[Amps] filament instant heating query / simple remedy

[Ian White GM3SEK]

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