thickwood, does your attenuator have a treble bleed? I know people complain about simple attenuators, but I built one I've really been happy with, though I use it more to lower output conveniently rather than to cook the power tubes. A bonus is that it in effect reduces the post-gain background noise from the amp - a valve amp can easily sound noticeably hissy/hummy when run at such low output.
Crustycabs: yeah, the power control on the Rebel is more like a power tube headroom control. Not really my ideal. It does bring additional compression and earlier distortion, I'm sure more so as you crank the amp, but when I bought it I hoped it would make a powersoak unnecessary, but no dice, especially as the Rebel is not the easiest amp to dial down quiet. I have a 60w Peavey valve combo which sounds nowhere near so sweet, but something in its gain structure makes it simple to dial down to bedroom levels without feeling like you're teetering at the very end of the potentiometer tracks.
Incidentally, as a quick and dirty way to quieten a loud amp I have in the past just put a passive potentiometer in the FX loop, though of course that runs the power tubes at low signal level and again tends to require a treble bleed capacitor.
