Engineering:Model 500 telephone

Short description: Type of American telephone set

Western Electric model 500 telephone made in the 1950s

The Western Electric model 500 telephone series was the standard domestic desk telephone set issued by the Bell System in North America from 1950 through the 1984 Bell System divestiture. The successor to the model 302 telephone, the model 500's modular construction compared to previous types simplified manufacture and repair and facilitated a large number of variants with added features. Touch-tone service was introduced to residential customers in 1963 with the model 1500 telephone, which had a push-button pad for the ten digits. The model 2500 telephone, introduced in 1968, added the * (star) and # (square, pound) keys.

The model 500 telephone series and its derivatives were very popular and common among North American businesses and households throughout the latter half of the 20th century. The development of new simpler telephone set designs, the advent of mobile phones, and the decline of traditional landlines into the 21st century led to the decline of the model 500 series and its derivatives, and most sets still in use are primarily kept by seniors and phone enthusiasts for familiarity, collecting, and nostalgia. However, the model 2500 is still produced by several manufacturers as of the early 2020s, with modernized components to ensure compatibility with modern Bluetooth and voice over IP telephony systems.

History

The Western Electric 500-type telephone replaced the 300-type, which had been produced since 1936. The model 500 line was designed by the firm of industrial designer Henry Dreyfuss, the product of several years of research and testing in collaboration with Bell Laboratories and Western Electric. Development started in 1946 with early sketches by Bell engineer and Dreyfuss associate Robert Hose, leading to pre-production units in 1948 and field trials with 4000 telephone sets in 1949. AT&T announced the new telephone publicly in 1949 and communicated the first availability of approximately 23,000 sets in the second quarter of 1950 to the Bell System operating companies on May 1, 1950. Third and fourth-quarter production was estimated at 49,000 and 93,000, respectively. Including 20,000 units of a special purpose set (501B), approximately 183,000 units were produced by the end of the first production year.

In the following years, the systematic replacement of 25 million 300-type telephones commenced because of the new model's much improved electrical and acoustic efficiency. This efficiency permitted the new model to be used on long rural loops, which previously required special sets with local batteries to power the transmitter, not just on urban short loops because it contained a self-adjusting gain control. This also permitted the use of thinner loop wires and thus delivered cost savings in the build-out of the network. A 1953 Western Electric ad noted that the “500” phone “has already been introduced on a limited scale and will be put in use as opportunity permits, in places where it can serve best.”

From the 1949 field trials until 1953, only black sets of the 500-type telephone were manufactured. Telephones in color were introduced in several stages from 1954 until 1957, as manufacturing capability was refined and material selection processes were completed.

Ownership and AT&T divestiture

As with most telephones in the United States, the 500-series telephones were owned by the local Bell Operating Company and leased on a monthly basis to customers. Choices for telephone styles and colors were limited. AT&T, the principal owner of the operating companies and Western Electric, strictly enforced policies against buying and using telephone sets by other manufacturers on their network to ensure the technical integrity of their network and avoid competition. Most phones made by Western Electric, starting in about 1968, carried this disclaimer molded into their housing: "BELL SYSTEM PROPERTY--NOT FOR SALE." Telephones were also sometimes labeled with a sticker or ink stamp marking the operating company's name that owned the phone. After consumers started buying telephones from other manufacturers, in the wake of legal developments not favoring AT&T's ban against third-party equipment, AT&T changed its policy for the Design Line telephone series by selling customers the telephone housing but retaining ownership of the electrical components, so customers were still required to pay AT&T a monthly leasing fee.

Design features

By 1975, the model 500 design was essentially unchanged, but it used a revised dial, modular cords, and was available in a variety of new colors.

For the initial years, from 1950 to 1953, the 500 was available only in black with a metal finger wheel. In 1954, color telephone sets were available in ivory, green, dark gray, red, brown, beige, yellow, and blue. Gray, blue, yellow, and red sets were initially assembled with black dials until the colored parts became available by 1955. So-called two-tone color varieties were available, which consisted of a black set having the housing substituted with a color plastic part. They were offered as an attractive color combination for a reduced fee from the price of a full-color telephone. In 1957, gray, blue, beige, and brown sets were replaced with lighter pastel hues in light gray, aqua blue, light beige, white, and pink colors. Issuance of brown sets continued for multi-line business sets for several years. Turquoise sets were added in 1964, and several colors, including pink and light gray, were discontinued in the late 1960s.{{citation needed|date=January 20 By 1955, all color 500s were produced with clear finger wheels, while black sets retained the metal finger wheel until about 1964 when a new dial design was released.

Construction

Internal components of a model 500 produced in 1951

The 425A network component of a model 500 produced in 1951

The 500-type telephone consists of a rotary dial, a handset cradle, switch hook, and a handset (sometimes called the receiver) wired to the base and has a molded plastic housing covering a steel chassis. The user interface consists of only the dial and switch hook buttons. No other components, switches, or controls are necessary, except a loudness control for the ringer, which is accessible on the bottom of the phone. The handset cradle is a molded part of the housing, formed of two U-shaped chairs that cradle the handset's handle between the receiver and the transmitter cups. Each side of the cradle has a round plastic plunger positioned above a pair of levers connected in a spring-loaded yoke that operated the hook switch; pressing the plungers down, end the call, and place the phone on hook. The plastic face of the dial under and surrounding the finger wheel is a part of the dial assembly and is exposed through the circular opening in the housing. On the bottom, the flat steel plate of the chassis is exposed. The handset cord exits from the left side of the housing at the base, and the line cord emerges from the rear at the base.

The telephone contains circuitry composed of many passive electrical, electronic, and mechanical components. The set does not require a separate power supply as it is receiving transmitter current from the telephone line; when it is on hook and not ringing, it uses no power, as the ringing bridge includes a capacitor for blocking direct current (DC) from the local loop.

The most complex part is the rotary dial mechanism, an assembly of gears, cams, springs, and electrical contacts which mechanically generate a timed train of line loop-break pulses when the dial finger wheel is released after windup. During the period of dial windup and return, the receiver is shunted to avoid hearing the dial pulses.

The electromechanical ringer consists of two bell gongs of slightly different dimensions to produce different pitches and a striker between them that is driven by a solenoid; when the solenoid is energized by alternating (AC) ringing current, typically about 90V at 20Hz, it strikes the two gongs alternately, producing a distinctive effect of two superimposed sounds. In telephones with a ringer loudness control, one gong is mounted off-center on the loudness control wheel; turning the wheel moves the gong toward (quieter) or away (louder) from the striker. The model 500 ringer was fairly loud and could be heard a few rooms away. The ringer could not be turned off by the user but could be disabled by an internal adjustment.

The model 500 telephone was designed for long service life. Telephones in the Bell System were owned by and leased from the telephone company, which was responsible for keeping them in good condition. The telephones were rugged and reliable and intended to last for decades with little maintenance. The 1940s-era technology of the 500 made extensive use of metal components and point-to-point wiring, and most components were modular and easy to remove and replace. The wiring system employed wires terminated with crimped spade lugs and slotted-screw terminals; most electrical connections inside the set could be disconnected or reconnected with a standard screwdriver.

Development

A 1959 Western Electric model 554 wall phone, derived from the model 500 desk phone. It uses the same internal components, dial, and handset as a desk phone.

Several telephone models were derived from the basic model 500, using some of the same components. The model 554 was a wall-mounted version. Other special-purpose models included additional features. This included phones with dial lights (500U), party line sets (501), keysets (540 and 560 series), call directors, panel phones (750 series), industrial and outdoor phones (520 and 525), and automatic dialers (660).

Other manufacturers

Cortelco model 500 rotary phone made in July 2003

Touch-tone successors

Model 1500

Western Electric model 1500D, made in March 1968 in the color aqua blue with hardwired handset and line cords

The Western Electric model 1500 telephone adapted the 500 design for touch-tone dialing with a push-button pad for the digits 0 through 9. It was produced from 1963 to 1968. In addition to the basic single-line model 1500D, the 1500-series included many related variations and special purpose models with additional features. This included sets with a headset jack, 2-line sets (1510F), key sets (1560), call directors, panel phones (1750), industrial phones (1520), and automatic dialers (1660).

Model 2500

Western Electric Model 2500 telephone, manufactured in March 1980. The front is squared compared to the model 500, and it featured modular cords.

By the late 1960s, interactive response systems in some industries required additional signaling beyond the ten digits. In 1968, the push-button dial pad was extended with two additional keys, the * (star) and # (square, pound), which marked the introduction of the 2500-type telephone. The additional keys were located on either side of the 0 button to fill the matrix of 4-by-3 keys. These keys were initially unused by most customers but would later be used for vertical service codes and voice mail menu navigation. In 1974, when modular connectors were introduced, the 2500 telephone was fitted with modular connectors on handset and line cords, resulting in type designations suffixed with M, e.g., 2500DM.

In addition to the basic single-line model, the model 2500-series included many related variations and special purpose models with additional features. This included sets with a headset jack, 2-line sets, keysets (2560), call directors, panel phones (2750), industrial phones (2520), wall phones (2554), automatic dialers (2660).

Though less common than it was in its heyday, modernized model 2500 sets are still produced by several companies as of 2024, primarily Cortelco, in numerous variants including basic sets and those with hook flash and message-waiting indicator features.

In popular culture

The Model 500 series, and its distinctive ring, are near-ubiquitous in late 20th-century U.S. and Canadian film and television. Model 500s are featured as a weapon in the movie True Lies.

See also

• Model 5302 telephone

External links

• Western Electric Model 500
• Western Electric Telephone Models