The DTF104B is a Numitron display tube produced by RCA. Internally, it is nearly identical to the more common DR2000, but it is designed to be read from the top rather than the side. A spot exists on the backplate where a left decimal point could have been included, but it lacks filaments and is therefore non-functional on this model. Its flat top gives the DTF104B a distinct look and helps reducing reflections from adjacent tubes.
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Numitrons utilize multiple incandescant filaments to represent digits and other symbols, similar to other types of segmented displays. The key advantage of Numitrons over Nixie tubes was that they did not require high voltages, allowing them to be driven directly by logic-level signals or cheap low voltage transistors.