GB322814A - Improvements in and relating to thermionic amplifiers - Google Patents

Abstract

322,814. Green, H., and Celebritone, Ltd. Sept. 21, 1928. Thermionic amplifiers.-An inter-valve coupling comprises an inductance K, Fig. 1, in the anode circuit of the preceding valve V<1> coupled by a pair of condensers M<1>, M<2> of ample size to pass all low frequencies to a transformer L in the grid circuit of the succeeding valve V<2>. The resistance of the anode coil approximates to that of the valve V<1>, and the primary coil L<1> of the transformer, to which the terminals of the anode coil are coupled, has an inductance approximating to that of the anode coil. The anode coil and the transformer are constructed as sectional windings on an open core of very fine wires. The anode coil embodies resistance windings, when the valve V' is of high impedance, and at least the primary of the transformer is wound with very fine wire of high conductivity to minimize weight and bulk. To handle the outputs from two parallel valves V<3>, V<4>, Fig. 2, having theirgrids fed from separate inputs, for example the regulated inputs from a pair of gramophone pickups, a single centre-tapped coil K<1> provides anode coils for the two valves, the resistance of each half matches the resistance of the corresponding valve, and the inductance of the primary of the transformer, which is coupled by condensers M<1>, M<4> to end terminals of the anode coil, matches the inductance of each half of the coil. To prevent back coupling between successive stages a resistance R is inserted in the plate supply lead of the valves V<3>, V' to bye-pass pulsating-currents through a condenser M<3>.