[rotcoddam]

Can this tube be used in place of the ax7's. Be interesting to try if it will go.  
http://www.zeitmann-tubes.com/Tubes/NosRussianAudioTubes/Nos6n2pev.htm

[SHIF]

I think not.
Pin 9 is shown as an internal shield with no electrical connections. Pins 4 and 5 are either ends of the parallel heaters.

http://www.gstube.com/data/ECC83_6H2nEB.shtml

Of course you can always hack on your PCB and get the heaters to work, but why?