The DR2010 is a Numitron developed by RCA, with units sold under the Apollo brand by IEE bearing the same model numbers but substituting “DR” with “DA”. The DR2010 is identical with the DR2000 except for the latter lacking a decimal point. As shown below, some units feature a flat top, while others have a convex top. This seems to be a manufacturing variation and does not necessarily correspond to different model numbers.
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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.
The DTF104B is a Numitron display tube produced by RCA. Internally, it is nearly identical to the more common DR2000 and similar to the DR2010, 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.