DC power amplifier with fault indication

This circuit is a power amplifier circuit composed of V, PC1342V and Sanken pair tubes C2922 and A1216, as shown in Figure 2-127.
The characteristic of this circuit is that the feedback capacitor is cancelled, and at the same time, IC2 is used to form a DC servo circuit. This servo circuit The offset voltage of the output midpoint can
be controlled within ±2mV, making the circuit a DC power amplifier circuit with excellent performance.
    Another feature of this circuit is the addition of a fault indication circuit, which can provide a fault display when a fault occurs in the circuit.
The fault display circuit is equipped with a set of multivibrator at the output end of the protection circuit {uPC1237. When the circuit fails
, pin 6 of the protection circuit jvPC1237 outputs a signal voltage. On the one hand, it drives the relay to act and on the other hand, it indicates
the circuit. When the power is turned on, the multivibrator starts to oscillate, and the light-emitting diode connected to the oscillator circuit starts to oscillate, indicating
that the circuit has failed.
    The multivibrator is composed of VT6, VT7, etc., and the oscillation frequency is twice per second.
    The circuit is powered by front and rear stages respectively, cp: PC1342V is powered by ±65V power supply, the power amplifier output tube is powered by ±56V
power supply, the protection circuit VPC1237 is powered by a 10-25V single power supply, and the DC servo circuit is powered by ±15v power supply.
The separate power supply method is more complicated in power supply production, but separate power supply can reduce
the mutual interference between circuits through the power supply and improve the quality of the circuit output signal.