GB808530A - Improvements in or relating to transistor push-pull amplifiers - Google Patents

Abstract

808,530. Transistor amplifier circuits. PHILIPS ELECTRICAL INDUSTRIES Ltd. Aug. 2, 1956 [Aug. 5, 1955], No. 23857/56. Class 40 (6). In a transistor amplifier comprising at least one pre-amplifier stage feeding a class B or AB push-pull stage through a transformer, variations due to temperature of collector currents of the push-pull stage transistors are reduced by applying to these transistors a biasing voltage whose variation with temperature is determined by variation with temperature of the collector current of at least one of the pre-amplifier, transistors. The Figure shows two pre-amplifier stages 1, 2 feeding a class B or AB pushpull stage 4, 5, negative feedback being provided through resistor 10. The collector current of transistor 1 which itself is temperature dependent, or the combined collector currents of transistors 1 and 2, is passed through a resistor 7 to produce a voltage which is smoothed by a capacitor 6 and fed through a potentiometer 8, 9 to the transistors 4, 5 to maintain their collector currents constant. In an alternative arrangement (Fig. 2, not shown), the collector current of transistor 2 is fed to the centre tap of the transformer primary and the bias is derived from a potentiometer connected between one end of the transformer and earth. By this means the magnetization current of the transformer primary may be balanced out.