I wrote an article on fan noise including in amplifiers. See http://www.eham.net/articles/38328. Ignacy, NO9E -- View this message in context: http://elecraft.365791.n2.nabble.com/KPA-500-Running-hot-on-20m-tp7625577p7625633.html Sent from the Elecraft mailing list archive at Nabble.com.