The California Historical Radio Society is home to more than 2,000 electrical transcription (ET) discs. These look a bit like a standard 12″ LP photograph record, but they’re not the same thing.
ET discs are grooved audio recordings on 16-inch diameter records developed by Frank Jewett, an engineer working for Western Electric. They were developed specifically for radio broadcast and were in use from the 1920s through 1960s. Transcription discs were used to record original radio programming as well copies shared between affiliated radio stations for broadcast or purchased by others. Programming included religious, music, drama, and entertainment. ETs play at a speed of 33-1/3rpm for up to 20 minutes per side; some transcription discs play from the center outwards. Sound grooves are cut into a coating of shellac, black cellulose nitrate, or vinyl (polyvinyl chloride) over cores made of aluminum, glass, or vinyl (vinyl was used after 1940).
A preservation team has been working to inventory and catalog our collection of ET discs. We hope to publish that catalog in a form that will allow researchers to determine if we possess a particular recording.
In the meantime, a few of these discs have been digitized. You can find these recordings as well as information related to them at this link.