Xicom XTU-400K, Operation And Installation Manual

Page: 108 / 189

MNC-0400-001 48 of 54 Revision G
Operation, Rack and Digital HPAs
Standby Mode
In this mode, there are no faults and the TWT is ready for high
voltage to be applied.
Heater Standby Mode
The purpose of heater standby is to extend the life to the tube
when the high voltage is off.
The temperature of the cathode is the primary determinant of
tube life. The emission of electrons from the surface of a
cathode has a cooling effect on the cathode surface. Therefore,
when high voltage is turned off the cathode surface temperature
increases shortening the life of the tube. This is a special
concern when the amplifier is in standby mode for extended
periods of time; that is, when it is the standby unit.
Heater Standby reduces the heater voltage when high voltage is
off. The temperature of the cathode is reduced to a temperature
slightly below the normal operating temperature. When high
voltage is turned on, it overrides the heater standby command
and returns the heater voltage to its normal setting. When the
high voltage is turned off again the heater voltage is reduced.
When the amplifier has been online and then placed in the
heater standby mode, there is no time delay when high voltage
is turned on.
High Voltage ON Mode
When high voltage ON is selected, an internal relay is latched
ON. This enables High Voltage ON.
Note
When the Beam On switch is turned ON high voltage will be applied to
the TWT any time the FTD cycle is completed and there are no faults
present. Interruption of prime power for any reason will force the power
supply into the FTD Mode.
When high voltage is ON (applied to the TWT) RF input signals
are amplified. If high voltage ON is selected before the Filament
Time Delay cycle is complete, high voltage will remain OFF until
the FTD cycle is complete.