GB216589A - Improvements in thermionic valve circuits - Google Patents

Abstract

216,589. Willans, P. W. March 2, 1923. Thermionic amplifiers and detectors; heterodyne receiving systems.-The oscillations set up by a back-coupled valve are prevented from energizing an aerial or other input circuit by a bridge arrangement of the circuits. As shown in Fig. 1, the plate circuit of the valve V is back-coupled to a tuned grid circuit B. One side of this circuit i connected to the grid of the valve and the other side is connected to the filament through an impedance X equivalent to the grid-filament impedance of the valve. The aerial coil A is connected between the filament and the mid-point of the grid coil B, which are points of equal potential as regards oscillations in the circuit B, which therefore do not affect the aerial coil A. The coil A may be connected to a point between two condensers instead of a mid-point of the coil. In a modification shown in Fig. 2, the aerial A is coupled to a coil C, which is connected at one end to the grid of the receiving-valve V, at its midpoint to the filament through a tuned circuit F, B, and at its opposite end to a balancing impedance X shown as an unlit valve similar to the valve V. The plates of the valves are connected to each other and the plate coil E is back-coupled to the tuned grid circuit F, B. An electrostatic shield D separates the aerial coil A from the coil C. A resistance Q may bel provided across the grid and filament of the unlit valve X, if the receiving valve passes grid current.