[Elecraft] KPA500 - Not Going To Full Power

[Jack Brindle]

Did you hear any clicks from the KPA when this was happening? Did the FAULT LED blink?

It sounds like the amplifier is experiencing an issue that requires it to start to protect itself.
It does this by switching in a 3db pad, which cuts the output power in half. If it sees no further
issues while the pad is engaged, it will switch out the pad. If the issue recurs, so will switching
in the pad. If the KPA is sensing a problem in its output, such as high reflected power, it will
protect itself exactly as you describe. This very well may be due to a problem in the antenna
system involving arcing or other issues as others have described. look for burn marks at the 
antenna (most likely inside the connectors). We build our stations for low power operation, then 
when we upgrade with an amplifier, we experience just these sort of issues with the antenna
system. It could be connectors, adapters or the antenna itself. In your case it sounds like you
may have a matching system at the antenna that is overheating due to high power and thus
changing the load presented to the ATU and amplifier. The KPA will see these sort of changes
faster than the KAT and thus it will react faster.

The advice is good - check the antenna system to make sure it is not being overloaded.

73!
Jack Brindle, W6FB
Elecraft Engineering


> On Jan 6, 2019, at 1:36 PM, fyredude901 <sdonnell2 at comcast.net> 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!!
> 
> 73
> KD9EGK
> 
> 
> 
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