GB880475A - Transistor amplifier providing a balanced output signal - Google Patents

Abstract

880,475. Transistor amplifying circuits. MURRAY, J. S. Feb. 7, 1958 [Feb. 9, 1957], No. 4522/57. Class 40(6). A transistor amplifier comprises a driver stage in which two transistors 13, 14 having a common emitter resistor 15 and individual collector resistors 16, 17 are connected either as a long-tailed pair as shown or in push-pull, Fig. 9 (not shown), and an output stage in which two transistors 10, 12, connected in push-pull, have their base electrodes connected to the collector electrodes of the respective transistors of the driver stage and their emitter electrodes connected to opposite ends of the primary winding of an output transformer, which primary winding is split centrally with its two halves connected through a blocking capacitor C, wherein in addition a resistive potentiometer chain is connected between each side of the blocking capacitor C and earth and a further resistor 21 is connected between the base of each transistor of the driver stage and a point on the respective potentiometer chain, whereby appropriate bias voltages are provided for the base electrodes of the transistors 13, 14. The potentiometer networks connected to the opposite sides of the capacitor C also act as a common emitter resistor for signal currents and hence assist in balancing the signal currents in the two transistors 10 and 12. Further the out-of-balance signal between the capacitor C and earth provides negative feedback to the transistor 13 and, if the capacitor 19 is omitted, positive feedback to the transistor 14, thus further improving the signal balance in the output of the amplifier. Additional negative feedback may be provided by providing a signal connection between the emitter of transistor 12 and the base of transistor 14, Fig. 6 (not shown), or between the secondary winding of transformer 11 and the base of transistor 14, Fig. 7 (not shown), the capacitor 19 being omitted in both cases. In Fig. 8 (not shown) negative feedback is provided by a tertiary winding of transformer 11 connected in the emitter lead of transistor 13, while in Fig. 9 (not shown), wherein the driver stage 13, 14 is represented as being driven in push-pull from a preceding stage, the transformer 11 comprises a centretapped tertiary winding having one half connected in each emitter lead of the transistors 13, 14. Specification 809,207 is referred to.