[Amps] Miller-Larson effect on thoriated tungsten filaments / neat electronic soft-start

[Chris Wilson]

>  

> Yes those GE CL-60 NTC inrush limiting thermistors are helpful albeit still
> yield a fairly fast rise time constant in the filament voltage.  The far
> gentler slow 3 to 4 second ramp up from the Triac controller is more
> elegant. The slow soft-start circuit is based on the ON Semiconductor
> TDA1085C IC chip and a 40A Triac.

>  

> In fact I've also got a couple of CL-60 thermistors (one in each leg) the
> primary of the Kenwood TL922 amp's filament transformer to trim / fine-tune
> the steady-state filament voltage measured right at the tube socket to circa
> 4.9 Volts, as the factory stock filament voltage is on the high side; around
> 5.2 to 5.3 Volts. That slight over voltage can also shorten the 3-500Z tube
> emission life.

>  

> Leigh


25/06/2013 10:24

Do you a schematic you would share for the  Triac soft start setup
please Leigh?

Thanks.

-- 
       Best Regards,
                   Chris Wilson.