GB499665A - Improvements in or relating to electron discharge devices - Google Patents

Abstract

499,665. Thermionic valves. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. July 26, 1937, No. 20671. Convention date, July 25, 1936. [Class 39 (i)] A thermionic valve contains an electron velocity filter in front of the control grid whereby the steepness of the characteristic curve is increased ; the velocity filter consists of two electrodes parallel to and enclosing the electron beam and a magnetic field transverse to the field of these electrodes, and the stream. In one form, the tube comprises a cathode 9 with an emissive tip 11, an accelerating grid 13, filter electrodes 15, 17, producing a transverse field and forming, with the magnetic field producing means 43, 45, a velocity selector, a control grid 19 and an anode 21. One or more electron multiplier stages may be inserted between the control grid and the anode, and the multiplier may be of the crossed magnetic and electric field type, with the control grid arranged in the plane of the secondary cathodes and the same magnet serving to produce the fields of the multiplier and the filter. In order to reduce the effect of the magnet in the filter to the required amount the filter may be enclosed in a thin screen of magnetic material. Specification 464,413 is referred to.