Just curious on my part, with my K3S I ran FT-8 for about an hour making
1 contact after another on 20M. Power output was set to100 watts
although the external powers meters (2 different ones) show a bit more
than 100 watts. Started with PA temperature at 36°C and never saw it
go over 50°C. The fan is on automatic so it normally is off but does
step up in speed as the PA temp climbs. Still with that duty cycle 50°C,
I believe is quite safe as 84°C is the cut-off limit for the PA.
I mounted my KXPA100 in my truck under the back seat for mobile
operation. Ford made a nice lockable compartment accessed by tilting
up the seat and the amp just fits but the seat bottom rests on the
top of the heat sink fins. As we were traveling thru hot weather, I
was concerned there would be enough air flow so I attached two 1-1/2
inch square fans on the connector end of the amp to force some air
thru the fins. I used the spare power-pole connector for 12v power
which runs when voltage is applied to the amp. I also cut several
3/4 inch holes in the sheet metal seat base for air flow to/from the truck cab.
It survived running 80w on 6m-SSB so guess its enough (I did not monitor temp).
I have the amp connected to the KX3 for remote control (nice when mobile).
Adding a fan to solid state amps is good insurance (esp. when running digital).