[Amps] filament instant heating query / simple remedy

[David C. Hallam]

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 ;-)
>
>