Been occupied with other things lately, but finally got to test my new setup with the variac and filament transformer. Turns out there's not nearly enough juice to run either the light bulb filaments or the filament in the first pic of this post. All the way up on the variac, and they just glow red like a heating element.
Decided to cut out the filament transformer and only use the variac. Perfect! Excellent control and I get a very intense output from the large coiled filaments.
Being a cheapskate, I originally used a Menards dimmer switch before which gave good control for the light bulb filaments. But those filaments would burn out easily, short, and kill the dimmer switch. And I had lousy control over the large coiled filaments. Very touchy, and they would melt every time.
With the combo of the variac and the big filaments, I'm getting very fine control and intense output at 35V for extended periods without melting them.
For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.