[overdriver]

Originally Posted by lineboss58

Air in a vacuum? Oh yes indeed, it is not possible to remove all atmospheric gasses from a tube. The best tube factorys had the best pumping techniques to evacuate as much gas as possible, the heater filament is coated with a "getter". The first time the heater is turned on it vapourises the getter which nutralizes any contaminants left in the tube, this is the silver residue you see coated on the inside glass of the tube. Hope this helps.

Thanks for that!