Pentodes

Author: E.E. Kimberly

While some characteristics of a tetrode are superior to those of a triode, the unstable region is undesirable for most uses. This region may be made usable, however, by the addition of still another grid, called a suppressor grid, interposed between the screen grid and the plate.

Fig. 27-21. The Pentode Used as an Amplifier

The suppressor grid is connected directly to the cathode and is therefore at cathode potential. Being at cathode potential, the suppressor grid repels the electrons of secondary emission back to the plate and prevents loss of plate current at low plate voltages.

Fig. 27-22. Average Plate Characteristics of Type 6SJ7 Pentode

Furthermore, the suppressor shields the plate from the control grid and cathode, and gives an amplification factor even higher than that of the tetrode. Fig. 27-21 shows a pentode in a simple circuit; and Fig. 27-22 shows the characteristics of a 6SJ7 pentode.