12AU7 and 12AX7 long black plates vs short black plates. Any difference ?

Hi Joecastillo, i also concur - just wish we had measurements to demonstrate this, ie 3s soundstage, musicality etc.

Do long black plates with square getter, usually earlier production, sound slightly better than with D getter ? I understand, this might be going into extreme details, but we are high end and small is big for us.

Just compared this. I did not hear any difference between square and D getter Sylvania 12au7 long black plates from 1950s. This does not necessarily mean that you wouldn't. Besides, VAC Avatar SE is an excellent amp but I consider it audiophile entry level.