This amplifier is a 500W or 700W design based on the Microsemi VRF2933 or VRF2944 MOSFET. We have an eval board that supports both devices.
This board is available in our store. It measures 10 X 15cm (4" X 6") and it is 1.6mm (0.063") thick with 2 oz copper and emersion gold plating for good heat dissipation and maximum conductivity.
Run it with a pair of VRF2933's at 60V for 5W in, 500W output or use a pair of VRF2944's at 65V for 10W in, 700W output.
December 8, 2019 - I built one of these up and made some component changes in the BOM (now Rev A1). I had to change the thermal bias adjustment and some of the input components to eek a bit more gain and stabilize the bias over temperature.
The AN1819 board is used in the Hardrock-500 and appendix B of the Hardrock-500 assembly manual has very detailed assembly instructions for the board. I have added Appendix B to the files below.