An element of a vacuum tube (the anode) that accepts the flow of electrons from the cathode. When positive voltage is applied to the plate, the electrons within the tube (most of which are emitted by the cathode) are attracted to it – the amount of attraction being relative to the amount of positive charge applied to the plate. The plate can also be thought of as the “output” of the tube. The resulting signal (or voltage) present there is then passed on to the next device in the circuit.
Plate is also known as a type of artificial reverberation system. Back in the days before digital reverbs, recording engineers developed a number of methods of creating simulated acoustic spaces for recordings done in the studio (as opposed to concert halls and cathedrals). One of the most (and still very) popular systems was the plate reverb. (We’ll cover that in one of next week’s WFTD’s)