GB789875A - Improvements in or relating to glow discharge devices - Google Patents

Abstract

789,875. Cold-cathode tubes. WESTERN ELECTRIC CO., Inc. March 23, 1956 [March 24, 1955], No. 9129/56. Class 39(1). A glow discharge tube comprises a molybdenum wire anode 20 supported within a glass envelope 21 by a lead 22. A helically coiled molybdenum wire cathode 24 is welded near one end of a bimetallic strip formed by a molybdenum plate 26 and a nickel plate 27, the other end of which is welded to a support lead 28. The tube is operated at a point away from the Paschen minimum of the breakdown voltage-pressure x distance curve, and changes in gas density in the discharge gap due to localized heating of the cathode by the discharge are compensated by the bimetallic strip which increases the anode-cathode spacing so that the breakdown voltage remains constant. The anode-cathode spacing may be adjusted initially by etching the end of the anode by positive ion bombardment as described in Specification 789,876 and the spacing, shape of the cathode and gas pressure are preferably chosen to attain a stable negative resistance characteristic as described in Specification 686,427, which also discloses alternative forms of cathodes which may be used. A preferred gas filling is neon at 100 mm. pressure. If the tube is to be operated under conditions of severe ambient temperature variations, the anode may also be mounted on a bimetallic strip so that changes in the ambient temperature will not affect the anode-cathode spacing. The tube is suitable for use in the telephone switching networks described in Specification 704,108 [Group XXXIX].