GB374695A - Improvements in or relating to radio and other high frequency receivers - Google Patents

Abstract

374,695. Valve circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London.-(Assignees of Koch, W. R. ; 220, Cooper-Street, Camden, New Jersey, U.S.A.) Aug. 19, 1931, No. 23403. Convention date, Aug. 19, 1930. [Class 40 (v).] In a high frequency receiver having automatic volume control, a relay is provided for operating an indicator when the volume-controlled signal strength reaches a certain level. The Figure shows a superheterodyne receiver comprising a high frequency valve 1, first detector 3, local oscillator 5, intermediate frequency amplifiers 7, 9, second detector 11, in parallel with which is a volume control valve 15, and a push-pull low frequency stage 13 feeding a loud-speaker 43. In the output circuit of the amplifier 9 is connected the operating winding of a relay 35 which in one position short-circuits the coil of the loud-speaker 43 ; and in the other completes the circuit of an indicating lamp 46 fed from the transformer secondary 47. Grid bias and plate potentials for all valves are taken from a potentiometer 19 across the output of a rectifier 17. The control valve 15 is normally biased to the cut-off point when no signal is received and no current flows through resistances 53, 55. The grids of the amplifiers 1, 7, 9 are connected to resistances 53, 55 and are normally biased to give a predetermined anode current with no signal. The plate circuit of the valve 9 comprises two parallel branches, one containing the relay 35 and the other a potentiometer 51 which is adjusted, again with no signal, until the relay armature 37 is held against contact 39 to short-circuit the loud-speaker. When the receiver is tuned to a signal the control valve 15 passes current and the negative bias on the amplifiers 1, 7, 9 increases ; the anode current of 9 decreases and the relay armature falls on to contact 41 opening the loud-speaker circuit and causing the lamp 46 to light.