The contest calendar was on my mind. The ARRL North American QSO Party for CW was this weekend and despite all of my attempt to be ready for that I could not really participate.
I tried.
The problem was rooted in a very pernicious RFI problem in the shack. When I installed the second (replacement) KPA-500 I noticed that the KPA would switch bands during Tx -- even with very low power from the K3. The problem was even worse when high power was used. And, it didn't matter if the load was the antenna or a dummy-load.
The issue is critical because it would be unfortunate if the KPA got a driving signal from the K3 that was expected on a band but not the band the KPA was ready to handle. A sure fire way to blow those precious finals on the KPA.
As much as I tried to limit the amount of RF(I) in the shack, I could not eliminate it fully. The KPA would encounter a situation where the KPA was wrongly changing the band even though the K3 (driving exciter) was not changing band.
I've narrowed the problem down to emissions and I will just need to re-do the way the shack is setup by changing one thing at a time until I can find correlation.
Good news is that the WX is getting warmer so I can work more easily in the shack.
Just in time... TX5S (Clipperton) is expected to go up in a couple days and I also need to get back into the MST contesting scheme. And then there's the slew of State QSO Parties to do.
Finally, got the bill from Elecraft for the repair of the KPA-500. The cost to replace the MOSFET finals (VRF-2933) is $850 plus shipping. The KPA-500 is a tough little unit and does a good job, but take care of it. If the magic smoke comes out, it's about 1/4 of the cost of the amplifier to replace them.
I took care of mine and I still don't know what the real cause was for the failure -- and neither does Elecraft. Don't expect the warranty to apply. It really looks like the problem I'm having with KPA-500 number two is why number one failed -- the KPA-500 got driven off band.
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