GB792365A - Improvements in and relating to electric discharge devices - Google Patents

Abstract

792,365. Discharge lamps; thermionic cathodes. SYLVANIA ELECTRIC PRODUCTS, Inc. July 9, 1954 [July 10, 1953], No. 20217/54. Class 39(1). An electric discharge device such as a discharge lamp comprises an envelope and two lead-in wires sealed through the envelope and connected by a cathode comprising a cable constituted by at least two wires wound together in parallel to form a helical coil, the cable being wound helically again to form a coiled-coil, the wires in the cable being spaced from one another, and no other wire being connected in parallel with the wires within the envelope. Four 1À25 mil. tungsten wires 1, 2, 3, 4 are wound, with 51 turns of each wire per inch, on a 2À5 mil. molybdenum mandrel 5, Fig. 1, and the structure is wound with 105 turns per inch on a 9 mil. molybdenum mandrel 6, Fig. 2, to form a coiled-coil. The structure is annealed in wet hydrogen at about 1550‹C. for a period of about 5 or 6 secs. and then wound on a 26 mil. steel mandrel 7, Fig. 3, with 28 turns per inch, the steel mandrel being then mechanically withdrawn to form a coiled-coiled-coil. The structure is then annealed in dry hydrogen for 10 mins. at about 1500‹C. and the mandrels 5 and 6 dissolved out in a mixture of four parts nitric acid and one part sulphuric acid. A coating or filling of one or more alkaline earth carbonates is applied to the coil, the carbonates being changed to oxides by heating during exhaust of the device.