Just got this from TBer the dude. Thanks the dude! I had an identical one that I sold about a year ago. That one had 6550s this one has 7027 (and GEs no less ) A short comparison on possible differences due to output tube type... First thing I notice is that the volume knob has a wider range then the one with 6550s. That is, this one takes more volume knob to get similar output levels and starts to clip out a little higher on the dial. Overall volume seems about the same between them from what I can recall. Ill have to give this one a rip with my NV 610 to really tell. So far I only have had a chance to punish my GK 112 though the speaker performed impressively I must say. The sound at clipping is different. I think the amp with 6550s may have had a more girthy sounding grind but again I have to crank this through the 610 before I pass judgement. Overall clean tone is just as I remember. Goes from sweet and thick to razor edgy with treble but in just the right way. Mids have lots of gain. What ultra low switch?