My pleasure, Major Dude! the 'Rambler' made for a natural fit...the rest just flows, right? that is one of their best songs from maybe my favorite album of theirs. I have never been around a Rambler....I just found a schematic for the preamp. IT is based in the BF Fender world. They didn't draw out the trem function, so I am going to guess that it is a bias vary??? I could see a switch to go from that cathode bias to fixed bias as a positive IF one were looking for a bit more power and headroom for certain applications. That 25K mid pot makes a difference in comparison to a stock vintage Fender reverb amp tone stack. I would love to see a schematic of the output section. NO negative feedback loop?