A couple of points and concerns expressed here are thus:
The Centurion when turned on, applies filament voltage and HV at the same
time. The opportunity to run the tubes with filament only does not exist in
the Centurion. Same true for most other amplifiers using direct heated
cathodes and thus instant on tubes. For those tubes which have a heater and
a cathode, that's another chapter in the book and a time delay and warm up
is required for proper tube operation and life.
As to running tubes outside of the amp, {for what ever reason} as long as
the filament pins and associated glass seals stay within their temperature
rating (base seal rating is 200 degrees C max.) then there is no problem.
However, exceed the temperature rating and the solder may melt out of the
pins and / or the seals expand such that outside air contaminates the
envelope. To that end, I have witnessed a fan failure on a commercial amp
using 3-500's. The solder melted out of one of the filament pins and thus
the tube ceased to function. These tubes operate at 5.0 volts, +/- 0.25
volts, nominal, at some 14.6 amps. Fortunately I was able to re-solder the
pin and save the tube. In order to prevent future failures, an airflow
switch was installed in the exhaust to activate the filament transformer
when adequate airflow existed. My CCA broadcast transmitter {4 x 4-400's}
has the same feature.
73
Bob, K4TAX
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