Date: 1955. Owner unknown
Here is something interesting I came across on eBay. The description was "Conn 12J bass, serial number 500xxx." There was a 12J Eb bass, front action upright bell in the 1920's. Visually the instrument pictured here resembles the drawing of that 12J (see seperate listing). As far as I can tell the most important difference is the angle of the leadpipe. The 1955 Conn catalog doesn't list a 12J bass. However, many models were discontinued around 1954-1955, and with this instrument having such a low serial number, it is entirely possible that there was a 12J up to 1955. So my guess is that Conn reinstated the 12J Eb bass sometime around 1947, since several models were reinstated in 1947, and discontinued it in 1955. The name of course is a guess, in the 1920's it was called "Professional", but in the 1940's and 1950's it may well have been called something else.