The Tung Sol 6sl7 and the two Raytheon 6SN7GT's do not require biasing. Therefore, test and replace at will! I say test because the Tung Sol 6SL7 is likely a VERY nice tube indeed. A good source of 6SN7GT, can be found at Andy Bowman of Vintage Tube Services, but Russian, and Chinese varities are plentiful and not bad at all. Try the Electro Harmonix versions, cheap and servicable. Ralph Karsten at Atma-Sphere.com can hook you up with Chinese versions, if you really can't find them anywhere else on the net (Tubeworld, Tube DepotVacuum Tubes, Inc., etc., etc.,). Just Google 6sn7gt and see what comes up. I hope that you had the KT 88's biased when you put them in. If not, get thee to a qualified technician (should not be too hard to find in the Yellow Pages of your area) Electronics professors at local technical colleges may also be able to help you. If you really can't find a good pair of 6SN7gt's, I can sell you a pair or two of mine.
