Hello Steven,
I would say that the 500V cap would do the job. To do the job more neatly,
I recommend that you replace the existing SM cap laid between the socket
ground ring and the chassis with a 400pF or 500pF or 510pF SM and that way
you have the additional bypassing value in one capacitor instead of using
two separate 200pF units. It is also much neater.
I have also found that the overall length of the tuned line is actually
measured from that point where the bypass cap and feedthru cap is located to
all the way around to where it attaches to the variable tuning cap. You
will only need three plates maximum on that variable cap.
The tuning is very sharp, indicating that the tuned grid circuit is very
high Q and you may experience oscillation due to RF feed back between the
tuned plate and tuned grid. The 8930 has decent gain and will tend to
oscillate.
In tuning the grid circuit I used an MFJ 269 unit plugged directly in the
input RF port on the back of the amp unit. By using a type N to BNC adaptor
on the MFJ 269 you can plug it into the connector very nicely. No need for
HV or filament power to do this. Be sure to have the tube in the socket.
You will find that the correct tap of the input cap is very close to what is
indicated in W3RJW's spec of 5/8" from the RF ground end, which is located
where the bypass and feedthrough cap is.
I've modified three of the amp units to 432 and they all worked out
extremely close to what I've described above. Hope you have success with
yours.
OBTW, I am able to get 450 Watts OUT with less than 25 Watts of drive,
easily.
73, Bill, WF4R (FM16ts)
----- Original Message -----
From: "Steven Raas" <sraas@optonline.net>
To: <vhfcontesting@contesting.com>; <amsat-bb@amsat.org>
Sent: Monday, October 01, 2007 10:39 PM
Subject: [VHFcontesting] AM6155 432 Conversion question
> Hello everyone,
>
>
>
> I am moving slowly along in my conversion of my AM6155 ( W3RJW Method )
and
> I am at the point of installing new 200pF silver mica caps in the grid
> compartment. I would have used the old ones, but I have lost them, and in
> the conversion paperwork they don't call for any particular voltage
rating.
> I have found these caps available @ 500v and 1000v ( Both 200pF silver
mica
> ) and I am wondering which I should use? Or if it really matters?
>
>
>
> Thanks
>
>
>
> 73
>
>
>
> Steven J.Raas
>
> QRV From FN20vg on 2/432 Terestrial-Sats-Digital-EME
>
> Member of - ARRL & AMSAT
>
> Supporter of N3FJP Software <http://www.n3fjp.com/> http://www.n3fjp.com
> Home Page - <http://n2jdq2007.tripod.com/> http://n2jdq2007.tripod.com/
>
>
>
> _______________________________________________
> VHFcontesting mailing list
> VHFcontesting@contesting.com
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>
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