[Amps] Alpha 76A 3cpx800 Conversion Tuning?

[Robert Harmon]

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>
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> 
> 
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