Thanks to all who provided input re my 3-1000Z filament voltage question.
I did manage to increase the filament voltage at the tube pins of the BTI
LK-2000 by .5 volt by using the boost winding on the filament xformer and then
using a dropping resistor to get about 7.25 at the tube with full load. The
effect on power output was a gain of 50 watts to 1300 indicated. This is about
60.5% efficiency so raising the voltagefrom 7.08 to 7.25 did not do much.
The real effect comes, of course, from boosting plate voltage ideally to 3500
volts or more. I am working to reduce the voltage drop under load which ranges
from 2825 to 2910 volts @ 750 ma.
Clearly, from the inputs, there is a great advantage in tube life by having
some way to adjust the filament voltage in your amplifier.
Homebuilders can easily do this with a variable resistor in the primary of the
filament transformer. It would be great if the commercial manufacturers would
include some way of measuring the filament voltage so a person would know
whether they are cooking their expensive tubes to death. On the other hand,
maybe they don't want youy to know!
73, Dennis W0JX
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