K2: KPA100 transmitted audio distortion on 80 meters

[radiotelegrapher]

On 80 meters only, I have moderate distortion of transmitted SSB ouput from
my KPA100.  It's not RF in shack or antenna related as I confirmed on-air
reports by listening on another receiver while transmitting into a dummy
load.  The distortion is present only with the KPA100 on:   At 10 Watts
(KPA100 off), no distortion; At 11 Watts (KPA100 on), distortion, which gets
no worse as I run up to 100 Watts.

The distortion is actually a loud "crack" at the start of a new word or
syllable.  However, a continuous sound is clean.  A tuning fork by the mike
modulating at full power sounds fine.  From this I suspect the TR switch in
the KPA100.  Tapping components doesn't reveal anything loose.

In the archives I found reports and fixes for this exact problem.  However,
my KPA100 (Rev E of January 18, 2007) already has the new components from
the fixes:  1K added in parallel to RFC3, C31 changed to .22mF.  I also
tried changing R4 to 39K, per Don's suggestion of 3/27/00, but no joy.

Any ideas?

--

Dick & Judy Lamb
44 Post RD
Iowa City  IA  52245-3622

Landline 319.338.2721
Dick's cell 319.471.3834
Judy's cell 319.471.3822
email [hidden email]
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[radiotelegrapher]

Please ignore this email & respond to email of same title yesterday.  I apologize for duplication, but I thought my earlier email was lost.  K0KK

radiotelegrapher wrote:

On 80 meters only, I have moderate distortion of transmitted SSB ouput from
my KPA100.  It's not RF in shack or antenna related as I confirmed on-air
reports by listening on another receiver while transmitting into a dummy
load.  The distortion is present only with the KPA100 on:   At 10 Watts
(KPA100 off), no distortion; At 11 Watts (KPA100 on), distortion, which gets
no worse as I run up to 100 Watts.

The distortion is actually a loud "crack" at the start of a new word or
syllable.  However, a continuous sound is clean.  A tuning fork by the mike
modulating at full power sounds fine.  From this I suspect the TR switch in
the KPA100.  Tapping components doesn't reveal anything loose.

In the archives I found reports and fixes for this exact problem.  However,
my KPA100 (Rev E of January 18, 2007) already has the new components from
the fixes:  1K added in parallel to RFC3, C31 changed to .22mF.  I also
tried changing R4 to 39K, per Don's suggestion of 3/27/00, but no joy.

Any ideas?

--

Dick & Judy Lamb
44 Post RD
Iowa City  IA  52245-3622

Landline 319.338.2721
Dick's cell 319.471.3834
Judy's cell 319.471.3822
email [e-mail]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[e-mail]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html