GB1007920A - Improvements in or relating to electrodes for gaseous discharge lamps - Google Patents

Abstract

1,007,920. Thermionic cathode constructions. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. Aug. 18, 1964 [Aug. 21, 1963], No. 33695/64. Heading H1D. An electrode covered with electron-emissive material for a gas-discharge lamp of the kind which is ignited by means of a glow-discharge, comprises a coil 2 of tungsten wire surrounding and supported by a central core wire 1 which projects 3 from the coil at the side of the discharge, the coil being wound from a length of at least two twisted tungsten wires 2a, 2b, having a diameter small relative to the diameter of the core wire 1 The two wires may simply be twisted together or may be twisted together with one or more wires of molybdenum. The twisted wire is wound about a steel mandrel which is afterwards removed and any molybdenum wires etched away. The coil is then dipped in carbonates of barium, calcium, strontium or thorium, then fitted on a tungsten core wire 1 and heated to convert the carbonates into the emissive material, i.e. the oxides. One or more coils similar to the first coil may be wound on top of the first coil (Fig. 2, not shown) or one or more coils may be wound with a coiled length of twisted wire (Fig. 3, not shown). Preferably, the coil wire diameter is less than one-third the core wire diameter. The coiled, twisted length for the coiled coil may be wound on a mandrel of molybdenum wires or molybdenum and tungsten wires preferably having a diameter less than one-third the diameter of the coil of twisted wire and the molybdenum etched away. An example with dimensions is given.