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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 ...
1 – Tetrode with a space charge grid (the 2nd grid is the control grid) 2 – Tetrode with a screen grid (the 1st grid is the control grid) 3 – Power pentode; 4 – Binode, a diode/triode or diode/tetrode; 5 – Remote-cutoff RF tetrode; 6 – Signal pentode; 7 – Remote-cutoff RF pentode; 8 – Sharp-cutoff hexode frequency changer; 9 ...
The control grid of the variable-mu pentode is constructed so as to result in a given incremental change of control grid voltage having less effect on change of anode current as the control grid voltage increases negatively relative to the cathode. [7] The control grid often has the form of a helix of varying pitch. [8]
This additional control grid modulates the current that flows between cathode and anode. The relationship between current flow and plate and grid voltage is often represented as a series of "characteristic curves" on a diagram. Depending on the other components in the circuit this modulated current flow can be used to provide current or voltage ...
The first grid, known as the control grid, (and sometimes other grids) transforms the diode into a voltage-controlled device: the voltage applied to the control grid affects the current between the cathode and the plate. When held negative with respect to the cathode, the control grid creates an electric field that repels electrons emitted by ...
The mutual conductance tester tests the tube dynamically by applying bias and an AC voltage to the control grid, and measuring the current obtained on the plate, while maintaining the correct DC voltages on the plate and screen grid. This setup measures the transconductance of the tube, indicated in micromhos. [3]
Alternatively, the cathode may short to the control grid, possibly causing similar effects, or, the control grid and screen grid (G2) [225] can short causing a very dark image or no image at all. The cathode may be surrounded by a shield to prevent sputtering. [226] [227]
Between the screen grid and the cathode is the control grid. The beam confining plates have been removed. The getter pan, getter pan supports and the upper mica disc have been removed. The elliptical helix of the screen grid surrounds the control grid. The screen grid support rods are on the left and right outside of the control grid support rods.