[Amps] Pre-heating of tubes

[Peter Chadwick]

Rich said:
>If gettering really works as claimed  
hereabouts, why do large tubes depend on built-in ion pumps?<
Because for many of them, they don't get hot enough except around the filament. The filament can be a long way physically from the bits that emit the gas. A YH1045 TWT is a case in point, being about 30 inches long. It had a collector that ran at 18kV and 2.5 Amps, with 22kV and 1 amp on the helix. Being water cooled, only the heater end got really hot. The vac ion pump current was measured to actuate trips if it got too high.
73
Peter G3RZP