1A2 Key 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.

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.

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.

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.

* RJ21

It is used to implement connections for up to 25 lines, or circuits that require many wire pairs, such as used in the 1A2 key 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 1A2 Key Telephone System is a business telephone system developed and distributed by the Western Electric Company for the Bell System.

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.

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

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

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

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.

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

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

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.

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.

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.

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.

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.

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

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.

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.

*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.

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