Look at supply current and see whether the current increase with time? I have heard that some PA suffer from overheating IF trap. Ignacy, NO9E -- View this message in context: http://elecraft.365791.n2.nabble.com/K3-Problem-during-transmission-on-SSB-tp5636428p5640417.html Sent from the [K3] mailing list archive at Nabble.com.