Last modified on 11 February 2014, at 16:16  History of
Computers/Early Innovations  The Vacuum TubeEdit   The vacuum
tube, also known as a valve because it controls electron flow
the way a faucet valve controls the amount of water flow, was
originally developed to amplify and demodulate ("detect") radio
signals. Later on, it also amplified audio for sound
reinforcement. In World War 2, radar (and sonar) used tubes for
more-sophisticated processes, many of which were described at
the time as "pulse circuits". Once the War ended, digital
computers using tubes were built, however the sheer number of
logic functions meant that very large numbers of tubes were
needed. Heater power, on the order of a few watts per tube, had
to be provided, and the heat removed. Large cooling systems were
needed to carry away the heat. While tubes designed for simpler
systems such as radios, as well as stereo and musical instrument
amplifiers could last for decades, for digital computers, tubes
were not adequately reliable. Later,