I've experienced silent operation and operation with hum (what I'd call more of a transformer buzz).
My mains are between 248V and 249V so I used the yellow tap per the table in the manual (the 231V to 250V tap). The HV then idles around 72.4V and on full power transmit, HV went down around 57V. In this configuration, full power transmit is silent, no buzz. But per the errata for the manual for best linearity HV should be 60V or higher during full power transmit. So, I switched to the red tap (the 211 to 230V tap). HV now idles at 80.0V and goes no lower than 64V on full power transmit. Linearity achieved, but in this configuration I get a noticeable transformer buzz. I opened the top and made sure everything was secure - no change. So, by changing the transformer voltage selection tap I've had both silent and with-buzz operation. At first I was concerned the buzz was an indication I was tapped too low for the high mains voltage but the 80V to 64V range is well within spec so I assumed I was ok to leave it that way. Still seems odd that I have to tap down when I'm so close to the max input voltage. Dan AE9K -- View this message in context: http://elecraft.365791.n2.nabble.com/KPA-500-HUM-from-PA-and-not-from-Speaker-tp6647675p6660348.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ 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
