How did people get DC power from AC before semi-conductors? I’d honestly never thought about it before until Kevin sent me this:
There were a few options, motor-generators being one, but efficient options were limited. These valves act like a physical diode, that uses a pool of mercury (!?!) Look at this thing, its friggin crazy:
Paraphrased from Wikipedia: http://en.wikipedia.org/wiki/Mercury_arc_valve – Current enters the pool of mercury, which boils off. Thus the large evacuated glass tube containing mercury vapor, which condenses the mercury back into the pool. When an arc forms, mercury emits electron freely form the surface of the pool. Ionization of the vapor occurs along the path towards the carbon anode. The carbon anodes do not emit very many electrons, thus rectifying the power.
I’ve never heard of this before, even though this was apparently very commonly used technology prior to the 1960s. To me, it looks like a hollywood movie alien technology prop:)