1A2 Key Telephone Systemwikipedia
1A2 Key System1A21A2 key systems1A2 key telephone system1A2 key telephones

Business telephone system

PBXprivate branch exchangekey telephone system
The 1A2 Key Telephone System is a business telephone system developed and distributed by the Western Electric Company for the Bell System.
The systems marketed in North America as the 1A, 6A, 1A1 and the 1A2 Key System are typical examples and sold for many decades.

66 block

66 block6666 type
The keyset cables were typically routed to a wiring closet or wiring panel where the Key Service Unit (KSU) was installed and were terminated on a 66 type punch block, typically a model 66M1-50.
The B style is used mainly in distribution panels where several destinations (often 1A2 key telephones) need to connect to the same source.

AT&T Merlin

MERLINAmerican Bell Merlin
The successor technologies to the 1A2 Systems include the AT&T Merlin, AT&T Spirit, and AT&T Partner systems.
It was designed at the beginning of the 1980s prior to the Bell System Divestiture as a modern electronic replacement for the dated electromechanical 1A2 Key System.

Wink pulsing

wink pulsingwinkingWink start
On 1A2 key systems or similar key-operated telephone instruments, the hold position, i.e., the hold condition, of a line is often indicated by winking the associated lamp at 120 impulses per minute.

Registered jack

RJ11registered jackRJ45
* RJ21
It is used to implement a 25-line (or less) telephone connection such as that used in the 1A2 key telephone system.

Telephone plug

telephone plugtelephone jackphone jack
*50-pin miniature ribbon connector for RJ21X, used for up to 25 lines for multiline phones such as the ITT 2564, key telephone systems such as the 1A2 Key System, and PBX systems.

Centrex

centrex
Centrex obviates the need for separate exchange lines delivered to a site for use with a 1A2 Key System or similar, or PBX.

Ringdown

ringdownPrivate line automatic ringdownnon-dialed connection
In the wire spring relay key service units of the Bell System 1A2, a model 216 automatic ringdown was used to operate the circuit.

Western Electric

Western ElectricWestern Electric CompanyWestrex
The 1A2 Key Telephone System is a business telephone system developed and distributed by the Western Electric Company for the Bell System.

Bell System

Bell SystemBellBell Operating Companies
The 1A2 Key Telephone System is a business telephone system developed and distributed by the Western Electric Company for the Bell System.

Bell Labs

Bell Telephone LaboratoriesBell LaboratoriesAT&T Bell Laboratories
Introduced in 1964, the 1A2 system represents a stage of key telephone systems development at Bell Laboratories that started in the late 1930s with the 1A Key Telephone System, and was an improvement over the 1A1 system introduced in 1953.

Nortel

NortelNortel NetworksNorthern Electric
Compatible 1A2 equipment was manufactured by competing vendors, such as Northern Telecom, Automatic Electric (GTE), ITT, and Stromberg-Carlson.

Automatic Electric

Automatic Electric CompanyAutomatic Telephone & Electric Co. LtdStrowger Automatic Telephone Exchange
Compatible 1A2 equipment was manufactured by competing vendors, such as Northern Telecom, Automatic Electric (GTE), ITT, and Stromberg-Carlson.

GTE

GTE CorporationGTEGeneral Telephone and Electronics
Compatible 1A2 equipment was manufactured by competing vendors, such as Northern Telecom, Automatic Electric (GTE), ITT, and Stromberg-Carlson.

Model 500 telephone

model 500 telephone2500500-type telephone
The most commonly used telephone sets for the 1A2 systems were modifications of the Bell System standard 500-series telephones for rotary dial systems, and the 2500-series Touch-Tone desk sets.

Power supply

power supplypower suppliesPSU
A power supply was either mounted within the panel or separately nearby.

Interrupter

interrupter
Lamp and signaling voltages were routed through a mechanical interrupter, to create lamp flash (incoming line), lamp wink (hold), and interrupted buzzer and ringing.

Tip and ring

tip and ringpair of wirestip
For each telephone line from the central office, a key system required five pairs of internal wires: The central office tip and ring leads, the station (telephone instrument) tip and ring wires, the A and A1 control leads, lamp power and lamp ground, and the ring signaling pair.

25-pair color code

25-pair color codeeven-count color codebinder
Most keysets with up to nine lines are connected to the system using a single 25-pair cable terminated with an Amphenol 50-position "MicroRibbon" connector.

Amphenol

Amphenol JaybeamAmphenol Corp.
Most keysets with up to nine lines are connected to the system using a single 25-pair cable terminated with an Amphenol 50-position "MicroRibbon" connector.

Micro ribbon connector

micro ribbonminiature ribbon connectormicroribbon
Most keysets with up to nine lines are connected to the system using a single 25-pair cable terminated with an Amphenol 50-position "MicroRibbon" connector.

Punch-down block

punch blockpunch-down blockpunch down block
The keyset cables were typically routed to a wiring closet or wiring panel where the Key Service Unit (KSU) was installed and were terminated on a 66 type punch block, typically a model 66M1-50.