[TenTec] Problem on 160 meters, Whats up?

[Jeff]

Let me lay out the question I installed a center feed  dipole it is 138 feet long. Feed with 450
ladder line. Using my Palstar AT1KP tuner which I have raved so much about it
tunes this antenna on 160 meters at 100 watts cw. Now turn on my AL-811H amp and
every thing (swr) Goes nuts !!!  I am
assuming the Balun in the tuner is acting up. But I am here begging for advice.
Or at least an explanation. I under stand the dipole is to short. But why is it
loading at 100 watts but not 600.

 

Also the amp works great on 160 in to a dummy load.. Jeff