Good news from Elecraft. They have increased the KX3 power output on 80-20. With their Beta MCU 2.38 / DSP 1.37, 01-03-2016 you can now get up to 15 watts output. Measured on my Byrd, I am getting between 16 and 18 watts output depending on the band. This is more than enough to power a modified KPA 500 to over 500 watts on those bands! Check out the KPA 500 modification page on this site (drop down selections are in the picture block at the top of this page).