Dan Armstrong's Storytone piano sounds quite interesting.  I cannot
imagine, however, that anyone restoring such a historic artifact would
consider even for a moment replacing the original vacuum tube amplifier
with solid state components of modern origin!  That's very much like
ripping pneumatic parts out of a rare and valuable reproducing piano so
it can be "modernized" with solenoids and a disk player.

Vacuum tubes are NOT difficult to obtain.  One excellent source of
tubes, as well as other parts (e.g., high voltage electrolytic
capacitors, et. al.) needed to refurbish old electronic equipment is
Antique Electronic Supply [address above].

Dan, I truly hope you will reconsider your restoration approach and
preserve the unit as it was originally built.

Dave Saul