Batwing transistor questions (KA-3500)

[mikepick]

Well, I matched and replaced the four differential transistors on the power board and no change, I'm still getting 39mV and 42mV on the speaker posts. (Related, testing the buggers is a tricky thing, with how heat sensitive they are, I ended up shaking them out onto a paper and using the Peak tester clips to pick them up.) Anything else I should look at?

 

[mikepick]

While I'm at it, another odd thing is that the amp is making a small squeaking noise on power up. It's not affected by volume, and happens 3 or 4 seconds after the switch is flipped.

Here's a recording: https://www.dropbox.com/s/480bnxpqk63ihc7/KA-3500-speaker-squeak.mp3?dl=0

It's recorded with the phone Voice Memo app, so not great quality, but you get the idea.

(Yes, I've checked inside for mice. No signs.)

 

[mikepick]

Working on a case. Just answered my own question about whether I should keep the metal case on inside the wooden case—I've made the fit a little tight, so it's in here now without it!

Just released it from the glue-up clamps and cut the vents across the top:



Next step: sanding, finishing, and finding longer screws for the feet!