1A2 Key Telephone System

1A2 Key System1A21A2 key systems1A2 key telephones
The 1A2 Key Telephone System is a business telephone system developed and distributed by the Western Electric Company for the Bell System.wikipedia
25 Related Articles

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.

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.
After the breakup of AT&T in 1984, it was rebranded AT&T Merlin. 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.

66 block

6666 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.

Wink pulsing

Wink startwinking
Lamp winking fast: A call on the line is "on hold"
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

RJ11RJ45RJ-45
* RJ21
It is used to implement a 25-line (or less) telephone connection such as that used in the 1A2 key telephone system.

Western Electric

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

Bell System

BellBell Operating CompaniesBell Telephone
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

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

GTE

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

Model 500 telephone

2500500-type telephone1500
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 suppliesPSUpower supply unit
A power supply was either mounted within the panel or separately nearby.

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

pair of wiresR and Ttip
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 cable25-pair colour 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 Corp.Amphenol Jaybeam
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
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.

Music on hold

hold music.mohMOH
Key telephone systems also supported manual buzzers, intercom lines (with or without selective ringing), music on hold, and other features.

Backplane

backplanesmidplanebackwiring boards
The features were provided on a line-by-line basis by the selection of particular Key Telephone Units (KTUs) plugged into a pre-wired backplane in the central control unit.

Telephone hybrid

hybridhybrid circuits
This is because, being analog, they are easily connected through a telephone hybrid into the studio's audio equipment for switching calls into broadcast signals.

List of telephone switches

MD110/MX-ONENECTadiran Telecom
1A2 Key System (Electro-mechanical Key System made by Western Electric)

Telephone plug

telephone jackphone jackjack
*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.

Ringdown

Private line automatic ringdownmagneto crank telephonessecure line
In the wire spring relay key service units of the Bell System 1A2, a model 216 automatic ringdown was used to operate the circuit.