For those going what the fuck is bird on about, the circuit is a power supply. Normally you'd use a diode tube here, a device that conducts one way only so you can get DC. It chops off half of the AC line voltage, and you stick a capacitor on it to get something that looks like DC. This circuit took a military RF triode, a tube used as an amplifier, and wired it to be a diode. Why? Probably because the triode was cheap after the war and they had millions of them.