I am also about to embark on construction of a pair of Svetlana 4CX800As. I
want to run 160M. thru 10M. Including 6M. might be impractical unless you
make arrangements to switch the entire output tank circuit to a "6M.
channel" and provide a different plate choke etc. I think I will keep the
VHF separate and perhaps build another amp for 6M.
As for the HF tank circuit, has anyone utilized the tank coil that Henry
Radio has been selling on eBay? I have purchased a couple of them, however
they look rather short on turns for 75/80M. and certainly I would need to
add an additional inductor for 160M. I believe the Henry coils were used in
a 70s vintage amplifier using a pair of 8874s, 2K Ultra??? Any sources for
tube sockets, or did you build your own?
I am interested in what experiences any of you have had with these tubes and
suggestions for building an amp. I built a tetrode amp a number of years
ago with a 4CX1500B and it worked great. Some debate, however, on the
validity or wisdom of using a "passive" input circuit using a big 50 ohm
resistor to swamp the input power. Much of the literature contends that a
tuned input is better for IMD, however, that leads to possible requirements
for neutralization and other complicating factors. It all becomes quite a
bit more complicated than a simple GG amplifier, but in consideration of the
low cost of Russian tubes, seems like a great way to QRO. Anyway, I would
sure like to hear from anyone who has built an amp with these critters and
any info on your experiences.
73, Jack, W9GT
----- Original Message -----
From: "John Peters" <pe1ogf@iaehv.nl>
To: <amps@contesting.com>
Sent: Monday, December 03, 2001 2:53 PM
Subject: [AMPS] Question : 4CX800 Amplifier 6-10-12-15-17-20 meters
>
> Hi All,
>
> I want to construct an amplifier for the following bands 6-10-12-15-17 and
20m
> using a 4CX800 Tetrode. Is there anyone here who can help me with some
designs
> ?? I'm mainly intrested in the plate circuit.
>
> I've read on the Svetlana page that input can be very easily done by a
> resistive input
> circuit,
>
> >From : http://www.svetlana.com/docs/TechBulletins/technoteNo42.html
>
> The 4CX800 may be run with a passive grid circuit, nominally 50ohms. This
is
> to ensure stability, without requiring neutralization. However, to obtain
a
> peak RF voltage of 35V across a 50ohm resistor, a driving power of 12.3w
would
> be needed.
>
> Any info will be very welcome,
>
> 73! de John pe1ogf
>
>
> --
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>
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