[Phonosandradios]

33rpm vinyl disks have been around for much longer than many people think as they were used as a recording medium for professional uses since the late 1930's. Mainly for providing recorded content for radio stations. They were at that point 16" in diameter but had a coarse groove cut which limited the playing time to about 15 minutes per side but at a very good quality and wide dynamic range.

Before that 16" disks were used as part of the vitaphone system of sound for films but those although turning at 33rpm were made of a quieter form of shellac called vitrolac.

The picture below is one disk in my collection from 1940 which is definitely a form of vinyl as it has the same kind of give as a modern vinyl disk. I have others from 1938 which whilst a silent surface doesn't have the same bendability as vinyl nor does it feel like shellac although the surface is completely quiet.

If it hadn't been for WWII then 78's would probably been dropped far earlier that the late 1950's as the technology was all there ready 2 decades earlier.