OK – now things are getting a little weirder.
Since my first post, I’ve been playing the amp some more (without the pilot light bulb) and I’ve noticed a couple of other strange things.
1. After playing for a five minutes or so, the sound level slowly fades out (sounds like it would if you turned off the amp while playing). Within 5 – 8 seconds, the sound returns – as if nothing had happened.
2. Most recently, it has started making a “static” sort of noise that sustains after a chord is played – until I mute the guitar strings and then all sounds stop (including the static sound). The only similar sound I’ve heard before was with a Fender Super Champ that needed replacement power tubes.
At this point, I turned the amp off to do some more research about what might be going on.
Thanks for any possible insight!