Mesa D180 - Power Issues/Burning Tubes, Help!

chaosMK · #1 02-24-2013, 11:36 PM

I transported my D180 *very* carefully in a kind of crappy rack case that was snug but had no screws... plugged it in today and couldnt really get any volume out of it.

I noticed one tube running super hot and turned it off. I opened up the guts to check if a screen grid resistor blew or if anything was obviously wrong down there... they all looked good.

I removed the tube in question and swapped its opposite matching tube into the problem slot, and put a different (probably unmatched) 6L6 that I had on hand in the "good" slot.

No volume at all! All of the power tubes were firing up fine, when I took if off Standby, they all got a typical blue glow, etc. After a second thorough general inspection of obvious things I tried it again and managed to get a hair of volume. The tube in the bad slot started glowing and I turned it off. Final test- swapped speaker cable (since the cable I was using was brand new and I'd never tried it before), same issues and looked like additional tubes were getting hot (beam forming plate looking orange in a scary way) as the tiniest bit of sound squeaked out.

I'm done tinkering, time to ask you guys. Any thoughts?

Downunderwonder · #2 02-25-2013, 12:37 AM

No idea but please keep us posted. Mine has never had a tune up.

craig.p · #3 02-25-2013, 05:53 AM

When you say the tube was running "super hot," I assume you mean the plate was glowing red. And another tube in that slot exhibited the same behavior, right? That tells me that socket's bias has severely drifted or has gone out altogether. So, this is one of those deals where if you have to ask what to do next, it's probably tech time, especially when we're talking about poking around inside the guts of a tube amp, which is serious business safety-wise. The good part: It's probably a real simple fix, like maybe just a broken solder joint. Have your tech bias the outputs while it's on the bench. Also, 2 tubes were red-plated, so they may be questionable now; the tech may tell you they're due for replacement. It'll depend on whether the amp can be biased and how it performs at full power into a dummy load (dyno test).

chaosMK · #4 02-25-2013, 06:06 PM

I busted out the D180 again today, just cause I don't like giving up easily. Cleaned out the tube sockets, checked for broken connections in the guts again... amp checked out.

I plugged it into a different cab... my PH410... worked fine. Loud as a beast on 2. I plugged into another guitar cab of mine, worked as well.

I plugged into the cab I was using the other night (a 1x12 Krank cabinet that I recently installed a Swamp Thang into), issues... fizzy noise, low volume, tubes looking like they were getting ready to be unhappy.

Open up the cab to see if my connections were faulty... they were excellent. But! There was a little piece of tin foil in there that I was using to catch any solder while I was wiring it up. ZING! The cab worked fine in this dangerous state the first that day I tried it, but after transporting it on the back of my truck it must have jarred the foil a bit.

My tubes probably lost a few days or years.. fortunately I kind of enjoy retubing power sections even though it's pricey (maybe time to try Tung Sols).

Anyway... one the many foolish lessons I've learned while learning to do things myself!