GB890561A - Improvements in cold cathode tubes and in apparatus using such tubes - Google Patents

Abstract

890,561. Cold-cathode tubes. PHILIPS ELECTRICAL INDUSTRIES Ltd. July 4, 1958 [July 8, 1957], No. 21494/58. Class 39(1) [Also in Group XXXVI] In a cold-cathode glow-discharge tube comprising a main anode, a cathode and an auxiliary anode, the main anode and the cathode are so arranged as to provide between them two separate and distinct discharge paths which extend from different discharge portions of one of the electrodes and have different breakdown voltages, and the auxiliary anode is located nearer the discharge path having the higher breakdown voltage. In one arrangement, Fig. 1, the main anode 3 consists of a wire loop, the ends 4 and 5 of which are spaced 2mm. and 1mm. respectively from a molybdenum plate cathode 2. An auxiliary anode 6 is spaced 1.1mm. from the end 4 of the main anode. The filling consists of neon with 0.1% argon at a pressure of 27 cms. of mercury. In an alternative arrangement, Fig. 3, the cathode is a plate 7 bent to L-shape with the legs 9 and 10 spaced 1 and 2 mm. respectively from the main anode 8. The auxiliary anode 6 is located adjacent the leg 10. The filling is as above. In a further arrangement, Fig. 4, two rods 15 and 16 forming the main anode are spaced 0.4 and 0.8 mm. respectively from a plate cathode 13 supported by wires 14. An auxiliary anode 17 is spaced 0.6 mm. from the cathode. The filling is again neon with 0.1% argon, but at a pressure of 10 cm. of mercury. The tube is utilized in a circuit (see Group XXXVI) for indicating the presence of potential differences of at the most a few volts such as exist for example between the electrodes of a transistor. If the potential difference is present the discharge, which is intermittent, is switched to the path having the higher breakdown voltage. The light from one of the two discharge paths may be at least partly shielded to provide a contrast between the two paths.