Abstract
This paper reviews some recent vacuum tube and photoelectric cell developments which are of interest in sound recording and reproduction systems. An indirectly heated cathode triode is described, in the output circuit of which the current components due to the a-c. power supply of the heater have been reduced approximately 20 decibels below previously obtained levels. This tube makes it possible to use an a-c. supply in amplifiers having flat frequency characteristics with over-all gains of the order of 100 decibels. The microphonic disturbances in vacuum tubes are discussed. A measuring system for evaluating the microphonic noise currents is described, and the characteristics of a filamentary cathode tube of low microphonic noise level are given. The characteristics of a double anode, thermionic, gas-filled, rectifier tube for use in a d-c. power supply unit for the sound lamp and vacuum tube filaments of reproducing systems are given. A photoelectric cell of high sensitivity for use in sound reproduction work is described.
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