GB636700A - Improvements in or relating to circuit arrangements for selectively causing a desired potential to appear at a desired point in the circuit - Google Patents

Abstract

636,700. Valve circuits. STANDARD TELEPHONES & CABLES, Ltd., McWHIRTER, E. M. S., DUNN, R. H., and LENNOX, P. W. Feb. 14, 1947, No. 24096. Divided out of 636,667, [Group XL (b)]. [Class 40 (vi)] A circuit comprises a number of branches which connect a common point via rectifiers to a number of control points which are also each connected via a low resistance path to a reference potential so that only when equal control potentials are simultaneously applied to all the control points is a control potential of equal value applied to the common point. The circuit may comprise a principal and a number of additional grid-controlled coldcathode gas-discharge tubes arranged so that a desired potential is applied to the control electrode of the principal tube only when all the additional tubes have been rendered conducting, the cathode of each of the additional tubes being earthed through a low value resistor with a point on each of these resistors connected via a rectifier to the control electrode of the principal tube. The Figure shows a circuit comprising a principal tube 26 and a series of additional tubes 21 to 25, the cathodes of which are earthed via resistors 27 to 31. When any one of the additional tubes, e.g. tube 21 is rendered conducting by a positive potential applied to its anode and control electrode the anode current flow causes the potential between the tapping point on its cathode resistor 27 and earth to increase positively, but since rectifier 32 is reversely connected and presents an impedance of say 20 megohms the positive voltage applied at the control electrode of the principal tube 26 is insufficient to cause this tube to conduct even when a positive pulse is applied to conductor 38. If all but one of the tubes 21 to 25 is rendered conducting the rise in voltage of the control electrode of tube 26 will still be very small. When however all the tubes 21 to 25 are conducting the voltage at the tapping points on their cathode resistors will be equal and therefore the conductor 37, and thus the control electrode of tube 26 will assume this value and the tube wall conduct when a positive going pulse is applied to conductor 38. In a modification, Fig. 1 (not shown), two additional tubes only are used, the tapping point on the cathode of one being connected via a reversely connected rectifier to the control grid of the principal tube and of the other via a resistor having a value which is high compared with the forward resistance of the rectifier but low compared with its backward resistance.