GB765683A - Improvements relating to electrical amplifiers - Google Patents

Abstract

765,683. Valve amplifying circuits. FIELDEN ELECTRONICS, Ltd., [formerly FIELDEN (ELECTRONICS), Ltd.]. April 7, 1955 [Jan. 14, 1954], No. 1099/54. Class 40(6) A direct-current amplifier comprises a leaky-grid detector-oscillator coupled with an anode-bend detector. The leaky-grid detector-oscillator V1 is of the cathode-tap type and the anode-bend detector V2 is connected across the oscillator coil L1. Each detector has a pair of series resistors R1, 3 and R2, 4 respectively, in its anode circuit with the ratio R1:R3=R2:R4. The common points in each pair, A, B respectively, are bridged by a pair of input terminals E2 in series with a moving-coil meter movement M the pointer a of which forms, with a fixed electrode b a variable capacitor. This capacitor forms, with the series grid capacitor C1 a variable tap across the oscillator circuit, since the anode of the valve V1 is earthed for oscillator frequency via a capacitor C2. A pair of output terminals E2' are connected to the valve anodes. The circuit is adjusted so that in the absence of any input at the terminals E1 the anode potentials of the valves are equal and the current through the meter M zero. Any change in oscillator amplitude then causes the anode currents in the two valves to change in opposite directions; the resulting current through the meter M alters the grid tapping point of the valve V1 in such a sense as to restore the amplitude of oscillation to normal. The insertion of a potential at the terminals E1 likewise tends to upset the balance and the circuit responds so as to reduce the current in the meter M to zero. An equal and opposite potential then exists across the points A, B, and a potential amplified in the ratio (R3+R1):R1 across the ouput terminals E2.