a. Figure 58 shows a HYDROGEN THYRATRON used as a switch in a high-
level modulator. In Part A, the hydrogen thyratron is nonconducting as the
PFN charges to the source voltage.
At the instant the PFN reaches its
maximum charge, a positive trigger from the timer unit comes in on the grid
of the THYRATRON (Part B of Figure 58).
To start conduction, the trigger
must be at least 150 volts.
The positive trigger causes grid current to
flow, which produces electrons and ions outside the cathode-shield
structure.
Some of these electrons and ions reach the baffles just below
the grid:
When the number of electrons and ions in this area is large
enough, the anode produces ionization and causes the tube to conduct
heavily.
Figure 58. The HYDROGEN THYRATRON is an Electronic Switch.
b. The HYDROGEN THYRATRON now acts as a closed switch in Part B of
Figure 58.
The PFN discharges quickly through the conducting tube and
produces a rectangular pulse across the load.
As the PFN discharges, the
plate voltage of the THYRATRON falls rapidly until the tube deionizes. Then
the tube becomes an open switch again.
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