GB706201A - Improvements in or relating to cold cathode gas discharge tubes - Google Patents

Abstract

706,201. Cold-cathode tubes. MULLARD RADIO VALVE CO., Ltd. March 28, 1952 [April 13, 1951], No. 8696/51. Class 39(1) A cold cathode gas discharge tube has an anode, a' main cathode, an apertured screen and a plurality of auxiliary electrodes comprising at least a primer cathode, a control electrode and a transfer cathode, which latter extends through the aperture of said screen, whereby a discharge can be maintained between the primer cathode and the control electrode in a space screened by the said screen from any part of the main cathode-to-anode discharge path, which path is wholely on one side of the screen, and, by increasing the potential difference between the control electrode and the transfer cathode, said discharge can be extended through the aperture in the screen into the region of the main cathode-toanode discharge path, whereby the main discharge is initiated. The tube shown comprises a cylindrical envelope 3 butt-welded to a moulded glass base 10 through which pass eight lead-in wires serving externally as contact pins for the tube and internally as supports for the electrode structure. A rod anode 1 is bent at a right angle so that it faces the centre of a circular aperture 5 in the front face of the main cathode 2 which also serves as the screen and has two sides extending away from the anode 1 and enclosing the region of the auxiliary electrodes. The latter comprise a transfer cathode 6, primer cathode 7 and control electrode 8. The end of the primer cathode is formed into a loop 16 which is located opposite the aperture 5 and surrounds the transfer cathode 6. In an alternative construction the main cathode is a cylinder coaxial with the tube envelope and closed at one end by a circular plate having a central aperture opposite a rod anode sealed through the top of the envelope. The transfer cathode is sealed through the side wall of the envelope and is bent at right angles at the end to pass through the aperture in the cathode. The primer cathode is a straight wire arranged on the axis of the main cathode, the loop 16 being omitted, and the control electrode is bent at the end at right angles to the axis of the main cathode and lies approximately opposite the mid-point of the gap between the transfer and primer cathodes. The electrodes are made of molybdenum and the cathode 2 may be a fine wire gauze. Electrode dimensions and spacings, are given. The gas filling is 99 per cent neon and 1 per cent argon at a pressure of 20 mm. of mercury. In operation, the main and transfer cathodes may be connected together and to earth, the primer cathode being connected to a negative potential. The tube is primed by applying a positive potential to the control electrode and the auxiliary discharge is then caused to extend along the transfer cathode through the aperture 5 by applying an increased positive potential to the control electrode, or the tube may be triggered by applying a negative pulse to the transfer cathode. The primer cathode can be used as a " gating " electrode, since until the appropriate negative potential is applied to the primer cathode, the tube cannot be triggered by the application of the normal operating potential difference between the control electrode and transfer cathode.