Also see cathode ray tube ( CRT ), the specialized kind of
vacuum tube that is in most desktop display monitors. A vacuum
tube (also called a VT, electron tube or, in the UK, a valve )
is a device sometimes used to amplify electronic signals. In
most applications, the vacuum tube is obsolete, having been
replaced decades ago by the bipolar transistor and, more
recently, by the field-effect transistor . However, tubes are
still used in some high-power amplifiers, especially at
microwave radio frequencies and in some hi-fi audio systems.
Tubes operate at higher voltages than transistors. A typical
transistorized amplifier needs 6 to 12 volts to function; an
equivalent tube type amplifier needs 200 to 400 volts. At the
highest power levels, some tube circuits have power supplies
delivering several kilovolts. Vacuum tubes are making a comeback
among audiophiles who insist that tubes deliver better audio
quality than transistors. These old-fashioned components are
more electrically rugged than their solid-state co