GB480867A - Improvements in or relating to electron discharge tubes - Google Patents

Abstract

480,867. Discharge apparatus; thermionic valve circuits. FERRANTI, Ltd., and TAYLOR, M. K. Sept. 2, 1936, No. 23976. [Classes 39 (i) and 40 (v)] An electron - discharge tube comprises a cathode a, which may be thermionic or photoelectric, a control electrode b, a secondaryemitting electrode g and an anode e, each of the two latter electrodes being formed in two or more elements, which are arranged alternately and on the surface of a cylinder of circular cross-section. The elements of the electrodes g and e are respectively connected together by leads h, f and an annular permanent magnet or a magnetic coil k surrounds the tube. The electrons emitted from the cathode are constrained to follow two fan-shaped paths between the control grid support wires c, and impinge on the elements g, whereby secondary electrons are liberated which are collected by the anode elements e. A screen grid d may be provided and the electrodes e, g may take the form of coatings on the glass envelope of the tube. Additional small plate-like or wire electrodes at a small negative potential may be provided between the screen grid d and the electrodes g, e along the line joining the rods c, c which serve also to concentrate the electrons into beams, and the electrode g may be provided with heat radiating fins or a blackened surface. The tube may be used as a mixer in a superheterodyne receiver, by connecting a tuned input circuit to the control grid and a second tuned circuit to the electrode g, this latter circuit being self-oscillating and providing the local oscillation; a beat frequency is thus generated in the anode circuit. When used as an amplifier operating uniformly over a large range of frequencies, the secondary emissive electrode is used as the output electrode, the mutual conductance of the valve with respect to this electrode being negative, whereby feed-back through the valve capacity increases the input signal. By varying the magnetic field, the valve may be used for modulation or gain control. In the latter case, as applied to an A.V.C. circuit, the magnetic field is varied at the same time as the control electrode potential changes and in such a direction as to maintain the anode current unaltered in value.