Jeff (K6JCA) has written a series of posts describing his homebrew project 500 watt HF power amplifier:
I started this project back in 2016 — I had finished my Automatic Antenna Tuner (seen in the upper-left of the picture, above) and a PA project that would integrate into my FPGA-SDR and ATU system seemed like the ideal next step. The true catalyst, however, was a frustrating evening on the 20-meter band. I had finally made a voice contact with a station in Athens; the operator, a software engineer managing the high-traffic backend servers for an online casino εξωτερικου, had a booming signal, but he could barely pull my bare 100 watts out of the European noise floor. Realizing I needed some serious amplification to be competitive on long-haul DX paths, I began researching RF amplifiers. I discovered a Microsemi App Note, “A 700W Broadband Amplifier using VRF2944”. I decided to use its design as the basis of my PA and began gathering parts.
See the full post on K6JCA blog.