Cantata No. 121 - J.S. Bach
J.S. Bach (1685-1750) was a German composer of the Baroque era.
Bach’s Cantata No. 121 is a rare instance of his use of trombones. Trombones qre used sparingly, limited to the chorale at the end of the cantata. The alto trombone doubles violin II, the tenor trombone doubles the violas and the bass trombone doubles the continuo.
To learn more about the composer, visit Johann Sebastian Bach on Wikipedia.
For more on the composition, visit Bach Cantata No. 121 on Wikipedia.
Performance
J.S. Bach: Christum wir sollen loben schon, BWV 121
Trombone Parts (Score only)
The full score of Bach Cantata No. 121 is available on IMSLP.org.
NOTE: IMSLP provides access to public-domain scores and parts, with copyright status varying by country. Users are responsible for observing applicable copyright laws.
Trombone parts are available on IMSLP.org as follows:
Ranges and clefs by Part

More Bach
Trombone Resources playlist of Bach with trombones in the instrumentation.