> >Of course, we know that running voltages that are too high will kill
the
> >life expectancy of the tube, by why is running too little voltage bad
for the
> >tube, if it's developing full emmission at a lower voltage?
>
If the lower filament voltage does not affect the emission of the cathode at
peak plate current, it will not harm the tube. But even if the average
plate current seems normal, but the lower filament voltage limits the peak
even slightly, tube life will suffer.
The procedure with an AM transmitter is to modulate the transmitter to its
maximum positive peak capability, with full filament voltage. Then reduce
the filament voltage until you begin to notice a dropoff of the positive
peaks. Run the filament voltage back up just past the point where positive
peaks are fully restored. The point is to run the filament just above the
first indication that the cathode is being starved of emission.
Don K4KYV
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