More fool I. Just read a little further and "Nixie" is a former trademark of Burroughs, soon used generally to refer to the family of cold-cathode displays. So these are actually low-pressure cathode systems similar in principle to neon lamps. No "filament", or heating, involved. A very cute site showing nice pictures of old display systems; www.vintagecalculators.com/html/ calculator_displays.html