[Elecraft] advice please

[KC6CNN]

I have been trouble shooting a problem that arose in the shack. 
The problem is that while in a qso my kat500 will start rising in SWR's. 
I decided to check the system out by hooking a dummy load to the coax
connector at the tower. 
The K Line performs as expected. SWR are 1:1 and it sits there during key
down never changing. 
So I hooked up the antenna again and tried it. After the tune the SWR is
1:1. If I sit there with it keyed for a little bit, I start seeing the swr
rise and it faults. 
Something is breaking down. 
I have a Ultimax End feed no tuner needed antenna. It is basically a 9:1 UN
UN connected to a 133' of wire. The shielded end is on the UN UN is
connected to a 8 foot cooper ground rod. 

So my question is other than the 9:1 UN UN inside the little box breaking
down because of heat, is there any other thing I should check? I wanted to
check everything before calling UltiMax tomorrow. 
I think I have ruled out coax, and station but running it in dummy load. I
can run qrp all day long on the antenna with 5 watts, even at 100 the swr's
do not start rising. But I only run my amp at about 400 watts max on power
and it starts rising with that amount of power. 

Any suggestions or opinions are welcomed. 
Thank you
Gerald
 



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KC6CNN - Gerald
K1 # 0014
K3 # 6294
KX3 # 757
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