GB697064A - Balanced low-frequency amplifiers - Google Patents

Abstract

697,064. Valve amplifying circuits. NEDERLANDSE CENTRALE ORGANISATIE VOOR TOEGEPAST-NATUURWETENSCHAPPELIJK ONDERZOEK. Oct. 18, 1951 [Oct. 18,1950], No. 24365/51. Class 40 (vi). A push-pull amplifier the output of which is independent of H.T. supply voltage fluctuations comprises two valves directly connected over a pair of resistances 3, 4 the junction point 8 of which is maintained at the same D.C. potential as the valve anodes. The output is taken from adjustable tapping points A, B on the resistances 3, 4. A static. balance having been obtained by adjustment of the valve characteristics so that both anodes and the point 8 are at the same potential, no D.C. passes through the resistances 3, 4 and so the circuit may be balanced dynamically, by adjustment of the tapping points A or B, without disturbing the static balance. The potential required for the point 8 may be obtained from a potentiometer across the H.T. supply, Fig. 3 (not shown). It is shown in the Specification that this may lead to an adjustment of the tap A or B giving low gain; this may be overcome by making the dynamic impedance of the valves much greater or much smaller than the resistance of the anode loads 1, 2. Alternatively, one or other of the resistances comprising the potentiometer may be non-linear, i.e. have a dynamic impedance much greater or smaller than its D.C. resistance. The anode resistances 1, 2 may in addition be returned to a tapping-point on a potentiometer of this type.