[Boatanchors] Confussion

[Carl]

----- Original Message ----- 
From: "Barrie Smith" <barrie at centric.net>
To: "Boatanchors Mail List" <boatanchors at mailman.qth.net>
Sent: Sunday, August 08, 2010 7:32 PM
Subject: [Boatanchors] Confussion


>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


Apply all voltages, twiddle the knobs and see what happens. If its not an 
oscillator go to the next step and pray.

Carl
KM1H