Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: frpax on December 08, 2016, 05:05:21 pm
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I just got a new-to-me 2011 Mesa Boogie Lone Star (not the Special) 2x12 combo. Switchable from 10/50/100 watts.
Channel 1 is clean, and it sounds fantastic. But then after several minutes and without touching any knobs on either amp or guitar, the channel gets muffled-like with a teeny bit of volume loss and more gain which is especially noticeable on the B & e (unwound) strings. I have that channel at 100 watts with silicone diode rectifier. After a few minutes, it goes back to great sounding. OR, if I hit a note with super heavy attack. That kind of "knocks" it back normal.
Channel 2 is my gain channel and when I turn the Gain knob past, say, 10:00, it squeals and howls like a banshee until the knob is dimed, then it quiets down again. Same with the Master Volume knob. Howl and squeal past about 11:00-ish. This channel, I have set at 50 watts.
In either case, changing wattage doesn't affect either problem.
Now, I'm figuring that this is all tube related. After dropping a lot of money to get the amp, I'm not super keen on replacing every tube (5 12AX7's, 4 6L6's & a 5U4). Id like to fix both problems with as little replacement as possible.
Any help, you experts out there?
P.S. I have a friend who is an amp builder, but he doesn't know very much about these rocket fueled high power amps that I love.
[edit] I was just fiddling with it and the Channel 1 Reverb makes that same squeal/howl. I'm totally stumped. :dontknow:
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I almost guarantee its in the FX loops input jacks. Those are switched jacks. They get corroded. When it happens again, take a patch cable and plug in and out real fast in the fx loop jacks. They most likely need a good cleaning.
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I almost guarantee its in the FX loops input jacks. Those are switched jacks. They get corroded. When it happens again, take a patch cable and plug in and out real fast in the fx loop jacks. They most likely need a good cleaning.
Should I wrap a piece of paper around the plug? Would that help clean it? Or a Q-Tip and some alcohol?
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I tried the in-out thing on the FX Loop jacks. No change.
HOWEVER, when I unplugged the reverb tank from the chassis, ALL that howling and squealing stopped. Just now, no reverb. :help:
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Have a good look over that reverb cable. Make sure it's properly intact. My friend had the same issue, and his rca cable for the reverb tank was broke inside.
I would also take a closer look at those effects loop jacks too. Spray them with contact cleaner, and work a 1/4 inch jack in and out several times. They cause bizarre issues with almost every Mesa amp I have owned.
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Have a good look over that reverb cable. Make sure it's properly intact. My friend had the same issue, and his rca cable for the reverb tank was broke inside.
I would also take a closer look at those effects loop jacks too. Spray them with contact cleaner, and work a 1/4 inch jack in and out several times. They cause bizarre issues with almost every Mesa amp I have owned.
The white, non-shielded RCA plug had some corrosion, so I cleaned that up. Sprayed contact cleaner into the RCA jacks as well as the effects loop jacks.
Problem seems to be fixed. I'm also getting better reverb than before as well.
Thanks for the advice!