Mark IV issue, all channels

Pre Recto days. Boogie modified Fenders, Mark I-IV, Dual Calibers, etc

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Mark III
Posts: 197
Joined: Sun Feb 18, 2007 7:55 pm

Mark IV issue, all channels

Post by fatbagg » Fri Nov 17, 2017 12:39 pm

Just moved and got my amp delivered (finally), but there are problems... The ch.1 treble pot is broken, and the entire amp is wack. All channels are quiet and very thin, almost out of phase. I can turn ch 3 channel vol up to 5-7 and the master volume up to 5 and almostntalk over it, and it is very thin and very strange sounding. Very little drive on any channel. All tubes are glowing, tapping doesn’t indicate any issues. I will be changing them all out, but does this sound like anything in particular?

Back knob is on Ft Sw (with foot switch plugged in).

Bottle Rocket
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Joined: Sun Oct 29, 2017 9:31 am

Re: Mark IV issue, all channels

Post by skarkowtsky » Fri Nov 17, 2017 12:53 pm


Sorry to hear this. I received my first Mark IV by mail a few weeks back and through trial and error learned that a lot of my tubes suffered damage in shipping. Although most of them passed the tapping test and seemed fine, they were the source of my problem.

Tone was flat, Triode mode was very loud, and volume and tone eventually started to intermittently fade in and out while I was playing. Unlike your broken pot, there were no physical signs of damage to my amp. So, sometimes visual inspection is a false positive.

I swapped out all power and pre-amp tubes with new Mesa 6L6s and 12AX7s. Thankfully, the amp is operating normally. So, yeah, I dropped an additional $200 on top of purchase price. I'm far from an expert, but given our similar situations I'd recommend starting with new tubes.

This might help: Rich at Mesa also had me run a patch cable from FX Send to FX Return Mono (right) to see if that cured some of my problems, but it didn't. The theory is that if unused, those jacks will accumulate dust that could disintegrate tone, even if you aren't using them in your chain. Maybe a little grit was dislodged in shipping and settled on the leads? He also recommended spraying contact cleaner on the patch cable and working it in and out of those jacks a few times to help clean them.


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