[Neo6425]

My neighbor is a kindly older fellow who has always been quick to lend a helping with whatever projects I have going on and, best of all, he has every tool imaginable and is quick to lend it out to anyone in the neighborhood. He is also not shy about sharing his advice in all matters – including my restoration of my Philco 620. Since my workbench is in my garage, and I usually work with the garage door open, anyone walking by can clearly see what’s on my bench, including my neighbor. Now due to social distancing he didn’t step into the garage but he started a conversation that he used to be a HAM radio operator when he was younger and his father, who was in the Signal Corp during WWII, gave him his old Army manuals to read and that how he learned about electronics and radios. He said that I shouldn’t be content with swapping out parts, that I should actually learn the theory behind how the radio works. 
He said this as I was removing a 30-2079 cap  [Image: http://www.ispdi.com/Philco/images/30-2079.jpg] , because I said to him I know this is a capacitor but I am not really sure of its function in the circuit. The next morning on my doorstep there’s a manila envelope and inside is the “TM 11-242 War Department Technical Manual Radio Set SCR-300-A SCR1945”. The note attached says, “If you plan on working on radios, especially old ones, I want you to read this US Army Manual first.” (I found a PDF of a later edition of this online and I’ll share it here if anyone is interested in taking a look. - Radio Set SCR-300-A )

So here’s the reason I’m writing. I feel fairly confident I can switch out parts from my chassis and get this radio to work. Yet, I would really like to learn more about how a radio works and better understand its electronics. My neighbor really made think about what it is I hope to accomplish by restoring my radio and I realized I don’t want to be just a “parts swapper”.
These past few weeks I have been exploring books on the topic and looking at Army manuals (thanks to my neighbor) that were used to teach soldiers basic electronics and I’m confused which path to take. So can anyone recommend the best way for me to learn radio repair on my own? I can’t afford to go back to school and I am hoping someone can recommend a way I can start this journey.