Mark III - Sparks and Smoke

[genius loci]

I recently bought my very first tube amp, a Mark III combo blue stripe. This decision was based on many things including a lot of info from this forum. Thanks! It showed up at my door in impeccable, as-advertised shape and I love it. I've played roughly 6 shows and numerous practices with it without a problem, until last night.

We (my band) tripped a circuit breaker and when it was restored my amp had no power. I switched to an alternate circuit and as soon as the amp was plugged-in, there was a loud, electrical pop from the rear of the amp and and small plume of smoke. Fuse blew. I replaced and repeated. Same result. Mind you, this is with the power switch in the OFF position. It's worth noting that no other equipment plugged in to this circuit suffered failure. It could be a complete coincidence. Unfortunately I'm hours from a qualified amp tech, but can anyone give me the shortlist of what this could be?

I realize that its near impossible to accurately troubleshoot this from such limited info, but I'm curious as to whether anyone else has encountered these specific symptoms and what I can expect. I really love this amp and I'm hoping to find a way to nurse it back to health.

Any insight is appreciated.

Regards

 

[Boogiebabies]

Maybe the Varistor blew up.

 

[Monsta-Tone]

****! I hate it when that happens!

If it does this with the amp's power switch in the OFF position, you just might be in luck.
There is not very much going on before the power switch.

It might be a bad cord, or a bad switch, or something touching ground that shouldn't.

Post some pics of the insides of the chassis where the power cord goes into the amp, the fuse, the power transformer and the power switch.


Maybe one of us can see something out of the ordinary.

 

[Boogiebabies]

Here's a pic so you know where to look. It's lightly circled in red.

 

[zeeman]

You circled the varistor in red - why? I don't see anything there that looks like a problem.

Can you post some more pics? Take pics of everything.

Also, do you have a better camera? You will probably need a camera with a MACRO function so you can take closeups without them being blurry. If you don't have a better camera, try to borrow one.

zeeman

 

[JD]

Zeeman
BB is not the guy with the problem
genius loci is
BB is simply using a reference photo to show genius loci where to look.

 

[zeeman]

Zeeman
BB is not the guy with the problem
genius loci is
BB is simply using a reference photo to show genius loci where to look.

Oops... missed that. Thanks.

zeeman

 

[Tuna141]

Don't forget to check the power tubes too. A bad tube could cause the fuse to blow.

Good luck.

 

[238839]

I had the same problem too. Found out I was replacing the fuse with the wrong type. I needed to use a "Slo-Blow" fuse and because I wasn't, the amp would blow the fuses as soon as I turned it on...Hope it all works out for you.