MLA

Koch, Frederick R. (Frederick Robinson). Music/Unidentified/Waltzes for orchestra. Box 283, folder 1625. n.d.. https://collections.library.yale.edu/catalog/12298619.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 283, folder 1625"])(n.d.)[Music/Unidentified/Waltzes for orchestra]. https://collections.library.yale.edu/catalog/12298619.