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Why Build the Tribute to Vintage Telephone Relays?


I then shouted into the mouthpiece the following sentence: "Mr Watson – Come here – I want to see you." To my delight he came and declared that he had heard and understood what I said.           

                                     -- Alexander Graham Bell, 1876

This pivotal moment initiated the race to connect people globally via telephone. The progression began with manual switchboards, transitioned to dial-based electromechanical systems, and eventually evolved into computer-based systems. Telephone subscribers continue to increase as the world population grows [Endnote].    

In 1915, approximately 50,000 switchboard operators in North America managed telephone call routing, particularly in major metropolitan areas.  Some smaller cities had limited automatic dial exchanges, but they did not scale to metro-size. Engineers dreamed of building a large automatic switching system (10,000 lines/office with many offices) that would allow customers to dial other subscribers without operator involvement. Bell System engineers got to work and developed the “Panel Exchange”, optimized for large cities.

October 2022 was the 100th anniversary of the first 7-digit, metropolitan, Panel-type, automatic telephone exchange. It was installed in New York City and held the now famous, and still operating number, “Pennsylvania 6-5000”.   















The Panel telephone switch stands as an engineering marvel, with the relay serving as a supportive element in this electromechanical system.  The Panel system was only one of several rotary dial-based switching systems used to complete calls in the Bell System. Other exchange generations with names like Step-by-Step, Rotary and Crossbar, all relied on relays for almost all logical, counting, and routing operations.  These systems are explored in detail on this site. 


Some telephone exchange systems had up to 60,000 relays each.  Relays were in heavy use starting from the 1890’s until about 1970 when computer-based systems began their ascendency.  Visit here to learn more about relays and their place in telephone exchange history.                                  

Over the years, the Bell System manufactured ~500 million relays with peak usage in about 1970.  They were indispensable for connecting ~100 million subscribers (1970) and making ~380 million calls/day. See the Exchange Anatomy section for a deeper dive into what makes exchanges tick with lots of pictures and short videos

The Motivation

So, why was The Tribute to Telephone Relays machine made?  To showcase the electromechanical switching age -- before the transistor, before the internet, before personal computers.  It was an analog world then and the telephone network was a joy to discover and experiment with. [Meszar]

This site focuses on electromechanical telephone systems from about 1892 until the early 1960's. There is no coverage of the systems or technology that replaced it such as computerized exchanges, VoIP methods, or mobile phones. 


Check out this DIY 8-line automatic telephone system made using 53 relays and 4 rotary stepper switches and built in the 1960's. 

The Demos

If you have familiarity with electromechanical exchanges, the six demos will likely trigger some memories. However, if this is your first encounter with this technology, the demos and supporting content will give you a glimpse into the sights and sounds of telephony’s golden era. 


The device below (prototype version pictured) was built using the 5 relay families mentioned previously. The interactive demos explore telephone exchange history, with the relay as a supporting actor, with images, methods, soundscapes, and recorded voices using over 100 pieces of sound media. Take a look under the hood. 

telephone exchange diagram basic
Protpotype of Tribute to Telephone Relays

The hardware device provides users with the capability to select a demo and interact with it using five designated “control buttons.”  Additionally, the device is equipped with an attached speaker.


Here is a ~1 minute video of it in use.

For this site, you can interactively play with a virtual Tribute machine using control buttons on each demo page. 

The virtual machine uses replays of prerecorded device responses based on live user inputs.   For example,  Demo #2 lets you explore the 31 different actions that 5 relays can produce. Any demo control buttons you see in a playing video are non-responsive.  


First, try Demo #1. It’s a narrated short story of the relay and its essential place in the history of the automatic telephone exchange. It’s told in 3 parts. Total time about 6:30 minutes.

Endnote -- Who invented the telephone?

It's widely recognized that Alexander Graham Bell invented the telephone. Unless you're aware that Elisha Gray, Antonio Meucci, Johann Philipp Reis, and Amos Dolbear also may have invented it. There's even a notion of Thomas Edison's involvement. Ever since that day in February 1876 when both Bell and Gray submitted competing patent applications to the U.S. Patent Office, debates have persisted regarding the paternity of the telephone. 

The question is not easy to answer. There have been some 600 legal cases related to the invention. Bell was the victor in the cases that mattered.  Who invented the telephone has as much to do with patents, lawyers, political maneuvering, and intrigue as with inventors. 

Christopher Beauchamp, Invented by Law: Alexander Graham Bell and the Patent That Changed America, 2015. 


Meszar, J., The New Splendor of Switching, Bell Laboratories Record, Nov 1953

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