I agree with the few who have said that the JJ 12ax7 don't sound very good. I much more enjoy both the early Siemens 12ax7(Ecc83) with the dual support on the getter and the infamous Mullard late 50's with the "D" getter. However, the new JJ EL84 power tube is very good in the right amp. There is more input on the tube asylum from other users of the JJ 12ax7:
http://db.audioasylum.com/cgi/search.mpl?forum=tubes&searchtext=JJ+12ax7