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Just a dumb question I couldn't find an answer for --- who started putting valves on slide trombones, and when? I figure it was after the Stolzel valve came along, and probably postdates the first valve trombone, but that's all I have.

According to wikipedia,

wikipedia wrote:The F attachment originated in an instrument developed by German instrument maker Christian Friedrich Sattler during the late 1830s and patented in 1839.