----- Original Message -----
From: <donroden@hiwaay.net>
To: <amps@contesting.com>
Sent: Saturday, August 18, 2012 7:05 PM
Subject: Re: [Amps] Schematics  for 4CX250B GG HF amplifier
>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.
But on SSB that 700W could be heard all over the band in stock condition. I
rebuilt several T Bolts for area hams using the G3SEK Tetrode Boards which
made them almost respectable with just the tubes they came in with.
These days the VHF riceboxes are worse to start with and when clowns put
them into any big amp a good part of the band is gone.
> So GG isn't that efficient, but as an exersize in "will-it-work ?" ....
>
> Yes it will.
>
> Don W4DNR
Id love to see an IMD plot.
Carl
KM1H
>
>
>
> 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
>>> _______________________________________________
>>> Amps mailing list
>>> Amps@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/amps
>>
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