GB406744A - Improvements relating to circuits including thermionic valves for the amplification of electric signals - Google Patents

Abstract

406,744. Valve amplifying circuits. ROBINSON, E. Y., Garvary, Dryden Road, Bush Hill Park, Enfield, Middlesex, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Crown House, Aldwych, London. July 8, 1932, No. 19397. [Classes 39 (i) and 40 (v).] The two valves 4, Fig. 1, of a push-pull amplifier each have an additional electrode 8, at high potential located between the control grid 3 and the anode, and means for suppressing secondary emission from the anode, the voltages applied to the grids 3, 8 being such that the valves operate with a low quiescent current and each amplifies alternate half-waves of the signal. Secondary emission from the anode is preferably suppressed by an additional electrode 11 tied to the cathode. Alternatively the anode may be of slatted construction, the slots being arranged edgewise to the flow of electrons. A common source of grid-bias 5 is used, the high resistance 10 preventing parasitic oscillations. The quiescent currents of the valves are matched by adjusting the potentials of the grids 8, an ammeter 9 indicating the optimum condition. The ammeter may have a differential winding, the currents through the valves being equal when the indicator is at zero. (Figs. 2, 3, not shown). The two valves may be contained within a common envelope, Fig. 4, the characteristics of the valve being modified so that with a low or zero grid-bias the optimum quiescent current is obtained. In this case, a condenser 15 across one primary of the output transformer prevents parasitic oscillation. Specification 399,703 is referred to.