Model 500 telephone
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 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.
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.
[2] 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.
[citation needed] 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.”[4] The replacement of 300-series telephones with 500-series sets created large stockpiles of 300-type components that had not reached their intended service life.
It was produced until the mid-1960s in the refurbishing shops of each Bell Operating Company, not on the assembly lines of Western Electric factories.
Telephones in color were introduced in several stages from 1954 until 1957, as manufacturing capability was refined and material selection processes were completed.
[5] In the 1960s, after the introduction of touch-tone service in November 1963 in various locations of the telephone network, the basic 500-type chassis was retrofitted with a new housing and face plate, and a ten-key push-button keypad.
Most phones made by Western Electric, starting in about 1968, carried this disclaimer molded into their housing: "BELL SYSTEM PROPERTY--NOT FOR SALE."
The earlier 302 had been equipped with an enamel-coated dial plate that displayed the numerals and letters through the holes of the rotary finger-wheel.
The earliest experimental touch-tone phones used the original Dreyfuss design almost unchanged; the keypad, in varying layouts, was placed in a roundel in the dial opening, with the subscriber number label in a small window below.
In 1954, color telephone sets were available in ivory, green, dark gray, red, brown, beige, yellow, and blue.
[6][7] Gray, blue, yellow, and red sets were initially assembled with black dials until the colored parts became available by 1955.
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.
Starting in 1955, all sets, except dark blue were equipped with color-matched cords as dyes and manufacturing methods became stable.
For the trial period, the dial was replaced with circular closure containing a keypad and a telephone number label.
[citation needed] Standard touch-tone telephones generate twelve DTMF signals in a grid of three columns and four rows of buttons.
In contrast, some special purpose telephones are equipped with a fourth column of keys for the A, B, C, and D DTMF signals for service priorities in the AUTOVON system.
While faithful from a cosmetic point of view, they are internally very different from the original, including a rotating tone dialer based on optical technology.
[citation needed] 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.
In 1968, the push-button dial pad was extended with two additional keys, the * (asterisk) and # (pound), which marked the introduction of the 2500-type telephone.
These keys were initially unused by most customers but would later be used for vertical service codes and voice mail menu navigation.
