[Amps] 4-400 Amp Help

[Rahul Sathe]

Hello Experts,

I just finished building a QB4-1100 / 4-400 Grid Driven amp. with
following configuration..

1 X QB4-1100
450 V DC Screen
-150 VDC on CGird, switched / keyed to ~ -50V DC for idle current of 80mA
2800 VDC on Anode which drops to 2200 on key.
Input is applied to CG using a 2 turn: 6 turn air core transformer
(1/2 inch dia, 1 inch spacing) with bias feed through 6 turn winding.
The 6 turn winding is resonated with a 30 pf variable cap.

With ~ 5 W input from my TS130 I get ~ 120 mA plate current giving ~
130 W output. if I increase the drive the output does not increase
beyond 130, and the plate current stays ~ 120 to 130 mA.  Where am i
going wrong?

The tube can deliver 400mA in case I reduce the bias on grid.... but
not with the drive?

can someone  help?

Regards /// VU3RAZ