We've all been enthralled by tales of the original Phone Phreaks -- Captain Crunch, Steve Wozniak, and the Blue Boxers of Yore.
This years entry in the RetroChallenge takes a look at telephone switching equipment through the years and will involve a Western Electric Model 551(B) PBX System with a patent date of 1927 and components dating from the early 1930's. No, this is not a computer. No, the PBX itself is not Turing Complete, nor does it contain anything that could be described as a Central Processing Unit. It does, however, share a number of similarities to "modern" data processing equipment and even used a common artifact of the computer age -- the ubiquitous Punch Card.
My goal is to make this particular system "Work" -- not just to serve as a simple telephone answering point, but to examine the overall structure of the public-switched telephone network and see how it evolved from a simple manual switchboard.
Western Electric Model 551(B) Private Branch Exchange (Circa 1927)
October 6, 2021 -- An Actual Retrocomputer Makes its Appearance
October 8, 2021 -- Texas Instruments 99/4A Power Supply Issues
October 22, 2021 -- Preliminary Thoughts on Automatic Switching and Common Control
October 24, 2021 -- Switchboard Photos and Descriptive Survey (May 2021)
October 25, 2021 -- A Matrix Switch and TI 99/4A Control Software
October 27, 2021 -- DTMF Decoding Troubles and Switchboard Reconfiguration
October 2, 2021 - Common Battery Circuit and Loop Demonstration
October 3, 2021 - Telephone Magneto and Ringer Demonstration
October 31, 2021 - Video Demonstration of (Almost) Working Switchboard
GTE Automatic Electric - Catalog Section M (Station Equipment, October 1975
Service and Equipment Manual - Part IV - SWBT - Released 1949 (Switchboard Manual)
This web-page created on August 15, 2021 by Micheal H. McCabe. Last updated 10/31/2021 Original URL is http://phreak.paleoferrosaurus.com/