GB642731A - Improvements in and relating to volume controlling electron discharge amplifiers - Google Patents

Abstract

642,731. Automatic volume control. BRITISH THOMSON-HOUSTON CO., Ltd. May 22, 1947, No. 13780. Convention date, May 23, 1946. [Class 40 (iv)] [Also in Group XL (c)] An impedance Z2, Fig. 1, is connected between anode and control grid in an amplifier and the gain is controlled by variation of a further impedance Z3 in the cathode lead. The Specification gives mathematical expressions for the gain and shows that it may be made zero for chosen values of the impedances Z2, Z3. As applied to a peak-limiting amplifier, Fig. 3, in which push-pull output valves 39, 40 are driven from a push-pull pair 24, 25, each of the valves 24, 25 is provided with an anodegrid impedance 35 and a cathode network comprising resistances 29, 30 together with the anode-cathode path of a valve 31. A fixed amount of feedback is applied to the valves 39, 40 by means of anode-grid resistances 44 and cathode resistances 41. In order to limit the peak output the transformer 49 is provided with a tertiary winding feeding a fast-charging slow-discharging circuit 60 which is described in Specification 642,730, [Group XL (c)]. The output voltage from the network is applied to the grids of the valves 31 thereby varying the anode impedances so as to reduce the gain of the amplifiers 24, 25 ; the threshold above which gain limitation occurs is determined by a delay bias derived from a potentiometer 75. In the arrangement of Fig. 1, complex impedances Z2, Z3 may be used in order to obtain a frequency-selective gain control.