[IBeOmega]

Well, I have a Couesnon Monopole Conservatoire tenor here which gets the new record for the oldest tenor I have ever seen or heard of with an original high F# key. SN is 53xx, which puts its manufacture date somewhere between 1936-1938, from the info I can find.
(Please correct me if I'm wrong - other than SML I'm not very familiar with the various extinct European sax makers, only aware of them.)

This leads me to wonder, when did high F# keys become 'a thing' on tenor?

The previous oldest I was aware of was a stunningly patina'd 1950 (I think) Selmer Super Action that was up for sale a couple years back. I know King and Keilwerth also made tenors in the 1950s with high F# keys.

Does anyone here have any more info?

 

[saxoclese]

The high F# was first introduced on the Selmer Balanced Action model as an "option" starting in about 1936. I have done a patent search and could find no patents for that key.