For you who will be soon getting a KPA500 to add to your K3, don't forget to download the latest firmware for the K3: MCU 4.36, DSP, DSP2.73. Probably most have already routinely downloaded these .Among other things, these updates enable the individual band buttons on the KPA500 to set the band on the K3 and allows two sets of power per band on the K3:One for use of the K3 only["barefoot"] and the other for the amp on line. We certainly don't want to overdrive the KPA500.
Yes, I forgot, briefly, to do this download on my factory assembled serial nr 71 and could not do the control mentioned above.. All is fine now..this is my first amp[after 61 years a ham] If this is to be your first amp too, don't forget the power limitations on some bands, such as the 30 meter band. I really like this amp.As my antenna is just a "screwdriver", it can help me be heard.....
The K3 has a per-band/per-antenna DIGOUT1 line on the 15pin AUX connector. If you use the Elecraft 15-pin AUX cable, DIGOUT1 is tied to the KPA500 inhibit line. So, DIGOUT1=ON means AMP INHIBIT=ON.
For example, if you have a SteppIR (which can be resonant at 40m and up) on ANT1, you can set DIGOUT1=ON on ANT1 for all bands 30M and below, and it will never key the amp on the low bands for that antenna. If your have ANT2 connected to a 40M dipole, for example, you could set DIGOUT1=ON for ANT2 on all bands except for 40M.
Even if you have a high-power external ATU, you might still want to set DIGOUT1=ON for 60m and 30m, (though the US does allow up to 200W on 30m).