[Amps] Alpha 76A 3cpx800 Conversion Tuning?

Sun Apr 5 17:05:36 EDT 2015

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.

Thanks...
Rich

-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of Robert Harmon
Sent: Sunday, April 05, 2015 1:48 PM
To: amps at contesting.com
Subject: Re: [Amps] Alpha 76A 3cpx800 Conversion Tuning?

Hi Rich,

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 resistors.
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.  

73,
Bob
K6UJ

On Apr 5, 2015, at 12:36 PM, Rich Hallman - N7TR <rich at n7tr.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
> 
> Rich N7TR
> ex KI3V, N3AMK, WB3JOV
> www.n7tr.com<http://www.n7tr.com>
> http://www.qrz.com/db/N7TR
> Telnet: dxc.n7tr.com N7TR DXCluster
> 
> 
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