Hi Jerry
I also have the LA-1K and HF-Auto tuner and I have quirky things happen when I am on 160 mtrs . My situation is with a 75’ run of high quality RG213 where the tuner is set for 1.08 to 1 and the amp matches at 1.1 to 1 transmitting with 700 watts CW. As I transmit the SWR on both the amp and tuner slowly rise over a 20 sec period to 1.7 to 1 and trips off to Bypass. My research narrows my problem down to two possibilities. One the dielectric in the coax is heating up and changes characteristics effecting the tuner settings for minimum SWR. The second though is that the 4:1 Balun at the base of my vertical is over heating and looses its magnetic properties. I do not experience this problem on any other band. I wonder if you added a ferrite isolator on the coax just before it enters your shack if that would alleviate the problem. After this weekend’s 160 mtr CW contest ends I will do some more investigation of my problem by installing a dummy load at the coax end that would connect to the Vertical.
Good luck
Alan
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On Dec 4, 2020, at 6:22 PM, JERRY <JERRY@...> wrote:
?This might be the strangest behavior of this amp I have heard of so far. I have a 257' EF wire with a 9 to 1 UNUN (grounded). My HF-AUTO tuner shows SWR 1.08 for example. Only in SSB as soon as I begin to talk the amp trips off with the SWR. I'm watching the SWR on the tuner, its not budging but on the amp it is jumping all over until it bypasses. Driving the amp with only 10 watts causes this to happen and I have tried it with my 7610, 7300, and 991A. Now what I'm not understanding is this. This behavior occurs only when I use a 75' run of LMR 400 coax. I have even tried a different piece of 75' LMR 400 and the result is the same. If I use a 150' run of LMR 240 the amp doesn't trip at all. I have replaced all the jumpers between the components to eliminate them as the cause. Same result. I can tune this same wire for 80M and the amp works fine regardless of the coax feed. Any thoughts?
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73,
Jerry
