These models, regardless of what manufacturer or specific instrument, all have tunable bells.
Type: Cornet
Brand: Conn
Maker: C. G. Conn, Ltd. [Conn-Selmer today]
Model: Connquest
Model №: 76A
Where made: Elkhart, IN, U. S. A.
Dates of manufacture: 1961 - 1971 [approx.]
This, in turn, was based on the Conn 20A flügelhorn design made before 1927:
...originating in Charles G. Conn's own design patent 45555 from 1914...
...which is similar to this early 1900s Conn Wonderphone tuning bell design closest to Amati and other European examples:
This even goes back to the Conn & DuPont First Class model cornet in the possession of Eric Totman, circa 1879:
Type: Cornet
Brand: Conn & DuPont
Maker: Conn & DuPont [Conn-Selmer today]
Model: First Class
Model №: [N/A]
Where made: Elkhart, IN, U. S. A.
Dates of manufacture: 1879-1880
This design is similar to the Olds Recording:
Type: Cornet
Brand: Olds
Maker: F. E. Olds and Son
Model: Super Recording [later Recording]
Where made: Los Angeles & Fullerton, California [?]
Dates of manufacture: [?]
This design was also seen in a variation of the Bach 182 flügelhorn:
Type: Flügelhorn
Brand: Bach
Maker: Vincent Bach Corp. [Conn-Selmer today]
Model: Stradivarius
Model №: 182 [the № 165 is similar]
Where made: New York, [Elkhart, IN?], U. S. A.
Dates of manufacture: 1950s ? [approx.]
A design which had several variations and was eventually scrapped.
The European manufacturers took inspiration from the above design:
Type: Cornet
Brand: Glassl [Heribert Glassl/Musik Glassl]
Maker: Kühnl & Hoyer/VEB Sachsen [parts]
Model: [?]
Where made: Nauheim, [West] Germany/Markneukirchen, [East] Germany [parts]
Dates of manufacture: [mid-20th century]
Type: Flügelhorn
Brand: Kühnl & Hoyer
Maker: Kühnl & Hoyer/VEB Sachsen [parts]
Model: [?]
Model №: 2014
Where made: Markt Erlbach, [West] Germany/Markneukirchen, [East] Germany [parts]
Dates of manufacture: [mid-20th century]
The "Germany" bell mark is the kind K&H used in the 1990s, though this model had existed for many years.
A. K. Wunderlich, a manufacturer in Markneukirchen, Germany, used a similar setup with this flügelhorn or cornet:
Type: Flügelhorn
Brand: Exakta (by A. K. Wunderlich)
Maker: A. K. Wunderlich
Model: Exakta
Model №: [none]
Where made: Markneukirchen, Germany
Dates of manufacture: 1938-1948 [approx. - "A. K. Wunderlich" mark indicates post-1938 instruments, but MIGMA [later VMI?] was the distributor indicated on the bell in the late 1940s]
...not to mention the design that was used on Amati and Amati-stencil cornets:
Type: Cornet
Brand: Amati/Bohland & Fuchs [plus many others]
Maker: Amati
Model: [?]
Model №: 2551 [B&F], 1038 [Amati]
Where made: Kraslice, Czechia [then Czechoslovakia]
Dates of manufacture: mid-20th century
Notice the B&F [Bohland & Fuchs] trademark on bell - the Bohland firm was one of the constituent companies that formed Amati in 1945, and horns bearing trademarks of both operatives were made into the 1980s. The Amati firm was completely nationalized in 1948, encompassing all Czechoslovak instrument manufacturers. This design can be found in numerous stencil horns, some which were Amati brands, others mere clients. This instrument looks old, but this design (and concurrent models) don't appear until after the 1950s! The 2551 appears in a 1976 catalog, with the B-1038 successor appearing in a later catalog.