The Evolution of Annunciator Signaling for Telephones
Some of the text and images below are derived from Thomas A. Watson’s book, “The Birth and Babyhood of the Telephone", October 17, 1913.
From day one, the problem of announcing an incoming call was a challenge. What we call a telephone “bell, buzzer, or ringer” (an annunciator) would not be invented until a few years after the telephone’s invention in 1876. So how did a caller know of an incoming call? Could a pencil or hammer help? Let’s see.
Charles Williams, a business associate of Alexander G. Bell and Thomas A. Watson, is credited by Watson for using the butt end of a lead pencil to vigorously “thump” on the diaphragm of his (calling) telephone’s mouthpiece. If there was someone close to the called-telephone, the thumping sound would announce the call. This case was for a one-to-one call before the switchboard was invented.
However, pounding a pencil against the diaphragm could seriously damage the vitals of the calling-telephone and therefore wasn’t practical. Also, according to Watson, “We might have to supply a pencil with every telephone and that would be expensive.”
Hammer Signaling
Watson saw an opportunity to make improvements. He said, “I rigged a little hammer inside the box with a button on the outside. When the button was thumped (by the caller) the hammer would hit the side of the diaphragm where it could not be damaged. The usual electrical transformation took place, and a much more modest but still unmistakable thump sound would be emitted from the telephone at the other end.”
Figure 1 shows a box telephone with the Watson Hammer. Notice the push button on the lower left. A caller would operate it repeatedly and the hammer would hit the diaphragm to subsequently make a sound on the called-telephone’s ear/mouth piece. Crude, but it worked to an extent. Note that for this early telephone the mouth and ear pieces were the same transducer.
Fig 1, Box Telephone with Watson Hammer Signaling, showing a combined ear and mouth piece
Buzzer signaling
With the obvious disadvantages of the hammer method, Watson moved to devise a “Buzzer.” It was a big improvement over Watson’s hammer, but it had only a short future. According to Watson’s reminiscing in 1913, “When the caller operated the Buzzer, it made a sound (at the called side) quite like the horseradish grater automobile signal… and it aroused just the same feeling of resentment which that does.”
Confusingly, Watson’s invention was not actually a buzzer. Rather, it provided the needed high voltage to “buzz” the called-telephone’s ear/mouth piece. See Figure 2. The generator part was an adaptation of an “electric shock” machine Watson found in “Davis’s Manual of Magnetism (1842), Fig 93.”
Figure 2, Watson’s “Buzzer” voltage generator
The Buzzer operated using a swinging arm that intermittently opened and closed the battery current to the large coil. This would generate the large voltage necessary to make a loud sound at the called end. To operate the device, the caller (and operators by 1878) moved a lever from side to side, which caused flat steel spring to oscillate rapidly and thereby create current interruptions in the coil. See a picture of it as employed in George Coy’s first switchboard.
Why not use a magneto generator?
Watson may have invented his Buzzer because he was not familiar with the existing magneto-generator, or its cost was prohibitive or for some other reason. The hand-cranked device can easily generate 80 volts AC for remote signaling. The user operated magneto follows the form of a machine first constructed in 1858 by Dr. Werner Siemens, in which a cylindrical armature revolved between the poles of a horseshoe magnet. See Ref 1.
Eventually, the magneto became the standard way to “ring up” the operator or a called party. It likely replaced Watson’s Buzzer by 1881. Western Electric produced a version of the Gilliland Peg Switchboard in 1882 and it included a magneto generator for signaling. See Western Electric catalog, Ref 2. The catalog references magnetos at least eight times.
Incidentally, magnetos were in use for many years and hand-cranked by subscribers and operators alike. See Fig 3 below for a typical AC magneto generator. An operator would quickly tire of cranking one during busy hours so Western Electric and others provided water and motor-powered magnetos. Fig 4 shows six ganged magnetos driven by an external motor.
Fig 3, A 5-bar magneto from the Swedish American Telephone Company
Fig 4, Six ganged magnetos driven by an external motor (1882 Western Electric catalog)
So, solutions for the calling-end voltage generator were making good strides. What about the sound annunciator at the called-station? Watson gave this consideration too.
The invention of the telephone bell
(Some of the text below is based on materials from Exploring Life: The Autobiography of Thomas A. Watson, 1926)
Using the telephone ear/mouth piece, as described above, to announce a new call was not very practical. For one, users did not like the harsh screeching sound it made. So, Watson worked on a bell-ringing mechanism to be installed in or near every telephone. According to Watson, “It was much more troublesome to invent than my “Buzzer.”
Watson continues, “The bell had to be polarized because the received current was AC. The first bell I made was adapted from a polarized telegraph relay. It worked all right in the shop, so I made and sent out several hundred of them, but soon complaints began to pour in from the agents reciting their woes with the bell which, they said, often failed to respond to the frantic crankings [of a magneto or Watson Buzzer] of the man who wanted you.”
“It was months before I devised a reliable bell which, as General John J. Carty, vice-president of the American Telephone and Telegraph Company, told me recently, has never been improved upon in principle. That polarized ringer I devised early in 1878 does today (1926) practically all the world’s telephone calling.” How satisfying it must have been for Watson to hear Carty’s compliment.
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Watson received US patent 210,886 (filed August 1, 1878) for inventing the two-chime ringer. It consists of two closely spaced bells (sometimes of different resonance frequencies), a movable metal clapper, and an electromagnet (EM). Alternating current passed through the EM causing the clapper to alternately hit each bell. See Fig 5 with a Watson bell and included magneto (crank on right side) for calling an operator.
Fig 5, Watson-like ringer, Smithsonian Institution, circa 1885
Conclusion
Thomas A. Watson significantly contributed to the development of telephone technology starting in 1875 by assisting Alexander Graham Bell in building the first functional telephone (More about the first telephone, see Endnote). Watson invented the telephone bell (ringer) to alert subscribers of incoming calls. Additionally, he created the first hand-activated voltage generator (the Buzzer) used to loudly announce incoming calls. Watson deserves considerable praise as a visionary and clever inventor during the early days of telephony.
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References
1- Poole, Joseph, The Practical Telephone Handbook, 1906
2- Western Electric 1882 equipment catalog​