[Boatanchors] Confussion

[Barrie Smith]

I got the push-pull pair of VT-127As neutralized, I think.

I then tried increasing the drive, with no HV.  As I increase the drive the grid current goes up until it reaches 105 ma, which occurs at about 50 watts of drive.  Increasing the drive beyond that point causes no increase in grid current.

According to the only specs I have for the tubes, I will need 140 ma of grid current for the two tubes.

I'm thinking that the grid circuit is fighting itself.  With no safety bias applied, the bias voltage rises with increased drive.  At 50 watts drive the bias voltage is -550 volts.

That's 180 volts more than the tube specs call for.

The tube specs call for a 5000 ohm grid resistor, which is what I have (actually two 2500 ohm in series).

I believe that if the bias voltage were not so high I could achieve my 140 ma of grid current with the 50 watts of drive, which, according to the tube specs, is what I need.

Any thoughts as to what I should do next?

73, Barrie, W7ALW