Boogie Studio Caliber lead channel goes out after 5 minutes

thozzman

Member
Messages
28
Hey guys, any help here would be appreciated.
I found a vintage Mesa Studio Caliber amp at a local guitar store. Mfrd. late 80's to early 90s.
About 20 watts with 2 EL84s. Class A amp with two separate channels.
But here's the deal: after trying it out on two different days, about 5 minutes after being turned on,
the gain channel suddenly goes bad. It still produces sound, but volume level is drastically reduced, virtually no gain, and hum
is heard big time. The sales guy first time removed and reinserted all the tubes and then tried it out and the gain channel was fine. He called me to say its ok now. Today I went in to possibly buy it, but after a few minutes of playing both channels, the gain channel did the same thing again. Clean (rhythm) channel is fine.
So it appears that when the amp and tubes warm up, something must overheat and screw up the gain channel.
The sales guy has no idea what the real issue is but says they'll mark it way down and sell as is.
Any idea what the problem may be and how expensive to fix? Thanks.
 

Vibroluxman

Member
Messages
2,139
If it's heat related I would look at the board and see if any traces are starting to lift. Cold solder joint perhaps? Shoot Mesa an email and they can help.
 

Vibroluxman

Member
Messages
2,139
and before opening the amp up try fresh tubes! Since it takes a bit to kick in I doubt they're the culprit but they're the easiest thing to check.
 

critter74

Silver Supporting Member
Messages
5,461
Change the tubes. Preamps first, then Power if Ybarra didn't fix it. 98% chance thsts all it is.
 

GasMask

Member
Messages
3,419
If it's heat related I would look at the board and see if any traces are starting to lift. Cold solder joint perhaps? Shoot Mesa an email and they can help.

This is a good thing to check. It's a known issue with this amp, and its board mounted tube sockets. Check the tubes themselves first- but if you can rule out a bad tube, this is a likely cause.
 




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