I have a Bogen TPU-35A that has been on the shelf for a couple of years. I thought it was working when I took it out of service. I plugged it in yesterday and hear a loud hum with my butt set on Com and 70v terminals. Nothing else is connected to it.

Is there anything serviceable inside, or is the unit most likely toast? Thank you.

Jim

Not sure about the hum with a butt-set, but across the 70 volt line, there may just be a lot of residual noise. I would suggest hooking a speaker up instead of the buttinsky. Use the Com and 8, now thinking that might not have an 8 ohm out, but the 25v out should be wanting to see about a 16 ohm load at 35W. Those are really reliable amps. Still being made but now a 35B. Or if you have a speaker with a 70v xformer, hook that up instead. If you still have the hum, I would suspect that one of the power supply filters has crapped out, although not a big deal to repair.