1 AndyJ 3 months ago As many of you know, I own one of the latter-day Ampeg J20 combo amps (hand-wired, all-tube, basically a Fender Brown Deluxe circuit).It has been sitting in my drummer's basement, un-played, for about a year, as I have mainly been playing bass during that time. I fired it up last week, let it warm up, and plugged my HiLo Tenny into it and was disappointed to discover that the amp was very dark and murky, which I have never experienced before with any guitar I have played through that amp. I had to crank the tone all the way up and play on the bridge p'up in order to get it to sound even reasonably clear.I wasn't terribly surprised that there was an issue of some sort, as the amp has been sitting for as long as it has. My quick question is, any idea of what the particular issue could be? Also, I would like to be able to take care of this myself, as simply as possible (if possible), before having to take it to an amp tech.The amp has only a single tone control knob. I am wondering if I can just replace the preamp tube in the tone position. I doubt it's that simple (probably it's a cap issue), but it doesn't hurt to ask . . .