That may be true but it is hard to come up with any argument to say
that it is not beneficial to run the filament at the nominal voltage,
rather than some higher value chosen by an amplifier manufacturer who
sells tubes as spare parts.
73, Alek
VK6APK
At 07:25 PM 29/01/2010, Paul Christensen wrote:
> > I understand that high filament voltages is a contentious issue among
> > hams and amp manufacturers. One camp claims it drastically shortens
> > the tube life, whereas the other claims that in ICAS operation that
> > other factors will kill a tube long before the excess filament voltage
> > will do so.
>
>Data is needed to assess the effect of relatively short duration power
>cycles on filament life. We can read all the conjecture about monitoring
>rated filament voltage in an effort to extent filament life, but much of
>that data pertains to VT's with directly-heated cathodes in continuous
>service emission modes like that found in the broadcast industry.
>
>Anything we glean from this mail list is nothing but an opinion unless its
>backed by valid, measured data. Comments by amplifier designers are of no
>use either unless those comments are based on valid, measured data that can
>be cited.
>
>Last year, I undertook a project to lift the high-current filament return
>off the chassis of my Alpha 77Dx. The side "benefit" was that what had been
>high filament voltage of approximately 5.5 V was brought down to 4.9 V with
>just enough series resistance from the filament choke I added. Will the
>lowering of filament voltage from 5.5V to 4.9 extend tube life? Does the
>fact that the amp is power-cycled several times a week undermine any benefit
>offered by the reduction in F voltage? I don't know and I doubt anyone else
>does, including the amp designers unless they have solid evidence to back
>their claims.
>
>I would like to know more about the subject myself. If anyone knows, I'd
>put my money on John Lyles. But unless the data has already been assembled
>by one of the major power tube suppliers in past years, then I doubt it will
>ever be presented as high-power RF technology gradually shifts to
>solid-state devices. Notwithstanding that data, it is then left to amateur
>experimenters like ourselves to measure and present it. There's nothing
>wrong with that if the results are valid. Anything less is just a guess or
>it's based on limited empirical data that may not have universal relevance.
>
>Paul, W9AC
>
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