For example, in Ann Lingg's biography of Sousa, published in 1954, she writes the following on page 135:
To improve the sound of his band he even turned inventor. He found that the Helicon Tuba (that brass giant curling around the marcher's body, with the weight resting on his shoulders and a large bell blaring music far ahead) was not well suited for the indoors; its frontal attack was too powerful. So Sousa suggested a new type whose bell could be turned up, so that, as he said, "the sound would diffuse over the entire band like the frosting on a cake." The firm of Wurlitzer & Company made the instrument to his specifications and called it the Sousaphone.She's on the right track, although the helicon was used as a concert instrument by Conrad - both in Gilmore's Band, and for the first few years in Sousa's Band, until Sousa came up with the modified helicon dubbed the "Sousaphone." But Wurlitzer & Company?
Let's move on to Kenneth Berger's work on Sousa, which came out three years later (1957). On page 29, he writes this:
To many who are not musicians, the name Sousa is remembered primarily in connection with the sousaphone. He is often credited with inventing this instrument; however, the transformation from the old circular helicon (bass) to the sousaphone is more of a slightly evolutionary change than a stroke of inventive genius. Actually Sousa did not claim to have invented the new musical instrument (for which no patents were taken out, which should prove it to be a modest development), and he did not take any credit for this project. In 1898, he made some suggestions regarding the improvement of the helicon, and the first Sousaphone - called the Sousaphone Grand - was built by Ted Pounder, an instrument maker with the C. G. Conn Company, of Elkhart, Indiana.Okay, so it wasn't Wurlitzer, but Conn who made the first Sousaphone - and in 1898? Actually, Ted Pounder did make Conn's first Sousaphone that year (or more likely in late 1897), but it was not the very first Sousaphone to appear. And it wasn't called a "Sousaphone Grand" (that name wasn't used until 1913, five years after Conn pointed the bell forward); it was called a "Monster Sousaphone"!
And did Sousa really "not take any credit for this project"? I think not - see this post, and this post!
Moving to 1971, we encounter Sousa's greatest biographer - Paul E. Bierley. In the 2001 revised edition of his treatment of Sousa, he writes this on page 16:
The musical instrument know as the sousaphone was, of course, named after Sousa. The first one was built to his specifications, but who actually constructed it is debatable. According to one of Sousa's few references to it [again, see this post], it was built by J. W. Pepper, a Philadelphia instrument manufacturer and music publisher. Another story comes from the Conn Corporation, whose instruments Sousa endorsed for many years. They claim credit for building the first sousaphone. The Pepper sousaphone, allegedly built around 1892, was evidently used very little and was not widely publicized. Conn's first sousaphone was built in 1898 and was widely promoted.Now we're really close! Not Wurlitzer, and not Conn, but Pepper - but "around 1892" is actually 1895, as I've clarified in my research. And that Sousaphone, while it didn't last long in Sousa's Band, was played on tour in the early months of 1896.