Re: LA1K LDMOS died while operating 10M
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Craig, Thanks, that parallels my experience. Antennas in trees aren't the best combination I guess. I have never seen the sparking but I wouldn't be surprised given what you said. My tube amp somehow managed to survive those, but maybe I need a different approach with a ss amp.? The sad thing for me is that antennas always test good with the swr meter, so I don't have a way to ensure that a replacement antenna won't have the same problems. My problems seem to occur on 10m so maybe I relegate the tube amp to 10m !
73, frank
On Sun, Nov 3, 2024 at 8:27?PM Craig Williams KA6RWL < ka6rwl@...> wrote: Frank,
My LA-1K has been in the shop 3 times for the same replacement of the Q1 LDMOS chip. I run a couple wire antennas up in some Doug fir trees. The 160m antenna is a full wave with a very low SWR. The other antenna is a 80m horizontal Delta Loop that has a HF-AUTO in front of the LA-1K. These antennas are up at about 80 feet. I have heard the arc off that chip operating SSB on the 160m at an input of 40w, the others were off the Loop once in FT8 outputting 200w and once on SSB with an input of 40w. These have occurred twice in 2-21 and once in 2024.?
This is what Mark (Palstar Tech) said the second time it happened.
"I just wanted to ask that if your amplifier faults for BYPASS SWR, ??make sure that your antenna system is in order, as certain types of faults can damage transistors very suddenly. These would tend to be faults that happen only at peak power levels, such as a wire antenna arcing to a tree branch.? Or a lightning arrester used on a non-resonant antenna with tuner. ? I did not find any cause for the failed transistor we replaced.? A couple associated parts were also replaced “just in case”. ? It is very unusual to have a repeated failure of this part.”
The amp did not fault to Bypass SWR and all antennas were checked each time with no issues found. The arc occurred between the chip and the same solder spot each time. So sometimes this may happen at least it is a relatively light weight amp to ship to Ohio for repairs. Despite this experience I still love the amp and the Palstar crew was great to work with.
Craig
KA6RWL
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