Old school Stetsom 7kD clipping

I have an old school Stetsom 7kD amp that boots up and draws about 8 amps at idle. This is a beast of an amplifier. It has two separate motherboards, so it’s basically two complete amps in one heat sink.

All of the power supply FETs and output FETs test good in circuit.

When I feed a strong signal into the amplifier it will start to show clipping on the LED with no load attached to the speaker terminals and the current draw on the amp becomes erratic and bounces around from 4 amps to 12 amps and everywhere in between.

Does anybody know what could cause this?

I don’t have a strong enough power supply or test speaker or static loads to handle the power that this amp can produce to drive it into clipping. Is there a way to test the circuit at reduced power or is it ok to keep testing it with no load attached to the speaker terminals.

David
 

Attachments

  • 3AA535A3-6642-44A5-A3BD-3C3E990F88ED.jpeg
    3AA535A3-6642-44A5-A3BD-3C3E990F88ED.jpeg
    491.1 KB · Views: 55
  • 83963840-A6D6-46C5-B4E3-F787D9B812CE.jpg
    83963840-A6D6-46C5-B4E3-F787D9B812CE.jpg
    1 MB · Views: 48
this amp consists of two 2k6 amps in parallel. the carrier frequency of the "master" pcb is also fed to the "slave" pcb.
The great thing about this amp is that you can parallel as many amps you want, since the output is current limited by shunt resistors.