[Amps] Alpha 78 in Digital Modes

[Allen Brier N5XZ]

I have an Alpha 78 and just started using it for digital modes (RTTY & PSK-31). I also have a supplemental fan, sold by Alpha, mounted on the back of the '78 providing additional air flow. The cabinet is sealed as best as I can to maximize that airflow. Now I have a couple of questions:
1. What is the maximum power output the '78 should run in these modes (essentially 100% duty cycle)?
2. What is the maximum air temperature I should allow coming out of the top of the cabinet, above the tubes? (I intend to put a small temperature probe above one of the tubes to turn the supplemental fan on and off as required as it is louder than I would like. That way I don't have to listen to it when the amp is idling and when I make a quick QSO, but will come on with a resonable temperature rise. The side benefit is that I can see when the tubes are running too hot, also.)

Allen Brier N5XZ / KL5DX