, working backwards, 12 turns were added to the second tap choke. The choke has four layers of which gives the approximate voltages (115X2.4 =276). Different positions on wire, 16 turns per layer, a total of 64 as shown in Fig. 3. the primary switch will vary the d.c. turns. Insulating paper .008 inch thick Whatever type output in cabinet is chosen for small steps. The eliminator was used between each layer of wire. the eliminator, plenty of ventilation has been operated for over an hour with As shown in Fig. 3, a capacitance- should be allowed. APRIL. 1949 Construction 541 20 -Meter Vacation Converter

EACH year, the writer and a friend By P. F. EGERTON JR. like to take a week's bachelor holi- day. Two years ago, according to custom, we seized some canned the number of turns varied on L2. How - goods and a battery portable, and re- ever, the latter should not be necessary. treated to a cabin in the Northern Best results will probably be obtained Woods. with C3 set at maximum. We both like to listen to 20 -meter The regeneration control does not dx over hot coffee in the small hours, have to be touched for locals. It is, and the battery portable just wasn't however, very useful when fishing for up to it. So we had an "engineering ses- weak stations or separating signals on sion" to design a converter with a crowded bands. of batteries and a maximum The rest of the controls are used as minimum The batteries fit into the converter's case. of performance. in any shortwave superhet. The results obtained with the 20- The converter was tried in our cabin, MATERIALS FOR CONVERTER meter converter we built were so grati- which is surrounded by tall trees. The Resistors: I- 47.000. 1- 100,000 ohms, 1/= watt; 1- we felt it would interest aerial was 20 feet of wire up in the 10,000 -ohm linear potentiometer with switch. fying that Capacitors: 1 -100 µµí, mica; 1 -.01 gf, 200 volts, other readers of RADIO -ELECTRONICS. rafters. A four -tube battery super- paper; 2 -3 -30 -µµf mica trimmer; 2- 220 -1tuf Trim- completed the setup. Ama- mers from old i.f. transformer; 1 -35, I -50, 1 -100 Two miniature tubes are used. A 1R5 heterodyne gut, air variable. serves as regenerative mixer, while a teurs on 20 meters in Hawaii, England, Tubes: 1 -IRS, I -IUS. the local oscillator. and Australia, just to mention a few, Batteries: I -1.5 -volt A, 1-45 -volt B. 1U5 functions as Miscall : 2-7 -prong miniature tube sockets; These tubes work well on a single 45- were heard at speaker volume. 2 -I' /77-inch coil forma (plug -in) and sockets; I -5 x We don't want to brag -but we have 7 x 31/2-inch chassis nd cabinet; necessary knobs, volt B- battery. dials, and hardware The converter output is at 1500 -1600- used the outfit at home too, and the bat- kc, which, with the controlled regenera- teries are dying of shelf life! ANT / REGEN t '- nonexistent. The writer would like to acknowledge L2 tion, makes images almost 10N 'l IáMC who BC for successful op- the assistance of E. L. Houston, Jr., CI LS TO Most of the credit RCVR eration of this circuit goes to the output was the "associate engineer," and the coil L5 and its padding capacitor Cl. photography contributed by Don Mowat. This coil determines the output frequency of the converter. C1 is a dual 20-METER COIL TABLE 5 7 trimmer from an old i.f. transformer; Coil Turns Wire (AWG) Spacing 440 µf. the two sections in parallel total Ll 5 24 enam. close a high -C cir- C3 A+1.5V This combination makes L2 4 24 enam. close 3-301'Af IU5 cuit which keeps the converter stable. L3 7 18 bare 1 inch 8+45( The layout of parts may be seen in L4 4 24 enam. close The extra -deep chassis 1.4 2 ...01 A-B- the photos. L5 80 30 enam. close 0 ® (5x7x31/z inches) serves two purposes. .0001 SW ON It allows a symmetrical control arrange- REGEN COAT L2 wound 1 inch below Ll, with 3 -30- on the front panel, and also keeps ment µµf trimmer inside form. L3 tapped 21/2 the batteries in place when the whole 17 from ground end. L4 wound 1/4 A+1,5V is in the cabinet. turns outfit inch below L3. All coils on 11 -inch - Short leads are essential, especially diameter plug -in forms except L5, which TUNING and plates. Do not trust the on grids -diameter polysty- 2.IC' /2 TURN ground points is wound on %- inch chassis as a ground. Join rene rod. Complete schematic of the converter. with bare hookup wire, treating the chassis as though it were made of a nonconductor. When wiring is completed, check carefully. Connect batteries, antenna, and the output cable, which should be attached to the aerial and ground posts of any receiver tuning the 1500 -1600- kc range. Rotate the mixer capacitor C2 with the regeneration control full on, and tune the broadcast receiver to find the converter output frequency. The converter output will appear as a series of "plops" or a hissing sound. Adjust Cl so that the "plops" come in at some clear spot between 1500 and 1600 kc. All tuning is now done with the converter controls. Back off the regeneration control until the mixer stops oscil- lating. If this does not occur at half scale, two adjustments are provided. The antenna capacitor may be varied, or Extra -deep chassis allows symmetrical control placement and keeps the batteries in place. RADIO -ELECTRONICS for Test Instruments Iss Ohmmeter Reads To 300 Wegohms

A novel circuit powered by the 117 -volt line makes a wide -range, accurate, easily constructed ohmmeter for the technician

By JOHN T. BAILEY

the mid -scale marking. The mid -scale ficulty in laying out the scale for good value is equal to the total resistance of readability. the series circuit with the terminals The power supply (Fig. 2) is a full - short -circuited. The total resistance is wave voltage doubler employing a pair determined by the battery voltage and of selenium rectifiers fed by a 1 -to -1- by the meter's current rating. For in- ratio transformer. The transformer iso- stance, using a 1 -ma meter and a 20- lates the circuit from the power line so volt battery would require a total re- that there will be no danger of a short sistance of 20 divided by .001 or 20,000 when probing in an a.c. -d.c. chassis. ohms. The meter scale would be cali- The voltage -doubling circuit is re- brated from zero at the right to 20,000 quired to produce a high enough start- ohms at mid -scale with a value of 200X ing voltage for the OD3 /VR150 regu- 20,000 or 4 megohms at the left. lator tube, the constant voltage across This scale is fairly open and easy to which is used to energize the ohmmeter The ohmmeter ranges are push -button- selected. read from center to the right and com- circuits. Note that all heat -generating ANEW ohmmeter has been depressed and increasingly hard to read components of the power supply are signed to meet all the needs of to the left. However, with suitably mounted above the chassis and cannot modern servicing and to avoid overlapping ranges, this compressed cause temperature errors in the meas- the limitations of certain com- scale is more serviceable than a linear uring- circuit resistors, which are all mon types. Its advantages are: one. mounted under the chassis. 1. It is always ready for use at the OD3/VRI5O snap of the switch -no waiting for BVTRIAL;SEETEXT PUSH BUTTON ASSEMBLY S SEL RECi 500/2W tubes to heat up. IK25W +145V 2. -- hM There are no batteries to run down II?VAC 510N or to compensate for because of reduced HV l voltage due to age. 3. No zero adjusting is required when 4K switching between ranges. 1.5 K 4. Maximum and minimum ranges NEON are adequate for the most exacting IN/25 7.25V servicing requirements. 5. It cannot burn out low-current RESISTORS WITH VALUES UNDERSCORED ARE PRECISION UNITS t 1%/IV/ 100µA tube filaments. 400n 6. It is not affected by line -voltage fluctuations. Fig. 2 -The complete circuit 7. It is simple to use -just select the proper of the push -button ohmmeter. range. -.15V The ordinary basic ohmmeter cir- TEST TERMINALS cuit of Fig. 1 consists of a series ar-

Rm I It is obvious from this example that Not all OD3 /VR150 regulator tubes, the maximum range can be increased even of the same manufacture, strike at BATT by using a higher -voltage battery, a the same voltage. Therefore it was de- more sensitive meter, or both. Each of cided to use 145 instead of 150 volts to these possibilities has its limitations. power the ohmmeter. A 500 -ohm rheo- RADJ Larger batteries are expensive and stat R1 is connected between the tube bulky; microammeters are expensive and the ohmmeter circuit to absorb Fig. I. -This is a standard ohmmeter circuit. and delicate. whatever difference exists between 145 rangement of battery, meter, and re- The obvious solution is an a.c. power volts and the voltage established by the sistance, with means for switching supply. In the ohmmeter shown in the regulator. This rheostat is adjusted ranges and adjusting for zero balance. photos, a 145 -volt power source is used from the front panel and, after it is This simple circuit, regardless of range, with a 100 -microampere meter move- once set, need not be touched unless theoretically reads from zero to infinity, ment. The mid -scale reading is about tubes are changed. (It might be more but from the practical standpoint it 1.45 megohms, and a maximum reading tamper-proof if placed on the chassis. falls far short of being a perfect solu- of 300 megohms is obtained. Actually, -Editor) tion. The highest value ordinarily the model shown has a maximum of 200 A bleeder made up of several series marked on the meter scale is 200 times megohms indicated because of the dif- resistors is connected across the 145 APRIL, 1949 56I Test Instruments volts so that lower voltages can be ob- ranges by acting as a voltmeter to check almost all pass enough to burn out the tained for the lower ranges. This the 145 -volt setting of the power -supply filaments of a subminiature or hearing - rheostat. aid tube. With this circuit there is no The second highest range (the K danger. range) has the same calibration curve Fig. 2 shows that the ohmmeter uses SELECTe8Y TRIAL -SEE TEXT 1250 as the M range but reads 1/20 as much. This ratio provides good overlap. Since the M range reads 1.45 megohms at exact mid -scale, the K range must read 1.45/20 or 72,500 ohms at mid -scale. This is accomplished by another simple series circuit as shown in Fig. 4. The voltage is picked off at the 7.25 -volt tap, making a multiplier of 72,500 ohms TEST TERMINALS necessary. Subtracting the meter resistance (1,400 ohms for the meter used in Fig. 5-C range has a 20,000 -ohm maximum. this model) and disregarding the power - supply and bleeder resistances as neg- 5720 TEST TERMINALS ligible on this range, we find we need 71,100 ohms. If we break this down into Fig. 3 -High range is simple series circuit. 64,300 plus 6,800, we get a total of 145V IOOyA - 80 71,100 and can use the 64,300 -ohm sec- bleeder totals 5,800 ohms; 25 ma flows tion in the next range. Values of 64,300 2V 70.5 through it at all times. Except for the and 6,800 ohms are not generally avail- TEST TERMINALS high range, it is important that this able in precision, wire -wound meter be so extra- heavy- current constant, multipliers, but they can be approxi- Fig. 6-X range reads 150 ohms at mid -scale. wattage, wire-wound resistors are used, mated by combining standard multi- four in series, to make up the top pliers. The 6,800 ohms (actually 6,860) 5,510 -ohm section, so that the tempera- is made up of a 4,000 -ohm resistor in 145V 5800 ture rise will be small and will not series with a 10,000- and 4,000 -ohm 8.025 change the resistance materially. These shunt combination. The 64,300 value 100 TEST TERMINALS four resistors are mounted vertically (actually 64,000) results from 50,000, under the chassis. Two are 1,250 ohms 10,000 and 4,000 ohms in series. The each, and the other two are 1,500 ohms difference between the actual and cal- so each. Select these resistors carefully culated values is less than 1% and Fig. 7- Low -range scale reads left to right. that their total will be as close to 5,510 therefore acceptable. Because of the ohms as possible. The other sections of substantial overlap and the difficulty in a push- button transfer switch for se- the bleeder consist of 210, 80, and 6,025 reading the crowded portion of the lecting the various ranges. This trans- 6880n NET scale, this range was marked to only fer feature is necessary to prevent damaging the meter if more than one button 5510 50K IOK 4K 4K 4n 500,000 ohms. The third or C range is carried out is held in at the same time. The usual to 20,000 ohms and reads 3,000 ohms at type of push- button assembly used on 200 848 TOTAL 10K mid -scale. The circuit is shown in Fig. home receivers, it is readily available. must be used or i, 10 7.5V 10011A 5. The 7.5 -volt tap and the 64,000 -ohm The best -quality switch multiplier section of the K range are else its own leakage resistance will 145V A 80 used, plus a shunt resistor of 2,860 cause error on the high range. simple ohms. This shunt resistor is a parallel two -gang, five -position rotary switch TEST TERMINALS combination of 10,000 and 4,000 ohms. could be substituted. The fourth or X range of Fig. 6 uses Calibration of the ohmmeter is rela- Fig. 4 -The K range reads 1/20 of the M range. the same calibration as the C range and tively simple. The scale divisions are is 1 it, reading 1,000 ohms calculated using the formula: scale wound. The latter may /20th of ohms, all wire- maximum and 150 ohms at mid-scale. reading (assuming a 100 -division scale) by winding the necessary be home -made 2 is used with an 8,000 -ohm = 100- (100R /R +Rm). R is the resist- wire on a The -volt tap length of enameled copper series resistor and a 70.5 -ohm shunt. ance being measured and R,,, is the high -value carbon resistor. The 70.5 -ohm resistor should be a wire - meter -circuit resistance, both values ex- wound one with an adjustable slide. pressed in the same units. For example The meter circuits The fifth or low range is different on the high range, a 500,000 -ohm re- To describe the ohmmeter circuit, it from the others and can be seen in Fig. sistor being tested would read 100- is best to take one range at a time. 7. It is typical of low -range scales in (100x.5/.5 +1.45) =74.36 divisions on Starting with the high or M range of that it reads backward. The meter is a 100- divisiorl scale or almost three - 300 megohms, we have a simple series deflected to full scale with terminals fourths of full scale. Additional points circuit, as shown in Fig. 3, with 145 volts open. The resistance to be measured is are calculated in the same manner. d.c., a 100 -microampere meter, and a connected as a shunt across the meter, When carefully constructed and cali- multiplier. The multiplier value is 145 causing the meter to back up. The brated, this ohmmeter will prove a valu- divided by .0001 or 1.45 megohms. From unusual part about this design is that able piece of test equipment in any serv- that value we must subtract the resist- it reads only 6 ohms at mid-scale, and ice shop or laboratory. In service in the ance of the meter and the effective in- a low reading of .05 ohms is possible. author's laboratory for over a year now, ternal resistance of the power supply. When we consider that the resistance of it still retains its original accuracy. This is easiest to do by trial. Start with a pair of test leads is about this much, MATERIALS FOR OHMMETER of 10,000, a 1.5- megohm multiplier consisting we realize that this range is more than Resistors: I -100, 3- 4,000, I- 8,000, 3- I- 1- megohm and 510,000 -ohm resistors in 50,000 ohms, I watt, precision (± Iy,); 2-40, 1- adequate for low- resistance service in 270000, I- 510,000 ohms, 1 -I megohm, I watt; I -10, combination 25 1,250, Then this 10 watts; 1 ohms, watts; 2- series. shunt coils, instance. Another 1 -200 ohms, -1,000 measuring for 2 rhea. with a resistor of whatever value gives 2-1,500 ohms, 100 watts; I -500 -ohm, -watt very important feature of this low stat; I -100 ohms, 2 watts, adjustable; I -100 ohms, full -scale deflection with the ohmmeter watts, range is that it is impossible to pass IO adjustable. test terminals shorted. An approximate Miscellaneous: 2-40 -0, 150 -volt electrolytic capaci- more than 25 ma through the resistance tors; I- I -to -I -ratio power transformer; 2-5-plate value will be 4 or 5 megohms. Pay par- selenium rectifiers; I -neon lamp; I -1- ampere fuse Most back -up -type, 100 meter with ticular attention to getting this circuit being measured. assembly; I -003 /VR150 tube; 1- -ua low -range ohmmeters pass considerable Internal resistance of 1,400 ohms; I -2 -gang, 5-but- exactly right because it later serves as ton, transfer -type push -button assembly; I-s.p.s.t. a check on the calibration of the other current, some as high as 300 ma, and togg:e switch; case, hardware efc RADIO -ELECTRONICS for 57

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APRIL, 1949 581 New Devices

able output impedances range from 2 TV PROJECTION LENS 5 -INCH OSCILLOSCOPE PLUG -IN LINKS to 500 ohms. Model 12A2 is identical this type electrically, but controls Spellman Television Co., Inc. Electronics Corp., Barker & Williamson, Inc., to Telemark and amplifier are on one chassis. New York, N. Y. Brooklyn, N. Y. Upper Darby, Pa. f /1.9 projection Standard r.f. tank coils may be The new Spellman Model 450 -A 5 -inch oscilloscope has is to project o TV image matched to a wide variety of im- lens designed vertical and horizontal amplifiers with from o small size up to 7 x 9 feet. cycles to 450 ke, ex- pedances by using various links. These a bandwidth of 2 arm, The lens is in o barrel 7 inches long tending to 850 kc at 6 db down. Sensi. plug into o special swinging to the coils. The old and 41/2 inches in diameter. The barrel easily attached lens for use removed by tapping out the has a special corrective arm is This lens can be re- pin which forms the hinge. Links are with 5TP4 tubes. moved when the set has a flat-face available with I, 3, 6, and 10 turns. C -R tube. A slotted mounting ring is available for hand focusing adjustments. This TRACER -TESTER ring has four holes for mounting on SIGNAL the plate. Test Craft Instrument Co., New York, N. Y. TV1, STUDIO MONITOR Model TC -75 is a combination test incorporat- speaker and signal tracer Allen B. Du Mont Laboratories, ing o single -stage audio amplifier. The tracer probe contains a IN34 crystal Inc., Passaic, N. J. detector. Components are provided in Type 2116, large- screen picture moni- addition, for substitution testing, 7 tor has a 215-square -inch screen and capacitors and 10 resistors. Various may be used at any point in the tele- speaker impedances may be selected vision studio plant. Only brightness by o switch to match most output and contrast controls are on the front tubes, and various field values are panel. A speaker is provided for high - available as well. fidelity audio monitoring where that is desired. The monitor operates from o with is 0.15 volt per inch of deflection. composite signal on o 75-ohm line tivity between Frequency -compensated attenuators. o a peak -to -peak voltage level Z -axis input, and calibration test volt- 0.5 and 2.5 volts. Over -all dimensions age ore provided. ore 38 x 22 x 30 inches. Weight is LIGHTWEIGHT HEADSET 300 lb. Telex, Inc., PHONOGRAPH ARM SOUND PROJECTOR Minneapolis, Minn. is dual -receiver head- Clarkston Corp., Jensen Manufacturing Co., The Twinset a set said to be wearable with a mini- Los Angeles, Calif. Chicago, Ill. mum of discomfort. A ball -and -socket The new Trionic arm is suitable for The VR -241 ST -789 Hypes projector is joint connects each receiver acoustical- any pickup cartridge not over K. inch intended to be hung from the ceiling ly with a small ear -plug, which can wide. The cartridge can be replaced LOCATOR to cover a circular area. The unit has o be adjusted exactly to suit the wear- without soldering, and adjustment of RADIO NOISE maximum power rating of 25 -.acts for er's ear. The headband of Z- Nickel needle force from five grams up is Eltron, Inc., steel encased in Tenite plastic, can be possible. The arm is made in two bent or twisted into any shape, to fit sizes for use with 12 -inch records or Jackson, Mich. the head or for carrying in the pocket. 16 -inch transcriptions. device locates rodio noise The cable is a single cord rather than This small may be in electrical power circuits. Weighing the more usual yoke; its end receiver. 11 pounds, it has only one operating plugged into either CRYSTAL PRESSURE control. The sensitivity is adjusted for maximum and the loop antenna is GAUGES probed the circuit. Noise level AMPLIFIER CHANGES indicated loon a eter,athenaise Cambridge Thermionic Corp., can be heard in headphones. Hermon Hosmer Scoff, Inc., Cambridge, Mass. Cambridge, Mass. Developed during the war, this piezo- Changes in the output transformer electric gouge will measure instantane- SMALL CO -AXIAL and the chassis finish of the 210 -A ous or explosive -type pressures ranging amplifier (which includes the dynamic from a few pounds to 30,000 pounds RELAYS noise suppressor) result in better per- per square inch. The gouge, available formance and appearance. An oversize for the first time to industrial and lab- Advance Electric and Relay Co., provides very low a frequency output transformer oratory users, contains a piezoelectric speech and music, with hum level to 86 Los Angeles, Calif. cycles and a distortion and reduces range from 140 to 6,000 below maximum power output: Two new types of small co -axial re- of 16 ohms. The db voice -coil impedance hum level is .05 microwott. A lays hove been designed for mobile phenolic diaphragm and actual driver has a new anodized aluminum chassis elimi- and other low -power transmitters. employs an Alnico V magnet. It is resists damage only 2.15/16 inches long over- removed and nates tarnishing and Though enclosed but may be from rubbing and chafing. all, the relays maintain o voltage replaced if necessary. The projectors standing -wove ratio of 1.04 at 80 me are mode largely of stainless steel, and 1.4 at 300 mc. They ore built for use aluminum, and other corrosion -resistant with 50 -ohm cable. Terminal positions materials for maximum protection on the relays can be varied for special against weather. purposes. They may be had with N -type connectors and d.p.d.t. auxiliary con - tocts. - CHIP REMOVER Audio Devices, Inc., New York, N. Y. crystal which generates a voltage the instantaneous value of which is propor- The Chip -Chaser is a felt strip to the stress which it undergoes. backed with aluminum and supported tional - Because the voltage appears only while by an arm embedded in a heavy cost the pressure is varying (as in a phono- iron base. The felt strip, placed on graph pickup), steady stresses cannot discs being cut, sweeps the thread of keeping be measured. Units of this type were cut -out lacquer to the center, SELF- HEATED stylus. Two used fo measure air and underwater it out of the way of the SOLDERING IRON pressures at the Bikini atom -bomb tests. sizes are made, one for turntable di- They are commonly employed for meas. ameters up to 12 inches and another Kemode Manufacturing Co., Inc., uring large -magnitude shocks trans- for 16 -inch tables. The chaser requires New York, N. Y. is merely set down mitted through liquids, gases, and no installation; it no electric current or ex- the felt is Requiring sometimes solids. Typical applications beside. the turntable and of any kind, the Ouik -Shot record. The device was ternal heat are evaluating the explosive forces in dropped on the iron utilizes a chemical cor- a time before soldering big guns and in the cylinders of in. manufactured for short that heats the iron to working the war but material shortages delayed tridge ternal combustion engines. in S seconds and maintains renewed production run un- temperature the start of heat of 800 degrees F for til recently. on overage 7 minutes. To charge the iron. the tip HIGH -VOLTAGE 'SCOPE ALL -TRIODE AMPLIFIER is unscrewed and a cartridge inserted. rod at the end of the Electronics, Inc., LENS When a spring Allen B. Du Mont Laboratories, Brook TV MAGNIFYING handle is pulled bock and released, the Inc., Clifton, N. J. Elizabeth, N. J. RCA Manufacturing Co., Inc. handle is pulled bock and released. the cartridge is ignited and the iron Type 248 -A oscillograph may be op- The 12A series amplifiers are 10 -watt Camden, N. J. the Brooks all- triode, high - heats. erated on accelerating potentials as versions of - Images received on 7- or 10 -inch The cartridge contains magnesium high as 14,000 volts without modifica- quality, 30 -watt units. Model 12A3, a separate TV receivers can be enlarged to ap- type powders whose heating action is tion. The built -in supply furnishes 4,000 shown in the photo, has No gas remote Frequency proximate the size of the image on a known as the thermit process. volts; but, where higher writing speed console for control. the cortridge is is constant from 20 15 -inch tube with the new RCA oil. is generated so that must be recorded and greater deflec- response virtually The iron is especially to 20,000 cycles, and distortion is neg- filled plastic lens. The manufacturer non -explosive; tion sensitivities ore needed, an ex- trans- to outdoor work -installing Inclusion of a ligible, even at peaks in excess of 10 claims it is lighter in weight and applicable ternal supply is used. lenses or antennas, for instance--where a.c. is -ray tube in the instru- watts. Inputs are provided for both mits more light than similar 5RP -A cathode glass or plastic. not available. ment allows use of the higher voltage. crystal and magnetic pickups; avail. solid RA DIO- ELECTRONICS for 9 mu) 2 vo LT Ik q Brand new, compact, svr of n hydrometer,w,c mpac ,s cal together to get higher voltages. Fully guaranteed. Shipped dry, add 35c to postage and handling.

Input 27 Volts at 44 amps, 8300 R.P M Output 60 Volts at 8.8 amps, or 530 watts. Manufactured by G. E. or Marathon Electric. Shipped Express Charges Collect.

Rodio Compass Receiver 433 Complete with tubes. Used but good. Shipped Express charges collect. TUBE BARGAINS!

$2.00 ARC-5 Control Box Minimum Order indicates Postpaid

1 indicates 25c postage 2 indicates 35c postage 3 indicates 50e postage

215-A $ .79c 211 .69c '

3 CP-1 .95c 1 3 DP-1A 95c 1 COMMAND SET RACKS 3 FP-7A 1.35 1 Double Transmitter rack. Brand n 3 IiP-7 1.45 1 in original carton. No. FT.226 only 5 FP-7 1.75 2 99c postpaid. 5 CP-1 1.95 2 Triple receiver ock. No. FT- 220.A. Brand new n original cartons. Brand new original cartons, only e Button Control Box. 2.45 2 C -30 /ARC -5 Push S BP-1 $1.59 postpaid. Only Postpaid. $1.29 5 HP-I 2.45 2 705 A 1.19 7C4 .29c Control Box 7 BP-7 2.65 3 BC--616 aantom 7CP-1 3.25 3 Originally used with the command set between Modulator BC456A and Con. fintenrta 9 GP-7 Express Collect 3.50 trot Box BC451 A. Contains 3, 24 volt l0Y .49c relays and other parts an excellent buy or only $1.39 postpaid. 1626 .39c HY615 .59c ' x 85, 531 3.95 A transmitting antenna,for use on Bargains approximately s 450 MC. Complete with standard coax con. IN nector. A weather. All merchandise subject to prior proof unit. Add sale, minimum order $2.00, No Plugs 25c to cover hand- C.O.D. ordersorde accepted. Michi- ling postage and ,. `IMPORTANT! gan residents add 3 must ". State AN - 3102 - 40 - IP sales tax. AN-3106-20-2P AN-3106-8S-1S Brand New Tube Sockets TIME DELAY RELAY AN-3108-16-2P AN-3108-28-2P Tube Sockets 12 ocrols i2 different types) 24 volt, 200 ohms Resistance, approxi- AN - 3106 - 24 - 5P 79c postpaid. mately 1/50 of 1 second delay. Brand new type B -9 manufactured by Gaur- AN - 3106 - 18 - 3P d an Electric. Port No. 34464. Price, only 99c post paid. All Brand New Brand New Antennas Your choice any 4 plugs ... New Rectifiers $1.00 Postpaid AN -131.A Collapsible 10'8" Antenna. Brand new Selenium Rectifier 48 volt AC I $1.49 ea., postpaid Amp. .79c postpaid. N. SILVERSTINE CO. MICH 6532 EAS T McNICHOLS ROAD DETROIT 12, (CIIIIIIIMS'ewriiReff/s o APRIL, 1949 Gol Radio-Electronic Circuits

DISTORTION METER with a bias tap on the high -voltage tube, producing a sharp, short- duration Sound enthusiasts frequently go to winding. pulse of light. When the capacitor is considerable trouble to run response A novel bias supply without these discharged, the voltage on the plate and curves and power output measurements disadvantages was described recently if shield grid drops below normal value, on their pet amplifiers, but they are T.S.F. Pour Tous (Radio for All), the tube de- ionizes and is ready for the usually stuck when it comes to measur- Paris, France. This circuit develops next firing pulse. ing the harmonic content in the output from 10 to 30 volts of bias from a 6H6. The average watch ticks five times - signal. Unlike most circuits of this general thus producing five pulses of light- type, both sides of the supply are iso- each second. When the flashes IN OUT IN OUT of light lated from the a.c. line and from the fall on a disc rotating at 300 r.p.m. (5 high -voltage supply. The cathodes of r.p.s.), a dot or line on the disc will the 6H6 are paralleled and connected appear to stand still if the watch is to the line through 0.1 -µf, 1,500 -volt keeping good time. If the watch is fast, RI capacitors. Rl completes the d.c. path the disc will appear to rotate backward, IN FROM AMPL between the plates and cathodes of the or forward 25K if it is slow. tube. Vary this resistor between 50,000 The rate with which a watch is gain- and 100,000 ohms to OUT TO SCOPE vary the output ing or losing time can be determined by OR VTVM voltages between 10 and 30 volts. For measuring the angle that the spot on lower voltages, use a tapped resistor the disc covers in a given time interval. for R2, and set the taps for the voltage desired. SAFETY FOR AMPLIFIERS A simple circuit for measuring Overload relays the .I J, are often used to total harmonic distortion present in the 1.55V 6H 6 remove high voltage from a grid -leak- output of any complete amplifier, or RECT FIL biased 117VAC triode class -C amplifier when ex- single amplifier stage, was shown in citation fails or plate current rises to The C -D Capacitor. It consists of an in- SW an abnormal level. This method has the put control R1 and a bridged -T filter ó NV 6\ disadvantage that u R the relay may oper- composed of CH, Cl, C2, and R2. CH I.5KV 50-IOON ate while the load is being adjusted or is a 20 -henry filter choke rated at 175 e6.3V-6H6 during transients that may originate ma with 100 ohms d.c. resistance. It is 50/50V in preceding stages. a Stancor type C -1410 or equivalent. If ---1 This protective circuit, 60K -I0-30V described in 400 cycles is your standard test fre- Electronic Engineering (London), is quency, Cl and C2 are each 0.312 µf. based on a ratio between the maximum For 1,000 -cycle test frequency, each has The 6H6 heater may be operated from permissible grid and plate currents. a value of .05 µf. This filter will remove any 6.3 -volt winding on a power trans- the CLASS C AMPL fundamental of a distorted test sig- former. Other duo -diodes such as the nal while passing the harmonics (dis- 25Z6, 50Y6, and 117Z6 -GT can be used TO PRI OF PLATE TRANS tortion), which can then be measured in this circuit if supplied with proper and compared with the total signal volt- heater voltages. age to determine the amount of dis- t Bt OF tortion present. 117VAC HV SUPPLY After STROBOSCOPIC WATCH TIMER building the unit shown in the A number of methods have schematic, connect its been devel- GRID S LEAK input terminals oped for regulating the speed of watches to the output of a good sine -wave gen- and clocks. One erator and its output terminals of the more common to the electronic devices for this purpose uses vertical amplifier of a scope or to an RELAY R a circuit that produces a flash of light 2 a.c. v.t.v.m. Set switch S IN. to Set Rl each time the watch ticks. The flashes to the maximum voltage position. SMALL DIODE Ad- are compared with a standard fre- just the oscillator to the test frequency quency. -400 or 1,000 cycles, depending on the A device such as values selected this, described re- for Cl and C2. Tune the cently in the magazine Electronics, uses oscillator gently about the test frequen- a carbon microphone Resistor cy while adjusting working into a Rl is inserted between the grid R2 for minimum de- 6SF5 that is biased to cutoff. The watch leak and the flection of scope or meter. When the cathode, and R2 is con- is placed on the diaphragm of the mi- nected between the cathode and ground. null has been found, R2 will not require crophone. further adjusting. Each time it ticks it produces The values of these resistors should be a positive pulse in the secondary of the chosen so the ratio R1 /R2 equals the To use the instrument, connect the transformer. oscillator This pulse overcomes the maximum permissible plate current di- to the input of the amplifier bias on the 6SF5 and permits it to vided by the maximum to be tested and set the amplifier volume draw grid current. R2 current. The voltage on the plate drops, should be low enough so it does not sub- control to the desired output. Connect producing a negative pulse the input of on the grid tract appreciably from the operating the distortion meter across of the strobotron which may be plate voltage. the voice coil or plate load to a Syl- the ampli- vania 1D21 or equivalent. The voltage A small diode and relay fier. Short -circuit the filter by throwing are connected difference between the two grids in the as shown. Under correct operating con- S to OUT. Adjust Rl to give full -scale strobotron deflection causes the tube to ionize. The ditions, the voltages across Rl and R2 on the meter or scope, and 4 -pf capacitor discharges are record the voltage reading through the equal with opposite polarity so the as El. With- diode will not conduct. out touching any controls, throw S to IN If excitation e fails, point A becomes less negative, the and record the new 120N 15K 30K +300V voltage as E2. The diode conducts total percentage of harmonic distortion and opens the relay con- A03 150K 4 tacts in is E2 /E1 x100. series with the a.c. line to the t- high -voltage supply. Excessive plate current caused by NOVEL overmodulation or an BIAS SUPPLY arc in the plate circuit will make The advantages of fixed bias in B (and re- the diode plate) more positive so the ceivers, transmitters, and audio ampli- relay will open. fiers are well known; but this type of EG 47 Rl may be a bias is part of the normal grid seldom used, probably because leak with point A fixed by a slider. The most circuits require a separate power relay should be a sensitive type operat- supply or a special power transformer 6SF5 STROBOTRON ing with low voltage and low current. RADIO -ELECTRONICS for 61

Here's amazing GIGANTIC VALUE! 1 VIfilcv OVER zoo PRESENTS THE NEW SQ. IN. PICTURE MODEL 12CL TV -FM KIT VISIBLE from ALL ANGLES with FM RADIO Brings the biggest and best in tele- (Has De Luxe TV -FM Inputuner) vision within the reach of everyone. (Picture bigger than o tabloid newspaper page) IS EQUAL to that of a 20" tube Features 121/2" tube with fitted All -Angle Lens, giving over 200 sq. IMAGE -even and clearer from all angles. inch picture which is visible from any place in a room. sharper -visible Gives ideal long -range reception with CONTINUOUS TUNING Has Luxe TV -FM Inputuner. on ALL CHANNELS. De EQUIVALENT OF $1000.00 SETS ! Antenna, Lead -in Wire. COMPLETE with Cabinet, Lens, Roto -Table, Price of the new 12CL electromagnetic kit in- A BIG PROFIT -MAKER for service dealers. This kit is TOPS -ideal MODEL 12CL TV -FM KIT cludes these outstanding features: for homes, clubs, taverns, and other commercial installations. 121/2" picture tube with special fitted All - Angle Lens and color kit. Beautiful select -grain cobinet and reto- table. EASY TO ASSEMBLE , , . $ 00 NO TECHNICAL KNOWLEDGE REQUIRED De Luxe Continuous TV -FM Inputuner. NET Transvision's simple step -by -step Instruction Sheet makes assembling a New all -channel hi -gain antenna and 60 feet TV Kit a pleasure. Each kit comes complete with all- channel double - of lead -in wire. folded dipole antenna and 60 ft. of lead -in wire. Nothing else to buyl Includes Cabinet, Lens, Table, Antenna Nothing else to buy.

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APRIL, 1949 621 Radie -Electronic Circuits RESISTANCE-CAPACITANCE the receiver. This type of circuit is al- BRIDGE most invariably used in a high -impe- Originally described in Radio and dance circuit where it is likely to pick GREEN Hobbies, (Australia) this resistance - up hum from a.c. circuits and cause STOCKS COMPLETE LINE capacitance bridge can be used to meas- feedback because of coupling to the a.f. ure resistors between 1 ohm and 50 circuits. These disadvantages can be INSTRUMENT KITS megohms and capacitance between 1 tuf overcome by using the selective a.f. fil- and 50 of with a high ter described in The Wave Lis- HIGH PRECISION degree of accuracy. Short Values between 50 and 100 microfarads tener (London). VACUUM TUBE or megohms can be approximated close- This is a medium -impedance device VOLTMETER ly. Power factor can be measured with that is inserted between the receiver Model 221K a calibrated control, and leakage is in- phone jack and a pair of 2,000 -4,000- Complete Kif 9395$.

x_ 6B6-G ON YOUR RADIO BENCH! - - is- 6Ú5/6G5 to C. nd A.C. ranges O -5, IO. try w _ RES -CAP tan. 500, and 1000 volts. RANGE 5W uhnuneter ranges from .2 ohm to 1.1100 megatons In steps at - itN1. RxIii. Rx11111O. RslU.11lln - ay and Rxl megohm. Db scale from -20 to 55 Db In 5 tames. I) t'. input r Is 25 megohms. II A.C. Input impedance Is over 1 .01 .0001 megolims. 1)11.10 :\.t'. rectifier lot gieater accur.er :1r. wider e !women, range tit 3n Iec. I.arre. tng.e[l. ; 2.5 meter with all A.C. and D.C. readings on ne alma!, + scale. All multiplier resistors matched to 1% accuracy EXT SID Complete with 6H6. 6X5. 6SNT tubes and test prods o LEAKAGE All numbers etched Into panel; can never rub off. Hear, gauge steel cabinet. Size: 9 -7/16 x 6' s 5. swoon, POWER FACTOR CONI 2.S0 /WWL Wt. 10 lbs. NOTHING ELSE TO BUY! Model P -75 germanium crystal probe for visual RI signal tracing, and measurements to over 200 mega 10 cycles $7.51 /3W{'x° ASSEMBLED VTVM Model 221 -Includes all dicated with neon lamp. advantages of above. Corn a Terminals e pletcly assembled. hand calibrated and tested an, ready to use, at the amazingly low are provided for matching resistors or price of $49.95-7aFJ .7 capacitors regardless of their values. 6X5-GT POCKET The shadow angle on the 6U5/6G5 is 90 degrees g3 VOLT -OHM. when the bridge is bal- 5 3 s se anced. The shadow gets smaller as the 40MA illp ti MILLIAM. Sv 560V 6.3V bridge becomes more unbalanced. METER COI- s -3 Values of unknown resistors or ca- sL , odoo yL s-- PLETE KIT pacitors are read by multiplying the 0001 Model 511 -K A 117V AC "MUST" FOII setting of the range switch by the set- 4 EVERY SERVICE. MAN! The small. ting of the ratio dial. This dial is cali- ohm headphones. Using the filter in this . handy Instrument brated by connecting known resistors makes that every repairman uses a thousand times a day. circuit it unnecessary to alter Large 3- meter. beautiful etched panel. Simple to as- and capacitors across the RES -CAP most receivers. semble. A PERFECT KIT FOR BEGINNERS. Rantres, DC -0/5/50 /250 /500 /2500 volts. AC -0/10 /100 /500 /1000 terminals and balancing the bridge. De- The circuit, as shown in the figure, volts. Output -0 /10/ /100 /500 /1000 volts. DC Ma - 0 /1 /10. DC Amps. -0/1/10. Ohmmeter -0/500 /100.000 termine the ratio between the standard is simple. The filter peaks sharply be- ohms/0/1 meg. Db meter -8 to 55 a7 1 095 Db $14 x7.7 and known values and mark this ratio tween 1,200 and 1,500 cycles. Signals on the dial. ASSEMBLED -READY TO USE are down 10 db at 900 and 2,000 cycles, Model 511-Completely wired. tested and assembled A 2,500 -ohm power- factor control is and 20 db down at '700 and 3,000 cycles. at the factory. Rugged, built for heavy $17. 9[ duty x78 in series with the 1 -µf standard. This The performance of the filter depends control is calibrated using the formula: largely on the Q of the tuned circuits. OSCILLOSCOPE power factor equals .03768 x RC; where Each coil consists of 500 turns of No. KIT R is the resistance in series with the 36/47 Litz wire on a 1%-inch length of Model 400.K Indi.p.." sable - standard capacitor, and C is the capaci- \M. FM, and l TO PHONE PLUG TO RECEIVER SIONtor . ,weep - PHONE JOCK Horizontal ci ..- tance of the standard in microfarads. cultuit to 30.000 cycles.ntclepanel. l. on front a The 10 -ohm resistors in each leg of 1 .2 2 N C q 2 2 Linear sweep o'1 889 gas miasu. peak screen lt- the 5 -volt winding are to limit the cur- measuringreq peak to peak volt- rent when two very low resistors are 1 age. Frequency ame of T Iii., horizontal 50d vertical ampli- s being matched. L LSEE TEXT fiers trfrom Im cnce m 50 Ec. ,y('1i1Jj', 34 inputInput Impedance 1 mcgulim The 100 -µµf and 0.1 -µf capacitors ,.^ i s are -inch bakelite or fiber tubing, 1½- and o0 mined. Etched panel { y er silver micas with tolerances of 2.5% for tong life. Tulle c 0 / or inch circles of the same material being -. } ant: i -6317, 2 -aY3. 1 -öö9. ' better. The 1 -pf 11511P1. Provision for ex- standard is a paper fitted on the ends of the tube to make ternal synchronization. test voltage and In easily unit with a narrow tolerance. It may be modulation. Deflection sensitivity:. 30 rolls per Inch full a spool or bobbin. Small holes should gain. Detailed Instructions and pictorial diagrams In- made from two 0.5 -µf paper units whose be drilled in one end to bring out leads. cluded. NOTHING ELSE TO BUY! actual values Size: 854.W x 13.11 s 171D. Shpg wt $39.95 are over and under the The form should be filled either with 90 lbs rated value by an equal amount. 'thin strips of mu -metal or a powdered - COMPLETELY FACTORY WIRED The components can be laid out in any iron slug. Mount the coils where there OSCILLOSCOPE convenient form. This was Model 400-Same as above but wired, tested and as- unit built on is minimum coupling between them. sembled. A sturdy well- designed Instrument. ready to a small chassis with panel. The six termi- use on your work bench. Don't waft, The coils are tuned by 2 -4 paper con- order NOW! $69.95VJ a7 nals are in a row across the top of the densers paralleled by 0.2 -4 papers. panel, the null indicator is above the The filter introduces a loss of about SENSATIONAL PRICE REDUCTION! range switch on the left side, neon Model 113 -A MULTI- ANALYST- the 20 db, so the volume control on the re- Completely wired, ready to operate. lamp above the power factor dial on the NOW FOR THE FIRST TIME $69.95V.7 ceiver'will have to be turned above nor- right, and the ratio is A Complete VTVM that follows signal from antenna dial in the center. mal when the filter is used. When work- to speaker! Extremely sensitive wide range AUDIBLE signal tracer. 6 tubes-gain over 90 In probe alone' ing from impedances other than 2,000 Limited Suantity NOW! SELECTIVE -order A. F. FILTER to 4,000 ohms, try different values of C 20% Deposit required milk C. O. O. Orders. All orders Recently a number of articles have until satisfactory results is obtained. F.O.B. NeteYoek. All orders min el include shipping charges. appeared on improving receiver selec- This circuit will not work too well on THE FAMED HOUSE OF BARGAINS tivity for c.w. reception. Most of the receivers with the phone jack in the methods entail installing a converter voice -coil circuit. GREEN RADIO DISTRIBUTORS and special low- frequency i.f. amplifier To use the filter, tune in a signal and just before the second detector Electronic Supplies and Equipment of the adjust the b.f.o. until the background receiver. Another method is to insert noise and other 482 Sutter Avenue, DI 2.4444, Brooklyn 7. N. signals are sharply at- Y. a selective filter in the a.f. section of tenuated. RADIO -ELECTRONICS for 63

WORLD WIDE MAIL ORDER SERVICE ! ! RADIOMEN'S HEADQUARTERS +

"RT 1711" AMAZING BICYCLE RADIO COMPRESSED AIR RT1711 Brand New 12 Tube, 110 Volt Re- LATEST Iver.mmcator-oscuwacope complete with The year's hottest sensation. Powerful sup - all tubes and power upply 1455 telescoping erhet in beautiful maroon crackle finish case INSTANTLY, ANYWHERE!! TELEVISION RECEIVER hood over scope tube. which Is equipped w,th bulls 3 foot gleaming chrome tele- a detachable calibrated screen. Has cen- -in Portable Air Compressor with and video whip Exactly Ilke a ear The lowest priced TV re- and amplitude controls scopic antenna. and storage tank. Rug - ...53 3 radio except works off self -contained stand- ceiver to retain All the Inputs gedly built of best ma- important technical refine ard portable radio batteriec easily obtin- using lifetime lu- necessary and P.M.pe SPEAKERS" terials melts found In the most expensive se s. able anywhere. Theft -proof unning bricated ball -bearing on TV Himmel, . Ilus 26-In'I bracket attached by anyone to m bike or connecting rod and ell Works all ype" motorcycle in 3 minutes. Readily Installed screen. automatic picture luck which elinsl fully enclosed finished mletai L- impregnated main bear- during by cabinet speaker and on any vehicle from a wheelbarrow to a de- notes need for returning ptolframa ing on shaft. Unusual presenting front drifting. Idas ad r receives.match witch's broom. Radio removable from sign forevereliminates valve pictures and In °additio a matte sound level control. Minimum numb - 0 mounting bracket instantly by means of most common make perfect intercom trouble, the if manual controls make set easiest of any Our price. rp,, lai key provided. so that It can be car- in air compressors. stations. fault 10 operate. 54te.50. Including o tout 0 ried anywhere for use as a portable If de- PATENTED unique air In- Iteautlfully grained genuine mahogany cal transformer 34.95 sired. Weight 5 Iba. Your cost with bat - take system Increases effi- Mel hand-rubbed to a finish of distlnrtio . teries -521.0.5: without batteries-$22.50. ciency tremendously over edition Fully covered by Radio Manufacturers Assn. nd other compressors so that air output is much andard guarantee. thherwRadio °Handbook in Moth binding than that from larger compressors hard cover at the sensational reduced price. 1000 Cycle AUDIO FILTERS greater Free indoor aerial included. for a limited time only. $1.49. powered by heavier motors. Will deliver apps. Table motel -$149.95 Navy P052010 -I low pass audio fillers as at maintained MICROPHONES-Super Special-Highestqual- 3500 cu. In air per min. Floor model with oserslce speaker -$189.95 top chrome bullet mentioned in the "Peaked Audio' article pressure of 30 lbs., or will Inflate a 90 lb. who designated by the above Nothing else to buy except for those ht nationally noTorknwn brand-25.95. in June CO. and truck tire in less than 1 min. Complete with Bullet DYNAMIC MIKE -57.95, MIKE Jr.- electrical and physl need outdoor aerials because of their great number, are the exact 100 lb. gauge. fingertip adjustment allows from 60c. PUSH TO -TALK MIKE with switch on cal equivalent of commercial audio filter value, istance TV station. handle-90e. LAPEL MIKES -(Specify whether setting of output pressure at any carton or magnetic units selling fir $35.00 wholesale. They which will automatically he maintained. -934. surplus "Radio are infinitely better than the Works from any % 11P. motor. l'seful for GENERAL ELECTRIC 15 -TUBE Range Filters" being sold for reducing spraying paints or lacquers, disinfectants. QRM. and ut 2 KC off resonance for ex- Insecticides. annealing or brazing with natu- TRANSMITTER-RECEIVER SET any ample. a 2 section filter using PD52010 -I ral gas. inflating tires, etc. Price $14.50 "SO" RADAR eá iiy pre-adjusteddjusted fre- twice Maantis) selected. Is capable of the selectivity available postage prepaid anywhere In U.S. Efficient "SO" RADAR SET. complete with 9 tubes quencies from to 500 Me. Transmitter thru the use of the QS -er (the BC453 sty- adjustable syphon type spray gun complete Including tube. This Plan uses 2 tubes including western Electric 318 picture -Position A as final. Receiver uses 10 tubes including Ben of the 274N which has provided the with 12 ft. of 100 Ib. tested hose for only Oscilloscope has self -contained highest atandanl of In- -Indicator 955's. as detector amateur's previous $7.75 with pint container, also prepaid. pack designed to run from the 110 V. power 711'. as Ws withwrith 51U'--turfed 40 M . terference elimination). h:STRA RPECIAI apply on LST or PT boats. It provides 5" IF transformers, plus 7H7. 7E8's and -NAVY PD52010 -1 with diagram.. $5.00 7F7's. In addition unit relays diameter picture adjustable at will to an 80. designed to sort of 40, 4 or 2 mile circle with the boat at the hen actuated by received sig- center, showing location of land, other ships. net from similar set elsewhere. Originally $12.95 TAKE ALL BIG or any obstruction, so that navigation can designed for 12 Voltsoperation. power awl- Signal Corp Re. be carried darkness or densest ply is not included, a It 10a . fur any THREE -816 out in pitch experimenter to connect this unit for Ito BARGAINS lay Box BC fog with as much safety as in brightest sun- of 400 VDC made by Bell . e AC. using any supply capable HOME WORKSHOP AT BARGAIN light. Your cost $39.95. at 135 Ma. °Theside 1 unit for in mobile e Citizens Radio toille e' service in the PRICE. Accurate and precise 2 speed due[pol where no teur license hobby lathe- the essential phone type Testationarylephone Band. guaranteed lays. condone- is necessary. Instructions and diagrams sup - machine for the home workshop. Sturdy ere. 0m 00 for running the RT -1248 transmitter enough for light production work or terminals. etc. pliedon either code o voice in úM or FM trans- with in a O1yx5Vax 6.95 TAKES ALL THREE mission reception. for a mobile factory standby service. Supplied beautiful e e public ddress ystem, 80 to 100 MC 56" of belting for connecting to any pshede alumi- MIND! as an FM broadcast receiver, as Facsimile available electric motor or power take- num 31.95 7s- BIG BARGAINS or receiver. an n Amateur Tele- off. Also included in this unbelievable BANDSWITCNING TUNING TUR vision transmitter or receiver for remote relay Geiger-Mueller as a RET made by Western Electric. Covers control hookups. for offer are such accessories %" drill unter apolications. Order 11T -1248 chuck with specially hardened tool steel 4 bands above 100 MC. Ali coils wound for my $29.95 or two for $53.50. If de- jaws. a r electric furnace high speed with R14 silver- plated wire. Complete sired for marine or mobile use the dyna- wheel, a cotton buffing wheel with condensen and powerful motor which will w k on either 12 or 24 grinding ALL PURPOSE NEON TESTERS. 60 to 550 tuning ate power for the set, le a of buffing com- electric motor. Diagram in- and supply with large supply volt. Indicate all kinds of current, AC. DC driving volt ÿ pound, a 4" steel scratch MOST TER- and wire or RF, and comes complete with instruction cluded. ONE OF OUR brush. Your cost SLOG. Sole export outlining various testa on radio sets, RIFIC VALUES -ONLY $2.95. LINE FILTERS-Each containshi¢h agent. Distributor inquiries invited. booklet lfil ndnrs in- including the location of fading, dead stages, AUDIO AMPLIFIER -Brand new. 2 ductance 50 Amp choke In fully shielded ALUMINUM GEAR BOX 15x8x7 that shorts, and making screen -grad and plate stage triode amplifiers having 2 of the pease. Suitable heavy current connectors contains two powerful electric motors circuit tests. 35e ea. Per doz. on attractive valuable and scarce ouncer type audio rovided to attach to the input and output connectors at each e d of the filter from and two matched gear trains, 62 gears display card -$3.50. transformers that sell for over $10.00 and wires. A 4 case, en- in all varying in sine train % to piece. Neat aluminum fully Innumerable uses on burners. refriger-e inches in diameter. This unit is readily closed (largest dimension 6 inches). ators. boats, autunurtult, and converted to rotate a beam antenna or Perfect for Intercom system. phono am to r any other similar use... SLOO puffier. mike amplifier or signal tracer abolished. 517suppressedaforr$1.90 SENSATIONAL FASCINATING, VALUE IN amplifier for testing radio sets. A sen- SENSATIONAL $3.40 each AT LAST AMAZING SELSYNS. Brand new AC -DC POCKET TESTER sational bargain at only... srlsyns made by G. E. Co. Two or more DUAL METER -One 50 uA and one YOU CAN a sensitive repulsion connected together work on This analyzer. featuring 200uA movement in the same case. This AFFORD A perfectly housed In bakelite case. repre- 110 of the shaft of type meter is suited for use as a VAC. Any rotation of 15 achieve- meter ideally LABORA- one and to sents the culmination years and aelam all others connected field by large combination modulation percentage TORY it will rotate exactly as many degrees ment in -the instrument carrier shift indicator. If desired the company specializing ln electronic test STAND- in the same direction, following uner- movements may be removed from the ARD ringly as if the units were connected equipment. case and used separately for voltmeters. Specifications of the AC -DC Model MICRO - together by shafting Instead of wire.. )ammeter: ohmmeters, meters, etc. All meters are whether the Volt- Ohmmill condition. but a This Is true you twist shaft -25. 50. 125, 250 in perfect operating VOLTER of the master unit a fraction f a rove- AC Volts -0 few have glasses. This super DC Volts-025. 50, 125, 250 cracked The famous ludic, or many revolutions. Useful for AC to 50 value costs only $1.95 Measure - indicating the direction of weather Milliamperes -0 le Corp. vanes. DC Milliamperes- Model 78E, 5 rotating directional antennas. or 0 to 50 Labora- innumerable inn. Tube 7E itaaeare i,a^al Grn.ra- controlling Operat from Ohms Full Scale - tory Standard l0 70 hMCaOO,.nodu; a distance. Com- Signal tlal8edSO w r with dia- 100,000 (tht plete Ohms Center Scale - RT 1579 sold new. modulation. 2400 With Tubes. FOB.BOOnton, structIo s. Per Capacity- N. J., for 6310.00 net), Is available In per- matched pair $4.95 Diagram and fect condition for 25 to 00 cycles, 115V AC .05 to 15 Mfd. operation. Until now this Is the sort of top- Total Price. pre "old Parts Usf flight equipment that discriminatingwould ree- anywhere In the USA s hve y OUR PE -109 DIRECT CURRENT -$7.00. Simile? DC $1495 tlhewanufa turrerbargain ks.ebut avWorth ilable, FOB POWER PLANT Meter. lacking the AC hue our limited supply taste for ranges of Buffalo This power plant consists of a gasoline en. operated $79.95. above, $5.50 prepaid. Sonlyucra Vante. as Admiral Corp. and John vine that is coupled to a 2000 tt 32 volt from s and - This nit is Ideal a for use in Meek. Inc.. have ordered DC. generator. Consists of three stage (cascade 6577'e foled many times on these 78 generators locations that are not serviced by commercial and une and OFG output stage) high gain, high fidelity r use In their labn production thatsrequire 24-32v-DC f for peration The amplifier with 60 cycle 110V power supply tenting. power want tested and good Uses trice of this chassis, which le iiub1-7Y4. . condition is on the same 13%104% bcs°ttctinouva putconusly by a substantial steel cover over from O to 100.000 Microvolts. h strictly ihn protected able for $50.95 F.Ó B. YYork Ciitty. 'These ita- tubes and parts. Made by Western Electric ter are exactly SOS EMERGENCY TRANSMITTER SOS with typical quality components such as a DEALERS! as received. In husky power transformer and oll condensen. AUTO RADIO steel- This Is the famous Gibson Girl Transmitter is obviously intended to give yeah strapped R 't way. this unit ATTENTION! sns that saved so many lives during the It of trouble -free service with no more need for on r e' able to Is used as distress call transmitter repairs than a telephone. Disconnecting one Nationally advertised determine if the boats and airplanes. The Gibson Girl Is the ire each, from the special Input and output brand of 1949 car Iv easiest transmitter in the world to operate. filters, will result In as high a fidelity ampli- radio which will fit re what necessary. No the c ition i, No inatruction or experience fier as an be obtained. pracically any car and if d. white external power supply required for opera- every pocketbook. Six the $79.96 turn tile I te same tion. tube superheterodyne s the top of thentraensmitter and power is with three gang con- that we have brought to Buffalo for tenting signal is auto - and repair if necessary. We do of recom- generated and the distress denser and 6%" on international dis- for mend gambling on the ' as Is" condition. matically sent out the rectifiers -Dry disc type lrh" g speaker. $32.20 Pt for .quantity purchasers. We can lao tress frequency. Brand New Gibson Girl Selenium sample, or Dealer 1Ì0v 1 1.2 Amp. maximum. Suitable for n converter that ill supply complete with tubes $9.95 ". price $29.97 each, In AsupplyC from the `bove unit or from any 32v tiansniitter convening DC relay's to AC, for supplying source for Antenna Kit for Gibson Girl Transmitter. radios, convert- lots of two or more. DC $12.95. hnprove the ef- filament source in portable This kit was designed to AC applications. Can also of the Gibson Girl Transmitter ing DC meters to fectiveness be used in low current chargers-9.90. RT1655 by increasing the range several times. The RECORD kit includes 300 feet of special antenna only $14 wire. two balloons for raising the antenna in PLAYER tam weather, two hydrogen generators to eeeee heterodyne Inflate the balloons. a special box kite for BARGAIN 11 tube crystal controlled he used for replace- thnt covers the FM band. ultra antenna erection in windy weather. and Meter Rectifiers -Can All you need for a record playing attachment t of test hWreceiverern circuit uses the latest off tubes searchlight, powered by the crank operated ment. or In construction of all types your radio except the cabinet.binet. Special including 7 iniature 8ÁJ5 Beautiful the Complete equipment -Full Wave- 51.25. Half Wave arrn and 115 chassis aluminum cabinet. -Tubes and generator In transmitter. - cycle motor. both top quality $7 95 e andlu kit $9.95 9.90.

BUFFALO RADIO SUPPLY, 219 -221 Genesee St., Dept.RE -3, BUFFALO 3, N. Y. APRIL, 1949 611 Foreign News

European Report By Major Ralph W. hallows

RADIO -ELECTRONICS LONDON CORRESPONDENT

NE of Brit- v.h.f. radio transceivers, and the drivers his receiving unit is sets of figures ap- ain's big - listen at regular intervals for headquar- pearing in the square apertures of a gest banks ters calls. At headquarters is a map on dial, just like the figures which are seen has found which snow -blocked roads are shown as in the mileage recording part of an a unique use for telephoned reports come in, as well as automobile speedometer. Provided that television. During the position of every plow. A sudden he has a chart marked with the Decca the wartime bombing raids, the ledgers shift in the wind may cause drifts to hyperbolic lattice he can fix his position were removed from large towns and start piling up on the road through within a few yards at any instant. No sent to out -of-the -way spots in the coun- some distant valley. One glance at the matter what the weather may be, he try for safety's sake. Since the war, some map shows the location of any plows can confidently set a course with the of the banks continue to keep their books that are available for the job, and they help of the lattice, and can check in places some distance from their main are sent where they're wanted without whether or not the ship is being kept to buildings. Until now a bank manager loss of time. Another interesting use of it, by means of the succession of figures wishing to examine a customer's ac- radio control is by the authorities of a appearing in the apertures of the dial. count has either obtained particulars by hospital service in a large country dis- The Decca system has already given telephone or had the documents sent to trict. Here it is applied to ambulances proof of its complete reliability. The him. The bank in question has found an and its usefulness was strikingly proved coasting ships which bring tens of thou- ultra -modern way out of the difficulty; within a day or two of its installation. sands of tons of coal each week from it has installed TV transmitters at the A telephone call came through from a the mining districts of the North of places where the books are kept and re- small village- desperate case, ambu- England to London and other southern ceivers in its managers' offices. Now lance needed at once. The map showed areas are all equipped with Decca ap- when a manager wants to know the best that one ambulance was traveling on a paratus. They used to be held up by fog or worst about a client who has called road not far from the village. It was or falling snow; now they make their to see him, he just picks up the tele- contacted by radio. Within five minutes trip in any kind of weather almost as phone and says, "Show me Mr. Smith's of the call the case was picked up by regularly and as punctually as the account." At the other end the clerk the ambulance, which brought it to the trains of a railroad. places the ledger, opened at John hospital in less than a quarter of an The commercial aspect is interesting. Smith's page, in front of the TV cam- hour. (This kind of quick service would The radar centers are installed, oper- era. The manager then sees all the re- be a boon even in a large American city! ated, and maintained quired information by the Decca Com- displayed on the -Editor) pany, which gets its profit by leasing screen of his receiver. A special transmission system receiving units to ships of all sorts. The is, of course, used to Navigational aids terms are quite moderate, prevent others from being able to look and they include the cost, not only in on the televised accounts and know Within a short time from now, radar of supplying the somebody else's business. navigational aids be receivers, but also of maintaining them will available to in first No bad idea, I think. It seems likely ships sailing along any part of Britain's -rate condition and of training that in large offices and factories the coastline or approaching it from any members of the ship's staff to make the plant phone and the intercom systems direction. The whole of the North Sea best possible use of them, an important will be supplemented in the near future and a great part of the English Chan- necessity. by plant TV systems. You don't have to nel are already covered. New radar do a lot of thinking to see how useful centers, soon to be in operation, will Ferry radar serve those parts of the coast which they'd be and what a lot of time they'd are If you look at a map of Britain, you save. (See "Office Television Systems" not yet provided for. The system used will notice is the Decca, that many of its most im- on page 67 of the March issue of RADIO - which has many interest- portant ing features. seaports are actually quite a ELECTRONICS for a description of just Unlike Loran and Gee it long way inland. London, does not use pulses, though, like them, Southamp- such an office-industrial TV unit. - ton, Liverpool, Glasgow, Leith, Hull, Editor) it gives its directions by means of a and criss -cross latticework Grimsby are all on rivers with many of hyperbolic miles of wide estuary curves. A Decca center of which there between them and Radio control increasing the sea. These estuaries are mostly un- are now two in Britain and one in Den- suitable for bridges It's a long time now since I described mark, high enough to consists of a master station and allow ocean -going ships to Britain's first radio -controlled fleet of two slaves. pass; hence Instead of pulses, these ferries must be used to carry the heavy taxicabs at the university town of Cam- transmit very long radio waves. Position traffic across the gaps bridge. that they make in Since then central control by fixing in a ship or plane using the sys- busy main roads. In the past fogs have radio has been extended in kinds all of tem is done by means of the phase dif- caused bad delays in the ferry services, directions, some of them quite unex- ference at the receiver of the waves which, of course, cut right across the pected. One northern county council, for from the three transmitters. The pres- streams of instance, has shipping. More and more of a fleet of snow plows entation to the navigator is delightfully these are now being fitted with which needed in radar are often widely scat- simple, for he has nothing to work out navigational aids. With these they can tered places to deal with wintertime and need not even know what phase or follow their courses no matter how thick emergencies. All are now fitted with phase difference means. What he sees in the weather may be, for the marker RADIO -ELECTRONICS for Foreign News (65 buoys and beacons are always plainly seen on the radar screens. And the radar eye enables them to "see" their way through the shipping moving up- stream and down. As the ferries are largely used by automobiles and trucks making long- distance runs, radar is thus beginning indirectly to have a big influence on the speed and safety of road travel in winter and when the w.adher is foggy. TV progress At the time of writing, the number of televisers in use is just on the 100,000 mark -even though we have still only one TV transmitting station. Just 20 months ago the total was 18,000; so the increase has averaged rather over 4,000 a month. It would have been considerably greater if the manufacturers could LOW -DOWN ON have produced the televisers fast enough to meet the demand. The chief problem, QQ''''AATDDH,,Eww as I mentioned recently, has been the , edijyp tutti shortage of cathode -ray tubes. This erJ'VW Ice trouble, I learn, is mainly due to difficulty in obtaining the glass "bottles" which are required -so there's literally AND a bottleneck in TV production! The 10- TYPES TM MB inch tube is by far the most popular (600 volts) (1600 volts) viewers. They won't have size amongst first practical phenolic- molded tubular find Sprague's introduction of the anything smaller because they the capacitors was probably the most revolutionary capacitor development picture size unsatisfactory with tubes in radio servicing history. It is to clarify any misunderstandings which under 10 inches. Many sets with 12 -inch may exist regarding this remarkable advancement and explain things and 15 -inch tubes are sold, but the draw- fully that the following information is given. back here is the big jump in cost. Peo- ple are also a bit scared of the cost of DO THEY COST MORE? replacing one of these big tubes when Not as far as you are concerned. Sprague TM and MB Melded Tubulars cost them at the some prices as a considerably more to manufacture, yet you buy it comes to natural or an accidental ordinary wax cardboard tubulars. TM's and MB's are truly premium capaci- end. C -R tubes are expensive, and it's tors of no premium price. not funny to be faced with a replacement cost which is equivalent to $60 ARE THEY REALLY BETTER? to $80. Most emphatically yes. Sprague Molded Tubulars rep I just about as much improvement over conventional wax cardboard types as the new Wired TV Ford does over the old Model A. They're tested at 95% relative humidity for 250 hours. They operate at temperatures from -401.te +165 °F. withul There are schemes afoot here to pipe batting an eye. They're life -tested at 1% times rated voltage for 250 hours. television to many homes from a single Their high -temperature thereto- setting phenolic jackets mean that they'll One of these proposes not only outperform c banal wax capacitors under severe conditions receiving center. of heat, moisture, vibration and rough handling but last much longer and to give its subscribers a service at video give better performance on ordinary jobs. frequency. Their receivers would be of

the simplest kind, with no r.f. or i.f. WHERE SHOULD 1 USE THEM? stages. This system is interesting, but Use them on any by -pass application where you want capacitors that won't its main application is to quite small trouble later. Thy're tops for auto and aircraft radio, television and centers, such as groups of apartment other difficult jobs. And, because they cost you nothing extra, Sprague Molded Tubulars make ideal replacements for any service work where you 1 homes under the same roof, for it does want to do a really first -class job. not lend itself easily to distribution over any but short distances. Another pos- DOES EVERYBODY MAKE THEM? sible system distributes the programs at Not by a lustful! Nowver, the remarkable f Sprague i.f. A third distributes the carrier and TM's and MB's there will soon be plenty of imitations. This means you'll be wise to ask for them by name and be sure of getting the original practical its sidebands after collection by an molded tubulors - thoroughly rested and proved through years of service. antenna high enough to be unaffected by man -made static and preamplifica- WHO SELLS THEM? tion, if this is found necessary. I be- Sprague Molded Tubulars are featured by leading distributors throughout lieve that there is quite a future for TV the country. If you don't know the name of the one nearest you, write or supplies of one or other of these kinds wire and well advise you promptly. piped over co -axial cable, particularly I COMPLETE INFORMATION? if -free reception can be WHERE CAN GET interference Bulletin giving complete catalog information on Sprague TM and MB guaranteed and if televisers are sup- Molded Tubulars can be obtained from your Sprague jobber -or we'll plied on hire for a weekly or monthly mail one on request. payment which includes full maintenance. Many concerns here supply broad- SPRAGUE PRODUCTS COMPANY, North Adams, Mass. cast -band sound programs under similar Jobbing distributing organization for the products of the Sprague Electric Company schemes and most of them have proven gold mines for those who run them. I don't see any reason why piped TV should not be just as popular and just CAPACITORS as profitable both to the operators and to the public. E *R°OS °ORS U rtn Pe¢ u S. Pri. On APRIL, 1949 661 question Box

RECORDER -AMPLIFIER ? Please print a diagram of a 30 -watt FAULTY CIRCUIT LOCATOR amplifier for recording and playback. I have a high -fidelity output transformer 9 I need a locator for grounded and capacitor of such value that the circuit with a plate -to -plate load impedance of shorted wires in conduits. The equip- will resonate at the oscillator frequency. 6,600 ohms for 6L6's, a 30 -watt hi-fi 105 SENSITIVITY 105 speaker with built -in 500 -ohm output IMEG transformer, and a 4 -ohm magnetic cut - .02 3.3MEG 0 ter.-A.R., Huntington, W. V. HI IMP PHONES

10MEG 1 45-90V A. Here is a recorder amplifier de- A- E` signed to your specifications. The sound 1:3 AUDIO TRANS 4. 1.5V can be monitored with phones and re- SIG SOURCE.; cording level checked with the 6U5 I------i I I electron -ray indicator. A 5 -pole, 4 -posi- s I tion switch alters the input and output I 1-04-6. LINE 1 6 circuits for the various operations. Sep- GND -VOLT SUPPLY arate pickup and turntable are needed ? I have two when recordings I-!: srslswJ magnesium- cupric sul- making from a record. phide bridge rectifiers that will deliver Place the major components on the L 1.5V -45V DEPENDING ON RATING OF BUZZER 7.5 volts at 20 amperes into an inductive chassis so that the power -supply sec- ment must be battery -operated and must load from an a.c. input of 19.8 volts. tion is as as possible far from the in- be able to locate faulty points without Can I use these to make a supply to put circuits. Shield all plate and grid any necessity for opening the conduits. deliver 6.6 volts at 30 amperes? If so, leads up to the input grid of the 6N7 -R. L. A., San Leandro, Calif. what voltage and keep should be supplied by the them as short as possible. Use A. A suitable fault transformer and how shielded cable and plugs. locator appears in is this computed? the diagram. The buzzer signal (a 400 - -A.P.P., Lima, Ohio. MATERIALS FOR RECORDER -AMPLIFIER to 1,000 -cycle audio oscillator tone can Resistors: 2-4.7, 1 -3, 2 -2.2, 7 -I megohm, I/f be used, if desired) is fed into the line A. Since each of the rectifier watt; 3-470,000, 2- 330,000 2- 270,000, 2- 100,000, units 2-56,000, under 3- 27,000, 1- 15,000, 1- 1,500, 1 -560 ohms, test. The pickup coil L is held you have will deliver only 20 amperes, 1 watt; 50,000 I 1- -500 ohms, 50 watts; I -250 close to the conduit and moved along it, it is necessary that you connect them in ohms, 10 watts; 1,600 ohms 4 watts; I- 12,000, I -4,700 ohms, 2 watts; 7- 500,000 -ohm potentio- the coil picking up the signal from the parallel as shown in Figs. 1, 2, and 3. meters. line by induction. When there is a break When dry rectifiers are connected in Capacitors: 1- .0005, I- .006 -sf, 450 -volt mico; 2- 0.25, 7 -0.1, 2-.006, I- .05-,sf, 600 -volt paper; 2 -.01- or a short in the wires at any point parallel, it is recommended that they 400 µf, -volt paper; 3-10, 1 -40 -0, 450 -volt electro- reached by the coil, the operator will be operated from separate transformers lytic; 3- 10 -pf, 500 -volt electrolytic; I-50, I- 25 -0, 25 -volt electrolytic. no longer hear the signal. and their outputs connected in parallel Transformers: I- output, high -fidelity, 6,600 ohms The exploring coil is wound with 200 as shown in Fig. 1. With this circuit plate -to- plate, 30 -watts, multi -tap secondary; (- power, 780 volts center- tapped at 150 ma or more, turns of No. 36 s.c.c. wire, taped so you can draw up to 40 amperes from the 5 volts, 3 amperes, 6.3 volts, 5 amperes; 2- chokes, that they will not fall apart. Make the supply. If you do not care to use 7 h, 150 ma or more. the Tubes: 2 winding about 12 inches in diameter, two transformers, -6L6, I-6N7, 2 -6SK7, I -65N7, 1-5U4-G, then use the circuit I- 6U5/6G5. and fasten it to handle made of a light in Fig. 2 or 3. Miscell : I- chassis about 10 It 17 s 3 inches, stick. 7 -octal, sockets; I- tuning- indicator assembly; (- Most manufacturers specify that the recorder assembly with magnetic cutter and stol For greater sensitivity when an oscil- current rating of the individual recti- pickup; 2-s.p.s.t. toggle, -5- circuit, 4- position ro- is tary switches; 1-1N34 crystal diode; 3- shielded lator used, the secondary of the input fiers be reduced to 75% of the maximum microphone connectors; assorted hardware. transformer may be shunted with a rating when used in these circuits.

6SK7(2) TONE CONTROL_ 6S N7 6L612) S00/50W 500 PM I r--- 4 0Á -- 2 W IA .25 5 6 S .0005

.I INE I GAIN 1 MICA 33015 4 3 2 MIKE NU IN 50015 4 .006 27K SW 91E CUT BO OST 500 o25on 2.2MEG 10/450V 1: 6.6K . ° 1Sn n o eAe - 27K CUT BOOST 10/450V .1 I a , eif- 10/450V BA S J

270K 4° 3°2 S MIKE IN 2 I MEG SW 1E 6N7 9 .2S I.5K 006. 500K . 1001) 2.2ME 4.711EG MIKE 2 I. 10 27K 12K/2W 4.7K

450V 500K 1Mµ +380V? 290V W IC PHONO GAIN PHONO OR RADIO INPUT PLUG TO 40 PHONO SW* PHONOINPUT STAL PICKUP MAG CUTTER SW IO F SW - 2 4 SV/ 3A SOON 111V AC a 4 7H/ISO MA 470K SW IA, IB, IC, ID, IE e4 GANGED WITH POSITIONS THUS: - MONITOR PHONES 40 450V 50K /SOW RECORDER MOTOR INOT 504-G SHOWN ON SECTIONS ABOVE) EG 11134 500K ~S0 -OFF JV/5A INDICATOR LEVEL 4 0- RECORD- MIKE ONLY 605 /6G5 ICATNs PL Z CONTROL f3 0- MIKE L PHONO OUTPUT LEVEL INDIC .01 50V IMEGT4SOV CONDS 600V UNLESS NOTED 06-+0- PHONO OR RADIO

RESISTORS 1 /2W .10-PLAYBACK UNLESS NOTED RADIO- ELECTRONICS for question Box 167 To determine the correct a.c. input voltage for your rectifier units, subtract the difference between the rated output voltage and desired output from the rated a.c. input voltage. The resultant is the a.c. voltage to be applied to develop the desired d.c. output voltage. For example: 19.8 (7.5 6.6) = 19.8 -0.9 = 18.9 volts a.c. A transformer delivering 18.9 volts with the current ratings necessary for either circuit will probably have to be made on special order, but you can im- .DISH / 30A OR MORE f 3A

117V AC

Fig. I- Paralleled outputs supply 40 amperes. provise by using a number of high - current 6.3 -volt filament transformers in series parallel to deliver the required voltage and current. Three of these transformers with their secondaries in series aiding and primaries in parallel will deliver 18.9 volts. Connect enough of these series strings in parallel to de- Model 260 in liver the current you want. II.Ba6epee It will be worth .11 rey while to use a heavy tase series resistor or an auto -transformer tarrying in the a.c. line to control the voltage. You should put an a.c. voltmeter across

.015H/ 30A OR MORE 3A

Fig. 2- Rectifier has single input and output. the input terminals of the rectifier and make sure that the no -load a.c. -input to the rectifier units does not exceed manufacturer's specifications, or damage is likely to result. If you would like a supply to deliver 6.6 volts to separate 15- ampere loads, then use the circuit in Fig. 3. Each set

.0211 /ISA OR MORE

Fig. 3 -This circuit has two separate outputs.

SIMPSON ELECTRIC COMPANY of terminals will deliver up to 15 am- Both Om S200 Sill W tic SI , Chltngo 44. II/ In Conodo S,r.pwn, ud London, peres when used alone. Connect them in parallel for 30 amperes maximum out- RANGES at 20,000 ohms per volt DC, 1000 ohms per volt AC put. The outputs can be connected in VOLTS: AC 8. DC -2.5, 10, 50, 250, 1,000, 5,000 DC CURRENT: 10, 100, MA AMP -100 MICRO AMP series to deliver 13.2 volts a maxi- 500 -10 at OHMS: 0 -2,000 (12 center), 0- 200,000 (1200 center), 0.20 MEGOHMS (120,000 ohms center) 15 mum of amperes. DECIBELS: (5 ronges) -10 to +52 DB APRIL, 1949 ii

INDIANAPOLIS I ESSE RADIO CO. I Esse's Special Offer INDIANA

TELRAD 18 -A FREQUENCY SURPLUS RADIO CABLE CONNECTORS AND PLUGS New STANDARD CONVERSION MANUAL Choice .25-All Brand Checks signals in the range of 100 Kc. to Manufacturer Type Price Edited and printed by TechnoGraphic Amphenol AN3101- I6 -10P 25r each 45 Mc. with a high degree of accuracy. Self - Publications. If contains 115 pages, size is Amphenol AN3101- 18 -18S 25r each contained power supply is 110, 130, 150, 220, Amphenol AN3101 -22 -55 25r each 7" x 101/2", printed on good paper stock, and 250 V. 25 -60 cycle AC. Complete with 22 25e each covers well bound. A partial list of contents Amphenol AN3102- -15P Amphenol AN3102- 28.10P 25c each tubes, dual crystal, and instruction book. includes complete information on the con- Amphenol AN3102 -32 -5P 25r each Brand new. war sur- version of the following popular Amphenol AN3106 -18 -1 IS 25c each plus items: BC -221 Frequency meter, BC342, Amphenol AN3106- I8 -18P 25e each Price $24.95 BC312, BC348, BC9468, SCR274N, SCR522, Amphenol AN3106 -24 -6S 25r each BCI068A receivers, BC412 cathode ray oscil- Amphenol AN3106.24 -7P 25c each AN3106 -32 -SS 25r each loscope, BC645 transceiver for citizen's Amphenol Harwood AN3108 -145 a 25e each transmitters, SCR522 trans. band, SCR274N Aero AN3108- 145 -2S 25r each MARKER -BEACON miller, TBY transceiver, various dynamo - Cannon AN3108- 14S -2S 25r each tors, and a cross -index on tube numbers Amphenol AN3108- 14S -2S 25r each RECEIVER frequency allocation chart, electronic sur- Amphenol AN3108- 18 -12P 25r each AN3108.22 -55 25e each Can be adapted to radio controlled de- plus index with listing of over 135 items and Amphenol AN3108 -22 -5S 25e each functions or frequencies or Cannon vices. Was used by pilots to flash a signal description or Amphenol AN3108 -24 -6P 25e each tube line -ups etc. of same. Circuit dia- Amphenol AN3108.24 -16S 25e each lamp on aircraft instrument panel when in grams of original items, and of converted Cannon AN3108 -24 -165 25c each a transmitter. Responds jobs, together in the manual. The text is Amphenol AN3108 -32 -5P 25, each range of beacon clear, concise and with values of various Amphenol AN3108- 28 -10P 25r each to modulated signals over a variable component parts abound easy to read and range of 62 to 80 Mc. Tube plates and follow. filaments operate directly from 24 V. DC. The price per copy is $1.25 BC -375 GE MOPA TRANSMITTER Can be adapted for rodio control of experimental apparatus, opening garage The most famous of all surplus transmitters. Was used by the Army bombers and ground stations during the War. Frequency doors, etc. Circuit diagram and parts list MINE DETECTOR AN'PRS -1 is by means of plug -in tuning units as shown range covered included on either model shown below: below. Each tuning unit has its own oscillator and power The detector is designed to detect metals. amplifier coils and condensers, and antenna tuning circuits all BC- 357 -contains 12C8 and 12507 tubes non -uniformities (rocks, tree- roots) and designed to at top efficiency within its particular fre- and sensitive relay (size 5% /s "x51/4"x31/,x "). may be used to detect metal buried in logs, operate quency range. Transmitter and accessories are finished in to locate cables, pipes, sewer tile and etc. Price $1.95 black crackle, and the milliammeter, voltmeter, and RF am- It is widely used by lumber camps, miners, on the front panel. Frequency Range: 200 6SL7 12SN7 prospectors, plumbers, treasure hunters and meter are mounted BC -1033- contains 65H7, and 500 Kc. and 1500- 12,500 Kc. (Will operate on 10 and 20 meter explorers. tubes, sensitive relay (size 5' /r "x51/4"x31/4"). band with slight modification). Oscillator self- excited. thermo- A portable device used in the detection of compensated, and band calibrated. Power Amplifier. neutral- Price $2.25 both metallic and non -metallic by aural ized class "C" stage, using 211 tube, and equipped with and visual (eye) means. These are (ear) antenna coupling circuit which matches practically any length brand new outfits, complete with instruction antenna. Modulator: Class "B" -uses two 211 tubes. Power book and spare tubes. Shipped in original Supply: Dynamotor which furnishes 1000 V. at 350 Ma. instruc overseas moisture -proof container. R -89 ARN SA GLIDE tions and diagram for IIC V. AC furnished upon request tor the detector head with The set consists of $1.00 PATH RECEIVER antenna and reflector meter, a meter hous- PRICES: As follows ing and lower section of exploring rod, - Formerly used for blind landing but Transmitter only . $12.50 amplifier assembly, exploring rod esten- adaptable to many other uses such as re- sion, bag designated to carry equipment Tuning units TU -6B, TU -7B, TU -BB, TU -9B, new police citizen's band. while operating, and wooden case for stor- TU -10B, TU -268, choice 2.50 ceiver for or ing or transporting the complete unit when Dynamotor PE -73C 4.95 Band of operation 326 -335 mc. on any of This detector is not nearly as not in use. Antenna tuning unit (BC -306A) 4,95 three predetermined crystal controlled tre. sensitive as the SCR -625 Mine detector. However, because of its price and its sim- quencies. Contains eleven tubes, 6 relays wrong on buying one plicity, you cannot go and other valuable parts. For 24 V. DC for $14.95. Shipping weight, 125 lbs. Weight operation. Size 133/4"x5' /4 "x6%/8" in operation only 22 lbs. ATTENTION! PROSPECTORS, MINERS, OIL COMPANIES, we can sup- Batteries are not included but PLUMBERS, etc. Below is the finest metal detecting mine Price, complete 59.03 ply them for $8.25 per set. detector ever constructed . Our Price $14.95 SCR -625 MINE DETECTOR Shipping Weight 125 lbs. BC -645 ULTRA HI- 22 lbs. Weight in Operation Only Brand New FREQUENCY TRANS- Metallic Objects Only MITTER- RECEIVER buried metallic mines. Its private Used by the Army to detect You read about it recently in OSTI Orig- AIRCRAFT RADIO use suggests the location of underground or underwater pipes, cables and ore bearing rock, the location of metallic frag- inally operated in the frequency band FILTER FL -8 -A RANGE ments in scrap materials, logs, etc., and the screening of per- from 450 to 500 Mc. Can be converted to For helpful reduction of ORM on crowded sonnel in plants for carrying of metallic objects. 420 Mc. amateur band. Consists of corn - CW bands. When attached to output of The unit consists of a balanced inductance bridge, a two -tube pieta transmitter and modulator system, any communications receiver: amp. and a 1,000 cycle oscillator. The presence of metal dis-

I -Will pass signal of 1020 CPS, eliminat- turbs the bridge balance, resulting in a volume change of the and receiver. Complete, brand new, with ing others. 1,000 cycle tone. The tubes used are low -battery drain types 15 tubes. The may be modified for control 2 -Will pass voice frequencies and elimi- such as IG6 and INS. circuit $11.95 nate 1020 CPS code signal. of warning signals, stopping of machinery, etc., when metal is Compact, light weight, with switch. Size detected. Operates from two flashlight batteries and 103 V. 23/4"x23/8"x3% ". "B." However, a power supply operating from 110 V. may be with tubes, resonator and Price $1 25 ea. used. Comes complete spare spare OXYGEN TANKS instruction manual -in wooden chest 8l /4 "x281/4"x16". Weight in operation is IS lbs. New, complete in original overseas pocking 500 -LB. PRESSURE container. Originally sold by War Assets for $166.00. Aviators oxygen breathing bottles. Non - BC Service has recommended procedure for JACK BOX -1366 The U. S. Forestry shafteroble. Ideal to use for air tank on using the SCR -625 Mine Detector to find concealed metal in Contains 2 -pole 5- position switch, rheostat. tree logs and other timber products. air horns, paint sprayers, pneumatic tools. two phone jacks, etc. In aluminum case Excellent condition. 31/4 "x4Vs "x2/4 ". Complete with headphone Price $59.50 match high to low impe- set adapter to $4.00 extra $3.50 dance. Price $1.00 Batteries

RADIO -ELECTRONICS for 69

INDIANAPOLIS ESSE RADIO COJ INDIANA Esse's Special 011er i

LS -3 LOUDSPEAKER SCR 274N COMMAND SET 6" PM type, housed in heavy metal case. For use on BC -348 Receiver. OR Self- contained output transformer to BC -348 POWER SUPPLY match 4000 ohm impedance. Used To convert the BC -348 receiver for but guaranteed satisfactory. 110 V. AC operation. Constructed especially for Price $4.95 the Esse Radio Com- pany by a leading transformer company. BC -221 FREQUENCY METER These power supplies hove gained Covers 125- 20,000 Kc. Battery or 110 great popularity due to quality, price V. AC or vibra -pack operated. A and simplicity in conversion. Filament beautiful instrumenf.The finest supply 24V. Rectifier tube used 6x5 (not included). we have ever had $69.50 Price S5.95 ea. SN -7C APQ -13 CLOSED VIEW Sensational offer for television engineers. Contains 19 Mc. IF strip containing 5-WE 717A tubes, other HF strips containing 2- 6AK5's, 3 -6SL7- vor GT's, I- WE717A, 4-6SN7GT's, 2- 6N7's, 2- 6L6's, I-6H6, 3- 6AC -7's, N '' 2- 6AG7's, I -6V6, a total of 26 , v tubes. Other parts such as DPDT re- z lay, 7 pots, 12 Amphenol 831 R chassis connectors and numerous condensers, toggle switches, RF chokes, variable condensers and transformers. Wgt. approx. 25 lbs. Size 20" L. x I lye" W. x 73/4" H. $14.50 MG-lti cR

Input 24 V. DC ] rs. Output 115 PP -51 APQ -9 OPEN VIEW V. 400 cy. AC, _ A V, A. Output 90°/, P.F. RECTIFIER POWER UNIT at S5.95 400 cycle 115 V. Contains 4 -5R4G1 REMOTE CONTROLLED tubes, 2-4 Mfd. 1000 V. DC con- COIN INSERT AND SPEAKER densers, 2 -I Mfd. 1500 V. DC con- BOX densers, 400 -2600 cycle transformer, Made by Personal Music Corp. power resistors, etc. Wgt. 18 lbs. Size Newark, N. J. 21" L. x 51I/ W. x 73/4'. Model F H. $4.95 24 Volt operated, fused Weight 61/2 lbs. Size 43/4 x 71/2" x 51/2" high CP -11 APS 15 Sloping front PM Speaker 5" size Contains following tubes: 13 -6SN7- Has 2 Pilot Lights GT's, 3- 6SA7 -GT's, I- 5Y3 -GT. I: 24 V. for illumination ATTENTION AIRLINES! motor and blower (blower will oper- Finished in chrome metal and grill with red plastic BC -348 COMMUNICA- Accepts I to ate on 110 V. 60 cy.), 4 -one megohm 6 nickels Each 5Q coin gives TIONS RECEIVER precision wire -wound resistors, 80 -86 about two phono records of music Should 6 bands, 200 -500 Kc. and 1.5 -18 Mc. Kc. crystal, numerous other transform- be mounted on a flat base Has Hoydon 2 stages RF, 3 stages IF, BFO, crystal ers, condensers, etc. Shipping weight Mfg. Co. timer Has provision filter, manual or AVC. Complete with approximately 25 lbs. for locks (lock furnished) tubes and 24 V. dynamotor. These re- Easily removable coin box, size 6" x 31/2" x 11/2" ceivers have been thoroughly Price $6.50 Requires 4 wires from power unit checked in our work -shop and A beautiful piece of equipment that found could be built to in excellent house coin operated radio. condition. S149.50 WILLARD LEAD ACID Worth several times our asking price. CELLS, $2.00 Price brand new 54.00 (Brand new) 6 V. (dry-charged) $2,00 6 V. in metal carrying case A TREMENDOUS BARGAIN (dry -charged) ap Quartz Crystals without Holders (Add electrolyte specific gravity 13/65 Get an assortment of these and grind to your own fre- -any drugstore.) quencies or use them as they are. .5X.6" B -cut lapped on faces and wired on edges (Ready to use). We will give you an assortment of these from approximately 13 thou- T39 APQ -9 RADAR sandths of an inch fo 24 thousandths of an inch whereby XMITTER you can grind to frequencies desired. Contains many excellent parts for the These crystals are now ground to the approximate following VHF experimenter such as a cavity frequencies: (HRU) DC POWER SUPPLY oscillator using 2 -RCA 8012 tubes 3500 4300 5600 6300 7306 24 -28 V. at 70 amp. 2000 watts gaso- rated at full output to 500 Mc. Tubes 3700 4600 5800 6700 7400 line engine generator with electric ore forced air cooled by 24 V. DC 3900 4900 6000 6800 7500 starter. Power supply which can be motor, which is easily converted for 4100 5300 6200 6900 7800 used to operate 24 110 V. AC operation. Other valuable -28 V. equipment, 7900 start airplane engines, charge bat- parts such as a pair of 807's, 2 -6AC7, Formula for converting thicknesses of B -cut crystals to fre- teries, as a welding machine, lighting 1 -931 and I -6AG7 tubes; ceramic quency is as follows: F - 98.4/T where F is frequency in system, or for amateur radio switch, potentiometers, gears, kilocycles station. and T is thickness in inches. AN ASSORT- 171/2 x245/8 ". Wgt., revolution counter, etc, C1,]! MENT OF 20 DIFFERENT THICKNESSES S1.50 22.15 lbs. S `5.00

APRIL, 1949 70

INDICATOR PILOT'S CONTROL BOX MAGNESYN HONE cued WHETSTON To be used for beam antenna. TYPE CRY -23254 Practically same as I -81 -A Selsyn indicator. 15.25 V. 60 cycle AC. Used with CRV-46151 Receiver for HUNTER'S and FISHERMAN'S SPECIAL! 3" size. of volume, selec- remote control ORDER Excellent condition. 31.25 ea. FOR HOME WORKSHOP and MACHINE SHOP tion of any one of six frequency NOW connection .50 knife, fish- Plug for bands, has off /on switch or se- Fine quality, high -grade hook, tool and hand -axe sharpener TELEPHONE WIRE lection of C.W. and M.C.W. and and polisher. U.S. Government sur- FIELD M.V.C. or A.V.C. Black crackle plus. Light weight (weight less than 3- conductor, stranded, insulated wide n 4 I ounce). Size, inch 15c and weather-proofed. Ideal for in- finish. Size, 2 "x21/2 "x5" high. -half of instrument inches long. One tercommunication systems, tele- Brand new. is finest possible whetstone and each other halt is cork rust remover and phones, Selsyn indicators. Use it ea. polisher. Any trapper, hunter, fish- $1.00 inside or out of doors. 525 foot Price $1.50 hobbyist or machinist can- erman roll. Brand new. not afford to pass up this bargain. dozen Brand New per Price $4 25 ea.

Battery BA -41, delivers 41/2, 60, 25,7. Volts. ARGON BULBS RECEIVER TUNING HEAD sup- BATTERIES Used with BC -620 Transceiver, for bias 2 -watt, 110 V., Edison base. Ideal CRY -23253 ply, or portable equipment. Size 2 "x21/4 "x31/2". Outdated 255c night light. but tests okay. Unused. for R.F. indication, Brand new. Box of ten. Used with CRV -46151 Receiver for Battery BA -32. 1442 41/2 and 3 Volts positive and 131/2 Volts negative. Used with BC -222 Walkie- Talkie Transceiver. Size Price per box $1 75 vernier tuning. Has beveled dial and has long life. Outdated 5 "x8 "z7 ". Husky 3 with hairline cursor. Bands are 200- but tests okay. Unused. for 59.95 WESTINGHOUSE 1600 -4450, 4450- 560, 560 -1600, with RECTIGON BATTERY over with lid. Size about, 3 "x3 "x21/2" 9050 Kcs. Each band spread ALUMINUM BOX pointed end at top. Ideal for meter CHARGER BULB holding about 280 degrees of dial edge. case, switch and fuse box, control box, for Style 289416, 6 ampere rating. For re- Brand new Ea. 30c Has provision for flexible tuning loose parts. placement in most chargers or for building power supply to use on D.C. shaft or can be adapted for di- overall length. operated equipment. Brand new. rect drive on any tuning shaft. PHILLIPS SCREWDRIVER Blade long.e Insu- Price $1.90 ea. non 2 diameter. 1 c finish. Size, 5 "x3 "x2" lated -slip handle /s" Black crackle Brand new Ea. CO -AXIAL CABLE overall. Brand new. For high frequency low -loss trouble -free weather proof, durable service. Fully $1.50 ea. Price PORTABLE TRANSMITTER d DIePM1 2462 shielded, cut to length. Brand new. RG8/U -52 ohm. Price - 100 ft (made by RCA). Sound powered microphone trans- for $4.95 mitter with push -to -talk switch. Metal formed chest - about opera- AMPHENOL LOW -LOSS ANTENNA KIT plate with adjustable strap for support tor's neck. Pivot adjustment for placing of micro- UHF CONNECTOR 2A- 264 -126 phone. Has 7 -wire color -coded rubber covered heavy For RG type cable. Rugged construc- duty cable, 20 ft. long. Units will work up to several tion, heavily silver plated, provides I contain- easy assembly and positive connection_ Consists of canvas bag thousands of feet apart, no batteries or external sup- 3" Type 83 -IAP Angle Plug Adapter poly- ing 20 ceramic insulators each ply needed. Several units may be connected together styrene insert, pin and socket -very I long, I covered wire 5' long, on same circuit. Indispensable for television antenna special -.... $15.00 per hundred covered wire 10' long, I covered installation, electrical wiring work, plumbing contrac- Type 83 -IR Receptacle, chassis type, low -loss Mica filled insert, very spe- 2 covered wires 25' to work. Transmitter wire 35' long, tors and other point point cial $25.0,3 per hundred long each, 5 covered wires 20' only. Receiver not included. long each (all wires included for Brand new Ea. $7,50 LIP MICROPHONE 1/2" thimbles and 6" connecting Lip microphone, made by Western long, Electric, Navy type CW- 51071, with in- leads at each end),wire 150' GLASS TELEPHONE -POLE INSULATORS struction sheet, brand new75c each (all this is stranded copper wire, Hemingway size 680. Fits 3/4" wooden crossarm pin. covered with weather- proofed in- Overall height 5 ", diameter 4 ". Will hold two single TYPE 813 TUBES sulations). Useful to any ham, steel wires, or two pair of stranded wire cables. Type 813 tubes (New) ... $4.25 ea. Ea. 40c serviceman or experimenter. Brand Brand new Type 813 tube sockets (New) .50 ea. new overseas boxes. $4.50 A -5 AUTOMATIC PILOT BL- SELENIUM RECTIFIER SERVO M1

110 V. AC input; 110 V. DC out- Made by Delco -Remy. Hos 1/. horsepower shunt type put, .75 amp. rating. DC motor, 27.5 V. 11 amps V J input, speed 6000 rpm. Has $1.25 hydraulic lift - (Intended ^ use -Hydraulic lift actuates Ailerons on airplane) Overall length 16 ", width DYNAMOTOR DM -35 -D 12 ", height II ". Net weight TURBO AMPLIFIERS Western Electric Model No. 5DY83AB7. 28 lbs. Shipping weight 35 Manufactured by G.E. for Signal Corps, lbs. Hardware for cable drum included. phono - U.S. Army. Used for ports or small Brand new 18.7 amps. Output complete with Input 12.5 volts DC at pack- amplifier, shipped amps. Diameter 31/2 original 625 volts DC at .225 ing boxes. r$9 95 the following tubes: 2- 7C5's, I- length 71/2 ", mounting rack 81/2' long. Ideal power supply for mobile 7Y4, I -7F7. Our greatest bar- ine/e stallations. Brand new in orig l*ro VY gain. See July 1947 "Radio Craft" fool boxes. for conversion data. Each $1.25

Unless Otherwise Stated, All of This Equipment Is Sold As Used CASH REQUIRED WITH ALL ORDERS Orders Shipped F.O.B. Collect

RADIO -ELECTRONICS for Try This One I71

SELECTIVITY IMPROVEMENT USES FOR MASKING TAPE TRACING PAPER CHECKS Many of the old -style t.r.f. midgets A roll of masking tape is very handy CIRCUIT are not very selective where there are in the service shop. Here are some pos- When building an electronic device strong local stations. sible uses: from a circuit diagram, lay a sheet of I wanted to hear a station on 590 kc, When replacing a speaker cone, it thin tracing paper over the diagram. As and there was a strong station nearby may be difficult to clean out the air gap. each part and wire is connected, trace on 610 kc. The drawing shows the modi- Insert a piece of tape and move it the corresponding portion of the dia- fication I made. around until all the dirt has stuck to gram with a pencil. When the last wire SET the gummed side. has been soldered in place, the completed tracing will tell the builder so. LT ISOLATING COND When moving record players and r_ When this or a similar method is not FEEDBACK LINK changers, fasten the pickup arm down used, it is very easy to forget some k-SOLDER I OR 2 TURNS with a strip of tape. Use the tape to fasten repair bills connection. HOWARD A. MILLER, W2WLZ, RF and job cards to receivers. The tape will stick but the adhesive will not mar the Rochester, N. Y. cabinet. Cables can be "laced" with masking TINNING AN IRON ANT COIL tape and small parts can be fastened When you buy a new iron (or clean together with it. Where voltages are an old one), remove the tip, heat it with not high, it will serve as insulation. ------J TIMING WIG a blowtorch to the temperature re- When restringing a dial cord, use quired for melting silver solder, and pieces The end of a piece of insulated wire of tape to keep the string from flow silver solder all over the tip, prac- connected to the top of the antenna coil slipping off the pulleys until the job is tically plating it. When the tip is cool, was wound around the grid lead of the done. put it back in the iron. It should never next stage (the detector in my receiv- ALAN MCFARLANE, require tinning, fluxing, or filing, since er), making the set regenerate. The Aberdeen, S. D. temperatures ordinarily needed for sol- number of turns -that is, the coupling dering will not melt the silver solder. so the set is VADI GEN NIS, -must be adjusted that REMOVING always just below the oscillation point CONTROL KNOBS Cleveland, Ohio all over the dial when the volume con- When a control knob is hard to re- trol is turned up. The entire receiver move from its shaft, don't pry it off V.H.F. TUNING WAND with a screwdriver, as this is likely to was realigned. The old tuning wand used on broad- The improvement in selectivity was ruin the cabinet and break the edge of the knob. Wind a piece of heavy cord or cast receivers is no longer particularly ample, and sensitivity was increased. useful because of the iron cores in many WILLIAM JOYCE, thin rope once around the shaft in back of the knob, then pull the ends of the r.f. coils. A modified type of wand, how- Derry, N. H. very handy for v.h.f. cord outward. The knob will come off ever, is testing without damage. circuits. This one is intended for the SMALL CAPACITORS 2 -meter band. D. SRINIVASA RAO, amateur When small capacitors are needed Madras, India Use a phenolic or polystyrene rod 7 for experimental purposes, use radio inches long and at least 1/4 inch in diam- tubes. The tube handbook supplies data eter. Drill %- inch -diameter holes in concerning the interelectrode capaci- SHORTED TUNING CAPACITORS each end, each hole being X,4 inch deep. tance of each tube. Into one hole, force a 1 -inch length of Use very short connecting leads to One way to locate and remove shorts %- inch -diameter powdered -iron core avoid adding extra capacitance. Other from a tuning capacitor is to discon- salvaged from an old i.f. or r.f. coil; elements of the tube, of course, should nect all leads from the "high" side of into the other hole place a brass slug not be connected to anything, nor can the capacitor and insert it in the circuit of the same size. sockets be used. When you have built a v.h.f. tuned For v.h.f. and u.h.f. work, acorn and circuit which seems unable to hit reso- miniature tubes are best because they I17V AC -11 {,FAULTY TUNING CAPACITOR nance, try inserting each end of the have smaller residual inductances. moo .51600V PAPER wand into the coil. If inserting the iron HAROLD FALLATZ, end resonates the tank, more inductance Brooklyn, N. Y. shown. If filings are shorting the plates, is needed because the iron adds induct- sparks will be seen when the shaft is ance. If the brass end does the trick, TWO -BAND ANTENNA rotated. The shorts can often be re- Il 7- The 20 -meter half -wave dipole shown moved by continuing to rotate the ca- in a is a very good standard transmit- pacitor until no more sparks are seen. ting antenna. However, is useless as JOHN W. TURNER, I /8- X1 /2- PLASTIC :/8 -XI /2- it IRON CORE a dipole on 40 meters. It can be used on Newark, N. J. BRASS SLUG SEE TEXT 40 meters, however, by converting it less inductance is needed because the into a Marconi, as shown at b. Tie the brass lowers the inductance of the coil. ends of the transmission line together SURPLUS MICROPHONES If neither end improves matters, either and connect them to one end of the link. Surplus T -17 microphones will re- the circuit is at resonance or it is very Ground the other end. produce speech more clearly if addi- far off. VADI GENNIS, tional small holes are drilled in the cap DAVID GNESSIN, Cleveland, Ohio covering the diaphragm. Be sure to re- Columbus, Ohio move the cover before drilling it to avoid damaging the diaphragm. Fur- ther improvement can be made by care- KEEPING SOLDER OFF CHASSIS a II b fully removing the cloth protective To prevent solder from sticking to a n 65' 0- and remov- chassis while making a joint on a tube- EMISSION UK EMISSION LINE cover from the diaphragm ¡RIBBON, FEEDERS ing the capacitor connected across the socket lug, rub the chassis with the end TIED TOGETHER mike on the rear. Talk across the face of a small candle. Any solder that falls ANT TANK - FOR MARCONI of the mike rather than right into it. will not stick to the waxed metal. L. E. KLINGBERG, GEORGE WECHSLER, LINK COUPLING Inglewood, Calif. Brooklyn, N. Y. GND END OF LINK APRIL, 949 721 New Patents

highlights are brilliant. Since highlights may EXPANSION DETECTOR ORTHICON CONTROL vary from one moment to the next, the beam Patent No. 2,451,640 control should be automatic. Patent No. 2,451,908 Robert R. Thalner, Princeton, N.I. In this new method, the video output is ampli- Marietta B:au, New York City (assigned to Radio Corp. of America) fied in two stages. The output of the first ap- (assigned fo Canadian Radium and across the load consisting of R and C In an orthicon television camera tube, the pears Uranium Corp., New York City) a light- sensitive cathode in series. The video signal is like the one illus- image is focused on to detect which emits electrons. These are accelerated and trated at B. The positive portion is the blanking This apparatus is sensitive enough only 2 microns (millionths of an focused on a mosaic capable of secondary emis- pulse (originally applied to the orthicon screen), a change of sion. Positive charges remain where electrons and the negative peak varies with the brilliance leave the mosaic. The beam from an electron of the televised image. gun scans the mosaic, neutralizing positive The latter passes through the left -hand diode charges where they exist. The electrons r,ot of E and appears across condenser A and the absorbed in this way are returned to a signal control grid of tube D. The blanking pulse plate. This is the video output which corre- passes through the right-hand diode and does sponds to the televised image. not affect the control circuit. It is preferable to maintain a high modulation To illustrate how the circuit operates, as- percentage of the electron beam. A dark optical sume that the image highlights become more image can be accommodated by a weak electron brilliant at some instant. Then highly positive beam, but a strong beam is needed when the charges appear at the corresponding points

PHOTOCATHODE displacement SIGNAL PLATE inch). The change may be due to SCREEN a body c EusEd, for examp:e, by OBJECT or expansion of GRID variation in temperature, pressure, or magneto - striction. The body whose expansion is to be meas- or M ured may be made of any material -a conductor may be of any shape -a CATHODE a non -conductor-and it ACCELERATING MOSAIC SIGNAL OUTPUT cylindrical rod, a spiral or helical coil, etc. ELECTRODE -1 VIDEO AMP VIDEO AMP Two rods about }',o -inch in diameter are im- mersed in a liquid which can be ionized. Xylol, BLANKING PULSES benzine, or pure water may be used. The upper rod is clamped to the body B under measure- IMF ment, leaving a gap G between the rods. This gap changes in length with expansion or con- traction of B. on the orthicon mosaic. The A radioactive cell C on the lower rod ionizes signal plate current is re- the liquid over a short distance. Normally the - duced, and a higher poten- gap is adjusted so that it is just too large for tial appears at the camera the ionization to reach the upper rod. If B tube output circuit. The negative peak of expands, the gap is slightly reduced and ioniza- the video signal is greater, and a more tion current begins to flow through battery D. negative potential excites the grid of D. The positive potential of D partly overcomes the Therefore the orthicon control grid goes effect of the negative battery A, and the ioniza- more positive and permits a more intense tion current increases further. This current in- beam to accommodate the brighter. picture dicates the length of the gap, and consequently which must be transmitted. the expansion of B.

For GREATER Earnings . . LEARN RADIO- ELECTRONICS

This fast -growing science of RADIO, TELEVISION, RADAR

and ELECTRONICS, offers tremendous opportunities, and in no industry is I RADIO -ELECTRONICS more important than in aviation. A skilled technician / who knows the modern application of electronic devices, as used in the aircraft / industry, is always in demand ... not only in aviation, but in many other industries. Many large organizations call on Spartan regularly for graduates. Often, students are hired months before graduation. / Don't confuse the RADIO -ELECTRONICS course offered by / SPARTAN with other courses, offered anywhere! As a graduate from this I famous school ypu will know the application to industrial control devices; / to the search for petroleum; and the important uses of radar, television and other electronic equipment. SPARTAN offers two complete and thorough courses. / You will work on the most modern and complete equipment. You will / 21 years of teaching civilian and You may join the SPARTAN "Ham" Club. Either f SPARTAN'S build equipment. army personnel is your assurance of receiving the course prepares you for Federal Communication Commission license / best possible training in the least possible time. tests - first class radio telephone,, second class radio telegraph, or class / You'll not need MORE than Spartan training - you "B" radio amateur. / cannot afford to take LESS. SPAR TAN NAME SCHOOL OF RADIO AND ELECTRONICS

ADDRESS

SCHOOL e1 AERONAUTICS COLLEGE of ENGINEERING CITY STATF ,SAXWELL W. BALFOUR. DIRECTOR ADDRESS DEVI RE 49 Dept. RE -49 TULSA, OKLAHOMA G. I. APPROVED -Write TODAY for Complete Information RADIO -ELECTRONICS for Patents New 73 SIGNAL BUOY Potent No. 2,448,713 Clarence W. Honsell, Port Jefferson, N.Y. (assigned to Radio Corp. of America) In this adaptation of the walkie- talkie idea a tiny transmitter, operated at very high frequencies, is self -contained with antenna and batteries in a water -tight buoy. Dropped into the water, its microphone enables distant listeners to hear the approach of submarines or ships. An automatic switch turns on the transmitter when water pressure acts on the diaphragm, pressing it in- ward and making contact.

r LIGHT +ANT TV BOOSTER I(° CHECK THESE FEATURES

HIGH STABLE GAIN . LOW IN- HERENT NOISE FACTORY TESTED FOR "FACT" SPECIALLY DESIGNED INPUT CIRCUIT FOR HIGH SIGNAL TO NOISE RATIO AND GAIN UNIFORM GAIN WITH 5 TO 6 MC. BANDWITH ON ALL CHANNELS GROUND BRAIDS TO AVOID REGEN- ERATION ALL COMPONENTS FULLY FACTORY RESONANT TESTED AND GUARANTEED LINE FRED MAHOGANY OR WALNUT CABINETS STABILIZER - FURNITURE TYPE FINISH Fringe area condition test. Only definite List $28.50 procedure for assuring perfect perform - once with o TV Booster. Siightly Higher West of the Rockies

QOD RFC

CHECK THESE FEATURES

ADAPTABLE TO ANY BROADCAST OR TELEVISION RECEIVER

S TUBES PLUS SELENIUM RECTIFIER

A - B AND HEAVY DUTY POWER TRANS- FORMER

-AMINE COIL UNUSUALLY SENSITIVE STATIC FREE FM CIRCUIT CROSS SECTION PRESSURE OPERATED SW DIAPHRAGM TEMPERATURE COMPENSATED OSCIL- L OPTIONAL LIGH ; EIC- ELECTRICALLY INSULATING CAP; LATOR TO MINIMIZE DRIFT MT - MOD. TRANSMIT TER; AS -AUTO Sw.LMIKE UNIT; D-DIAPHRAGM BUILT IN ANTENNA CIRCUIT FOR LOCAL RECEPTION List $29.95 MICROWAVE TUBE Slightly Higher West of the Rockies Patent No. 2,449,975 Write for information on spectacularly priced 121/4" TV receiver Harold O. Bishop and Donald Kirk, Jr. United States Navy Write for descriptive literature and name of At very high frequencies, most radio tubes are local representative. Or send order direct. limited by transit -time problems. Above 200 me the period of a cycle is so short that it compares with the time needed for an electron to move PERFECT PRODUCTS CO. SOLE NATIONAL SALES REPRESENTATIVE through the tube. This new tube is effective L. S. KRULL SALES ASSOCIATES at frequencies as high as 1,000 me because 82 -27 217th STREET 41 PAYSON AVENUE NEW YORK 34, N. Y. transit time is not a factor. QUEENS VILLAGE, N. Y. C=1:111

RF OUT M

collected at the upper and lower plates al- This inventor uses two dipoles mounted at a ternately. Therefore current flows in M at the 45- degree angle and positioned in front of a sheet - same frequency as the input, but the output is metal or wire- screen reflector. The whole antenna amplified. If the input and are connected may be rotated about its vertical B+ output axis to scan the together, the tube can be made to function as an Electrons from a source (1) pass through a oscillator. grid and between deflecting plates. At each side of the tube the plates are connected by quarter- SHEET REFLECTOR wave stubs so adjacent elements are out of DIRECTION- FINDER a phase. The last plates on each side are fed from ANTENNA a transmission line L which is coupled to a coaxial cable. Potent No. 2,448,017 At the far end of the tube, electrons are col- Henry G. Busignies, Forest Hills, lected by plates connected to the line M. A coupling loop transfers r.f. energy to the co- and Nathan Marchand, New York, N.Y. axial cable. (assigned to Federal Tel. and Radio Corp.) P\ AXIS When a microwave voltage is fed to the input Two separate antenna systems are usually line, the electron beam is deflected. Since ad- needed for radio direction finding because radio entire azimuth. Each dipole is effective on both jacent and opposite plates have opposite polarity signals may be polarized vertically or horizontally, vertically and horizontally polarized signals. at any instant, the beam becomes wavy. The sometimes both at the same time. If an antenna is Therefore, it may be rotated for a null without more plates built into the tube, the greater the rotated for a null on one component, the other regard to the polarization of the wave being re- deflection. At the receiving end electrons are may still be received. ceived. APRIL, 1949 74 FIM THE VIDEO HAND BOOK "Back- Porch" Booster 800 pages -hundreds of illustro- tians covering everything in television!

14 sections, bound in handsome DuPont Fabrikoid $5.00 This is the newest book on television -for anyone Brings Up FM Signals working at or interested in television -order now to reserve your copy. THE RADIO By JAMES C. DRAKE* DATA BOOK 1148 pages -hundreds of illustra- ANY owners of the popular tions, tables and charts- cover- ing everything in radio! Pilotuner or other small FM The complete radio book, bound tuners may live, like myself, in handsome DuPont Fabrikoid. $5.00 outside a metropolitan area - FM broadcast sta- This famous book -combined with away from strong the VIDEO HANDBOOK will form a technical library tions. My tuner is capable of fine audio that cannot be equalled -order your copy today! reproduction but lacks sufficient sen- RADIO sitivity to bring in fairly distant sta- MAINTENANCE tions with little noise. MAGAZINE Tuning was extremely difficult, and The outstanding service- Techni- seldom could a station be heard with cians' Trade Journal. Each AM monthly issue a valuable refer- less noise than on the band. Vari- ence work os well as interesting, ous antennas were tried, but even with informative reading. the best antenna there was noise. One year (12 issues) $3.00 Two years (24 issues $5.00 The next (and successful) attempt Fig. 2 -The booster attaches to center rear. Handsome green and gold binders are also avail- was to provide more gain in the tuner. able to preserve your copies of RADIO MAINTE- Adding the i.f. amplifier diagrammed NANCE $2.00 ea. in Fig. 1 provided these desirable re- r 'I chassis from a piece of aluminum about BOLAND E. BOYCE, INC. sults: 2 x 3 inches. This is bent into an L MONTCLAIR, N. J. RC -49 1. Increased the audio output voltage shape by folding it along its length to am- Send me the VIDEO HANDBOOK. Enclosed as much as one triode audio make a chassis 11/2 x 3 inches with a is $5.00. plifier stage. % -inch mounting flange (see Figs. 2 Send me the RADIO DATA BOOK. Enclosed 2. Increased the gain so much that is $5.00. and 3). The one shown was cut from Send me One Year of RADIO MAINTENANCE. many new stations were added to an aluminum recording disk. Drill two Enclosed is $3.00. the receiver log. The measured small mounting holes in the vertical Send me Two Years of RADIO MAINTE- gain of the stage is 12. flange as shown in Figs. 3 and 4. When NANCE. Enclosed is $5.00. The requires only a simple Send me binders for RADIO MAINTE- 3. tuner drilling these holes, keep in mind that NANCE at $2.00 each. Enclosed is antenna for good results. the small mounting bolts must come 4. Made it possible to receive many through the tuner chassis at a clear NAME FM stations without noise regard- OCCUPATION spot which will not interfere with its less of atmospheric conditions- wiring. ADDRESS CITY 70N day or night. Next, cut the holes for mounting the The improvement in reception makes STATE J tube socket and the 10.7 -mc i.f. transit well worth while to build and install former. It is important that they be the additional "back -porch" i.f. ampli- in Fig. 2. Notice that -TESTER" MODEL 30 mounted as shown "MULTI fier. The cost is less than $5 for all new the tube on the outboard amplifier is parts, and most experimenters and mounted so that it is immediately be- radiomen will have several of the com- hind the last i.f. transformer of the ponents on hand. tuner. Notice also that the i.f. can is be- This "back -porch" or outboard style hind the last 6BA6 i.f. amplifier of the of mounting requires only two small tuner. They are placed thus to mini- bolt holes in the tuner chassis and dis- mize the length of the input and output turbs only one wire of the original r.f. leads of the auxiliary amplifier. circuit. Alignment requires only an AM When mounting the tube socket and signal generator tuned to 10.7 mc. i.f. can, pay attention to orientation, In Fig. 3 notice that pin 1 on the socket Construction is nearest the mounting flange to keep is make a small sub - Model 30 (Illustrated) 315.95 net The first step to the input wire short. The output of the Model 30K (Complete KIT and intruclons) 11.111 "nee: *Valparaiso Technical Institute, Indiana. i.f. transformer is likewise nearest the SIGNAL GENERATOR MODEL 300 IST 613A6 IF w.r.y SUL i-" LAST 613A6 IF AMPI. -_ I ott 11 WIRING ( 1 REMOVE THIS ORIGINAL ______II ..IC. IMSIRIIafMIS ñe. iREarw,wua,n STIES. B+ 5 6BA8 er' I /rI + Q tt I I 2 6 II I 10.IMC IFT L II I I _J I 7 4 3

.00IS I A015 470 .0015 IOOK iI Supplier 456 Ar. 465 Kr. 000 Kr, and I' I Kr. net Model 300 ( Illustrated ) ...... $16.95 h- Write for FREE. CATAI.OG. SEE vnur local distributor. I ° I If not (wallable. WRITE to B+ I, NEW BRADSHAW INSTRUMENT CO. -J 42 Flatbush Ave.. Dept. RC. Brooklyn 17. N.Y. the two present ones. Fig. I -The booster is on additional i.f. stage inserted between RADIO -ELECTRONICS for Rdt 17; flange. Be sure that the grounds for the cathode, filament, and all bypass capacitors are made to one common United Cuts Prices!!! is ASSEMBLY point on the chassis. This particu- bakellte MINIATURE SOCKET AND SHIELD METERS -G. E. Type AO -22. 3 %" round New. Each -25e: 4 oscilla- V.A.C. Shipping weigh appruximeteIY- -9 pin. black phenolic suckeL larly important in preventing cane. 0 -150 for 9'c. 2 Lbs. Brand new- $3.5u: Ammeter, G.E. 2" round Type F -1. Used. has been done in Fig. 50 Mc shunt) 5 MICROPHONE CAPSULES -W.E. tion. See how this bakellte case. 0 -50 Amps. (less but in excellent condition. Shipping weight approxi- Amps. full 'scale. Shipping weight approximately- 3. In this picture, the only leads not Sun 3" round bakellte mately Y. Lb.75e. ] Lb. New -$1.95: Voltmeter. Quantities are limited -order now! Prices subJect to 0 Y.D.C. at 1000 Ohms per volt. Shipping yet in place are the B -plus, filament, cue. -500 change without notice. SIininwm order-$2.00: 25% weight approximately -l% Lbs. New -$2.75: Weston All orders shipped round bakellte case. deposit required. Balance C.O.D. input, and output. Model :507. Output -O -10. 2" F.O.B. Chicago. All foreign shipments. minimum 2.2 Ma. movement. Mounted In O.D. wood case. 3 %" connect the input approximately 2% order -$50.00. To have a place to 14 % x 4 % ". Shipping weight TUNING UNITS-BC -796. The basic unit for a Lbs. New-52.39. With two crystals. two leads of the amplifier to shunt. Weston low power crystal transmitter. and output METER ACCESSORIES- Ammeter and one tuning condenser -150 Slmf. A.P.C. 50 31v. Mounted on colli terminals 3 and Type D- 91207. 100 Amps. D.C. Shipping weight Lb. 79e: With one 80 meter the tuner, I pulled out 1 Lb. -1 bakellte base. Shipping weight approximately erystal-95e: With two 80 meter cyetals-$i.29: of new -$2.95: Transformer. Weston Type 5 from the strip on the rear apron the Brand Current 11C -191 and BC -375 Tuning Units- TU -26. 200 -500 880. Ratio 15:1. 50 -133 cycles. With mounting Mc. (Ship- 2 was New Kc.- $1.49: TU -10. 10 51c. -12.5 -$1.79 tuner. The wire from terminal bracket. Shipping weight approximately-1 Lb. ping weight-17 Lbs.) (Less eases): Push Button -52.75. Assembly for BC -7281 push buttons select inasmuch as a folded dipole assorted popular types. Tuning removed KITS -Ceramic Insulators, preset frequencies from 2 to 6 Sic. 12 colts permea- and twin -lead transmission line were Shipping weight approximately 3 Lbs. 15 for 59e: bility tuned for R.F.. mixer and Ow. Completely Bathtub Condensers. single and multiple units in and Shipping weight aDproximately- weight approxi- wired aligned. assorted values and types. shipping 4 Lbs. Brand new- 51.95. mately 2% Lbs. 15 for 69c: Carbon Resistors. as- CABLES AND -CORDS -Patch cords -Red fabric sorted values. mostly insulated. Shipping weight en- covered cable contains 2 rubber covered tinsel con- proximately 1 Lb. 100 for $1.95; Mica or Ceramicon with -47 plugs on ends. capacities ductors. Complete -PL Condensondensers, silver and ruby micas, assorted L. and 39' L. Shipping approximatel- condensers. all 21" weight and voltages. 100 for $2.95: Filter 2 Either type. new for 51.00: Extension for Kit, consists Liss. -3 new and usable. 10 for 89e: hardware IIS -30 -CD -605. 6 %' long with transformer and of 3 lbs. of standard nut, bolts, washers. etc. Only PL -55 plug. New --45e: SCR-522 Power Phut and 51.29; Tube socket, all types and sizes. New. 20 Cable -]loused in Aluminum 11X. 3 44' long 12 con- for 95e:: Coil forms. Ceramic, phenolic, bekelile weight approximately Lbs. 39e: ductors. Shipping -2 etc.: In various types and sines. New. 15 for New. $1.00. Relays. choice sorted of A.C. and D.C. Standard .VOLUME CONTROLS AND POTENTIOMETERS -. and special units in excellent condition. Shipping Volume Control Assembly- 500.000 Ohms. S.1'.H.T. 6 for Precision weight approximately-3 Lbs. $1.75: switch. 1 %' Dia. Brass shaft 2V.' Le. slotted 500 Ideal UI. resistors. 5000. 10 K. 100 K. 150 and K. and knurled end. 2 leads. one .1 Mf. at 400 V. and for multi -range voltmeter. All 5 for $1.19. one .005 31f. 400 V. condensers are attached. Shipping COILS-12 Mc. Transmitting. Isolantite form wound weight approximately -6 Oz. New -50e: Rheostats - with No. 12 tinned virr3le: 4 Mc. Transmitting. Ohmlte baked enamel wirewound. Air- cooled and coupling coil inter -wound on phenolic form- shielded. Aircraft type. 90 Ohms at 1.35 Amps. Ship- 29e1 12 Sic. I.F. for SCR -522. (4292) Slug -tuned ping weight approximately -2 Lbs. New -49e: Tor and shielded. New -59e: 915 Kc. Output I.F. for roidal Potentiometers-Precision unit completely en- SCR -348. Slug tuned and shielded. New -49e: 455 closed in heavy aluminum casing. 500 Ohms wire - Kc. Crystal filter I.F. Ihallicrafters) Slug tuned wound. W.E. or G.E. New- 51.19; l'otenllnme.ers- and shielded. New-59e: 465 Kc. B.F. Ose. coil. with 5000 Ohm- 1.11.C. type 1)11 -114 Silent Spiral. In L air trimmer pitch control. Slug tuned. Shielded. New cartons. with hardware and universal shaft. -274 -N original Booster underchossis, partly wired. -59e: 1415 Kc. B.F. coil as used in SCR Shipping weight approximately-6 Oz. Only --45e: Fig. 3- series receivers. Air tuned and shielded. New-I9e: I Megohm- Midget C.T.S. Short Molted shaft. 20 Mc. I.F. Slog tuned and shielded. New-49e: 30 Shielded. Shipping weight approxlmatel -6 Oz.- Ste. I.F. Wound on Polystyrene form. Air tuned 25e: 10.000 Ohm-Midget C.T.S. 5/16" draft. to be used. Terminal 3 was then ground- and shielded. New-49e: 20 -28 Me. Osc.. Ceramic or Shielded. Shipping weight approximately-6 Oz.- Stye:des form. Slug tuned and temperature com- 25e; I)ual Wirowound- 10.000 Ohms each section. making terminals 1 and 2 the an- pensated. For B.C. 603 Receiver. Shielded. New-59e. screwdriver adjustments. 2 Watt. Shipping ed, Carlt- Separate -line connections. VARIABLE TUNING CONDENSERS -2 weigh -6 Oz. New -65c: Dual H.D. Ormite -1200 tenna transmission Osc. section: Minimum 23 Mmf. 'Maximum 200 Mmf. Ohms at .35 Amps. and 3 Ohms at 4.7 Amps. Baked wire which was for- Antenna section: Minimum 45 Sim!. Maximum 450 enamel elements. Complete with knob and tenet The phono input 44 plain or knurled shell. Mmf. With trimmers. Plate. Shipping 2 merly on terminal 5 was soldered to Counter -clockwise. Sire: 1 %" x x 2t4 ". Shinning Single Ire wend 100.000 gory 70.000 s'Ohms weight pProxlmately -1 Lb. EitEither her type-49e: 3 Walt. Bakelite case. I %' Die. %' Deep. Long shah terminal 4. Of course the original Gang T.R.F. or Super. All sections: Minimum 18 Shipping weight approximately-8 Oz. New -65c: 4 4 be re- Simi. Sm 950 Mmf. Clockwise. 3% to 1 Gang Wire- around- (Clarostntl Heavy duty taken.. ground on terminal had to vender. 2%" dial drum mounted on %" hub. Ceramic constroct ion with metal support s. 6000. 2500. 30.0Uo x 444. Shipping In only loss here was the Insulation. Sloe: 1 %" x and 30.000 Ohms. Sire: 1 %° x 2 % ". %' Sheft. moved. The weight approximately-2 Lbs. Now-75e: 3 Gana original cartels. Shinning weight -1 lb. 75e. built-in antenna. Variations in this ar- T.R.F. or Super. All sections: Minimum 16 Mmf. FILTER CONDENSERS -W.E. 25 + 25 Mf. at 900 Maximum 370 Mmf. Counter- clarnie. 3% to 1 V.D.C. Octal socket mounting. Hermetically sealed. rangement are possible. gear vernier.m Direct and vernierventer shafts. %" New -65e: Mallory FP. 50 51f. at 150 V.D.C. New. Die. x %" long. Trimmers on two sections. Size: 3 for $1.00: Slattery FI'. 40 + 15 Ill. at 300 V.I) i. can now be mounted on weight approximately- The chassis 1 %" x 2'4 x 4 % ". Shipping and 20 Mf. at 25 V.D.C. New-55e: Filter Strip V. apron. Be sure it makes 2 I.bs. New -75e. Assembly- Bakelite strip contains 2 -8 Slf. 450 the tuner's rear CONTROL BOXES --C -30 /ARC -5 with 7 push but - type condensers. resistor approximately 2 good electrical contact -poor contact tons. Brand new. Shipping weight and a New uniiits1130forn $Ì00t 1.1,,. $1.19: C -30A /ARC -5 with 4 position ewlrh. JOHNSON UX SOCKET -Heavy duty. Ceramic basr. can be a source of trouble. The filament Shipping weight approximately-22 1.hs. New-79e: Ideal for type 666 tubes. Shipping weight approti- 12 r 24 V.1) C. 5 Prong Sockets RE- 1 /ARR -1 Antenna Switching. m tely -1 Lb. New -37e: loolantllc wire is run through the opening in the relay. Sire: 4" x Y 2" Shinning weight National NC -5. Shipping weight-6 Os. New. " mien - Panel to the terminal strip (un- prexlmately -I Lb. New --49e: Microphone Adapter for 25e: Telephone lacks -To it PL -68 plug. chassis next M -299. Used with SCR -522. Permits using carbon mowing type. 10 for 98e. der terminal 2) to pin 4 of the first microphone in dynamic. Excellent condition.dlt ton. ALUMINUM line approximately m raid. % at 61 per Ft; 8e per ls Ft ; hipping Mini- 6BA6 i.f. amplifier socket. The black ALUMINUM PANELS -All 19° wide with standard 1" at 10e per Ft.: 1 %" at 12e per Ft. (I.D.) relay notching. Unfinished natural aluminum. 16 mum Order -10 Ft. B -plus lead shown in Fig. 5 enters the gauge I0 %' high. hard-69e: 10 gauge (.10221 "ELK'S ANTLER'S" AS- 27 /ARN -5 ANTENNA - (.051) half aircrafL Carefully a hole already 10 %- high. half hard -$1.19: 10 gauge (.102) Now being used on commercial tuner chassis through Isard. 12 %" high- S1.39. ,ked$ Shipping weight approximately-10 Lbs ASSEMBLY -For small in- punched in the rear and is connected BEAM ROTATING Auto stallations. RL -42 motor and gear box. 24 V.D.C. NEON BULBS-G.E.Ó C F.. NE -48 % W. to the main B -plus lead on the mount- reversible. Approximately 2% R.P.M. New -$3.29. bayonet 1. Type Bobbins -49e. PL -68 PLUGS-3 contact microphone type. 10 for 955 ing lug at the left. button carbon mike to PLAN -O- VERNIER DIAL -(Crowe). Instrument TRANSFORMERS -Single 360 dr. Lug terminals. Upright mounting. type. 4" Die. 5 to 1 ratio. Calibration 0 -200 in output leads are then single grid. weight aDproxl- The input and Shielded. New -49e: Double button carbon mike to groes. Shipping eingle grid. With leads. Shielded. 59e: 6- 122 -24 Volt S3 oth. planets filament transformer-Shielded in heavy metal case. THROAT MIKES -T -30 (Shure). New In cartons - on bottom. Primary: 115 or 230 V. 50e. All terminals AF -1 230 V.A.C. x x Shipping weight CIRCUIT BREAKERS-G.E. Type ..laet 35 Amps. Single circuit. Overall size: 3' s 454' x 6'. -5 Lbs. Use-$2.19: Square D Ma. (lead In IgCt speech amplifier) Black Shipping weight-4% lbs. New -$1.85: wrinkle caee with lug terminals. Brand new. Only- size: 120-240 s weight-2 Lbs.- 75e. 4% . Shipping normally closed. 10 New-81.75. SWITCHES - Micro- switch - Ideal for steering V. operated. Shipping weight ap- FABRIC LOOM- Weather -proof. Amps. 125 Pin -ins. Uhm Mulleins Proximately -6 Oz. New-45e; Motor switch -3 P.D.T. on T.V. and FM Antenna lead I.D. 14 . %" and % ". (Specify 3 buttons labeled "Manual -Off -Automatic." Locks and around comen. shop equipment sleet. 50 feet. any Ize- 51.45. in both operating positions. Ideal for PACKAGE. operation. Shipping weight approximately -9 Os SPECIALS- ELECTRONICS PARTS Switch- (Siosaman) An assortment of parts and aesemblfes which are al. New -39c: Anti -Capacity Lever items may duty contacts. Center position: 3 poles closed. ways useful to any electronics man. The Heavy from new equipment. A REAL let position: 4th pole closed. (Momentary) 2nd twist- he new or removed leaves. Spring PARTS BUT!!! Shipping weight appmximetely- eon: all poles open. Phosphor bronze Dia. action. Size: 1%' x 1 %" x 6'. 10 Lbs. 51.29; MAGNIFIER REFLECTOR -8" loaded lever. Positive lens) Metallic coated silver Shipping weight approximately 1 Lb. New -98e: Parabolic. (Lancaster Fenwal cartridge type S39. She: surface. Useful in photographic work. (Glass) Ship- Thermnswitrhes. 1% Lh,. New -5195: Dia. x 4" long. Normally closed. Rated at 115 V. ping weight approximately AdAntahle from PE -117 C. VIRROPACKS-6.12 -14 Volta. Good, 10 Amps. 250 V. 5 Amps. A.C. Shippi -100° to +400° F. at 90° per turn. Normally set at used condition. Less tubes and vibron. Asbestos covered leads. New -95e: weight appmximately 20 L,s.-$l.95; 6%' CORDS- 275 °. 2 shielded on both ends. En- S15 -Same se 839 except 3 %" long, rated at 5 2 conductor coded leads with lugs Type 3 for 25e: 15 for 115 V.A.C. and leads not shielded. Originally closed in flexible rubber jacket. New. Amps. CONTROL CABLES -For MN -26. boxed -79e. 51.00: REMOTE AID 4 Ohm, 433. ABB. etc. 20' long. New -52.39: REARING RECORDING HEADS -(Shure) Magnetic. 67 V. With cord and stvin, screw. Slightly SI!BSIINIATURES- Triodes. L2V. Filament. at 400 cycles. TOGGLE SSS'ITCUES-Assort- scratched. Good condition. Shipping weight Internal- plate. New -39e: ment of five different types. Kew-51.00. mate U' -1 1 h Only -79e. post -card brings you United's new catalog of * SAVE MONEY!!! A pennyrwoney-aaving values. Write today! UNITED SURPLUS MATERIALS 6, ILL. ¡ CHICAGO _ 314 S. HALSTED ST. Fig. 4-Top view, showing holes in flange. APRIL, 1949 761 FA1

connected. These leads should be made as short as possible and kept close to the chassis. Alignment Since a new stage has been added to the i.f. system of the tuner, it as well as the others needs realignment. Two methods are given because not everyone has all the equipment necessary for the usual alignment procedure. An ordinary AM signal generator can be used provided it has a fair amount of output on 10.7 mc. It would be a good idea to calibrate or note the error of the generator at 10 mc by tuning in W W V and zero- beating the generator with the station. Then the generator will probably be accurate enough for alignment at 10.7. mc. Connect the signal generator through a .05 -µf capacitor to the signal grid (pin 7) of the 6BE6 and ground. If a v.t.v.m. or 20,000- ohms -per -volt d.c. meter is available connect it between pin 1 of the 6AL5 and ground. If no meter is available, connect the output of the tuner to an audio amplifier. Set the dial of the tuner to 88 mc and allow at least a 30- minute warm -up period. Begin alignment by tuning the primary (the upper adjustment) of the ratio -detector transformer for maximum reading on the meter or for maxi- r mum audio volume. Amplitude modulation must be used in the Fig. 5- Underchassis view signal gen- shows where the connecting wires are led through main chassis. erator for this latter method, but need

ESTIMATE REPAIRS ON THE SPOT! TO TO LEARN IF YOU WANT THIS NEW FIX ANY RADIO NOW SIMPLIFIED WAY accurate Some os large generoforsJ pocket size HOW TO GET THE MOST FROM economical YOUR RADIO "KNOW -HOW" A.M. Signal F.M. Signal Generator Here Is your opportunity to learn all Model #710 Generator Model #720A about an amazing new simplified way of fixing any radio. Here are There's nothing complex to learn, no calculating is TWO great units that will pay for themselves in 30 required. Can be used by beginners or experts. It's as simple as ABC days. Helps -and quick, too. locate faults quickly and accurately-estimate a You can use It on easy or "tough" jobs. repair job In simple, direct language, this informative 28 -page illustrated or do a complete alignment right on the spot. manual, 'The Inside Story" explains why old -fashioned methods actu- Safe for A.C. ally hamper your servicing ability. It explains why experts have agreed or D.C. operation. Instrument cases and chassis that you can't blame yourself when you're stumped on those extra - are completely isolated from power tough supply. No chance of shock, jobs . obsolete servicing methods are p }Ina you from short circuit, using your real ability. or burnout. Both units complete with individual trimmers for recalibration. Size: 3 ". So why not find out for yourself how you, too, can take advantage "x6 "x2g Weight: 1% lbs. the remarkable of new STETHOSCOPE SERVICING METHOD. You owe it MODEL #7I0 to yourself fo get this FREE manual at once. MODEL #720 It's chock -full of useful and Fixed frequencies helpful information, too. Page after page of valuable hints and kinks of 1500. 550 -456- Calibration accurate within 1% for from the experience of top radio engineers. 465 K.C. Complete with tubes, fixed frequencies of etc. 9.1, 10.7, 88 MAIL & 108 mc. Complete with tubes, COUPON OR $17.95 etc. PENNY POST CARD 1FEILER ENGINEERING CO.. Deot. 4RC9i $19.95 FOR TOUR FREE COPY TODAY 945 George St., Chicago 14, Illinois WRITE FOR CATALOGUE R 0 Please RUSH my FREE coca of "The Inside Story." 'Rame RADIO CITY PRODUCTS CO., INC Address

12y Cons. Stets 152 WEST 25th ST NEW YORK 1. N. Y. RADIO -ELECTRONICS for Fí\1 177 not be used with the meter method. Proceed toward the front, tuning each stage in the same manner. To complete the i.f. alignment, connect (temporarily) two 100,000 -ohm resistors between pin 1 of the 6AL5 and ground. Connect the meter from the junction of the two resistors to the detector side of the audio -output coupling capacitor. Adjust the secondary of the ratio detector transformer (the lower adjustment) for zero meter reading. The meter should register reversed polarity when the slug is rotated through zero output. If not using a meter, adjust the slug for minimum sound output. This completes the i.f. alignment. To touch up the r.f. portion of the tuner, the most practical method is to use FM broadcast stations as signal sources. Tune in on the lowest- frequency FM station that can be received and whose frequency (preferably about 90 mc) is known. If it is not received at the proper dial setting, set the dial to the frequency at which it should appear low-frequency oscillator and adjust the FOR TV SERVICING padder (P8 underneath) until the sta- VITAL tion is received. Then adjust the low - A new and highly important book! Gives a com- frequency mixer padder (P8 on rear plete understanding of working principles behind maximum audio volume or oscilloscope operation, and how to use the instru- gang) for ment effectively. Clearly written with a single greatest d.c. reference voltage (pin 1 purpose-to help you use and understand the of 6AL5 to ground). oscilloscope. No man servicing television receivers Now tune in the highest- frequency can afford to be without this knowledge. Invaluable who uses the oscilloscope. station heard on the band, preferably for anyone about 108 mc. If it is not received at the proper dial setting, set the dial to ALL ANGLES COVERED the frequency at which the station Chapter I- Direct Current and Alternating Current. Visual should appear and adjust the high -fre- observation and measurement of varying voltages and currents quency oscillator trimmer (center on ,the cathode -ray tithe. Chapter 2 -How beam from electron "gun" projects image of current and voltage variations onto gang) to bring in the station. Then fin- fluorescent screen. and how beam Is deflected by electrostatic ish by adjusting the antenna trimmer. and electromagnetic means. Chapter 3 -How signal deflects electron beam vertically In a -r tube and sweep voltage deflects MATERIALS FOR I.F. AMPLIFIER beam horizontally. Role of the saw -tooth oscillator -the gas synchronization -locking. Resistors: 1-470, I -1,000 I- 100 000 ohms, i/2 wait. discharge tube -the multivibrator- 4 cathode -ray tube -accelerating and foclrsaing Capacitors: 3- .0015, I -.b1- f, 400 volts, paper. Chapter -The sweep horizontal and ver- Miscellaneous: i -6BA6; 1- 10.7 -mc i.f. transformer; power supplies -the generator -the controls on oscilloscope -how to operate I -octal tube socket; I -piece of aluminum for tical amplifiers- chassis (see text); necessary hardware. 'scope. Chapter 5- Aligning TV if. channels -TV front-end alignment- Alignment of 1.f. amplifiers In AM and FM sets. Use of signal generators-I.f. alignment of a.c. -d.c. receivers -bandpass alignment- aligning the discriminator-the ratio detector -r.f. alignment of AM and FM receivers. Chapter 6- Audio output measurement-voltage gain -power output - CANADIAN GROUP MEETS audio response curve plotting -peak a.c. measurements. Check- The Associated Radio Technicians of ing saw -tooth amplifiers- magnetic deflection circuits -synchronizing pulses. Ham transmitter measurements -over and British Columbia met in convention last under -modulation. Locating hum -Incorrect adjustment of October 5th at Stanley Park. Garth vibrator power supplies. Phase shift in audio amplifiers. Pither of RCA Victor explained the GBNSBA[K Magic Monitor, a device used in phono- 112 PAGES 103 ILLUSTRATIONS graphs to reduce record surface noise. Jack Gray of Canadian General Electric described the 30- station, 250- mobile- Only 75c unit FM system used by the Ontario U PAY Provincial Police. Service and operation of motion -picture projectors was dis- See your jobber today or send for THE CATHODE- cussed by Wilfred Wheatcroft. RAY OSCILLOSCOPE along with other titles in Nick Foster, Superintendent of Tech- the GERNSBACK LIBRARY. nical Schools in Seattle, Wash., talked about the servicing of television receivers. When, some time after the conven- - MAIL THIS COUPON NOW -- tion, Seattle's KRSC went on the air, Ed Mullins, a member of the ARTBC, RADCRAFT PUBLICATIONS, Dept. 49 10 OTHER BOOKS was the first person in Vancouver to 25 West Broadway, New York 7, N. Y. ' No. 29 -Mandy Kinks No. 34- Radio -Elec- Send me the books checked, postpaid. and Short Cuts. tronic Circuits, I receive the broadcasts. He had built a 50e 50e CI NO. 40 CATHODE -RAY OSCILLOSCOPE Ne. 30- Unusual pat- No. 35-Amateur Radio receiver many months before. Reception 75c ented Cireults, Builder's Guide. reports were fair, but Mullins predicted 50c 50e I enclose 8 No. 31 -Radio Questions No. 36 -Radio Test In- I that Vancouver residents would not and Answers.50e strumenta, 50e

Your Name - No. Advanced Serv- D No. Elementary Ra- I have acceptable television until a station 1 Print clearly) S2- 37- ice Technique, die Servicing. was erected in the Vancouver area. The IAddress 50e 50e CBC is presently considering plans to IJobber's Name ONo.33-Alifier No. 36 -Now to Build I Builder's Guide, Rid lo Reeeivers, introduce TV to Canada (RADIO -ELEC- Address 50e 50e TRONICS, February 1949, page 13). MEN WWI= _J APRIL, 1949 781 PM

Regulate Your Line Voltage FM STATION LIST to fit Your Needs STATION LOCATION FREQUENCY KAGH -FM Pasadena, Calif. 98.3 KAKC On 117 V. line, variable from 95 to 145 Volts, If line -FM Tulso, Okla. 95.5 drops to 90, variable from 75 to 115 Volts. KALB -FM Alexandria, La. 96.9 Output adjustable KALW San Francisco. Calif. 91.7 in 113 volt steps. KARM Metered out -put Voltage. -FM Fresno. Calif. 101.9 KBEE Modesto, Calif. 103.3 140 Watts, max., 50 -60 cycle. KBIX -FM Muskogee, Okla. 98.5 Here is a Voltage regulating isolation transformer KBMT San Bernardino, Calif. 99.9 KBOA Kennett. Mo. 98.9 that will make your bench test voltage exactly KBON what you want -FM Omaha, Nebr. 98.7 ... Only S15.00 ... Capacity 140 KBTM -FM Jonesboro. Ark. 101.9 Watts max. Every service engineer needs it for KBTR Minneapolis, Minn. 98.5 more accurate work and time saving short cuts. KBUR -FM Burlington, Iowa 92.9 KCBC -FM Des Moines. Iowa 94.1 KCFM Kansas City, Mo. 94.9 Vari -volt Junior...s15.00 DEALER NET KCKN -FM Kansas City, Kans. 106.7 KCLI Los Angeles, Calif. 105.1 KCMC -FM Texorkano, Tex. 98.1 KCRA -FM Sacramento, Calif. 96.1 PARTIAL KCRC -FM Enid, Okla. 102.7 LI ST OF USES KCRK Cedar Rapids. Iowa 96.9 KCRW Santa Monica. Radio and Television receiver testing at Controlled voltage for meter Calif. 89.9 under or over voltage. calibration. KCVN Stockton. Calif. 91.3 KDFC To isolateehash ^and live ground from AC. Son Francisco, Calif. 102.1 Speed up or retard heating of light solder- DC Equipment. KDKA -FM Pittsburgh, Pa. 92.9 ing irons. KDNT -FM Denton, Tex. 106.1 For Schools and educational laboratories. KOON -FM Monterey. Calif. 94.5 KDTH -FM Excellent Dubuque, Iowa 100.5 control for primary of high volt- Adjusting line voltage photo KDYL -FM age breakdown transformers. to lamps for Salt Lake City, Utoh 98.7 uniform exposure, and many other uses. KECA -FM Los Angeles, Calif. 95.5 KENO -FM Los Vegas, Nev. 103.9 OTHER NEW HALLDORSON KERN -FM Bakersfield, Calif. 94.1 TRANSFORMERS KEX -FM Portland, Ore. 92.3 KFAB P- 2067 -Power -117 volts to 240 -0- T-4303 -FM Lincoln, Nebr. 97.9 -Step up -117V. to 140V.- KFAC -FM Los Angeles, Calif. 104.3 240 @ 60 M.A. -6.3 @ 2.75A. 12 Watts (plate voltage booster KFAM -FM St. Cloud, Minn. 104.7 for AC -DC sets) KFBK -FM Sacramento, Calif. 96.9 P1596ß -Isolation -115V. to 115V. KFDA -FM Amarillo. Tex. 100.3 N- Vibrator to KFEL-FM Denver, Colo. 97.3 -150 Watts. 91- -6V. 250V. @ 50 KFEO M. A. (CAN- 3.04" x 2.4" -FM St. Joseph. Mo. 92.3 x 2.2 ") KFH -FM Wichita, Kons. 100.3 P- 2040-Stepdown -230V. to KFI -FM 115V. S- 210 -Plate Trans.- 1150. 500 -0- Los Angeles, Calif. 105.9 -1000 Watts. KFMB -FM Son Diego, Calif. 101.5 500-1150 @ 150 M. A. KFMV Los Angeles, Calif. 94.7 KFMX Council Bluffs, Iowa 96.1 TELEVISION UNITS KFMY Fort Dodge, Iowa 102.7 KFOR -FM Lincoln, Nebr. 102.9 L- 211 -Power- 365 -0 -365 @ 250 M. D4 -612- Vertical Blocking Oscilla- KFPW -FM Fort Smith, Ark. 94.9 tor (Replacement KFSA -FM Fort Smith, Ark. 107.7 A. D.C. -5V. @ 3A.-5V. @ 2A. for RCA type KFSD -FM Son Diego, Calif. 94.1 No. 208T2) . KFUO -FM Clayton, Mo. 104.1 6.3V. @ 6A. -6.3V. @ .8A. KFVS -FM Cape Girardeau, J Mo. 95.7 -96- Vertical Output Trans. (Re- KFXD -FM Nampo. Idaho 101.9 KFXM -FM D4- placement for RCA type No. San Bernardino, Calif. 95.1 61I- Horizontal Blocking Oscil- KFYO -FM Lubbock, 204T2) . Tex. 99,5 lator (Replacement for RCA type KGAR -FM Garden City. Kans, 99.3 C4. 216 -Choke-2 by @ 200 M.A. KGBS -FM Harlingen, Tex. 94.7 - KGDM.FM Stockton, 92.9 No. 208T1). D.C. Resistance Approx. 60 Ohms. Calif. KGKB -FM Tyler, Tex. 101.5 For more information KGLO -FM Mason City, Iowa 101.1 see your Radio Parts Distributor or write KGNC -FM Amarillo, Tex. 104.3 KGO -FM Son Francisco, Calif. 106.1 THE HALLDORSON CO., 4500 Ravenswood Avenue, Chicago 40, M. KGPO Grants Pass, Ore. 96.9 KGW -FM Portland, Ore. 100.3 KHJ -FM Los Angeles, Calif. 101.1 KIDO.FM Boise, Idaho 106.1 KI MV Hutchinson, Kans. 105.7 KING -FM Seattle, Wash. 94.9 KIRO -FM Seattle, Wash. 100.7 KISS Son Antonio, Tex. 99,5 KIXL -FM Dallas, Tex. 104.5 KJBS -FM San Francisco, Calif. 98.9 KKLA Los Angeles, Calif. 97.1 KLCN -FM Blytheville, Ark. 96.1 KIT! Longview, Tex. 105.9 KLX -FM Oakland, Calif. 101.3 KLZ -FM Denver, Colo. 94.1 KMAR Bakersfield, Calif. 92.5 KMBC -FM Kansas City, Mo. 100.5 KMFM Monroe, La. 104,1 KMGM Los Angeles, Calif. 98,7 KMHB Belton, Tex. 97.1 KMPC -FM Los Angeles, Calif. 100.3 KMUS -FM Muskogee, Okla. 101.5 KMYC -FM Marysville, Calif. 99.9 s -FM N _s-o I KNBC San Francisco, Calif. 99.7 , KNEX -FM McPherson, Kans. 103.3 KNX -FM Hollywood, t Calif. 93.1 Hov t KOA.FM Denver, Colo. 95.7 from- KOAD Omaha, Nebr. 92.9 KOCS -FM Ontario, Calif. 93.5 u n KOCY.FM Oklahoma City, Okla. 94.7 o KOIN -FM BASVLS- Portland, Ore. 101.1 Substitution KOKX -FM Keokuk, Iowa 102.7 ! receiver KOMA -FM Oklahoma City. by Signal to Okla. 105.9 approach KOMO -FM Seattle, Wash. 98.9 Servicing IV. KONO -FM Son Aode'DemcSpeedmproblems, VIA-AM- Antonio, Tex. 92.9 tells HOW In KOPP -FM Ogden, Utah 103.9 The Simple, S -S -S - KOPY Ñingodadu simple, direct language. Houston, Tex. 97,9 alignment comPlee l r KOWN Conway, Ark. 97,7 mropurchase KOZY Kansas City, Mo, exno equ'p New 9th edition now off the press. 98.1 pósolescenr KPFM Portland, Ore. 97.1 - Equipment 100 pages of valuable information. KPOJ -FM Portland, Uni enol Test Ore. 98.7 only KPOR Riverside, Calif. 97.5 Employs Available from oil leading radio parts and KPRA Portland, Ore. 95.5 KPRC -FM Houston, Tex. 102.9 equipment distributors or directly from factory KQV.FM Pittsburgh. Po. 98.1 al only 40c per copy. KOW -FM Son Francisco, Calif. 103.7 KRBA -FM Lufkin, Tex. 95.5 PRECISION APPARATUS COMPANY, Inc. 92-27 Horace Harding Blvd., Elmhurst 4, N. Y. KRBC -FM Abilene, Tex. 96.9 KRCC Richmond, Calif. 104.5 RADIO -ELECTRONICS for FM 79 STATION LOCATION FREQUENCY

KRE-FM Berkeley. Calif, 102.9 IT'S NOT HARD TO FIGURE e e e KRED Eureka, Calif. 96.3 Quam Adlust- KRFM Fresno, Calif. 93.7 Why so many servicemen are using KRIC-FM Beaumont, Tex. 99.5 A-Cone Speakers for all their replacement needs! KRIM Santa Maria, Calif. 103.1 KRKD-FM Los Angeles, Calif. 96.3 KRLD-FM Dallas, Tex. 92.5 Here are a couple of good reasons. KRNT-FM Des Moines, Iowa 104.5 KROC-FM Rochester. Minn. 94.7 Only Quam Adjust -A -Cone heard of in a Quam Adjust - KRON-FM Son Francisco, Calif. 96.5 Speakers have the adjustable A -Cone. KRO5-FM Iowa 96.1 Clinton, The Shaped Pot, ex- KRPO San Jose. Calif. 92.3 voice coil that permits accu- U- Coil KRSC-FM Seattle, Wash. 98.1 rate centering alter assembly clusive with Quam, offers a KRVM Eugene, Ore. 90.1 and before it leaves the fac- continuous path for the mag- 100.5 KSBR Son Bruno, Calif. This means that rub- netic lines of force, and re- KSBS Kansas City, Kans. 105.9 tory. KSC1-FM Sioux City, lowo 94.9 bing voice coils, a common sults in a stronger magnetic KSD-FM St. Louis, Mo. 96.1 complaint when permanent- field. This means higher effi- 96.5 KSDO Son Diego. Calif. in ciency and perform- KSEI-FM Pocatello, Idaho 96.5 ly glued position before better I(SEO-FM Durant, Okla. 107.3 assembly, are virtually un- ance. KSFH Son Francisco. Calif. 94.9 KS1O-FM San Jose, Calif. 95.3 KSL-FM Solt Lake City. Utah 100.3 KSO-FM Des Moines, Iowa 97.3 KSPI-FM Stillwater, Oklo. 93.9 KSTP-FM St. Paul, Minn. 102.1 KSUI Iowa City, Iowa 91.7 KTEM-FM Temple. Tex. 107.5 KIFI-FM Twin Foils. Idaho 99.7 Take a tip SPEAKERS KTNT Tacoma, Wash. 97.3 QUAM- N1.JHOLS CO. KTOK-FM Oklahoma City. Okla. 104.3 from successful KTRB-FM Modesto. Calif. 104.1 servicemen 521 E. 33rd Place Tex. 101.1 - KTRH-FM Houston, Chicago 16. Illinois Falls, Tex. 97.3 with Quam. KTRN-FM Wichita replace Please send QUAM Catalog KITS-FM Springfield, Mo. 94.7 KTUL-FM Tulsa, Okla. 97.1 Nome KUGN-FM Eugene, Ore. 99.1 MAIL COUPON KUOA-FM Siloam Springs, Ark. 105.7 Address FOR FREE CATALOG KURV-FM Edinburg, Tex. 104.9 State KUSC Los Angeles, Calif. 91.5 City KVCI Chico, Calif. 101.1 KVEC-FM San Luis Obispo, Calif. 99.9 KVME Merced, Calif. 97.5 CRYSTAL SET- TELEPHONE COMBINATION DIA- KVN1-FM Fargo, N. D. 92.3 -LETS gram and Instrnrtlons 25c. Includes attractive offer. liter- KVOB-FM Alexandria. La. 99.7 OPPORTUNITY AD ature. year's membership in "XTAL -X CRYSTAL SET E-FM Santa Ano, 96.7 Advertisements In this section cost 55c word for CLUB." Box 808, Torrance. Calif. KVO Calif. be 103.9 each Insertion. Name, address and Initials must KVRE Redding, Calif. should accompany 93.7 Included at the above rate. Cash KVSO-FM Ardmore. Okla. all classified advertisements unless placed by an or trade for Television Kit, recorder or what -have- Vernon, 98.7 Sell, KVWC-FM Tex. accredited advertising agency. No advertisement for you-a78A A.B. Dick mimeo and postal card mimeo KWBR-FM San Francisco, Calif. 97.3 less than ten words accepted. 'Ten percent discount machines and colored inks. Herbert Hash. 418 E. 53 St., KWBW-FM Hutchinson, Kans. 93.1 six issues, twenty percent for twelve Issue.. Oblee- Brooklyn 3, N.Y. San Diego, 104.7 tlonable or misleading advertisements not accepted KWFM Calif. must reach St. Louis. Mo. 98.1 Advertisements for May. 1949, Issue. KWGD r. not than March 24, 1949. 90.5 later "ALL ABOUT HEADPHONES." ONLY 24 PAGE COSI- KWGS Tulsa. Okla. neurs- Eiectronrea, 23 W. breaway, New York7. N. Y. Experts Ore. 101.7 plete repair. operation Handbook. All types. praise KWIL-FM Albany. It. Including 10e Experimenter's Radlobuilder." unusual K W FT-F M Wichita Falls. Tex. 99.9 Catalog -total 25e. Laboratories, 578 -B, San Carlos. KWK-FM St. Louis, Mo. 99.1 California. KWKH-FM Shreveport, La. 94.5 1288 & 2588 TUBES. ADAPTER UNIT USING 2 KWLK-FM Longview, Wash. 103.9 miniature tubes (BAT(' & 8BA8 for 1288. and 12AT8 & leas space than original tube KWNO-FM Winona, Minn. 97.5 12RÁ8 for 25B8). Takes - TELEPHONE DIALS. USED. NATIONALLY KNOWN nothing else to buy -lust plug ln e it works. Money -back Re KWOC-FM Poplar Bluff. Mo. 94.5 each, 10 make. Standard speed. 10 pulses per second. -built guarantee. 1288 or 2588 unit ro plete: 12.48 ad)usled Kissel Electric K W OS-FM Jefferson City, Mo. 98.5 deposit, balance C.O.U. Write $2.25. Re- 51.25 postpaid. unite for $22.50. Send 25% Products, 431 -C. Sherman. Gallon, Ohio. KWPC-FM Muscatine, Iowa 99.7 for tree parts catalog. COMMERCIAL RADIO, 38 Braille KWRN Reno, Nev. 95.5 St.. Boston. Mass. Waterloo, Iowa 105.7 KXEL-FM ENTHUSIASTS! BRITAIN'S FOREMOST. RADIO KXLW-FM Clayton, Mo. 101.1 LANCASTER. ALLWINE & ROMMEL, 438 BOWEN monthly-PRACTICAL W11tELESB -keeps you up-to-date KXOA-FM Sacramento, Calif. 107.9 Building, Washington 5. D.C. Registered Patent Attorneys. with latest radio news and events. Covers entire British KXOK-FM St. Louis, Mo. 93.7 Practice before United States Patent Office. Validity and and European radio -television developments. Authoritative San Antonio. Tex. 101.5 Infringement Investigations and Opinions. Booklet and constructional data; television and electronic features, die - KYFM request. Houston, Tex. 96.5 form Evidence of Conception" forwarded upon asion columns, etc. Leading experts contribute regularly. KXYZ-FM from KYSM-FM Mankato, Minn. 103.5 For annual subscription mailed direct to your address London send only to George Newnes, Ltd., (PW.38) 92.5 SEND FOR $2.00 KYW-FM Philadelphia. Pa. TELEVISION. RADIO. TUBES. PARTS. 342 Madison Avenue. New York 17. WAAT-FM Newark. N. J. 94.7 free bargain list. Hallmark, 592A Communipaw Ave.. WABB Mobile, Ala. 102.1 Jersey City, New Jersey. WABE Atlanta, Ga. 90.1 WANTED: Salesmen to sell Nationally Advertised Brand N. Y. 99.5 WABF New York. SELECTED GROUP OF MEN. GRADUATES OF WELL - Itariio Tubes to Dealers and Servicemen at liberal discounts. WABX Harrisburg, Pa. 100.9 known trade school. desire employment In Radio Held. Good Commissions Paid. c/o Radio- Electronics, P. O. Box W ACE-FM Chicopee, Mass. 100.3 Will travel anywhere. puallned in radio servlrIng, Instal- RE -32. 25 W. Broadway. New York 7. N. Y. W AER Syracuse. N. Y. 88.1 lation, test instruments, circuit operation. etc. Contact WAFB-FM Baton Rouge. La. 104.3 Placement Dept. Eastern Technical School. 888 Purchase WAFM Birmingham. Ala. 99.5 Street. New Bedford, Mass. RECORD CHANGER PARTS for leading makes of changers. We ship everywhere. Mall orders Invited! FRIEND'S WAGA-FM Atlanta. Ga. 103.3 Wholesale Distributors, 108 North Sixth Street. Phila WAGE-FM Syracuse, N. Y. 98.5 WE REPAIR ALL TYPES OF ELECTRICAL INSTRU- delphla 8, Pa. WAIR-FM Winston-Salem, N. C. 93.1 menus. tube checkers and analyzers. Hazleton Instrument WA1L Flint, Mich. 107.1 Co. (Electric Meter Laboratory). 140 Liberty Street. New BArclay 7 WAJR-FM Morgantown, W. Va. 99.3 York N. Y. Telephone- -4239. TELEVISION -BRIGHT AND CLEAR. ADJUST PRES- WAKR-FM Akron. Ohio 97.5 ant aerial. Build low -cost Precision Antennae. Instruc- WA MS-FM Wilmington, Del. 96.1 BARGAINS: NEW AND RECONDITIONED HALLI- tion., charts, diagrams. dimensions, plans. FREE -Tele- WAND-FM Canton. Ohio 92.5 craften, National, Collins, Hammarlund, Meisaner, RStE. vision Stations, kilowatts, tower heights. C. F. Propson Co.. W APO-FM Chattanooga. Tenn. 94.7 other receivers, tuners. television receivers. transmitters, Lumberton. N. J. WARD-FM Johnstown. Pa. 105.3 etc. Wholesale prices. Terms. Shipped nn trial. Linens' WA RI-FM Arlington. Va. 105.5 trade -In allowance. Write. Henry Radio, Bottler, Missouri and West Loa Angeles, RECORDS Scranton, Po. 105.7 11240 Olympic, California. PHONOGRAPH CHEAP. CATALOGl'E. WARM-FM Paramount. B.1 -313 East Market. Wilkes -Bure, l'erma. WASH Washington, D. C. 97.1 WATG Ashland, Ohio 101.3 AMATEUR RADIO LICENSES. COMPLETE THEORY WAIL-FM Atlanta, Ga. 97.5 preparation for passing amateur radio examinations. Home resident "Schematic Diagrams Necessary for Radiotelephone Li- wAUX-FM Waukesha. Wis. 95.3 study and courses. American Radio Institute. In for amateur 101 West 63rd St., New York City. See our ad on Page 01. cense." Helpful atudying commercial or WAVZ-FM New Haven. Conn. 95.1 license. Send 51.00. Pramgrim, P.O. Box 1094. Akron 9, WAYS-FM Charlotte. N. C. 107.7 Ohio. WBAB-FM Atlantic City. N. J. 100.7 MAGAZINES (BACK DATES)- FOREIGN, DOMESTIC WBBB-FM Burlington. N. C. 101.1 arts. Books booklets. subscriptions. pin -ups. etc. Catalog. WBBM-FM Chicago Ill. 97.1 100 (refunded). Cicerone's, 883 Find Are.. New York FOR SALE-Signal Tracer with probe. Battery operated. W BBO-F M Forest City. N. C. 93.3 17, N. Y. . Gosrontred Ilke new condition. ('ass $29.95. Yours for WBCA Schenectady. N. Y. 101.1 $18.50. Also several EDWARDR FM Turners list $48.50. WBCM-FM Bay City. Mich. 96.1 Yours for $22.50 each. George Terpay. 7005 Wells Parkway, BARGAIN HUNTING? RADIO SERVICEMEN WRITE. College Heights Estates. Maryland. WBCN Highmarket, N. Y. 107.7 Sensational catalog. Ilenshaw Radio Supply. 3619 Truant. W BEC-FM Pittsfield, Mass. 94.3 Kansas City 3. Missouri. W BEN-FM Buffalo, N. Y. 106.5 WANTED-Modem Elertrles and Popular Electricity v"9ET-FM Brockton, Mass. 97 7 1909. .1. Landa. 157 Lererett. Boston 14. Mass. wBEZ Chicago. Ill. 91.5 MAKE RADIO PARTS AT HOME. BLUEPRINTS 11.00. WRGE-FM Atlanta, Go. 95.5 Tell you where to sell. Clifford Ort. 711 Washington. Ludington. Mich. Newark, J. 91.1 wBGO N. 27 YEARS EXPERIENCE RADIO REPAIRING. SIM- WEIB New Haven, Conn. 100.7 plined system. No calculations. No formulas. Total $2.00 WBIK Chicago. Ill. 96.3 20 -TUBE. HI -FI FM -AM SW -PHONO COMBINATION postpaid or COD. Ross Radio. 14815 Grandriver, Detroit WBKA-FM Brockton, Mass. 107.1 cheap. Forcier. 293 Jefferson, Salem, Mass. 27. Michigan. APRIL, 1949 PM 80 I

STATION LOCATION LARGEST FREQUENCY AHARD-TO-GET PARTS WBKY Lexington, Ky. 91.3 POWERFUL ALL -PURPOSE INDUCTION SURPLUS STOCK WBM L-FM Macon, Ga. 100.7 MOTOR WBMS-FM Boston. Mass. 104.1 in the COUNTRY IDEAL FOR EXPERIMENTERS -1O1 USES WBNB Beloit, Wis. 107.3 WBNU Aurora, III. Sturdily constructed to precision at the LOWEST PRICES! 103.9 standards. m,a a Ifstarting shaded WBNY-FM Buffalo, N. Y. 92.9 pole A.C. induction motor is pow- WBOC erful enough fora mber of u DYNAMOTORS & INVERTERS Salisbury, Md. 97.5 Some of these are: Automatic Tim- WBOE Cleveland, Ohio 90.3 mDvices. Current Interrupters. BD -77 Electric Fans, Electric Chimes. -Dynamotor Unit 14v In. 100r, 350 WBON Bowling Green, Ky. 101.1 ma out with relay fuse box and Window Displays, Photocell Control fil- WBOW-FM Terre Haute. Ind. 101.1 Devices, Electric Vibrators. small ters. FOB Chicago only 55.75 Grinder., uaera and Polishers, WBOX Louisville, Ky. 100.7 PE- 101 -C- Dynamotor unit: 12 or 24y ln, out- WBRC-FM Sirens,, Birmingham, Ala. 102.5 sod applications. puts 800v, 20ma, 400v, 135ma. 9v, WBRE-FM 2.75 Wilkes- Barre, Pa. 98.5 about °ha,, speed 11 WBRL Baton Rouge, Lo. 98.1 powerrand of t3 00 PE -55 -Dynamotor unit: 12v In. 18 amp. W BT-FM area down, tb, 500v out. 200 ma. FOB Chicago only 3.75 Charlotte. N. C. 99.9 sturdy unit will constantly ape.- WBTM-FM Danville. Va. 97.9 leaned PE -208 -Inverter unit, rotary converted, 28v WBUZ with 200 lbs. ded aeight-THAT'S POWERS in, 80v at 500VA, 800 cy. out. FOB Bradbury tits., Md. 96.7 coient high wide Chicago only 3.95 WBYSFM Canton. Ill. 100.9 ow stu4 i, /g -dIon, WBZ-FM by 3/160 diameter. and runs In If-ligning Dyf -32A -Each 95e. Three for 2.00 Boston Mass. 92.9 timing bearings. Designed for 110 -20 volts. 50.800oil. W BZA-FM Springfield. Mass. 97.1 y lea. A.C. ly. Shp. Wt. 2 lb DM -53 -Dynamotor, used with the BC -733 WCAC ITEM NO. 147 24v in. 240v, 60ma out. New 2.95 Anderson. S. C. 101.1 YOUR PRICE $1.95 WCAE-FM Pittsburgh, Pa. 96.1 WCAO-FM Baltimore, Md. 102.7 ULTRA MAGNET SURPRISE PACKAGE WCAP-FM Asbury Pork, N. J. 107.1 LIFTS MORE THAN 20 TIMES 20 pounds assorted radio parts. A $1.95 WCAR-FM Pontiac, Mich. 99.5 ITS OWN WEIGHT $25.00 value for only WCAU-FM Philadelphia, Pa. 98.1 LITTLE GIANT MAGNET WCBC-FM Anderson, Ind. 106.3 Lifts 5 lbs. easily. Weighs os. WCBS-FM New York, N. Y. Made of ALNICO slew high- moirnetlo OUTPUT TRANSFORMER 101.1 eel. Complete with keeper. World' WCBT-FM Roanoke Rapids, N. C. 98.5 most powerful magnet ever made. BI -FI. Used ln Scott -made Navy receiver. Fully WCEC-FM Rocky Mount. N. C. 100.7 The xperimenter and hobbyist will potted. 5000 hid hundreds of excellent use. for Pri. ohms. output secondary 800 ohms WCEDFM DuBois, Pa. 102.1 this high permanent feedback see. 60 ohms CT. quality magnet. $1.49 WCFC Beckley, W. Va. 101.3 measures 1% i4 . Ship. WI. CTLInverse WCFL-FM inn. Chicago, Ill. 104.3 ITEM NO. 159 PE -117 UNIVERSAL POWER SUPPLY WCFM Washington, D. C. 99.5 YOUR ram. $1,25 WCFR Fall River, Moss. 93.5 6 or 12v input; out. 145v and 90v, less vibrator. voltage WCHA-FM Chombersburg, Pa. 95.9 GENUINE MICROPHONE TRANSMITTERS regulator and rectifier tube; ideal mobile WCIL-FM power supply unit; excellent condition. FOB Chicago Carbondale, Ill. 100.7 Regular telephone trans- only. Each WCLC-FM Clarksville. mitters taken from large 52.95 Tenn. 106.7 telephone aUpyply company's WCLO-FM JanesvilleJanesville, Wis. 99.9 overstock. Work perfectly BC -709 INTERPHONE AMPLIFIER WCLT-FM Newark. onr d cella. Can be 100.3 on P.A. systems. call Ideal for aircraft, booster for telephones, WCM I-FM Ashland. Ky. 93.7 inter-communica- etc. FOB Chicago only $3.49 WCMW-FM Canton, Ohio üvstems.mt° Beta. short -line tele. 94.9 phone circuits. house -to- WCNB-FM Connersville, Ind. 100.3 farm -to -farm VHF TRANSCEIVER WCNT-FM Centralia, III. 'phone lines.. also to talk 96.5 throughru concealed own radio Ideal substitute for SCR -522, freq. range 140 -144 mc. WCOA-FM Pensacola, Fla. 98.9 as gstal controlled. 10 watts. The receiver section has WCOD Richmond. Va. 98.1 lck'up. Useful replace - two individual RF sections. enta on hattery.operated feeding a common 3 stage WCOH-FM Newnan, Ga. 92.3 10ine IF amplifier. Both RF sections may be operated rural telephone linea. simultaneously, or either WCOL-FM Columbus, Ohio 92.3 THESE ARE GENUINE one individually. The receiver WCON-FM MADE HY unit has 13 tubes. Tite transmitter is of straight Atlanta, Go. 98.5 KELLOGG. WESTERN E,.F.(TRICh AND STROMBERG. forward design. Transmitter unit has 7 one WCOP-FM Boston, Mass. 100.7 CARLSON. excellent in appearance and peration A tubes, remarkable =832 as finsi modulated by a pair of 6L6 and push - WCOU-FM Lewiston, Maine 93.9 ius and on seldom offered le WO pull. Complete unit in case with tubes, crystals times. Ship. Wt. Ialb. diagram and W COV-FM Montgomery, Ala. 94.5 less dynamotor. YTOEUR PRICE EXCELLENT CONDITION 1$14.95 WCRS-FM Greenwood. S. C. 95.7 $1.95 WCSC-FM Charleston, S. New Phantom Antenna for above unit; 3 lamps C. 96.9 in parallel with sockets, complete for 95c. WCSI Columbus, Ind. 93.7 WATTNOUR METER WCTC-FM New Brunswick. Completely overhauled and SMASH VALUES IN N. J. 98.3 ready for Immediate COMMAND EQUIPMENT WCTS Cincinnati, Ohio 01.9 reentere 11`00. BC- 453 volt. BO cycle 2.wire A.C. -EXC. $ 12.95 WCTW New Castle. Ind. 03.1 BC- 454 -EXC. *3.95 -NEW 4.95 BC- WCUM Cumberland. Md. 02.9 1p` ires from hethe lineand 455 -EXC. 7.95 WCVS-FM Springfield, 1 wires to the load. Sturd- BC -456 -NEW 2.95 III. 02.9 ily constructed84yhgh. BC -457 -NEW 8.95 WDAEFM Taripa, Fla. 05.7 mtace. á0/ BC -458 wide. 50 deep. weetinghouN,in WDAK-FM -NEW 7.95 Columbus, Ga. 07.9 G. Wayne. BC -459 -EXC. 9.95 WDBJ-FM Roanoke. Va. 94.9 theFort ilsb She. BC -696 -EXC. Wt. 14 Ins. 11.95 WDBQ Dubuque, Iowa 03.3 WDET-FM ITEM CONDENSER Detroit. Mich. 01.9 YOUR PRRICE.... WDHN New Brunswick, N. J. 93.5 $5.95 2 SIFD, 9400000 , Pyranol 2.99 ea. y(LBFM Marshfield, Wis. f10.0Ó 03.9 AMAZING BLACK LIGHT!! WDNC-FM Durham, N. C. 05.1 Powerful 250 -Watt WDOS-FM Oneonta, Ultra -Violet Source GEARED TUNING DIAL N. Y. 99.1 Thehe best and t 5 WDRC-FM Hartford, Conn. 93.7 source !practical band, vernier. BRAND NEW. Frequency Range: l experimental andId enter-enter- 3.2-4; - WDSU-FM New Orleans. La. 105.3 6.4 -8; 12.8.16; 19.2 -24: 25.6 -32. Ideal $1.39 WDTR tainment Makes Room. - for many applications. An exceptional buy Detroit. Mich. 90.9 rent nub/dances brilliantly luml- WDWS-FM Champaign, Ill. 97.5 NO t of y ndent. Nded. Fits a sr dard APS-13 UHF ANTENNA WDXY Spartanburg. S. C. 100.5 lamp socket. Bringsó out beau- W EAU-FM Eau Claire, Wis. tiful opalescent hues In v ioun Suitable for 400 mc citizen band. ideal for UHF 94.1 110e` of materials. Swell for experimenter.- With director and reflector WEAW Evanston, Ill. 105.1 amateur niqulees. effects elements mounted. BRAND NEW. 2 for.. $1.49 W EBC-F M Duluth. Minn. 92.3 lighting W EBO-FM Harrisburg, utb only. Shp. Wt. 2 Ins. BC-659 TRANSMITTER -RECEIVER UNIT III. 99.9 ITEM NO.57 WEBRFM Buffalo, N. Y. 96.9 YOUR PRICE s95 FM transmitter-receiver, crystal $1 controlled, two chan- WEED-FM Rocky Mount, N. C. 92.1 nels, freq. range 27 -30.9 mc. 13 tubes 2$16.95 crystal.. NEW W EEI-F M Boston, Mass. 103.3 WESTERN ELECTRIC BREAST MIKE WEEU-FM Rending Pa. 92.9 BC WEEX cr ft (carbon microphone.te.`Itgweighs -620 TRANSMITTER- RECEIVER UNIT Easton. IPa. 98.3 only 1 lb. WEFM Chicago, 111. 99.5 muse comma with breastplate FM transmitter- receiver, crystal controlled, two chan- mounting 2-way i nels, freq. range 20 -27.9 me. 13 tubes, dual meter WEHS Chicago, Ill. 97.9 dluetment so that it can be for testing filament and plate circuits. Used. WEI M-FM Fitchburg, Mass. 104.7 to any position. good ;9.95 TBluntedhere are 2 woven straps: a goes WELD Columbus. Ohio 97.1 around eck.° other around Mobile Installation Kit for BC -859 or BC -820 consists WELI-FM New Haven, Conn. 107.9 can of -13; tofStraps kly ingenious TS SEP -48; 4 section whip antenna, WELL-FM Battle Creek. Mich. 102.1 insulators, 2 maintenance $12.95 manuals; NEW. WEMP-FM Milwaukee. Wis. 94.1 This for I broadcasting WENE-FM Endicott, R. Y. 101.7 private communication WENR-FM Chicago, III. 94.7 nting can be used It WENY-FM Elmira, N. Y. 106.9 Comesompedclte with 6-foot cord WEOL-FM Elyria, Ohio 107.3 and hard rubber Finished ereralzed oleo, Shipping 2ntbs WEPM-FM Martinsburg, W. Va. 94.3 ITEM NO. 152 FREE! ERC-F M W Erie, Po. 99.9 YOUR PRICE Our new $1.45 8 page catalogue featuring many excel WERE-FM Cleveland, Ohio 98.5 lent surplus values. Write for copy ESB-F M your today! W Bradford, Pa. 97.5 HUDSON SPECIALTIES CO. It's FI4EE! WESC-FM Greenville, S. C. 92.5 40 West Broadway, Dept. RE -4.48, Nor York WEST-FM Bethlehem, 7, N. Y. Pa. 107.9 I have circled below the number@ of the Item. I'm All shipments W EVR Troy, N. Y. 91.3 remittance or ros Chicago Los Angeles untes shipping11 npecl5ed. 2O°cc Deposit required ali rders. Mini WEW-FM St. Louis, Mo. 95.1 udel° is enclosed 1N0 C.Ó.D. California and emit ORDEes UNLESS `ACCOMPANIED WITH A DEPOSIT.) esidents ` please add regular WEWS-FM Cleveland. Ohio 102.1 lance. tax ourllremit OR my deposit of S IN enclooed (209 ° WEXL-FM Royal Oak, Mich. 104.3 Ired). Ship order C.O.D. for balance. NO C.O.D. OR DERS FOR LESS THAN 55.00. DE SURE TO IN- W FAA-F M Dallas, Tex. 97.9 CLUDE SHIPPING SALES, INC., Dept. R WFAH Alliance, Ohio 101.7 Circle No. MAIN OFFICE: WFAM Lafayette. Ind. 95.1 159 SO 57 132 33 1712-14 W FAS-FM White Plains, N. Y. S. Michigan Ave., Chicago 5, Illinois 103.9 Name NORTH SIDE BRANCH: WFBC-FM Greenville, S. C. 93.7 WFBG-FM Altoona; Pa. 1902 N. Humboldt Ilvd., Chicago. 103.7 W FBL-FM Syracuse, N. Y. 93.1 Address WEST COAST BRANCH: W FB R-FM Baltimore, Md. 101.9 nNN Runt CINr17 1260 S. Alvarado, Los Angeles, Calif. WFHA New Britain, Conn. 103.7 City State WFHR-FM Wisconsin Rapids. Wis. 103.3 RADIO -ELECTRONICS for FM 81

STATION LOCATION FREQUENCY ONLY $99.50 IS THE COST! You CAafí:'JAtch these WF1L -FM Philadelphia. Pa. 102.1 WFIN -FM Findlay, Ohio 1003 l'IfiP/CfI Wiles/ WFJS Freeport III. 102.5 IN!It WFLA -FM Tampa. Fla. 93.3 WFLN Philadelphia, Pa. 953 ELECTRIC MOTOR SCOOP! WFLY Troy, N. Y. 92.3 WFMF Chicago, III. 100.3 11 S -volt 60 cycles WFMI Portsmouth, N. H. 107.3 Get tille motor and make the WFMJ -FM Youngstown, Ohio 105.1 handiest tool on your workbench! WFML Washington, Ind. 106.5 Attach a flexible shaft and you're 98.1 all set for grinding. sanding and WFMR New Bedford. Moss. hufne operations. Great for WFMU Crawfordsville, Ind. 102.9 model- makers. 1/20 h.p. motor WFMY Greensboro. N. C. 97.3 turns at 2900 RI.3h -does the job WFMZ Allentown, Po. 100.7 in half the time! yr" shaft. %" WFNC -FM Fayetteville. N. C. 98.1 long. 34 x 2%' x 354" high: WFNF 107.7 neighs only 3ïi lbs. May he Wethersfield, N. Y. used for many motor applications. WFNS -FM Burlington. N. C. 93.9 WFO8 Fostoria, Ohio 105.5 $3.95 WFOW Madison. Wis. 104.9 WFPG -FM Atlantic City, N. Y. 98.5 METAL UTILITY CABINET WFRO Fremont, Ohio 99.3 for the SENSATIONAL -NEW- IMPROVED WFRS Grand Rapids. Mich. 92.5 Shady steel cabinet. com- WFTW -FM Ft. Wayne, Ind. 103.7 10 INCH plete with handsome front WFUV New York. N. Y. 90.7 panel for construction of WGAA -FM Cedartown, Ga. 96.1 vacuum tube voltmeter. WGAL -FM Lancaster, Po. 101.3 WGAN -FM Me. 101.9 KIT May be used for other test Portland. TELEVISION WHAS -FM Louisville. Ky. 99.7 equipment. amplifiers. WGAY -FM Silver Spring. Md. 102.3 Complete with new built -in pretuned and =Milers. etc. 8" wide. 10" WC,BA -FM Columbus. Go. 95.1 aligned 13 Channel tuner, all parts and easy hlgh,7 "deep. WGBG -FM Greensboro. N. C. 100.3 step -by -step instructions and schematics. Black crackle WG81 -FM Scranton. Po. 101.3 $99.50 less tubes finish $1. 9870 WrIBR -FM Goldsboro, N. C. 93.3 WGBS -FM Miami, Flo. Kit. complete with all tubes $149.50 WGCH Greenwich, Conn. 95.9 Specially designed cabinet for kit 25.00 101.5 W.CM -FM Gulfport. Miss. An amazing value! Keen beginner can assemble one WGFM Schenectady. N. Y. 99.5 of these fine. new Improved television kits. Vera tile 3 -Inch Scope Shield WGH -FM Newport News, Va. 96.5 new 13 channel tuner. prewlred and factory aligned WGHF New York, N. Y. 101.9 for the entire television spectrum. High quality parrs I)edmted for either front or rear WGNB Chicago, Ill. 98.7 and excellent circuit assure perfect performance. Cir mounting. 9" overall. Black. cor- cult designed by outstanding T.V. engineers. Contains tube W .NC -FM Gastonia, N. C. 101.9 1tF otage. and mixer. Uses new I.F. coils ro tun -proof metal. Improves N. Y. 93.5 oscillator $oast inn and protects from WGNR New Rochelle, providing maximum gain and picture definition. Sound damage. MA -2075. WHOP -FM Hopkinsville, Kv. 98.7 reception is high quality FM for years of listening WGOR Ft. Lauderdale, Fla. 106.5 pleasure. wGOV -FM Valdosta, Ga. 92.5 Same quality and features far 7" KIT complete. 69c each WGPA -FM Bethlehem, Pa. 95.1 less tubes $59.50 94.1 Complete, with tubes 99.5n WGST -FM Atlanta, Ga. Specially designed cabinet for 7" kit 21.00 WGTM -FM Wilson, N. C. 106.7 FM and AM This Alt can be used with Sylvania IO HP4 10' pic- Iron Core WGTR Worcester, Mass. 99.1 ture tube without modifications. IF TRANSFORMERS WGUY -FM Bangor, Me. 93.1 7' and 10' KITS AVAILABLE FOR IMMEDIATE WGYN New York, N. Y. 97.9 DELIVERY FROM STOCK! Highly eMclent for new construction and replacement. WHA -FM Madison. Wis. 88.7 111 -t! adjustable Iron cores provide high selectivity and WHAD Delafield. Wis. 90.7 gain. Only 254 "x14," square- spade lug mounting. WHAI.FM Greenfield, Mass. 98.3 The New Model 2201: Ste IP Transformer 49e ea. SIA- 10.7 Pa. 105.3 NIA -2n39 I:$5 KC IF Transformer 35e ea. WHAT -FM Philadelphia, TC -75 TEST C RA FT WHAV -FM Haverhill, Moss. 92.5

WNB -FM Kansas City. Mo. 102.1 A COMBINATION TRANSFORMER SET WHRC -FM Canton, Ohio 94.1 INTERCOM wHBF -FM Rock Island. III. 98.9 TEST SPEAKER sformer to match vit roil to grid. another Ws1PL -FM Sheboygan, Wis. 100.3 AND for 50L6 and similar output tutus. Roth of these tine 95.1 push- WHBS -FM Huntsville, Ala. units PLUS momentary DPDT spring Mum Ithaca. N. Y. 97,3 SIGNAL TRACER button en 'MI for les, than value M one transformer WHCUFM alone! These are smell. st rap-moonting transformers. WHDH -.M Boston, Mass. 94.5 WHEC -FM Rochester, N. Y. 96.5 plus speaker substitution plus field substitutor ONLY 98e FOR ALL THREE UNITS! plus stor il WHcB -FM Benton Harbor, Mich. 99.9 tester substitution Rochester. N. Y. 98.9 nl us eonldensere e WHFM plus resister substitutor plus anal tracer BRAND NEW WHHM -FM Memphis. Tenn. 106.9 plus conenser plus WHIO -FM Dayton, Ohio 99.1 substitutor nstagea audio amplifier METERS WHIP Silver Spring, Md. 103.9 pills output indi100cator output WHISFM Bluefield, W. Vo. 104.5 plus substitute V. transformeplus Dejar Model 810 meter for 100,7 D.C. power supply ham and teat WHK -FM Cleveland, Ohio including signal tracer probe and all -around 98.7 Complete applications. 10 ma MO mgHKC -FM Columbus. Ohio full instructions. basic movement. 31/4" di- WOKW Chilton. Wis. 89.3 A must for every radio serviceman and engineer. ameter lianas: 2% body. WHKY -FM Hickory, N. C. 102.9 1%" deep. Stock up on Niagara Falls. N. Y. 98.5 NET $29 .50 last. wHLD -FM these while they WHLI -FM Hempstead. N. Y. 98.3 IMMEDIATE DELIVERY FROM STOCK MA -2036 WHM 4 -FM Anniston, Ala. 1003 earls WI- INC -FM Henderson. N. C. 92.5 The New Model TC -50 $1.95 WHO -FM Des Moines, Iowa 100.3 TEST CRAFT wHOO -FM Orlando, Fla. 96.5 GRILLE CLOTH WHP -FM Harrisburg, Pa. 97.3 TUBE Never before at our low price! Highest quality. WHPE -FM High Point, N. C. 95.5 -tone cloth. styled to harmonize with golden grille i .11 e7 s+/HTN -FM Huntington, W. Va. 100.5 AND SET all cabinet designs. Generous 50' width. i Poughkeepsie, N. Y. 104.7 per yard WHVA WHYN -FM Holyoke, Mass. 93.1 TESTER VARIABLE CONDENSERS WIBA -FM Madison, Wis. 101.5 A complete laboratory. WI 80-FM Philadelphia, Pa. 94.1 .;,...'!ta all purpose test-In- Mich. 92.3 0 strument,trament. this - MA -996: 425 and 150 mmf section. com- W1BM -FM Jackson, tile combination tube plete with mica compression trimmen. WIBW -FM Topeka, Kans. 1023 . 4" 49e \ tester Has cable drum OO WIBX.FM Utica. N. Y. 96.9 ,-00.1. e curately allwill up- MA -940: SPECIAL! 3 -gang. 365 mmf Ind. 104.1 tubes. per section with hand -spread rotor for WIKY -FM Evansville, a'w to -date designed WIL St. Louis, Mo. 97.3 The multi -meter sec each section. Shafts have 2%. cable -FM tlon affords many drums. Ideal for communication re- WILA Woodstock. Ill. 92.1 necessary measure. ceivers 7M WILK -FM Wilkes -Barre, Pa. 107.3 ment. for everyday's WIMA -FM Limo, Ohio 102.1 service work. NA- 8825: 25 mint butterfly for high frequency Implica- WINX -FM Washington. D. C. .96.3 The New Model TC -50 Tube and Set Teeter com- tions. Rotor floats on ball bearings. Ceramic insulation. -FM Miami, Fla. 97.3 bines aoven instrumente, D.C.V., A.C.V., D.C.M.A.. deep 32e WIOD Measure. lei' square Ice WIP -FM Philadelphia. Pa. 93.3 Ohms. Output Meter, Decibel Meter and Tube Tester. MA -8830: 50 mud. same as above 32e Columbia. S. C. 94.5 Full scale accuracy to 2%. English Reading GOOD WIS -FM and RAD scale for testing tithes. Obsolescence reduced WISC -FM Madison, Wis. 98.9 to absolute minimum. Simple and quick reading charts ORDER FROM THIS AD! WISE -FM Asheville, N. C. 102.5 for tube tenting. Multimeter section affords most pop- Send 25% deposit with order. Pay balance plus postage on WISN -FM Milwaukee, Wis. 102.9 ular everyday's measurements. delivery. Get your name on Mid- Amerlci a select mailing WISR -FM Butler, Pa. 97.7 Complete with teat leads, tube charts and all detailed, list and get first crack at latent, greatest values in radio WIST Charlotte. N. C. 104.7 operating instructions. part., electronic equipment. tithes. etc. Send orders to WITH -FM Baltimore, Md. 104.3 Size 8 x low 5' NET $39.50 Desk RC -49. Minimum order $2.50. Urbano Ill. 91,7 WIUC IMMEDIATE DELIVERY FROM STOCK WIZZ Wilkes -Barre. Po. 103.3 -FM Johnstown, Pa. 95.5 WJAC All orders filled same day received W J A R -F M Providence. R. I. 95.5 WJAS -FM Pittsburgh, Po. 99.7 WJAX -FM Jacksonville, Fla. 95.1 ELECTRONIC F. STORE WAREHOUSE W18C -FM Bloomington. Ill. 101.5 911¢thopolitan INSTRUMENT CO. 2412 S. Michigan Ave. 2307 S. Archer Ave. WJBK -FM Detroit, Mich. 93.1 Ch,s,go Is, in Chleaeo 16. III. WJBY -FM Gadsden. Ala. 103.7 RC-4 WJDX -FM Jackson, Miss. 102.9 iradiliklialiMMIMINII APRIL, 1949 RA1 821 NEW! STATION LOCATION FREQUENCY W1EJ-FM Hagerstown, Md. 104.7 $i The Dollar Corner W1EM Springfield, Ohio 103.9 Different! W1HL-FM Johnson City, Tenn. 100.7 u Down to- WJHP-FM Jacksonville, Fla. 96.9 ALL ITEMS $1 Postpaid I W1IZ Get your llar's worth and much more at sois Hammond, Ind. 92.3 dollar radio bargain counter! WJJw Wyandotte, Mich. $i 103.1 RCA earth! W1LB-FM Detroit, Mich. 97.9 $1 954 Acorn Tubes 3 for $1.00 si METER WILD-FM Birmingham, Ala. 104.7 RECTIFIERS, full wove, lov- 3Omo W1LK Asbury Pork, N. J. 94.3 3 for $1.00 WJLS-FM Beckley, W. Vo. $1 MALLORY 550 C, 6Volt sync. 99.5 Vibrators J W1MC-FM Rice Loke, Wis. 96.3 si $1.00 $1 COAX F WINO-FM West Palm Beach, Fla. 98.7 ITT INUGG-S M/3U5 9, UG -21 /U,

UG , 1 . s1111 WJPF-FM Herrin, III. 98.5 00 3 $11.000 Si BC , W1PG-FM Green Bay. Wis. 101.1 87O . 2nd, oor WJPR-FM Greenville, Miss. 101.9 $I ARC -5 BFO COILS, 85kc, I415kc, 2830kc WIR-FM Detroit, Mich. 96.3 3 for $1.00 WJSW-FM Altoona, CERAMICONS asst. sixes Pa. 96.5 $i 8 for 51.00 W1TN-FM Jamestown, N. Y. 93.3 $1 W1W-FM Cleveland, Ohio 104.1 BARGAIN RADIO, Dept DB -2 WJZ-FM New York, N. Y. 95.5 $1 249 N. Juanita, Los Angeles 4, California WKAP-FM Allentown, Pa. 106.3 WKAR-FM Eost Lansing, Mich. 90.5 W KAT-F M Miami Beach, Fla. 93.1 WKBH-FM LaCrosse, Wis. 93.1 WKBN-FM Youngstown, Ohio 98.9 GREYLOCK WKBR-FM Manchester, N. H. Now ready for delivery! 100.1 A DEPENDABLE NAME IN WKBZ-FM Muskegon, Mich. 106.5 WKID-FM Urbana, III. 103.3 RADIO TUBES WKIL Kankakee, Ill. 100.7 PRACTICAL WKJF Pittsburgh, Po. 93.7 GT, Glass, and Miniature Types WK1G-FM Ft. Wayne, Ind, 106.1 All Tubes in Individual Cartons WKMO-FM Kokomo, Ind, TELEVISION 99.9 5 304 12SA7GT SERVICING WKNP Corning, N. Y. 106.1 185 3V4 12SK7GT By J. R. Johnson and J. H. Newltt WKOK-FM Sunbury, Pa. 94.1 375 pages, 6 x 9, over 230 Illustrations WKPB Knoxville, Tenn. 93.3 1U 6BA6 (and many 9 W K PT-F M 3S4 6BE6 others) each Price only $4 Kingsport, Tenn. 98.5 WKRG-FM Mobile, SPECIAL OFFER! All 39e tubes may be purchased Ala. 99.9 In At Ia.L you can get a book that really gives you the WKRS loti of 100 assorted, at $35 per 100. low -down Waukegan, Ill. 106.7 on television servicing -one that tells step by WKRT-FM Cortland, N. Specials: step what to do and also guides you specifically Y. 99.9 2E24 .. 89c 6BG6G .. 89c on pre- WKST-FM New Castle, Pa. cautions to take and the mistakes to be avoided. PRAC- 101.1 TERMS: Net C.O.D., F.O.B. N.V.C. TICAL TELEVISION SERVICING is all the name 1m- WKWK-FM Wheeling, W. Va. 97.3 Minimum order Sá.00. plies -a complete, down -to -earth working manual for those WKY-FM Oklahoma City, Okla, 98.9 Write for Bargain who want Catalog C -4. to understand television servicing fully. get WKYC Paducah, Ky. 93.3 straightened out on the vast amount of MISlnformation Greylock Electronics that WLAB Lebanon, Pa. 104.1 Supply Co. is creeping into the television picture, and really WLAD-FM be able to do television servicing. Danbury, Conn. 98.3 30 Church Street New York 7, N. Y. WLAG-FM LaGrange, Go. 104 I WLAL Shows Exactly How to do the Lakewood, Ohio 104.9 Work! WLAN-FM Lancaster, Pa. 96.9 This Isn't a book of theory, mathematics and general WLAV-FM Grand Rapids, Mich. discussions. The 96.9 SURPRISE authors -one a radio editor, the other a WLAW-FM Lawrence, Moss. PACKAGE well -known engineer -actually owned 93.7 and operated a tele- WLBR Lebanon, Pa. Contains over 32.50 worth of vision service shop to get the specific, how-to -do Infor- 100.1 mation -it WLCS-FM Baton Rouge, rodio parts such as Superhet they now pass along to you In easily understood La. 101.1 Var -tond, form. In addition to a clear explanation of how television WLDM Detroit, Mich. 95.5 Elect Cand, Volume Cfl, Trans, components. construction and operation differ from radio. W LDS-FM Jacksonville, III. 100.5 Coils. Micos, they show exactly how to perfortn all specific operations In WLEE-FM Richmond, Resistors, Hdw, etc -5 troubleshooting, diagnosing Va. 102.9 ;01- and remedying television re- WL ET-F M Toccoa, Ibs. ceiver troubles. You don't bother with Ga. 106.1 ALL PARTSLisTED needless theory. WLEU-FM Erie, IN OUR CATALOG You are actually shown how to do the work! Pa. 97.9 Please enclose postage WLEY Elmwood Park, Ill. 107.1 RADIO MAKES TELEVISION REPAIRS EASY WLIN Merrill, Wis. 100.7 MAIL ORDERS WLIV Providence, R. I. 75 Barclay St., Dept. RE TO UNDERSTAND 107.7 WLLH-FM Lowell, Moss. 99.5 N. Y. 7, N. Y. Hero aro the subjects colered: W LOG-FM Logan, W. Va. 103.3 I. Television is Here 10. Test Equipment and WLOK-FM Lima, Ohio 103.3 2. Fundamentals of the Alignment WLOS-FM Asheville, N. C. 104.3 Television System II. Wiring and Repair WLOW-FM Norfolk, Va. 98.9 3. The Radio -frequency, Techniques WLPM-FM Suffolk, Va. 107.7 TELEVISION SCREEN VIEWING FILTERS Intermediate- frequency 12. Common Troubles in WLRD Miami Beach, Fla, 93.9 Make your own and Detector Sections Television Receivers WLSU Baton Rouge, Lo. 91.7 filters for only a few cents each. 4. Video Amplifiers 13. Troubleshooting WLTN Lewistown, Pa. 97.9 Different colors, all very easy and inexpensive fo 5. Cathode Ray Tubes 14. Servicing Hints and WLVA-FM Lynchburg, Vo. 97.5 make. Send 35(` for complete instructions. 6. Synchronizing and Case Histories WLWA Cincinnati, Ohio 101.1 Sweep Circuits 15. Color Television WLYNFM Lynn, Moss. 105.5 ELECTRONIC DEVICES CO. A. WMAL-FM Washington, D. C. 7. Power Supplies Intermediate Fie. 107.3 Box twenties of Standard WMAO-FM Chicago, Ill. P.O. 1016, Morgantown, W. Va. 8. Antennas and Wave 101.1 Receivers WMAR-FM Baltimore, Md. 97.9 Propagation B. Receiver Layout WMAS-FM Springfield, Mass. 94.7 9. Television Receiver Diagrams WMAZ-FM Macon, Installation C. Glossary Ga. 99.1 W M BD-FM Peoria, 111. 92.5 FACTUAL SERVICING DATA ON WMBH-FM Joplin, Mo. 96.1 TELEVISION RECEIVER WMBI-FM Chicago, III. -$1.00 Now to test 95.5 Complete Instructions for an intermittent peaking coil W M BR-FM for building your own television Jacksonville, Fla. 96.1 receiver. 16 11'a17' or transformer WM pages- of pictures. pictorial dia- How get BS-FM Uniontown, Pa. 105.7 grams. clarified schematics. 17'x22' complete schematic to a signal over untain WMCA-FM New York, diagram What to do when N. Y. 92.3 & chassis layout. Also booklet of alignment the linearityy of the picture WMCF Memphis, Tenn. 99.7 Instructions. Voltage & resistance tables and trouble- is poor shooting hints. -All for $1.00. How WMCP Baltimore, Md. 94.7 to WMFM North Adams, Mass. Checkinggu video aresponserlwith 97.5 CERTIFIED TELEVISION LABORATORIES a square wave WM FR-FM High Point, N. C. 99.5 Dept. When to use mica capacitors in placelace of other WMGK-FM McKeesport. C, 5507 -13th Ave., Brooklyn 19, N. Y. types Pa. 104.9 WMGM-FM New York, N. Y. 100.3 . and scores of other WMGW-FM Meadville, Pa. 100.3 practical problems WMGY-FM Montgomery, Alo. 107.5 W M I N-FM St. Paul, Minn. 99.5 FREE 10 DAYS SEND NO MONEY WMIT Charlotte, N. C. 106.9 WMIX-FM Mt. Vernon, Ill. 94.1 Send name and address for our free catalogue, JUST WMLL Evansville, MAIL COUPON Ind. 94.5 chock -full of standard brand radio and TV sets, TRIAL WMLN Mt. Clemens, Mich. 106.3 parts and equipment at rock bottom WMMW-FM Meriden, Conn. 95.7 bargain WMOB-FM Mobile, Ala. 97.5 prices. Dept. WMOH-FM Hamilton, Ohio RE -49, Murray Hill Books, III. 103.5 COMMERCIAL RADIO, DEPT. C 232 Madison Ave., New York IS, N. Y. WMOT Pittsburgh, Po. 94.5 Send me Johnson & Newitt's WMOX-FM Meridian, Miss. 98.5 36 Brattle St. Boston B. Mass. PRACTICAL TELE- WM RC-FM VISION SERVICING for 10 days' examination on Greenville, S. C. 94.9 approval. In 10 days I will send $4, plus a few cents WMRI Marion, Ind. 106.9 postage. or return book postpaid. Postage paid on WMSAFM Mossena, N. Y. 105.3 cash orders; same return privilege. (Books sent on WMUN Muncie, Ind. approval in U.S. only. Price 104.1 WANTED outside U.B. 34.50 post- WMUR-FM Manchester, N. - - paid). H. 95.7 WMUS-FM Muskegon, Mich. 100.5 RADIO MECHANICS At least 2 yes.' mechanics WNAC-FM Boston, Moss. 98.5 experience Name on aircraft radio equipment WNAD-FM Norman, Okla. 90.9 WNAE-FM 2nd class F.C.C. Radio- Telegraph Lie. nec. Address Warren, Pa. 92.1 Amateur Radio License desirable WNAM-FM Neenah, Wis. 98.5 Apply 11-1 Mon. tltru Fri.. or write City, Zone. State WNAO-FM Raleigh, N. C. 96.1 PERSONNEL DEPARTMENT WNAV-FM Annapolis, Md. 99.1 PAN AMERICAN WORLD AIRWAYS Occupation New WNBC-FM York, N. Y. 97.1 LaGuardia Field Long Island, N. Y. WNBF-FM Binghamton, Brrr rr ======rrrrr rrrrr N. Y. 100.5 or phone HAvemeyer 448400, ext. 503 (N, Y.) RADIO -ELECTRONICS for FM 183 CONVERT DIRECT VIEW TV TO WNDB-FM Daytona Beach, Fla. 94.5 RUSH YOUR ORDERS IN! WNDR-FM Syracuse, N. Y. 102.5 WNEX-FM Macon, Ga. 96.9 PROJECTION TELEVISION WNHC-FM New Haven. Conn. 93.1 TELEVISION TUBE, #6C4 .19 WNIO 106.5 Uniontown. Pa. 30 KY RF POWER Damen ONE POUND ROSIN SOLDER ,S9 WNJR-FM Newark, N. 102.7 J. SUPPLY Mons: WNLC-FM New London, Conn. 99.5 Length 14 ". ANTENNA HANK. IS ft. on spool .09 WNN1 Paterson. N. 1. 103.5 Width II ". WNOW-FM York, Pa. 105.7 Height LINE CORD, 6 ft. with plug .12 WNYC-FM 11'.'4' New York, N. Y. 93.3 TOGGLE SWITCH, SPST .15 WNYE Brooklyn. N. Y. 91.5 WOAI-FM Son Antonio, Tex. 102.5 TOGGLE SWITCH. DPST .25 WOAK Ook Park, Ill. 98.3 WOAP-FM Owosso, Mich. 103.1 RESISTANCE CORD. 150 ohms .29 WOAY-FM Ook Hill. W. Va. 94.1 RESISTANCE CORD. 180 ohms .39 WOC-FM Davenport. Iowa 1037 New Improved WOCB-FM West Yarmouth, Mass. 943 unit of exceptional A.C. -D.C. CHOKE. 50 ma 10 by .29 96.1 WONS-FM Shelby. N. C. regulation. Has a focus WOKZ-FM 99.9 OUTPUT TRANSFORMER (2- 25L6) .36 Alton, III. control pot built in for use with WOL-FM Washington, D. 98.7 C. STP4 Tube. Voltage variable from 77 to 30 KV. VOL. CONTROLS. w/s 50K & 1/2 meg. .39 WOMI-FM Owensboro, Ky. 92.5 Supply utilizes 6 tubes. WOPI-FM Bristol, Tenn, 96.9 VOL. CONTROLS, w/s I & 2 meg .39 WOPT Oswego, N. Y. 104.7 Nef price, including DC Power Supply..S99.50 WOR-FM New York, N. Y. 98.7 RADIO CHASSIS, with 8 sockets .39 WOSH-FM Oshkosh, Wis. 92.9 SPELLMAN F1,9 VAR. CONDENSER, 420/420/420.... .95 WOTW-FM Nashua. N. H. 106.3 WOWO.FM Ft. Wovne, Ind. 96.1 PROJECTION G.I. TWO SPEED MOTOR .. 4.95 WPAD-FM Paducah, Ky. 96.9 L.P. PICK -UP 3.75 WPAG-FM Ann Harbor, Mich. 98.7 TV LENS -CRYSTAL WPAM-FM Pottsville, Pa. 95.5 WEBSTER XTAL CARTRIDGE L45 WPAR-FM Parkersburg. W. Va. 06.5 Dimensions: Length WPAY-FM Portsmouth, Ohio 04.1 7". Diameter 41/4" WPDX-FM Clarksburg. W. Va. 95.1 Fl.9 EF.5 in. 1127.0 ASSORTMENTS 100 OF EACH WPEN-FM Philadelphia, Po. 02.9 m.) This lens in- WPICFM Sharon, Pa. 02.9 corporates in barrel a corrective lens for use with 100 -CONDENSERS. .001 to .02.... 3.95 WPIT-FM Pittsburgh. Pa. 01.5 a STP4 projection tube. It is easily removable for 1.50 WPJB Providence, R. I. 05.1 use with flat type tubes. Lens can be utilized to 100 -RESISTORS. 1/2 watt WPLH-FM Huntington. W. Va. 02.5 project picture sixes from several inches to 7 x 100 -SOCKETS, octol, loctol, min 4.95 WPMD-FM Frederick, Md. 01.5 9 feet. Complete with mounting ring. Machined WPOE Elizabeth, N. J. 96.7 slotted Mounting Ring avail- only 90 100 -PILOT LIGHTS. #44, 47, 49, 51 4.95 WPPA-FM Pottsville, Pa. 01.9 able for hand focusing adjust- and push on 4.95 WPRO-FM Providence, R. I. 92.3 ment. Has 4 holes for easy mounting on plate. 100 -KNOBS, screw W PTL Providence, R. I. 91.5 $8.00 extra. WOAM-FM Miami, Flo. 94.9 5TP4 PROJECTION TUBE CARTONS WOAN Scranton. Pa. 92.3 WODI Quincy, Ill. 105.1 KINESCOPE TUBE 100 -SMALL PEANUT, I "x1 "x21/8 " .75 WOOW-FM Washington, D. C. 103.5 Featuresdres eta WnXR-FM New York, N. Y. 96.3 ) backed white fluor- 100 -LARGE PEANUT, I "x1"x23/4 " .85 having WRAK-FM Williamsport Pa. 100.3 escent screen .95 i"R nL-FM Raleigh. N. C. 101.5 high brightness and 100 -GT TYPE. 11/4"111/4 "33W WRBL-FM Columbus, Ga. 93.3 ,Jcontrast. Net Price $67.50 100 -SMALL G. II/2 "x11/2 "x41/2" 1.25 W RC-FM Washington, D. C. 93.9 Conreraion diagram supplied milk pate. Please specify WRCM New Orleans. La. 97.1 type of TI' art. 100 -LARGE G. 2 "x2 "x5" 1.45 WREN-FM Topeka, Kansas 94.1 Include 25% Deposit with order, Balance C.O.D. WREV Reidsville, N. C. 102.1 WRFL Winchester, Va. 92.5 SPELLMAN TELEVISION CO., Inc. Dept. B, 130 West 24 Street, New York 11 BROOKS RADIO DIST. CORP. 80 VESEY ST., DEPT. A, NEW YORK 7, N. Y.

H. F. ANTENNAE AN -130, snort Flea 21.75 DYNAMOTORS TRANSTATS Base, 121/2 L, Approa. 235 Input Output Radio AT-5, ARR1. with Low-Loss 11.5 KVA: Input U -115 1', s,0 -60 C)'fle. Maximum OIIL- TYpe Volts AMPS Volts Amps Set Price' ANTENNA, AN '100-A. for RC 103 $3.00 put: i15 . 100 amp. All units are new, guaranteed, ANTENNA. AN 104 -A. for SCR 522 51.75 PE 86 28 1.25 250 .060 RC 36 83.05 599 50 each 3311 18 15.91N 6- SECTION CERAMIC CAPACITOR. 10.960 mmf (Collins DM 416 14 6.2 .170 RU 2 KVA: 90 -130 v input, 50 -60 cycles. output 116 rolls. $ . DV2 /AR R -2 8 1.1 250 .066 ARC -5 4.75N 2 1:t A T)'pr llli Ainr riran $29.95 each ac J06'Á ANTENNA LOADING UNIT for BC 375'23.75 ea. DM 36 28 1.4 220 .080 SCR 508 8.75N POWER SWITCH. Poe. 80 amps, 800 . Arrow DM 53AZ 14 2.8 220 .118U BC 733 7.00N HAY 54.25 Ro7ARr vac. motor. 4 ewrk ImP PE 73CM 28 19 1000 .350 liC 375 N sARK GAP. 24 el.,. DM 21 14 3.3 235 .090 BC 312 3.45N NBFM -465 KC DISCRIM XFMRS. PEés e68[ wP108'1 10 ide. 84 diem. roux 5aó 312 3.45N iiPi. wr. DM 21 CX 28 1.8 235 .090 BC FOSTER -SEELEY CALE ASSE . 45 pr. 102W L. Telephone wpe DM 25 12 2.3 250 .050 BC 367 2.49LN WITH CIRCUIT -w88039 220,000 per lens,. 1.25 275 .070 BC 348 8.95N SONAR SouNO DETECTOR: Underwater detector with DM 28R 28 DIAGRAM. $2.50 EA. microphone units eased In rubber sheath. Mohr, DM 3M 28 7 540 .250 BC 456 5.50N DM 42 14 46 515 .110 SCR 508 8.50LN mr452N Aaimuth control box for aircraft radio compass 1030 .050 AUDIO TRANSFORMERS 51.25 2/9 TRANSFORMERS for Collins ARTI3 Transmitters, CF. ARC3 AUDIO COMPONENTS .7472063- GE .7472065, PE 101C 13/26 1 "_.6 400 .135 SCR 515 5.25N 6.3 800 .0211 T -101, .53545 1-104. 355547 T -105. - BD AR 93 28 3.25 371 .150 4 95N T -102. .55545 :55554 BAND PASS FILTER 23350 27 1.75 285 .075 APN -1 3.511N T- 103..55548 T -206, a55320 35X045B 28 1.2 950 .000 3.50N Prise, aaeh $.95 1/70473. Sham band pass peaked at ZA .0515 12/24 4/2 500 050 3.95N MOD NP5IR: I'P 007'5 to PR. 807'. CL. "C' $1.65 700 cps. Band -width: 650 cycles at 20 ZA .0518 12/24 8/4 12/275 3/.110 5.50N DRIVER ZE5tR: 6v6 Driver to PP 811 Grid. $1.45 db. Down from peak. High -to -high B.I9 pack 12 9.4 275 .110 Mark II 9.95N UNIVERSAL OUTPUT: Ameriran Sileor. PSI: 250000/ Impedance. Can be plugged into 'phono 500 .050 18.000/5000/4000 ohms. Sec: 500/15/7.5/3.85 ohms. 30db. output of receiver for good reaulta. D -104 12 225 .100 14.95N e0ntin. Flat to 17,000 CY $4.75 Cuts out QRM New. with circuit dia - 440 .200 POWER CHOKES gram $2.25 DA -3A 28 10 sun .090 SCR 522 8.95 1 150 .010 Swing. Choke: 4.5 .116 hy. 15 amp. $ 4.50 14 5 .5 to .8 hy: .2 to .01 hy. 2.5 amp. 1.50 COAX CONNECTORS .35 031SP u0 21 U .5053 29 1 4 750 .060 APN -1 3.95X I amp...... $10.95 h ^..35 p. 7.50 ... 5.35 5 e5 00255 /u.. , .$1.25 BON .03 by 2 amp. 1.45 Dual 2.5 hy, 130 ma 1.25 831AP.....35 Oa 86/U 95 UG14e U.. , , 1.00 DA -7A 26.5 1100 .400 TA -23 25 .... 831141...... 15 uS 13 128 400 .135 17.50N 8.5 hy. 125 ma. ... 1.50 .1 hr, 12 amp.. 46 254/0.... 75 0005 /U 1.25 CW 2IAAX Nemeoen male to type 65 1.10 _ 16.00 'N" male adapter 28 6.3 800 .020 25 by. ma. ohms ...... D-166366 Roby $1.25 9 6 hy. 150 ma. .. 1.50 Dual .5 by. 380 ma. .95 .e5 1.12 Adapter Cable Assay. Type Male to Type N" BD 77KM 14 40 1000 .350 BC 191 N Dual 7 hy. 75 ma. 11 5 hy. 40 ma. 312 ohms .65 Female N 2,25 14.00LN hy. 60 ma. 1.65 2 hy. 200 ma. .75 Adapter Coble Aeay Sperrrrrr Male Type 'N" Male 2.25 PE 94 28 10 .260 15.00N Dual 2 hy, 100 ma. .75 Dual 120 hy. 17 ma 2.45 Connector, x49379 for PG 18 /U to 1.80 300150 010 522 14.5 .5 CERAMICON CONDENSERS COAX CABLE RG 9 /V. 52 ohms 5 IN--New. LN-T.ike New. Filter Box dr Relaya $7.50 per 100 Rc l7 /V. s2 bm Imp, Replacement dynamotor* filter box f 12.00 5úii: 3 mmf 5% 60 mmf 0C AND GENERATORS RG 3 i V: twinGoa :m{ssaohm Im . armored..... so 4 mmf +5% mmf x-22% Rc 2rin s0 ohm n. v, 60 ma; 8s,, 2.5 A. New. with hand crank. imp. V ulse eahle. Corona min. GN 35: 350 4 mmf ±5 mmf 120115 mmf ±5% starting voltage 17 1Ey Sont. $con. 8.5 mmf ... mmf 120 mmf ±3% RG 57 /U. ohm imp. armored sont. 5 RG 57 /U, 95 ohm GN 45: as V. 100 ma; 6v. 3 amps. Slight use. ex. 15 mmf ±.5% 240 mmf 3% Imp. twin coax Js /n. with cranks .. .. $12.50 15 mmf -I-^ 5 mmf _50 mmf INVERTERS 50 mmf .....- ... ±20% no mmf ±5% . . 1 CROSS POINTER INDICATOR PE 218 -E: Input: 25 -28 vde. .Silver-Mita Button Capacitors ID 24 -ARN -9 Dual 0 -200 microamp 92 snip. Output: 115 v. O movement In 3" etas. Each movemen 350 -500 cy. 1500 rollamps. (Erie, C00 slab) 59.50 per 100 brought out to 8 -term receptacle a t rear. Dim: 17' x 854' x 10'. New. 1A5 mmf .. -±2.5 mmf .. - Originally used in ILS equipment. 0 0 export packed ..$49.95 175 mmf ±2.5 mmf o a. New $5.5 PE 21844: Same all ahove. 500 mmf 4-lnr; 2A Type .. $10.00 except else: 1854 x 5 %' 10'. New $49 95 All merchandise guaranteed. Mall orders oily filled. All prices. F.O.B. New York City. PE 218 -N: Used good shipping Charges sent C.O.D. $25.00 131.0 Send Money Order or Check. Only PHONE ... PE 208: Input: 29 vde. 38 -í .mpg. Outpu BA .. 800 Liberty t. DIGBY Cy. 500 vo1L-emDe. Dl.5 Ï 13' I 5X4' x New COMMUNICATIONS EQUIPMENT CO. GE vogua:Input: ode. amp. m5115 r. Newilorkl,N.T 9-4124 400 Cy, 485 volt -amps. Dim: 9' x 4ys' diameter. MANUFACTURERS QUANTITIES AVAILABLE New 549.95

APRIL, 1949 811 FM

NOW! RAp{OSg STATION LOCATION FREQUENCY Low FACTORY -TO -YOU Prices oca r 75 F ,r W RGA-FM Rome, 106.5 Atit s cal CoaPl.,f R,rOMI, di Ga. WRGK LaGrange, III. 103.1 WRHI-FM Rock Hill. S. C. 97.5 Nao! M I DWEST "-_' Absolutely No Knowledge WRIN-FM Racine. Wis. 100.7 1 of Radio Necessary. You WRLD-FM Lanett. Ala. 102.9 Need No Additional Parts. The WRNL-FM Richmond, Va. 102.1 WRNY-FM Rochester, N. Y. 97.9 PROGRESSIVE RADIO KIT is the Only Coln WROL-FM TELEVISION Knoxville, Term. 97.3 píete Kit. Operates on 110.120 Volts AC /DC WROV-FM Roanoke, Va. 103.7 5 contains ¢ver ytn ne you need. lnstruc on book, metal WROW-FM Albany. N. Y. 93.9 cube., condensers. re,ston and all other C.C. WRSW Warsaw, Ind. 107.3 essarry radio parts. Thee 36-page Instruct, on Book writ- sic 75 che SCREEN ten radio engineers teaches WRUF-FM Gainesville, Fla. 104.1 You to radios in WRUN-FM Utica, N. Y. 105.7 les de o aprpovdes tellmanner.formance. eogether. fifteen circuits a. constructed, WRVB Richmond, Va. 94.5 Offer/nq 11 receivers, 1 audio amplifier 3 transmitters. WRVC Norfolk, Va. 102.5 WRWR-FM Albany, N. Y. 95.5 SPECIAL OFFER WRXW Louisville, Ky. 95.1 121/2" E, ectriñat and Radio Teter se t absolutely FREE WRZE York, Pa. 98.5 with each Prop restive Radio Kit. Plus FREE Mem. bershlp c the Propre e Radio Club. Entles you WSAI Cincinnati. Ohio 102.7 PICTURE TUBE to free experti advice and consultation service WSAM-FM Saginaw, Mich. 98.1 lice need radio technicians. ORDER YOUR KIT NOW! WSAN-FM Allentown, Po. 99.9 12 WSAP-FM Portsmouth, Va. 99.7 TELEVISION WSAR-FM Fall River, Mass. 103.7 CHANNELS BUILD KITS!! WSAU-FM Warsaw, Wis. 95.5 WSAV-FM Savannah, Ga. 100.3 WSB-FM Atlanta, Go. 104.5 PICTURE -HOLD SAVE!! LEARN!! WSBA-FM York, Pa. 103.3 CONTROL WSBF South Bend, Ind. 101.3 VACUUM TUBE VOLTMETER KIT $23.95 WSEL-FM Springfield- Mass. 101.9 Other Models Indude of (('Cl t you need for FM Montgomery, i` 9.,.,k on Adv..... vit servicing Techniques. WSFA-FM Ala. 103.3 SYMPHONY GRAND WSGN-FM Birmingham, Ala. 93.7 SMFM RADIO - TELEVISION- PHONOGRAPH 5 OSCILLOSCOPE KIT $39.95 WSHS Floral Pork, N. Y. 90.3 \ .n. .,,]] , for Imlay radioman. WSIC-FM Stotesville. N. C. 105.7 with NEW DUAL -SPEED RECORD PLAYER nle (lay oscilloscope. WSIX-FM Nashville, Tenn. 97.5 VOLT1OHM- MILLIAMMETER KIT $14.95 WS1S-FM Winston -Salem, N. C. 104.1 nl WSLB-FM Ogdensburg, N. Y. 106.1 IF'Itl ,.,k on Elemnentary Radio Servicing.81498 WSLS-FM Roanoke, Va. 99.1 SIGNAL TRACER KIT S21.95 WSM-FM Nashville, Tenn. 103.3 %n valuable aidtel In troubleshooting New riti-E; 1100k on Test Instruments. WSMB-FM Orleans. La. 102.7 WSNJ-FM Bridgeton, N. J. 98.9 HIGH FIDELITY HUMLESS AMPLIFIER WSOC-FM Charlotte. N. C. 103.5 KIT $1e.00 Henderson, Ky. Attractive aluminum chassis: complete Witt, five tube, WSON-FM 99.5 and two selenium rectifiers. WSOU South Orange, N. J. 89.5 FREE: Book on Amplifiers. WSOY-F M Decatur, III. 102.1 ECONOMY AMPLIFIER KIT...... $5.95 WSA-FM Spartanburp, S. C. 98.9 Simple to build; complete with five tubes. WSPD-FM Toledo. Ohio 101.5 FREE FREE: Book mm Amplifier.. SEND THIS COUPON FOR WSPR-FM Springfield, Mou. 97.9 TELEVISION AND RADIO LITERATURE r TELEVISION KIT $59.50 WSRK Shelbvyille, Ind. 101.3 Complete tub. kit 39.59 WSRS-FM Cleveland Hts., Ohio 95.3 MIDWEST RADIO A TELEVISION CORP. FREE: Television Servicing Nob.. $ WSTC-FM Stamford. Conn. 96.7 Dap. 365, 909 I eollway, Cincinnall 2, Ohio 10" TELEVISION KIT $99.50 WSTP-FM Salisburg, N. C. 106.5 $ Complete tub. kit 57.30 WSTV-FM Steubenville. Ohio 103.5 PRE.,.: Television Servicing Notes. WSVA-FM Harrisonburg, Va. 100.7 10" TELEVISION SUB -ASSEMBLY KIT.$229.50 Sylacauga, Ala. Sub assemblies fnrtor5. wire,,; Complete with tubes. WSYO 101.9 FREE: Television Servicing Notes. WSYR-FM Syracuse. N. Y. 94.5 12" TELEVISION SUB -ASSEMBLY KIT.S259.50 WTAD-FM Quincy. Ill. 99.5 as Sub ansemblies tubes. WTAO-FM Worcester, Mass. 96.1 Televi.tonrSeevicingl Notas. WTAL-FM Tallahassee, Fla. 103.9 15" TELEVISION SUB -ASSEMBLY KIT.5349.50 WTA M-FM Cleveland, Ohio 105.7 Sub assemblies factory-wired: lute.. FREE: Notes. WTAO-FM Green Bay, Wis. 102.5 WTAR-FM Norfolk. Va. 97.3 5 TUBE AC-DC SUPERHET KIT $14.25 WE ARE Complete with tubes ana cabinet. WTAX-FM Springfield. III. 103.7 FREE: Book on Building Receiver.. WteO-FM Cumberland, Md. 106.9 4 TUBE AC-DC 24AND SUPERHET KIT.$17.45 WTCN-FM Minneapolis, Minn. 97.1 LOOKING Complete cabinet. WTDS Toledo, Ohio 91.3 FREE: Book on (AmateurRa Radio Building. WTFM Tiffin, Ohio 98.3 7 TUBE ACDC FM RECEIVER KIT $29.95 Complete with tubes and cabinet. WTHI-FM Terre Haute, Ind. 99.9 FORTUNES! FREE: Television and FM Servicing Notes. WTHT-FM Hartford. Conn. 106.1 4 TUBE SUPERHET PORTABLE KIT.. $12.95 WTIC-FM Hartford, Conn. 96.5 WHAT HAVE YOU GOT? Complete with tubes and cabinet: leu batteries. WT1S-FM Jackson. Tenn. 100.7 FREE: Rook on Unusual Radio Circuits. WTMA-FM Charleston, S. C. 95.1 Interested in small or large quantities of all LP RECORD PLATER KIT $20.95 WTMJ-FM Milwaukee, Wis. types of Transmitting, Industrial, and Receiv- Complete with motor, pick -up. permanent needle. 93.3 ing Tubes. Iffier. tubes, speaker, cabinet. WTOA Trenton, N. J. 97.5 Send offerings to FREE: Book on Radio Questions and Answers. WTOC-FM Savannah, Ga. 97.3 T. L. BLACK, WHOLESALE TUBE DIV. AUTOMATIC WTPS-FM New Orleans, La. 95.7 Car Radio Model M -90 IU.iversal Mnuntin $27.97 WTRC-FM Elkhart. Ind. Ca Radio Model M -92 -C Ill. pli., It Battery Charger) 34.97 100.7 NIAGARA RADIO SUPPLY CORPI Bike Radin lantimer, falun).. . 17.7 WIRF-FM Bellaire. Ohio 100.5 Ton, Thumb "Ruddy" Portable 15.wa1 pÌU.battery charger) 37.97 WTRI Troy. N. Y. 102.7 160 Greenwich St.. New York 6, N. Y. Te Table Model Television Receiver 149.85 WIRT Toledo, Ohio 99.9 !MS WTSP-FM St. Petersburg, Fla. 102.5 All- Channel Video Booster (excellent for fringe areas) ...... WISV-FM Claremont, N. H. 106.1 AI Ántenna ii$12.75folded WITH-FM Port Huron, Mich. 99.1 < < iesel 2 `Mcr)r,ectos ' 15.00 Ann »TUBES Harbor, ° WUOM Mich. 91.7 FACTORY SEALED CARTONS EICO RADIO CRAFTSMAN WUSI Lockport. N. Y. 99.3 V.T.V. M $49.95 FM /AM Tuner YOUR ASSORTMENT 25 FOR $9.25 5. Oscilloscope 89.95 Model RC 8...$110.00 WV8T South Bristol, N. Y. 101.9 50 FOR $18.00 100 FOR $35.00 Multimeter 17.95 Amplifier Model WVCN De 1R5 I2SA7GT RC fier 39.00 Ruyter. N. Y. 105.1 354 35W4 WVCV Cherry Valley, N. Y. 101.9 135 3V4 I2SK7GT ESPET IT4 HATS 12SQ7GT 5085 rM'sM Chesis Model 7ití Ill tube receiver)..994.00 WVFC Ithaca, N. Y. 95.1 IU4 128A6 12S17GT 50L6GT FM /AM Chassis Model 511 tube 39c f1 receiver).. 98.00 WV1S-FM Owensboro. Ky. 96.1 3Q4 128E6 Each 3585 I I7Z3 VM WVKO Columbus, Ohio 94.7 ASSORTED BULK PACKED -25 for $8.75 Dual Speed Record Changer Model 50 FOR $17.00 Longlaying 533.90 WVUN Chattanooga, Tenn. 98.1 100 FOR $33.00 WWCF The following tubes at FEILER Greenfield, Wis. 94.9 6AG5 6AL5 BFSG 6TH Pocket Stethoscope Model TS 5 ...... fla.9s WWDC-FM Washington. D. C. 101.1 6AKS BAUS 6SN7GT Ram I987 Cathode Stethoscope Model T87 (less phones WWJ-FM Detroit, Mich. 97.1 nC and probe) . .3.25 MANY OTHER TUBE TYPES AVAILABLE. SEND Stethoscope Probe (compicte with eC1 WWHG-FM Hornell. tube)... 3.25 N. Y. 105.3 FOR FREE TUBE LIST. X.N. SCOTT WWLH New Orleans, La. 100.3 Complete stock of replacement parts available for the Dynamic Noise Suppressor Type 110 A $49.10 WWNI Wabash. Ind. 97.5 RCA 630TS TV Receiver. our bargain FERRETT W WNY-FM Watertown, N. Y. 100.5 Send for parts list. EM -TV Sweep Generator (20 MC sweep width) 164.95 WWOD-FM Lynchburg, Va. 107.9 HALLMARK ELECTRONIC CORPORATION ALL MERCHANDISE SHIPPED WWOL-FM Buffalo, N. Y. 104.1 594 Communippw Ave. FOE NEW YORK WWPB-FM Miami. Fla. Jersey City 4, New Jersey BErgen 4 -6365 Deduct 200o if full payment accompanies order. 15 101 5 deposit required on COD orders. W W PG-F M Polm Beach, Fla. 97.9 Write for further information concerning the above WWST Wooster, Ohio 104.5 merchandise. Send for our Free catalog. Parts of the old 160 -meter band are WWVA-FM Wheeling, W. Vo, 98.7 open WXHR Cambridge, Moss. 96.9 again to the amateur. Regulations PROGRESSIVE ELECTRONICS CO. WXLW-FM Indianapolis, Ind. 94.7 which vary according to the geograph- WXNJ Plainfield. Dept. RE -24 497 N. J. 103.9 ical location permit operation on various Union Avenue WXRT Chicago, Ill. 101.9 Brooklyn 11, New York WXYZ-FM Detroit. Mich. 101.1 bands between 1800 and 2000 kc, with W2xEA Alpine, N. J. 93.1 powers between 50 and 500 watts. RADIO- ELECTRONICS for People 85 Walter Albert Buck has been elected operating vice -president of the RCA Victor Division, Radio Corporation of America, it was announced by John G. LET THIS "AUTOMATIC TEACHER" Wilson, executive vice -president of the division. show you exactly how to repair over Mr. Buck, a re- tied rear -admiral of the U. S. Navy, has served since March 15, 1948, as 4800 RADIO MODELS president of Radio - marine Corporation without expensive test .equipment ! of America, a serv- ti ice of RCA. In re- tiring from the GHIRARDI SAVES YOU TIME Navy last March, Mr. Buck ended a distinguished Navy -HELPS YOU MAKE MONEY Ghirardi's RADIO TROUBLESHOOTER'S career of thirty years, the last two of HANDBOOK is the ideal manual to show you which he served as Paymaster -General exactly how to repair radios at home in spare time-quickly and without a lot of previous ex- and Chief of the Bureau of Supplies and perience or costly test equipment. It contains Accounts. For his wartime services, he MORE THAN 4 POUNDS OF FACTUAL, Merit. time -saving, money -making repair data for re- was awarded the Legion of pairing all models and makes of radios better, faster and more profitably than you may have Terry P. Cunningham has been ap- thought possible! pointed as director of advertising and NOT A "STUDY" BOOK sales promotion for Sylvania Electric RADIO TROUBLESHOOTER'S HANDBOOK Products, Inc., it was announced by R. can easily pay for itself the first time you use it. You don't have to study it. Simply look up the H. Bishop, vice -president in charge of make, model, and trouble symptom of the Radio sales. Mr. Cunningham will direct ad- you want to repair and go to work. No lost time! Clear instructions tell exactly what the trouble is vertising and sales promotion for the likely to be- EXACTLY how to fix it. Actually, lighting- fixture, this big 714 -page manual -size HANDBOOK brings you factual, specific repair data for the common lamp, radio -tube, troubles that occur in over 4800 popular models of and electronics di- Home and Auto radio receivers and Automatic record changers of 202 manufacturers! In addition. visions and the Wa- there are hundreds of pages of helpful repair charts, bash Corporation. tube charts, data on tuning alignment, transformer troubles, tubes and parts substitution, etc., etc. - He was formerly all for only $5 ($5.50 foreign). Read it for 10 advertising man- days ... at our risk! Use coupon. ager of the radio - tube, electronics, and international division and has Get a Complete RADIO- ELECTRONIC been associated with Sylvania Electric and subsidiaries since 1942 as an advertising executive and sales manager of SERVICE EDUCATION Colonial Radio Corporation, a Sylvania subsidiary. AT HOME- WITHOUT AN INSTRUCTOR Louis G. Pacent, Jr., has been advanced to the post of vice -president in charge COMPLETE DATA ON TEST INSTRUMENTS of manufacturing of Radio Speakers, -TROUBLESHOOTING -REPAIR Inc. of Chicago, it was announced by A. A. Chirardis big I300 -page ment typ,s; how they work (with Dorman D. Israel, president. The firm is MODERN RADIO SERVIC- wiring diagrams), when and why a subsidiary of Emerson Radio and Pho- ING is the finest, most com- to use them: how to build your York. plete instruction book on Ra- own; preliminary trouble checks: nograph Corp., New dio- Electronic service'work for circuit and parts analysis ; parts either the novice or the profes- repair, replacement. substitution: sional Radio- Electronic service- obscure radio troubles: aligning Sidney L. Chertok has been appointed man -bar none! Read from the and neutralizing: interference re- to the application engineering staff of beginning. it is a COMPLETE duction - and hundreds of other COURSE IN SERVICING by subjects including How to Start Sprague Electric Company, North scientific methods. Used for and Operate a Successful Radio Adams, Mass., Julian K. Sprague, vice - reference, it is an invaluable Electronic Service Business. 723 president, announced. Mr. Chertok will 1300 pages. 706 Illus. means of brushing up on any self -testing review questions help 723 review questions servicing problem. you check your progress EVERY also serve as sales promotion manager Gives complete information STEP OF THE WAY. Only 15 of the Sprague Products Company, on all essential service instru- complete $5.50 foreign). jobbers' distributing organization for You Can't Go Wrong on a Sprague capacitors, resistors and other Ghlrardi Radio look products, it was announced by Harry Technical Division, MURRAY HILL BOOKS, INC. Kalker, Sprague Products president. Dept. RC -49, 232 Madison Ave., New York 16, N. Y. Well known in the electronic and ra- send nie the books checked below for 10 days examination on approval. In 10 days I will pay for the books plus a few cents postage, or return dio industry, Mr. Chertok was formerly them postpaid. (Postage paid on cash orders; same return privilege. sales promotion manager of Solar Man- Books sent on approval in U. S. only.) fir.. rjl owe Q MODERN RADIO ID RADIO TROUBLE- ufacturing Corp., North Bergen, New SERVICING SHOOTER'S HANDBOOK Jersey, and its distributing subsidiary, $5 ($5.50 foreign) $5 ($5.50 foreign) D Special MONEY -SAVING COMBINATION SAVING Solar Capacitor Sales Corp. Both big books for only $9.50 ($10.50 foreign) MONEY-

Name OFFER! Get BOTH big Frank D. Peltier has been appointed books - Radio's most fa- director of engineering, appliance divi- Address mous Service Library - over 20.30 pages at a sion of the engineering department, No State - City & Dist. Philco Corporation, Philadelphia, it was (Plea.. print or write plainly) bargain combination price. announced by David B. Smith, vice- J See coupon. APRIL, 1949 People 861 president in charge of research and engineering. Peltier, an authority in the T U B E S! ADVERTISOED BRANDS TUBES! field of refrigeration engineering with RCA - Kenrad - Sylvania - Tung-Sol - Notional Union - Raytheon - Philco - Hytron many years of experience, has been with All new tubes. 100 °0 guaranteed. Individually boned. Philco since 1939 and has been responsible for development of the company's TYPE PRICE TYPE PRICE TYPE PRICE TYPE PRICE TYPE PRICE TYPE PRICE refrigerators, home freezers, and air 0A4ß $0.96 3A4 $0.72 6K7ß $0.60 6Y6G $0.85 12A H7GT .$1.15 3355744 $0.45 01A .60 3/37/1291 .. .96 6Kß .85 6Y7ß 1.15 12Á16 .80 .65 conditioners. During the war, he made a 0Z1 60 306/1299 .. .96 61.50 .96 6278 1.40 12ßA8 .65 352101 .54 80 3 4 .80 616 .. 1.28 BZYSB .60 128E6 .65 35287 .45 notable contribution to ordnance engi- A4P 1.40 30501 .... .85 6L60A .. 1.15 7A4 .72 1208 1.15 36 .96 A5GT ... .65 384 .72 6L7 1.15 7A5 .72 12146 .65 37 .65 neering. AB 1.15 51140V .... 1.15 6147 .88 7Aß .72 1215ßT .... .54 38 .80 6Pß87 .60 7A7 .72 1217ßT .... .72 89/44 .96 A7GT ... .72 574 1.40 12K7GT Louis Silver, vice- and sales 5114G 607 .72 7M .72 ... .60 40 .80 president B4P 1.40 12K8 .65 1.15 .85 607 .86 784 .72 41 .60 85/258 ... 5V711 .72 120701 manager of Garod Electronics Corpo- C5GT .80 5W4 .96 ßT .. .65 45 .60 06 1.15 5X40 .65 687ßT .96 786 45 .60 ration, Brooklyn, New York, has been 787 .7Z 12807 C7 1.15 5Y3GT .... .45 68Á70T ... .60 128F5 65 68801 .85 7B8 72 ' 45Z5ß7 .65 appointed executive vice -president and DSGP .... 1.40 5Y413 .54 .... 72 6ß87.Y .85 7C5 .M 128F7 070 1.15 5Z3 .65 .... 12887 .72 I6 .96 general manager, DSGP .... 1.40 5Z4 .96 6807 .72 7C6 72 .80 47 .85 7C7 126H7 E5GP .... 1.40 6A3 .96 68070T 1.15 12817 6SFS .72 7E8 .72 according to an an- E7GT .... 1.40 6A4 /LA ... 1.15 0 128K7GT .. .60 50 1.40 .96 .72 7E7 I2SL7GT .. .85 50A5 .80 6S67 .72 7F7 . 80 nouncement from F5ß .96 6M .72 1128/4701 .. .80 50B5 .72 04 .96 6Á8ßT .... .72 .80 7F8 90 12307GT .. .60 501601 .66 Leonard Ashbach, ß6ßT .... .96 6A137 1.15 68177 .60 707 .96 I2SR7 ,80 50X6 .80 68K7ß7 .. .60 7H7 .72 HOG .80 6ÁC7 .96 1223 .96 50Y6GT .65 president. Mr. Ash - HSGT ... .80 6AD7G .... 1.15 6817ßT ... .85 717 .96 12Zß(825) 53 .96 68N7ß1 .80 717 .80 1.15 146G 1.15 6AF6G ... .98 ... 14A1 56 .65 bach also announc- 160 .96 6A G5 1.25 6507 .60 7147 .80 57 .72 1.4 .72 6AG7 1.15 6SR7 .65 707 .65 ÌiBB .B6 70L70T 1.15 ed the appointment LA4 .96 6ÁK5 1.25 .55 7V7 .96 14C7 .80 71A .72 LAB .96 6415 1.25 6677 .96 7W7 .96 75 .60 68V7 IeF7 .RO of Paul Graf as as- 184 .96 6AL7 .96 1.15 7X7 14H7 AN 76 .60 1.15 LC5 .96 6Aß7 .80 1417 .96 77 .60 sistant vice- presi- 6115 714 .96 78 .60 LGS .96 6B4Ó .96 6U6 I4Q714N7 .80 79 .96 dent in charge of LE3 .96 687 1.15 667fiU7 .665 104 IIR7 .80 80 .45 1.144 .96 6880 1.15 81 1.40 6V6GT IaW7 .96 production and LN5 .96 6C4 .60 1.72 I2Á5 19 1.15 82 .96 NSGT .... .72 6C5 .80 6W7ß .96 l2Á6 72 1.15 B3 .96 Robert Leykum as plant superintendent. 6C6 .72 96 I2Á7 251601 .60 83V 1.15 6X501 .54 12M .... Messrs. and Leykum have been . . Graf Q5GT .....g6.96 6080 1.15 2525 .54 84/6Z4 .65 R4 606 .60 265Z88T ... .80 85 .80 associated with Garod nearly ten years .72 6E5 .80 2 .65 89 .80 I17L70T 1.40 6 6F5F5 .72 27 .54 Maurice Raphael, assistant to the presi- .65 ß7 .... 11714701 84 6F6 .72 2007 1.15 1.40 .72 TERMS: 25% with Order 11723 .65 74 6F7 1.15 31 .96 dent of Garod, was elevated to the post 1.15 117Z6GT .85 .... 6F8ß 1.15 -Balance C.O.D. -F.O.B. 32 V .860 321701 .... 1.15 V R-90 .96 of vice -president. Mr. Raphael, one of 2A3 1'15 Chicago. Prices Subject 33 1.15 VR-105 .96 radio's has been 7:50 1,RÓ 614601 .... .80 34 1.15 VRI50 .96 pioneers, associated 615GT fo Change Without Notice. ... .54 35 ...... 72 9001 .80 with the industry over 30 years. 2A6 .96 616 1.25 Minimum Order 52.00. 35AS .72 9006 .80 287 .96 617 .72 ?885 . 7, FM-1000 1.15 2X2 1.15 61(601 .... .54 351607 ... .66 HY-I17 1.15 Joseph B. Elliott was appointed vice - president in charge of all RCA Victor 1313 West Randolph Street consumer products and L. W. Teegarden FRANKLIN -ELLIS CO Dept. RE 4 Chicago 7, Illinois as vice -president in charge of all RCA technical products. The announcement was made by J. G. Wilson, executive Order a model 247. Disregard the unbelievably low price and compare It s A CHALLENGE - on the basis of appearance. quality and performance to any other Tube 4 vice -president of the Radio Corporation l1 Tester (ANY MAKE. ANY PRICE). If you are not completely satisfied with the model 247 after a 15 day trial. I 1 return it to us for lull refund -no explanation necessary. of America, in charge of the RCA Vic- 1 The model 247 is not surplus nor is It a hashed over pre -war model. It Is newly designed and Incorporates new i j advances in Tube Tester design. Read the description below and order one today! 1 tor Division. *,.. At the same time, Mr. Wilson announced the promotions of Henry G. THE MODEL 217 NEW Baker to general manager of the Home Instrument Department and Richard TUBE T. Orth to general manager of the Tube Department. ais- Mr. Elliott, who for the past four 40 years served as vice -president in charge TESTER of the RCA Victor Home Instrument Department, will in his new capacity Checks octals, loctals, bantam jr. peanuts, direct the over -all activities of all con- television miniatures, magic eye, hearing sumer products, including radios, Vic - 8 aids, thyratrons, the new type H.F. minia- trola radio-phonographs, television re- tures, etc. ceivers and phonograph records. For- Features: merly vice -president in charge of the A newly designed element selector RCA Tube Department, Mr. Teegarden switch reduces the possibility of obso- will direct the company's activities in lescence to an absolute minimum. the electronic equipment and apparatus When checking Diode, Triode and field as well as in tubes, parts and bat- Pentode sections of multi- purpose teries. Included in this field are broad- tubes, sections can be tested individually. A special isolating circuit allows cast and communications equipment, each section to be tested as if it were in a separate envelope. sound products, aviation and theatre The Model 247 provides a super sensitive method of checking for shorts and motion -picture equipment, and scientific leakages up to 5 Megohms between any and all of the terminals. instruments. One of the most important improvements, we believe, is the fact that the General sales manager of the Home 4 position fast- action snap switches are all numbered in exact accordance Instrument Department since 1945, Mr. with the standard R.M.A. numbering system. Thus, if Baker will be in charge of design, engi- the element terminating in pin No. 7 of a tube is under ONLY neering, and manufacturing of radios, test, button No. 7 is used for that test. television receivers and Victrola radio- Model 247 comes complete with new speed -read chart. Comes housed 90 phonographs, in addition to sales, ad- in handsome, hand -rubbed oak cabinet sloped for bench use. A vertising, and promotional activities slip -on portable hinged cover is included for outside use. Size: NET 10%" x 8ÿ'á' x.534 ". which had previously been his responsi- 20% Deposit Required on All C.O.D. Orders blity. Mr. Orth will assume similar enlarged responsibilities in the Tube De- DEPT. N. Y. ST. MOSS ELECTRONIC DISTRIBUTING CO. NEW YORK partment of which he has been merchandise manager since 1947. RADIO-ELECTRONICS foi, Freccenore.

- ... MEISSNER 24 -TV Some receivers were shipped without a width control. The necessary coil for THERE'S A adding this control may be added by simply drilling a hole and making the connections indicated in the drawing. CINAUDAGRAPH SPEAKER To minimize the effects of ignition noise, insert a 100 -ohm, 1/2 -watt, bias resistor bypassed with a 250 -1A4 capacitor between the cathode of the 6AC7 FOR first video amplifier and ground. Re- turn the suppressor to chassis, not to cathode. EVERY

CONNECT WIDTH CONE. COIL LEADS TO THESE 2 TERMINALS ON THE NOR12. OUTPUT TRANS. PURPOSE!

7/8- 83 DIFFERENT MODELS I/2- in the World's Most Complete Line! h` Do you have your FREE copy of the new CINAUD- L 5/16 -HOLE TO MOUNT From two -inch units for portable radios ... to fifteen - /COIL ON UPPER RIGHT FRONT CATALOG? AGRAPH CORNER OF SHIELD inch models for commercial phonographs and public Write to Dept. 1S3A, Cin- address systems . . . there's a CINAUDAGRAPH 2s audograph Speakers, 1401 SPEAKER tailored for each job. Fairfax Trafficway, Kansas Models with serial numbers higher City, Kansas. Whether you need a standard speaker, or a special- than 1398 have a provision for keeping ized unit for a particular application, CINAUDA- d.c. out of the deflection yoke. This GRAPH meets your exacting requirements with pre- change can be made on previous sets by cision engineered equipment. When you buy speakers, inserting a series 0.5 -µf, 400 -volt always specify CINAUDAGRAPH . . . and be sure blocking capacitor instead of the 22 -ohm you're getting the best' resistor now in the circuit. Dealers may neces- obtain all parts DIVISION OF AIREON MFG. CORP. sary for these modifications from the SALES OFFICE and FACTORY 1401 FAIRFAK TRAFFICWAY KANSAS CITY, KANSAS manufacturer without charge. CANADIAN OFFICE: Charles W. Pointon, Queen at Bay St.. Toronto. Ont EXPORT OFFICE: 13 E. 40th St.. New York, N. Y. Cable ARLAB .... HALLICRAFTERS T -54 The front end of the picture tube is supported by a rubber bushing on the NEW TELEVISION WHIP ANTENNA FOR MOBILE panel of this set. Place a soft pad under ANTENNA ROTATOR AND STATIONARY USE removing Ideal reversible motor for rotating all 111'-48 Mast Base Mounting with the tube before the front types of antennas at the top. Weighs heavy vertical coil spring, Insulated at panel. This prevents the tube from drop- only 4% lbs. Siee: 7 %" L. less shaft. top to receive Mast Section MS-53. Gear box and Nita.: 4%": 3 % ". Motor Shoot Base only $2.95 ping and possibly breaking against the Mee: 5' L. s t%" D. Shaft size: MAST SECTIONS: For shove NIP -48. %" x 1 %" threaded. Operates front 24 tubular steel. co-ner coated. painted chassis. 2 - V. DC, amps 4.5 RPM or 36 V.A.C. In 3 foot sections. Bottom section MS -53 ran he used G. J. MACHEAK Tonnle: 70 lbs. per itch. Price. $8.95 to make any length. NIS -52 -51 -50.49 for taper. eterewIn TRANSFORMER -For above Rotator type. Any Section-Price ... .50 each San Pedro, Calif. -110 Volt 60 cycle- Primary: 36 Y.A.C. See Price $2.95 TRANSFORMERS -110 Volt 60 Cycle Primaries Sec. 2 . . . . KNIGHT G9511 24 Volt amp. $2.25 ANTENNA POSITION Sec. 14 -14 or 28 Volt T'A or 15 amp 4.95 Volume and tone changed intermit- Sec. 12 Volt 1 amp ISO INDICATOR -Ideal for lndicat- Sec. 24 Volt 1 amp 1.95 tently. Signal tracing indicated faulty {a . log direction of antenna from a remote Sec. 24 Volt .5 amp 1.50 a.v.c. action, which was finally traced ( position. Units are Sente as 11198 ers ]rated nod have 0 -300 dial scales. MOTOR CONTROL RHEOSTAT 75 r.. with two autosyns and 12 to a which was bad, even though it V Complete Heavy -duly. wire around control for e gulating speed of tested good on a Volt 60 cycle trans.. and wiring AC or DC motors. toy trains. etc. 150 watt. 8.28 ohut.. standard tester. instructions. ]'rice $6.95 5 amps. Price 91 75 JOHN C. CHEPLA, Springfield, Ill. SELSYN MOTORS: INTERPHONE AMPLIFIER BC -347 115 Volt AC 60 cycle, Size V r78411 3fh' x 5 1,4". Can Army Aircraft Type. Uses 6FS Tube. Completely enclosed. Here: s s 0 be used to turn small antennas or for position Indicator 21/2" 4" ". Less Tube, Pt ice-Luth 79e Or -Three (31 for WESTINGHOUSE WR -305 systems. Price per Pair $5.95 $2.60 Selsyn type 22.1101 -Can be used as This set burned up its output trans- antenna position indicators, 110 Volt TRANSTAT VOLTAGE REGULATOR 80 cycle. instructions. Normally op- For 00 cycle AC voltage regulation. 103 V -126 V at former and later its power transformer. erates Irons 5 5 Volts 400 cycle. 2.7 amps. ]'rice: NEW $9.95 The 6F6 output tube was passing too Price per Pair $3.00 DYNAMOTORS much plate because a bad tone - MOTORS: current INPUT: OUTPUT: STOCK NO.: PRICE: Motor control contact broke connections be- C or 12 Volt AC -DC Heavy Duty reversible with 9 V. UC 403 V. 95 NIA DM 635 X $3.95 5/16" x 7/16" shaft. Price: New $2.95 12 V. DC 220 V. 100 NIA I) 902 3.95 tween the 6F6 grid and the bias supply, 6 Volt AC -UI Motor -ideal for auto fans. models. etc. 12 V. DC 440 V. 200 MA 1) 401 7.95 as shown in diagram a. replacing Shalt 14 It 'Ti'. Used- Tested $1.50 28 V. DC F/ SCR 522 PE 94 7.95 After Model Klotor -12 Volt AC -DC % double end shaft 12/24 V. DC F /No.19 MARK II P/S *3 9.50 the tone control, the bias -supply con - Motor. Size: 2 %' L x 2 %' W x 1 %' H. Price.. _$1.50 13/26 V. DC F/ BC -845 PE 101 2.95 110 Volt GO cycle. Ball Bearing Motor. approx. :4500 12/29 V. DC 500 V. 50 NIA USA /0151 1.95 BIAS POINT CHANGED RPM. 1/25 H.P. Shaft: 3/16' x % ". Motor size: 61/2" 28 V. DC F/ Comm. Re- 1.95 L s 4" H. Converted type. Price $2.95 ceivers DNE 32 -!-1 14 V. DC 230 V. 100 NIA DM 20 3.95 6F6 1 ¡ 6F6 Hand Tool Klotor -12 Volt AC 11C -5600 RPM. 3%.' I. z with spitned shaft D %" L. Price $2.95 12/24 V. DC 440 V. 200 NIA - 1'4" Dia. 6' : and 220 V. 100 MA D 104 9.95 DYNAMOTOR -Use your electric shaver in your car! B+ 28 V. DC 400 Cycle Inverter MC .149E Dynamotor will supply 110 Volt 100 MA from 6 VDC tltecondltlnnnll 12.95 S and will operate most types of AC -DC Shavers. Normal operation 12 VDC input: 220 V. 100 MA outpost. Price 91.95 RECTIFIER UNIT 110 Volt 60 cycle input: output 12 V. DC 10 amps. Can NEW TONE 1 T Address Dept. RE All Prices Are 8+ C- CONTROL e he used to charge batteries or operate DC equipment. - C- F.O.B., Lima. Ohio 257, Deposit on C.O.D. Orders Electronic Lab. mfg. Price -NEW 629.95 BAD CONTACT HERE

ORIGINAL CIRCUIT REVISEO CIRCUIT b. "LIMA," OHIOT. Bias is made independent of the tone control. FAIR RADIO SALES APRIL, 1949 881 Tech notes nection was made directly to the grid, as in diagram 6, so that a future break EVERY SERVICEMAN in the tone- control circuit would not affect bias. JOHN T. BAILEY, CAN Cigi4'td Short Hills, N. J.

. . PHILCO AUTO SETS A frequent cause of low volume is a SUPERIOR coating of grease and dirt on the 10- megohm resistor connected from the TEST EQUIPMENT grid of the first audio stage to ground. Do not draw the mounting nuts on THE NEW MODEL 770- the car's dash too tight when replacing the set; the material used on the control An Accurate Pocket -Size head is weak and will break after a period of vibration VOLT -OHM MILLIAMMETER on the road. (SENSITIVITY: 1000 OHMS PER VOLT) E. E. BALDWIN, Features: Grand Island, Neb. 354" s 5 ;4" x 29a". Compact-measures type Use latest design 2% accurate 1 SIII. D'Arsonval meter. zero adjustment for both resistance ranges. from It Is not necessary to readjustwh nswitchig SILVERTONE RI16I resistance range to another. This is an important time- saving feature never before Included In a V.0.51. In this When the set hums loudly and all fil- prim range. lioueed in round-cornered. molded case. ter capacitors are good, check the bal- Beautiful filled last resistor R17 (manufacturer's part permanlentwhited Inures long-tileeevent with constant use. number) A.C. VOLTAGE RANGES: 0.15/30/150, for shorts to the chassis. If it 300 1500 ttS: is shorted, replace 5 D.C. VOLTAGE RANGES: 0 -75a IS 75'150:750'1300 or reinsulate it. volts. CURRENT RANGES: 0 -11/2 15 ISO Ma. 0.11'a Amps. HURLEY D. ROBINSON, D.C. Megonm. 2 RESISTANCE RANGES: 0.500 ohms. 0.1 Pullman, W. Va. The Model 770 comes complete with self -contained batteries. test leads and 9 0 all operating instructions 3.9°NET wa manufacture of .o test a ui pmvnt. DELCO R119 MFR. BY n Wrote Dept. RC- for FREE catalog today When the set lacks volume, check the .02 -µf capacitor between 6C5 plate and SUPERIOR INSTRUMENTS CO. grid (manufacturer's part No. 88189). 227 Fulton St., New York 7, N. Y. Leakage causes the trouble. There may or may not be distortion. at your regular jobber HURLEY D. ROBINSON, y Pullman, W. Va.

YOU'LL SAVE iltabío aïfjírtp-1Fíbe pearl% Ago tt eernsback Publications MANY DOLLARS HUGO GERNSBACK WITH THIS Founder BIG 180 PAGE Modern Electries 1908 Eleetrical Experimenter 1913 Radio News 1919 FREE Science & Invention 1920 Radio -Croit 1929 CATALOG Short-Wave Craft 1930 Wireless Association of Amueles 19N

Some of the larger libraries in the country still have TELEVISION, ELECTRONIC PARTS, copies of ELECTRICAL EXPERIMENTER on fils for HIGH FIDELITY RADIO, HAM GEAR, Interested readers. PUBLIC ADDRESS EQUIPMENT, Bid ALL P PARTS AND WORKSHOP TOOLS IN APRIL 1915 ELECTRICAL A penny postcard will bring you the 1949 EXPERIMENTER Lafayette- Concord catalog. It's a bargain guide that means big savings to you. There are 100,000 -Cycle Alternators, by Frank C. TWIN -TRAX pages and pages of the finest equipment at Perkins "The Tope Recorder amazing low prices. Use it to order everything Unique Method of Recording the Voice you need, and pocket the difference. Helps you A Handy Radio Circuit, by Paul F. the Engineers are Buying '' save both time and money. You'll like shop- ping from this mammoth Shney When it comes to high fidelity sound book of bargains. Write Commercial Radio Transmitting Con- equipment, it the specifications that count for your copy today. Its free? densers with engineers. And that's why they're buy- World's l ing Twin-Trax the popular -priced tape A Novel Aerial for Radio Experiments, - LAFAYETTE- CONCORD organizationnpplYea` recorder with professional specifications. by Philip E. Edelman v MIV Extended frequency response, wide dynamic The Mignon Radio Coupler range, low hum level, easy operation, trouble - LAFAYETTE- CONCORD, Dept. JD -9 D. L. & W. Railrod Wireless free performance! And two tracks means 100 Sixth Avenue, New York 13 Hammond Radio Boat Goes 56 Miles twice the playing time on standard tape 901 West Jackson Blvd., Chicago 7 The D.C. Arc for Wireless Telegraphy reels, with tape costs cut in half -a saving 265 Peachtree Street, Atlanta 3 and Telephony, by G. G. Blake you don't have to be an engineer to Please rush free catalog No. 89 Tikker for Undamped Waves, by James appreciate. L. Green Write today for technical literature and Nome How to Construct a Radiation Indicator, professional factory discounts. Address - fr.,.m.s by Chas. Rosenthal City tone Stale A Clever Mineral Detector, by Irving AMPLIFIER CORP. OF AMERICA Byrnes RUSH THIS COUPON FOR FREE 398.10 Broadway New York 13, N. Y. CATALOG Audion Amplifier Transformer RADIO -ELECTRONICS for Miscellnnny Iss TELE- OR RADIOVISION? TV LENS FILTERS SAVE SO-REDUCE GLARE & EYESTRAIN - TUBES! TUBES! TUBES! IMPROVE PICTURE QUALITY!! Heavy acetate, blue tinted, EASILY ATTACHED IN NATIONALLY ADVERTISED BRANDS A FEW SECONDS!! ... A "must" for complete TV his editorial " Radiovision" in the enJoymenL BRAND NEW! BRAND NEW! IN 1948 issue, your editor pointed out For 7" tubes 50.75 For 15" tubes $1.89 July For 10" tubes .89 For 20" tubes 3.39 the present state of the art permits For 12" tubes 1.39 TYPE PRICE TYPE PRICE TYPE PRICE that OZ4 S .55 GATE 5 .69 12)5 S .49 transmission of video signals either by IA7GT .69 6AÚ6 .69 121í8Y .89 18307 1.9 66Á6 .69 125A7 .55 the air. It was advo- HAND SIGNAL LAMP- Precision -built 5 colored 1DSGP 1.29 68G6G 1.89 125)7 .55 wire or through 1D7G 1.19 6C4 .29 12587 .49 be lens turret I1 " -Ited. Green, Blue. VIilte. Clear). 1115GT .69 606 .49 12507 .49 cated that the word radiovision AdJ. trigger switch & V- sight. Operates on 2 Sash. ILC6 .99 6F6GT .49 14A7 .55 video signals cells. Black wrinkle finish. With 2 bulbs. Shea. wt. 1LDS .99 6G6G .95 1496 .55 adopted and applied to 51bs. WHILE THEY LAST. lLNS .69 686 .49 1407 .55 INSGT .69 6,5GT .49 2516 .59 transmitted through space just as radio- GENERATOR VOLTAGE REGULATOR (GE) -Navy IRS .69 616 .89 2525 .49 type GBD- 1 -A -18. Contains valuable 24 stepped con- 154 .69 6L6GA 1.09 2528 .49 telephone differentiates between wired tact 24V. asstd. resistors, sockets. 155 .59 65Á70T .45 30 .39 adjustable; plugs & 1T4 .59 65D7GT .45 34 .39 transmissions. shock mounts. etc. Shpg. wt. 4 lbs. A STEAL AT 304 .59 65117GT .45 35AS .55 and wireless 51.49 305GT .59 6SL707 .79 3516 .55 354 .59 6SN7GT .69 35W4 .45 Copies of the editorial were forwarded STA .89 6507GT .45 35Y4 .49 5U .59 65,17 .39 3523 .69 to some of the leading figures in the 5V4 .89 6557 .59 35Z5 .40 HEARING AID 5x4 .49 6577 .79 39 44 .39 radio and television industry -both here SY3GT .39 605/655 .69 50Á5 .55 AMPLIFIER ASSEMBLY 6A6 .89 6V6 .69 5085 .55 and abroad -and they were asked to 6s7 .69 6x5 .69 SOLO .55 /Sonotone vacuum tube type). MAKE A BAC7 .79 6v6G .79 57 .39 opinions in the matter. It REAL VEST POCKET RADIO or 6AD7G .99 7A8 .79 76 .39 express their AMPLIFIER adding only small tuner & 6shs .89 l2Á6 .29 80 .42 speaker or phone. Ready-wired miniature 6A86 .89 12Á76 .49 11726 .69 was interesting to note that almost GALS .79 I28Á6 .59 components include: 2 controls. output 6A05 .79 128E6 .59 everyone who replied stated that they trans.. choke. switch. resistors, Condens- ers. etc. Overall ONLY: 2"x,4x5"- felt that radiovision is definitely more Weighs 3% ois. Less tubes & AAea WRITE FOR COMPLETE NEW CATALOG specific than television as a term for case. Complete with Diagrams for `9.7 2 or 3 tube set-NOW ONLY MINIMUM ORDER $3.00 defining video transmission through ALL PRICES F.O.B. N.Y.C. space. Extracts from some typical let- ON COD ORDER 25% DEPOSIT ters are shown here: PORTABLE AC -DC AMPLIFIER Here's a One quality professional unit- AMAZINGLY LOW PRICED! Wide tree response for use with THE ROSE COMPANY MUSICAL INSTRUMENTS. SPEECH or PHONO 98 Park Place, Dept. E, New York N. Y. only INPUT. FM TUNERS. etc. FEATURES: S' FM 7, Of course radiovision is the speaker, 2 inputs, vol. & tone controls. 110V. AC or logical term. I hope you will be able to DC. Beautiful Blue or Brown simulated leather case. 16%313025%". Complete with tubes. 895 both technical and non- techni- Shpg. wt. 11 lbs. persuade BUY!!! cal minded people to accept your pro- ONCE IN A LIFETIME posal. JUMBO RADIO PARTS ASSORTMENT -MORE FOR GOVERNMENT SURPLUS! U. Christiansen, YOUR MONEY!! DON'T MISS tills GIANT kit of new Ejner dismantled Radio FULL Radio POUNDS S. n TRANSFORMERS,ORMERS, WIRE, HARD. WORLD'S LOWEST PRICE Dansk Industri WARE. SPEAKER ACCESSORIES. RESISTORS, C DENSERS, CONTROL, ETC.. ETC. ALL THESE -AND MUCH MORE (Shog. wt. 21 lits.i for ONLY 295 FLASH . Your suggested adaptation of radio - PHOTO of television is certainly vision instead Drin. order 52.00. tory Deposit nos. on 11 C.O.n.'s. EQUIPMENT to be recommended at least for radiated I please add sumcient postage -- excess refunded. video. The prefix "tele" means afar and LEuRADIO COk. Yeas i 6T Dey RAD New Yor 7, N. Y. COMES CCMPIETE WITH has been associated with communication EDGERTON The great difficulty lies in FLASH TUBES by wires.... 4 & REFLECTORS effecting the change after so many EASY TO years of television. CONVERT INTO A 2 -WAY PHOTO Benjamin F. Meissner, FLASH UNIT Meissner Inventions, Inc. OPERATES ON 110V. AC & 12V BATTERY Brand new at a fraction of origina cost. Contains finest component parts available. All necessary parts and complete instructions Intl . Radiovision is a better and more ex- conversion, works on 110V AC or pressive word than television. Persuade 12V battery by a flick of a switch. WRITE FOR MORE DETAILED IN the industry to confine television to wire FORMATION. IMMEDIATE DELIVERY use radiovision for CINEX, INC., 165 N. 4ó'h Sr., N. Y. IF, N. Y., Doe,. 4E.4 transmission and present broadcasting and you will have made a useful contribution toward clari- fying the scientific vocabulary. G. Parr, Managing Editor, 500 FORMULAS TO SUCCESS Electronic Engineering (England) ANitnnatkitoin51e formula for iw I\4 they paid a big price. Here y have 500-no leas -tried and est,, formulas, recipes and processes n. Television should be applied solely making things t the rldir low price of 25c. wires, Here to Mart to transmission of sight over witOpportunity dollars' Mtel and with undreamed or pronis while radiovision should be confined to in also medi- formulasn In yourr ow home to h on the transmission of sight via the household to the bone. to you putxpÌnses use um of the ether. rrkshop to cut costa s much a. I oo %. Boucheron, Oult paying t many dollars it Pierre profits to manufacturers,fa wholesalers. Wayne, and n Mr- Radio WGL (Fort Ind.) thing yourself for a few rents It's easy when you follow ou r simple inatrvctlont. 66 PAGES, 47,000 WORDS IN TEXT . Personally, I think you have a very a serviceman's paradise, when he Send for 50O FORMULAS AND RECIPES" today. En- It's close 25e, that's all! You won't be asked for another good point, and I would like to see it steps into our store. We hove lost the use cent now r later. Sold on a money-back guarantee. NATIONAL PLANS COMPANY adopted before it is too late. of the word "no" when these boys walk 19668 Broadway. New York 23, N. Y. G. B. Rowe, in or write for parts. "Yes" is the word John F. Rider Publisher, Inc. to all their requests because we try to satisfy every serviceman. And don't forget, our prices are subject to regular dealer ... Personally I am all for changing the discounts. How about getting on our NOTICE TO name in view of the probability of mailing list? Write Dept. E4. TRUCK JOBBERS wired vision. Wo can supply you with complete stocks of all James Turner, Editor types of Nationally Advertised Brand Tubes, individually boxed, at 10% to 20% below dis- Scottish Radio Trade Digest hLADal tributor's cost. Write -Wire -Phone For Detalla RADIO L ELECTRONICS CO. REX PRODUCTS COMPANY. Dept. C -3 7, 1313 W. Randolph St., Chicago 7, Illinois . We are happy to tell you that we 221 Fulton Street New York N.Y. Phono: SEeley 3.5030 share your views in this respect and APRIL, 1949 90 MisccllnNY glad to report that a number of per- vision for transmission by radio, I en- TELEVISION IS HERE ! ! sonalities consulted do the same. tirely agree with you that the matter is Karl Pinsker, Editor urgent. Our new catalog lists hundreds of new television items: sets. parts and accessories at un- Radio -Service (Switzerland) D. Capolino, Editor believably low prices. Write today -its free! Radio Schemi (Italy) Television Transformer. In our opinion, radiovision in place Pri. 115 Volts 60 Cycles. See. 2500 Volts @ of television is more appropriate. . ... It is my belief that your suggestion 2 ma.; 6.3 Volts @ .6A.; 2.5 Volts @ I.75A No doubt the new term will sound bit PRICE $3.85 a comes too late. While the number of strange to people used to television, but television stations and receivers is rela- MODEL NFRD-RADIO NOISE all will soon get used to it. tively small, television is literally a FILTER D. D. Lakhanpal, Editor household word. If it doesn't work, sand If back!' Radio Times of India James Hillier, We absolutely guarantee that our Model RCA Laboratories Division NFRD will eliminate all line noises when properly connected to radios, television sets. ... Radiotelevision seems to me much short wave sets, motors, electric shavers, re- more logical, but it has the big disad- would frigerators, vibrators. oil burners. transmit- It seem that television (for ters. and all other sources of interference. vantage of including four syllables. For vision) is appropriate whether used for This unit will carry up to 12 amperes or 15,4 this reason, I think radiovision would transmission by wire or radio. Radio - KW of power and may be used right at the source of interference or at the radio. be even better. I think too, that if any vision is confined to the latter only, and Small size only V'zli1/2":7%". Very change is to be made, it should be made today radio transmission is almost allow price only íl95 now. ways associated with co -axial cable or John Moyle, Editor wire transmission. EASILY ASSEMBLED RADIO KITS Radio & Hobbies (Australia) R. 5 Tube AC -DC superhet kit furnished in L. Triplett, brown plastic cabinet of artistic design, cab. The Triplett Electrical Instrument Co. inet size (9"z5 "z6 ") . I think it a very good idea to use Variable condenser tuned; with 2 double tuned I. F.'s. radiovision instead of television for For many years, Commander Mac- Tubes used: 1 - 12SA7, 1 - 12SQ7. 1 - 128K7 video transmissions through space. Donald advocated use 1 - 35Z5 and 1 the of radionics - 50L6 Surely it is of great value if PRICE television instead of electronics, yet all groups $11.95 s..ßá:á' "Yaé.. can be reserved for video transmission still prefer to use the latter expres- 3 WAY PORTABLE by wire. sion. . . Once a word is imbedded in KIT John For operation on 110 volt AC or DC and Schroder, Editor the public's mind, it stays there. Radio - battery Popular Radio (Stockholm) vision, I think, will never replace tele- Superheterodyne circuit Full vision dial vision. High gain loop . It seems to me that we could profit- J. R. Poppele, Two-Tone brown leatherette cabinet. size 7512i 4x61/2" ably follow your line of thought and Vice President, WOR Tubes used: 1R5, 3S4. 1SS. 2 - adopt radiovision as applying to trans- rectifier 1T4, plus mission by radio, and perhaps, . . . PRICE leaving Your suggestion referring to the $13.15 gerr:1e, kit ¡3ers3.7s television for transmission by wire. present television as radiovision will A SCIENTIFICALLY DESIGNED E. T. Flewelling probably never be adopted. Words never PHONO SCRATCH FILTER come into popular usage unless the mus- Resonated at approximately 4500 cycles effeetively Radiovision is more truly descrip- cular effort and expenditure of energy reducing ebJeetionable needle scratch without alter- ing the brilliancy of reproduction. tive word for radiation of visual in- required to pronounce the new word is Contains a HI -Q SERIES resonated eireuit. Tested formation in all directions, as against less than that to by means of an audio oscillator and an oscilloscope required enunciate the to give 22 db. attenuation with very low signal loss. television which should mean video in- older form. The pitch of the human voice EASY TO ATTACH Just two wires to clip on. Compact formation aimed in one direction, as is determined by the tension of the vocal Price $1.98 over a wire. cords, and the contour of the frequency THREE TUBE PHONO AMPLIFIER Hamilton Hoge, President spectrum is determined by the four An assembled unit ready for installation using tone United States Television Mfg. Corp. major resonances of the mouth, throat, and volume control and six feet of rubber á295 and nose. A large muscular effort is (Not including Tubes) As to my opinion with With regard to required to change the resonant points Complete Set of Tubes $3.95 adopting radiovision instead of tele- of these resonances. Television requires PHONO OSCILLATOR Wireless phono oscillator transmito recording for crystal pick -ups or volee from carbon mike through radio without wires. Can also be used u an intercomm by using P.M. speaker as mike. Price (excluding tube,) ác 2a95 With Complete Bet of Tubes $3.95

DUAL SPEED RECORD CHANGERS VM Model 80I A. Economleally Driced, will play the new 831/3 and the standard 78RPM records automatically. Features single tone arm with duel reversible cartridge. Price $26.LY 65Val VM Model 400C. A high fidelity low cost two speed record player. W111 play either type of record by quick Hip of the finger. TIMIPM records can be played Intermixed -Ir and 1r slue; only one tone arm used with reversible needles. Price de VM Model 402. Deluxe Model has all the features of Model 400C above plus a quick quiet changing cycle - less than 4 seconds between records, automatic cut off and quick gentle handling of records. Beau- Way finished. Price r Y .00 SPECIAL! SPECIAL! Mammoth assortment of radio and electronic parts, not lees than TEN POUNDS of new transformers, chokes. condensers, resistors, switches, coils, wire, hardware. etc. A super - buy for experimenters servicemen, and amateurs for only ál.25

Satisfaction guaranteed on all merchandise. All prices F.O.B. New York City WRITE FOR FREE CATALOG T -4

RADIO DEALERS SUPPLY CO. 154 Greenwich St. New York 6, N. Y. 8upgeeted by Louie Jolioet, Haverhill, Maas. Nol Nol Junior, you've got too much contrast! RADIO -ELECTRONICS for Miscellany I91 a minimum of muscular activity during 630 Type its pronunciation. Radiovision, while substantially the same length, neverthe- TELEVISION IN BULK LOTS less involves a rapid tuning of these OF 100 EACH resonances. CHASSIS Individually boxed, assorted, 34c each L. A. de Rosa, THOUSANDS OF SATISFIED BUYERS! Federal Telecommunication Laborato- IN KIT FORM Made by leading manufacturer -RMA Guarantee. ries, Inc. or Money back if not completely satisfied. ASSEMBLED IRS 384 6C8G 6SF5GT 6X5GT 12S17GT PRICES ON REQUEST 185 PATS - 6K5GT 6SG7GT - I2AT6 12SK7GT IT4 6BA6 6SK9GT PK6GT 12BA6 35W4 IUS 613E8 6SA7GT 6S8GT 12BE6 50B5 WITH THE ASSOCIATIONS PARTS FOR SAME SOLD SEPARATELY 304 6B8G 6SD7GT 6V6GT 12SA7GT11723 6SN7GT, 12SN7GT -48c ea. The Pennsylvania Federation of PUNCHED CHASSIS 5.45 Radio Servicemens Associations elected No. KRK2W- R.C.A. TUNER 39.50 RCA GE SYLVANIA RALTHEON new officers at its January meeting, held GENERAL ELECTRIC TUNER 28.95 NATIONAL UNION TUNGSOL in Harrisburg. Dave Krantz of Phila- KEN -RAD HYTRON POWER TRANSFORMER. 295 ma, delphia was elected chairman, Robert I IS V Individually boxed Standard AMA guarantee 14.95 5Y3GT-45c: 6F6GT -55c. SN7GT -90e: 12S07GT Reidy of the Lehigh Valley association, VIDEO and I.F. KIT, w /peaking coils 11.97 -70e: 25 L6GT-70c: 2525-60e: 25260T -60c; vice- chairman, and John Rader of the 35L6GT -650; 35Z5GT -49c: 50L6GT -65c FOCUS COIL 4.70 Above ten Reading group, secretary and treasurer types show manufacturer's brands. Ship DEFLECTION YOKE ment will be made of makes available when order is for 1949. Arrangements were made for 5.45 received. WIDTH CONTROL .47 ... Specify Prise When Oderinu .. . the annual award of a plaque to the individual or organization who had done HORIZONTAL CONTROL .54 FORTHEUNFBUOS the most for the radio technician and YOKE MOUNTING HOOD .97 Here's the beet bet yet in UHF gear! A porta- the radio servicing industry during the FILAMENT CHOKE .15 ble test oscillator de- past year. signed for the Navy. SPECIAL TRANSFORMERS Gold- plated cavity res- The Associated Radio Technicians of onator provide, freq. VERTICAL range of 234 to 258 British Columbia are issuing their Bul- OUTPUT 3.15 mes. Includes 2. 955',. Ready to go. Plenty of letin in a bright new format. Beginning VERTICAL BLOCKING 1.80 room In the battery compartment to house with the December, 1948, issue, it is a HORIZONTAL OUTPUT 5.45 small modulator and little magazine, 7 x 8 inches, folded and HORIZONTAL BLOCKING power supply . . . Olt 2.25 Rip out the parts stapled. Paper and type are good and and you have a dandy I /16- aluminum bi- easy to read. The December issue had GUARANTEED C.R. TUBES nnett (no hooles)x with handle. Deus fastener,. $3.95 twelve pages, and the January issue, eight. 10 -INCH, 10BP4 34.50 The Mid -State (Harrisburg, Pa.) as- 12'/2 -INCH, 12TP4 51.95 RADTONIC OMPANYT sociation reports two unexpected results 15 -INCH, ISCRT 79.50 from recent the Preventive Mainte- TWIN LEAD-IN, 300 ohms 100 ft.... 1.95 Tribune Theater Entrance Month. one is nance First that the TWIN LEAD -IN, 300 170H Nassau Street New York 7, N. Y. campaign increased the number of ohms, 500 ft.... 7.95 WOrth 2.0421 radios in operation in the district by at CO -AX CABLE. RG59U, 100 ft. 5.25 Open dally 9-6 Saturday 9 -5 least 25%. Large numbers of people CO -AX CABLE, RG59U, 500 ft. 24.75 brought in radios which had been lying around since "shortage of parts" made BROOKS RADIO DIST. CORP. 80 VESEY FREE. TODAY it impossible to repair them in wartime. ST., DEPT. A, NEW YORK 7, N. Y. Second unexpected result is that people in the Harrisburg district were awak- RADIONIC EQUIPMENT COMPANY Dept. 104 PTOU.,10 RAP/ 0 R CfP T/ O N 170H Nassau St., New York 7, N. Y. ened to the existence of the Association /f Please rush free copy of latest bulletin of rodio by the Maintenance Month advertising and television bargains in parts, tubes, sets and to an extent that would have been im- 4 accessories. atai/ possible with any mere publicity cam- Name paign. Set owners now know about the with thee Mid -State Association and look for mem- N ÁL Address ber shops when their radios are in need of repair. City State The Monterey Peninsula (California) A featherweight unit that gives greatly increased signal pickupI when attached to any Radio -Electronics Trade group reports lypa whip car aerial. Attached instantly -ad- HEADSET H -16U SPECIAL a successful lecture justable for any angle -will not wind -whip- meeting, attended highly decorative- not- rusting, allows use of 8000 ohm Dual. Headset H -18/U rod in telescoped or -most sensitive phones built- by technicians who came from as far as position estended- i greater volume distance. noiseproof-may be used as a San Jose, 74 miles away. Plans are be- -greater round powered Intercom - Also The Signal Soc is the most unusual auto radio I(r ( used with simple Xtal to make ing made to erect a cooperative tele- item to appear tV co plete radio receiver -light. Le on the market in the pad ten durable. efficient, molded. soft vision antenna to learn the possibilities years. - - -- neoprene eareutn. shaped to of television reception from San Fran- ,l Available in Red, Blue, Green, or natural snugly and comfortably envelope finish. the entire ear. Everyone BRAND cisco. anodized aluminum NEW. Complete with Illustrated manual. Send money List price S2.00 order or check today. The Radio Electronic Technicians Your Cast $1.20 Special per pair $1.89 Plus 25e each for postage Association (RETA) of Orangeville, Ontario, counts members in five neigh- ATTENTION Amateurs- Specify colon wanted. Check with order. Postpaid In U.SA. boring towns. Meetings are being held !Jobber inquiries invited.) Experimenters-Inventors monthly at one of these towns, 50% of WORLD IN COLOR PRODUCTIONS Cut your coat on radio supplies and equipment In lid W. Church Se. OWa, N. Y. half. Clip coupon today. all meetings being held at the Orange- Hundred. of "hard to get" war surplus Items along with the beet in standard brand equipment -all at ville headquarters. great savings to you. Let us know your particular The Associated Radio SERVICEMEN'S requirements. IMMEDIATE DELIVERY. Technicians of RADIO PARTS KITS PLEASE PUT MY NAME ON YOUR MAILING Alberta are working out their own loo Asst. Inaul. Res. $1.45 20 Asst. Knob ..S .89 LIST FOR SPECIAL BULLETINS. 10 Asst. ay -Pass ... .49 1 Lb.Asst. Radio Hdw. .25 classification system. Technicians will 20 Asst. Trimmers.. .59 15 Asst. Sockets . .99 25 Asst. Micas...... 89 10 Asst. Elect. cond. 2.89 NAME probably be rated in five groups: no 10 AsatVol.COntrols .59 20 Asst Term. Strip .69 ADDRESS ZONE 1 Lb. Asst. cut wire . .69, 209. length Snag.. .15 certificate rating, beginners, radio tech- guy All Above Kits for 59.75. Enclose Postage. CITY STATE DONGENE FM -AM 13 -TUTE TUNER. Complete Ready nicians, radio service engineers, and to Operate $39.95 88 -los Mc -550 -1800 Kc. NIAGARA RADIO SUPPLY CORP rado service managers, reports L. V. REMIT IN FULL FOR FAST DELIVERY Devitte, secretary of RADIO MAIL ORDERS 160 Greenwich St., New York City 6, N. Y the Calgary branch of the Association. 75 Barclay St. Dept. RE N. Y. 7. N. Y. APRIL, 1949 Miscellany 921

The famous ACA -100 Amplifier - a self -balancing, drift -correcting, direct -coupled amplifier - the most satisfying musical amplifier ever designed. Based on early Loftin -White circuits, perfected by A. C. Shaney in 1936. and now brought to standard of quality far above that of any corresponding amplifier. Exclusive features include:

rosb -Pull Trials Ea ha fro -diserimloatiug nH From left to right: GL-5610, CK -5654, 6AN5, CK5704 /CK606BX and CK5744 /CK6I9CX. Pesb -Fell bl and Is frog. variable egealinrs. If you are satisfied with nothing less than the best, write today for free technical literature. NEW MINIATURE AND SUBMINIATURE TUBES Special models for all magnetic cartridges. Five new miniature and subminiature pecially for aircraft and other services tubes have made their appearance re- where dependability and long life are cently. important. General Electric announces the GL- Raytheon's 6AN5 is a miniature pen- 5610, a 7 -pin miniature designed for in- tode usable in many cases as a replace- dustrial jobs, such as operating a relay ment for the 6AG7. Normal plate cur- in a control circuit. Maximum rated rent is 35 ma, transconductance 8,000 plate voltage is 300 and plate dissipation ohms. It is also useful at very high fre- is 3 watts. For typical operation, heater quencies and as a switching tube for voltage is 6.3, plate curent 17 ma, and computers. AMPLIFIER CORP. OF AMERICA plate resistance 3,500 ohms. The tube's The CK5704 /CK606BX is a submini- seated height is 17/s inches. ature diode with characteristics similar 398.10 way New TarK Id, N. T. Raytheon has announced four tubes. to half of a 6AL5. The resonant fre- The CK5654 is a rugged version of the quency of the tube is over 1200 mc. 6AK5. The heater will withstand at Another Raytheon subminiature, the least 5,000 on- and -off cycles at 7.5 volts. CK5744 /CK619CX, is a high -mu triode Other improvements suit the tube es- for general -purpose use.

Assembled for your convenience CUSTOMERS SELL THEMSELVES SOUND Facts, standards With the emphasis placed by manu- Sun Radio and Electronics Company facturers in the last few years on high of New York has allocated a large room practices, data fidelity in sound reproduction, the buyer to audio equipment. At one end, all the for the whole field of tuners, amplifiers, record players, popular high- fidelity speakers are ar- and speakers is confronted with a prob- ranged in three tiers; at the side is a of radio engineering lem in selecting the components he likes large group of FM and AM tuners and best. Recognizing that the best way to record players. A large push- button decide is to compare them directly, two board allows the customer to select any Radio Engineering large radio suppliers have set up un- combination of components and to usual electrical comparison circuits in change the combination as often as he Library their sound salesrooms. RADM specialists of the McGraw -Hill publications selected the books for this library as those giving the most complete, dependable coverage of facts needed by engineers whose special fields are grounded Library includes: on radio fundamentals. 1. FUNDAMENTALS They cover circuit phe- OF VACUUM TUBES nomena tube theory, -Eastman networks, measure- 2. RADIO ENGINEER - ments, and other sub- ING-Terman jects . . . give special- 3. COMMUNICATION ized treatment of all ENGINEERING fields of practical de- Everitt - sign and application. 4. HIGH -FREQUENCY * Spaalal Lew Price MEASUREMENTS - Bought singly, the Hund five volumes would 5. RADIO ENGINEER- cost $30. Under this ING HANDBOOK - offer you save $2.50. Henney Pay easy Installments * in 3559 pages! *FREE TRIALY 2558 illustrations!

MCGRAW-HILL BOOK CO., 330 W. 121 SL, N.T.C. Ill Send me Radio Engineer) R Library, 5 vols., for 10 days' examination on approval. In 10 days I will a 32.5 plus cents monthly nt 10 $27.50a is paid, or returfew postpaid. Name Address City .Zone State Company RC -4.49 Position Switching panel on wall combines any of the pieces of equipment in Suns sound sales room. lialaala III NM MMMMMMMaa,aaa II al RADIO- ELECTRONICS for Miscellany 93 wishes. Best of all, since the mere push of a button changes source, amplifier, or TELEVISION speaker instantly, he has the rare opportunity of comparing the sound qual- SERVICING at a ity of two speakers, for instance, with- INC. out the usual time lag required for pitKE YOU CAN PAY CONICAL plugging in. The "sound memory" is no- ANTENNAS toriously tricky, and this time lag usual- RUTHERFORD AVENUE ON ROUTE 35 ly makes a comparison between two R.S.E. 3 inch ASBURY PARK, N. J. PHONE: ASBURY PARK I 0119 BOX 879R, ASBURY PARK, N. J. good -quality sounds unreliable. With instantaneous switching, however, any TELEVISION SCOPE difference in sound is unmistakably apparent. Features: THE 4XTV WIDE BAND VER- TICAL RESPONSE "America's FLAT TO 750kc -1 Outstanding Television DOWN 3db Boom AT lmc VOLTAGE GAIN OF 20 AT 5mc AR-3

The R.S.E., AR -3 Scope has been built by Hi -Gain Stacked Conical "V" Armstrong to our rigid specifications. Its a complete unit that embodies standard hori- Beam zontal amplifier and sweep circuits with Channels 2 to 13 Plus FM normal sensitivity. Low Inception Angle The case is 8' high x 5" wide x 14" long, Extremely High Signal to attractively finished in "hammered" opalescent blue enamel. Operates on Noise Ratio PRICE standard 110 volts - 60 cycles 150 Ohm Non -varying Imped- -40 watts. Tubes, 3BPI -6AC7 Jnce - 6517 - 6X5 -5Y3 -884. In- 4995 Use72, 150 or300 Ohm Trans- structions included. Complete mission Lines specifications upon request. Satis- F. O. B. faction or your money back. DETROIT Universal Mounting Clamps William Rivkin of the New York store demon- SEE YOUR DISTRIBUTOR strates Lafayette -Concord's switching system. PUSHBACK Sun encourages the customer to operate the buttons himself so that he can WIRE change combinations as often as neces- $1,000 A MONTH sary to convince himself of the right- e BELOW MILL PRICES! ness of his choice. Twenty -six hundred 2,000,000 feet tinned copper -oil component - JUST ONE of the many plans In combinations are possible, ist. class, double cotton serve, waxed -,,,.. -t_ _ this brook brought In over $1,000 and the customer literally "sells him- - month steadily from radio sors. finish. Available 1,000 foot rolls. seas Ire alone. Now To Make More self." .tor . Money In Radio Service Is so full 22 gauge (6 colors) $3.98 roll of money -nuking plans It will Lafayette- Concord Radio has made a - ze you. EVEN BEGINNERS somewhat 20 gauge (6 colors) 4.98 roll using the easier plena made WAY similar system available in gasuyeador OVER $100 a week working from its New York, Newark, Boston, Chicago, 18 gauge (brown only) 6.49 roll home. why work for wages? Be. come your own boss and make and Atlanta stores. Here ten record - money. This book Is making players, 45 amplifiers, and 21 money for radiomen everywhere: speakers MIDGET F. U.S.A.. Canada. Puerto Rico. Mex- are interconnected with rotary I. . con, Hawaii. switches. ths;. other fin cones. iily. of The salesman can select any combina- thanks come in continually. TRANSFORMERS tion of units at the customer's request. Original At discounts List $2.10 -Rook rryy helpful -fol. In business 17 years. Book The instantaneous selection system up to 86% lowing advice In the look contains many things which canted high as $100 a took me many years to learn appears to benefit both customer -who week radio repairing. In the hardm y Book worth 400 -500 Kr range y apartment. many times" lis small cost. can quickly satisfy his own desires - 11/ "square, 3" high C. C. Seidler, F. V. Puan,, $reoklyn, N. Y. Elmwood, Illinois and the salesman -whose sales talk is hi -gain iron core. largely unnecessary. It may well be INPUT -A826 (rook ey Gale. adaptable to the requirements of other Among MANY other thing you where money lisnd how to et It FASTö 1lowyto test sets gwithout OUTPUT -A827 taking them out f r binvts and give estimates RAPID- dealers. LY: How much to charge: slow much work to do on Speci fy Type sets: Huw to tagrt spare and build to full time: Now to Matched Craft big-m ey concerns: How to get plenty of THE ORIGIN OF Pan Dozen Egg connect with . "VIDEO" 0100 Video was first used to designate tele- 69c $3.95 $29.00 NOW TO BUILD A MONEY -MAKING RADIO MAIL ORDER vision back in 1932, Dr. Orestes H. BUSINESS- another hit by Gale. OB pages. Two easy -tool,uw plans. Real opportunity to gel in BIG -PAYING revealed iness. Start spare or full time. How to start with Caldwell recently. Dr. Cald- other dealers' money and stock: How to work with ORDER INSTRUCTIONS customers' money: How to olotain sales Items easily: well, former Federal Radio Commis- How handle your Incoming ofnthe Minimum order -$2.00. 25%a de- e, akd psales:: Thechecks.secret sion chairman and now publisher of posit with order required for all chain and MANY other things. Millions $F going in the mails. Get your share. The world is your market; Tele -Tech, recalled that it was at an Demand Va. C.O.D. shipments. Be sure to include you attic. Swat of Quality sufficient postoge-excess will be here Is MAGIC in jour x. tenn i to use and RMA subcommittee meeting in New start streams of cash, hecks, and money-orders toward refunded. Orders received without you from North, East. South. and West. York, when committee members ap- postage will be shipped express collect. All prices pointed to propose TV standards were F.O.B. Detroit. Price each book ONLY $3 postpaid. C.O.D... In U.S.A. only. at $3 Plus few cents postal fee. Books shipped asked to find a name for the frequencies A e day. You have NOTHING TO LOSE: Examine 1,1 5 days. if not positively delighted return it andk we which produce Immediately. More Information pictures. After an hour on books FREE. price of cogitation, each member came up KHVIV SUPPLY & with a list and "video" was finally ENGINEERING CO., Inc. MERIT PRODUCTS. DEPT. RE. chosen. The word is believed to have 85 SEEDEN AVE. DETROIT 1, MICH. 218 -32 132 Avenue Springfield Gardens 13. N. Y. come from John V. L. Hogan's list. APRIL, 1949 -94

RADIO and TELEVISION Thorough Training in All RADIO SCHOOL DIRECTORY Technical Phases APPROVED FOR VETERANS DAYS- EVENINGS WEEKLY RATES RCA GRADUATES ARE IN DEMAND For Free Catalog Write Dept. CC.49 S P E C I A L I Z E S P E C I A L I Z E RCA INSTITUTES, Inc. A Service of Radio Corporation of America 350 WEST 4TH STREET NEW YORK 14, N. Y.

You can become a Radio and JOBS IN TELEVISION YOUNG MEN 16 TO 60 Television Technician now! There Is a Job Opening for Every Qualified Trained Television Technician A million new jobs - almost 4,000 a week - will be created in the television industry during the next five years according to estimates of WE CAN TRAIN YOU industry leaders. Actually, during 1948, television grew faster than any other industry in the history of America. Free Employment Service Here is a real opportunity for you. Trained television technicians are Visit Our Modern Laboratories and Class Rooms in demand. By starting now, you can get in on the ground floor - grow as television grows. APPROVED UNDER G.I. BILL OF RIGHTS To help supply this needed manpower, the Milwaukee School of Engi- AMERICAN RADIO INSTITUTE neering has expanded its radio and television courses. Now you can New York Buffalo. N. Y. Syracuse, N. Y. get complete practical, technical training in the MSOE laboratories. 101 W. 63 St. 640 Main St. 131 Shonnard St. This is not just a serviceman's course. It prepares you for a career in "Teaching Radio Since 1935 all of the technical phases of television and radio. This special course Prepares you for any of the following ca Television Serviceman Supervisor In Radio and Police, Tadi -Cab and Rail- Radio Serviceman Television Assembly road Transmitter Operator tELEVISION "ETH NICAL CAREER Radio and Television Radio and Television Tester Police, Taxi -Cob and Rail - As Television gains momentum, rapidly. Retailer Broadcast Radio- Operator road Receiver Serviceman constantly. it offers tO properly -trained technicians careers with a future in Industry. Broadcasting or own Business. OTHER COURSES AVAILABLE Train at an Institute that pioneered SERVICE TECHNICIAN PROFESSIONAL in TELEVISION TRAINING since 1938. 6 to 12 Months 1 to 2 Years 3 Years Morning, Afternoon or Evening Sessions In Electricity Electrotechnics Electrical Engineering laboratory and theoretical instruction, un- Welding Radio and Television Bachelor of Science der guidance of exports, covering all phases Electronics Degree of Radio, Frequency Modulation, Tele- Refrigeration vision. Licensed by N. Y. State. Free Refrigeration, Heating and Air Major in Electronics Placement Service. Approved for Veterans. Heating Conditioning or Power ENROLL NOW FOR NEW CLASSES Visit, Write or Phone `""41--MILWAU#CEE--4.1. RADIO -TELEVISION 5CHML of ENGINEERING INSTITUTE A 480 Lexington Ave., N.Y.17 (46th St.) Technical ,Il.ll Institute Plaza 34585 2 blocks from Grand Central s I Founded 1903 qt by Oscar Werwitb

y it . RADIO MILWAUKEE SCHOOL OF ENGINEERING, Dept. RE-449 N. Broadway and E. Slate Milwaukee, Wis. COURSES Without obligation send me free booklet "Ca Building" and mare details on course in Preparatory, Service, Broad- Radio and Television or course cast, Television, Marine Op- Name Age erating, Aeronautical, Fre- Address quency Modulation, Radar. City State Casses now loi ming loi the summer le,m June 1st

L Entrance exam. Mav 16 Veterans. Literature. COMMERCIAL RADIO INSTITUTE (Founded 19201 LEARN RADIO! 38 West Biddle Street, Baltimore I, Md. RADIO ENGINEERING PREPARE FOR A GOOD JOB! COMMERCIAL OPERATOR (CODE) FM-Television -Broadcast RADIO SERVICEMAN Police Radio. ALrine Radio. Radio Servicing. Avia- tion Radio and Ultra High mobile applications. TELEVISION SERVICING Thorough training in all branches of Radio aid Elec- tronics. Modern laboratories and equipment. Old es- Bea man. BROADCAST ENGINEER tablished school. Ample housing facilities. 7 acre messags how to campus. Small classes. enrollments limited. Our in tetegnph Veterans $130.00 Equipment anIvea radio. Commerce need. thousands of get graduates are in demand. Write for catalog. men for Jobs. Good pay, adventure, in- Veterans teresting work. Learn at home 9ulekly SEND FOR FREE LITERATURE Approved for u famou VALPARAISO TECHNICAL INSTITUTE r tryfor Commercial Ll- BALTIMORE TECHNICAL INSTITUTE r se. for FREE BOOK. Write 1425 Dept. C VALPARAISO. INDIANA Eutaw Place, Dept. C, Baltimore 17. Md. Dept. i-D. Box 929. Denver 1, Colo., U.S.A. RADIO- ELECTRONICS for Communications 195 LIKED SERVICING STORY The variety of articles you print should make every issue interesting if it Dear Editor: is read -not just glanced through.. RADIO TUBES The article "Using Your Ohmmeter," Many times I find small items more in the January issue, is well worth interesting than many feature articles, All Brand New reading by the average plant electrician yet they could be passed over unread who services electronic equipment such when glancing quickly through the MONEY BACK GUARANTEE! as automatic welders and photo -electric magazine. relays. I also like the articles on photo- JOHN KWIETINSKAS THIS LIST COMPRISES electric relays which have been printed Duquesne, Pa. OVER 8500 TUBES in RADIO -ELECTRONICS. I had trouble with some and the articles were a great NO TV FOR CANADA Kenrad .19 help. Dear Editor: 6C4, EARL MYERS, 1 B5, Sylvania .29 Brantford, Ont. I know the U. S. serviceman needs all 106, General Elec. .29 those articles on television, but it will .29 long they are any use 1H6, Sylvania NOT ENOUGH be a time before .29 ONE LIMITER to us in Canada. 1G4, R.C.A. .69 Dear Editor: I find J. R. Langham's articles very 1 LA6, Sylvania .69 I had the same trouble with automo- informative. 1 LC6, Sylvania bile ignition interference on the FM D. DODD, 1105, Sylvania .39 band as Mr. Zarattaro ( "Communica- Winnipeg, Canada 1 LE3, Sylvania .79 tions," August, 1948). I was using an 1 LH4, Sylvania .69 "old- band" receiver with a single lim- REPORTS TELEVISION DX 574, R.C.A. .69 iter and a discriminator. Dear Editor: 594, Sylvania .85 by a I modernized the set adding be interested in 5X4, Cunningham .69 detector. With the I thought you might tuner with a ratio my television dx. I was in sort of a General Elec. .69 and lead -in, there was no 6E5, same antenna "hole" so I put up a 40 -foot tower and a .59 noise. 6G6, Philco more ignition Taco 495 I get New Haven a single limiter antenna. 6F5, Stand. Brand .59 My conclusion is that most of the time; that is about 100 miles If you can't afford a tuner 6H6, Kenrad .37 is no use. away. Channel 4 in both New York and with dual limiters, use a ratio detector. 6K7, R.C.A. .49 Boston comes in so I can't watch one Elec. .39 ALAN M. PALMER, unless other is off the air. Some 6597, General N. Y. the Brooklyn, nights WFIL -TV in Philadelphia inter- 7A6, Sylvania .59 feres with more local reception on chan- 7B6, Sylvania .59 VARIETY OF ARTICLES nel 6. I am using a Hallicrafters T -54 7C7, Sylvania .59 .59 Dear Editor: and two boosters. 7F7, Sylvania has improved DONALD E. SMITH, 7F8. Philco .59 RADIO - ELECTRONICS .29 greatly both in quality and in contents. Northfield, Mass. 12SR7, Kenrad The editors can be proud of the great 12SJ7, R.C.A. .49 variety of subjects so well covered and CORRECTIONS 12Z3, Cunningham .69 illustrated. There should be a ground connection 14A7, Sylvania .49 at the junction of the 250 -ohm and 470,- 14B6, Sylvania .49 AUDIO ENGINEERING SCHOOL 000 -ohm resistors in the output stage of 14Q7, Sylvania .49 Funda- A practical Audio Engineering r In Sound the TG -10 conversion diagram on page mentals: FILM and MAGNETIC Recording: Transmission 14R7, Sylvania .49 Monitoring nd Mixing. Laboratories Measurements: Ana. 78 of the February 1949 issue. contain Tranemis,lon Sets. Oscillators:O Harmonic Hytron .55 lyser. Distortion Sets. Intermodulatton Anal and 35L6, other equipment. Rea-onlineq Studio a imulating BroadBroad- - We thank Mr. Theodore C. Smith, of cast.at. Motion Picture and Commercial Sound Recording. 35W4, Sylvania .39 .oTrentaine. Director. Approved for Veterans Rome, New York, for calling our atten- Pres.- .39 ap tion to this omission. 3525, Kenrad HOLLYWOOD SOUND INSTITUTE, Inc. 50A5, Sylvania .79 1040 -E North Kenmore Hollywood 27. Calif. The value of R10 was omitted from the parts list of the Phono Amplifier on 5085, Sylvania .55 page 78 of the January 1949 issue. This 50L6, Kenrad .55 RADIO COURSES resistor is a 1,000 -ohm 5 -watt unit. 1171-7, Tungsol .88 RADIO OPERATING CODE Our thanks to Mr. Walter Johnston, 117N7, Philco .88 RADIO SERVICING ELECTRONICS of Atlanta, Ga., for this correction. F.M. TELEVISION 117Z3, Tungsol .69 REFRIGERATION SERVICING 117Z6, Sylvania .88 Write for Catalpa and Picture Brochure Stand. Brand .59 Tub ASSEMBLY DEPT. 1- OZ4, Y.M.C.A. !RADE & TECHNiCAL SCHOOLS 26, Cunningham .36 229 W. 611 St. IWest of Weak) New York City 30, Cunningham .19 34, R.C.A. .29 CORRESPONDENCE COURSES IN 56, Hytron .29 RADIO -d ELECTRICAL ENGINEERING 75, Stand. Brand .69 ELECTRICAL ENGINEERING °e1 eai °ir,7m é.lé'. 76, Philco .39 Low r for e and course. So simphried anyone quickly. 77, Nat. Union .39 RADIO ENGINEERING aiáárecour work. Trains you to be super -service man, real vacuum. 80, Stand. Brand .39 tubeoServicemen t'Vhnfe on c cl earning big pay.aDlDloma Substitutes of other standard brands will Electronic given to Either out of stock by 1 WRIstudents fie. be made if listed tubes are $25 Course FREE details ofdeferred poeme t man. eta' Lincoln Engineering School, Sox 931 -eE -4, Lincoln 2. Neb. TELEVISION TUBES Guaranteed Brands ELECTRICAL TRAINING 10" -10BP4 $34.50 Intensive 32 weeks' residence course in funda- 51.95 mentals of industrial electrical engineering, in- 121/2" -12TP4 cluding radio, electronics. Prepares for technician, 15" -15CRT 79.50 engineering aides. Approved for veteran training. 56th year. Enter April 4. Sept. 6. Catalog. 113, Suedeeted by Isadore Water, Philadelphia, Po. ELECTRICAL SCHO RADIO DIST. CORP. "Y' know. sometimes I feel like these BROOKS BLISS WASNiNGTON 12. 0. C. darned things are coming out of my ears." 80 Vesey St.. Dept. A. New York 7, N. APRIL, 1949 96 ADVERTISING INDEX -939 PHONO AMPLIFIER - 2 Tube AC -DC APRIL 1949 AT LAST! A LOW COST 3 at S I .25 2 tubes-50L6 -3525 51 Adson Radio & Electronics Company 89 PHONO OSC -2 TUBE $2.75 Allied Radio Corporation 57 Uses 35Z5, 12SA7, 2 tubes 51.20 Amplifier Corporation of America 88, 92, 97 PHONO AMPLIFIER POWER UNIT Arrow Sales, Inc 80 Bargain Rodio 82 3 Tube AC -DC a, Bell Telephone Laboratories, Inc Bock Cover 69 for Service Work Boland i Boyce, Inc. 74 3 at sí.49 Bradshaw Instruments Company 74 Volume and Tone Controls. Brooks Radio Distributing Company.... 83, 91, 95 Uses 12507. 35Z5. 50L6. Set of 3 Tubes $1.35 Buffalo Radio Supply 63 Output Trans. .32 Capitol Radio Engineering Institute 5' Alnico Speaker 1.10 9, Inside Back Cover 6" PM Speaker 1.45 ALLIANCE. PHONO MOTORS .. 2.50 Certified Television Laboratories 82 PICKUP SI.79- 1111aí e)u'rl'UT l'ICKUP 1.99 Cinaudagraph Speakers 87 ALL ABOVE WIRED & TESTED Cines, Inc 89 SI Deposit on all orders. Free Catalog RE Clarkston Corporation 96 RADIO MAIL ORDERS 75 Barclay St., New York 7, N. Y. Cleveland Institute of Radio 18 Columbia Electronics 97 Commercial Radio 82 Communications Equipment Company 83 Get Started in Radio Coyne Electrical School 96, 97 "A" Eliminator Kit =KC I -I0 DeForest's Training, Inc 7 10 "HOW- TO- DO -IT" BOOKS Esse Radio Company 68, 69, 70 Including pictorial and Fair Radio Sales 87 Get a solid foundation In ratio by $ means these 10e timely text books. schematic diagrams ONLY 1950 Feiler Engineering Company 76 Fsh clearly written. profusely Illus- 86 Yrated, contains over 15,000 words. Franklin -Ellis Co ou'll be amazed the wealth of These kits fulfill the long - standing need of ever General Electronic Distributing Company Into these serviceman and technician. They are designed to Inside Front Cover books.. Excellent. al and for technical library. Your money operate from a 115 V.A.C. 50/60 cycle source, Green Radio Distributors 62 back If not satisfied. 6 V.D.C) well -altered from three to eight deliver Greylock Electronic Supply Company... 82 amperes. with a peak rating of ten ampere.. The S BOOKS A.C. ripple percentage is held to remarkably low Halldorson Company, Inc 78 for 50c values. Hallmark Electronic Corporation 84 10 BOOKS for $1.00 This unit charges a standard auto battery In one Heath Company 12, 13, 14, IS day!! Hudson Specialties BO Sent to You Postpaid Do away with bulky batteries! Instructograph Company 96 No. 1-How To Make Four tionary (Leading Terms) Do away with corroding fumes! Lafayette -Concord 88 Doele snort Wave Sets No. 6-HO To Nave Fun Leotone Radio Corporation 89 No. 2 -How To Make The With Radio Simplify your service operation! Most Popular s No. 7 -How To Read Radio McGee Radio Company 8 and 2 T Receivers Diagrams Order this fine kit for your bench today!! -Hill 92 No. Alternating urrent No. R -Radio for Spinnen McGraw Book Company, Inc for3- Beginners No. 9-simple Electrical Ex. received without sufficient Merit Products 93 NO. 4-All About Aerials No C.O.D.'s, please. Orders No. a- Beginners' Radio Die. NO e10- Television allowance for postage mil be shipped Via Railway Metropolitan Electronic and Instrument Co BI Express collect. Mid -America Company 81 Remit by cheek o money order-register letter If you send or stamps. Shipping tot., 12 tbs. Midwest Co 84 Miles Reproducer 96 RADIO PUBLICATIONS Montgomery Ward II 25A West B'way. New York (7) OPAD -GREEN COMPANY Moss Electronic Distributing Company 86 71 Warren SI. New York 7, N. Y. 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RADIO SCHOOL DIRECTORY niche up conversation a few Inches away rom telephone $20.00 (Pages 94.951 20% Cab with order, balance C. O. D. .Send orders to Dept. RH. American Radio Institute REPRODUCER CO., INC. TRAIN QUICKLY! Baltimore Technical Institute MILES 812 Broadway New York 3. N. Y. OLDEST, BEST EQUIPPED Bliss Electrical School Candler System Company SCHOOL of ITS KIND in U.S. Commercial Radio Institute .2 gi.VdA Hollywood Sound Institute, Inc. Opp°R í Lincoln Engineering School Come to the Great Shops of COYNE in Chicago dur- Milwaukee School of Engineering EASYTOLEARNCODE ing our 50th Anniversary War! Get quick, practical Institutes training RADIO- TELEVISION ELECTRIC- RCA It is easy to learn or Increase speed ITY. C; I Approved. Finance plan for non-veterans. Radio Television Institute with an lnstructograph Code Teacher. Mail Coupon Today for complete details. Valparaiso Technical Institute Affords the quickest and most practical method yet developed. For be- NOT "HOME- STUDY" COURSES! YMCA Trade & Technical Schools ginners or advanced students. Avail- You learn on real, full -size equipment, not by mail. able tapes from beginner's alphabet Finest staff of trained instructors to help you get to typical messages on all subjects. ready quickly for a better job, a fine future. Speed range 5 to 40 WPM. Always Clip coupon for big illustrated Radcraft Publications, Inc 77 ready -no QRM. FREE BOOKS Coyne book on either ELEC- Radio Products Inc City Company, 76 ENDORSED BY THOUSANDS! TRICITY or RADIO- TELEVISION. Both books Radio Dealers Supply Company 90 sent FREE if you wish. No obligation; no salesman The Code Teacher will call. Act NOWT Radio Distributing Co 96 iterally takes the placedplace an Radio Mail Orders 82..91, 96 for- Instructor and to learn and master ode without fur- B. W. Pros. Radionic Equipment Company 91 ther assistance. Thousands of sUccessfill operators have coolie, the and purchasesssIenSystem. COYNE Electrical & Radio School, Dept. 4S-811.11 Radio Publications 96 tor dnyh forcode'convenient tal 500 S. Paulina Street. Chicago 12, Illinois Radio Supply L Engineering Company 93 Send FREE BOOK and full details on: Rea Products 89 D ELECTRICITY D RADIO-TELEVISION The Rose Company 89 COMPANY Senco Radio, Inc 16 NAME 4701 Sheridan Rd., Dept. RC, Chicago 40. III. N. Silverstine Co 59 ADDRESS Simpson Electric Company 67 tiCITY STATE Spartan School of Aeronautics 72 COUPON -OF- THE-MONTH Spellman Television Company 83 TURFS -STD. SRAND 573 CT 3 for $0.99 TUES-STO. 12SQ7 or I2ATe 2 for .99 Sprague Products Company 65 VOL. CONTROLS -STD. SR. .5 Meg. W. SW 3 for .99 CLARKSTAN Stephens Manufacturing Corporation 4 CONDENSERS -40 -40 Mfd. 150V. 2 for .99 150V 3 for .99 Superior Instruments 88 CONDENSERS -20.20 Med. PHONO NEEDLE LOOP ANTENNA -HI GAIN 5 "x8'1 3 for .99 Sylvania Electric Products 17 I.F. COILS 455 KC Il'/ax2l.ol 3 for .99 GAUGE Television Assembly Company 6 OSC. COILS 455 KC for 12SA7) for .99 F.ssentlal for Micro Groove S PASS COND. KIT-18 Asstd . .99 Telres, Inc 93 DIAL CORO KIT -100 ft. Asstd. & 0 Springs .99 & standard equipment. Ac - rate to one gram -has both gram and ounce scales Tranavision 10, 61 GRILLE CLOTH-fl Asstd. e "106" & 10 Knobs .19 for nroper weight adjustment of all types tone arms. COMBINATION KIT -All Above Items - Only 10.00 Net 11.50. United Surplus Materials 75 price WITH THIS COUPON -ORDER AT ONCE SEE YOUR 105ES TODAY. The Videocraft Company 82 Blvd. Write for Monthly Coulons and Bulletin CLARKSTAN CORP. ;;lÁns :.e Wells Sales, Inc 98 ;; World in Color Productions 91 RADIO DISTRIBUTING CO. PASADENA I0, CAL. RADIO -ELECTRONICS for Book Reviews 97 1949 BBC YEAR BOOK, published by the British remaining chapters, Coaxial Lines, Broadcasting Corporation, London. 5 z 71V, inches. 152 pages. Price 3 shillings sixpence. Waveguides and Cavities, The Produc- Like the previous editions of this tion of Microwaves, Microwave Tech- COLUMBIA yearly report, the 1949 BBC Year Book nique, Pulse Circuits, Cathode -Ray Tube Gem of the Surplus! is a compilation of articles by British Indicators, Tuned Amplifiers, Amplifi- Broadcasting's performers, officials, and cation of Very Weak Signals, Servome- * engineers. Of interest to the shortwave chanisms and Computers, Miscellane- TCS RECEIVER-3 -BAND ous Radar and its Accessories, listener, it does an excellent job of tell- Circuits, 1.5 Mcs to I2Mcs. Designed by the top ing how the BBC operates and what it Microwave Communications, and Micro- commercial communication equipment has accomplished during the year. The waves in Physical Research are defi- manufacturer -Collins. A proven, rugged large number of illustrations of famil- nitely college -level text book material performer. Standard on every Navy ship iar broadcasters give the BBC listener but can be understood by anyone with afloat. Good used condition. Ea. $34.95 a chance to see the people whose voices a slightly more than average knowledge he hears from afar.-R.H.D. of radio and electronic fundamentals. ASB RECEIVER Three appendices cover The Fourier Complete with lighthouse tubes in R.F. THE ADVERTISING AND BUSINESS SIDE OF sections. Ideal for citizens' bands. Used Published by Prentice - Integral, Curl and Stokes' Theorem, RADIO, by Ned Midgely. but good condition. Ea. Hall, Inc., New York. 5% x 8%. 363 pages. Price and Units. The latter describes the $17.95 $5.35. NOTE: Brand new sets also are available. While intended primarily for those units of measurement used by the au- in and mag- interested in selling radio time (and thors discussing electric GO -9 HIGH FREQUENCY buying it) and in the financial end of netic fields. -R.F.S. TRANSMITTER volume will be of in- broadcasting, the THEORY AND APPLICATION OF RADIO-FRE- Frequency range 300 to 600 Kc -3,000 to terest to the technical and program QUENCY HEATING, by George H. Brown. Cyril 18,100 Kc. No plug -in coils needed. Man- staffs of the larger radio stations, who N. Hoyle', and Rudolph A. Bierwirth. Published ual band switching system. Power output: by D. Van Nostrand Company, Inc., New York. 125 wafts. Has very stable E.C.O. Ready usually look upon the business opera- 9%/e z 6 inches, 370 pages. Price $6.50. tions of the station as an unfathomable This is a mathematical treatment of as is to go on the air -no changes nec- mystery. radio heating theory and essary. Its hot on 20, 40 and 80 meter -frequency bonds. Extra! We'll supply a technical in The text explains adult language practice based on the findings of the au- manual with first 25 sets sold! External the why and wherefore of rate fixing, thors, research engineers in the RCA power supply necessary. Used, excellent discount figures, contract provisions, Laboratories. It contains a wealth of in- condition. Rock -bottom low price: $67.95 network procedures, spot sales, and the formation on the design of radio -fre- like. The various sales adjuncts are quency heating equipment and heating LORAN SCOPE covered fully -audience research, pro- techniques. 6A /APN -4-a terrific piece of lab equip- motion, campaign planning. A valuable Although highly mathematical, the ment! With 110V supply it can be used feature is the inclusion of specific data material is supplemented by charts and for many tests. Contains 27 tubes such as -financial and historical -on the major diagrams that offer graphical proof of 6SN7GT, 6H6GT, 6SL7GT and a raft of networks and their affiliates. Sections the mathematical derivations. others, plus 100 Ka crystal, 22 pots, etc. on FM and TV bring the information The 24 chapters are illustrated with switches, condensers, transformers, In aluminum approx. 9''x12 "xle ". right up to R.H.D. and com- case date,- photographs of experimental Used but in very excellent condition. used mercial equipment for radio -fre- Schematic supplied FREE. Each $27.50 ELECTRONIC MUSICAL INSTRUMENTS, by quency heating. Some of the more inter- S. K. Lower. Published by Electronic Engineering, London, England. 516_ z 81/2 inches. 101 pages. esting chapters cover such topics as sol- TUBES! TUBES! Price 3 shillings sixpence. dering, brazing, baking paints, welding, 12DP7 -brand new! A welcome addition to the pitifully pasteurization of foods and drugs, and Each $13.95 small supply of literature on electronic efficiency of heating equipment -R.F.S. music, this little book describes and APN -1 ALTIMETER - classifies electronic musical instruments, 420 MC FM TRANSCEIVER then devotes a chapter each to oscillat- IN RADIO & ing -tube circuits, and electrostatic, elec- With tubes, dynamotor. Used, but in ood tromagnetic, and photoelectric tone gen- BIG MONEY TELEVISION condition. $4.95 erators. Another chapter deals with $64.00 QUESTION: Have YOU re- amplifiers and control circuits. These New 5-Volume Set ceived our NEW, hot-oft-the-press latter are important in electronic mu- catalogue/ THEN SEND FOR IT ! ! ! sical instruments. A volume control FREE Oft 7daya01tal All prices F.O.B. Los Angeles. 25% deposit with which would be satisfactory on a radio, order. Balance C.O.D. for example, would wear out in a short APPLIED time under the constant use to which it PRACTICAL RADIO * would be subjected in an electronic Be the radio expert of your local- COLUMBIA ELECTRONICS musical instrument. ity -The one they come to with Department R -C 522-524 S. San Pedro Street Some interesting material on the the toughest service jobs. Los Angeles 13. California This new 5 volume t gives you acoustics of music is found in an intro- solid working kn ...ledge of Radio and Television. Covers1 everything from basic principles newest In ductory chapter, and a bibliographical FM. Television. Testing Inatru. Clear.nstructr Tell- selection is furnished in an appendix. you how to Install, ice. Gives your short -cut trouble shooting methods. More than 1500 pages, 1000 illustrations. charts. diagrams. MICROWAVES end RADAR ELECTRONICS, by Examine these great, pay. raisin% books for 7 days at Ernest C. Pollard and Julian M. Sturtevant. FREE TRIAL OFFER our mall coupon below. That's IIMEMINIMW Published by John Wiley & Sons, Inc., New York. Coyne se FREED Triial !Offer! Written by a foremost Audis design engineer- 5% z 8% inches, 426 pages. Price $5.00. FREE! ISI RADIO I TELEVISION DIAGRAM ROOK! The so If you act at will include with ours al authors have prepared this APPLIED RADIO our e big practical book I50 Radio and Television Diagrams Ex- Tape Recording book that it is easily read and under- plained" Elements of Magnetic 2St wanttthe et, send it back at our Oeexpense and 999 Applications stood by almost anyone with a back- withinthin 7 days. you keel, the set, send Manual 25f $15 cash. $3 in I days and $ n Direct -Coupled FM -AM Amplifier ground of elementary college physics until $19.75 Is paid. Either way. Amplification 3e in postage e Diagrams book la yours to keep! Send 20 Steps fo Perfect and mathematics and a working knowl- not request to se' the and the Dla-Dia- !. edge of electron -tube theory. grams book Free. Act now! get Thousands Sold The first chapter, Electromagnetic Famous Twin -Tree Instruction Book! GOOD FOR FREE TRIAL and FREE 800R1 Practically a course in tape re- Fields and Microwaves, introduces the Educational gook Publishing Division cording. 30 diagrams. illustrations. COYNE ELECTRICAL & RADIO SCHOOL, SOO S. Paulina Et. reader to the background material re- !rdw na/ b..pph.d ag.iml Dept. 49 -TI, Chicago la. 111. $250 el ck.nir.l quired for understanding microwaves. PRACTICAL postpaid, L7 1 Pvmbu dasy FREERPE ER anaoCp r yI o'offer. includele If the reader lacks a college background FREE Book of 150 Radio Diagrams Explained. Name Age in physics and mathematics, he is likely Address to have trouble with this chapter. The Town zone... . State J 398.10 Broadway New York 13, N. Y. APRIL. 1949 98

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Brand new, standard make tubes by the thousands are ready for immediate delivery at the lowest prices in our history. Check this list for exceptional values in magnetrons, cathode ray tubes, voltage regulators, transmitting tubes and also neon, pilot and flashlight bulbs. Be sure to order enough for future needs directly from this ad or through your local parts jobber.

Type Price Type Price Type Price Type Price 01A $0.50 10(.34 50.45 RK.71513 $7.95 874 $2.15 0Z4 1.05 36 .55 717A .90 884 1.50 1622 5.55 37 0.55 721A 3.95 954 .55 1P4/1294 .65 38 .55 724B 4.25 955 .55 1R5 1.12 39.44 .34 725A 19.95 956 .55 15 1.12 41 .55 726A 19.95 957 .55 1T4 1.12 45 Spec. VT.52 .55 801 .60 1005 .45 2C26 .55 46 .85 801A .80 1148 .40 2C26A .70 49 .75 803 7.75 1201 .95 2C44 1.25 EF50/VT-250 .65 804 10.45 1616 1.25 2J22 14.85 RK60/1641 .65 805 5.75 1619 .55 2J31 14.85 72 1.10 807 1.20 1624 1.25 2J32 14.85 CEi-72 1.55 810 7.95 1625 .45 2J38 18.95 76 .55 811 2.35 1626 .45 2J48 16.55 77 .55 813 7.85 1629 .45 2X2/879 .75 VR-78 .68 814 3.75 1636 4.75 3A5 1.10 80 .41 815 2.85 2050 .78 3822 3.95 83 .85 826 .49 2051 .95 3825 1.15 83V .95 829 3.25 7193 .35 381,1 3.75 VR-90 .70 8298 3.95 8011 2.55 3C24/24G .49 VT-90.8011 2.55 8308 3.75 8012 4.35 3D6/1299 1.25 VR92 .65 832A 3.50 8020 3.25 3E29/8298 3.95 100R 3.45 837 1.25 9001 .70 3FP7 2.95 FG-105 10.95 838 3.25 9002 .65 3HP7 2.95 VR105 .90 841 .55 9003 .55 305 .95 VT-127 English .35 843 .55 9004 .55 REL-5 19.95 VT-127A Triode 2.55 851 39.50 9006 .55 SAP1 3.75 VR150 .70 WL-860 2.55 5E1.1 2.85 VT-158 9.85 861 34.50 NEON BULBS FOR RADIO USE 5EP4 3.95 211 .65 864 .55 NE-2 $0.06 5CP1 3.85 215A 1.95 865 2.55 NE15 .06 5GP1 6.55 218 4.45 866A 1.40 NE-48 .24 5J23 14.85 249C 2.95 8698 28.95 NE-16 .24 5J29 14.85 2828 4.35 872A 2.45 NE51 .06 6AC7 .95 304TH 6.55 687 .99 3047L .90 6C6 .75 316A/V7.191 .75 6C8G 1.05 350B 2.55 PILOT AND FLASHLIGHT BULBS 6C21 19.95 3718 2.55 606 .60 388A 6.45 6F8G 1.05 417A 19.85 Stock Maeda Volts Watts Bulb Base Price 6H6 .52 GL434A 4.95 No. No. Each 6J5 .52 446A 1.55 350-40 64 6-8 E3 CP G-6 DC Bay $0.07 6L7 .90 446B 1.55 350.50 1820 28 .1 Amp 7-31/2 Min. Bay .12 6SG7 .95 GL47IA 2.95 350-31 57 12.16 1.5 CP G-41/2 Min. Bay .08 6SL7 .65 WL530 24.95 350-42 Spec. 12 6 Watts S-6 Cand. Scr. .13 6SN7GT .85 WL-531 19.95 350.20 1446 12 .2 Amps G-31/2 Min. Scr. .07 7A7 .70 532A 3.55 350-14 49 2 .06 7-31/4 Min. Bay .06 7C4/1203 .45 GL559 3.75 350-15 3S6 120 3 Watts 5-6 Can. Bay .11 10 '1/7-25 .52 KU-610 7.45 348-22 PR-10 6 .5 Amps B-31/2 Min. Flan .05 12A6 .35 Hy-615 1.25 350-18 1477 24 .17 Amp T-3 Min. Scr. .16 12C8 .35 WL681 19.95 350-55 323 3 (Aircraft) 7-11/2 953 .22 125G7 .68 700B 9.95 350-19 Proj. Bulb 120 500 W T-20 Med. Pf. 1.45 12X825. 2 amp. Ungar 2.95 700C 9.95 LB-103 44 (Ruby) 6-8 .25 Amp T-31/2 Min. Bay .04 FG-17 2.95 700D 9.95 LB-102 1195 12-16 50 CP RP-11 DC Bay .14 RK20A 4.95 702A 2.95 LB-104 313 28 .17 Amp T-31/2 Min. Bay .11 REL-21 3.65 704A 1.95 350-24 12A 12 .09 Amp 11 T-2 Tel Base .18 23D4 Ballast .35 705A 2.65 LB-107 24-A2 W E 24 .75 Amp 105 T-2 Tel Base .18 28D7 .45 707A 19.50 350.63 S-14 ARGON 105 2,2 Watt Med. Screw .22 30/V7.67 .iFor .95 707B 23.25 LB-109 TELEPHONE TYPE NEON T-2 .17 33/V7-33 ONalkie Talkies .. .95 710A 2.15 350-41 943 6.8 100 CP G-161/2 S. S. Pref. .65 34 .35 714AY 9.95 350-43 11A/T4C 18 .11 Amp T-4 Cand. Scr. .14

Use This Page Manufacturers: We carry thousands of electronic parts in stock. for Ready Reference Send us your requests for quotations. Distributors: Our standard jobber arrangement /WELLS/ applies. Order directly from this ad. SALES, 320 N. LA SALLE ST. DEPT. Y, CHICAGO 10, ILL.

PIIIIITED IN IKE U. S. A. FY TUF CUNLO PRESS, INC -

Change Your Uncertainty to PROFIT with CREI's New Home Study Course in Tdevis(on and FM gervicin

TELEVISION'S growth has been so rapid that it has nas; picture synchronization; TV troubleshooting- exceeded the forecasts of even the experts. And it and much more, all of a practical nature that you can has exceeded the abilities of a lot of radio servicemen, put to work immediately. because they aren't properly qualified to work with TV Chairman Wayne Coy of the FCC estimates there will and FM. be 400 TV stations on the air within two years -and If you want to make your future secure in the 1,000 in eight or nine years. David Sarnoff, chairman expanding servicing field, CREI can show you the way of the board of RCA, predicts about 18 million TV sets this new, practical Servicing Course. It helps you earn will be in use by the end of 1953. FM figures are more money faster because it assumes you already equally impressive, with about 4,000,000 more radios rmj know radio fundamentals. Yet you do not have to be with FM forecast in 1949. There can be no doubt about an engineer to reap the benefits. The course is not the importance of, and the need for, experienced TV-FM over the heads of those with limited experience -if they servicemen. Are you going to be qualified for the have natural ability and a real desire to get ahead. It increased earnings that lie ahead? teaches what you need to know to install and repair VETERANS! TV and FM sets. It gives you sound instruction in THIS COURSE IS G.I. APPROVED. basic radio math, lenses and mirrors, modern test equipment, inductive coupling and condensers at ultra- high frequencies; practical applications of resonant íOr/G 77244W circuits; TV tubes; FM receiver alignment; TV anten- e ...... CAPITOL RADIO ENGINEERING INSTITUTE

16th k Park Road, N. W., Dept. 154A, Washington 10, D. C. RADIO SERVICE DIVISION OF Gentlemen: Send me complete details of the new home study course and the booklet that explains the CREI self- improvement program CAPITOL RADIO and courses. I am attaching a brief resume of my experience, education and present position. ENGINEERING INSTITUTE NAME An Accredited Technical institute STREET CITY ZONE._ STATE Dept. 154A. 16th & Park Road, N. W., Washington 10, D. C. T AM ENTITLED TO TRAINING UNDER C. I. BILL. Branch Offices: N. Y. 7, 170 Broadway; San Francisco 2, 760 Market St. rt Vibration Control

Columbian Humming Birds, one of the famous drawings from nature by John James Audubon.

Wing vibration, nimbly controlled, keeps the wires. Among their inventions have been oscil- humming bird in flight, enables it to feed with- lators, modulators, filters, coaxials, wave -guides, out alighting. and radio lenses. Electric vibration is the essence of telephone Constantly Bell Laboratories scientists discover transmission. Voice, music, pictures, teletype - new and better ways to control and adapt electric no matter what type of signal - the story is told vibrations by wire or radio to the needs of the tele- by the frequency and strerigth of not one, but phone user. Their pioneer work in this field is one many vibrations. important reason behind today's clear, dependable Learning how to control electric vibrations to and economical telephone service. pin -point accuracy has been one of the basic jobs of Bell Laboratories scientists in their develop- BELL TELEPHONE LABORATORIES ment of the "carrier" art which enables the send- Exploring and inventing, devising and perfecting, for con- ing of many more conversations over existing tinued improvements and economies in telephone service.