This is essentially a small improvement over the Super horns -- minor adjustments in keywork and bore size. The major interesting feature of some of these horns is the interesting "teakettle" octave vent. This feature continued with some of the early Balanced Action horns (see the gold plate alto, below).

I have seen a couple of baritones that are around this serial number range, and they do not have the "Radio Improved" engraving on the bell. These horns are either Super models or are early versions of Balanced Action horns. I believe this holds true for the sopranos, but they're rare enough that I haven't seen one in over three years of searching.

I believe that this is Selmer's most glaring example of poor maintenance on their serial number chart. The horn that is the header for this page has a serial number 3000 higher than Selmer puts as the official end of the Radio Improved horns. I believe these later horns are special-order models from people who liked the Super keywork and thought the left-hand bell key arrangement was faster. If it's true that the Jimmy Dorsey model was essentially a Super body with Balanced Action keywork, it's probable that Selmer sold other previous models as a specialty item.

Finally, I have been told, by two different people that have horns that have s/n higher than 21750, that the engraving is similar to that on the header of this page, i.e.: a bit of the Super engraving combined with a bit of the Balanced Action.