GB265223A - - Google Patents

Abstract

265,223. British Thomson-Houston Co., Ltd., (Assignees of Charlton, E. E.). Jan. 28, 1926, [Convention date]. Void [Published under Sect. 91 of the Acts]. Vacuum tubes.-In electric glow-lamps, rectifiers, voltage-regulators or other devices having a gas-ionization discharge between unheated electrodes which may be of the point-toplane type, the point or inner electrode is surrounded by a shield of refractory gas-free material except at its exposed point. A rod anode 5 may be surrounded by a sleeve 8 of alumina, magnesia or other refractory oxide freed from water vapour and other gas by heating in hydrogen to 1600-1800‹ C., the lower part of the rod being surrounded by glass 7 joined to or integral with the inwardlyprojecting stem 15. The sleeve 8 does not liberate gas under bombardment by electrons and positive ions and thus avoids the increase of the starting and operating voltages due to the contamination of the rare gas filling by gaseous impurities which would take place if the sleeve were of glass. The cathode may comprise a cylinder 6<a> and an inner cylinder 6b of less diameter and height arranged to form a shield receiving the reverse discharges during the half-waves of current when the electrode 5 is negative as described in Specification 265,222. In a modification, the cylinder 6<b> is omitted. A spur 11 projecting from the cylinder 6a into the neighbourhood of the anode 5 assists the starting of the discharge. The filling may be argon, neon or helium at 5 to 20 mm. of mercury, introduced after the bulb and other parts have been freed from water vapour &c. A getter may be volatilized from a capsule 13 of nickel, iron or other metal by highfrequency induction. The capsule may contain calcium or other alkaline earth metal mixed with a reducible compound of an alkali metal such as a halide of potassium or caesium.