GB1144571A - A.c. amplifiers - Google Patents

Abstract

1,144,571. Transistor amplifying circuits. JOSEPH LUCAS (INDUSTRIES) Ltd. 6June, 1966 [7 July, 1965], No. 28746/65. Heading H3T. An amplifier comprises a pair of amplifying circuits each with a feedback path, operating in push-pull into a centre-tapped inductance, the tap of which is connected to a point of fixed potential via an inductor or resistor. A.C. source 5 is coupled by one half secondary 7 of a transformer to an amplifying circuit comprising a long-tailed pair of transistors 12, 18 coupled by emitter-circuit resistor 13. An output stage comprising series-connected transistors 23, 24 is driven from the collectors of transistors 12, 18 by means of transformer 16; this output stage feeds into one half of the centre-tapped primary of an output transformer 10 and resistor 31 provides overall negative feedback. The other half secondary of transformer 7 drives in opposite phase a similar amplifying circuit comprising transistors 12a, 18a driving output transistors 23a, 24a which feed into the other half primary of output transformer 10. According to the invention, the centre-tap of transformer 10 is returned to the centre-tap on power supply 25, 26 via an inductor 28, or alternatively via a resistor. As shown inductor 28 is shunted by resistor 34 and clipping diode 35.