Here is a rear view of my Heathkit AR-3. You can see the hefty power transformer, 4 of the 5 tubes, tuning capacitor, dial string, pilot lamps, IF transformers, tuning coils, and speaker. Underneath the chassis is a maze of soldered wires that connect everything together. Note the warm glow from the tubes and pilot lamps.
My early electronics education was based on electron tube theory. In my early Air Force days, I repaired autopilot systems for F-101 and F-102 fighter aircraft, both of which used tubes. Later on, I maintained many tube-based radios including (old) UHF and VHF transmitters and receivers. I most enjoyed working on the Collins 208U-10, 10 Kilowatt auto-tuned HF transmitters. Today, everything I worked on is no longer in the inventory – “antiques”.