I don't know about "modern" tubes, but years ago, when many of you may have
been in diapers (or not yet born ?), we had many picture tubes, (in
television) that failed due to "open filaments " and we "repaired ' them
with "dc' on the filaments, along with judicious tapping on the side of the
tubes, after which the tubes would again function properly for sometimes
several years. !! Just another hint from "many years" past.; !!!
as for the "military" tubes in the the R-392 , etc. there were many
examples of DC on the filaments and no known failures , but then again the
"military " always changed tubes at a regular interval, which may have been
the reason for mimal failures !!!!! I know for I was there.. !! many , many
WWII radios ran on "total dc".. !!!!! (except for the dynamotors for HV. )
carl / kz5ca
----- Original Message -----
From: "Ron" <w8ron@stratos.net>
To: <MorgusMagnificen@aol.com>
Cc: <amps@contesting.com>
Sent: Wednesday, October 09, 2002 2:56 PM
Subject: Re: [Amps] DC On tube filaments
> The technical point here was that the filaments evaporate over time. No
> one was saying that one could not use DC to power filaments , just that
> there was an observed lifetime difference when using DC where one side
> of the filament would tend to plate/evaporate differently over the life
> of the tube. The static electric field across the filament would
> evidently cause a migration of the metal. Running on AC would cause a
> more uniform evaporation and thus a higher filament resitance instead
> of an open at one end.
> ---
> Ron
>
>
> MorgusMagnificen@aol.com wrote:
> >
> > Those who are opposed to DC on filaments should immediately notify the
> > Department of Defense, as they have apparantly being erroneously doing
this
> > in all of that aircraft electronics since the days of the Wright Bros.
> > (almost).
> >
> > Remember the 1625? It was an 807 with a specially re-designed
filament
> > to run on 12VDC, with two of them (wired in series) in the ARC-5 TX's
powered
> > directly from 24VDC.
> >
> > Eric von Valtier K8LV
> >
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