I'm a little confused. If this is a 1935ish instrument, I thought Besson couldn't make compensating euphoniums until they were bought by Boosey & Hawkes in the 1940s?
From that PDF you linked to:
"The British arm of the Besson Company was bought by Boosey & Hawkes in the 1940s"
also
"Brass instruments bearing the Besson name that were manufactured by Boosey & Hawkes (the UK instruments with serial numbers 185200 - 890008)"
Does that mean this is pre-merge since this is 143871?
So...is this a compensating euphonium? It looks like one to me, but I'm confused about the history of Besson/Boosey & Hawkes and compensating euphoniums.
I think what made me think this was more like ~1950ish is this image from Mr. Werden's link:
http://www.dwerden.com/blog3/postima...ialNumbers.png
on the bottom left it shows Besson serial numbers and 143871 would be sometime after 1948. It also shows "Boosey & Hawkes" in the middle of the page for 1935, but this instrument is branded "Besson" not "Boosey & Hawkes".
This would make sense if this is a compensating system, since Besson wouldn't have made those until their purchase by Boosey & Hawkes in the 1940s.
The "Boosey & Co./ Boosey & Hawkes Serial Numbers 14345-560000" lists this:
143643 1934 January
145199 1935 January
But I think since this is branded "Besson" and not "Boosey & Co" or "Boosey & Hawkes" it wouldn't follow that list and would probably follow the bottom left list from this:
http://www.dwerden.com/blog3/postima...ialNumbers.png