GB426803A - Improvements in volume control in radio receivers - Google Patents

Abstract

426,803. Valve circuits for wireless reception. MURPHY RADIO, Ltd., and MOXON, L. A., 62, Brook Street, Hanover Square, London. Oct. 12, 1933, No. 28213. [Class 40 (v)] For automatic volume control a varying master bias voltage is arranged to vary the bias of each controlled valve only between definite limits both independently determinable for each valve. As shown, three intermediate frequency amplifiers 1, 2, 3 with tuned grid circuits 4, 5, 6 respectively feed the tuned input circuit 7 feeding the diode rectifier 8 of a double diode triode valve 12. The rectified D.C. potential developed across the load resistance 9 is applied through a resistance 11 to the grid of the triode portion of valve 12. Delayed amplified A.V.C. potentials are derived from the point 25 as follows. Connected across the H.T. supply are two parallel circuits one comprising the triode 12 and resistance 14 and the other the resistance 13, which may be that of the rest of the receiver, and a resistance 15, which may be a loud-speaker field winding. Connected in series between the points 20 and 21 which are the intermediate points of the above-mentioned circuits, are a resistance 24 and diode 23. As the potential of the point 21 falls relative to the point 20 owing to the change in impedance of the triode 12 due to a rectified signal voltage on its grid a point is reached at which the diode 23 becomes conducting and the point 25 thereafter follows the potential of the point 21. The master bias thus produced is distributed to the valves 1, 2, 3 as follows. The grid of valve 3 is connected to the point 25 through a resistance 26, that of valve 2 through a resistance 31 and rectifier 28 and that of valve 1 through rectifiers 33, 28. The cathodes of valves 1, 2, 3 are connected to points 20, 30, 35 respectively of suitable potential, on the resistance 15. The point 30 is also connected through a rectifier 27 to the resistance 26 and through a resistance 29 to the rectifier 28 while the point 35 is also connected through a rectifier 32 to the resistance 31 and a resistance 34 to the rectifier 33. When no signals are being received none of the resistances 24, 26, 29, 31, 34 is carrying current and all the grids are at cathode potential. As the point 25 becomes more negative, after a certain signal strength is exceeded, the grid of valve 3 is affected through resistance 26 until the rectifiers 27, 28 pass current. The grid of valve 3 is then connected to the point 30 and the potential of the point 25 reaches the grid of valve 2 through resistance 31. As the point 25 becomes increasingly negative the rectifiers 32, 33 pass current, the grid of valve 2 attains the potential of the point 35 and the potential of the point 25 is communicated to the grid of valve 1. By returning the parallel branches such as 26, 27 and 28, 29 to points of different potential, the control of one valve may be caused to begin before or after the cessation of the control of the valve previously controlled. Specification 407,317 is referred to.