How to adjust bias on superphon preamp

I own a "F" series Superphon Revelation 2 preamp from 1989. I would like to tailor the sound: make it a bit warmer, less edgy. Also, cannot move volume past 8-9 oclock if that means anything. Would appreciate some help in the matter, thanks. cody
Call Stan Warren at 541-344-3696 and have him update it. He designed it and knows how to ugrade and modify it.
Yes, Call Stan.