>> I have the amp connected to an FT-847 exciter and a large
>> Bird dummy
>> load. HV is between 2500 and 3000vdc on the plate. I
>> see
>> about 300mA
>> current on the plate when I'm getting 300 watts out but
>> very little
>> current on the grid meter, which I find a bit odd.
Here's the thing.
We don't know how much drive you are applying (you didn't
say), but the efficiency appears low. If we can believe your
meters the amp is running 800 watts input and only 300 watts
out. That's only about 37% efficiency.
That, along with no grid current, is a sign the tank is
either not fully resonant or is overcoupled.
If you are driving it with 50-100 watts plate current should
be around 500 mils to an amp. If drive is that high and the
plate current is low either you have a lot of loss on the
input or the tube could be soft.
It could be a lot of things. The tube, the input circuit,
the tank (only if you are using low exciter drive).
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