The Russian mil spec 6H23 might be a tube to look at for the subject. Super quiet, good dynamics and not outrageously priced. I got some from ATSI as Dekay mentioned. Can't remember the guy's name at the moment, but they were only $20 each. They came in original stapled military boxes with instructions in Russian rolled around the tube and they've got chrome pins. Maybe Dekay can tell you how to contact the guy. I've misplaced his number, since I don't plan on buying from him again. I had one of those experiences where things just didn't "click".
