[Elecraft] Strange KPA500 problem on 6M

[AJ8MH-Radio.Joe.Hutchens]

Had a similar problem when working for Motorola.  Couldn't get the SWR 
down with the antenna connected.  Even changed antennas. Dummy load OK.  
Finally looked at the signal on a spectrum analyzer and 80% of the power 
wasn't even close to the crystal frequency.

Did you try driving the amp with another radio?  You would see the same 
problem if the amp is oscillating.

I'm assuming the K3 works fine into the same antenna...

73,
Joe ( AJ8MH-Radio )