I went to play my little tweed amp today. That's what I built it for. I played it two days ago, so it wasn't too weird to think I would be able to play it today. No dice. It's just been sitting there, but now it has a crazy hum with no input. Now on top of my bass amp being in pieces I have to take apart the tweed as well. It's troubleshooting week here at the Vernon household.
I know I always promise pictures, but this time I will actually try to post some.
In my tweed the first two filter caps became ungrounded. That's a problem. If I re-ground them that should fix the problem.
Grounding those caps indeed fixed the problem. The wire coming from both of those caps had come loose from the 'star ground' point back behind the fuse holder and light bulb holder. It is a pain in the ass to get to that grounding point without desoldering 5 other things. Instead I pulled the grounding wire forward and grounded it to another point which I had available. It doesn't look as pretty but it works and is FAR more serviceable.
To diagnose the problem I started testing voltages throughout the amp. Some voltages were a little low compared to the last time I tested the amp out, but all voltages were well within spec of the Fender drawing. From that I assumed no components, tubes, or transformers had gone bad mysteriously. Next I started testing continuity throughout the amp. I am ALWAYS fooled by the positive lead going to the speaker jack being shorted to ground. I do not understand why this is the case. Someone needs to explain it to me. After fooling around with the speaker jack with no progress I started back tracking from that point looking for continuity to ground. Low and behold I found the two caps not grounding out. I gave a little tug to the grounding wire and found it to be loose.