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I recall, several years ago playing on an absolutely immense Buescher Sousaphone that a friend of mine owned (I'd say at least as big as a Conn Jumbo).

I remember it played quite well. Other than that, I have no further details

Several photos of Buescher sousaphones in Bb, Eb, and BBb in my Yahoo-based gallery. Also helicons in Eb, CC, and BBb. Go by the index.

Klaus

I have two, although I am not sure of the vintage. Neither is a jumbo, but both are big sousaphones. Both are silver plated. Both play very well. One has three valves, and the other is a four valve horn. I only have one third valve, but that is not too problematic because I can only play one at a time.
I bought the three valver from a pro in Cincinnati in 1971. It was the first horn I actually owned, and I think it was fairly old when I bought it. I still play it a little almost every day. They are good horns.