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You might think that a grid with a negative potential placed close to the plate would interfere with
the electron stream. However, this is not the case. Because the suppressor grid is negatively charged, it
will not draw grid current. Additionally, the wide spacing within the mesh of the suppressor and its
location between two positive elements of the tube ensures that the suppressor grid’s effect on the electron
stream will be minimum. Only the electrons emitted by secondary emission from the plate are affected by
the suppressor grid.
Because pentodes do not suffer from secondary emission, they have replaced the tetrode in most
applications.
Q32.
The suppressor grid is added to a tetrode to reduce what undesirable characteristic of tetrode
operation?
Q33.
On the diagram below, name the elements of the vacuum tube and their potentials relative to dc
ground.
SUMMARY
This chapter has introduced you to the four basic types of vacuum tubes. The following is a summary
of the main points of the chapter.
THERMIONIC EMISSION is caused when metallic substances are heated to high temperatures.
Electrons liberated by thermonic emission provide the conduction currents of vacuum tubes.
A DIODE VACUUM TUBE is composed of two elements: the cathode and the plate.
