[Elecraft] K3S QST Article

[Joe Subich, W4TV]

On 10/17/2016 8:48 PM, Guy Olinger K2AV wrote:
>
> What would be a practical way to actually introduce such a change? Lay out
> all the specifics involved. Let's see your critical path item by item plan.
> It's cheep and easy to just blurt out "they oughta go to 28 volts."

Provide an *optional* 28V PA that would drop into the existing space.
If heat and/or maximum gain are an issue, it does not need to be
specified for 200 W output ... 150/160 is good enough.

As to power supplies, Yaesu had a dual voltage switching supply for
the FT-1000MP MK V for many years.  A "KPA4" could certainly have its
own 28V connection to avoid changes to the K3/K3S (the present design
keeps 13.8V on the PA all the time).

Once one has a 28V option, the K3/K3S controller can be modified to
limit power from the 12V KPA3A/KPA3B to 80 watts max which should
further decrease IMD by keeping the FETs out of compression.  Most
published power transistor/FET data sheets show a sweet spot for
IMD at around 60 - 80% of the CW ratings.

73,

    ... Joe, W4TV