Figure 5-14. Klystron Failures and Probable Results Normal protection for rf tube dc arcing is generally provided by an electronic crowbar circuit. This circuit effectively diverts energy from the load within a few microseconds of an arc. As usually employed, an electronic crowbar requires manual resetting for resumption of normal operation. In systems such as MPTS employing a large number of tubes, this is an unacceptable procedure. Raytheon has performed experimental testing on a recycling crowbar (Reference 5-2) intended to provide automatic resetting of crowbar faults. A concept for the dc-rf conversion device and the crowbar unit is given by Figure 5-15. An increase in current above a preset reference is detected by the voltage increase across the energy diverting resistors. The logic and trigger generator circuits then trigger a vacuum spark gap TVG-1. TVG-1 fires and effectively short circuits the load, removing voltage from the faulted tube and allowing for the arc to recover. The short circuit of TVG1 allows LI and Cl to form a resonant loop, conducting on one-half cycle through TVG-1 and on the alternate half cycle through CR-1. TVG-1 recovers during the conduction of CR-1. Full voltage is reapplied to the load after one resonant cycle of LI and Cl. L2 provides isolation from the power source during this time.
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