Learning the hard way not to take shortcuts

[messonic]

This is my first post on this forum. I have been searching around and reading up, I like the ideas and ideals here. I've always enjoyed the DIY aesthetic.

enough fluff, right?

I play a Mesa-Boogie F50 and when I was setting it back up from a gig, I had it on an amp stand and put another amp on top of it. Not thinking ahead to have everything plugged in, I just reach around and plugged the cables where I remembered them going. The effects loop was easy, but I didn't recall exactly which input was the 8ohm vs 4ohm for my attenuator.

I did something very very stupid.

I run a 100w Weber Attenuator because I can never really crank the F50 to get all the full tube goodness out of it. Aside from what I've read on MB and the F50, the problem at hand:

I wasn't get much volume and stepped on the distorted channel, and that's when the amp was cutting in and out, as though the instrument cable was a problem. I checked the solder connection and it looked good (mogami). Moments later I smelled smoke and before I could turn the amp off, it was already off.

It was very distinctly the smell of wiring and after some looking I think I've isolated it to a wire that look rough near one of the power tubes. I also checked the fuse and it wasn't blown, but it didn't look entirely healthy either.

I included the picture I could snag of the wire heading to a power tube.

http://web.me.com/messonic/temp/wire.jpg

I read in several places you never want to connect the speakers to the wrong impedance because you could potential blow your amp or speakers.

I'm looking for tips on where to start.


cheers
Tim


TIA

[Rhodesplyr]

The issue of tube amps and impedance has to do with the output transformer. If you run a signal into a tube amp with no load on the output transformer, it looks like an infinite impedance to the OPT's primary winding. This can cause very high transient voltage peaks inside the OPT windings that exceed the insulation ratings of the windings, leading to a shorted output transformer. In general, you don't want a tube amp to see a much higher impedance than it "expects."

If the fuse didn't blow, how was the amp "off."? Did you measure the fuse with a meter to test continuity?

My suspicion is that this equipment failure and the issue of the attentuator may be unrelated--other than the fact that you were pushing the amp to work hard.

Where to start? I don't mean this in a mean, sarcastic, or derisive way; I'm being purely pragmatic. Where to start would be to learn how amplifiers work and how to repair them. In my opinion, an amp that's given off smoke and died needs to be taken to an experienced technician. Maybe I'm reading too much into the fact that you can't say for sure whether or not the fuse is blown, but that's a big red flag to me that you don't really know enough at this point to dive in and try to repair this amp.

[messonic]

Calm rational thinking!

It was a very pragmatic suggestion. I wasn't sure that the fuse was blown because I've never worked with slow blow before, just auto and smaller applications (I was expecting the fuse to be broken, but it was just "tweaked" a bit). After a continuity test showed it had none, I replaced it and the amp plays.

Now I'll do some more poking around the site and try to determine whether the attenuatoR is making that much of a difference and what other choices I have with the F50. At some point I'd like to build from scratch, but I'm not on a place with my time to be able to take on a project.

Thank you for your reply. I appreciate it.