Radio Broadcast (May 1929-Apr 1930)

"Z_ -RADIO BROADCAST ADVERTISER. Thordarson Transformers and Chokes For Use With "245" Type Power Tubes and "224" Screen Grid Power Detectors Input Couplings Single "245" tube, from any audio amplify \ R-260 $5.00 ingtube, use any oneof three transformers •< R-300 8.00 (R-400 especially suited to "226" and "227" / R-400 9.00 tubes) Push-Pull "245" tube, from any audio amplifying tube. Use 1-to-l ratio input transformer T-2408 $8-00 Use 2-to-l ratio input transformer T-2922 12.00 Screen grid power detector "224" to any single power tube, use "Autoformer" for choke-resistance type of standard circuit R-190 $5.00 Screen grid power detector "224" to any push-pull power tubes use R-190 Autoformer for parallel feed to detector plate and 2-to-l coupling transformer T-2922 $12.00 Speaker Couplings Single "245" tube to dynamic speaker with built-in transformer, to cone speaker, or to magnetic speaker — Use either one or two 1 T-2876 S0.00 transformers ) T-2901 12.00 Use choke-condenser coupling, employing one choke r-196 5.00 Single "245" tube to moving coil of dynamic speaker — Use transformer T-2902 $12.00 Push-pull "245" lubes to dynamic speaker with built-in transformer, to cone speaker, or to magnetic speaker— Use coupling transformer T-2880 $12.00 Use choke coupling, employing double choke T-2420 8.00 Push-pull "245" tubes to moving coil of dynamic speaker— Use either one of two transformers J T-2629 $10.00 I T-2903 12.00 Filament Supplies For six "224" screen grid tubes or six "227" tubes — Use filament transformer (10.5 amps at 2.5 volts) T-3660 $9.00 For two "224" tubes or two "227" tubes and one or two "226" tubes use double voltage transformer T-3081 $6.00 Power Compacts For filament current, plate current and bias on "245" push-pull power stage, also plate current for set. Contains filter chokes. Uses one 280 rectifier tube R-245 $24.00 For filament current, plate current and grid bias on single "245"' power tube and one "226" audio tube, also plate current for set. (Requires extra T-3081 filament transformer. ) Contains filter chokes R-480 $17.00 DARI RADIO TRANSFORMERS Thordarson Electric Mfg. Co. Transformer Specialists Since 1895 WORLD'S OLDEST AND LARGEST EXCLUSIVE TRANSFORMER MAKERS Huron and Kingsbury Streets Chicago, 111., U.S.A. TYPE 360 TEST OSCILLATOR One of the new test oscillators for the radio service laboratory is now ready. It will deliver a modulated radio-frequency voltage at any point in the broadcast band (500 to 1500 kilocycles) and at 175 and 180 kilocycles. The tuning control is calibrated with an accuracy of 2 per cent. The Type 360 Test Oscillator is intended to be used for neutralizing, ganging, and tuning of the radio-frequency stages in a receiver, and it is fitted with an output voltmeter for indicating the best adjustment. Price $110.00 GENERAL RADIO COMPANY 30 State Street Cambridge, Massachusetts 274 Brannan Street San Francisco, California BALANCED TUNING with ; The HAMMARLUND "Battleship" Condenser TJEAL One-Dial Control! Units are matched to -within of one percent of each other. Absolute precision obtained by mounting a Hammarlund Equalizing Condenser in the recess of each section. Warpless, die-cast frame, with terminals on Bakelite strip underneath. Non-corrosive brass plates. Two capacities: (350 mmfd. and 500 mmfd.) 2, 3, and 4 gang models. Write Dept. RB10 for Folder Hammarlund Manufacturing Co. 424-438 W. 33rd Street, New York Sots'&aiisih. 'Radio' ammarlund PRECISION PRODUCTS Zeh Bouck says: "MORECROFT is the finest engineering interpretation of Radio's first quarter century we have." John H. Morea ojl Second Edition — Revised and Enlarged Principles o£ Radio Communication BY JOHN H. MORECROFT Again Mr. Bouck says: "No radio book has ever been of greater utility to the engineer and student than this classic — the only reliable reference of its kind six years ago and today the most astounding collection of answers to technical questions from the analysis of radio frequency phenomena in terms of complex formulae to why a particular amplifier howls." $7.50 JOHN WILEY & SONS, Inc. 440 Fourth Ave., New York Please send me Morecroft's RADIO COMMUNICATION for free examination. Within ten days after its receipt, I will either return the book or send you $7.50. Name Address Firm RB 10-29 • OCTOBER 1929 • • 367