I can't agree with you there. Mine is much punchier and tighter than any SVT I've ever played, and that's through two Mesa/EV 1x15s. Never flubby.
OTOH the bottom end is not especially bassy compared to the best SS power sections. I don't think you can have it all in a tube head.
My other tube bass amps have that 'punch in the gut' factor, the s/s-like low end. I suspect my 400+ could do with a rebias that I don't have time to do right now, so I may not be giving it a fair shake, but I've played several over the years and they all had the same general characteristics. Mesa doesn't make tube bass amps for punch, IMO. (Their s/s hybrid stuff OTOH- is huge in lows) They're all modified Fender Showman tonestacks with undersized power supplies feeding too many tubes. The Buster is basically a half 400+. The D-180 is probably the best sounding bass distortion amp ever and the Bass 400 and 400+ are just slightly tweaked versions of its preamp with bigger power sections. Dave's Mesa EV cabs are where his amps really shine, and back in the day, ALL the Mesa Bass cabinets came with EVM drivers.
That Peavey VB-2 you were asking about earlier is MUCH closer to what it seems to me what you're looking for outside of some very rare and esoteric tube amps. You'd love the Trace VA/VR series as well as the V-type, and the new Fender Super Bassman is supposed to be very good, but I haven't heard one to verify that. The long discontinued Aguilar DB728 is an absolute beast, likewise with the Peavey Classic 400. Any GOOD Hiwatt or Hiwatt clone will have plenty of clean punch as well. The OLD Eden VT300 made by Koch Electronics is also a VERY sweet amp. I have all of those except for the Super Bassman and Hiwatt, but I did have the DR103 that the Georgia Satellites used to record "Keep Your Hands to Yourself" for several years. If you can find one and get it in good running order, the Fender 300PS and 400PS are monsters, but be aware that you have to have THREE 4 ohm cabs for the 400PS and that the 300PS only has a single 8 ohm output. Sunn 2000S's have a great sound all their own, too.
Tube bass amps can do big, tight lows with that wonderful tube compression, but they have to be set up VERY well to do it. Low end requires current, which increases exponentially as frequency drops to maintain output power. That requires two things: a design that supplies enough drive current to its power section- that's why the Fender 300PS and 400PS can have the same modified Showman/Bassman preamp as their lesser powered brothers and be much more punchy- they have a completely different output section drive scheme and a power supply that has the current on tap to do so. The Mesa 400+ is a 225 watt amp on a good day. The dozen 6L6GC's in its output section are capable of 360+ clean watts depending on their quality, but the amp's power supply can't provide them with enough current to do that. The Mesa 400+'s main supply rail runs at around 550 volts on the plate and 300 on the output tube screen grids. An SVT runs around 700 volts on the plates and 550 on the screens. The Trace VR/VA series uses an ultralinear output transformer and puts over 725 volts on the plates AND screens.
