Patent GB-665982-A (GB)
Title: Improvements in or relating to electric discharge tubes
Inventor: REEVES ALEC HARLEY
IPC: H01J17/48
Filed: 1947-05-28
Abstract: 665,982. Discharge apparatus. STANDARD TELEPHONES & CABLES, Ltd. May 28, 1948 [May 28, 1947], No. 14202/47. Class 39 (i). A cold cathode gas-filled electric discharge tube, comprises an ordered array of glow discharge gaps arranged in pairs, the cathodes of each pair having discharge surfaces of different effective areas differently spaced from a common anode so that the cathode of larger effective area forms with the said anode a long gap of higher striking potential than the short gap formed by the other cathode but may pass a glow discharge current of such greater magnitude than the other, for the same gap voltages, as may be caused to extinguish discharges at both gaps due to the action of a resistance capacity network common to both, the said pairs being arranged so that discharge at the short gap of a pair shall reduce the striking potential of the short gap of the adjacent pair. The tube 22, Fig. 3, comprises a plate anode 23 and a plurality of cathode pairs 3, Fig. 2, comprising a rod 4 and plate 5 connected together by a wire 7 which is bent away from the anode plate and is preferably coated with alumina or similar insulating material to inhibit spread of cathode glow along the wire between the two electrodes. Alternatively, the two electrodes may be joined together externally of the tube, and separate anodes may be provided for each cathode pair. The general level of ionization in the tube is regulated by an auxiliary cathode 24 and is adjusted, together with the voltage of battery 9 and the amplitude of pulses applied to terminal 12, so that on a first pulse the only gap which is fired is that associated with the cathode rod of the left-hand pair of cathodes 3. The second pulse fires plate 5 of the first cathode pair simultaneously with rod 4 of the second pair. Due to the considerably larger effective area of plate 5 as compared with rod 4, a large increase of discharge current is produced, which in flowing through the resistance capacity network 8 extinguishes the discharge at both gaps of the first cathode pair while the rod of the second pair remains discharging. Subsequent pulses continue the process along the array and output pulses corresponding to the discharges at either of the electrodes of each cathode pair are obtained at terminals 25. The time constants of the resistance capacity networks 8 are made considerably longer than the total time occupied by one pulse train, in order to prevent the left-hand cathode pair 3 from firing again before the last pair has been fired. As an alternative mode of operation it may be arranged that each plate cathode fires automatically at a definite time interval after a discharge has been established at the corresponding rod cathode. This time interval may be modified by the application of appropriate voltages to the terminals 25. A suitable filling for the tube comprises 92 per cent neon, 1 per cent argon and 7 per cent hydrogen at a total pressure of 100 mm. of mercury. Specification 639,827 is referred to. The Provisional Specification also refers to Specification 659,805 and mentions an alternative mode of operation, for which the priming discharge electrode is not necessary, in which it is arranged that the rod and plate gaps of a pair fire on consecutive pulses. The two cathodes of a pair may be provided with separate anodes or the cathodes led out of the tube separately and a resistance capacity network placed in a common anode circuit. The Provisional Specification also describes an arrangement, Fig. 4, in which the tube 26 comprises an anode plate 2 and a plurality of cathode pairs 28, the rod of one pair being connected to the plate of the next pair. The rod of a pair after firing is not extinguished until the plate of the next pair has fired, the rod of the said next pair being fired intermediately. This delay may correspond to two pulse intervals.