GB684552A - Improvements in or relating to circuits embodying cathode-ray tubes - Google Patents

Abstract

684,552. Automatic exchange switches. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. Dec. 16, 1947 [Oct. 23, 1946], No. 33132/47. Class 40 (iv). [Also in Groups XIX and XL (c)] A circuit for a cathode-ray tube for use as a line selector or a group selector in an automatic telephone system, of the kind in which the beam can be stabilized in any one of a plurality of rest positions and can be displaced from one such position to another, is characterized in that in each position of the beam the beam current is distributed between a first collecting electrode 4 and a second collecting electrode 3, the first collecting electrode being connected to one member of a single pair of deflecting plates 2 and through a resistance to a source of potential which is positive with respect to the cathode, in such a way that the beam assumes rest positions in response to the effect on the deflecting field of the beam current flowing through the first collecting electrode and can be shifted from one rest position to another by means of voltage pulses applied between the deflecting plates. As shown in Fig. 6, the collecting electrode 4 is directly connected to one of the deflecting plates and may be connected to an H.T. supply through a resistance 7 in parallel with a condenser 9. The tube is preferably so designed that the current ia flowing to the electrode 4 depends on the deflection voltage according to the curve 11, Fig. 2, stable positions 13, 14, 15, 16 and 36 occurring where the curve cuts the line 12 which represents the current and voltage across the resistance 7. The tube may be provided with a further collecting electrode 29 connected to the anode of a blocking oscillator valve so that when the beam reaches the end of the row of collector electrodes 3 it impinges on the electrode 29 which triggers the blocking oscillator and thus restores the beam to the beginning of the row. In a modification, Fig. 5 (not shown), the electrode 29 is omitted and a thyratron is connected across the condenser 9 and is arranged to be triggered when the condenser 9 is charged to a potential corresponding to extreme deflection so that the condenser is then discharged and the beam restored to the beginning of the row. In the modification shown in Fig. 9 the beam is shifted from one position to the next by pulses applied through resistance 27 which is connected to earth through a condenser 26, the time constant of these two being equal to the time constant of resistance 7 and condenser 9. The return of the beam is arranged by a resistance network which cuts off the valve 37 at extreme deflection and thus allows condenser 9 to discharge, the time constant of the bias resistance 40 and condenser 41 being greater than that of mixture 7 and condenser 9. The electrode 4 may be secondary electron emitting, in which case circuits generally similar to those described above may be used, Figs. 13 and 14 (not shown), or the circuit shown in Fig. 15 may be used wherein the valve 93 is normally cut-off but becomes conducting at extreme deflection; when it conducts the voltage applied to the final anode of the cathode-ray tube is reduced, thus reducing the effective beam current and causing the beam to return to the beginning of the row. Specifications 684,574 and 684,590, [Group XL (a)], are referred to. The Specification as open to inspection under Sect. 91, comprises also the subject-matter of Specification 684,574. This subject-matter does not appear in the Specification as accepted.