Patent GB-499897-A (GB)
Title: Improvements in auxiliary electrodes in electric discharge devices
IPC: H01J61/36
Filed: 1937-08-26
Abstract: 499,897. Sealing leading-in conductors; discharge lamps. GENERAL ELECTRIC CO., Ltd. (Patent-Treuhand-Ges. f³r Elektrische Gl³hlampen) Aug. 26, 1937, Nos. 23431/37, 31334/37, and 5409/38. [Class 36] [Also in Group XL] In a high-pressure mercury vapour-discharge device having a quartz or other hard glass envelope and,comprising at least one auxiliary electrode located near one of a pair of main electrodes, the auxiliary electrode is constituted by the inner end of a thin adherent metallic layer extending along a vitreous rod or tube passing through the wall of the envelope, the remainder of the layer serving as a lead to the auxiliary electrode. The layer, which is preferably of tungsten or molybdenum, may be of high resistance so that the normal series resistor for the auxiliary electrode is necessary. The layer may be partially oxidized to increase its resistance. In the construction shown in Fig. 1 a quartz rod 4 coated with a tungsten layer 3 is sealed into one end 2 of a tubular quartz envelope 1, the inner end of the rod carrying a main electrode 5 consisting of a tungsten helix coated with or enclosing thermionically active material, the helix having spaced turns 5<1> which are wrapped around the layer 3 and sealed between this layer and the tubular end of the envelope. The layer 3 serves as a lead to the electrode 5. At the upper end of the envelope a main electrode 5 is similarly attached to the end of a quartz tube 9 which is coated with a tungsten layer 11 and seated in a tubular end 2 of the envelope. Within the tube 9 is sealed a tungsten-coated quartz rod 8, the inner end of the rod projecting into the main electrode so that the end of the coating 10 thereon may act as an auxiliary electrode whilst the remainder of the coating serves as a lead to that electrode. External connection to the tungsten coatings 3, 9, 10 is effected by clamps 7, 14, 15 which engage wrappings of wire arranged on the ends of the coatings. In a modified construction a main electrode is carried by a tungsten or molybdenum strip sealed within a flat quartz tube the outer surface of the tube being tungstencoated so as to constitute an auxiliary electrode and the lead thereto. The tube is sealed into the end of the envelope of the discharge device with the inner end of the coating projecting into an enlarged portion of the envelope. As shown in Fig. 4, tungsten-coated quartz rods 4 connected by a quartz strip 19 and carrying main electrodes 5 are sealed into the envelope 1 of the discharge device. The tungsten layer 3 on the lower rod is extended over the strip 19 to form an auxiliary electrode 3<1>. Fig. 5 shows a construction in which the lower end of the envelope 1 is sealed by a metal-coated quartz rod 8, the coating being circumferentially divided to form a main layer 11 and a narrow strip 10 which is separated from the layer 11 by gaps 20. The layer 11 serves as a lead to a main electrode 5 whilst the inner end 10<1> of the strip 10 constitutes an auxiliary electrode to which current is fed through the remainder of the strip.