Is this a legit vintage Ampeg B-15???

[bostero77]

Well, whadya know! Mine worked the same way, so maybe this was common mod. I did purchase mine in '75 from Prune Music, where the Mesa Boogie amps were being developed in the back room by Randall Smith. That looks like it would be easily reversible. Do you like the way it sounds? I loved it. Or are you more worried about the resale?

"This allows a little more EQ flexibility" says it all.

i actually like it. combining both channels gives me a real full punchy sound.
not looking to resale anytime soon, once i like a sound i stick with it for a long time. im worried about if using this channel will shorten the amp's life somehow.

 

[bostero77]

Looks like they changed it to a fixed bias instead of cathode biased circuit, set up the middle input as a bridged input, and added a protection circuit of some kind. There is some mention of the hum balance but that should be there already I think, maybe modified that? I'd have to look back at some schematics to be sure.

thanks for your input corey. what are the effects of changing to a fixed bias?