Amplifier Power tubes - important to sound?

I’ve always found power tubes more important to shaping the sound in ways that are meaningful to me. Small tubes can also be important to be sure, but a lot of times it’s an initial "wow!" impression, then over time I either tire of that variant or just want to hear a different flavor. I listen loud (more strain on power tubes), so perhaps that explains my findings.

With power tubes, my initial impressions tend to stick. The change from a KT88 to KT120 is especially significant in amps where I’ve tried this swap. Anyways, what’s your tube amp that has 16 freaking KT88 slots to replace with a non-existent Siemens 6550? (I know op won’t answer) To be fair, if the Siemens 6550 did exist, I’d prefer it over JJ.

I actually have a pair of VAC Master 300 that use 16 KT88 (plus 8 6SN7), and even with auto bias it’s a kind of a PITA to swap. The KT120 sound great here, too.

@mulveling 

Yes I am looking for siemens 6550. It does look elusive.  And will have to revisit the source of recommendation whom is very good at what he does. I like to biamp so I'm using MC 901 monos from McIntosh.  I like them a lot and they blend tube and solid state very nicely.

I do like VAC quite a bit and still think about it. 

I did a lot of rolling on this class tube, kt88, kt66, 6L6, 7581a, 807A, russian tubes I don't remember the number of,  and they all sounded different.  It seems invariably I liked the new sound (human nature) at first but after going thorugh perhaps a dozen sets of tubes, I ended up back at the tube that the maker (Decware, Steve Deckert) had designed the amp around.  Makes sense really.

Jerry