Beefchicken Industries

Northern Telecom SG-1 'Pulse' EPABX


The Northen Telecom SG-1/SG-1A "Pulse" EPABX (Electronic Private Automatic Branch Exchange) is commonly regarded as the first fully electronic PBX. The system combined digital controls with an analog speech highway. Unlike most other analog systems at the time, the SG-1 did not have a hard wired speech path. Instead, it used time division multiplexing to multiplex all voice channels onto a single pair of wires, the "speech highway".


From US patent 3,444,326

Northern Telecom's description of the technology inside the SG-1 is a mouthful: Pulse amplitude modulated time division multiplex with resonant energy transfer. The SG-1 speech highway is divided into 24 individual timeslots, with a per-timeslot sample rate of 12KHz.

My Systems

Read more about my SG-1 story here.

I have ended up with two SG-1As. This is my first, equipped for 40 lines:

This is a view of the trunk cards (brown), which control access to the central office from the local extensions. The design of the Pulse also put things like dial tone generators on this shelf. Below the brown cards are the yellow line cards. Each of the line cards serves two extensions. Some of the yellow cards are common equipment, leaving 20 actual line cards (40 lines) on each shelf. This system is equipped for 120 lines. I picked this unit up a little while after my first.

This is what the back of the shelves look like:

This is the operator's console. That big white thing coming out of it is a 150 pair (300 wire) cable that connects the console to the cabinet.


No CPU? No problem! A not-so-deep-deep-dive into the design of the SG-1.


553-5011-00079-09-04Product Index 553-5011
553-5011-10077-05-06General Description
553-5011-10177-04-01Telephone Consoles QCNIOO and QCN102 Type Description and Features
553-5011-15077-04-27Physical Description and Ordering Information
553-5011-15176-11-29Hotel/Motel Numbering Plans, Translation Tables, Ordering Information, and Records
553-5011-18077-05-10Engineering Data
553-5011-18174-11-19Line Circuit Function and Description
553-5011-18277-04-22COX/FX/WATS Trunks (Gain/Non Gain) Function Description
553-5011-18374-11-19Loop Signaling Trunk Function and Description
553-5011-18474-11-26E & M or DX Signaling Trunk Function and Description
553-5011-18574-11-27Paging Trunk Function and Description
553-5011-18674-11-25Dictation Trunk Applique Function and Description
553-5011-18772-02-18Traffic Interface Function and Description
553-5011-18874-10-23Summary Transmission Characteristics
553-5011-18977-05-13Music-On Hold CO/FX/WATS Trunk Function and Description
553-5011-19076-11-29Engineering Data (Hotel/Motel Service)
553-5011-20074-12-09General Installation Information
553-5011-20174-11-28Shipping and Receiving
553-5011-20279-09-21Assembly of Apparatus
553-5011-20376-11-29Cable Connections at the Cross-Connecting Terminal
553-5011-20477-05-06Clas-s-of-Service Selection and Feature Strapping
553-5011-20577-04-27Cable Connections to Miscellaneous Equipment
553-5011-20677-03-21Tests and Inspection at time of Installation
553-5011-20777-04-01Installation Class-of-Service and Feature Record Charts
553-5021-20878-09-29Integrated Power Shelf QSP7L- Description; Operation and Installation
553-5011-30074-11-13Console Operation and Tests
553-5011-30177-03-21Station Operation and Tests
553-5011-50074-11-29General Maintenance Information
553-5011-50177-04-27Circuit Operations and Cabinet Cabling
553-5011-50277-04-01Maintenance Aids Description and Maintenance Tools
553-5011-50374-12-11Fault Classification
553-5011-50477-05-10Control Logic Tests and Fault-Clearing Procedures
553-5011-50574-11-29Station Line Tone Fault-Clearing Procedure
553-5011-50674-11-27Ringing Fault-Clearing Procedure
553-5011-50774-11-27Station Line Transmission and/or Dialing Fault-Clearing Procedure
553-5011-50874-12-02Station Line Option Fault-Clearing Procedure
553-5011-50977-03-21Telephone consoles QCNlOO and QCN102 Type Operation, Transmission, and Traffic Measurement Fault-Clearing Procedures
553-5011-51074-12-03Telephone Console, QCNlOOB and QCN102A Mechanical Fault Repair
553-5011-51174-11-27Busy Lamp Field Fault-Clearing Procedure
553-5011-51274-08-29Outgoing Trunk Selection Fault-Clearing Procedure
553-5011-51374-11-29Trunk Transmission Fault-Clearing Procedure
553-5011-51474-12-02Incoming Trunk Call Fault-Clearing Procedure
553-5011-51577-04-27Trunk Option Fault-Clearing Procedure
553-5011-51677-04-01Power Failure and Power Fail Transfer Circuit Fault-Clearing Procedures
553-5021-51679-01-19Power Failure and Power Fail Transfer Circuit-Fault-Clearing Procedures for QSP7L Integrated Power Supply
553-5011-51777-06-09Message Registration Fault-Clearing Procedure
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