What's the deal with Microgrove LPs?


I recently raided my girlfriend's elderly aunt's record collection and came away with a few 7" records labeled: "CBS Masterworks." They're from the 1950's and say they are
"microgrove" LP's, but nowhere does it say at what speed they play.
I can't tell if they're 45 or 33 1/3 or something else.
Has anyone heard of these and is there any issue with respect to today's needles?
The grooves do look very close together.
ebuzz

Showing 1 response by casey33

Microgroove is a term from the 50s.The first records after the 78 were 10" to fit the shelving which already existed for the 78.The 78 has a wider groove.The new groove was narrower therefore called microgroove.This is the same size groove used today,so play on.On some 50s-60s turntables you had a flipover cartridge with a 78 stylus on one side and a LP (microgroove) stylus on the other side.