History Of Teletype Development

R. A. Nelson

K. M. Lovitt, Editor

October 1963 Teletype Corporation 5555 West Touhy Avenue Skokie, Illinois



The success of the modern teletypewriter began with Howard L. Krum's conception of the start-stop method of synchronization for permutation code telegraph systems. The purpose of this paper is to provide a brief historical account of events which led to that achievement and of those which ensued.

Four areas of development will be covered:

(1) The contributions of Sterling Morton, Charles L. Krum and Howard L. Krum. (2) The contributions of E. E. Kleinschmidt. (3) The contributions of AT&T and Western Electric. (4) The contributions of L. M. Potts



Area I. In 1902 a young electrical engineer named Frank Pearne solicited financial support from Joy Morton, head of the Morton Salt interests. Pearne had been experimenting with a printing telegraph system and needed sponsorship to continue his work. Morton discussed the matter with his friend, Charles L. Krum, a distinguished mechanical engineer and vice president of the Western Cold Storage Company (which was operated by Joy's brother, Mark Morton). The verdict for Pearne was favorable, and he was given laboratory space in the attic of the Western Cold Storage Company.

After about a year of unsuccessful experimenting, Pearne lost interest and decided to enter the teaching field. Charles Krum continued the work and by 1906 had developed a promising model. In that year his son, Howard, a newly graduated electrical engineer, plunged into the work alongside his father. The fruit of these early efforts was a typebar page printer (Patent No. 888,335; filed August 22, 1903; issued May 19, 1908) and a typewheel printing telegraph machine (Patent No. 862,402; filed August 6, 1904; issued August 6, 1907). Neither of these machines used a permutation code.

They experimented with transmitters as well, applications filed in 1904 and 1906 maturing into Patents No. 929,602 and No. 929,603. These patents covered modes of transmission which depended both on alternation of polarity and change in current level.

By 1908 the Krums were able to test an experimental printer on an actual telegraph line. The typing portion of this machine was a modified Oliver typewriter mounted on a desk with the necessary relays, contacts, magnets, and interconnecting wires (Patent No. 1,137,146; filed February 4, 1909; issued April 27, 1915). As a result of the successful test of this printer, Charles and Howard Krum continued their experiments with a view to developing a direct keyboard typewheel printer.

They sought most of all to discover a way of synchronizing transmitting and receiving units so that they would stay "in step." It was Howard Krum who worked out the start-stop method of synchronization (Patent No. 1,286,351; filed May 31, 1910; issued December 3, 1918). This achievement, which more than anything else put printing telegraphy on a practical basis, was first embodied (for commercial purposes) in the "Green Code" Printer, a typewheel page printer (Patent No. 1,232,045; filed November 28, 1909;issued July 3, 1917).

The transmitters first used by the Krums were of the continuously- moving-tape variety. (A stepped tape feed, they maintained, would have reduced transmission speed.) In order to permit sequential sensing, the rows of code holes were arranged in a slightly oblique pattern (with respect to tape edges). This method of transmission is more fully elaborated in Krum Patents No. 1,326,456, No. 1,360,231, and No. 1,366,812.

Keyboard-controlled cam-type start-stop permutation code transmitters were developed by Charles and Howard Krum in about 1919. Such a device is the transmitter component of the Morkrum 11-Type tape printer (Krum Patent No. 1,635,486). This kind of transmitter employs a single contact to open or close the signal line.

In about 1924 the Morkrum Company introduced the No. 12-Type tape printer (H. L. Krum Patent No. 1,665,594). On December 23, 1924, Howard Krum and Sterling Morton (son of Joy Morton) filed an application on the 14-Type type-bar tape printer which matured into Patent No. 1,745,633. [1]

Area II. It appears that the early efforts of E. E. Kleinschmidt were directed toward development of facsimile printing apparatus and automatic Morse code equipment. He patented first a Morse keyboard transmitter (Patent No. 964,372; filed February 7, 1095; issued January 11, 1910) and later a Morse keyboard perforator (Patents No. 1,045,855, No. 1,085,984, and No. 1,085,985). (The latter became known as the Wheatstone Perforator.)

In 1916 Kleinschmidt filed an application for a type-bar page printer (Patent No. 1,448,750 issued March 20, 1923). This printer utilized Baudot code but was not start-stop. It was intended for use on multiplex circuits, and its printing was controlled from a local segment on a receiving distributor of the sunflower type. Later, around 1919, Kleinschmidt appeared to be concerned chiefly with development of multiplex transmitters for use with this printer (Kleinschmidt Patent No. 1,460,357).

It seems that Kleinschmidt first became interested in modern start-stop permutation code telegraph systems when H. L. Krum's basic start-stop patent was issued in December 1918. Shortly after that Kleinschmidt filed an application entitled "Method of and Apparatus for Operating Printing Telegraphs" (Patent No. 1,463,136; filed May 1, 1919; issued July 24, 1923). The system described therein employed the start-stop principle with a modified version of his earlier multiplex distributor. That patent, accordingly, was dominated by the Krum start-stop patent. The conflict of patent rights between the Morkrum Company and the Kleinschmidt Electric Company eventually led to a merger of the two interests.

Shortly after the new Morkrum-Kleinschmidt Corporation (later called the Teletype Corporation) had been established, Sterling Morton, Howard Krum, and E. E. Kleinschmidt filed an application covering the commercial form of the well-known 15-Type page printer (Patent No. 1,9904,164). [2]

Area III. Teletype entered the Bell System in 1930. From this point on, advances in the Teletype product can be considered the result of the pooled efforts of the AT&T Company, the Western Electric Company, and the Teletype Corporation. Teletype Corporation, of course, holder of the basic patents and expert in the art, was the chief contributor.

Although it appears from the report of R. E. Pierce, dated December 24, 1934, that the Bell System was active in the development of telegraph printers and transmitters as early as the year 1909, a review of the patents issued to Bell reveals no significant contribution to modern teletypewriter development (using start-stop permutation code) until the introduction in 1920 of the 10-A teletypewriter (Pfannenstiehl Patents No. 1,374,606, No. 1,399,933, No. 1,426,768, No. 1,623,809, and No. 1,661,012).

The 10-A teletypewriter was the first embodiment of such basic design features of the 15-Type printer as stationary platen, moving type basket, and selector vane assembly, but the majority of improvements incorporated in the 15-Type were proprietary to the Teletype Corporation.

Area IV. The earliest contribution of Dr. L. M. Potts to the start-stop method of synchronization appears to have been set forth in a patent application filed November 18, 1911, covering a reed-type start-stop selector (Patent No. 1,151,216).

In 1914, Dr. Potts filed an application for a single magnet page printer which used an eight-unit code (Patent No. 1,229,202; issued June 5, 1917).

In 1915, Dr. Potts filed an application covering another single magnet page printer, this one using the start-stop permutation code (Patent No. 1,370,669; assigned to AT&T March 8, 1921).

Potts Patents No. 1,517,381 and No. 1,570,923 were also assigned to AT&T.


[1] For anyone who is old enough to have seen a Western Union Telegram where the typing is on narrow gum-backed tape that is moistened and stuck to a telegram blank, this is the machine that produces that kind of printing. The same mechanism is the basis of a typing reperforator, a machine which punches received signals into a tape for retransmission and also types on the tape so an operator can read it.

[2] This is the machine used until the 1960s or so by the news wire services. Some radio stations still use a recording of the sound of one of these machines as background during news broadcasts.


AT & T Telegraph Service

BASKING RIDGE, N.J. -- Familiar to the world over through the clickety-clack of ticker tape machines and teletypewriters, telegraphy has been gradually bowing out of the telecommunications picture during the last twenty years.

The nonstop chatter has been replaced by the hum of laser printers and the electronic beeps on computer screens. AT&T, a leading innovator and major service provider of telegraphy, announced this year it is withdrawing the service due to the universal availability of lower-cost, higher quality digital telecommunications services.

"The incredible advances in our industry means customers can get more for less," said Wes Bartlett, AT&T district manager, Business Communications Services. "Today's digital technology can transmit information hundreds of thousands times faster than telegraphy and is considerably more cost-effective for users.

"Telegraphy has been to the twentieth century what state-of-the-art digital telecommunications services will be to the next century," Bartlett added. "We are proud of our contributions in both areas."

The transmission of telegraph service is based on analog technology, which sends information by continuous electrical waves. Today's digital technology breaks information into its smallest components, the binary "ones and zeros" of computer language.

However, telegraphy was the actually the first digital service -- although a very simplified version compared with today's technology -- since it was produced on the customer's premises in terms of "on or off," or "dash or space." It was converted to analog for transmission.

Telegraphy usage accelerated rapidly during the 1920s when the financial industry adopted the technology to send records of transactions. At this time, news organizations began using telegraph service for transmitting stories between offices.

In November, 1931 the Bell System inaugurated the teletypewriter exchange service, often called the TWX (pronounced "twicks") service. It provided a complete communications system for the written word, including teletypewriters, transmission channels and switchboards.

Telegraphy was adopted by many kinds of businesses, including utility companies, alarm companies, airlines, and brokerages as well as government agencies. It was used heavily through the 1960s.

Most of AT&T's telegraph service customers have been converted to digital private line services such as DATAPHONE (R) Digital Service and ACCUNET (R) Spectrum of Digital Services.

"Our name remains American Telephone and Telegraph," Bartlett said. "It is an historic name and our legacy. We are proud to have a corporate name that spans generations of communications technology.

"Despite rapid technological change, AT&T remains focused on helping people communicate," Bartlett added. "Telegraphy helped bring us to this point. Digital technology is taking us into a new era of global messaging."


Telegraph service made it possible to communicate large volumes of information between two or more locations. Telegraph circuits permitted customers to send to each other a printed or hard copy version of the information at reasonable cost, which was impractical with the telephone.

A telegraph circuit consisted of four components: station equipment installed on the customer's premises, such as a teletypwriter and teleprinter; the local loop, or wires, between the customer location and the AT&T central office; the central office equipment in the AT&T telegraph serving test center (STC); and the wires connected to the telegraph STC serving the other customer.

Here's how it worked: Customer A sent information to customer B by typing the information on a teletypewriter keyboard. The teletypewriter converted the message to a coded signal which was sent out on the local loop to the STC and central office equipment. There the signal was converted to make it compatible with the carrier's lines and sent on to the STC serving the distant city. The central office equipment then converted the signal again and sent it over the local loop to customer B's teletypewriter which decoded the signal and printed the information.

The procedure was reversed if customer B wanted to send information to customer A. This method of sending information, where only one station could send at a time, was accomplished over a simple half-duplex, or two-wire circuit. When both customers wanted to send and receive at the same time a full-duplex, or four-wire circuit, was used.

At its peak in 1970, telegraph service could transmit data at 150 bits per second.

AT&T and Telegraph Service

1887: First private-line telegraph service, for L. H. Taylor & Co., brokers, between their offices in New York and Philadelphia.

1888: First service for news media customer, Globe Newspaper Company, between New York and Boston.

1915: Teletype offers speeds of 30 or 50 words per minute.

1920s: Press and financial markets create a boom for usage of the service.

1939: Speed reaches 75 words per minute.

1944: Speed reaches 100 words per minute.

1957: Teleprinter introduces speeds of 300 words per minute.

1970s: Decline in usage begins as electronic data processing replaces many telegraph functions.

1980s: Wireless and digital methods accelerate decline.

1991: AT&T exits telegraph service.


A Little More TWX History Message

Telecom-Digest: Volume 13, Issue 151

Well of course the original TWX goes back to about 1930, used 3-row machines, and manual switchboards. In fact the introduction of TWX was what caused AT&T to buy the Morkrum-Kleinschmidt Corp. and rename it Teletype. At the time the service was provided using telegraph-grade circuits. You'll occasionally see a picture of an old TWX switchboard, maybe in an old encyclopedia. The switchboard operators used tape-strip printers to communicate with the customers. Telex was in use in Europe in about the same time frame, and used SXS switching technology and telegraph-grade circuits.

Western Union introduced Telex to the U.S. in the early 60s. This was probably a bad mistake for them.

1) They had to buy a lot of electromechanical switching equipment which was soon to be obsoleted by electronic switching.

2) AT&T was about to move TWX to the voice switched network, where the enormous volume of voice service had driven the cost of connections and bandwidth way down. The telegraph-grade lines were no longer cheaper than voice circuits; they were in fact more costly to AT&T.

3) It put W.U. into practically head-to-head competition with an AT&T service; and AT&T was a much stronger company financially.

4) W.U. was usually dependent on the telephone companies for local loops between customers' offices and the nearest W.U. office. Thus W.U. was at the mercy of its competitors rates for these private lines.

As an aside, European Baudot machines tended to have four-row keyboards. The digits were on the fourth row, like a typewriter. There were blocking bars such that if the machine was in FIGS case the digit keys were unblocked and the corresponding letters keys were blocked. So the user still had to send FIGS and LTRS as in the U.S.; it was just that the European machine design took a slightly different direction from that in the U.S.

The European machines also tended to have built-in paper tape facilities of the limited sort that Teletype introduced into the Model 32 and 33 machines. In previous Teletype designs the paper tape equipment was mechanically independent of the keyboard and printer. You could, for instance, be punching a tape from the keyboard at the same time you were receiving a message on the printer; and you could be sending from tape at the same time you were punching another tape from the keyboard. In the European machines, and later in the Teletype 32 and 33, the tape punch had some parts in common with the printer and the tape reader shared some parts with the keyboard. Hence you couldn't use the keyboard while sending from tape; you couldn't punch a tape from the keyboard while printing something else, etc.

The Teletype Model 15 has been mentioned as a heavy-duty machine dating from 1930. In the late 1930s some of the Bell companies asked for a less expensive machine for TWX service, recognizing that a lot of offices could use TWX but didn't need the heavy-duty machine. (The Model 15 is what was used for AP and UP news wires through the 1950s. It could stand up to the around-the-clock printing that occurs in that service.) The answer to this request was the Model 26. The 26 used a rotating type cylinder holding individual slugs of type. The cylinder stayed in one place and the paper platen moved from side to side as in a typewriter. (In the Model 15 and the later machines the paper platen is stationary and the printing element moves across the page.)

The Bell System phased out the Model 26 machines in, oh, the late 40s and 50s. The machine didn't save enough in first cost to be worth supporting both it and the Model 15 in terms of parts and maintenance training. Lots of Model 26 machines wound up in amateur radio service. The hams formed organizations to plead with the Bell companies to sell their used machines to hams rather than breaking them up (to prevent their falling into the hands of those who would use them in competition with Bell services). Hams had to sign a legal form to the effect that they would not use the machine outside the hobby, and would not sell it to anyone without requiring a similar promise.

In the late 50s and early 60s came all the work that resulted in ASCII -- first the upper-case-only 1961 ASCII and then the up/low 1968 ASCII. Prior to ASCII there were lots of codes floating around. Teletype made the Model 29, which was an eight-level four-row machine working on one of the IBM BCD codes. I believe this was used only internally in Western Electric; AT&T was scared to put an IBM coded machine out to the public lest non-IBM computer makers complain that the AT&T giant was favoring the IBM giant at their expense. The Model 35 was based on the 29; in fact I'm aware of some people converting 29 printers to ASCII by changing just a few parts. Many parts were common between the five-level Model 28 and the eight-level Model 35.

The Model 32 and 33 machines actually started as a project to develop a light-weight machine for the military. The light-weight project didn't get very far; but a lot of the ideas wound up being used in the low-cost printer project. Again the Bell companies and Western Union saw a need for a machine that would cost a lot less than the heavy-duty machines, for use in offices that didn't have a lot of traffic. I might mention that Western Union dabbled in making its own teleprinters from time to time; occasionally one will see a sample of their Model 100 family. I believe W.U. was the main customer for the 32, for Telex service and the Bell companies were seen to be the main customers for the 33 for the new four-row dial TWX service. These machines had most of the parts in common. They were available with and without paper tape; where paper tape was present it followed the European style, so you couldn't do all the things with these machines that you could with a 28 or 35.

The design objective for the 32 and 33 was that they would be used on an average two hours per day. Cost was held down by not heat treating and hardening and nickel plating the parts; some adjustments were made by bending parts rather than by moving parts on elongated holes and that sort of thing; assembly was designed for high volume with a die cast base and self-tapping screws and parts that snapped together without bolting. Meanwhile along came the minicomputer companies who adopted the 33 as a console device, where it often ran around the clock (and generated a lot of cursing about the frequent need for maintenance).

For manual TWX Teletype supplied a basic machine to the phone company, which added some kind of Western Electric box on the wall for line interface. This might be a carrier channel terminal or some relays for a D.C. line; and there were schemes where ringing was used to control the motor on the Teletype machine, and schemes for cutting off current in the line when it was not in use. Telex and dial TWX required additional components for setting up and controlling the call. The Model 32 for Telex had a built-in Call Control Unit with a dial and line relays, all ready to connect to the D.C. local loop. For dial TWX there was a Western Electric modem stashed in the Teletype stand and a variety of call control units (pulse dial, tone dial, card dialer, loudspeaker vs. earphone, etc.) made by Teletype and connecting to the modem. This was a source of considerable annoyance to Teletype, as the interface involved 99 wires, each of which was negotiated between the modem designers at Bell Labs and the call control unit designers at Teletype. A little later some of the Bell companies would save money by furnishing a Bell modem with built-in telephone connecting over a few-wire cable to a Teletype private-line-version machine having no call control unit.

There is a lot of weird and interesting (perhaps) lore connected with the modems. Since dial TWX used a voice-bandwidth connection they could afford the luxury of full duplex modems using two different frequency pairs for the two directions of transmission. This introduced the complexity that a modem had to know whether it was originating or answering a call to know which pair of frequencies to use for which purpose. Even after Bell began supplying modems for connection of customer-provided data equpment (just before Carterfone) these modems could function in either originating or answering roles. After Carterfone the suppliers of modems for computer time sharing could take advantage of the fact that the terminal always originated and the computer always answered; so we got reduced cost originate-only and answer-only modems.

It always seemed to me that the TWX section of Bell Labs was controlled by old geezers who had been around since 1930 and couldn't imagine that a TWX machine would ever want to talk to anything except another TWX machine. If you wanted to use the same kind of Teletype machine to talk to a computer, well that was another matter entirely. The modems had separate originate and answer frequency pairs, each binary FSK. This permitted two options for which frequency pair would be originate and which would be answer, and four possiblities (two for each pair) of which frequency would be mark and which would be space. Thus it was possible by wiring options to set modems up for as many as eight mutually-incompatible services, all using the same voice switched network without any restrictions on area codes and numbers. I remember hearing about TWX, and TWX-prime, and WADS (wide area data service) and WADS-prime, all of which were to use the same modems and switched network without any of these being able to communicate outside its own service. I guess they had in mind different tariffs for TWX machines talking to TWX machines versus terminals talking to computers, versus some other things. Practically all of this was swept away by Carterfone.

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