GB483732A - Improvements in or relating to thermionic amplifier circuits - Google Patents

Abstract

483,732. Impedance networks. PERCIVAL, W. S. Sept. 15, 1936, No. 25095. [Classes 40 (iii) and 40 (v)] In an intervalve coupling for the intermediate-frequency amplifier of a superheterodyne television receiver, in which the interelectrode capacities 2C of the two valves form part of a band-pass filter, the effect of the earth capacity and the self-capacity of an inductance coil is compensated, and the need for using large coils is obviated, by arranging the coils to form an autotransformer. In a known arrangement. Fig 2, the filter, which is terminated at one end by a resistance R and at the other by the grid circuit of valve 2, comprises a half-section with a series arm L2, C2 and a shunt arm made up of inductance L1 and the intervalve capacities 2C, the two arms being tuned to the midband frequency, or so as to bracket the midband frequency closely, while the impedance of the shunt arm has the value appropriate to a full section instead of a half-section as described in. Specification 475,490. The invention consists in connecting the condenser C2 to a tapping on coil L1, Fig. 3, so that part or all of the inductance L2 may be replaced by the leakage inductance of the autotransformer L1. In this way the earth capacity of coil L2, which tends to narrow the pass band, and its self-capacity are eliminated or reduced ; the capacity C2 is correspondingly increased. In a modification, Fig. 4 (not shown), the resistance R is shunted by a reactance network forming an m-derived termination.