GB560844A - Improvements in and relating to cathodes for electrical discharge devices - Google Patents

Abstract

560,844. Thermionic cathodes. BRITISH THOMSON-HOUSTON CO., Ltd. July 8, 1942, No. 9466. Convention date, July 12, 1941. [Class 39 (i)] A cathode, more particularly of the coiled coil type and for use in fluorescent discharge electric lamps comprises a wire helix through which passes a core wire of larger cross - sectional area than the wire of the helix, the helix or core wire having a polygonal cross-section so that each convolution of the helix makes contact with the core wire only at a series of isolated points. The core wire constitutes a heat reservoir tending to prevent the formation of hot spots at points where the discharge strikes the wire helix. The helix may be welded to the core wire at the points of contact and may be coated with activating material, which may also fill the spaces between the helix and the core wire. The wire from which the helix is formed may be of tungsten and may be of round, flat or angular cross-section. In the constructions shown in Figs. 3 and 5 a fine wire 11 in the form of a circular helix surrounds a core wire 15 of triangular or square section, whilst Figs. 8 and 9 show a circular core wire 15a enclosed in helices 11a of triangular or square cross section. In other constructions a polygonal core may have convex or concave sides or may be of cruciform or star cross-section. The sides of a polygonal helix may be outwardly bent at the points of contact with the core.