The Automatic Electric Company was the largest manufacturer of rotary stepping telephone switching systems. Their products defined how telephone exchanges worked for most of the twentieth century. Although electronic telephone exchanges began to show the way to the future in the 1970’s, it wasn’t until the digital switching revolution of the late 70’s and 80’s that saw most mechanical switching systems being replaced. A few step-by-step switching systems remained into the 1990’s in the U.S., but were entirely gone by 2000.
Even with digital switching systems, most of the subscriber lines and telephone sets remain analog today. How they work, and why they work the way they do, is a direct result of work that was done a century ago to develop the dial telephone and automatic telephone switching systems.
Automatic Electric was very good at producing technical bulletins that not only served as great reference material when performing a specific maintenance task, but also served to teach theory of how telephone switching systems worked. Here is a collection of those technical bulletins, including some that provide a great introduction to analog telephony. Anyone interested in basic electronics or electromechanics will find these documents useful.
- TB 505 – Lubrication of Automatic Switching Equipment
- TB 543 – Operating and Service Inspections for Automatic Central-Office Equipment
- TB 945-800 – Electrical Principles of Telephony
- TB 945-801 – Mechanical Principles of Telephony
- TB 945-802 – Fundamentals of Apparatus and Trunking
- TB 945-804 – Ringing Schemes
- TB 945-806 – The Rotary Lineswitch
- TB-945-807 – The Connector