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.


   ... Joe, W4TV

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