The details for removing the grid collet fingers are shown in the ARRL
UHF/Microwave Projects Manual, Volume 1 for the K1FO single and dual
tube 432 MHz 3CX800 amps, and the 432 MHz 8938 amp. Not sure how this
would relate to K8RYU's original question in a 222 MHz application, but
at least the illustrations clearly show the grid fingers and describe
how to break these off.
73, Dave/K8CC
On 10/20/2015 4:37 PM, Dave Olean wrote:
Hi Bill et al.
The one I remember was the grid collet for the 8938 on 432. It needed
a slight bit of inductance for best neutralization. I remember that
Steve figured it out, although the amplifier worked fine without it,
you would see some drifting in the power output, no doubt due to some
regeneration in the grid crcuit. After removing a small number of
fingers from the grounded collet, the amplifier was much more stable
as far as power output went. When I got the tube initially, W6PO
indicated that it had flunked the stable power output test and was
rejected for an order to the Swiss gov't. The tubes were for remote
unattended sites where the tubes would normally be off until required
and then had to reach full power from a cold start. Bob indicated that
with use the tube would probably improve and be just fine. I did see
power drift, which improved, but, by removing teeth from the finger
stock, it got really stable. Now I do not notice much drift at all. I
think Steve removed every fourth finger. I could always take the 432
KW apart and look at the grid ring!
Dave K1WHS
----- Original Message ----- From: "Bill Olson" <callbill@hotmail.com>
To: "terry price" <w8zn54@verizon.net>; "VHF Contest Reflector"
<vhfcontesting@contesting.com>
Sent: Tuesday, October 20, 2015 4:48 PM
Subject: Re: [VHFcontesting] 3cx800a 222 amp
yeah, duh, I was talking about the grid collet!! so where I said
"cathode connection" was just me being stupid, what I MEANT was I
seem to remember there needed to be just a little inductance in the
grid connection, so with homebrew collets you had to diddle with the
number of fingers a little..
bill
From: w8zn54@verizon.net
To: callbill@hotmail.com; vhfcontesting@contesting.com
Date: Tue, 20 Oct 2015 12:39:16 -0400
Subject: Re: [VHFcontesting] 3cx800a 222 amp
I've built several 3CX800A7 222 amps and the cathode circuit that
was used
on the 8874 version was the same. The plate line changed.
Terry - W8ZN
-----Original Message-----
From: VHFcontesting [mailto:vhfcontesting-bounces@contesting.com] On
Behalf
Of Bill Olson
Sent: Tuesday, October 20, 2015 12:00 PM
To: VHF Contest Reflector
Subject: Re: [VHFcontesting] 3cx800a 222 amp
Ralph, I'm really straining my brain here, but I seem to remember these
triodes wanted a little inductance in the cathode connection to
"neutralize"
them. I remember with an 8874 on 220 back 35 or 40 years ago I build
a home
made grid collet with finger stock.. The finger stock was in a solid
ring at
first but in order to make the thing work I had to keep bending
fingers away
from the grid ring on the tube.. That's all I remember, don't have
that amp
any more..
Steve, W1SMS, now owns and runs Lunar Link, I'm sure he has the info
you
want..
bill, k1DY
> Date: Tue, 20 Oct 2015 11:23:01 -0400
> From: mathenyr@marietta.edu
> To: vhfcontesting@contesting.com
> Subject: [VHFcontesting] 3cx800a 222 amp
>
>
>
> I remember reading that there was a K1FO 222 amp using a single
> 3xc800a7 tube. I have tired to get such an amp to behave without
> success...cathode circuit problems.
>
> Does anyone know if the K1FO amp description was ever published?
Does
> anybody have one of the amps who could send me a copy of a manual or
> perhaps photos??
>
> Also looking for a proper grid collet for the thing...
> Eimac 720359 ... anybody know a source? The grid collet
> may be my problem, but I am on my second "hamstyle" version and
> getting frustrated.
>
> The 2M version of the thing worked first try....
>
> Thanks..
>
> de K8RYU
> _______________________________________________
> VHFcontesting mailing list
> VHFcontesting@contesting.com
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