GB580880A - Improvements in arrangements for automatic volume control in thermionic amplifiers - Google Patents

Abstract

580,880. Automatic gain control. GENERAL ELECTRIC CO., Ltd., BIGGS, A. J., and JONES, C. C. Jan. 12, 1942, No. 446. [Class 40 (v)] A delayed A.V.C. circuit comprises a gridcontrolled thermionic valve, with the output resistance shunted by a diode, which is arranged to conduct when the input is below a certain level, and becomes non-conducting when the input exceeds that level. The input terminal of the arrangement is connected through a blocking condenser C to the control grid of a valve V1. The other input terminal is connected to H.T. -, which is connected to the grid of V1 through grid lead R4. The anode of V1 is connected to H.T.+(1), which may be at earth potential, through output resistance R3. The cathode of valve V1 is biassed positive with respect to H.T. - by a potentiometer R1, R2, and decoupled by a condenser C1. The resistance R3 is shunted by a diode V2, the anodes of the valves V1, V2 being connected together and through a resistance R5 to H.T.+(2) which is positive with respect to H.T.+(1). The values of R5 and R3, and the H.T. voltages are chosen so that, for low inputs, the diode V2 is conducting, and the voltage across R3 remains constant. For larger inputs, the diode V2 becomes non- conducting, and the A.V.C. voltage developed across R3 increases with the input. In other arrangements, the output resistance R3 may be in the screen grid circuit of the valve V1, or in the cathode circuit.