Ampeg SVT III (non-pro)
Ok, so this thing was caked in dust and a bit of a death trap, the ground trace on the power terminal board was gone, so nothing was actually grounded.
There were some lifted/missing traces in a few other places as well. Whoever worked on this previously deserves the results of their work.
I tore it all apart, cleaned it up real good. replaced the various lifted/missing traces with jumper wires and got things back to the way they should be. The 5 position Mid freq select switch had a broken shaft. A direct replacement is like $40 or some shit, so I got some cheap used 2 position switches of the same style from ebay (stackpole/ Electroswitch C1 series) Drilled out the rivets, had to press off the disk with the detents and replace it with the one from the 5 position, re-assembled with some machine screws and nuts. Success.
Big ups to FM Nate Dort for calling out this listing, and helping clear up some misconceptions I had while going through and testing it all out.
Broke out the oscilloscope and signal generator and went through the test points. Once I had a clue what I was doing, it made sense and all the measurements were actually pretty close. Nice.
I haven't hooked it up to a cab yet, but everything checks out on a scope. Here's some pics.
Before:
After:
Front panel:
Mid Switch: