Amp volume drops significantly while playing

[Old Garage-Bander]

If it has an effects send and return, put a patch cable between them and see if that fixes it. If it does, it's dirty jacks. A little Deoxit on a plug pulled in and out a few times should fix it. Also, a dirty headphone jack can cause this.

I think where you're at is the pre to amp interface. And normally that would be a good thing to try. However we have enough info to point in another direction this time.

The same problem occurred with two different amps, one was brand new. I think the problem is post amp.

 

[Slevage]

Resistance is typically about 75% of the rated 8 OHM inductance IME , not exact but close enough to test for a bad cab.

This is usually a good method, but in the OP’s case, his equipment fails over time. Inductance is a better thing to evaluate a coil. Ohm meters are not accurate in the lower end of the DCR scale.
I spent several years in the coil manufacturing industry, evaluating/testing production pieces as well as field failures.

 

[cheechi]

OK. Thanks for the extra info. I wouldn't expect power in Canada to be bad enough to cause any of this. If you were in East Buhgrania (made up place but with a dodgy power grid ) then maybe.

Absolutely, a problem with the cab can cause this. Being on the road as it's been makes it even more likely.
Yes, rule out the easy stuff like cables and whatever, but definitely get that cab checked out. For starters I'd be looking for an intermittent wiring problem inside the cab. Many amps will go into some kind of self protection/shutdown mode when they see an improper load.

As far as it seeming to only happen at your friend's (though I think you said your SVT died at home?) this could be coincidence. If it happened a lot, and only when you played at your friend's place, I'd suspect something going on there. But only a couple or three times, could just be the luck of the draw.

I want to thank you on behalf of all East Buhgrania for mentioning our beautiful country. Also we East Buhgranians are severely offended and will be declaring war as soon as our dodgy power grid starts up again. Please expect a surprise attack on tuesday.

 

[Plain Old Barry]

If the wall voltage is sagging, you can measure it with one of these inexpensive monitors. Go to amazon and search for DM-55-1.
View attachment 4927691

These are handy to have in general. I bought a 3 pack, one lives in my gig power strip, plugged in all the time, and another in my RV. Far from lab grade, but compared to my Fluke 87, they're close enough for rock and roll.

 

[beans-on-toast]

These are handy to have in general. I bought a 3 pack, one lives in my gig power strip, plugged in all the time, and another in my RV. Far from lab grade, but compared to my Fluke 87, they're close enough for rock and roll.

Yes! Every player should have one on the power strip. Like you said, good enough for a general picture of what’s going on. Too low a line voltage can damage the amp or cause it to fault.

 

[Chaosanator]

According to Craig David, you know what to do.