Autotek MM4000.1D rail voltage

Hi,anyone here know the actual working rail voltage of the MM4000.1D?Cap rated at 120V itself.Got a on-hand unit with blown transient voltage suppressor,PK6E250A,on one rail.

Also duty cycle on the DC-DC PWM (TL494 based) is around 33%,is that normal?
I also had a similar problem.
Most of the time, due to lack of replacement, I simply eliminated the transient suppressor and the amplifier works perfectly even without that diode.
Could someone explain to me what these suppressor diodes are for?
 

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Most of the 3S-tech type amps are unregulated so they run at 50% duty cycle.

Does the rail voltage or the pulse width vary when you adjust the 12v supply input voltage?

I don't have a variable power supply but the supply voltage is rated at 12.4V.

Also,got 2 output fets were blown.....so i assume i should remove all remaining fets for further testing,on the rail voltage and also the gate voltage?