Deryk Barker writes in regards to the Beethoven 5th:

>Almost certainly 5, as a) it only uses the trombones in the finale and b)
>was the first appearance in a symphony of the trombone (and the piccolo for
>that matter).

Actually, that honor goes to Franz Beck (1723-1809) in his second symphony
from 1762.  For further information:

   http://www.nthwood.demon.co.uk/bts/index-v4.htm

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