"He reached into the exposed chassis of an ancient television and withdrew a silver-black vacuum tube"
Public Domain6N23P - Credit: Settembrini

A vacuum tube is a sealed glass tube with a cathode, filaments and an anode plate. It is used for amplification of a weak current, rectification of alternating current to direct current, and generation of oscillating frequency for guitar amps, radio and radar. Vacuum tubes function better when they are hot.

ENIAC the world's first general purpose computer ran on vacuum tubes.