Electrode electrode. In a vacuum tube or a semiconductor having polarity (diodes, electrolytic capacitors) the anode is the positive (+) electrode and the cathode the negative (−). The electrons enter the device through the cathode and exit the device through the anode. Many devices have other electrodes to control operation, e.g., base, gate, control grid. In a three-electrode cell, a counter electrode, also called an auxiliary electrode, is used only to make a connection to the electrolyte so that a current can be applied to the working electrode. The counter electrode is usually made of an inert material, such as a
Plate electrode tube envelope and is cooled by radiation cooling, forced air or water. A problem in early vacuum tubes was "secondary emission"; electrons striking the plate could knock other electrons out of the metal surface. In some tubes such as tetrodes these "secondary electrons" could be absorbed by other electrods such as grids in the tube, resulting in a current out of the plate. This current could cause the plate circuit to have negative resistance, which could cause unwanted parasitic oscillations. To prevent this most plates in modern tubes are given a chemical coating which reduces secondary emission. Plate electrode A