Editing Rectifier (section)

=== Diode vacuum tube (valve) ===
{{See also|List of vacuum tubes}}
[[File:FRec var.jpg|thumb|Vacuum tube diodes]]

The [[thermionic]] [[vacuum tube]] [[diode]], originally called the [[Fleming valve]], was invented by John Ambrose Fleming in 1904 as a detector for radio waves in radio receivers, and evolved into a general rectifier.  It consisted of an evacuated glass bulb with a [[electrical filament|filament]] heated by a separate current, and a metal plate [[anode]].  The filament emitted [[electron]]s by [[thermionic emission]] (the Edison effect), discovered by [[Thomas Edison]] in 1884, and a positive voltage on the plate caused a current of electrons through the tube from filament to plate.  Since only the filament produced electrons, the tube would only conduct current in one direction, allowing the tube to rectify an alternating current.

Thermionic diode rectifiers were widely used in power supplies in vacuum tube consumer electronic products, such as phonographs, radios, and televisions, for example the [[All American Five]] radio receiver, to provide the high DC plate voltage needed by other vacuum tubes.  "Full-wave" versions with two separate plates were popular because they could be used with a center-tapped transformer to make a full-wave rectifier.  Vacuum tube rectifiers were made for very high voltages, such as the high voltage power supply for the CRT of [[television]] receivers, and the '''kenotron''' used for power supply in [[X-ray]] equipment.  However, compared to modern semiconductor diodes, vacuum tube rectifiers have high internal resistance due to [[space charge]] and therefore high voltage drops, causing high power dissipation and low efficiency.  They are rarely able to handle currents exceeding 250&nbsp;mA owing to the limits of plate power dissipation, and cannot be used for low voltage applications, such as battery chargers. Another limitation of the vacuum tube rectifier is that the heater power supply often requires special arrangements to insulate it from the high voltages of the rectifier circuit.