GB393318A - Improvements in or relating to thermionic amplifiers - Google Patents

Abstract

393,318. Valve amplifying circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand. London, and ARMSTRONG, R. B., 130, Wood Street, Chelmsford, Essex. Dec. 2, 1931, No. 33460. [Class 40 (v).] In a valve amplifier in which the gain is controlled automatically by varying voltage, the varying voltage is produced by a resistance whose magnitude varies in dependance upon received signal strength. The Figure shows a valve 19 which serves as the biasing resistance of the amplifying valve 3 and whose bias is derived from the detector. A separate detector in parallel to the normal signal detector, Fig. 3. (not shown) may be used. The Provisional Specification describes modifications in which the bias of the amplifying valve is derived from a fixed resistance connected between the detector cathode and the anode supply source, the detector being either the normal detector or separate detector connected in parallel. In further modifications an auxiliary screen-grid valve is used and the voltage across a resistance in the detector valve is applied to the screening grid, the current through the screen-grid valve passing through a resistance the voltage across which controls the bias of the controlled amplifying valve. In further arrangement the detector current passes through a resistance the voltage across which provides the screen-grid voltage of the controlled amplifying valve, or the voltage across the resistance may be amplified by screen grid valve before being used as the controlling voltage.