Editing Control grid (section)

{{Short description|Electrode used to control electron flow within a vacuum tube}}
[[File:Triode schematic labeled.svg|thumb|[[Schematic symbol]] used in [[circuit diagram]]s for a vacuum tube, showing control grid]]

The '''control grid''' is an [[electrode]] used in amplifying [[vacuum tube|thermionic valves]] (vacuum tubes) such as the [[triode]], [[tetrode]] and [[pentode]], used to control the flow of electrons from the [[cathode]] to the [[plate electrode|anode]] (plate) electrode.  The control grid usually consists of a cylindrical screen or helix of fine wire surrounding the cathode, and is surrounded in turn by the anode.  The control grid was invented by [[Lee De Forest]], who in 1906  added a grid to the [[Fleming valve]] ([[thermionic diode]]) to create the first [[amplifier|amplifying]] vacuum tube, the [[Audion]] ([[triode]]).