Pentodes: The Fifth Element for Enhanced Tube Performance
To counter the attraction of secondary electrons toward the screen, designers introduced a fifth wire element: the suppressor. Tubes featuring this component became known as pentodes.

The suppressor is typically a wire coil or mesh positioned between the screen grid and the anode (plate). It is usually connected to ground potential. In certain pentode designs, the suppressor is internally linked to the cathode to reduce the number of pins that must penetrate the envelope.

By repelling secondary electrons back to the plate, the suppressor creates a space‑charge effect similar to that in beam power tubes. This increases plate current, lowers screen current, improves gain, and can allow operation at higher plate voltages.
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