Figure 1-32.Noise in a tetrode circuit.
For these reasons tetrodes are only used in very specialized applications of electronics.
How does the addition of a screen grid in a tetrode reduce interelectrode capacitance?
What undesirable effect does the screen grid in a tetrode create?
The problem of secondary emission associated with the screen grid of a tetrode has been reduced
byyou guessed it, the addition of another grid.
This third grid, called a SUPPRESSOR GRID, is placed between the screen grid and the plate. The
suppressor grid is normally connected either internally or externally to the cathode and bears the same
charge as the cathode. This is shown in figure 1-33. Because of its negative potential (relative to
individual electrons), any electrons that are emitted by the plate, through secondary emission, are repelled
back toward the plate.
Figure 1-33.Basic pentode circuit.