GB306003A - Improvements in or relating to electric circuit coupling devices suitable for use with thermionic valves and the like - Google Patents

Abstract

306,003. Marconi's Wireless Telegraph Co., Ltd., (Assignees of Roberts, W. van B.). Feb. 13, 1928, [Convention date]. Grant allowed. Thermionic amplifiers.-Energy is transferred from one circuit to another, for example from the plate circuit of one valve to the grid circuit of a succeeding valve, by a coupling arrangement which is equally effective at all frequencies within a given tuning range. As shown in Fig. 1 the plate circuit of the valve 1 includes an inductance coil L1, which has a condenser C and coil L2 connected across it. The natural frequency of the closed circuit 3 is lower than any frequency to be received. A series-resonant tuning-circuit 5, 6 is connected across the coil L2, and the output voltage for the succeeding grid 2 is taken across the condenser 5 or the coil 6, both of which are of high reactance. It is shown bv analysis in the Specification that for a given plate current in the valve, the voltage across the coil L2 (in the absence of the shunt 5, 6) can be expressed as a ratio of two expressions each involving the values of L1, L2, C and the frequency. By suitably choosing L1, L2, and C, the ratio can be made substantially uniform over a given range of frequency. Tuning can be effected by varying either the inductance 6. or the capacity 5, or both. The output to the grid of the next valve may include a grid leak and condenser. In a modification, shown in Fig. 2, the closed circuit 3 comprises two condensers C1, C2 and a single coil L, plate voltage being fed through a separate choke coil 4. Specification 273,639 is referred to.