When I first started using my KPA500 I found the hum/buzz during high power CW operation to be intolerable. Elecraft support sent me a paper on hum reduction, a longer transformer bolt, and additional rubber washers. I did not use any of this new hardware but now have acceptable hum/buzz during TX.
I learned that hum/buzz is strongly related to PA current. I first made a significant reduction in hum/buzz by changing the transformer tap from yellow to red. This gave a high voltage below warning level at my highest line voltage. A second significant decrease in hum/buzz was achieved by matching all antenna loads to better than 1.2:1 SWR. Although the KPA500 is specified to accept loads of 1.5:1 SWR, the PA efficiency is degraded and PA currents increase as the match become worse. For bands where I use my KAT500 tuner I have manually selected L and C to gives a match better than 1.05:1. Bottom line - if you don't like the KPA500 hum/buzz level consider changing the transformer tap and improving load matching. Neither of these factors is mentioned in "KPA500 Application Note - Hum Mitigation.pdf". I went from a hum/buzz level greater than fan speed 4 to less than fan speed 1. 73, 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
