Generally, traditional tube amplifier circuits are much more simple than modern solid-state designs. If a tube amp breaks, you are not just going to toss it. Most tube amplifier have schematics floating around for them on the internet so anyone who might be inclined can fix one. Additionally, some HiFi designs are fairly minimalist which makes them easier to understand. Swart amps are a good example of this.

I bought a busted JCM 800 combo for $20 when I was 18. I fixed it with a soldering iron, multimeter, a copy of the schematic from ampage.com, and Forrest Mims III electronics book from radioshack.