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 ;-)
--
73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek
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