[Elecraft] Question Regarding KPA-500 on 117 VAC
My test data show that, of all the bands my KPA500 will work on, 20 m has the lowest PA efficiency. My test data also show that the KPA500 efficiency, and therefore PA dissipation, is very sensitive to load matching. So, if you are on 20 m and with a poor match, your 60 V PSU will have a high current demand and may sag below 60 V. A spot check shows my line input voltage is 123.4 V and my "60V" supply is 81.7 V while receiving. Line voltage is lower when the neighborhood transformer is loaded by heating or cooling systems. A TX at 14.074 into a dummy load gave 505 W out with PA 61.8 V and 14.3 A giving a PA dissipation of 378 W and an efficiency of 57%. It took 35.6 W drive to achieve this output. A TX a few minutes later with same drive power setting gave 527 W out, PA Diss of 369 W, and PA efficiency 58 %. LP-100A shows drive power still 35.6 W. One of the problems with making measurements like this is that you have to decide which data to believe. The controller that gives my real time KPA500 data is using KPA500 reported current , voltage, and output power. I think my LPA-100A is more accurate for power measurements but its data are recorded by a different logger. I'm not motivated to merge the two data sets right now. Andy, k3wyc __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Question Regarding KPA-500 on 117 VAC
Hello Bernie I have a KPA500 and run it on solar power with a 120 volt AC inverter. I have never seen the issues that you are recounting. The first thing to do is check the voltage going in to the KPA500 with a good voltmeter. The next thing is something in the KPA500 ac input circuit that might be mis behaving. Put an AC voltmeter on the transformer primary and monitor that. Those points should be pretty stiff. Bad circuit breakers could be a problem. You might also have a bad circuit connection in an AC box or even an outlet. I had such a situation and it caused poor regulation and a slight terrible smell as the plastic was baking. I ran my KPA500 only on 28 and 50 MHz, but had no problem getting gobs of output on each band. VSWR was under 1.5:1. As I recaqll drive was 19-20 watts and output would easily hit 500 or even more with the 117 vac input. My inverter is a sine wave type by Xantrex, fed with a 500 AH AGM battery. Lately I got a smaller 150AH lithium battery and the amp still works just fine with 117 volts. Dave K1WHS On 3/7/2022 1:54 AM, Bernie and Cheryl wrote: Dear Folks: I have been using my KPA-500 (driven by the K3s and transmitting through the KAT-500) for about five years now. I have long noticed that, when first using it, or if it has sat idling for a while, the amp's supply voltage will be low on transmit and won't go higher until the amp has been used for a couple of minutes. This becomes critical in some instances since, particularly on 20 meters, the supply voltage will be below 60 volts on transmit for a while and won't increase unless I reduce the drive power by a few watts. I do always reduce the drive power to make sure the supply voltage stays at 60 or above (I have been told that this keeps the amp operating within normal limits and the math indicates that this will make sure the current doesn't get too high). Once I've been transmitting for a minute or two (I almost always use CW), the amp appears to warm up and I can bump up the drive power a few watts for higher power output and still keep the supply voltage at 60 or above. For the record, the amp is plugged into a normal wall outlet supplying 117VAC (or whatever the house is supplying at that moment), though it is not using any of the same outlets that the rest of the shack uses. I realize it is highly likely that all the outlets in the shack are on the same breaker, but my prior tube-type amp used to dim the lights a bit when I keyed it and had it plugged into the same outlets as the rest of the shack. That stopped happening once I switched the outlet for the tube amp and now I'm using that same outlet solely for the KPA-500. My first question is whether any of you with a KPA-500 experience the same thing, i.e., supply voltage is a little low at the beginning and increases as the amp warms up? My second question concerns the fact that, even with the amp warmed up, I can seldom (if ever) hit 500 watts out on 20 meters, though I can do it easily on all the other bands (I recognize that this is likely caused by my antenna's characteristics on that band, though SWR doesn't exceed 1.7 at any frequency that I use, even without the tuner). I simply can't get the drive up high enough to get there, without the supply voltage dipping below 60. Usually, I can get between 350 to 425 watts out. Do you think this would be different if I had a 220 volt outlet installed in the shack? For the record, I recognize that the 100 watt or so decrease in power out doesn't make that much difference. I am asking because I wonder if it would be easier on the amp to run it off of a 220 volt outlet. As always, thanks for any help and advice. 73 de Bernie, KF0QS __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to k1...@metrocast.net __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Question Regarding KPA-500 on 117 VAC
As always, RTFM. The primary of the power transformer has three taps, intended to accommodate the wide range of AC power that each of us has, and the manual describes how to change those taps. It sounds like you need to change yours. As does Bill, K9HZ/J68HZ/six other DX calls (who I worked today on 10M in ARRL SSB DX), although he's in denial. The change involves choosing which of three colored wires is attached to a terminal strip, accessible by removing the top cover. RTFM, RTFM, RTFM. 73, Jim K9YC Jim: Not only did I RTFM, I built the amp in kit form. So, I did set the taps as you describe (if memory serves, I used the middle tap which gave me the proper setting according to the manual). Having resolved that, do you (or anyone else) have any other suggestions? 73 de Bernie, KF0QS __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
Re: [Elecraft] Question Regarding KPA-500 on 117 VAC
On 3/6/2022 10:54 PM, Bernie and Cheryl wrote: As always, thanks for any help and advice. As always, RTFM. The primary of the power transformer has three taps, intended to accommodate the wide range of AC power that each of us has, and the manual describes how to change those taps. It sounds like you need to change yours. As does Bill, K9HZ/J68HZ/six other DX calls (who I worked today on 10M in ARRL SSB DX), although he's in denial. The change involves choosing which of three colored wires is attached to a terminal strip, accessible by removing the top cover. RTFM, RTFM, RTFM. 73, Jim K9YC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
[Elecraft] Question Regarding KPA-500 on 117 VAC
Dear Folks: I have been using my KPA-500 (driven by the K3s and transmitting through the KAT-500) for about five years now. I have long noticed that, when first using it, or if it has sat idling for a while, the amp's supply voltage will be low on transmit and won't go higher until the amp has been used for a couple of minutes. This becomes critical in some instances since, particularly on 20 meters, the supply voltage will be below 60 volts on transmit for a while and won't increase unless I reduce the drive power by a few watts. I do always reduce the drive power to make sure the supply voltage stays at 60 or above (I have been told that this keeps the amp operating within normal limits and the math indicates that this will make sure the current doesn't get too high). Once I've been transmitting for a minute or two (I almost always use CW), the amp appears to warm up and I can bump up the drive power a few watts for higher power output and still keep the supply voltage at 60 or above. For the record, the amp is plugged into a normal wall outlet supplying 117VAC (or whatever the house is supplying at that moment), though it is not using any of the same outlets that the rest of the shack uses. I realize it is highly likely that all the outlets in the shack are on the same breaker, but my prior tube-type amp used to dim the lights a bit when I keyed it and had it plugged into the same outlets as the rest of the shack. That stopped happening once I switched the outlet for the tube amp and now I'm using that same outlet solely for the KPA-500. My first question is whether any of you with a KPA-500 experience the same thing, i.e., supply voltage is a little low at the beginning and increases as the amp warms up? My second question concerns the fact that, even with the amp warmed up, I can seldom (if ever) hit 500 watts out on 20 meters, though I can do it easily on all the other bands (I recognize that this is likely caused by my antenna's characteristics on that band, though SWR doesn't exceed 1.7 at any frequency that I use, even without the tuner). I simply can't get the drive up high enough to get there, without the supply voltage dipping below 60. Usually, I can get between 350 to 425 watts out. Do you think this would be different if I had a 220 volt outlet installed in the shack? For the record, I recognize that the 100 watt or so decrease in power out doesn't make that much difference. I am asking because I wonder if it would be easier on the amp to run it off of a 220 volt outlet. As always, thanks for any help and advice. 73 de Bernie, KF0QS __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
