How hot is too hot?

Burch Akin

Just got the 6300 setup for digital modes today.  I worked a PSK station for about 10 minutes and noticed DDUil was registering 57 degrees C after a long transmit.  Is that normal?  My radio seems to sit around 40 degrees C in standby.  The radio didn't feel hot and I don't think the fan sped up.    Seems to run hotter than my 5000.  I just want to make sure I'm not hurting anything.  The temp was still in the green mode/background on DDUtil.

Steve - M3SXA

Don't know if this will be of any help for you...
Fans

Burch Akin

So I guess the fan doesn't kick on until 70C.  I guess I'm OK then.  I had one long winded PSK contact last night and the temp got to 62C but as soon as I unkeyed, the radio cools down quickly.  Guess that's normal.

Steve-N5AC

The two chassis fans which pull air across the PA heatsink will switch from low speed to high speed at 70C.  They will return to low speed at 55C.  This temperature is measured on the flange of the transistors and is not exact, but it is close.  The absolute maximum for the transistor is spec'ed at 175C for the "channel" which I suspect is the junction temp.  Graham is really the expert on PA transistors and could give better recommendations on what you should be comfortable running the part at, but I wouldn't be concerned about running them at 100C.  As you may have noticed, the fans and the heat sink are very good at removing heat from the cabinet and the temperature will drop rapidly when you unkey the radio. 

Bill WW5M

"I've seen a 100 degrees C when running full power FT8 on 6 and 10 meters - should I be concerned - it there a way to get more cooling - increase fan speed? Perhaps I should add a fan? I have been running PGXL with 5 watts drive to keep temperature down at approx 100 watts out. Don't think Ive ever seen PGXL over 70 deg C even while running RTTY contest at full power. I have concerns with longevity on 6600 when that hot! Been using SDR monitor to watch voltage drop and temperature on the 6600!

Mike-VA3MW

If it is too hot, the radio will start to fold back or shut down.

It will also depend on your ambient air temperature and we see more questions in the summer regarding a warm PA.

Running the PGXL at 100 watts might not give you the cleanest signal (I would need to do more homework on that). If you only want to run 100 watts, then dial that back to 80 watts which is less than 1db less RF being transmitted.

There seems to be this thought that running hot all the time might shorten the longevity of the device. I would love to see the actual science/math on that. I think it is a bit of an old wives tale left over from the Tube era.

YMMV