I played a gig a few months ago at which I used the rig of the bassist for the headliner band - an original, well-maintained 1971 SVT - 300 watts of all-tube power atop a big 8X10" cab. Big, glowing tubes visible through the back, and that old-school smell....
I had my Modulus Q5, and I asked the guy where I should limit the vloume - he said "turn it up as much as you want - it can take it". I turned it up until it hit a sweet spot, just amazing, thunderous lows with a clear round midrange, and an overall tone that I just can't quite describe. It's one of those things you just have to experience. I play old-school rock music, mostly with a 2mm pick, and the grind and growl from that rig was bitchin'. I played a whole set through it, and it sounded better than any other stand-alone rig I have ever used. My own full rig can get a bit more ultra-low end depth, but the overall effect of the SVT was of a powerful rounded richness that was immensely satisfying. There is a difference between SS LOUD and all-tube LOUD.
I immediately wanted one.