> Did you give the new tube a reasonable amount of time to "cook in ?"
For directly-heated cathode tubes used in broadcast transmitters, both Eimac
and the transmitter manufacturers generally recommend the following
procedure for placing a new Final tube into service:
1) Wash the new tube to remove any residual dust, dirt, oil and grime;
2) Rinse tube thoroughly in water;
3) Dry tube to remove all traces of water -- use compressed air if
necessary;
4) Clean and inspect the transmitter's tube socket;
5) Install tube and run filament voltage at 100% rated F voltage - use True
RMS voltmeter;
6) Apply plate voltage after a 3-5 minute warm-up cycle;
7) Tune transmitter and gradually increase drive to full power while
optimizing drive and output circuits;
8) Run at 100% F voltage for 500 hours;
9) After 500 hours, gradually reduce F voltage to the point where emission
(and consequently power) just begins to fall;
10) Measure F voltage at regular intervals;
10) Maintain a record of the above.
-Paul, W9AC
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