Mercury-arc valve
![Mercury rectifier on display in the Beromünster AM transmitter in Switzerland, before being decommissioned](/Images/godic/202501/26/Quecksilberdampfgleichrichter_in_Betrieb4631.JPG")
![One of the first mercury arc bulbs built by Cooper Hewitt](/Images/godic/202501/26/Mercury_arc_rectifier_bulb4631.jpg")
![Glass-bulb mercury-arc rectifier from the 1940s](/Images/godic/202501/26/Mercury_Arc_Rectifier4631.jpg")
![A glass-envelope mercury-arc rectifier valve](/Images/godic/202501/26/MercuryArcRectifier.svg4631.png")
A mercury-arc valve or mercury-vapor rectifier or (UK) mercury-arc rectifier is a type of electrical rectifier used for converting high-voltage or high-current alternating current (AC) into direct current (DC). It is a type of cold cathode gas-filled tube, but is unusual in that the cathode, instead of being solid, is made from a pool of liquid mercury and is therefore self-restoring. As a result, mercury-arc valves were much more rugged and long-lasting, and could carry much higher currents than most other types of gas discharge tube.