>
>I have also heard that dc on the filaments causes migration.
/ True with filament type [directly heated] cathodes, but not true with
heater type.
> It makes
>sense. However, practicall experience leads me to question whether the
>conclusion may not be relevant.
>
>My old GE Progress Line 2 meter rig was all tubes and it ran on dc.
/ My guess is that the tubes used heater type cathodes and not filament
type cathodes.
>It was
>in my car for years without replacing any tubes and without reversing
>polarity of the battery. Finally replaced the Prog Line by little devices
>that do not have filaments.
>
>I have run the tube vfo's in many of my rigs on dc filaments. Left the tube
>on for years with no failure of the filament.
>
>I have never had a failure of a power tube filament - except for one I
>dropped off the table and one that failed while in the hands of United
>Parcel Service. So, even if the dc causes premature failure of the
>filament, it may still outlast the operator or other failure.
>
>After all this, would I occassionally change polarity if dc was applied to a
>filament of an expensive power tube - probably.
>
cheers, Colin
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
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