One interesting thing about carbon and even more useful the graphite
form of carbon.
All the oxides of carbon are gaseous. CO and CO2. So if the filament is
heated while pumping out
the oxides formed by the hot filament are also pumped out with nitrogen and
other gasses.
This makes this material very useful in high vacuum systems under
certain conditions.
73
Bill wa4lav
At 05:26 PM 6/17/2012 +0200, oz5tg@post2.tele.dk wrote:
>Leave them on.
>
>http://www.dailymail.co.uk/news/article-2004797/Worlds-oldest-light-bulb-110-years-old-Livermore-California-station.html
>
>
>Best 73 de OZ5TG, Verner
>
>
> > ----- Original Message -----
> > From: "Bill Fuqua" <wlfuqu00@uky.edu>
> > To: <dhallam@knology.net>; "Ian White GM3SEK" <gm3sek@ifwtech.co.uk>
> > Cc: <amps@contesting.com>
> > Sent: Sunday, June 17, 2012 4:41 PM
> > Subject: Re: [Amps] filament instant heating query / simple remedy
> >
> >
> >> You mean a digital light dimmer.
> >> Hey guys, lets not get so carried away.
> >>
> >>
> >> Lets look at other devices that have filaments.
> >> The light bulb is a prime example. It has a tungsten filament that is
> >> turned on and off more often that your amplifiers. It starts at the
>same
> >> start temperature and ends up much hotter than your filaments, thus
> >> surge current relative to final current ratio is less than that of
>your
> >> filament.
> >> And there is little difference between the (on life) of one left on
>and
> >> one
> >> cycled on
> >> and off.
> >> It is important to maintain proper cathode temperature to achieve
> >> emission and
> >> emission.lifetime.
> >> The death of a light bulb filament is due to tungsten evaporation, but
> >> it has
> >> a very thin filament and lower filament temperature. The filaments in
> >> your
> >> tubes
> >> are much thicker. I expect the lifetime for most tubes is due to loss
>of
> >> emission and
> >> not filament life.
> >>
> >> 73
> >> Bill wa4lav
> >>
> >>
> >> At 08:40 AM 6/17/2012 -0400, David C. Hallam wrote:
> >>>Has anyone tried an approach like Carel, PC5M, with a microprocessor
> >>>controlled soft start for the filament. The microprocessor controls an
> >>>optical triac driver The triac is turned on and off over an increasing
> >>>portion of the line AC cycle until full on is reached. His
> >>>microprocessor program does this in 100 sec. It is designed only for
> >>>soft start and does not do any regulation of the filament voltage
>after
> >>>full output is reached.
> >>>
> >>>David
> >>>KW4DH
> >>>
> >>>
> >>>On 6/17/2012 2:35 AM, Ian White GM3SEK wrote:
> >>> > Leigh Turner wrote:
> >>> >> That's right Pete, the SB220 had a well designed filament
>transformer
> >>> >> that self-limited the cold inrush current to a safer value close
>to
> >>> >> what the tube manufacturer Eimac specified. What the NTC
>thermistors
> >>> >> do
> >>> >> in both the SB220 and TL922 is bring the 3-500Z filaments up in a
> >>> >> nice
> >>> >> slow and controlled manner.
> >>> >>
> >>> >>
> >>> >>
> >>> >> Eliminating the inrush current surge completely like this just
>seems
> >>> >> so
> >>> >> intuitively a good thing to do to mitigate thermal stress on the
>cold
> >>> >> filament structure.
> >>> >>
> >>> > But after that initial surge, the truly dedicated obsessive must
>move
> >>> > on
> >>> > to worry about the stability of the filament voltage.
> >>> >
> >>> > So now our filament supply includes a hot, temperature-variable
> >>> > thermistor, connected permanently in circuit... and we are the
>group
> >>> > who
> >>> > can argue for weeks about +/- 0.1 volt.
> >>> >
> >>> > This should be good ;-)
> >>> >
> >>> >
> >>>
> >>>
> >>>_______________________________________________
> >>>Amps mailing list
> >>>Amps@contesting.com
> >>>http://lists.contesting.com/mailman/listinfo/amps
> >>
> >> _______________________________________________
> >> Amps mailing list
> >> Amps@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/amps
> >>
> >>
> >> -----
> >> Ingen virus fundet i denne meddelelse.
> >> Kontrolleret af AVG - www.avg.com
> >> Version: 2012.0.2180 / Virusdatabase: 2433/5075 - Udgivelsesdato:
> >> 17-06-2012
> >>
> >
>
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