Douglas,I checkesd several web sites.
Antique Electronic supply has them for $9.60 ea.
Tube Depot for $13.95 ea.
Fair Radio Sales in Lima has them for $7.00 ea.
None of these listed any quantities on hand.
I like the idea of it being directly heated. Been interested since I saw Gary Pimm's 47 amp. If we used your E-Linear topology, what are we looking at as possable drivers?
Keep it com'in...
Joe