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Modified Ampeg Gemini I

11/26/2005 8:46 PM
Modified Ampeg Gemini I
I have an Ampeg Gemini I (with the 12" Jensen) that is no longer stock. I am not certain exactly what the mods were, but here's the story...  
The amp blew in the early nineties (blown output transformer and power tubes at least) and 7591s were rare. The tech removed the 7591s and the output trans and replaced them with a pair of 6V6s and another output tranny instead. The amp is not as loud as it was, maybe 15-20W or so. It sounds great, but is in need of power tubes again, and last time I wound up paying a lot extra because the tech didn't have a schematic for the circuit and spent some extra time trying to figure it out.  
I am tired of paying someone else to work on that amp. I'm comfortable replacing tubes in my amps with a known schematic and rebiasing them, and I'd like to know exactly what's going on in that amplifier.  
I don't think the power transformer was replaced. What would you guys have done? Just lifted the power section from a Fender Deluxe schematic or something like that and slapped it on the end of the preamp section? I am planning to start by just drawing a schematic of the power section and trying to see where it becomes the Ampeg schematic again. The tech also installed a master volume at that time, maybe just a phase splitter or something? Not sure.  
It was a killer mod on that amp, though. It took it from kind of dull, with a somewhat flabby, nasal overdrive to a really, really smooth little amplifier. It sounds great clean, really warm, but sounds even better when you lean on it. There isn't a ton of gain, but it's a great AC/DC or ZZ Top kind of sound. And the amp has loads of high end. If the truth be known, if I could figure out what he did to THAT amplifier, I'd do the same thing to my Gemini II in a heartbeat.  
Any guidance or suggestions would be welcomed.

Mark Lavelle I'd just start drawing out the sche... -- 11/27/2005 11:01 AM