The Boogie Board

Hello:

Hoping someone maybe able to help me troubleshoot. I recently picked up a mesa triple rectifier, i have only been able to play it through my (crappy) marshall mg412 cab. Everything started off great but then i started to realize after an hour or so of playing the volume would all of a sudden drop, notes (especially bass side) got super flat, almost staticy sounding too. I turned it off, let it sit a bit and then it would go back to normal. This happened a few times but now it is just like that all the time. I changed all the tubes, cleaned it inside, nothing...it almost sounds like maybe the speaker is blown but that seems odd since it would go out and then come back ok after resting. I havent changed the fuse but would that be an issue if its powering up just fine?

Have you tried the amp with the FX loop set to "Loop Bypass"?

Are you using Bold or Spongy, Tube Rectifier or Silicon Diode?

Also, exactly what tubes did you replace, and what (brand) did you use. Certain 12AX7's do not hold up well in the cathode follower preamp positions, and have been known to fail in those positions.

Dom

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Hi Dom:

Thanks for the reply. The loop was set to bypass and the bias selector was correctly on 6L6 when I was having the trouble, this am I went and switched both of those back and forth and all of a sudden everything started to sound normal. I was only able to play for a few min so I'm going to try playing longer and see how it goes tonight.

I replaced all the power + recto tubes with mesa brand matched pairs directly from a mesa dealer in my area. The preamp tubes I replaced with JJ Electronics T-12AX7-S-JJ Vacuum Tube ECC83 in slots V2-V5 and a tung sol 12ax7 in V1.

I was having the same issue on all combos (spongy v. bold and the Tube Rectifier v Silicon Diode)

still having trouble...thinking it may be time for a tech visit. I changed all the tubes, all the pre amps and still am getting a huge volume drop and playing sounds flubby and flat esp. on the low end. Every time i let it sit for a bit and it comes back like nothing happened but then does it again. more recently it seems like it happens at the exact moment when i overdrive it (either with a pedal or change channels) but then it affects both channels. Not sure what do to.

was working fine last night and again this morning. Last night had it turned up more on both channels. This AM i had the volume pretty low on both channels, was playing a while then i turned up the volume a touch and it went out again...just like a power drop. so baffling.

Finally got this into the tech, turns out it was the output transformer. Going to be installing a MM. Tech said that signal is feeding everywhere and nothing else seems to be amiss. Not sure what would have caused it to blow...

That's definitely not a normal thing to go on a Mesa amp. They use very robust output transformers. However if the amp has been mistreated in the past, such a being turned on without a speaker load, that can blow up output transformers.

Was the tech able to tell you anything about why it went? Was there any physical damage to the OT?

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yea. I'm not sure how it was treated in the past. I picked it up used recently. it's a 96 rev g. I got a good enough deal on it where this fix isn't going to really make it a bad buy. just hoping this fixes it and the MM was the right call. I brought it to Pat who seems to be pretty reputable here in Chicago (http://sweetamplification.com).

I'll get more info from him on what caused it when I pick it up. I was at work when he called and didn't get a chance to talk through the why but he did say maybe some old tubes could have caused it. I was playing it for a bit when I first got it with the old tubes but I don't recall when I first noticed the issue. could the speaker load issue be from using that crappy ass Marshall mg cab I was using at first? never seemed like it could handle the amp. I got rid of it finally and now have a recto standard