A simple final power amplifier

Working principle (circuit as shown in the attached figure): V1 and V2 form a differential amplifier with single-ended input and single-ended output, and V3 forms a voltage amplifier. In order to ensure sufficient gain and improve distortion, V4 is used for temperature compensation. V5 and V6 are current-driven tubes, which mainly provide the necessary current for the power amplifier tube and dynamically reduce the input impedance of the power amplifier tube, reducing the influence of the back-stage tube on high frequency. The high-power tube adopts the popular ZSC5200/2SA1943 paired tube. R18 is a negative feedback resistor, and the closed-loop gain of the whole machine is determined by R18 and R17. C6 is a bootstrap capacitor. RP1 is a zero adjustment potentiometer. VD2 and VD3 are limiting diodes. The vibration elimination network composed of L1, R19, R20, and C8 effectively reduces the influence of the speaker's inductive load on the power amplifier and improves the stability of the amplifier. Except for R15 and R16, which are 5W cement resistors, the remaining resistors of this machine are 1/2W metal film resistors.