|Photo courtesy of The Music Trade Review|
This was picked up by The Music Trade Review of December 28, 1907 (vol. 45, no. 26, p. 42), featuring the above photo and the following short article:
One of the Remarkable Creations Made by the C. G. Conn Co.
In the front rank of enterprise may always be found C. G. Conn Co., Elkhart, Ind., as manufacturers of band instruments, and their reputation goes beyond the borders of the United States. One of the most unique examples of their craftsmanship and musical progress is the giant Eb bass Sousaphone, of which a splended illustration is presented herewith, and named in honor of the distinguished American bandmaster, John Philip Sousa, the "March King," as he is known the world over. This great instrument was designed by the skilled artists attached to the mammoth works of the C. G. Conn Co., and is manufactured exclusively by them. Its musical qualities and sonorous tone are the acme of perfection.
Of course, Conn continued to make available their other basses, including their popular three valve BBb Sousaphone, as shown in this feature page from 1907 (their four valve "Monster Sousaphones" presumably remained special order instruments):
|Photo courtesy of Mark Overton at saxophone.org|