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Built in a 302-style case with
F1 handset. Two rows of 5 keys on
the front plucked reeds to produce two tones for each digit. 2
out of 6 frequencies. Based on a design tested at Bell Labs in 1941 and put on the shelf during World War II. The same tones were used between phone company offices for signaling among operators. Tested in 1948 on the first No. 5 crossbar switch in Media, PA with families of 35 Pennsylvania Bell employees. "The plucked reeds were found not to be stable and rugged enough to maintain adjustment with constant usage in a station environment."* After the transistor was developed, research turned to electronic oscillator designs. * A History of Engineering and Science in the Bell System, Switching Technology (1925-1975), page 166. |
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For more on the evolution of
pushbutton dialing, click here. |
