If you value sound stage depth & width(excellent ambiance recovery), neutral reproduction(no phony warmth/tubey editorializing) and fast/accurate bass; either the 1940's round plate Tung Sol 6SN7GT(JAN CTL) or Sylvania 6SN7W(JAN CHS, TALL BOTTLE ONLY, metal or Bakelite base) tubes are phenomenal. The Sylvania possessing a bit more bass slam. Either choice will cost dearly, but- are worth every penny, IF you value faithful music reproduction. The 1940's, BOTTOM GETTERED, Sylvania(JAN CHS)and Ken-Rad(JAN CKR) 6SN7GT/VT231's are next in the accuracy department, with just a bit less depth of sound stage. Just as beautiful everywhere else. (http://www.ebay.com/itm/Pair-Awesome-Sylvania-JAN-CHS-6SN7GT-VT-231-T-Black-Plate-Audio-Tubes-/111720481029?pt=LH_DefaultDomain_0&hash=item1a030f4105) (http://www.ebay.com/itm/Matched-Pair-of-SYLVANIA-6SN7W-CV1988-B65-ECC33-Metal-Based-Tube-NOS-NIB-274-/291488621829?pt=LH_DefaultDomain_0&hash=item43de136505) (http://www.ebay.com/itm/TUNG-SOL-ROUND-PLATE-BLACK-GLASS-JAN-CTL-6SN7GT-VT231-Amplitrex-Tested-1264006-/191608860512?pt=LH_DefaultDomain_0&hash=item2c9cc72f60) (http://www.ebay.com/itm/Pair-Matched-Ken-Rad-JAN-CKR-6SN7GT-VT-231-Military-Spec-Vacuum-Tubes-ECC82-/371378091687?pt=LH_DefaultDomain_0&hash=item5677dbf6a7) for example