Last night, during light burn-in tests, the amplifier suddenly dropped gain.
No alarms, no nothing, but one of the MOSFETS was drawing a lot less current compared to the other, it was also operating in class C. It turns out that for some reason the gate2 on the failing MOSFET has broken down. DAMN!!!!!!!!
Digging in to the RF-deck
Failed MOSFET
Gate2 to source breakdown. 70 ohm dc-path between source and gate2 do not make any sense.