I have a late ‘70’s Princeton Reverb. I just installed cap-can #3 over a period of about 10 years. I gig at least once a week where the amp is on for 3+ hours and use it intermittently at home. When it has gone bad it will start hissing and belching, whether a guitar is plugged in or not. If I thump the cap-can with my finger it will stop for a while-sometimes days or weeks, but progressively get worse. When I put the new cap-can in it runs perfectly for a few years, then starts acting up again. I have swapped out tubes and cleaned connections. I’m wondering if some other component might be going bad, putting extra stress on the caps, or if there are other caps that should be replaced as well when I replace the can. I also have a Vibrolux that just keeps chugging along. Never seems to need attention- but I’d rather tote the Princeton.