[Elecraft] KPA500 - Not Going To Full Power

[Don Wilhelm]

What happens if you use CW or a constant carrier.
Data modes throw the proverbial "wrench" into the works because there 
are so many, each with different characteristics.

Test with CW mode or a constant keydown (for a reasonable time - 30 
seconds or so) and see what happens.

If that condition happens with CW, then take the KAT500 out of the 
situation and operate the KPA500 into a dummy load.  Is it OK up to 500 
watts or more?  If OK, the KPA500 and your Flex is OK - focus on the KAT500.

Did you train the KAT500 to your antenna(s) while in AUTO mode, then 
switch the KAT500 to MAN mode?  If not try that.  It may be that at 
higher power, something in your antenna system is breaking down and the 
KAT500 (if left in AUTO) is trying to tune, which will break the keying 
line to the KPA500 if cabled correctly until the tune is completed.

My bet is on something is changing in your antenna system at higher 
power - look for arc points, end insulators, and possible loose 
connectors (PL-259 connectors should be just a bit more than finger 
tight, use pliers lightly).

If you are using a balun, is it arcing inside?  Did it gather a bit of 
moisture inside?  Are you exceeding its saturation point - a good 
possibility if you are using a balun to transition to a parallel 
feedline as might be the case with a commercial G5RV antenna.

The very best test is to establish what happens into a dummy load.

73,
Don W3FPR

73,
Don W3FPR

On 1/6/2019 4:36 PM, fyredude901 wrote:
> Received my KPA 500 / KAT500 combo for Christmas.  Got them hooked up and
> they were working like a charm and have for several days.   I am mostly on
> digital and will typically run around 300 watts out.  I am using a Flexradio
> 6500 and my output on it is around 22 watts.  Today, I pushed the output up
> to around 27 (which drove the amp over 310 watts).  At that time, the power
> meter started surging (sorry, best way that I can think to describe it).  It
> amp never went above 310, but it was like the power was being cycled on and
> off to the unit.  The output was pulsing high and low.  When I backed the
> Flex back down to 22 watts, and the output of the amp was 300 or less, this
> issue stopped.  I am assuming it is the protection system for the amp.
> Still, I would like to know what the possible cause of this likely is so
> that I can troubleshoot and fix it.  Any advice that can be provided would
> be greatly appreciated!!