I've built lots of different hi-fi gear over the years, but I've never built a class A power amplifier. I hadn't planned to until I came into possession of a pair of 1.1C/W crocodile teeth heatsinks that I thought, why not. It wouldn't have been the biggest job in the world to start from scratch but I decided to keep it simple and buy a internet kit for JL Hood's original Class A amplifier and modify it.
This was a design published at the end of the 1960's and is really just a back to first principles design using 4-5 transistors and a simple power supply. Of course the reason that these amplifiers aren't common is that they typically run at 20% efficiency so my 10W+10W amplifier actually uses around 100W of power continuously, and consequently gets hot, so the big heatsinks have something to do, and even then they run at about 60C.