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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