Mercury Vapor rectifier
http://www.radiomuseum.org/tubes/tube_872a.html
872A A Mercury Vapor Diode with a peak inverse voltage of 10Kv and peak anode current of 5 amperes. Average anode current, 1250mA, forward drop, 10 volts. Heater voltage, 5.0 at 6.25A. Base fits R.C.A. UT-541A Socket.
