The complaint was something to the effect that libraries don't have many books on radio repairs and tubes. That may be true depending on the library but basic engineering knowledge is applicable to any repair or restoration. Ohms law works every time as do the mathematical formulas for impedance. Want to know the impedance of a capacitor at a given frequency? How about an inductor? Or the resonant frequency of a coil and capacitor? How to figure the impedance of an output transformer? It's all there in the books.
Now how about something radio related, like how a superhetrodyne radio works? That too. The principle design of converter, IF, det, af, and audio out is the same for transistor or tube radios. Once you learn the principles you'll be able to apply them to any set. You'll also find information on TRF and regenerative sets. Just look it up.
Now, if you can't get to a real library or find one that has the technical data you want, All this data is available on the internet if you take the time to look for it and then take more time to study and learn it.
Yes some of us did indeed learn some tricks from guys at the local TV shop, but that tended to be more "how" than "why". The real learning always came from books. I found my first "electrical" books in the school library when I was in grade school. Then I looked in all the school and public libraries I came across. I subscribed to electronics hobby magazines. I had almost no tube theory in college, what there was concerned modeling, much the same as the "h" parameters for transistors.
The key idea is reading, studying, and learning. That takes some work. Yes work, but it won't seem like work when it leads to being able to fix anything that comes across your bench.
Now as to being mean to the young folks, the truth is that if they are too lazy to learn then they'll never be any good at this hobby or much of anything else.
A monkey can be taught to change parts until the set works. Hey, if you just change all of them it has to work.
One reason that tube radios still enjoy a relatively high number of devotees is that such a huge number of them were produced in the pre-WW2 decade. The thousands of contemporary electronics hobbyists who value these items enough to conserve and preserve them ensure that they will be around as collector objects for many, many decades to come, even though the first generation of people who bought and used these radios new has long since passed away.
My son, age 29, has a 1933 Airline radio in his dining room. There is not a single AM station worth listening to in his area. Naturally, he uses the iPod, or get this ... he streams radio into the Airline from his cellphone.
The younger generation appreciates the workmanship and quality of the sound from the big speakers, granted it is mono. No they are not likely to need to learn the theory behind what makes it all work. If it's broke, Dad will fix it. Integrated circuits can't be fixed with a soldering iron.
I have a houseful of restored antique radios. My son from Seattle area visited us in SF bay area last Sept. He, both his daughters and his son in law went nuts over the radios. I am giving them seven of them. They will be here in July to truck them up to Seattle area. The interest is still there like steam engines.
CH