[Amps] 4-400A ratings

[Vic K2VCO]

I've come into a pair of 4-400A's. I'm thinking about building an amplifier with one tube 
and using the other for a spare. Looking at the data sheet for class-C CW, the maximum 
rated plate current is 350 ma. This means that at 3 kV on the plate I can expect to get 
only about 750-800 watts output. This does not come close to utilizing the 400-watt plate 
dissipation of the tube.

At 4 kV, I could get 1400 watts input and about 1050-1100 out. That's a lot better. But it 
means a lot of extra expense -- the power supply, tuning capacitor, etc. need to be bigger.

Is this correct? Why is the plate current limited to 350 maA? Is it a limitation on 
filament emission?

Of course I can use both tubes and get full legal power. But then I need another socket, 
chimney, etc. Or maybe I can use the "SB220 cooling method" and cheaper sockets.
-- 
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/