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 photocathode, typically by a factor of one million.
Naming
The dynode takes its name from the dynatron. Albert Hull did not use the term dynode in his 1918 paper on the dynatron, but used the term extensively in his 1922 paper.