Bieworm wrote: ↑Sun 04/17/22 2:51 pm
Does your amp work now?
Update - Does the amp work now? Yes, and no.
Good news: For the first time in six weeks it isn't blowing the fuse. I can't explain the difference in how my light bulb limiter is acting, but no fuse blowing is good. I tried a 1 amp 250v new fuse, and also the original spec 8/10 amp 125v fuse, and neither blows. Amp stays on, and it passes signal with a guitar plugged in. I suppose that means that the OT or PT has an internal short appearing under load as Bieworm and JMP predicted. I didn't try the amp with just the new OT without limiter, before new PT, to know if the fuse would blow still with just the OT replaced. Regardless, I'm happy it finally isn't blowing fuses.
Bad news/next step: With no instrument plugged in, amp on, and volume up, there is a squealy type sound. With guitar plugged in, amp on, squeal is gone but there is a good amount of hum and hiss. Amp does not have a shorting input jack with 1m resistor, its the original 1/4" jack isolated from the chassis with fiber washers and no resistor.
I've never rebuilt a full amp before, so don't know what it could be. I replaced every component, and carefully inspected every component including measuring before installing them and comparing to schematic to ensure they were correct, though I recognize there is the possibility for error there. All components have good mechanical connections and solder joints. Do components need time to break-in? Next thought is maybe it is lead dress related, so I need to chopstick, as wires were certainly moved around in this process. Additional thought is that I implemented the suggested mods to improve gain and bass response and I've never heard this circuit with those mods. I'm wondering how those changes naturally interact with the 5-position tone knob and its resistors/caps and functions?
I can take a video this afternoon of what I am hearing to figure out next step.