Is this even possible

[shaggyrun]

This may be a crazy or even dumb question, but I called my tech the other day and he has not found a thing wrong with my amp again. this is the second time he has had it. the problem I have had is that about once ever 6 weeks or so it stops working. When I say it stops working I mean the amp still has power the power tubes are still glowing and everything looks perfectly normal the amp just makes no sound. I have ran the crap out of the amp used all my pedals did everything I can think of to reproduce the failure, and the only thing that remains constant is the amount of time it takes for the failure to appear. Everytime the failure has appeared I have pulled the tubes and taken them to get tested, when they checkout fine other then the phase inverter tube (which they keep telling me is a little on the weak side). Then I reinstall the tubes and it works great for another 6 weeks or so. can the problem be coming from one of the pre amp or phase inverter tubes coming loose after about 6 months of operation? or would this not be even a chance since the power tubes are still glowing during the failure. the power tubes have a bear trap looking locking device to hold them from backing out,but the preamps have nothing just the sockets to hold them in. like I said be kind if this is a very stupid question.

[R.G.]

Intermittents are the very worst kind of problems, because they inevitably will not happen when you can look to see what's wrong, and then disappear if you do anything to them.

Anything happening on a time scale of weeks is likely to be mechanical, possibly even slow-chemical corrosion in contacts.

Since the problem seems to be fixed, have you tried removing and then replacing tubes and restarting one at a time? If the problem goes away reliably with a specific tube, there is something funny about that tube or its sockets.

Another thing to do is to see whether it makes *no* sound at all, or if there is a faint hiss from the speakers with your ear as close to the speaker as you can get it. These are different. If there is any hiss or noise at all, then the output stage is running, but not getting any input. If there is no sound whatsoever, the output stage is either unnaturally quiet (which is always possible, but not common) or defective.

I don't know your level of tech-ability. I suspect you probably don't know how to poke around inside a powered-on amp and live through it, though. The next step, and what an experienced tech would do, is to catch it not working, then put a test signal into the input and trace the signal with an oscilloscope. Equipment-poor folks can do much the same with an audio probe, or the "click test" by touching the grids of the tubes with a probe and listening for clicks in the output. But there is a real risk of death in doing this process if you touch the wrong thing.

If I were you, I'd catch it failed, then wobble the tubes around in their sockets (or remove/replace them) one tube at a time. You can do this with the amp on in most cases. Listen for changes. Note that the volume control must be non-zero to hear changes in the first tubes. Simply tapping on one tube at a time may turn something up.

[shaggyrun]

Yes thisvis exactly whatvmy tech told me that he had to make it fail to trace the problem. He has been running a signal through it 8 hours a day to try to make it fail. This has been going on for a week now, but he also has the chassis on one of his benches ready to test when it fails

[R.G.]

The very worst intermittents are the ones that will NOT fail on a tech's bench. These happen sometimes. Techs hate them.

Worse, it only happens to you about every 6 weeks. Unless your tech is good at making it fail, you can reasonably expect it may take that long to fail there. And then there's the question of whether it will ever fail at all on a bench. "On the bench" usually implies pulled open and sitting on the bench outside the chassis. That may cool it just enough to not fail. It may reduce chassis flex from mounting bolts just enough to make it not fail. Lots of things. Mother Nature is not only a stickler for detail, but sometimes She's devious.

[Jazz P Bass]

Have you taken the tech all of your loop stuff?

He may not have The problem.

[g1]

Don't know why you started a new post, there was important information in the original one:
http://music-electronics-forum.com/t35455/