If you have a K3S (or late K3, with the KPA3A type 100w amp). Please see the recent FW notes in the K3 Utility about setting the 6m Atn6 attenuator switch to prevent 6m oscillations. Also, what rev of KLPA3A and KPA3A are you at? There have been improvements. Keith WE6R, Elecraft K3 Tech.