A classic OCL discrete component power amplifier circuit

The rear stage power amplifier circuit is shown in the above figure, which is a power amplifier that I have developed.
Circuit principle analysis:
Taking the left channel as an example, the left channel signal of the right channel is the same as that of the previous stage, and the voltage is amplified by the differential input amplifier composed of Q7 and Q8 through C15, and the amplified signal is taken out from the collector of Q7, and the excitation transistor is sent. Q12 performs excitation amplification, and the excitation signal is taken out from the collector of Q12 and output in two ways:
All the way through R13, D4, D3 (the diode is in the on state, the impedance of the AC signal in the range of its characteristic curve is very small) is sent to the lower arm PNP composite tube base level (Q14 base level) of the complementary push-pull amplifier circuit, when the signal For the negative half cycle, the composite tube is turned on, the output current passes through the ground, and the speaker is connected to the Q13 negative power supply. When the signal is positive half cycle, the composite tube ends;

The other way is to directly send the NPN composite tube (Q6 base level). When the signal is positive half cycle, the composite tube is turned on, the current passes through the speaker to the ground, and the signal is turned off for half a week; the amplified audio signal is output by the emission stage of Q5 and Q13. Push the speaker to sound.
C6 is an anti-vibration capacitor used to suppress the high frequency self-excitation that may occur in the amplifier. C6 is also called Q12's neutralization capacitor, or negative feedback capacitor, hysteresis compensation capacitor, which can reduce the high frequency gain of Q12 and destroy the amplitude and frequency characteristics of self-excitation. Resistor R22, capacitor C7 can form a capacitive load, which becomes the impedance compensation circuit of the speaker to compensate the inductive component of the speaker. The negative feedback of the amplifier is close to pure electron, the amplifier is stable, not self-excited, and the output stage transistor It is not easy to overvoltage and it is safe to operate.