Chapter 9: PRACTICAL ANALOG SEMICONDUCTOR CIRCUITS
Amplifier Circuits -- PENDING
Note, Q3 and Q4 in Figure below are complementary, NPN and PNP respectively. This circuit works well for moderate power audio amplifiers. For an explanation of this circuit see “Direct coupled complementary-pair”, Ch 4 .
Direct coupled complementary symmetry 3 w audio amplifier. After Mullard. 
Circuits: Transistor audio amplifier.