TM 11-6625-3053-14
the left of R12 (Item C ) to be exactly -450 volts with respect to the -325 volt line (Item E ), which is the common point
for this circuit. Error amplifier AR1 (Item F is balanced when the voltage across CR8 (Item if G is equal to the output
of the feedback network (item H ).
Two additional low voltage DC power supplies are required to operate the klystron oscillator. Both these supplies float at
-325 volts. The filament power supply is operated from the main power transformer T1, terminals 5 and 6 (Item A. On
the A2A2 assembly, the rectifier and filter assembly CR1-4, C1, C2 converts the AC to DC (Item B ). Regulator AR1
regulates this voltage to 6.0 VDC (Item C). The grid voltage supply is turned on and off by the optical coupler U1 (Item D
) and shunt transistor Q1 (Item E. This circuit is controlled by the MODULATION switch S1 on the front panel (Item F
When shunt transistor Q1 is off, the grid voltage is positive with respect to the -325 volt circuit common (Item G). It is
regulated by AR2 on the A2A1 board (Item H). Adjustment of the grid voltage to cause the correct beam current to flow
in the klystron tube is provided by A4A1 R1 in the A4 tuning head assembly (item I ). When the shunt transistor Q1 is on
(Item E), the grid voltage is negative with respect to the -325 volt circuit common (Item G). This voltage is supplied by
rectifier and filter CR12, 13 and C6 (Item J on the A2A1 assembly. The positive voltage o operate the grid voltage
regulator (Item H is supplied by rectifier and filter CR11, 14 and C5 (Item K ).
Klystron oscillator V1, provides the rf power output. The klystron is mounted at one end of the cavity. The outer cylinder
makes contact with the first grid, and the inner conductor makes contact with the second resonator grid. The resonant
circuit is completed at the other end of the cavity by a movable non- conducting shorting plunger. The position of the
shorting plunger (Item A) determines the resonant frequency of the cavity.
The frequency of oscillation of the klystron oscillator is determined by the resonant frequency of the cavity and the
magnitude of the negative repeller voltage. For a given setting of the cavity, there is an optimum repeller voltage that
will cause the bunched electrons to return to the resonator at the proper time. The repeller voltage, therefore, cannot
remain the same over the frequency range of the oscillator. In order to produce the oscillation over the frequency range
of the oscillator, a tracking arrangement is used to vary the DC voltage on the repeller. This voltage is maintained at the
optimum value for maximum ampli- tude of oscillation at a given plunger setting
At the low end of the frequency range, the repeller voltage is at its lowest negative value and the klystron operates in its
1-3/4 mode. As the frequency increases, the repeller voltage increases in the negative direction until at 1.7 GHz, the
repeller voltage becomes excessive and it is more practical to change the repeller voltage. The repeller voltage is
lowered so that the klystron operates in its 2-3/4 mode. In this higher mode, the bunched electrons require a greater
number of cycles before returning to the resonator grids.
The DC voltage applied to the repeller is controlled by tracking potentiometer A4R1 (Item E). The movement of the arm
of A4R1 is mechanically ganged with the movement of the tuning plunger in the klystron cavity. Repeller mode switch
A4S1 (Item F) is operated by a cam driven by the tuning drive and changes the voltage applied to A4R1. Adjustment
potentiometers are provided in the tracking circuit to compensate for variation in klystron repeller voltage characteristics.
The maximum voltage across tracking voltage potentiometer A4R1 is 425 volts since it is connected from the -325 volt
beam supply to the -750 volt repeller supply. The FREQ VERNIER control A4R2 (Item G) provides a small variation in
the repeller voltage, which produces a vernier frequency variation of at least 1.5 MHz.
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