[ProAudio] Western Electric 111C transformers

Bob Olhsson olh at hyperback.com
Tue Feb 1 13:05:31 PST 2022

The phone company held patents on electrical recording, motion picture sound and broadcasting until the late 1940s. I understand the only gear available for sale was related to expired PA system patents from before 1920. Everything else needed to be leased from Ma Bell or one of their licensees. The gear was really high quality because reliability was in their financial interest.

Bob Olhsson

-----Original Message-----
From: Kevin P. Mostyn via ProAudio
Sent: Tuesday, February 1, 2022 9:56 AM

They were 15 kHz circuits. AT&T offered them in the late 1930s onwards, IIRC. They also offered, starting later, but definitely in the early 1960s, matched stereo pairs of 15 kHz circuits. They had to pass a strict test summed to mono. The paths were designed to match arrival time and phase. I used many of these in my career.


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