[Elecraft] KX2 heatsink

[Howard Hoyt]

Hi Linas,

There are many variables which come into play when quantifying the 
performance of a thermal solution.  First off, the PA efficiency is 
different on different bands, accounting for the differing amount of 
heat rejected.  As we state in the testing data, we do tests based on 
fully convective cooling with the rig in a thermal chimney to eliminate 
drafts.  In normal use with even slight breezes and starting at 24°C the 
performance of the Kx22 is better than that listed, as we have 
experienced using the rig portable ourselves. The starting ambient 
temperature is a major factor in the performance of any heatsink.  
Thermal flux is proportional to the temperature difference between the 
source and sink, and if the sink is the same temperature as the source, 
no heat will flow. Conversely with a large difference thermal flux is 
enhanced.

Here is the raw data we developed during testing with an early s/n KX2, 
3 trials averaged, initial key-down time from 24°C to 60°C thermal 
power-reduction, 1st column stock, 2nd w/prototype Kx22 (in seconds):

10M: 105 / 225
15M: 110 / 240
20M: 145 / 360
40M: 120 / 290
80M: 150 / 370

The newer Elecraft revision with the silicone electrical isolators and 
other PA differences will not show quite as good thermal performance as 
the original design where the PA FETs were mounted directly to the 
heatsink or right end panel.  We have not yet tested the new KX2 
revision to quantify the difference.  We have however had very positive 
reports from owners of newer rigs regarding the performance of the Kx22, 
both emailed to us and reported on the Facebook KX2 page if you wish to 
read them...

Please keep in touch with us as you test your Kx22,

Howie - WA4PSC
www.proaudioeng.com