This is normal and is due to the small low voltage transformer and
rectifiers that provide power to the front panel microprocessor. turning
off the rear switch will turn everything off, including this transformer.
Eric
elecraft.com
On 6/11/2013 10:13 AM, Stan AE7UT wrote:
I have a kit-built KPA500 that has the same issue.
It's well grounded and all the bolts are tight.
The humm is barely noticeable when off but definitely there.
73
Stan AE7UT
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