Sunn Concert Bass output. Large sine wave is at the speaker jack. Small sine wave is at the end of the preamp before the output section. Really using that dual trace potential. Putting out 24V into a 4 ohm load — doing 144W at clipping.
I received this amp in pieces. A previous shop declined the repair and returned the unit to the customer disassembled.
4 transistors in the output section were shorted and many parts on the output section PCB were burnt. This was a labor intensive repair so I could see why the other shop turned it down. The output section uses an interstage transformer to couple the signal from the preamp to the bases of the output transistors. You have to disconnect many wires from the PCB to be able to get it out and access the solder side, which is a hassle
Output section after repair. Lots of open emitter resistors and shorted 2N3055s. Some of the 22 ohm bias resistors were fried too
HUGE lot of service info here, basically the mother load if you ever need to service one of these amps. It has schematics from all eras, parts list, and mods — Sunn Concert Bass service info
Sunn Concert Bass