[Elecraft] Re: K2 fan turns on high with CW QSO 22 watts

[Wayne Burdick]

Andrew Moore wrote:
> 
> In a CW QSO tonight at about 22 watts my K2's fan came on twice at high
> speed and the heat sink was getting warmer that I'd expect for 22 W....

Andrew, 

As we mentioned in the manual, the KPA100's final transistors are biased and
matched for best performance at 100 watts. This is typical of nearly all such
amplifiers, with the result is that current drain is not proportional to power
output. At 22 watts supply current may be only 50% less than it is at 100 watts
(this is a rough approximation--I haven't measured it at exactly this level).
So, the heatsink will certainly get warm and the fan may turn on.

You said "Cal tPA is set to 32 deg. C." Did you mean that the ambient temp was
32 deg. C when you performed the tPA calibration step, or that when you noticed
the heatsink was warm, the value shown in CAL tPA was 32 degrees C? Either way,
the fan is likely to be doing the right thing if you calibrated it based on the
room temperature at the time. The fan will shut off within 2-4 minutes of the
tPA value dropping below 37 deg. C. (Transmitting again may shut the fan off
sooner. Keying the rig causes tPA to be checked again, possibly before the
temperature check timer times out.)

73,
Wayne
N6KR