GB569048A - Improvements in and relating to the manufacture of spiral vacuum tube filaments - Google Patents

Abstract

569,048. Discharge tubes. STANDARD TELEPHONES & CABLES, Ltd. March 9, 1943, No. 3798. Convention date, March 11, 1942. [Class 39 (i)] [Also in Group II] In the manufacture of vacuum tube spiral filamentary electrodes, a spiral is formed of the desired shape of ductible wire, which may be a thoriated tungsten wire, the wire screwed into a previously prepared sleeve provided with a spiral groove to fit the spiral and the whole heated to a temperature sufficiently high to set the wire and remove internal stresses which might cause deformation of the spiral, the sleeve then being removed. The wire may be simultaneously carburised if the sleeve or retaining enclosure is made of carbon. Alternatively, the electrode may be supported on a central mandrel provided with depressions to fit and hold the electrode which was then painted. with colloidal graphite or the assembled mandrel and electrode were embedded in granulated carbon and the whole heated to the carburising temperature, the mandrel then being removed. The filament may be in bi-filar or quadra-filar form, and may be lubricated with colloidal graphite as it is screwed into the carbon sleeve. Filament wires 10, 11 formed to produce a bi-filar filament are supported by a member 12 and screwed into a block or sleeve 13 of carbon or other inert material and provided with a threaded groove 14. The assembled unit is then inserted in a heater 15 which may be a heating coil supplied with current from leads 16, 17 and heated to the required temperature. The unit is then removed from the heater, allowed to cool and the filament removed from the sleeve 13.