A little less gain and greater linearity is preferred over tube self
destruction.
I hope to build a grounded screen 4cx250B when I get time. It will most
likely require
another driving it due to the fact that I am shooting for a full gallon.
But two could easily be driven by a 100 Watt transceiver to produce 500 to
600 watts output.
73
Bill wa4lav
At 10:43 AM 8/15/2012 -0700, Colin Lamb wrote:
>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
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