[Elecraft] Fault on KPA500 after 300w

[Alan Lambert]

I recently acquired a KP500/KAT500 for use with my Kx3/KXPa100. I know
the person I bought it from well and I am 99.9999% sure it is not an
issue with the amp or tuner.

 I was making some notes (a chart) for input to output power levels,
mostly just to ‘get to know’ the amp a little better.  At the time of
these issues, I was on 80m SSB and the Kat500 was showing 1:1 / 1.2:1.

The output watts  I have listed below are not ‘actuals’ I’m just
recalling them from memory so may be off a few watts.

I set the Kx3 to 8w and called “test test test 1 2 3  kn4bbc” I showed
~80w out with a 1:1 to 1.2:1 SWR.. GREAT!

Moved up to 9w and got 100w out… same SWR – more Great!

10w I got 175w same SWR – sill looking good!

11w I got  250w same SWR – Awesome!

Now this is where the problem comes in.

I set to 12w… As I starting calling my “test test test 1 2 3…”  At
first things looked great..I was getting 300w same SWR  but then
suddenly I get high SWR followed by  “High Refl” on the KPA5, fault
light comes on and I get warning tones.

So I tuned the KAT500 again and tried the whole thing again with the
same results.

Gear wise:

KX3/Kxpa100 with ATU disabled > KPA500/KAT500.

Ant1 on Kat500  >  1ft LMR400 jumper >  1:1 ATU Current Balun  > 225
feet of 450 ladder line > a ½ wave 80m center fed, inverted V  dipole.
Center point is ~90 feet off ground.

The Balun is a Balun Designs Model 1161

The shack is on 2nd floor in middle of the house and has no exterior walls.

The ladder line starts in the shack, there is about 2 feet  of in the
shack then enters my attic space thru and opening in a sheetrock wall.
Inside the attic space there is a long slow, wide loop about 50 feet
long. I was careful to keep it away from metals and it does not cross
itself however some of it  is lying on top of plywood. From there its
exits the house in the ridge cap at the tip top of the roof at about
(40 feet off ground)  The ladder line then hangs from a rope that runs
from the eve to the tree line about 175 feet away which is where the
center point of the dipole is.  In short 175 feet outside 50 feet
inside.


Ideas of what my problem might be?