Sunn beta bass- oscillating output

[gearhead63]

I have a Beta Bass amp (1982) that a friend brought over. As you turn the volume up it starts oscillating. I ran a 1khz signal into it, hooked up a dummy load and connected my scope to the load. You don't have to turn it up much and the output will just start jumping up and down, approx .7-.8vpp. Really does it when the master vol is turned up. Seems to do it more as the signal starts to clip. I can hear 3 of the output transistors making noise at 1kHz. I scoped the preamp and master outputs, they look ok. IC101 seemed to be making noise (it's a 4558) so I swapped it out for a new one and it does the same, but the output from the preamp looks ok as well as the outputs from the 4558 chips. Any ideas? Part of the problem I have is that the schematic is VERY hard to read and unprintable.

[loudthud]

I found some fairly decent scans of the Beta Service Manual here: Sunn Beta Lead (looking for schematics)

The first thing I would check is the plus and minus 15V regulators on the power amp board. Make sure they are the correct voltage and there is no noise feeding back to the preamp when the amp is acting up.

[gearhead63]

Those were the same as I have........BUT! I enhanced the them and am able to [pretty much see it.
I found that there are a number of bad caps. I did some leakage tests on a few of the orange non-electrolytics and they all failed.
And the large filter caps are trash. To be expected as this amp is 32 years old and all original inside.