Apollo Numitron Tube Clock:
Apollo Numitron Tube Clock: FFD-21
Like the high voltage Nixie tubes, I also have a love affair with low voltage incandescent display tubes, or Numitron tubes. These types of tubes were also used as numeric displays back in the 60s through the 80s, and now are available in surplus. I designed and fabricated a number of clock designs from 2010 to the present, and continue to refine clock designs based on various tube types.
One of my favorite numitron tubes of all is the flat bathtub style IEE Apollo Numitron FFD-21. These were common in avionics well into the 1980s, but replaced by LED dispays in the 1990s and onward.