Metal Disk...

[Hawkwind]

My Father went Amherst College, late 1930s/early 1940s. While there, a speech he made was recorded on a 12 inch metal disk. The hole in the middle was the common small size. It spun at 78 RPMs. Written on the sleeve was something like this: "Play with fiber needle". Played it anyway with an expendable cartridge. So, what is it? A master for a stamper?..