GB432618A - Improvements relating to the amplification of electrical oscillations - Google Patents

Abstract

432,618. Valve amplifying circuits. NUMANS, J. J., 45, Van Soutelandelaan, The Hague. Sept. 13, 1934, No. 26339. Convention date, Sept. 13, 1933. [Class 40 (v)] To prevent distortion, in an L.F. amplifier particularly of the mains-driven type, where the resistance of the input circuit causes a shift in grid-bias potential when grid current flows, the grid potentiometer is shunted by a neon lamp or auxiliary valve designed to maintain the biassing-potential constant. As shown in Fig. 3, the potentiometer 8 supplying grid-bias to the main amplifier 2 is shunted by a voltage-control valve 9. The grid-bias on that valve is regulated by a resistance 11 in the anode-cathode circuit in such a manner that the voltage across the potentiometer tappings is kept constant irrespective of changes in the grid current taken by the main amplifier 2. The curve A in Fig. 5 shows the normal increase of grid-bias voltage Vg1 across the potentiometer 8 as the amplifier grid-current Igl rises ; curve B shows the improvement obtained by shunting a suitably-biassed valve across 8 ; whilst curve C shows the straightline effect produced by a valve having a biassing- resistance 11 as in Fig. 3. Fig. 4 shows the invention applied to a push-pull amplifier of the kind described in Specification 298,169, [Class 40 (v)]. The grid potentials of the amplifiers 2, 2 are adjusted by a potentiometer 15 and resistance 14. The voltage-control valves 12, 13 are biassed from a no-load source E, and serve to offset the effect of grid current taken by the main amplifiers.