GB556762A - Improvements in electrical signal converting circuits - Google Patents

Abstract

556,762. Signalling by alternating current. WATSON, S. N., and WORSWICK, T. April 17, 1942, No. 5157. [Classes 40 (iii) and 40 (v)] An electrical circuit for coverting A.C. signals into double-current D.C. signals includes two electron-discharge devices the anode circuits of which carry respectively the two D.C. signal currents, means for applying to them biasing potentials such that in the absence of an A.C. signal their anode currents are substantially different, and rectifying means so associated with the biasing means as to change the sign of the difference in the anode currents when an A.C. signal is being received. In the circuit shown, the ends of the winding 1 of a teleprinter magnet are respectively connected to the anodes of two valves V1, V2. In the absence of a signal V1 passes a current controlled by the grid bias due to a resistance R 1 in the cathode circuit, and V2 is biased to cut-off point by the resistances R1 and R2 in series. When a signal is received in the input transformer T voltages are produced across the output resistances R3, R4 of two rectifiers 5, 6 in the grid circuits which increase the negative bias on V1 to cut-off point, and decrease that on V2 so that it passes an anode current about equal to that previously passed by V1, thus reversing the D.C. current in winding 1. Should incoming signals of large amplitude tend to produce a bias on V2 greater than the voltage across R2 a diode D becomes conductive, and holds the bias potential substantially to that of the junction between the resistances R1, R2.