GB371745A - Improvements in or relating to thermionic amplifying systems - Google Patents

Abstract

371,745. Valve amplifying circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London. -(Assignees of Turner, A. H. ; 259, New Jersey Avenue, Collingswood, New Jersey, U.S.A.) Sept. 16, 1931, No. 25974. Convention date, Sept. 16, 1930. [Class 40 (v).] Volume control is effected in an amplifier using multigrid valves by varying the grid bias of one of the grids and simultaneously varying the bias of another grid to avoid distortion. Fig. 1 shows an amplifier in which the screening grids are biased through voltage dropping resistances 65, 67, 69 from the anode supply. Volume is controlled by variable resistance 71 which varies control grid bias. Resistance 75 is provided to avoid excessive variation of the screen-grid voltage of the first valve which may cause cross-modulation. The screen-grids may be connected through voltage dropping resistances to a higher potential than the anodes as shown in Fig. 2. The screen-potential may be increased and the control grid negative bias be increased simultaneously by a double slider 76, 77 which in addition serves as an aerial input volume control. To prevent overloading of the later valves different values of bias dropping resistances 66, 68, 70 or a single tapped resistance 66, Fig. 2, may be used. The control grid bias instead of being manually controlled, as shown, may be varied by automatic means, as by an auxiliary volume control valve. A screen-grid valve may be used as an anode-bend detector or, as shown, or as a leaky grid detector, and may have the screen-grid biased by a voltage dropping resistance 81. One of the screen-grid amplifying valves may be so biased by voltage dropping resistances as to exercise a limiting action on strong signals.