more fender ?'s

daniel · Post by **daniel** » Thu Feb 17, 2005 7:35 pm

I was wondering if I could get some more help with my 68 bandmaster(AB763). I recently disconnected the vibrato(thanks rjgtr) and added a 25k mid pot. I also changed the the mid and bass tone caps to .022 sozo's and the the treble to a 500pf silver mica. My normal channel is completely stock. I really like the extra mid range I can now tap into with one exception. The vibrato channel now distorts sooner than the normal channel does and I like the volume level the normal channel distorts at better. Why would the gain be increased like it was? Is the phase inverter distorting sooner do to the added mids? Slightly unrelated ?, I do not use the vibrato so the tube is going unused and and all that circuitry is there for nothing. I like the idea of setting the vibrato channel with a tweed bassman preamp. Has anyone ever done this and how difficult would that be?

Flames1950 · Post by **Flames1950** » Thu Feb 17, 2005 10:34 pm

The only reason off the top of my head that you may get more drive sooner on the Vibrato channel than the Normal is not only the added mids driving things harder, but the Vibrato channel uses a .1uF coupling cap to the phase inverter; the Normal only uses a .047uF. So the Vibrato channel is driving more mids and low end both, which will distort quicker.
As far as the tweed preamp idea, there's a guy on the Fender Discussion Page that did something similar to a AB165 Bassman, with one channel modded to a tweed Bassman preamp, but with no tone controls, driving straight through to the phase inverter. He really likes it a lot, with a lot of variation between the two channels. Can't remember his member name off the top of my head, but you could post over there and see if he bites, he loves talking about it. But he's a little spotty on posting when he gets involved in a recording project.

daniel · Post by **daniel** » Fri Feb 18, 2005 12:00 pm

thanks for the reply flames1950. I stared at the schematic for the amp for half an hour yesterday and didn't even notice that. I'll lower the coupling cap, now I just have to decide whether to put the blue molded .047 I pulled out of the tone stack or to try a sozo .022 I have sitting aroung. More to play with. I've been learning a lot since I first started working on this amp as its the first I actually have done any work on. This forum really helps a lot too. thanks all.