[Elecraft] KPA-500 Loud Hum

Noted that my new amp is making a fairly loud humming noise when not under load, and a much louder hum when under full power. New thing, have not heard this before, power output still good, but noise is really concerning. Removed top, nothing loose, should I try retorting the xformer hardware

Re: [Elecraft] KPA-500 Loud Hum

Check the other case screws, particularly the ones holding the left side panel (the panel with the feet closest to the transformer). Unlike the K3, the KPA500 uses steel panels for greater strength to support the transformer. They, of course, want to vibrate from the magnetic field leakage around