KX2 heatsink

[hhoyt]

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
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[Tim McDonough N9PUZ]

On 6/18/2017 8:48 PM, Howard Hoyt wrote:

> 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.

Does anyone know at what serial number KX2 the PA changes were made?

Tim N9PUZ

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[wayne burdick]

This change was made very early on in production and is not significant in terms of thermal performance.

Wayne
N6KR


> On Jun 19, 2017, at 8:02 AM, Tim McDonough N9PUZ <[hidden email]> wrote:
>
> On 6/18/2017 8:48 PM, Howard Hoyt wrote:
>
>> 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.
>
> Does anyone know at what serial number KX2 the PA changes were made?
>
> Tim N9PUZ



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