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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 ...
The parallel tuned circuit (C1-L) is connected between the screen grid and the cathode (through battery B1). The negative resistance of the screen grid cancels the positive resistance of the tuned circuit, causing oscillations. As in the dynatron oscillator the control grid can be used to adjust the negative resistance.
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]
A triode has three electrodes: the anode, cathode, and one grid, and so on. 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 ...
EF8 – Selektode, a remote-cutoff pentode with a beam-forming extra grid between control and screen grids, intended to reduce screen current and hence anode/screen grid distribution noise (technically a hexode), EF38 with a side-contact 8 base; EF9 – Pentode, EF22/7B7, EF39/6K7 or EF41/6CJ5 with a side-contact 8 base with control grid on top cap
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]
Conductivity of a thyratron remains low as long as the control grid is negative relative to the cathode because the grid repels electrons emitted by the cathode. Space charge limited electron current flows from the cathode through the control grid toward the anode if the grid is made positive relative to the cathode.
Basic self-oscillating circuit. Beam deflection tubes, sometimes known as sheet beam tubes, are vacuum tubes with an electron gun, a beam intensity control grid, a screen grid, sometimes a suppressor grid, and two electrostatic deflection electrodes on opposite sides of the electron beam that can direct the rectangular beam to either of two anodes in the same plane.