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Re: OLD Tubes/Coils - filament power (fwd)



Edward V. Phillips wrote:
> 
> Re:
> "As far as I
> know,
> all directly heated cathode tubes are thoriated tungsten, the filament
> itself is
> the cathode."
>         Negative.  Lots of rectifier tubes (5R4G, for instance)
> have oxide coated cathose (glow a dull red at rated voltage) and
> some very high power and/or very high voltage tubes still use
> pure tungsten, which is very rugged and requires very much
> higher operating temperatures than thoriated tungsten.
> Ed