KS-20419L1 telephone buzzer

This is a recording of a KS-20419L1 buzzer inside of a Bell System/Western Electric 564HLM key telephone. A key telephone is a telephone that can access multiple lines through the use of interlocking buttons on the bottom of the phone, under the dial. Equipment external to the phone lights up the keys to show the status of each line and allows calls to be placed on hold and transferred. They were once cost-effective business phones for small shops or offices. The phone contains both a H1A one-bell ringer and a KS-20419L1 buzzer. The latter would be used to signal an incoming call when either a signal different from the ringer was required or the equipment in use couldn't generate the 90 VAC 20 Hz required to drive the ringer.

This buzzer is designed to be driven by 10 VAC 60 Hz, and consists of a metal disk above an electromagnet. The disk vibrates around 60 Hz but is loose enough that clattering and other harmonics ensue. It's a rather cacophonous sound compared to most modern signaling devices and most other signaling devices in the telephone world.

Recorded using the microphone of an iPhone 11 with no further processing.