Patent GB-426634-A (GB)
Title: Improvements relating to automatic volume control for radio receiving apparatus
IPC: H03G3/22
Filed: 1933-09-30
Abstract: 426,634. Valve circuits for wireless reception. STEVENS, S. A., THOMPSON, L. E., and WESTINGHOUSE BRAKE & SAXBY SIGNAL CO., Ltd., 82, York Road, King's Cross, London. Sept. 30, 1933, No. 26964. [Class 40 (v)] A dry surface contact rectifier is supplied with signals and its rectified D.C. output is applied to the grid of a preceding valve, a potential derived from the anode current of this valve being used for controlling the gain of another valve or valves. As shown, the carrier frequency amplifier Vl, Fig. 3, feeds a rectifier and demodulating detector D, the D.C. potential developed across its load resistance R4 being fed through lead 17, to the grid of valve V1. The cathode of this valve is connected to the negative high tension terminal through resistances R1, R2 and a resistance R3 connects said terminal to the earth line 4. Potentials for the gain control of other valves are derived, over lead 14, from the junction 19 of a rectifier M and resistance R5 connected between the junction 15 of resistances R1, R2 and a tapping on the resistance R3 or direct from the point 15, Fig. 1, (not shown). The arrangement shown delays the application of gain control potentials until the point 15 is negative to the tapping on resistance R3 when the rectifier M becomes conducting and the point 19 assumes substantially the potential of the point 15. Additional amplification of the volume control potentials can be effected by deriving from the anode circuit of the controlled valve a still further D.C. potential in like manner for application to a further preceding valve. For interchannel noise suppression, the grid 23 of a low frequency amplifying valve V3 is biassed to cut-off by positively biassing the cathode 24 relative to earth through a resistance R10 and lead 25 or passing current through the resistance R10 from the high tension source. When a signal is received, the drop in anode current of the valve V1 increases the positive potential at the end 20 of the anode resistance R6 and hence the potential applied to the gas discharge tube N connected to a variable tapping on a resistance R7 connected between the point 20 and earth. At a predetermined signal strength the tube N becomes conducting and passes current through a resistance R9 included in the grid circuit of valve 23 to neutralize the muting bias derived from the resistance R10. The tube N may serve as a visible tuning indicator. In a further embodiment, Fig. 4, the carrier frequency amplifier V 1, feeds through a condenser C1 a gain control rectifier M3 which functions similarly to the rectifier D of Fig. 3, but its action is delayed by a bias derived from the potential divider R13. A separate demodulating detector D is provided, the circuit of which includes in addition to the load resistance R4, a resistance R 11 through which a large muting current flows in the absence of signals above a predetermined strength. This is derived from the point 15 through a rectifier M2 when said point is positive relative to the variable tapping 28 on the potential divider R12 to which one end of the resistance R11 is connected. When the point 15 becomes relatively negative the rectifier M2 becomes nonconducting and the muting current through R 11 ceases. The valve V1 may function as a low frequency amplifier when the switches S1 and S2 are in their upper positions to connect a gramophone pick-up PU to the control grid of valve V1, the output developed across a low-frequency choke L in its anode circuit being fed to the output valve V7, through a condenser C2. Specifications 381,206 and 385,619 are referred to. Reference has been directed by the Comptroller to Specification 407,317.