The best example of this is the old "all American five" tube radio where they had tube filaments ranging from 12v to 50v and they all used 150MA but the effective resistance was selected so they could take 120v line power in series to light them all up.
(The octal set was 12SA7 converter, 12SK7 IF amp, 12SQ7 audio detector and signal amp, 50L6 audio power, and 35Z5 rectifier).
Later they came out with a 100MA "miniature" string but it worked the same.
That was what we had in your basic table radio until the late 60s early 70s when transistors took over. I still believe the tube radios were better at pulling in distant stations and sounded better but that is just old guy nostalgia.
