When the machine is working, voltage of acceleration tube electron gun filament detected by console monitor panel is normal. In the normal treatment of the machine, people can observe from the current scope that the magnetron MAG CU is normal, voltage of acceleration tube electron gun filament detected by console monitor panel is higher than the normal value. It can be seen that problems would be in the accelerating tube or filament assembly. Open the rack enclosure, for checking accelerating tube filament assembly and the filament voltage. Find that a filament wire sealing off filament assembly, this may because of rosin joint. After welding, the machine still cannot beam, malfunction is still exist. And then check the filament assembly again, but filament lead still has the sealing-off phenomenon. Welding the lead again, observe it in the open state of the switch. Four minutes later, the lead again sealing off the assembly. After welding again, measuring the voltage of the both ends of filament is only 2.7V, and the voltage of the resistors R1, R2 are 5.5V respectively, but it should only 2.4V under normal circumstances. This shows that the voltage of the failure filament assembly R1, R2 is more than twice the normal voltage value. The current is proportional to voltage, so the filament current is also more than twice the normal situation. 
And what causes the filament current is too large? First, check the ground of filament (including lead). Measure the lead resistance to ground, it is 2.5 kΩ, but it should be infinite under the normal state. This indicates that the gun filament insulation is not good. It is ground fault that cause the filament current is too large.
Electron Gun filaments are made of selected high-quality material of tungsten, with the properties of excellent thermal conductivity, finely processed, and long duration. Unusual stranded tungsten wires are applied as evaporator (heating element) in the vacuum metalizing (evaporation) process to coat thin film on surface of mirrors, and various decoration, etc.
