GB214262A - Improvements in and relating to electric discharge tubes - Google Patents

Abstract

214,262. Naamlooze Vennootschap Philips' Gloeilampenfabrieken. April 11, 1923, [Convention date]. Vacuum tubes.-In a tube in which an emission of secondary electrons is produced by bombardment of one or more electrodes by primary electrons, the surface emitting secondary electrons consists of a material having a Richardson constant less than 3 volts, as, for instance, the alkali and alkaline earth metals, magnesium, beryllium, titanium, scandium and certain metallic compounds such as copper oxide and the oxides of the alkaline earth metals. It is stated that a tube of this kind having a negative resistance characteristic will operate with a voltage of 30 between the anode and cathode. The material should be preferably a poor conductor of heat, and may be incorporated in or deposited on an electrode of tungsten, molybdenum or nickel. A compound which may be decomposed by heat to form the active material may be applied to the electrode before or after mounting in the tube. For example, barium oxide applied to an electrode may be heated during exhaustion of the bulb, so that nitrogen is driven off and barium is oxidized to barium oxide. In another method the material is deposited from an incandescent cathode by evaporation or disintegration. The vacuum is preferably high, but when the tube contains gas, ionization should be avoided by using voltages below the ionization voltage of the gas. In the tube shown for generating oscillations in a circuit 8, 9 the active material is contained in the anode 4, and a grid 3 between the anode and an incandescent cathode 2 is maintained by means of a battery 7 at a higher potential than the anode. The anode may be of cylindrical shape and of circular or ellipsoidal section so that any material " sputtered " from the active inside surface may be deposited elsewhere on the surface.