i have c.a.l. sigma 2 dac that has a 12ax7a stock. so far i have tried a JJ 12ax7 ( a bigger sound stage, more detail but not as smooth) a phillips 5751(didn't really notice much of a drop considering the gain difference, less detailed and not really as coherent). i bought a psvane 12ax7 from grant fidelity here in calgary, and have about 20 hours on it so far. it seems to have most of the qualities i was looking for-smooth with a nice big soundstage. so far it's my favorite, with the stock tube second. i'm gonna give the psvane a bunch more hours and see what happens, all the tubes so far are relatively cheap-$10.00-$37.00. if i'm still searchin', i may pay some big bucks for some nos mullards or the like for $100.00 plus for a single tube!
