Definition
A single-anode, mercury-pool electron tube used as a controlled high-current rectifier. A starting electrode (the ignitor) dipped into the pool of liquid mercury creates an arc when pulsed, which then conducts heavy current from the anode to the mercury cathode for the remainder of the AC half-cycle.
Plain English
An ignitron is an old type of heavy-duty electrical switch that uses liquid mercury inside a sealed tube. A small spark starts an arc in the mercury, and that arc lets a large amount of electricity flow through in one direction. It was used where very large currents had to be turned on and off quickly.
Context Anchor
Seen in older aircraft maintenance and electrical power discussions, especially where high-current rectifiers or older ground power equipment are described.
Derivation
The name combines 'ignite' (to start a fire or arc) with the '-tron' suffix used for electron tubes (as in 'magnetron' or 'klystron'). The term reflects the tube's defining feature: an ignitor electrode that fires the arc each cycle.
Why Pilots Care
Ignitrons are largely obsolete in modern aviation, but a maintenance technician working on legacy equipment or studying for written exams may still encounter the term in older schematics and references.
Intuition Check
Do not read “ignitron” as an aircraft ignition component. It is an electrical power device that is triggered into operation; it is not a spark plug, magneto, or ignition switch.
Example Sentence 1
The vintage ground power unit used an ignitron to rectify high-current AC into DC for battery charging.
Example Sentence 2
Older aircraft sometimes used an ignitron to handle heavy electrical loads from radios and instruments.