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PostPosted: Tue Apr 11, 2017 8:44 am 
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Bottle Rocket

Joined: Tue Apr 11, 2017 8:34 am
Posts: 3
My Boogie Mark IV lead channel has suddenly lost a ton of gain, such that at my normal settings of 8 gain and 6 drive, I have less overdrive than when I switch to the Rhythm 2 channel! Oddly I have no valve symptoms at all; no funny microphonics or noise and all look like they are glowing nice and evenly. I've not changed any settings on the amp since I last used it yesterday (fine then) and I have tried removing the footswitch and changing channels manually on the back of the amp. It doesn't sound bad per se, it just doesn't sound like it normally does and my lead sound is now almost a second clean sound for some reason.

I'm going to try changing the pre amp valves one at a time, assuming I can find a working replacement, but does anyone have any other ideas about what would cause this? I've checked and tried each switch on the front and back, including all the push pulls and power amp switches, to see if it affects things, but no changes other than what normally happens, just with a light crunch sound instead of the creamy high gain solo sound that's normally there!

I'm fresh out of ideas for what is causing it!


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PostPosted: Tue Apr 11, 2017 10:18 am 
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Mark III

Joined: Tue Apr 17, 2012 10:01 am
Posts: 259
You don't mention any issues with either channels 1 or 2, so I am going to guess it may have something to do with one of the 12ax7s used by channel 3. And, according to the manual, there are multiple: V3, V4, and V2 (in that order).

V1 is common for all channels (and probably is not the issue), and V5 is the PI tube.

Hopefully it is simply an issue with one of those tubes (V3, V4, or V2).

Good luck!

_________________
Lefty guitars: Gibson SG standard (1977) • Gibson LP custom (1979)
Amps and such: Mesa Boogie Mark IV-B • Mesa Nomad 45 • Peavey Vypyr Tube-60 • Effectrode Blackbird • Kingsley Jester • AMT SS-11a • Zoom G5


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PostPosted: Thu Apr 13, 2017 3:25 am 
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Bottle Rocket

Joined: Tue Apr 11, 2017 8:34 am
Posts: 3
That's really helpful thanks. I found the page of the manual I think you're talking about and I tried replacing all of V1-5 but no joy, so I'm stumped. I'm wondering if some other component on that channel has bust or something. Very odd!


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PostPosted: Sun Apr 16, 2017 1:09 am 
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Bottle Rocket

Joined: Sun Dec 07, 2014 5:28 am
Posts: 4
Location: France
Hello

Try with a bomb cleaner contact.

-Cut the amp and leave 10 mn
-Open the amp to see the main board
-Go from the contact bomb.

Do not forget the inputs and output jack (send and return)

-Wait 10 minutes and switch on again

Normally you should pick up your original sound...

dom

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PostPosted: Sun Apr 16, 2017 2:28 am 
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Bottle Rocket

Joined: Tue Apr 11, 2017 8:34 am
Posts: 3
domglop78 wrote:
Hello

Try with a bomb cleaner contact.

-Cut the amp and leave 10 mn
-Open the amp to see the main board
-Go from the contact bomb.

Do not forget the inputs and output jack (send and return)

-Wait 10 minutes and switch on again

Normally you should pick up your original sound...

dom


Appreciate the help Dom! What's the contact bomb/any idea where I could find the info I need? I'll check the jacks too!


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