As I wrote in one of my previous posts, until about 1930 most of the chromatic harmonicas at that time used an external spring for slider action. It was invented by Hohner in 1910. There were few exceptions. One exception was the horn chromatic by Koch from about 1926.
The text in the catalogue states: “this new style Mouth Organ has a brass horn which amplifies the volume. By turning the sounding horn forward or backward, a real chromatic scale is produced.”
As described above, twisting the bell of the horn moves the key either to “C” or “C#”. The comb and reed plate are under the mouthpiece. The harmonica has 10 holes and is Richter tuned.
It seems the horn chromatic harmonica was just a short lived experiment. The 1927 Koch catalogue did not advertise it anymore. This was just around one years after it was first produced.
Note:
I was I able to restore an old horn chromatic owned by Harland Crain that was missing the mouthpiece and logo.
A new custom made wood mouth piece was created, painted in the original color and attached to the body.
To re-create the logo, brass sheet metal adding a black coat was used. The original logo was re-trace with the help of design software. The black paint was lasered off where needed and the logo cut out.
Chromatic Harmonica History 