Patent GB-875484-A (GB)
Title: Improvements in cold-cathode stepping tubes and circuits therefor
Inventor: CROWTHER GERALD OFFLEY
IPC: H01J17/48
Filed: 1957-03-22
Abstract: 875,484. Electric counters. MULLARD Ltd. Dec. 4, 1957 [March 22, 1957], No. 9454/57. Class 106 (1). [Also in Group XL (a)] A cold cathode counter stepping tube has an electrode assembly, Figs. 1 and 2 of the Provisional Specification, comprising a central disc-shaped anode A coaxially surrounded by a circular row of rod-shaped outer electrodes consisting of cathodes K 1  &c. first guide electrodes GA 0  &c., second guide electrodes GB 0  &c., at least one rod-shaped marker electrode Ko to and from which the discharge can transfer during its travel around the electrode assembly, the breakdown voltage between the or each marker electrode K 0  and the anode A being greater than that between the anode A and any of the other outer electrodes, and the or each marker electrode K 0  being disposed at or near a position between a second guide electrode GB 9  and the next first guide electrode GA 0 . The above arrangement provides anti-clockwise rotation of the discharge, but clockwise rotation can be obtained by positioning the electrode K 0  downwardly. In a modified construction the marker electrode K 0  is positioned in the row of outer electrodes and has the majority or all of its discharge surface coated with glass or ceramic or resistive material to increase its breakdown voltage. The tube can thus be used for clockwise or anti-clockwise rotation of the discharge, and can be used to count forwardly or backwardly, i.e. for subtraction or addition. In the circuit arrangement shown in Fig. 3, the first guides GA are all connected together and the second guides GB are all connected together. The cathodes are divided into two groups of alternate cathodes, the odd cathodes K 0D  being connected together and the even cathodes K EV  being connected together. The connections are made preferably inside the tube. The anode A is connected through a resistor RA to the positive supply terminal V HT . The odd cathodes K 0D  are connected through the parallel combination of resistor R2 and capacitor C2 to a negative voltage - V x  which is negative with respect to the common negative terminal E and the even cathode K EV  are connected through the parallel combination of resistor R3 and capacitor C3 also to the negative voltage - V x . The marker electrode K 0  are connected through the parallel combination of R4 and C4 to a voltage - V y  which is more negative with respect to the common negative terminal E than is - V x . The second guides GB are connected through a capacitor Cl to an input terminal I, a direct current return for these guides being provided through resistor R1 to the common negative terminal E. The first guides GA are connected directly to the terminal E. Output pulses from the circuit appear at a terminal P connected to the anode A. The pulse appearing at the anode A when the discharge passes to K 0  is much greater than the pulses which appear at previous transfer positions and marks each rotation of the discharge around the tube. The output pulse can be limited by a diode so as to eliminate the small pulses and leave the large pulses. The second guides GB can be provided with a standing bias voltage by selection of the resistor R1. This bias voltage may be chosen so that it is greater than the amplitude of a small negative pulse appearing at the output of a preceding stage but much less than the amplitude of a large pulse from the preceding stage, thus avoiding the use of the diode referred to above. Fig. 6 shows a circuit suitable for the first stage in a chain of counting tubes. Negative input pulses are supplied through capacitor C5 and resistor R7 to the first guide electrodes GA at terminal I1 and through capacitor C6 and resistor R8 to the second guide electrodes GB at terminal I2. The marker electrode K 0  is again connected through R4 and C4 to a negative bias V y . The cathodes K 0D  and K EV  are connected to the common terminal E, a diode D being connected between K o  and the common line. The guides GA and GB are connected through resistors R5 and R6 to a voltage V b  which is positive with respect to the common terminal E. When the gap between the anode A and a guide electrode GA or GB has ionized and discharge current flows, then due to the voltage drop across R7 or R8, the guide electrode voltage is raised resulting in a reduced amplitude of the negative pulse at the guide electrode and also at the anode to clearly discriminate the larger pulse at the marker electrode K o . The output appearing at P can be applied to a succeeding counter-stage tube such as shown in Fig. 3. The diode D prevents the potential of the marker electrode K 0  from rising above that of the common line. The input pulses at terminals I1 and I2 either overlap or have no time interval between them. The tubes can be provided with more than one marker electrode K o , e.g. in a tube having twelve positions three electrodes can act as marker electrodes so that a large anode pulse is produced for every four input pulses.