I didn't have time to read all the posts in this discussion, so this answer may have already have been stated....

I have owned and listened to many tube amplifiers, and basically I have surmised that the bass sucks in most of them. It's the #1 problem I have by far in getting my systems to sound "good to me". I am currently running 604-8K's in 620 cabs, in one system, and 515B's in 828 cabs in another... the bass should be great in either, not earthshakingly low, but nice punchy midbass... Which is what I want. But unfortunately, about 75% or better of the tube amps I have tried fail miserably. Interestingly enough, the current incarnation of power for the 604-8k's (without mentioning brands) uses wee little el84's run in triode,class A,around 2 watts output, with the preamp using 6dj8 running full out in class A all the time. When I plugged this combo in, it was like I added a subwoofer!

So maybe it's not so much the speakers, but more of an Amp- Preamp problem......

Hope this helps.... Scott