Ampeg B1-r cuts out

[nosaj]

I have an ampeg B-1r that periodically cuts out. I have changed the pre amp tubes but it still does it. Should I be looking at the caps or the power transistors?

Thanks,
Jason

[Jazz P Bass]

I do not know how you isolated the problem to the caps or the output transistors.
But you must try to narrow down where the problem is.
There is an effects in/ out jack.
Try jumpering them.
There is also a preamp out jack.
Try running that to another amp (or monitor it to see if it drops out when the amp fails).
Divide to conquer.
Is it a power amp or preamp problem.
The power supply most assuredly can be checked for stability.
As well as the overall soldering that was applied to the amp at assembly.

[52 Bill]

Neither. I'd start by checking for dirty break jacks or bad solder joints at these jacks as well. I've seen a lot of Ampegs that suffer from this problem. So you need to check the FX loop jacks as well as the pre out and power in jacks.

With the top cover off and a signal going through the amp, I take a small wooden stick and press on the top of the jack's hot contacts. In many cases just the slightest touch will cause the signal to cut in and out. Then I spray a little Deoxit on the contacts and continue to push the contact with the stick until the signal no longer cuts out.

If cleaning doesn't help then check to see if the jacks are soldered solidly on the board.

[Enzo]

And if it has a headphones jack, consider it too.

Caps and transistors are very unlikely to cause the problem you describe.

[J M Fahey]

It might also be a thermal problem.
Even if not used at maximum power, a dirty (full of junk and debris) air path will severely cut cooling; then some thermal protection might cut audio or speakers.