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 Post subject: My 5:25 is cooking tubes
PostPosted: Thu Apr 26, 2018 10:14 pm 
Mark I

Joined: Fri Jul 16, 2010 4:23 pm
Posts: 21
So earlier today I posted the question about using a noise gate with my Express 5:25 to tame the hiss on the clean channel.
Well, I'm starting to suspect there may be something else wrong with my amp. Tonight I sat down to practice a bit, and after about 10 minutes there volume just dropped right out. I took a look at the back, and sure enough, one of the EL84 was red-plating :evil: .
These tubes are only a couple of months old. The pair previous were also only a couple of months old when one started red-plating. At the time I figured that was a one-off, bad tube.
Wondering if anyone has any ideas for diagnostics before I send it to the tech.

Verily, verily, I say unto you, The hour is coming, and now is, when the dead shall hear the voice of the Son of God, wailing through a Mesa Boogie. And they that hear shall live.
- John 5:25 (King Bee Version)

PostPosted: Fri Apr 27, 2018 7:45 am 
Single Recto
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Joined: Sat Jan 12, 2008 12:32 pm
Posts: 1334
My 5:25 did the same thing with a new set of Mesa power tubes! I swapped them and the red plating followed the tube, not the socket. I contacted Mesa and they had the dealer replace the tubes. It hasn't happened again, but the tubes sure smell hot when the amp is running! The old tubes did not seem to run as hot and they are both the same color (can't remember which). Maybe the smell will go away, but it's been a few months.
I've checked the bias and it's fine (I don't recall where it's at), as are all of the voltages within the amp.

PostPosted: Fri Apr 27, 2018 8:48 am 
Donating Member
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Joined: Sat Dec 24, 2016 12:19 pm
Posts: 15
I got mine as a "floor model" new. I figured the store just beat the heck out of it because it was red plating when I first got it. Mesa sent me new tubes and that hasn't happened since. I went ahead and replaced the preamp tubes as well just to see if I could get it a little quieter, it seems to have a hum when I'm not playing that's not really loud but noticeable. My Mark 5:25 doesn't hum at all. The preamp tube replacement really didn't make much difference. However, most of the time it's not noticeable. Just when I'm in the rehearsal room by myself.

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