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thumb|right|300 px|Two horizontal rows of arc-shaped dynodes in a photomultiplier tube. A dynode is an electrode in a vacuum tube that serves as an incident charge multiplier through secondary emission. The first tube to incorporate a dynode was the dynatron, an ancestor of the magnetron, which used a single dynode. Photomultiplier and video camera tubes generally include a series of dynodes, each at a more positive electrical potential than its predecessor. Secondary emission occurs at the surface of each dynode. Such an arrangement is able to amplify the tiny current emitted by the photocath