For your 6SN7 locations; the bottom-gettered Sylvania(JAN
CHS) or KEN-RAD(JAN CKR) VT-231's, from the 40's, will
provide you with a really clean, open sound stage and
imaging. ie: (http://www.ebay.com/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313.TR0.TRC0.H0.Xsylvania+jan+chs&_nkw=sylvania+jan+chs&_sacat=0)
(http://www.ebay.com/sch/i.html?_odkw=ken-rad+jan+ckr&_osacat=0&_from=R40%7CR40&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xken-rad+6sn7gt&_nkw=ken-rad+6sn7gt&_sacat=0) They'll perform very close to the
round plate TungSol 6SN7GT and Sylvania 6SN7W, without
costing an arm and a leg. You give up a little stage depth,
for the money. Far as the 6922; Mullards will warm things p
quite a bit. Most Amperex; not quite as much. The cleanest
are Siemens and Telefunken 7308/E188CC or E88CC. ie:
(http://www.ebay.com/itm/E88CC-pair-of-Siemens-tubes-6922-E188cc-ECC88-E88CC-CCa-grey-shield-/201148877183?pt=Vintage_Electronics_R2&hash=item2ed568497f) Note the
grey, metal shield, between the plates on the Siemens. The
later ones, with shiny metal, in that position, can get
strident, in the wrong system.
(http://www.upscaleaudio.com/telefunken-e88cc-6922/) Upscale
also sells Mullards, Amerex, etc and tests/grades their nine
pin miniatures for noise/microphonics. Especially important
for use in a preamp. Your interconnects, sources and
speakers all will contribute to, or subtract from, your
sound stage/imaging abilities. The tubes mentioned above
will insure that nothing is hampered, in your pre or amp.
Nothing above is cheap, but less expensive than the TungSol
RPs, tall bottle, Sylvania 6SN7W's and early 60's, grey
plate Siemens CCa's that I'm using. Hopefully, my stash of
those will last 'til I'm dead or go deaf. The prices on
those are nuts now!