[Elecraft] KPA 100 Instability

[John, KI6WX]

Mike;
The best way to check for feedback instability in K2/100 is to remove the
KPA100 from the K2 and set it beside the K2 with all cables still connected
(the procedure for doing this is in the KPA100 manual and is done for some
of the initial tests).  Then transmit and see if the instability condition
still occurs.  If the instability doesn't happen, the KPA100 improved
shielding kit, KPA100SHLDKT, should fix the problem.  There is another cause
for the problem if the instability still occurs with the KPA100 removed from
the K2 case.
-John
 KI6WX

----- Original Message ----- 
From: "Michael Clutton" <mike@mikeclutton.co.uk>


Hi All,
I have been using my K2 s/n 01319 with most of the various mods and
firmware upgrades available for about 3 years with no problems at all.
I recently went QRO with the KPA 100, this works great on 160, 80,  40
and 30 mtrs. Unfortunately on any band above this it becomes very
unstable within a few seconds of speaking into the microphone the
power meter just goes full scale.
I disconnected the KAT100 and fed the KPA 100 directly into my Yaesu
dummy load come power meter and exactly the same happens, full scale
deflection 150 w plus. I changed the microphone from the Kenwood MC80
desk microphone for a bog standard Kenwood fist mike, but my problem
is still there.
The KPA 100 is built into the K2 case, any suggestions would be very
much appreciated.

                       73 de Mike G4VQH