Hohner/Marlboro 1550 Bass Amp Schematic

[Steve Fundy]

Thanks again all. I was just beginning to check capacitors in the power supply. I know the causes of motorboating, but was mainly curious if my attempt to use a different transistor might be contributing to it. I understand the explanation as to why now & not before. I had been working on tracing & testing prior to attempting to replace the bad transistor. I tried 3or 4 different transistors, and 2N3904 had the most amplitude out of the preamp. I had begun to remove & test capacitors in the power supply when I stopped. I think one of the 2200uF is bad as I had tested it out of circuit just before I quit for the day. . More tomorrow.

[vintagekiki]

Yes, 2200 (red arrow) looks like as break + pole and then soldered.
Tip: Change C14, C16 (2200u / 40V) probably changed ESR or capacity due to long-term use.