[Amps] Schematics for 4CX250B GG HF amplifier

[Colin Lamb]

While Peter's reference to the Eimac article is excellent, I just want to report that there has been some reports by users that it might be possible to use the 4CX250 series of tubes in a ground-grid arrangement without a screen voltage.  The control grid on this tube is extremely sensitive and easily destroyed, so the "normal" grounded grid connections will destroy it.  A few ham have experimented with grounding the screen grid and connecting the control grid either to the cathode or through a large resistor to the screen.  

I only mention this because hams are experimenters.  I have seen such circuits and claims that they work, but no hard documentation.  I would not use a tube in such a circuit unless I was prepared to test and monitor the actual power dissipated by the grids to verify they are within limits - and that the total operation is desireable.  

Over the years, I have seen at least two articles on using the tube in this manner.  I am not recommending this circuit nor vouching for it.  Similar arrangments, with other tubes, are used in modulators and audio amplifiers - but just because a circuit appears in print does not mean it is good.

73,  Colin  K7FM