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 ;-)
> >
> >
>
>
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