Elenos T30000, Руководство пользователя

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Hand Book T30000 -
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ADJUSTMENT OF THE FILAMENT VOLTAGE
The filament of the thermionic tube installed in the T30000 is powered by an AC stabilised circuit with a
precision of better than 1.5%. The filament voltage has a very important influence on the operational
life of the thermionic tube, that is, the lower the voltage, the longer the life of the tube. However, if the
thermionic tube is working with the filament underheated (voltage too low for the working cathode
voltage) the tube life will be reduced by cathode pollution. There therefore exists an ideal filament
voltage for the power at which the thermionic tube is operating. Adjustments of the filament voltage
should be performed with the equipment operating at the desired RF power level; for this reason
personnel making these adjustments must be fully prepared technically in order to carry out this task
with the equipment open.
The sequence of operations to follow is:
1) Prepare the unit so that it is operating at the desired power level with the front panel open to allow
adjustment of the low-power trimmer potentiometer located on card E20127.x (reference P6).
2) Rotate the trimmer clockwise for 3 or 4 turns (this will reduce the voltage) keeping the front panel
voltage reading under observation. Continue with small steps until it is possible to detect the smallest
variation of anode current (I.A.) or RF power output (P.W.R.).
3) Rotate the trimmer very carefully in the opposite direction until the filament voltage is just beyond the
point at which the variations of the performance of the tube begin.
The final value of filament voltage obtained will be unique and will vary from tube to tube. The voltage
should not be reduced within the first 200 hours of operation of the thermionic tube; adjustments after
4000 hours are of no use. It is necessary to correct the filament voltage with a slight increase every
three months, in order to compensate for consumption of the thermionic tube's cathode. For this
operation it is necessary to first return to the nominal value and then repeat the three steps described
above. WARNING! Ensure that the safety precautions described at the beginning of the chapter are
complied whenever maintenance is carried out on the equipment.