can changing 6sn7 tubes affect the output voltage

I recently changed my input tubes, 6sn7, and eventualy, (about a 100 hours) fried a pair of eml 45 mesh plate tubes. I have a pair of eml non mesh coming and am a little nervous about cooking these as well. My preamp is a Supratek Cabernet, with a voltage selector switch that accepts the low voltage 45's as well as the 4 volt px and the 5 volt 300's. Should I go back to the stock russian tubes or am I "safe" with the rayethon 6sn7's I rolled out. Someone help! I gulping $400 a pair!! Until the went, the 45 mesh plates were fantastic. What am I missing? Supratek folks and tube lovers, please lend me you expertise.