A popular transmitter back in the day was based on the Hartley oscillator (PDF link). Using only a single triode tube and a tuned circuit with coils wound from 1/4″ copper tubing, Hartley ...

Figure 1 shows a stable, 18-MHz oscillator with automatically leveled output amplitude ... Reed, DG, editor, “A JFET Hartley VFO,” ARRL Handbook for Radio Communications, 82nd Edition, American Radio ...