[Amps] filament supply D.C or A.C

[Patrick Egloff]

--------------------------
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.
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About 60 times a second would be great !!  ;-))


2008/2/13, k7fm <k7fm at teleport.com>:
>
> 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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-- 
Patrick Egloff - TK5EP
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