I have seen this article before.
There are two issues.
One is the input circuit a T network and an inductor on the output.
This does will not produce the best IMD. A capacitor between the cathode
and ground would help.
But the real problem I have is the idea that the 100 Ohm resistor is
necessary.
It serves no purpose. Since there is no grid current the resistor can not
produce a voltage drop.
For some reason the author seems to think that is is necessary for plate
current to flow.
That is totally wrong. In fact when operating class AB1 the max plate
current in a tetrode is when
the control grid is at the same voltage as the cathode and naturally the
screen grid is at some fixed
positive voltage.
When the tube is triode connected and the control grid is connected to
the cathode, the
screen grid becomes the control grid the roles are reversed. The screen
grid swings to some
maximum voltage, say 250 or 300 volts, and the control grid is zero. You
get the same results.
Naturally, in grounded (screen) grid configuration just about all your
drive will go to the output when
using the 4CX250B.
The only thing the 100 Ohm resistor may have done is to snub out a VHF
parasitic oscillation.
73
Bill wa4lav
At 04:59 PM 8/15/2012 -0500, kc0hfl wrote:
>http://home.comcast.net/~k7rld/4cx250bamplifier.htm
>
>Try the above.
>
>Bob
>----- Original Message -----
>From: "peter chadwick" <g8on@fsmail.net>
>To: <JeanPierre.Behiels@electrabel.com>; <amps@contesting.com>
>Sent: Wednesday, August 15, 2012 11:31 AM
>Subject: Re: [Amps] Schematics  for 4CX250B GG HF amplifier
>
> > The 4CX250B is not suitable for use in the classic GG arrangement. Go to
> > http://ahars.com.au/documents/eimac01.pdf for an explanation.
> > 73
> > Peter G3RZP
> >
> >
> >
> >
> >
> > ========================================
> > Message Received: Aug 15 2012, 04:03 PM
> > From: JeanPierre.Behiels@electrabel.com
> > To: amps@contesting.com
> > Cc:
> > Subject: [Amps] Schematics for 4CX250B GG HF amplifier
> >
> > Hi guys;
> >
> > Anyone can help my with a full detailed schematic or documentation for
> > building a HF grounded grid amplifier with 4 times a 4CX250B tube on board
> > ?
> > All information will be mutch appreciated around this subject.
> >
> > Kindly regards Jean ON4AEF.
> >
> >
> >
> >
> > Electrabel sa, Boulevard Simon Bolivar 34, 1000 Brussels, Belgium
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