GB265222A - Improvements in electric discharge devices - Google Patents

Abstract

265,222. British Thomson-Houston Co., Ltd., (Assignees of Charlton, E. E.). Jan. 28, 1926, [Convention date]. Vacuum tubes.-In electric rectifiers operating by gas - ionization discharges, the cathode consists of two independent concentric hollow cylinders 6a, 6b of materially different diameters, the outer cylinder 6a being open at both ends and the inner cylinder 6b closely surrounding an anode 5 of smaller area than the cathode and reducing reverse discharge. The cylinder 6b of nickel &c. is connected by wires 9, 10 to the cylinder 6a of nickel, iron &c. The anode 5 comprises a rod projecting from a sleeve 8 of alumina protecting a glass sleeve 7 around the lower part of the rod 5 from electron and ion bombardment. During the half-waves when the rod 5 is positive, electrons proceed from the cylinder 6a to the rod 5 and produce cumulative ionization of the gas. During the other half-waves, electrons proceed from the rod 5 to the cylinder 6b and produce less cumulative ionization owing to the shortness of their path, thus decreasing the current during these half-waves. A wire 11 on the cylinder 6<a> extends into the neighbourhood of the anode 5 to reduce the starting voltage. The filling may be neon, helium or argon or a mixture of helium and argon at 5-20 mm.. the bulb and metal parts being previously freed from water vapour and other gases. After sealing, a getter is volatilized from a metal capsule 13 by high-frequency currents. Metallic calcium or magnesium may be placed within the capsule. To reduce the starting potential, an alkali metal such as caesium, rubidium or potassium may be introduced, a mixture of alkaline earth metal and a small quantity of an alkali metal halide being then placed in the capsule so that alkali metal and part of the excess of alkaline earth metal are volatilized. Specification 246,036 is referred to. The Specification, as open to inspection under Sect. 91 (3) (a), comprises also the use of magnesia or other refractory oxide freed from gas by heating in hydrogen to 1600-1800‹ C. as the material for the sleeve 8. This subject-matter does not appear in the Specification as accepted.