Hello
I have a small variac that was used as the speed control for an old floor-standing humidifier.
It has only 2 leads and a limited range (120Vac in/≈80-120v out).
Does anyone know how this works? Is it a bucking auto-transformer?
Thanks
Marty
(see photo)

 

yes, its basically a variable buck transformer. My guess is that with the voltage range you have it is a three layer winding set.

 

Thanks for yr reply.
Does this drawing look right?