This week I have been working on a vintage Reynolds Contempora double rotor bass trombone.
What's interesting about this particular horn is the dependent rotor system - something we don't see every day, and it's the first time I've seen one at all! As can be seen in the pictures, one rotor will not turn without the other rotor being depressed, so they must be level with each other and work in perfect unison - which is tricky to figure out the first time around.
I read some of the history on this design at yeodoug.com. A quote written by a trombonist named Dennis Clason reads: "Dependent systems were developed first as a response to a few composers treating the bass trombone as a completely chromatic instrument from low B (rather than low C). (Bela) Bartok figured prominently among that group."
An interesting horn and a little bit of trombone history from Teej's bench!