NEW issue with Mid knob on 50Cal+

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seth155

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this amp has been sitting in a closet for the last couple years. I can't really play it anymore because I can only use it at "thin-walled-apartment/cranky-neighbor-next-door-with-new-born-infant" volume levels. plus, my playing is so abysmal, I wouldn't want anybody else hearing it anyway.

I sent it to Monsta-Tone when it's first round of "issues" flared up a few years ago. I think some LDRs weren't functioning properly, along with some other fried doo-dads, and worn out this's-and-that's.

Now on to the current problem
the MIDDLE tone knob is giving me problems, and here are the symptoms:

in the clean channel with the "Gain" knob on a higher setting (approximately 6/10 and higher), and the Master volume set to 2/10 (cuz I can't turn up much louder than that) the "middle" tone knob (with the treble, and bass knobs set to lower settings so the **** thing actually has an effect) works as it should up until the 6/10 mark. then turning the Middle knob higher than 6/10 the sound from the speaker starts to fizzle, crackle, fart, sputter, spit and piss. sort of like there's dirt in the contacts inside the pot. but I don't think its dirty contacts, because this fizzling continues even when not turning the knob. and the sound also cleans up when I turn the gain lower. I think also that this issue changes/improves when the Master knob is turned up. but I really can't tell because I can't turn the amp up too loud.

HOWEVER, this issue completely clears up if I turn the Reverb knob up to 8/10 and above. but I get no reverb effect at all out of this amp.

also, this problem clears up if I turn up the Treble knob up past 6/10. but I think this is only because turning up the treble turns off the Mid knob function entirely

the G-EQ, and the Presence knob have no effect at all on this problem. and this issue doesn't seem to persist in the Gain chanel

I tried the pencil tap test on all the tubes and they seem ok

I might try to make a video
 
I only have 1 extra 12ax7 and I don't know if its any good. its an electro harmonix if that makes a difference.
I think the reverb tube is the 12at7.
is it safe to temporarily replace this with a 12ax7, just to see if the reverb comes back to life?
 
seth155 said:
I think the reverb tube is the 12at7.
is it safe to temporarily replace this with a 12ax7, just to see if the reverb comes back to life?
Yes, the 12AT7 is the reverb tube (V4).
My Studio preamp came with a 12AX7 where a 12AT7 goes.
Someone was using it like that. I'm guessing it's OK to use it.
I changed it back, just because it's supposed to be that way.

When I suggested rolling preamp tubes.....
Pull out your V1, replace it with the V2.
Replace the V2 with the V3.
Replace the V3 with the V5.
You'll end up putting the V1 in the V5 spot.

About the reverb, check inside.
Somehow, my thick braided cable that goes to the tank, broke in the middle and I had to solder it back together.
I'm still wondering how it came to be like that. There might be something like that going on.
 
i also have a couple 12au7a preamp tubes. might those work in stead of the 12at7?
 

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