Control grid Control grid The control grid is an electrode used in amplifying thermionic valves (vacuum tubes) such as the triode, tetrode and pentode, used to control the flow of electrons from the cathode to the 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 amplifying vacuum tube, the Audion (triode). In a valve, the hot cathode emits
Valve transmitters circuit. This circuit design has been used at 1296 MHz using disk seal triode valves such as the 2C39A. The grid is kept at ground, the drive is applied to the cathode through a capacitor. The heater supply must be isolated with great care from the cathode as unlike the other designs the cathode is not connected to RF ground. The cathode may be at the same DC potential as the grid if a valve such as the 811A (zero bias triode) is used, otherwise the cathode must be positive with respect to the grid to provide proper bias. This