For most of us, vacuum tubes haven’t appeared in any of our schematics or BOMs in — well, ever. Once mass-manufacturing made reliable transistors cheap enough for hobbyists, vacuum tubes ...

The major drawback to designing around vacuum tubes, if you can find them at all, is often driving them with the large voltages they often require to heat them to the proper temperatures.

The telephone company had problems with vacuum tubes, too, and hoped to find something ... but knowledge about how they worked was scant, and manufacturing semiconductors was difficult.