Roy Morris-6 wrote
I believe the 50 Mhz shutdown is SWR or possibly heat related. My first tests were conducted with the K3 output going through coax to my linear amp and tuner before arriving at my dummy load. Even though the linear and tuner were switched out of the circuit, there was a lot of coax cable before getting to the dummy load. At 50 Mhz the long coax length caused a 2:1 SWR. This was when I noticed the click and shutdown.
I then connected the K3 output to another dummy load through a short piece of coax. My SWR was 1.3:1 and did not experience a shutdown over any amount of time. The K3 was in TUNE mode long enough for the fans to ratchet up to a higher speed.
I observed jumping of the PA temperature reading with the dummy load fixed right on the ANT1 socket on the back of the K3. Notice that this happened with a PA that was cold. Unfortunately I am not able to do a 100W key down test because my dummy load is not rated for 100W key down. (I was robbed. It was advertised as rated for 100W, and it looked chunky enough in the picture, but when it arrived its spec said 100W PEP, 15W average. So it's little better than the two QRP dummy loads I already have.)
One odd thing I observed when setting up for the test. I went through all the bands, doing an ATU Tune into the dummy load. On all the HF bands there was just a brief "zzzzip" from the relays, lasting perhaps for half a second, and it found the match, as you would expect with a 50 ohm load. On 6 it took two or three seconds, on consecutive occasions, as if it was not that easy a job to find a match.
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