GB492984A - Improvements in thermionic valve circuits - Google Patents

Abstract

492,984. Automatic volume control. STANDARD TELEPHONES & CABLES, Ltd. May 28, 1937, No. 14852. Convention date, July 1, 1936. [Class 40 (v)] volume expansion in a low frequency amplifying valve L the bias of a gain control grid 7 is varied by the voltage developed across the load resistance 3 of a diode 2 fed with the signals. The gain control voltage is applied to the grid 7 over two parallel paths comprising a diode 19 in series with a low resistance 20 and a high resistance 21. When the bias is becoming more positive the diode 19 is conducting and the time constant of the control path is small but when it is becoming more negative the diode 19 becomes nonconducting and the path 21 only is operative with a large time constant. Said time constants depend also on the capacity of condenser 6 connected between the grid 7 and earth. The Specification as open to inspection under Sect. 91 comprises also a circuit omitting the alternative time-constant network and providing a potentiometer 23, Fig. 3 (Cancelled), for adjusting the amount of expansion by varying the input signal to the diode 2 which is ganged to a potentiometer 25 which adjusts the mean potential of the gain control grid 7 of the amplifier L. In this way the bias on grid 7 is made more negative with increasing expansion control and has the effect of suppressing weak signals such as parasitic noises. This subject-matter does not appear in the Specification as accepted.