GB550468A - Improvements in or relating to vacuum tube amplifiers - Google Patents

Abstract

550,468. Valve amplifying circuits. WESTERN ELECTRIC CO., Inc. Dec. 22, 1941, No. 16474. Convention date, Dec. 21, 1940. [Class 40 (v)] An amplifier having a plurality of push-pull stages connected in tandem is provided with a backward acting control circuit to maintain the output at a predetermined level and limiting means are associated with the output stage and a negative feedback path is provided to reduced the distortion produced by the .limiting means. The Figure shows a push-pull amplifier in which the bias of the input is controlled by voltage from the output applied through rectifier 17, resistances 20, 21 preventing excessive shunting of the output by the rectifier, which is delayed by the voltages across resistance 22. Bias voltage developed across condenser 16 is applied to both control and injector grids of the valves 4; 5 as described in Specification 506,128. The limiting or peak chopping is effected by grid current in resistances 48, 49 in the grid circuits of the output stages 12, 13 and by appropriate choice of bias voltage. Feedback paths 14, 15 are provided to limit the distortion while the effects of the longitudinal currents produced by control voltages are limited by the unshunted bias screen resistances 30 and 41 and by the retard coils 37, 38. The resistances 30 and 41 also assist to maintain the stages in balance while the use of push-pull stages avoids ripple voltage from the: power supply or: the control circuit producing disturbance while the absence of filters in the control circuit decreases the attack time. The amplifier may be a modulating amplifier for high percentage modulation to avoid sideband splash which is produced by over-modulation.