These tubes tested very strong (possible NOS) on a Hickok model 6000A tube tester.  The 6AX4 was originally designed as a television damper tube, but later found use as a high current rectifier in DYI audio amplifier (guitars, PA systems, etc.). With two tubes a high current full wave rectifier is possible. Four tubes can form a more efficient full wave bridge. If you only need one, this is a good deal at this price as it comes with spares!  You can be sure that they are not making any new ones.