I have a Peavey 5150 combo I bought second hand and was told the preamp tubes are probably pretty old but the power tubes are more new. I've had this amp for maybe a year or more and may have had this issue from the beginning but honestly can't remember. The issue is that when I turn the the pregain rhythm dial up or down it crackles (kind of like a dirty volume pot). The lead channel pregain dial does not. Knowing absolutely 0 about tube amps I was wondering if anyone knows what this issue might be (keep in mind I am not technical at all and might be too nervous doing any opening up or cleaning of anything so I might take it to a tech if need be)?
Do you turn the pot while you're playing? I don't mean to sound condescending, but as long as there's nothing wrong with the sound once it's set, I wouldn't worry. My Box of Rock crackles when I turn it, but they have assured me that there's nothing to be afraid of in this regard.
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No; however, like a volume pot in a guitar after awhile it can get worse and then it will start cutting out even when you're not turning it. I was wondering if this is a sign that something will need to be replaced/fixed/cleaned ?
That's a scratchy pot. You might try taking the knob off of the potentiometer, spraying some contact cleaner onto the shaft, and then turning it a bit to work it in there.

Do it while the amp is off, of course.

If it doesn't work, you might have to replace the pot, which will require some electrical experience.
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What the hell is a G&L.

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Gay & Lesbian I think, the box smelled funny
Greg what did you send me??
Replace the pot. Cleaning them is a stopgap measure at best. Get a new one fitted if doing it yourself is too much for you. An honest tech won't charge you much to do it, lifting out the circuit board is the hardest and most time consuming part of the entire job. If it was an old amp with chassis mounted pots it would be a 10 min job.

Dylan, there's usually a gap in the housing near the contact tags (which is where the filth gets in too). You stick the little tube attached to the can in there and spray. Of course that means opening up the amp so your technique may be the only option open to the TS but it's hard to get enough spray in there using that technique.
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Sometime in the next little while I'll probably take it into a tech to give the whole amp a 'once over' since it is used and point out the issue and see what they say.

Thanks for the advice Raijouta and Cathbard!!