Bob...Thanks for your email. I did install the RFC3 in the same location as
the old RF Choke and upgraded the blocking caps to 1000pf 5KV 858 door knobs.
The new RFC3 was a tight fit.
I wonder if the RFC-3 is throwing things off. I guess I can install the old
choke and see what happens, but I'll see what others say first. I did email
N4UQ as well to see if he has any ideas.
From: Amps [mailto:firstname.lastname@example.org] On Behalf Of Robert Harmon
Sent: Sunday, April 05, 2015 1:48 PM
Subject: Re: [Amps] Alpha 76A 3cpx800 Conversion Tuning?
I am in a similar quandary.
I upgraded my 76CA to two 3CPX800's along with the Peter Dahl transformer also.
I didn't change the
existing RFC though. It tunes up beautifully on all bands (except 12) (more on
that later) More power out
on all bands. While I was at it I put in new power supply caps and equalizing
I know the 76's don't like 12 meters with their existing RFC and I purchased
the RFC-3 to install later. I read that this choke would work fine and provide
12m. However, later on the Eham amplifier forum I asked for info about using
the RFC-3 and read that the RFC-3 is 1" in diameter and would be too close for
comfort and would cause tuning issues. It was suggested to find one that is
3/4" in diameter or install the RFC-3 but mount it farther away from the tank
circuit components than the original Alpha RFC .Also an Ameritron RFC is
supposed to be another alternate. That is where I am now, I need to find out
more on this. Hopefully we can hear from
someone that has done this mod successfully.
(I would suggest posting this issue on the eham amplifier forum. The
amplifier gurus like Carl, KM1H and Lou W1QJ have been repairing amps for years
and usually jump in to help.)
Anyway, thats my two cents. Please keep me posted on what you discover.
On Apr 5, 2015, at 12:36 PM, Rich Hallman - N7TR <email@example.com> wrote:
> After converting an Alpha 76a to 3CPX800's with a new Peter Dahl upgraded
> Transformer and installing the new upgraded RFC-3 Plate Choke I am seeing a
> problem with tuning on 15 and 10 meters. All bands except 15 and 10 seem to
> tune ok. On 15 and 10 meters....The tuning indicator is at 0 and it's the
> best tuning I can get. For those who have completed a conversion in the
> past, can you let me know if you have seen this issue before and if so, what
> was done to fix the problem? I've seen some info on the net from removing
> stators from the tuning cap to moving the taps on the tank coil.
> Thanks for any help you can give!
> Rich N7TR
> ex KI3V, N3AMK, WB3JOV
> Telnet: dxc.n7tr.com N7TR DXCluster
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