Patent GB-759929-A (GB)
Title: Improvements in or relating to cold cathode electric glow discharge devices
IPC: H01J17/44
Filed: 1953-12-01
Abstract: 759,929. Cold-cathode tubes; cathode materials and processing. GENERAL ELECTRIC CO., Ltd., and NEILL, T. R. Dec. 1, 1954 [Dec. 1, 1953], No. 33364/53. Class 39 (1). [Also in Group XI] In a cold cathode trigger tube comprising an anode a, Fig. 1, a cathode c in the form of a metal sheet, and at least one trigger electrode in the form of an auxiliary anode extending parallel to an adjacent part of the edge of the cathode, the auxiliary anode is located much nearer to the cathode than to the anode and is positioned within regions whose section is shown shaded in the drawing and which are bounded on one side by an imaginary smooth continuation b of the cathode, on another side by surfaces generated by imaginary straight lines e connecting points on the edge of the cathode c to points on the anode a, and on another side by a cylinder d whose axis coincides with the anode a and whose radius is equal to the least distance between the anode and the cathode surface. The cathode c may be rectangular or circular in shape or may be a curved sheet, for example part cylindrical or part spherical in shape. The main anode a and trigger electrode are preferably each in the form of a rod or wire, but may be metal sheets. In the case of a circular cathode two or more arcuate trigger electrodes may be employed, or a single trigger electrode in the form of a wire bent into a ring and mounted concentrically with respect to the cathode. The surface of the cathode facing the main anode may be provided with an emissive coating or may be cleaned by a discharge during manufacture of the tube. In the tube shown in Fig. 3, the cathode 1 is a flat rectangular sheet of a high melting-point metal such as nickel or molybdenum coated on one surface with electron emissive material such as barium oxide, and supported by two nickel wires 2 welded to two nickel rods 3 which are sealed into a pressed glass disc 4 on the circumference of a circle centred on the axis of the disc. A nickel rod anode 6 and two trigger electrodes 7 are also sealed into the disc 4 on the circumference of the said circle. The end of the anode 6 is approximately level with the top edge of the cathode 1. The trigger electrodes 7 are cranked at their lower ends so that the upper portions extend parallel to and spaced about 1 mm. from the side edges of the cathode, and a transverse nickel wire 5 is spot-welded to the electrodes to hold them rigidly in position. The rear surface of the cathode 1 is coated, after the attachment of the mounting wires 2, with aluminium paint, and is then heated to a temperature of about 900‹ C. in an atmosphere of hydrogen with a trace of oxygen for about 10 minutes to transform the paint to aluminium oxide. The wire 5 and parts of the trigger electrodes 7 not required to support a discharge are coated with a suspension of alumina in a suitable binder. The anode 6, trigger electrodes 7 and cathode support-rods 3 are continued within the glass disc 4 by lengths of copper clad nickel wire which are in turn continued by nickel-iron-chromium rods 10 constituting the terminal pins. The gas filling consists of neon with 20 per cent argon at a pressure of 40 mm. of mercury.