Elecraft K2

You can use the Hardrock-50+ with the K2 right out of the box, just connect the RF from the radio to the RF IN on the amp and detect COR mode on the amp. The amp will detect when the radio is transmitting and automatically switch to the correct band and start transmitting. Remember to keep the K2's power way down 1-2 watts.

Unfortunately, the K2 does not have a PTT out like most radios so if you want to operate PTT and have the amp switch bands when you change bands on the radio, you need to build an interface. Your radio must have the KIO2 board that has RS-232 connectivity. Below is the schematic of the interface and the connections to the KIO2 and the Hardrock-50+. When you build the interface and connect it you'll need to set the ACC Baud Rate to 4800 in the amp. You will have to turn on the radio first then turn on the amp because the amp sends the radio an AI command when it's booting. If the radio doesn't get the AI command, it won't send band data.