I tried to simulate the amplifier posted. below with ltspice.
It doesn't work. Can anyone say why? The centre line should be zero volts but is close to -38 volts!
It seems that the connection in the lower left corner between the MPSA06 transistor and resistor R24 is pulling the centre line voltage down
when it surely should not.

 

Are you sure all the values are correct, especially around the first two transistors?

 

See

 

See
View attachment 186550

Wow! What did you do to get it working? Thanks you.

 

It seems that the connection in the lower left corner between the MPSA06 transistor and resistor R24 is pulling the centre line voltage down
when it surely should not.

R23, R24, R16, and Q3 form a constant current source (along with the GND connection at the bottom of C3) that is the collector load for Q5. That all looks fine.

Note the square box at the bottom of C3. That usually indicates an unconnected pin or wire. Are you sure C3 is connected to GND? If it weren't (and there were no other problems), the circuit would revert to unity gain, not negative saturation, so it's probably not your main problem. Still, something to check.

ak

 

Not the square box there. That usually indicates an unconnected pin.

That applies to Q6 and Q7 base as well.

 

The power supplies limit the power into 8 ohms to something less than 90 W, but it looks like the current limiters come on at around 200 W. What are the design parameters?

ak

 

Specified a value for the Zener diode, and 'balanced' the VAS with it's CC source.