Finally I had a chance to change all of the electrolytics on the offending amplifier board. That was it! The amp is working great now and sounds good too. Thanks Enzo for pointing me in the right direction. Your help is always appreciated.

Mark

Sometimes it shuts off sooner. I was thinking the aged electrolytics may be causing the problem. I'll change those out and see what happens.

Nothing is getting hot. But yes I measured high dc on the low side .195v. High side is at .053V but that side works and that seems alright.

Working on a Hartke HA5000. Had 3 blown power transistors and both drivers on right amp. Replaced those with exact part numbers and also replaced the six .47 ohm resistors. The amp works fine in mono mode and in bi-amp mode through the high output jacks. When plugged into the low output jacks the relay opens after 30 seconds or so and cuts the sound. I can't find any info or setting the amp (there is 2 trim pots on the board) just a schematic. Both channels have equal B+ voltage going to them. Anything else I should check?

Upon further testing, I discovered the power transformer is shorted as well and will result in too much investment into this basket case of an amp. Looks like another bites the dust.

I have a box of wood scraps, theres always a block in there to support whatever I'm working on. Nice to know I'm not the only one!

It's actually a nice fat trace pcb, two boards, one for the preamp and one for the poweramp. I can fix the burnt trace. Whoever was in this thing also raided all the electrolytics so I'd bet this thing has been doa for quite some time. The rectifier looks fried as well. It's all rebuildable, just not sure my customer is going to like the price! Classictone has a tranny for $72, probably not as good as what was in there but should work. Looks like an old Kustom tuck and roll amp, but it's all tube. There was 2 of the 4 power tubes still in it, different brands too, I bet they just stuck whatever in there and fried it. I also heard they stole from Fender and Peavey, went out of business in '74.

I have a Plush PRB 1000S come in to the shop, no OT, no tubes, a burnt choke, no fuse holder, and a burnt trace on the power tube board. Off the bat I'm guessing a Showman OT may work? Also wondering what the preamp
tubes were? A schematic would go a long ways, I read it may be a Showman or Twin copy?

Did it to multiple guitars. It IS the amp. That's why its on its way out of my shop. Peavey should have never put this much gain on tap.

Well for starters, its not my amp, nor do I play with gain on "10". It IS unrealistic to play this amp cranked like that. I went through and cleaned any pots contributing to any noise. I did get the amp back to a controllable state. Again it only feedsback with that squeal if the switch on the Ultra channel  is set to Ultra or the Lead channel is set to High Gain. Both functions put it into high gain territory which normally is associated with feedback. After cleaning the pots I was able to play with the gain around 3-4 oclock, channel volume around noon and using the master for overall volume before I got the nasty squeal.  I did have to stand at least 5-6 feet away to be controllable. Cleaning the pots was a major improvement. Perfectly quiet on any other setting. No results from the chopstick test. I put it back together and sending this one on its way.

With a shorted plug inserted it the same high frequency squeal. Only does it with the voicing switch set to high gain. I went through and cleaned all the jacks, and all connections inside are solid. No obvious component failure. I cleaned all the ultra channel pots. Testing afterward the ultra channel is no longer squeling. But when I turn the LEAD channel gain to 10 - while on the ultra channel there it is squeel. I'm going to clean that pot and see if it makes a difference. Also no difference with effects loop jumpered.

I have a Peavey XXL (solid state) amp on the bench. Sounds great until you flip it to the Ultra channel then its squeal mania. It happens across all volume, gain, and eq levels and with different guitars, cables , etc. The issue is in the amp, in the Ultra channel only. The squeal goes away when your actually playing but as soon as you stop its there piercing your ears. Where should I start? I plan on getting it hooked up to my oscope today to see if I can see it.

That sounds feasible to me. It does have a 24v fan in it, so a simple circuit may be the right answer. I will call Fender today and see if thet tranny is still available (I figured it was an outdated part). I do like the idea of planting a smaller second transformer inside as there is plenty of room.

Transformer nonrepairable. I didn't have any luck yet finding a replacement either with those specs.

So the brown wire should be at 22 volts correct? If so I'll get a look at the transformer connections inside to see if anything came disconnected. Should I still disable the fan circuit for further testing or are we at a standstill until I fix/get a transformer?