[Amps] HF amp output power dropping

[Tom Rauch]

> I have an old Henry 3000d RF heater that was converted to 
> HAM use by someone else. It runs a 3CX3000A7 tube in 
> grounded grid.
> Recently the output power has begun falling off rapidly 
> whenever I apply constant drive such as during tune up.
> The tube is new and the plate voltage remains steady as 
> always.Is there anything else that could be causing this?
> It reminds me of a tube that has gone soft although I am 
> sure it's not the tube.
> Any help is appreciated
>

Assuming the drive is constant and the meters are good, it 
sounds like a bad tube.

It could be a capacitor or inductor drifting off value and 
making something get mismatched, it could be the bias is 
drifting up,  but a problem like that when it suddenly shows 
in an otherwise properly working amp is generally (but not 
always) the tube.

Watch all the meters especially plate current and bias, that 
should tell you something.

73 Tom