It is the gain on both the preamp and power amp that effects the use of the volume control.
I have a tubed pre, with adj. gain, combined with a 27db of gain on my amp. The pre`s gain set to 16 db= too loud; volume at 9:00, the pre`s gain set to 8 db= too loud; vol. at 12:00.
I also have a low gain integrated w/ passive preamp section with a gain of 20 db. Unfortunately for me, I had to turn the vol. knob all the way to 2:00 for same level of volume.