When in doubt ask the manufacturer. Transmitting tube filaments come in
thoriated tungsten and oxide coated; trying to compare all against a panel
lamp is rather ridiculous.
I can see the benefit of regulated DC on receivers and audio amps however.
Ive gone that route with many "boatanchors" that Ive rebuilt and use
regularly.
Carl
KM1H
----- Original Message -----
From: "k7fm" <k7fm@teleport.com>
To: <erniaba@netvision.net.il>; <amps@contesting.com>
Sent: Wednesday, February 13, 2008 8:34 AM
Subject: Re: [Amps] filament supply D.C or A.C
>I remember reading the same test about the ac on filaments. I recall the
> test was run because the lamp manufacturer specified a long life bulb and
> an
> aircraft manufacturer installed them and found substantially less life in
> the aircraft than specified. The lamp manufacturer ran the test, and
> changed the long life specifications to ac.
>
> There are some examples of dc on filaments, however. Almost all of the WW
> II aircraft radio equipment ran on dc - and many are still running (often
> on
> ac, however). However, the war was relatively short while amateurs
> expect
> their tubes to last 30 or 40 years. Radios from the 20s all ran on
> batteries, and many of those tubes are still running.
>
> Some say that if you run the tube on dc, you should alternate the polarity
> of the filament every so often, to offset the migration problem.
>
> There are other things that may apply to the equation, however. DC is
> easier to regulate, and may be easier to ramp up for a controlled start.
> Also, the more you otherwise abuse the tube, the less important the
> filament
> is. For example, if you overdrive it, under-cool it or overload it, the
> filament source becomes less important - because the tube is less likely
> to
> fail because of filament failure and more likely to fail for other causes.
>
> 73, Colin K7FM
>
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