Date: 1952. Owner unknown. Image courtesy Playground Music Center.
This is a somewhat mysterious, but not entirely uncommon, model of mellophone. It is without a doubt an instrument made for the U.S. Government (military). Such instruments between the mid to late 1940's and the 1950's were almost invariably silver plated with the serial number engraved on the bell and "U.S." on the case. This mellophone fits that profile perfectly. It is also known that Conn produced a series of mellophones of this model mellophone in 1952 because they do turn up now and then. All "Gov't" models. Produced in Eb with an additional slide for F.
Here is where it gets tricky though: Neither Conn, nor Pan American or Cavalier, have any models of mellophone listed and known to have been in production between 1947 and 1954. It is unlikely that Conn created an entirely new model of mellophone for the U.S. Government entirely from scratch. It was almost certainly based on an existing model. But which model?
There has been some debate within the "Conn community" about this, and at the moment the following appears to be the upshot of that debate.
First a side step to trombones. Between 1955 and 1958 Pan American (which was a subsidiary of Conn) produced a stencil trombone for Continental, called the 58H. This was a 0.484" (#2½) bore model. In the Conn listing, you will find a 58H Gov't model trombone, #2½ bore produced between 1955 and 1958. It doesn't require a great leap of the imagination that the Conn 58H Gov't Model was the same instrument as the Pan American 58H stencil for Continental.
We have already determined that there were no known mellophone models in production in 1952 by Conn, Pan American or Cavalier. However, people who have had the oppertunity to examine such Conn 1952 Gov't mellophones as well as other Conn or Conn-subsidiary models tell me that it is very similar to the Cavalier 96E. Same style of bracing and also in F and Eb.
Conclusion: this government model mellophone is probably the same instrument as a Cavalier 96E. Since on the Pan American 58H - Conn 58 Gov't Model the model number was retained, it is likely the same was done here. So, until further evidence appears, this model is provionally labeled the "96E F & Eb Gov't Model".