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Table of Contents for the Tribute to Electromechanical Exchanges site -

Topic and Description page: This website explores the golden age of electromechanical telephone exchanges with six hands on interactive demos. Using over 100 pieces of media and many pictures, users can interact with five relays and see their place in telephone system history. all-relay telephone exchange only used relays to make the talking path connection. There were two versions, one by the North Electric Company and one by Berulander and Palmgren of R.A.T Company. This page explains both systems and compares them.    

                                                             on the basics of electromechanical telephone exchanges. Including Panel, 7A Rotary, Crossbar and Step-by-Step (Strowger) switching methods.

All the key components are outlined including batteries, switching fabrics, common control,   dial control. Exchange architecture is explained with demos of exchange parts with explainer videos and many pictures electro-mechanical telephone exchanges use "common control" for controlling switching operations. Examples are provided for Panel and Crossbar systems using senders and markers. Common control is compared to "progressive dial control" for SxS exchanges Connolly brothers and McTighe patented the first dial driven switch for a telephone exchange in 1879 with images. This section is an explainer for the development of the Tribute to Telephone Relays demo device. for how the Number 5 Crossbar exchange works. This section is a short review of the crossbar exchanges designed by Bell engineers and installed in the telephone plant from 1933 to 1978 (last install). It is presented as a genealogical "family tree" for exchanges. There is a picture gallery with family portraits. page explains the invention of the telephone crossbar switch. Reynolds and Betulander's crossbar invention are explained. History, videos, images interactive demo for appreciating the value of telephone relays and electro-mechanical, vintage exchanges. This is a six min voice narration explaining the brief history of telephone exchanges and their relays. codes: Anything a modern computer can do, its relay-based cousin can do. Just much slower. Many operations need > 5 relays so the examples in this demo are illustrative only. The Demo sounds are meant for fun. Explore 31 combos of relay operations, each combo playing a different sound. Fun for kids. Office Equipment Sounds. Listen to nine recordings of sounds recorded inside a CO. intercept message is a recorded announcement concerning the status of the call. These messages were used extensively in the Bell System. Listen to the famous voices of Mary Moore, Jane Barbe, and Pat Fleet. themed remixes. Listen to Madonna, Jane Barbe, Lily Tomlin, Evan Doorbell, “relays dreaming” and more. The pieces are a fusion of telephone system sounds, voices, messages and music. A rare genre for those who appreciate vintage telephone systems. 

There are also seven other Evan Doorbell remixes. Contact the author for the secret access code. to the music -- It's a fun take on relays jiving to the music. with six interactive demos related to electromechanical telephone relays. With over 100 pieces of media learn about the golden age of relay-based telephone exchanges. This is an index to the six demos. STEM 8-line automatic telephone system. 54 relays and 4 rotary selector switches with line finder and final connector. Explainer for this hand built system . Entry in San Francisco Science Fair in 1960's. engineer E.B. Craft invented the flat spring telephone relay and became the president of Western Electric. for this 500 point polar coordinate telephone switch. It was used in electromechanical exchanges worldwide 100 point electro-mechanical switch to replace a stronger type in a SxS office. It had 2 degrees of linear motion so called the XY coordinate switch. It was originally designed by LM Ericsson in Sweden. Stromberg Carlson licensed the design for use worldwide. Doorbell, a pseudonym, was a 1970's explainer of electro-mechanical exchanges and their sounds and operations. He has a golden voice and recorded many hours of calls on panel, sxs and crossbar offices world of vintage electro-mechanical telephone exchanges is explored. Explanations of Panel, 7A Rotary, Step-by-Step and Crossbar is provided with many pictures and explainer videos.

~50 different explainer topics are explored. This is the main page that has links to many other topics using a graphical "map". basic ideas for how a call is made. Several "floorplans" are outlined showing the switch hierarchy for making a call. Starting with a 1-digit system, then 2-digits, then 3-digits, the switch train is explained. 

These ideas are the foundation for how Panel, 7A Rotary Crossbar and Step-by-Step systems are designed. for how the 7A rotary telephone exchange works with images and videos. Demo of the Ferrymead exchange system at Christchurch, New Zealand. are a network of switches and telephone systems depend on them for making the talking paths. The crossbar switch is used an example of building a network fabric for an exchange. telephone switch developed in Germany 1920's. Similar to the panel switch, motor driven, used gravity and a governor to time the brush stopping synced with the dial pulses. Known as the "falling selector" switch pictures of 8-line DIY 8-line telephone system built in SF in the 1960's, STEM project with 54 relays and 4 stepper switches. Was displayed at the San Francisco Science Fair at the Academy of Sciences in Golden Gate Park. Keith reinvented the first Strowger telephone exchange switch. These pages explain the basics of his switch design and how it improved on Strowger's original design. This design became the workhorse for SxS systems worldwide. Line Circuit is essential for all electro-mechanical telephone exchanges. It sits at the edge of the exchange and provides the logic to connect the phone to the switching system. It uses the Line (L) and Cutoff (CO) relays Lorimer brothers patented important switch technology for automatic telephone exchanges. These ideas others leveraged to build more practical designs. more button leads to a menu for; contact; credits; motivation, search and the Teleharmonium all related to electro-mechanical telephone switched systems about the motivation for designing and building the 5-relay based demo device. Also, explore how vintage telephone exchanges worked with many reviews of telephone switches including panel, crossbar, rotary, Strowger type and 10 other less popular switches. 5 Crossbar block diagram in high resolution. See the details for a complete electromechanical telephone exchange. first 7-digit electromechanical Panel telephone exchange was installed in NYC Oct, 1922. This is an explainer article with images. of components for electro-mechanical telephone exchanges incuding; ringing machines, wiring and structural support, power rooms, backup,  and battery rooms and testing methods to keep the exchange working 24x7. for how a panel telephone exchange works using images and videos. panel telephone switch is explained with pictures and videos. This switch was a workhorse in metro exchnages in North America from ~1921 until the 1960's. page reviews odd and pecular methods to make switch connections for an automatic telephone exchanges. All these methods were not sucessful but advanced the state of the of art for exchange switching. page explaines the equipment need to operate a vintage telephone exchange power toom including AC to DC generators for charging, backup gas powererd generators and large 77 ton 48 volt battey systems. relays are explained with pictures. Coverage of type E, R, U, UB and wire spring types. Simple circuits are provided showing the value of a billion relays used in electro-medhanical telephone systems. exchanges needed ways to generate ringing voltage, call-progress tones and interupters for ringing and busy tones. Electric 7A rotary switch explainer. Coverage and video demos of the Ferrymead (Christchurch NZ) display system. summary of the first rotary dial phones. A few pictures of classic phones and some reimagined telephones including one designed by Leonardo DaVinci and one from Einstein. the basics of rotary stepper switches. A clear explanation of their operation and how they are used in small telephone exchanges (PBX). See a short video on a stepper in operation. Plus a video showing a relay tester appliance. signs from the 1960's SF Bay Area Science Fair. They provided demo information on how a DIY 8-line telephone system operated. STEM project this site for words relay sequence diagram for a 8 line DIY telephone system, STEM, with 54 relays and  stepper switches switches are explained as used in the 7A rotary and panel telephone exchanges. Invented by F. McBerty of western electric. With explainer videos. Storwger built the world's first practical telephone switch and excyhange. This page explaines how the switch works, examines Strowger's patent for it, reviews how it was different from previous switches. page explores 15 different core (plus derivitives) telephone exchange switch types including: 7A Rotary, All-relay, Connolly brothers switch, Crossbar, Ericsson 500, first Strowger, Fallwähler Switch, Keith's plunger, Keith's Strowger (SxS), Lorimar switch, Panel, Sequence, Solo rotary, Ericsson/Stromberg Carlson XY, Zither.

Each switch is explained with a history, images/videos. of the Keith Line Switch - operations and pictures with videos. Keith was the first to design a "line concentrator" for improving exchange switching efficiency. It was the forerunner of the Line Finder. Strowger built the world's first automatic telephone exchange in La Porte Indianna in 1892. This page has images and history of the automatic exchange. The La Porte office was an "Exchange Lab" and had 5 different systems in a period of a few years. step-by-step (SxS) telephone exchange is explained with images and videos. of the Telharmonium streaming music machine. Cahill was the inventor of the first electronic music symthesizer using electromechanical parts. It shares much in common with telephone exchange technology so is included on this site. telephone exchanges needed large maintenance systems for repairing and testing the switches and relay-based components. This page explains how they work with examples and images for panel and crossbar exchanges. Overview of toll switching networks for long distance calling. Aspects of toll traffic are reviewed including office classes 1-5, and examples of how tandem exchanges switched toll calls. Voice transmission suffers at least 7 different impairments when travelling over local and toll lines. This section reiews each impairment with audio examples to demonstarte what the impairment actually sounds like. section reviews Traffic Engineering principles for vintage telephone exchanges. It covers how Erlang, Poisson and Molina developed equations to assist traffic engineers to design cost effective systems. It reviews the key metrics and provides examples with many diagrams and charts. offices were tied together using trunk lines. This enabled a connected network of smaller telephone exchanges to create the PSTN Reley Tribute demo system is expanded upon with closeup pictures. overview of how the 8-line automatic telephone system works, with many pictures and explanations. It was a DIY STEM project. section explores the wiring and structural framing of vintage electro-mechanical telephone exchanges. Learn about wiring measured in "miles per foot" and some metrics for installing a panel system. Keith invented the Zither or Piano Wire telephone switch. It could support 100 telephones. This page explains how it works and discusses the pros and cons of the device. This switch was a forerunner of an improved Strowger switch.

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