[Elecraft] Problem: KPA-100 10M SSB Distortion

[Brian Kassel]

Folks:

   I discovered an SSB audio distortion problem using the KPA-100 on 10M
only early in the SS contest this past weekend. The problem only occurs
on 10M and only when enabling the KPA100.  I confirmed that the
distortion was present during the above conditions on a dummy load, as
well as with all of my antennas. It seems worse on the antennas
however.  The amplifier has worked perfectly on the 10M band previously
to the contest.  In fact the day that I completed the amplifier option,
I spent 4 hours on 10M SSB, as I couldn't seem to be able to sign off
without still another station calling me, and complimenting me for the
good sounding audio. So, the problem has just cropped up recently to be
sure. This rules out any construction errors I think. I am certain as
well that the problem is present only on 10M, as I made almost 1100
QSO's, most on 15M, this past weekend in the SS SSB contest. I got bad
reports on 10M immediately when I attempted to use SSB.  I listened on a
separate SSB receiver to confirm the bad audio on 10M SSB.

   I first suspected RF getting into the microphone or low level audio
stages, so unplugged the microphone. In the USB mode, while listening on
the other receiver, when I increase the power with the front panel power
control, I hear a "clicking" sound as soon as the PA switches in at the
11 watt power level.  I take this to be an instability or feedback sound
or symptom.  The clicking does not occur on any other band either.

   In addition, I can easily hear the distortion begin when I do use the
microphone when I go to the 11 watt level, that is when the amp switches
on. It is a very sharp increase in distortion, not gradual either, again
pointing to the KPA-100 itself.

  Any ideas out there? I did a bit of research on the WEB, but can't
really find any reported symptoms to mine.  I'm thinking that something
has changed of course, but can't figure out what may cause the problem. 

   I was able to use my other K-2 and another external amp on 10M for
the purpose of the contest, so really didn't lose too much as far as
scoring. 

Brian K7RE