I am in the a similar situation. I completed a motor mechanics apprenticeship back in the early 80s then promptly got an office job in our public library service. Now I have retired, I decided to spend some time building stereo gear in the hope I will learn something new. So far I have only built some kits and I still need to learn how different components in the circuit can affect the sound. My first big build was an FU50 tube amp kit that works quite well. I have since fallen into the rabbit hole of the John Linsley Hood (JLH) 1969 Class-A solid state amp after finding literally dozens of different kits and completed amps on Aliexpress. Unlike many Ali solid state amp kits, the JLH kits are based on a design published in Wireless World in 1969 specifically for amateur builders to build so there are no copyright issues with these.