Bevalac injector final stage RE amplifier upgrades

The Bevalac injector final stage RF amplifier systems have been successfully upgraded to reduce energy consumption and operating costs. The energy savings realized at completion of the project was primarily obtained by eliminating the filament power required for operation of the hard tube modulator (HTM) system. The HTM system was used to key the plate voltage to two tubes, a TH-515 which provides 800 kW of RF output power and a TH-516 which provides 2.4 MW. The first phase required modifying the amplifier structure to remove the ground connection to the final amplifier grid while maintaining a low impedance path for the grid-anode and grid-cathode RF circulating currents. The second phase provided a fixed source of DC grid bias for the TH-515 and a pulsed grid bias source for the TH-516. The bias voltages appropriately interlock the DC plate voltage supply to the final amplifiers. Construction, design, and operating parameters are described.<>