Rca and Zenith were 2 major brands of US t.v.s . TVs used vacuum tubes until the early 70s when they were replaced with transistors and ics . Early tvs had lots of tubes later ones had fewer tubes . I can comment more if asked on vacuum tubes . Some call them valves .
https://en.wikipedia.org/wiki/Vacuum_tube
This is John Denver singing high flight . I am still looking for some of the old tv sine off videos .
https://www.youtube.com/watch?v=1xNGgWNRUf8