[AMPS] Fw: Help......Alpha 76 CA Problem

[Dennis Utley]

>During the 1st hour of the WPX CW contest I was operating on 15 meters.
>
>My antenna has a high SWR in the CW portion of the band.  (2.7/1) so I
>usually use a tuner, however on this occasion, I had tuned up with the amp
>in the CW position without the tuner.
>
>About 20 minutes into the contest, as QRM on my frequency was getting
worse,
>I decided to switch the amp to the SSB position.  This increases the plate
>voltage, as well as output.   Immediately I heard a buzzing sound, arcing
>with each keying stroke.  I turned off the Alpha and continued barefoot.
>
>This weekend I had some to do some trouble shooting.  I first checked out
>the Alpha on 40 meters.  Everything operates quite normal, with full output
>and all normal meter readings.  Howerver, on 20, 15, or 10 meters, even
with
>small amouts of drive,. there is arcing.
>
>I opened the Alpha 76CA and watched for the source of the arking.  The
>arcing is coming from the Pi L output circuit "LOAD"  variable capacitor.
>The arc is near the rotor shaft of the capacitor about 1" in from the rear.
>
>I suspect a failure somewhere in the output circuitry caused by high
>reflected power, however, why would it be a problem only on 20/15 and 10
>Meters?  Has the capacitor itself failed, or is the arcing a symptom of a
>failure further on down the output circuit.?
>
>Any ideas on what is happening and how to correct the failure would be most
>appreciated.
>
>Thank You,
>
>Dennis Utley, AF7Y
>
>
>
>
>




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