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Re: OLD Tubes/Coils - filament question



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<< 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
  >>

Ed, All,

I have an HF300, and an EE300 triode vacuum tube (they look something like a
204 A).  Does anyone know if the filaments are thoriated tungsten?  The
filaments do not glow as brightly as other tubes such as 845's, etc.  I've
been told that they are thoriated tunsten, but the mfr. keep the filament
temp low.  I did discover (the hard way), that when these particular tubes
arc internally, they quickly lose emission.  Thanks in advance.

Tube mysteries,

John Freau







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