I built a quad of Grunded Grid 250Bs in the mid-seventies... just to
see if it would work, and because I had a free supply of pulls at my
disposal.
No tuned input and I used a KWM-2A as a driver. It would show a solid
1100 watts on a Bird 43 key down.
Two in conventional ( fed-grid ) service in a Johnson 6N2 Thunderbolt would
output 700 key down with 10 watts drive from a FT-767.
So GG isn't that efficient, but as an exersize in "will-it-work ?" ....
Yes it will.
Don W4DNR
Quoting Bill Fuqua <wlfuqu00@uky.edu>:
> 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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>
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