Radio today (Sept 1935-Dec 1936)

Give the "OLD RELIABLE" new PEP MODERNIZED JEWELL No. 53S MODERNIZE your OBSOLETE TUBE CHECKER with "PRECISION" A This modernization service is available for most of the popular TUBE CHECKER and SET ANALYZER models. Instruments are brought "up-to-the-minute" with all the advanced and tested engineering refinements that go into the construction of a "new job." "Precision" modernizations incorporate accuracy . . . flexibility . . . ease of control . . . true professional appearance. When writing for details please mention make and model number of your old instrument. WRITE FOR OUR PLAN Modernization Div. Dept. T PRECISION APPARATUS CORPORATION 821 East New York Ave., Brooklyn, N. Y. SERVICE NOTES (From page 50) quency response, its noise level is high originally and increases with years, and requires an exciting current for operation. Velocity or ribbon type The velocity microphone does not require a diaphragm. It has a loosely suspended ribbon maintained in an intense magnetic field. Sound pressure waves hit against the ribbon, causing it to move. This cuts the magnetic field of the magnet, producing varying potentials across the extreme terminals of the ribbon. Advantages : It has a highly directional pick-up range which is advantageous for indoor work. Its noise level is at a minimum. Its frequency response is excellent and is largely limited by the design of its coupling transformer. Limitations: This type of microphone is not a good device for close talking, giving bassy reproduction and is not particularly adapted to outof-door work because of the delicately suspended ribbon. There are fundamentally two different types of crystal microphones. One — a diaphragm type, which em ploys a sound cell with a diaphragm attached to some point on the cell. In the diaphragm type of crystal microphone, sound waves strike the diaphragm and vibrate the sound cell. The sound cell is so constructed that feeble currents are generated in proportion to both the level and frequency which strike it. This feeble electric current is then sent to the amplifier. In the sound cell type of crystal microphone, no diaphragm is employed. This has the added advantage of producing a far better frequency response than the diaphragm type as there are no limitations to the mechanical vibration which is set up in the former. Advantages: The crystal microphone is rugged, is suitable for both indoor and outdoor work and has excellent frequency characteristics. Limitations: Low output and high impedance. Condenser type The condenser microphone operates upon the principle of changing capacity between two electrodes. A stretched metallic diaphragm is insulated and separated by a very small distance from a flat electrode. In this case the sound pressure waves, (To page 59) CORNELLD UBI LI ER CONDENSERS The majority opinion expressed by both servicers and jobbers at the I.R.S.M. convention in New York last month was that Cornell-Oubilier Condensers unquestionably were first in • DESIGN • PERFORMANCE • ENGINEERING • SALES APPEAL You, too, can enjoy the profit possibilities of the world's most complete condenser line! Dependable in performance, moderately priced, they are within the reach of all interested in furthering their business. Have your local authorized C-D distributor show you the complete line or write direct for latest descriptive catalogs. PAPER . WET & DRY ELECTROYLTIC . MICA . DYKANOL CORNELL DUBILIER CORP., 1022 Hamilton Blvd., So. Plainfield, N. J. c@iiau©iiniy 1 LEliU BESIDES the "noise test" that's causing so much comment among the trade and so many sales of tubes to customers — the Duplex Test for Output is another R-T-L feature at the forefront. Provides simultaneous check on both grid control and emission. How? Let us tell you — about both these and other R-T-L features — away ahead of all other testers! Ask For Folder THE RADIOTECHNIC LABORATORY H5"? EVANSTON, ILL. PTube £ff-& v .Test lipRTl-gy Equipment RADIOTECHNIC 52 Radio Today