GB237236A - Improvements in electric discharge devices - Google Patents

Abstract

237,236. British Thomson-Houston Co., Ltd., (Assignees of Charlton, E. E.). July 17, 1924, [Convention date]. Vacuum tubes.-A discharge device of the gas ionization type for rectifying both halves of an alternating current has a single cathode and a plurality of anodes, the cathode being of greater superficial area than the anode and so positioned as to shield the anodes from one another so as to prevent discharges between the anodes. The cathode may comprise a plate 2, Fig. 1, of nickel, iron, molybdenum, tantalum, &c. with anodes 3 consisting of tungsten, nickel, or other wires arranged close to and on opposite sides of the cathode 2. The bulb 1 is filled with helium or a mixture of helium and neon at a pressure of from 5 to 80 mm. of mercury. It is preferred to use helium at a pressure of 19 mm. of mercury. A small quantity of metallic magnesium, calcium, or other alkali-earth metal may be applied to one of the electrodes which, after exhaustion of the bulb and the introduction of helium, are heated by a high-frequency field to the vaporizing temperature of the magnesium &c. thereby depositing a film of the metal on the walls of the bulb. This film is chemically reactive towards gaseous impurities, the removal of which lowers the voltage consumption of the device as described in Specification 237,235. Caesium, rubidium, or other alkali metal may be introduced into the bulb and oxidized by admitting a little oxygen and warming the bulb. The anodes 3 may be connected to the terminals of the secondary winding of a transformer, the cathode being connected in series with a load to an intermediate point. A wave filter consisting of a series inductance and shunt condensers may be provided to produce a steady current condition. The cathode may consist of two electrically connected cylinders 16, 17, Fig. 3, each surrounding an anode, 18, 19, which may be a small wire or, as shown, a larger rod. In order to reduce the effective area of rod-shaped anodes, they are surrounded by insulating envelopes 22, 23 having apertures 24, 25 at the ends. The envelopes 22, 23 may be coated with metal on their inner surfaces, the metal coatings' being connected to the anodes by helical springs.