This technical talk is rather foreign to me, and I have no gear to test these things.
This did not start to happen right after the caps were replaced. The amp functioned well for months after, with no problems. The tech was a competent guy, as far as I could tell, but as I said I'm not totally experienced as far as in-depth electronic stuff goes. I do recall that he removed one capacitor and replaced it with two that equaled the value of the old one. I still have the removed capacitor, and I could write down the numbers on it if that is of any use.
rcrowley - I will give the pots a good cleaning and see what happens. I cleaned the tube sockets a few days ago, and did notice some of the pins on a few of the tubes weren't exactly straight. When I was at the shop last, I had the tech test all my tubes, and they were all in good or good-enough shape. I don't feel like I've used the amp enough since then to have worn them out, but you never know.
Another problem with this amp is that the built-in footswitch isn't always functional. You have to click the switch over and over and over until the reverb or tremelo engages. And sometimes, it simply doesn't work. Could these two issues be connected in some way?
I appreciate the help! I also realize this fix may be a tad beyond my scope, and that I'll have to take it in. We'll see...