GB303381A - Improvements relating to thermionic cathodes - Google Patents

Abstract

303,381. British Thomson-Houston Co., Ltd., (Assignees of Perrott. L. F., and Fitzpatrick, J. J.). Dec. 31, 1927, [Convention date]. Vacuum tubes.-A cathode, having a foundation of nickel, is coated with the carbonate of an alkaline earth metal, such as barium, and heated to more than 1050‹ C. until the surface becomes shiny and metallic in appearance. The sheet metal cathode 1, Figs. 1 and 3, preferably of nickel, is made into cylindrical form and may be welded to a wire 3 mounted on a conductor 4, a refractory heating spiral 5 being enclosed therein and connected to the conductors 4, 6. The coating may be applied as an aqueous solution or suspension by dipping or painting; a binder, such as a cellulose derivative dissolved in amylacetate, may be used. The bulb 8 is exhausted through a tube 11 and the temperature of the cathode is then raised above 1000‹ C. the vacuum being maintained. A gas, for example argon, neon, or hydrogen, may be inserted through a tube 13, or mercury 14 may be employed. The preliminary heat treatment may be carried out in any of the above gases but in this case a further treatment in a maintained vacuum should be applied. A full-wave rectifier embodying the invention is provided with two anodes 16, 17, Fig. 4, and a cathode 18 having a shield 25 which may be connected to the cathode 18 by a conductor 26 or may be insulated therefrom. Specification 278,750 is referred to. The Specification as open to inspection under Sect. 91 (3) (a) comprises also a foundation consisting of a nickel alloy, iron, molybdenum, tungsten or platinum and a coating material consisting of a compound of an alkaline earth metal or a mixture of compounds. This subjectmatter does not appear in the Specification as accepted. Reference has been directed by the Comptroller to Specification 298,906.