I've made a huge mistake.

DarkAndy · Dec 13, 2016

Well for the last year I've been using a cabclone into an eleven rack for wicked awesome headphone tones. Tonight I unplugged the speaker cable at the amp instead of the speaker cab and spent a minute wondering why all I got was the sound of a motorboat and not guitar... And then silence. Smells like burning plastic. Is that a screen resistor? Nearest Mesa tech is about 4 hours from me.

I'm making the trek next weekend anyway but is there anyway I can tell if I burned out my transformers? I can't really afford to drive that much plus pay bench fees and a new tranny without being 100% sure. I know for sure I blew a fuse and one power tube. Is there anyway I can check for any other damage?

The amp is a stiletto duece II can I run that on two tubes to see if it still works. What's the best internets advice.

Otherwise can anyone recommend a tech in Edmonton AB? Instead of going all the way to Calgary with it?

Thanks!

domct203 · Dec 14, 2016

Mesa transformers are pretty tough, I would think the OT is fine and you blew out a screen grid resistor. I had a powertube that I suspect developed an internal short and did the same to my Roadster- blew a fuse in the middle of practice, put in a new fuse and the amp fired right up and I finished our set. At the next practice (when my ears were fresh) I could tell that something wasn't right with the amp. That is when I found the blown screen grid resistor. Throughout all this, the OT was fine.

I would not continue to run the amp that way until it's looked at. As far as running at 50W, yes you could pull the blown tube and it's partner to run the amp that way to test it.

Just be careful to shut it down immediately if you see red-plating, or hear strange noises.

DarkAndy · Dec 14, 2016

Thanks. I've decided against doing anything and just taking it to a tech. Now I just need to find a good one here in edmonton

elvis · Dec 15, 2016

Oops. We've all done it.

I agree that the OT is tough and likely OK. I would replace ALL the power tubes. You can look for blackened components on the board near the output tubes, or melt-y looking PC Board areas.

You could check the impedance of the OT windings, but unless you knew where it started, it's hard to tell if you burned part of them. Plus, it may change with temp if some of the insulation has melted. Again, unlikely anyway.

All of this is high voltage and hazardous, of course.

Jorn218 · Feb 8, 2017

Also make sure to check the four diodes that smooth out the ripple of the DC between the PT and power tubes. I had a tube short out causing smoke from the amp. The tube socket had scorch marks where the tube shorted and threw a pin. All the screen grid resistors were actually ok, but shorted out the 4 bridges diodes bad enough to burn the traces between the diodes off the board. I only say this because the way the diodes sit and are cramped within so many other components, the Heat dissapation isnth E greatest. The replacements I put are actually off the board. It hurts seeing the damage on this circuit board.