c. The input cavity signal is a low-amplitude signal from an external circuit. The second cavity signal is
the resonant frequency of the cavity energized by the electrons that have partially bunched in the cavity gap. This
is a slightly higher amplitude signal than the input cavity signal, and the energy that is delivered to this cavity
from the electron stream is negligible. Bunching that occurs in the output cavity delivers a large amount of
energy to it. The energy is taken from the output cavity by a coupling loop and is delivered to a matched load.
d. The higher electron velocities in a klystron require more cavities to control bunching. Some klystrons
may have six or seven cavities and use very high electron velocities.
The multicavity klystron is commonly used as a power amplifier but may also be adapted as a frequency
multiplier. If it is used as a frequency multiplier, the output cavity is smaller and resonant to a harmonic of the
input cavity signal. The efficiency of the klystron used as a frequency multiplier is considerably lower than when
it is used as a power amplifier.
Section V. KLYSTRON POWER AMPLIFIER
The klystron power amplifier receives its driving power from an exciter. The cavity-type tube is designed to
boost the low-power angle-modulated driving signal to a high-power angle-modulated signal. The klystron
amplifiers used for this application will contain from three to five cavities, depending on the power output and
type of equipment in use. The klystron may or may not have an associated heat exchanger.
a. The electron gun shown in figure 15 is the source of the electron beam. The gun has a filament, a
cathode, focusing electrodes, and a modulating anode. The beam is a fast-moving stream of electrons emitted
from the cathode. The electrons are held grouped together by the focusing electrode, which is operated at cathode
potential or negative with respect to the cathode. This charge applied to the focusing electrode causes the
electrons to converge on the axis of the tube.
b. The entire beam flows through a hole in the modulating anode to the first section of the drift tube. In
this application, the modulating anode is grounded through a 10-kilohm resistor. This feature prevents damage to
the tube if arcing occurs within the electron gun section. When arcing occurs, a large current flows to the anode.
This current flowing through the 10-kilohm resistor develops a negative bias which cuts off the beam current until
a. When the beam enters the input cavity, the number of electrons is constant; however, their velocity is
changed by the signal to be amplified.