Hi,

I think I have similar problem to Arjune and I definitelly need slow rise of an AC voltage.
I am planning to biuld a softstart for Tube amp heaters. Tubes are heated with dedicated toroidal transfirmer - PRI 230V, sec 6,3V - power consumption about 40W.
I would like to put AC to the toroid primary with rising ramp voltage. This voltage rise time schould be approx 30 seconds.
What will be the best sollution for that purpose? (NTC thermistors are too fast for my project - I want to have much slower heater startup).

I would be gratefull for your help.

 

Don't mess with the Primary.
I'm assuming that You will be Rectifying, and Filtering, the Filament-Supply since You are
going to the trouble of having a separate Transformer.

With a DC Supply,
a simple Buck-Regulator can easily be configured to Regulate the Current going to the Filaments
which will prevent damage to the Filaments on start-up,
and will keep them operating very consistently.

A full ~30-seconds to smoothly warm-up is probably not necessary with Current-Regulation,
just let the Filaments dictate how long warm-up takes when supplied with a Constant-Current.

If You really want to get carried-away,
You can even have Current-Regulation for each individual
Filament if you're seriously worried about your Tubes.

Dual-Filament-Tubes would be a bonus for Ground-referencing.

If this sounds like something that You would be interested in, just say so.
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