[Amps] Low power output from 4-400A linear

[Bruce Lanning]

Several years ago, I built a GG amplifier using a pair of 4-400A. The grid 
and screen are grounded at the tube socket.

I feel that the power out is quite low. Below are some of the operating 
parameters:
 Measured power out: 855 watts
 Power input: 1216 Watts
 Ep:3200 Volts
 Ip: 380 Ma.( at max output)
 Ig: 250 Ma.
 Eg: Bias 00
 Static Ip: 120 Ma.

I am using the B&W Pi-network, model 850A output tuning inductor
.
I have checked the tube filament pins for a poor solder joint.
They both looked OK, but I resoldered them to no avail.

Maybe someone out there could throw some light on my problem, or if I even 
have a problem...