I have a transmitter that uses a 100 watt MRF-317 amplifier board. I noticed when it is operating at max power into a 50-ohm dummy load the RF output power drops off slightly after a couple minutes (to around 90 watts). When I measured the temperature using an infrared laser thermometer it was hovering around 150 degrees Fahrenheit (which equates to around 66 degrees Centigrade). My question is, is this too hot for an RF power transistor or is this temperature acceptable? The datasheet does not give a rating for max operating temperature. The amplifier is mounted on a heat-sink and the case it is mounted in has cooling fans.
The transmitter did seem okay running at this temperature for a few hours, but maybe it is thermal throttling (since the slight power drop).