Transistor radio shows common OTL power amplifier circuit, VT5 bias resistor driver stage. VT6 and VT7 is a pair of complementary symmetry tube. VT6 germanium material NPN transistor, VT7 is germanium PNP transistor. VT6, VT7 and the biasing resistor
composition typical OTL amplifier. To illustrate the process of the circuit, circle omitted satin bias resistor and incentives.