This horn started the Selmer dynasty: it's the first horn that had the same basic design of the Mark VI thru the Super 80's, and was the most advanced horn available at the time. Competition to this design didn't start until the 1950's with the Buffet's Dynaction and the SML "Rev. C" horns.

Oddly, these horns are not as popular as the Super Balanced Action horns. While the keyplay is a bit better on the SBA's, the Balanced horns have much nicer engraving -- the early horns generally feature a portrait on the bell of a sailboat, mountains and birds flying in the distance (this gets modified throughout the series and gets more elaborate, until it disappears into the "vine" fleur de leis engraving of late SBA's).

As mentioned earlier, some of the early Balanced horns have the same "teakettle" octave vent as some of the Radio Improved horns.

The Jimmy Dorsey model was also released early into the Balanced Action run. This is Selmer's rarest model, with possibly only 200 horns produced. SAXTEK also has a few comments:

"I've seen two Jimmy Dorsey model Selmer altos. They have sheet metal keyguards, like the Balanced Action, but the bell keys are on the left side, like the Cigar Cutter. The bell keyguard is a bit odd, because it has a keyguard just like the Mark VI grafted to the wire 'wishbone' of the earlier Supers (Cigar Cutters). My own personal opinion is that Selmer had some Super bells left after starting Balanced Action production, so they used them. The Jimmy Dorsey horns, however, play great and Jimmy did use one."

(Jimmy Dorsey with a Jimmy Dorsey Model alto. Note the keyguards)

Finally, I've recently found that there were some Super and Radio Improved horns available considerably later than the Selmer serial number charts would indicate. Beware of these horns: they are not Jimmy Dorsey models (unless they have the sheet metal keyguards). They may have Balanced Action engraving, though.

I believe these 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.