CMS:803C Ringing and Tone Plant

The 803C Ringing and Tone Plant is an exhibit on the third floor of the Connections Museum that demonstrates how ringing and tones were created in large metropolitan areas in the Bell System. It consists of a P-type motor generator set (known as a ringing machine) which was salvaged from the West office in Seattle, and a control board that served the Pearl St. office in Hartford CT. This tone plant was notable for creating the sweet sounding "city ring" tones that were emblematic of AT&Ts service in large cities for much of the 20th century.

Background

Both parts of the 803C plant were acquired by the Connections Museum at different times, and then mated together to make a functioning exhibit.

P-Type Ringing Machines

The ringing machine and its sibling were originally installed in the West central office on California Ave sometime in the early 1920s. They served that office until at least the 1970s, when they were shut down, and left on their table in the basement, still bolted to the floor. In late 2021, volunteer Sarah Autumn was talking to a Lumen outside plant technician, who told her of the machines existence. She reached out to the central office technician in West, and got permission to come look at the machines.

The machines were removed by museum volunteers in January of 2022. In addition, museum volunteers recovered pieces of 1XB equipment that were later installed in their switch, and parts that would later be retrofitted into the ringing control board.

803C Control Board

The control board, and its associated KS-5397 ringing machines were originally installed in the Pearl St. office in Hartford, CT in the early 1960s. Sometime in the late 1980s, the electromechanical switching system there was decommissioned, and along with it, the ringing and tone plant as well. The control board and its associated motor generators were recovered by Jim Day, of West Haven, CT. The equipment sat for several years in Jim's warehouse before he decided to donate it to the museum. In 2022, volunteers Sarah Autumn and æstrid Smith traveled to Connecticut to palletize the equipment for transport. Sarah drove it back to Seattle in the Fall of 2022, where it was temporarily housed in the museum's offsite storage until room could be found to display it in the museum.

Museum Life

In 2023, space was allocated in the museum for the new ringing plant. Several smaller exhibits were moved, and the area was streamlined to provide a more interactive and better experience for visitors. Although there were two ringing machines salvaged, (one powered by AC, the other by DC), it was decided to use the DC machine, because it was in much better condition, and it could easily be run on the museum's existing 48V battery plant.

The equipment was assembled by volunteers Sarah Autumn and Jay DeJaen in August - December 2023. Volunteer Eric Rhinelander built a custom steel table for the machine, and the original slate tabletop was bolted to the steel framework.

The ringing machine and control board had no official schematics detailing how to wire them together, so Sarah and Jay made custom cable forms using available schematics as a starting point. Several modifications were also made to the control board that integrated older equipment from the West office. These modifications include the double-throw knife switch, and the old style voltage regulators mounted on the board. A speaker was also mounted in the side of the cabinet with a rotary switch that allows visitors to hear the various tones that the machine generates.

The ringing plant provides ringing and tones for the 1XB and Panel switches, and is integrated into the floor alarm board (FLA 100) in the 1XB. Any alarms are sent there, and are displayed as lighted lamps on the wooden annunciator over the power board.