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I have owned two of them in the past and they were permanently soldered together. I always just assumed that it was easier to just take bells already made for trombones to make these rather than trying a custom design. I always thought it would have been nice to have the valve section be detachable for use with a slide as an option, but there were other braces connecting the valve section to the bell so to do so would have meant making those detachable too and it would have not been worth the effort.