GB567134A - Improvements in amplifier circuits employing automatic volume control - Google Patents

Abstract

567,134. Automatic gain control. STANDARD TELEPHONES & CABLES, Ltd. .Aug. 13, 1943, No. 13149. Convention date, Aug. 18, 1942. [Class 40 (v)] Instability of operation of an unbalanced push-pull amplifier due to the action of an automatic gain control potential is reduced by introducing into the circuit a degree of unbalance greater than the inherent unbalance and in a sense to produce de-generation with respect to the automatic gain control circuit. Signals from a source 10 are fed to the grids of a pair of push-pull amplifiers 4, 5, the output from which is fed through amplifiers 34, 35 to a transformer 37 feeding a load 42. A secondary coil 43 feeds a full wave rectifier 46 having a delay bias 51 to provide a gain control potential which is fed over lines 45 to the ends of a resistance 21 in the common portion of the grid circuits of valves 4, 5. A condenser 63 limits the suddenness of the action of the A..G.C. potential. To prevent instability due to lack of balance between the valves 4, 5, a resistance 60 is introduced into the anode cathode circuit of one of the valves according to the direction of unbalance. The resistance has an effect greater than the inherent unbalance and is placed so as to produce degeneration with respect to the A.G.C. potential.