Bootleg Triode Vacuum Tube, circa 1923

Vacuum tubes appear in older radios, televisions, amplifiers, computers, and other electronic devices. Their function: to amplify and strengthen weak electronic signals. Typical tubes are sealed glass bulbs evacuated of gas, allowing electron flow to be influenced by an interior cathode, plate and grid. This is a "bootleg" tube--a cheaper alternative to DeForest Audion tubes, then monopolizing the market.