Does a ballast from an NST primary need a core?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Garry Freemyer by way of Terry Fritz <twftesla-at-uswest-dot-net>" <garry-at-ndfc-dot-com>

I got a fine home brew NST from James T. It puts out 120 milliamps or 90 if
ballasted by an nst primary. I was just wondering if the primary needs to be
on the core. My first guess is no, the function is just to use up some of
the amperage in to limit amperage out. But I thought I'd ask.