Determining Fender Bassman Circuit

[cafehonda]

I recently had a client give me a Fender Bassman 50 Silverface head. It has a couple of broken pot shafts which are an easy fix but I would like to figure out what circuit I have so I can do a proper diagnostic job on it. I am going to "blackface" it so I want to make sure I get the right parts and do the right mods. Any sage advice for determining which circuit I might have?

BTW, I am a drummer with soldering skills so this is way outside my wheelhouse.

 

[fat_fleet]

Is the tube chart sticker not still on the inside? CBS was notorious for using whatever stickers they had in stock on 70s Silverfaces, but there's a chance yours could be accurate, or it could give you a starting point. You can probably narrow down the year on the Superior music page if you haven't already...

 

[ranjam]

I wouldn't worry. Just look at the bias potentiometer. If it looks like a bias 'balance' control, it's a terrible idea, and that's all you need to do. Your 'client' will thank you. Make it like any blackface bias circuit. You'll need one 220K resistor, and a small piece of wire.
Well, sometimes you need a 2nd resistor. You'll know when you go to bias the tubes. But start there, and worry about step #3 when you have step #2 finished.