Nice bikes. IF makes an excellent steel frame. I don't own any steel frame bikes at the moment - mostly high-end carbon road race bikes and a couple gravel bikes. I've got to pare down my stable at some point.
Here's a decent book to start with. It introduces basic electronics concepts before going into vacuum tube amp info.
Vacuum Tube Amplifier Basics by EJ Jurich
A more advanced book that covers vacuum tube amps in much greater detail is
Valve Amplifiers by Morgan Jones
This one requires a bit more basic electronics understanding though, and has a lot more detail than you will probably ever need. It's also several times the price of the first one I listed.