Conn 12H Coprion
Date: 1940. Owned by Mats Hübner
Instrument has a #2½ Bore (0.484"). The 12H, similar to the 12A and 12B cornet and trumpet, has a coprion bell. It is my belief that the 12H is essentially a 4H with a Coprion bell, since it has the same bore and physically closely resembles it.
I have changed my opinion on when the 12H (12A, 12B) Coprion instruments were first produced. All available Conn documentation indicates the Coprion process was invented in 1938. Nevertheless, there are instruments around with 1937 serial numbers (mostly 12B trumpets). My current theory is that since the 12H (and 12B) are based on other models (in the case of the 12H, the 4H. The 12B is based on the 22B), Conn may have used unfinished versions of the other models. Or, there may have been pre-production models. Who knows. The 12H was produced until 1955.
The 1955 Conn catalog shows a 12H with nickel trim and the word "Coprion" engraved on the mouthpiece receiver. This is a good indication that the 12H changed somewhat towards or in 1955, because earlier models didn't have either.
What Conn said in 1939:
Entirely new trombone in medium bore, developed especially to capitalize on all the advantages of the Coprion bell. You'll appreciate the amazing flexibility of scale, ease of response and beautiful tone quality which this seamless bell of Coprion gives. Brass, nickel and chromium trim, heavily clear lacquered.
What Conn said in 1955:
Built in Bb, medium bore, with famous seamless COPRION bell that assures superior tone quality, remarkable ease of response and far greater flexibility. Has those smooth, fast, lightweight "Airfloat" slides, with integrally-drawn stockings; and long slide bearing for smooth 6th and 7th positions. Outside slides of special Conn bearing formula alloy. Length 45 1/2"; weight 3 pounds 9 ounces; bell diameter 7". Furnished in attractive two tone tan and rawhide vinyl case (top grain leather binding), with mouthpiece and music lyre. Highly polished brass, beautifully nickel trimmed, with Coprion bell, clear lacquered overall.