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see electron tubeelectron tube,
device consisting of a sealed enclosure in which electrons flow between electrodes separated either by a vacuum (in a vacuum tube) or by an ionized gas at low pressure (in a gas tube).
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a five-electrode electron tube consisting of a cathode, a control grid, a screen grid, a suppressor grid, and an anode. Low-power pentodes (up to several watts of power) are used chiefly as receiving tubes; high-power pentodes (several tens of watts or more) are used as oscillator tubes. The pentode was developed from another electron tube—the tetrode. The introduction of the suppressor grid near the anode eliminated the distortion of the tetrode’s anode characteristics that was caused by the dynatron effect—secondary electron emission from the anode or the screen grid. Through the use of pentodes, electrical oscillations with frequencies of up to several tens of megahertz are generated and their voltage and power are amplified by factors of up to several hundred times.


A five-electrode electron tube containing an anode, a cathode, a control electrode, and two additional electrodes that are ordinarily grids.


A type of vacuum tube used in high-end audio preamplifiers, ham radios and a variety of other electronic circuits. A pentode is like a tetrode with the addition of a "suppressor grid" between the screen grid and the plate. Typically biased at or near the cathode voltage, the suppressor grid provides additional isolation between the control grid and plate. See tetrode, triode and diode.

The Pentode Uses Three Grids
In a pentode, the addition of a screen grid and suppressor grid between the control grid and plate controls feedback and oscillation.