GB301455A - Improvements in or relating to arc discharge tubes - Google Patents

Abstract

301,455. Naamlooze Vennootschap Philips' Gloeilampenfabrieken. Nov. 30, 1927, [Convention date]. Low - pressure metallic - vapour apparatus.-An arc discharge tube, adapted for use as a recti fier, consists of an envelope 1 con taining an incandescent cathode 5, preferably a Wehnelt cathode nickel or carbon anodes 8, 9 and a filling constituted by mercury vapour and a gas which is not a raregas, e.g., hydrogen, nitrogen carbon monoxide, or carbon dioxide. In addition, a small quantity of a rare gas, such a; argon, may be employed. The gas pressure and the distance be tween the cathode and the anodes are such that the potential between the, electrodes is lower than the ionization voltage of the gas. Preferably the gas pressure is lower than two centimetres of mercury and the distance between the electrodes is of the order of one centimetre. The tube contains some drops of mercury; the temperature of the tube being relatively low, under 100‹ C. The cathode core consists preferably of a highly refractory metal, such as tungsten, on which a wire of lower melting-point, e.g. nickel, is wound, a coating being added of an alkaline earth metal, e.g. barium, an oxide thereof, or a compound which will yield an oxide on heating. In an example, the temperature of the cathode is 1000‹ C., the pressure of the hydrogen employed is 0.5 millimetres, the interelectrode distance is about 5 millimetres, and the potential between the electrodes is about 10 volts. With a lower gas pressure or when used for rectifying high-tension alternating current, the inter-electrode distance mav be of the order of some centimetres. Specification 5557/15 is referred to.