u/Tiger_man_

posted because this community really likes rectifiers

inside this vacuum bulb is a directly heated double diode capable of rectifiying 500v at currents up to 60mA and up to 100mA on lower voltages

it was commonly used from 1934 to the end of the vacuum tube era

the voltage amd current shown is from the filament alone (nothing is connected), it was a bit tricky to get it running because it lost one of the filament pins. also technically its a light-emmiting diode. just mostly infrared