If your Clipperton amp doesn't have the same problem then it does indeed point to the KPA1500.
I don't own a KPA1500, but a quick look at the online manual shows that the tuning unit is an L-Network. Depending upon the load the unit is trying to match, an L-Network can require a very large amount of capacitance, especially on 160m ... which I suspect is achieved in the KPA1500 by switching in high power ceramic units for 160m. I had to replace a couple of high power ceramic doorknob capacitors for 160m in my own tube amp because I had degraded them with a high VSWR per my earlier post about an overheating common mode choke.
Of course you might not have the same problem, but it would be one of the things I'd check.
73, Dave AB7E On 9/2/2020 2:41 PM, Ken Ramirez de Arellano wrote:
Every bit of antenna hardware ( coax, balun, insulators, etc. have been changed out or proven good. Connections are all solid. My KPA1500 will transmit above 800 watts for about 15-30 seconds and then the SWR jumps up and it faults out for high VSWR. I can run 1500 watts on all the other “Legacy” bands (10,15,20,40,80) with no problems. I’ve forced an STU relearn and still the same issue. The antenna B amp is a Clipperton L and that transmits at a KW out and I see no change in VSWR in the external wattmeter using all of the same cabling. It’s starting to look like something heating up in the KPA1500. Is anyone aware of a known issue for this with the KPA1500 or a known fix? I would rather do a field repair instead of sending to Elecraft from KP4. TIA Ken, KP3MM
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