robert casey wrote:


You could make a fine tweeter with the 6BK4 but for a fullrange
fullsize electrostat you'd need hundreds. That's a lot of filaments at
0.2A 6.3V...


I'd then pick a radio transmitter tube, but the ones that I'm only at
best vaguely familiar with run at only a few thousand volts at most.
Depending on how loud you want your music, and how efficient
electrostatic speakers are, would determine how much power you'd need.
Someone mentioned 344 6BK4s each at 1.6ma at 16KV. That's about 550ma,
from a 16KV supply that's about 8KW of "input" power. That's an awful
lot of power, we must be off an order of magnitude or 2 here. Or are
electrostatic speakers really inefficient? But if I take a scientific
wild ass guess (SWAG) that 80W is more like it, then that would be 5ma
of plate current. 5 6BK4s (1ma each) could do that. But this must be
wrong as well...

Possibly the 4-65A, which is spec-ed for 3kV DC on top.
A PP pair of those (feeding a centre-tapped choke, rather than a
transformer primary) could give 6kV swing each side, which is getting
into the right area.