How do the Electro Harmonix 6sn7's sound?

I am curious as to how the EH 6sn7 gold pinned tubes sound relative to the classic vintage tubes like the Tung Sol round plate or the Sylvania W's or RCA grey glass, etc. I have only one 6sn7 tube in my preamp so the sound from this tube is very important and "shapes" the overall sound it get. thanks, Jim