Date: 1926. (Drawing)
The BBb New Wonder Helicon was available in 4 versions: the 30K and 32K Low Pitch and the 31K and 33K High Pitch. The 30K and 31K had three valves and were in production from 1919 to at least 1927 and were probaby discontinued in 1929. The 32K and 33K had four valves and were in production from 1919 to at around 1924.
What Conn said in 1926:
Marching bands use the Helicon model basses in preference to the other types owing to their advantage in weight and the consequent ease with which they may be carried. Conn Helicons are properly balanced, and as a result may be used in lengthy parades with a minimum of fatigue.
The tone quality of Conn Helicon model basses is one of the remarkable features of these instruments. The hydraulic expansion process of manufacture gives the instrument perfect proportions, and the interior of the sounds passage is absolutely smooth, so that the most discriminating performers declare the Conn Helicons to be perfect in tone.
The BBb Helicon is naturally slightly larger and slightly heavier than the Eb model of the same type. Like the Eb, however, it has the peculiar quality of tone which makes it extremely effective in military bands, where it is widely used.