These effects are from three collections that had previously been in the USC Hugh M. Hefner (yes, that guy!) Foundation Moving Image Archive:
The Gold and Red Libraries consist of high-quality, first generation copies of original nitrate optical sound effects from the 1930s & ’40s created for Hollywood studios.
Red Library:
https://archive.org/details/Red_Library_Trains/
https://archive.org/details/Re...Bells_Horns_Whistles
Gold Library:
https://archive.org/details/GO...APE_47_48_49_Trains/
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The Sunset Editorial (SSE) Library was also donated to USC around 1990. It includes classic effects from the 1930s into the ’80s. These effects are from 35mm magnetic film.
SSE Library: