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LA1K LDMOS died while operating 10M
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I was operating the CQWW SSB contest yesterday on 10M.? My SWR is fine on that band, as shown my by almost 100 Q's before having a problem.? Then it just went into bypass mode and when I reset it to operate, it put out perhaps 200 watts. ?This has happened before and Palstar replaced one of the LDMOS.
My antenna is a fan dipole up in the trees and the wind was blowing, so conceivably the swr could vary over time, but the amp has high swr protection that would cut off xmit if the SWR went above 2:1, I would think.???
Anyone else have an LDMOS failure and what did you determine caused this problem?? How did you prevent it from happening again??
I'm new to solid state amps, so wonder if this is to be expected compared to old tube amps.
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Thanks,
Frank
W4TG
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Frank,
?While I can't comment on what happened exactly to your amp, I will say that tube amps are much more forgiving of SWR being a little high. I have been using the Palstar HF auto tuner for a year now with an AL80A amp and didn't? really have any issues. This weekend I picked up the LA-1K and got it home and put it in line. Noticed right away that my SWR on the same antenna seemed a bit higher than normal. I put the LA-1K in stand by and hit the tuner with some RF and noticed it wouldn't get the low match as before. I had to put the tuner in manual mode and tune it. After I did this, the amp and tuner were happy and everything went well for the rest of the afternoon.? ?It sounds like your amp may need a trip back to Palstar for some new transistors.? Billy Parkinson KG5RQZ WRYA510 HH 11724 COR RACES 306 |
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Sorry to hear that Frank. Not sure. I have a lot of contest hours on my amp and been rock solid knock on wood. I made over 1500qso’s on 15m past weekend with full 1kw out and usually run the ssb contests this way rock solid amp. However, I have had a capacitor go on mine with 200w out scenario similar to yours. Hard to say what it is without further diagnosis, but I will say with solid state amps that are fairly new, things can happen. I have an Anthem solid state home theatre amp that lost its front channel for no real reason other than it being new. It went during the first year of use, luckily was under warranty. Sometimes things just happen for no good reason. My belief is, use the new piece of electronics as much as you can while under warranty as an old rule of thumb is, if something is on the edge, it will go within the first few hundred hours of use. If it doesn’t go, then chances are it is a solid unit with all the “bugs” worked out and anything that was weak would have shown its true colours. That’s the layman’s non technical theory I have for whatever it’s worth. The good thing is, your shipping cost to the repair depot won’t cost as much as I had to deal with. (Being a Canadian and our dollar is weak at this moment). So you have that going for you. And since my repairs on both units, many hours on them since and hoping I’m past that break-in sort to speak with many more hours of rock solid performance. Hopefully it won’t be anything more serious. Keep us in the loop as to how it goes for you. I have had nothing but good things to say about Palstar and their group of people. They have been good to me. Best of luck. 73 Barry VE6UM On Mon, Oct 28, 2024 at 18:41 Frank W4TG via <fstein=[email protected]> wrote:
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开云体育Frank, 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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You say the HF Auto in front of the LA-1K. I run my HF Auto after the LA-1K. Sent with Smoke Signals from my camp fire. ? On Sun, Nov 3, 2024, 5:27 PM Craig Williams KA6RWL via <ka6rwl=[email protected]> wrote:
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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:
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I probably didn’t phase that right, this is how my equipment is set up. Radio Ant 1 to LA-1K > LA-1K Ant 1 to HF-Auto > HF-Auto connected to 3 antennas? My setup is how it is described in the Palstar manual: “2) Connect PTT Cable (Customer Provided) from transceiver to the LA-1K PTT Connector.
This connection is required for the LA-1K and is located on the REAR PANEL of the amp.
3) Connect a PL-259 Patch cable (Customer provided) from your transceiver’s antenna output
connector to the LA-1K’s RF INPUT coax connector.
4) Connect antenna (OR HF Auto) to the LA-1K’s Antenna 1 jack. Resonant antennas may be fed
directly from the antenna outputs if desired.
If using the HF-Auto (or another tuner), connect a second PL-259 Patch cable from the LA-1K’s Antenna 1 jack, to the tuner’s RF Input. The output of the tuner used is then connected to your antenna. “ Craig KA6RWL On Sun, Nov 3, 2024 at 5:54?PM k6wez via <kj6wez=[email protected]> wrote:
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I had an issue with the LA-1K where they had put too much heat sync compound under the finals, and when it heated up, it oozed out from under the transistor and arc flashed.? Luckily, I was on SSB and instantly stopped transmitting.? ?Removed the cover, and used a toothbrush to remove the excess heat sink compound, and fired it up for a 10 minute RTTY keydown, and it operated flawlessly for the test, and has in the two years since I had that issue.? ?Might want to check to make sure no heat sync compound is visible coming out from under the finals.
N5GGG
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Billy Parkinson