Thanks Gordon and Gary. The 2N2219a drivers get hot enough to burn a finger so I added their own heat sinks, but that¡¯s only a fraction of the total energy so each final may be dissipating over 30 watts. An FT8 alternating transmit-receive duty cycle may be an appreciable fraction of that. I¡¯ll try that. By the way this was on 80 meters, and as I said with the Developers Edition. I also know that one of the my failures was near the end of a FT8 transmission so it was during a transmit/receive transition. Another FT8 PA failure was after less than a second of transmission so temperature alone could not have been the problem.
73,
Jack, N6LN
John Terrell, N6LN