Brian,
If you let the KPA100 cool for a sufficient time, the heatsink should be
at the ambient temperature. How long is long enough will vary from
temperature to temperature. I suggest that power off for 30 minutes or
more will give good results.
You need to measure the temperature directly below the PA transistors -
which is difficult to do. The best solution is to let everything to
acclimate to ambient and set CAL TMP at whatever the ambient temperature
may be (in degC). How much do you trust your infrared thermometer is
the real question. 2 degrees may not make a big difference. Light on
the heatsink can create an apparent difference in temperature. The
heatsink can absorb light and make it warmer than the ambient temperature.
IMHO, 2 degrees C will not make that much difference in when the fan
comes on to either low or high speed.
In other words, go with whatever is comfortable with you. The CAL TPA
parameter only defines when the fan will be activated. Some KPA100
owners who want to see the fan come on sooner than normal will set the
CAL TPA menu parameter to a greater temperature than ambient. In other
words, setting CAL TPA to 30 degC when the ambient is 23 degC will turn
on the fan earlier than the normal heatsink temperature.
Bottom line -- it is an individual decision (but don't go to extremes).
73,
Don W3FPR
On 2/9/2016 8:22 PM, Brian - N5BCN via Elecraft wrote:
I may be wandering into nit-picky land, but I noticed using a hand held
infrared thermometer that the heat sink of the KPA100 is usually about 2
degrees warmer than ambient air temperature (when the unit has been sitting
idle for several hours). For example, the heat sink will measure about 26
degs C and the room air temp is about 24 degs C.
For the purposes of the CAL tPA, which temp should I go with? Or does it
really even matter?
Secondarily, when I discovered all this, I also found out that I had never
calibrated CAL tPA! I was wondering why the fan NEVER seemed to kick on!
So, I've been using the KPA100 for YEARS without the benefit of the fan. I
hope I didn't cause any long term degradation of the unit.
Incidentally, it always seemed to get out at the proper power, but boy would
it get hot!
73,
Brian N5BCN
--
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http://elecraft.365791.n2.nabble.com/K2-KPA100-Temp-Cal-Room-temp-or-radio-temp-tp7613845.html
Sent from the Elecraft mailing list archive at Nabble.com.
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