I have tried three different (four including the Bat supplied pair} 6V6 tubes in the 75 SE. JAN military Nos-very nice bump up from the stock tubes...POPE from Upscale audio..very fat midrange, but not great highs ,but very seductive and warm sound.AND....A pair of 6V6 GT NOS GE original box...I have had these in for about two weeks and these are the bomb! Glow top tubes that burrow deep into the sound like no other 6v6 i have heard.These were purchased from RodneyMarion on Audigon.He is in North Carolina,he said they were the best.I was somewhat skeptical,but amazed after so much hyperbole is tossed around.You really need to hear these tubes in the BAT! I also put in a pair of nice 6h30 dr NOS and six NOS 6SN7's from Upscale-brownbase Raytheon.The 6v6 tube in in 75SE is the Queen Bee,watch it work miracles with your preamp!