Hello Jack
The grounded screen work ok for the 4CX800.
This configuration was used for sure by some hams
in Ukraine with very good results.
Using other sockets than the originals was
experimented also with good results.
Use more different value capacitors, not only one type/value,
and is preferable to use some sort of contacts/fingerstock for
the external screen connector, rather than the single screen soccket pin.
73's
Traian
W9GT wrote:
> Good suggestion Colin. I was familiar with the 4CX1500B (W5TMN) amp in
> Bill Orr's Handbook, but never tried the grounded screen arrangement. I
> built a 4CX1500B amplifier, but I used a conventional circuit and the
> regular SK-800 series socket which had the built-in bypass cap. Really, the
> grounded screen may be an excellent way to go and accomplish the desired
> results. It is only complicated by the requirement for floating the screen
> and bias supplies below ground. The thing that makes this intriguing is
> that you can use a cheap socket and just provide a good grounding ring with
> finger stock or a clamp for the screen. A few large holes or arc shaped
> slots in the chassis for air flow up through the anode and presto....a
> 4CX800A or two mounted very cheaply and (hopefully) with no sacrifice in
> performance or stability. Air chimneys could easily be constructed. Of
> course, building-in problems with "less than ideal" components is always a
> risk and could be termed as false economy. However, since the Svetlana
> sockets are much less common than the tubes, and are relatively expensive,
> this could be an excellent way to go to build a decent amplifier fairly
> inexpensively.
>
> 73,
> Jack, W9GT
> ----- Original Message -----
> From: "Lamb" <k7fm@teleport.com>
> To: "W9GT" <w9gt@home.com>
> Sent: Monday, December 17, 2001 7:22 PM
> Subject: Re: [AMPS] Bypassing Screen of 4cx800a for 50 MHz
>
> > Hi Jack:
> >
> > I would consider the 4CX800 similar in performance to the 4CX250. The
> > special socket is not essential - but if you do not bypass at hf for vhf,
> > you can have problems.
> >
> > A good bypassing job will work if you use short leads. Or, I used regular
> > sockest and grounded the screen while floating ell the other electrodes.
> > The screen is still positive with relation to the cathode, but shielding
> is
> > excellent. Collins did that on the 30S1. Bill Orr's Handbook shows how
> to
> > do it. It is a bit more complex, but works very nicely with a regular
> > socket.
> >
> > Using a 50 ohm resistor on the grid also reduces tendency to oscillate at
> hf
> > or vhf.
> >
> > 73, Colin K7FM
> >
>
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