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Besides Siemens-Halske, there have been other manufacturers of teletype machines that use the Hellschreiber printer principle. Presented below are the ones for which I have pictures and/or other information.

If you have any additional information or documentation on these machines (or on other Hellschreibers from other manufacturers), please contact me.

 [LMT]       [Teletype Model 17]        [EMA]          [PTW]        [NVA Hellschreiber]             

[TTK/Sony]     [Toho Denki K.K.]     [Thomson]     [RCA]     [F.I.A.T.]     [British Post Office]

[RC-58-B (BC-908/BC-918-B)]     [FACIT]     [Gretag ETK]      [Creed Teletape]    [Q]

©2004-2012 F. Dörenberg N4SPP

Ca. 1920, L.M.T. became a subsidiary of the american ITT group. In 1925, L.M.T. moved from Paris to Boulogne, on the banks of the river Seine. They co-developed the national PTT public telephone network, in which they introduced the rotary exchange switch. They also provided private exchanges to large companies such as Renault and EDF (national electrical power company). In 1937 they built and installed a very high-power transmitter on top of the Eiffel tower.

International Telephone & Telegraph was created from the Puerto Rico Telephone Company. From 1922 to 1925, ITT acquired a number of European telephone companies, through its subsidiary The Lorenz Company. This included STC in Britain, SEL in Germany, BTM in Belgium, and CGCT in France. L.M.T-ITT was acquired by Thomson-CSF in 1976, by Alcatel in1986, Nokia in 1987, et finally Semi-Tech in 1996.

	Ref. 1: "L.M.T. Laboratories 7-Frequency Radio-printer", L. Devaux, F. Smets, Electrical Communication (quarterly journal of International Standard Electric Co.), Vol. 17, No. 1, July 1938, pp. 22-34
	Ref. 2: "Der 7-Frequenz-Funkschreiber der Les Laboratoires L.M.T.", L. Devaux, F. Smets, Elektrisches Nachrichtenwesen (German edition of "Electrical Communication" of International Standard Electric Corp.), Volume 17, Nr. 1, December 1938, pp. 22-34
	Ref. 3: "Radio Teleprinting" [7-tone L.M.T. system], The Wireless World, 9 March 1939, p. 294
	Ref. 4: "Der 7-Frequenzen-Schreiber" [7-tone printer], pp. 166-167 in “Fernmeldetechnik“, Band 9 of “Lehrbücher der Feinwerktechnik“, Fritz Schiweck, 1st ed., 1942, 526 pp., C. F. Winter'sche Verlagsbuchandlung
	Ref. 5: "Der 7-Frequenzen-Schreiber", Fritz Schiweck, Section 9.5.5, p. 378 in Band 9 of "Lehrbücher der Feinwerktechnik", 4th ed., C. F. Winter'sche Verlagsbuchandlung, 1962, 894 pp.

Kleinschmidt is behind the development of Teletype Corp.'s Model 17 teleprinter. Model 17 transmits from a keyboard or a 5-bit punch tape, see ref. 1. Based on its characteristics it is, in essence, a copy of the Hell Feldfernschreiber, and should be compatible with it. Possibly, it was developed to be able to monitor Feld-Hell transmissions.

	7-column characters (of which 5 used).
	shortest pulse of 4 msec
	transmission rate of 122.5 Bd.
	the tone frequency is 1000 Hz, vs. 900 Hz of the Feld-Hell, but that does not prevent interoperability.
	printer mechanism with a 2-turn spindle, a knife-edge hammer, and a felt ink roller.
	prints on paper tape: "standard" ¾ inch (19 mm) ticker tape paper vs. the Feld-Hell's 15 mm wide tape.
	its motor runs at half the speed of the Feld-Hell’s (1800 vs. 3600 rpm), but that is just a design choice.
	it does automatically stop the paper transport if no signal is received for about 10 sec.

The Teletype Model 17 system - printer and keyboard-drum/punch-tape unit on SXT-1 table
(source: Teletype Spec S-5226, see below

The Teletype Model 17 character-drum unit
(stack of notched character-disks; source: Teletype Spec S-5226, see below)

The Teletype Model 17 printer
(source: Teletype Spec S-5226, see below)
 

Teletype Corp. was originally named Morkrum Co., after the founders Joy Morton and Charles & Howard Krum.

References:

	"Grundlagen der Springschreibertechnik“ (Part 1-5), F. Schiweck, Telegraphen-, und Fernsprech-Technik, Jg. 25, Nr. 3, March 1936, pp. 53-57, Nr. 4, April 1936, pp. 91-97, Nr. 6, June 1936, pp. 139-144, Nr. 9, September 1936, pp. 245-250, Nr. 11, November 1936, pp. 307-313; also: Fernmelde-Technik, 1937, Siemens & Halske A. G., Wernerwerk, Berlin-Siemensstadt; also: SH. 6623, 1939 - to be added nov/dec 2009
	Specification S-5226 "Description of Teletype Model 17 Radio Printer System Using 7 Line Character Pattern" Issue 1 of 1939, 5 pp.
	Specification S-5186 "Adjustment of the Radio Distributor (Model 17)", Issue 1, October 1938, 9 pp.
	Bulletin No. 1096: "Parts, Scanning Distributor (Model 17)", Issue 1, July 1942, 24 pp.
	WD-1747 "Wiring Diagram - Table for 17 Type Printer System", Issue F, March 1941
	WD-1902 "Wiring Diagram - 17 Type Rectifier Amplifier" (power supply), Issue A, April 1941
	WD-2004 "Wiring Diagram - Transmitter X-12 Type 17 Printer System", Issue A, December 1940
	WD-2012 "Wiring Diagram of Facsimile Syn. Motor", Issue C, March 1941
	WD-2014 "Actual and Schematic Wiring Diagrams of REC17", Issue A, January 1941
	WD-2036 "Wiring Diagram for 17 Type Printer Transmitting Table", March 1941
	WD-2039 "Wiring Diagram of Receiving Station Cable Connections between Apparatus Units. 17 Type Printer System", March 1941
	Specification S-5286 "Description and Adjustments of the Teletype REC17 Rectifier", Issue 1, January 1941, 2 pp.
	Specification S-5287 "Instructions for Mounting an REC-17 Rectifier on an SXT-1 Table Using the 101485 Set of Parts", Issue 1, January 1941, 1 pp.
	Specification S-5288 "Lubrication Supplies and Directions for Use", Issue 1, January 1941, 2 pp.
	Specification S-5298 "Instructions for Adjusting, Lubricating and Preparing Model 17 Radio Printers for Operation", Issue 1, March 1941, 16 pp.
	Instruction Manual No. 6 "Teletype Model 17 Radio Printer Systems", March 1941, 1 p. (list of applicable documents)
	Catalog of Copyright Entries. Part 4. Works of Art, Etc., 1938, New Series, Volume 33, No. 1; No. 4, 1938, Classes H-K; Library of Congress. Copyright Office; p. 229: "Teletype model 17 mobile radio printer" (reference only)

The above Teletype company documents are courtesy Jim Haynes, W6JVE; used with permission.

Links:

	History section of RTTY.COM
	Teletype Company section of RTTY.COM
	Vom Drucktelegraphen zum Telex-Netz

The swiss company EMA A.-G. made several models of Hell-printers during and after WW2. The company was located in the small town of Meilen, a little over 10 km (6 mi) to the south-east of Zürich, on the north-shore of Lake Zürich (Zürisee to the locals).The company was founded in 1945, moved to Meilen in 1947, and was closed in 1988. Their primary products were measurement instruments. These days, there still exists at least one (new) company named EMA in or near Meilen, but they are not related to the Hell-printer manufacturer of the same name. One EMA's major Hellschreiber-customers was the Schweizerische Bundesbahnen (SBB, Swiss Railway Co.).

HELL-PRINTER TYPE 125. The first EMA model that was brought to my attention (courtesy Remmelt-Jan, PA0RJW), is "Hell-Printer Type 125". As the name suggests, it is a printer-only unit - it does not have a keyboard or punch-tape reader for sending. It is unknown if there ever was a matching sender unit built by EMA.

Note that the legends on the front panel of this machine are in English. The British news agency Reuters started its Hellschreiber broadcasts in the mid-1930s. Because of the war, Reuters could no longer get Siemens-Halske built Hellschreiber equipment (for existing and new customers). The engaged an other companies to design and build Hellschreiber printers fro them (ref. A). EMA may have been one of them. The Italian company F.I.A.T. (not the car manufacturer), definitely made Hell-printers for Reuters - see further below.

Ref. A: p. 13 in "Telecommunications in War", S.A. Angwin, J. of the IEE, Part IIIA: Radiocommunication, Vol. 94, Issue 11, Nov. 1947, pp. 7-15

Front-panel of the EMA Hell-Printer Type 125
(original photos: courtesy Remmelt-Jan, PAØRJW)

The unit has controls for an audio bandpass filter (900 Hz, 1500 Hz, off), audio volume, "automatic on/off, speed regulator, printer start/stop, main power on/off, and "write control" (audio gain). There is a bracket for an external roll of paper tape. There are headphone jacks on the front panel, and jacks for 5 Ω (loudspeaker?), 600 Ω (phone line), and 10 kΩ on the rear. The unit has 3 tubes: EF22, EBL21, and an AZ1 (rectifier).

Top-view of the EMA Hell-Printer Type 125

 
Bottom-view of the EMA Hell-Printer Type 125

HELL-PRINTER TYPE HSG-2. This printer is fully compatible with the Hell Feldfernschreiber: 2.5 characters per sec, two-line print, same paper tape width, and same paper tape speed. This model also has three tubes: AL4, EF13, and AZ1 (rectifier). Controls and signal interfaces are very similar to those of Type 125 shown above, as are the switch and connector legends in English.

Plate on the HSG2 printer

Front-view of an EMA Hell-Printer HSG2

(original photos: courtesy Heinz, DG4CL)

Top-view of the chassis of EMA Hell-Printer HSG2

The photo above shows four shielded transformers marked "GELOSO". This was an Italian company, founded in 1931 by John Geloso in Milan. It manufactured electronic components, as well as radio receivers and transmitters (including military), TV and audio equipment.

Bottom-view of the chassis of EMA Hell-Printer HSG2

(transformers, tone-detector rectifier diodes (center), capacitors)

Rear-view of the chassis of EMA Hell-Printer HSG2

The centrifugal speed regulator of the HSG2

EMA developed at least one more model Hell-printer: the HPR-4. I only have the fuzzy photo shown below. It dates to the 1950s and measures approximately 38x24cm (WxH; ≈15x9½"). This particular one has serial number 5219, which suggests quite a production volume (or it is number 19 from 1952...).

If you have any additional information or documentation on these machines, please contact me.

Front-view of an EMA Hell-Printer - type HPR-4

(original photo: courtesy Miklós, HA5CMB)

This printer can be seen in action in this Youtube video clip.

The Post- und Telegraphen Werkstätte (P.T.W., workshops of the PTT) in Salzburg/Austria built at least one type of Hellschreiber printer: model HSI. The label on the front of the machine identifies it as a "Hellschreiber". It appears to be the equivalent of the Siemens-Halske T empf 14 "Presse Hell", so it may have been built under license. The printer mechanism and associated levers also appear to be the standard Siemens-Halske items. The unit measures 21x38x14 cm (HxWxD, ≈8¼x15x5½"). Shown below are the machines with serial number 319 and 323. It is unknown in which period they were built.

P.T.W. Hellschreiber type "HSI" - serial number 319

(original photo courtesy Oberst i.R. J. Prikowitsch, OE1PQ, curator of the Museum der Fernmeldetruppenschule (Army Signals School) in Vienna/Austria )
 

P.T.W. Hellschreiber type "HSI" - serial number 323

(original photo courtesy Oberst i.R. J. Prikowitsch, OE1PQ)

In the early 1950s, a Hellschreiber was developed in the German (not-so) Democratic Republic ("East Germany"). It went into service with the Kasernierte Volks Polizei (KVP - Barracked People's Police). In 1956 the KVP was absorbed into newly formed army of East Germany; the Nationale Volks Armee (NVA - National People's Army, 1956-1990), where these machines continued to be used. This Hellschreiber was directly based on Feld-Hellschreiber technology, and early production units actually contained components abandoned by the Hell company in Berlin at the end of World War 2. It is referred to as an Abtastfernschreiber (ATF, "scanning teleprinters"), probably so as to avoid using the "western" Hell name (and make the patent infringements too obvious ). The term "Abtastfernschreiber" was actually not new: Hellschreibers were refered to as "Abtast-Telegrafen" at least as early as 1940 (ref. ATF-1).

The NVA Hellschreiber

The printer-keyboard unit is hinged into the case, and can be folded up into it.
 

The printer/keyboard/drum unit of the NVA Hellschreiber

(photo courtesy Heinz, DC4GL)
 

Close-up of the printer - note the large diameter of the printer spindle (helix) and a plastic ink-transfer roller between the spindle and the felt ink-roller (to reduce wear on the felt roller)
 

Label of the above NVA Hellschreiber - "FFS" presumably stands for Feldfernschreiber 
 

The NVA operated these machines until ca. 1958. Very few of these machines were ever built, as they were not compatible with other teleprinter systems of the Eastern bloc. Early machines of this type are known to contain components marked "Hell" (e.g., the motor). Unlike the Feld-Hell machine, the anode voltage for the tubes is generated from 12 Vdc with a "Zerhacker" tube - an electromechanical "chopper" DC-DC converter.

The model shown is a cross-over between Feld-Hell and Hell 72 "GL":

	the character drum is like that of the Feld-Hell: as shown in the photo immediately below, pixels are captured as metal patches (the drum of the "GL" is a stack of notched disks).
	operation uses "start-stop" synchronization, like the "GL". Hence, the printer spindle has a single-turn thread and paper is 9.5 mm wide.

The character drum of the NVA Hellschreiber

(photo courtesy Heinz, DC4GL)

The character drums of the Feld-Hell (bottom) and the ATF Hellschreiber (top)

Note the start-bit at the top of the image (horizontally, across the entire drum), and the (vertical) wear marks of the spring contacts. In the Feld-Hell drum, the patches are separated by character and they are interconnected below the dark layer of insulation material. In the NVA machine, for each column of the font, the pixel patches of adjacent characters are interconnected into patterns at the drum circumference, in addition to interconnections below the insulation material. The NVA drum has a diameter of 4 cm.

7x14 font of the ATF-Hellschreiber
(9-pixel start-pulse in the first column)

Here is a 20 sec video clip of this printer in action:

(click here to start your own player)

A print-out made with an NVA Helschreiber 
 

The NVA-FFS was manufactured by RFT. RFT was a collective of telecommunications equipment and electronic component manufacturers, founded in 1946. More info about RFT can be found here (in German). The NVA-FFS was used by the KVP with transceivers such as the low power (0.3 W AM, 1.2 W CW) HF portable set FK 1a, ref. ATF-5, ATF-6.

	Ref. ATF-1: "Abtast-Telegrafen" [incl. Presse-Hell, Feld-Hell, 7-tone], chapter IV in “Taschenbuch für Fernmeldetechniker", H.W. Goetsch, Oldenbourg Verlag, 1940, pp. 411-427 of 787
	Ref. ATF-2: "Repairing vibrators for DC to DC convertors"
	Ref. ATF-3: "Die Wechselrichter und Umrichter, ihre Berechnung und Arbeitsweise" [Zerhacker], Walter Schilling, 27 May 1940, R. Oldenbourg Verlag., 160 pp., OCLC Nr. 6139075
	Ref. ATF-4: "Methodische Anleitung zur Ausbildung am Fernschreiber und Feldfernschreiber“, Dienstvorschriften Kasernierte Volkspolizei DV-KVP 14/5, Entwurf (draft), 1955, 106 pp.
	Ref. ATF-5: pp. 3, 82-85 in "Beschreibung und Bedienungsanweisung der Funkstation FK 1a", DV-44/14, Deutsche Demokratische Republik - Ministerium für Nationale Verteidigung; Berlin, 1956, 142 pp.
	Ref. ATF-6: "Funkstation kleiner Leistung FK 1 und FK1a", Gerd Balg, 3 pp.
	Ref. ATF-7: "Der KVP / NVA Feldfernschreiber FSS.02-00001", Bernd Rothe, V2.3, 23-Jan-2013, 26 pp.
	Ref. ATF-8: "Der RFT-ATF Fernschreiber von 1952", Bernd Rothe, V3.1, 2013, 13 pp.

My 3D/stereoscopic photos of the ATF-Hellschreiber are here.

Around 1947, Nobutoshi Kihara, an engineer at Tokyo Tsushin Kogyo ("Tokyo Telecommunications Engineering Corp., renamed Sony Corp. in 1958) reverse-engineered the Hellschreiber. It was referred to by its generic designator "tape facsimile equipment", rather than Hellschreiber.

Ref.: "Oral-History: Nobutoshi Kihara" (interview with Sony engineer), IEEE Global History Network, People and Organizations, January 2009.

The company only manufactured and sold a handful of these machines (10-20) in 1949, before it was discontinued due to other technological advances and pursuits.
 

The TTK Hellschreiber

The photo above was added to the corporate archive with the following caption:

TAPE FACSIMILE EQUIPMENT. This is a very simple printing telegraph equipment, by which letters typewritten on the transmitter side will be instantly reproduced on the receiver side. In a word, this is really a good combination of the features of teletype end facsimile. Its construction is simple and it's much easier to use it than ordinary printing telegraph equipments. Both Alphabet and Japanese phonetic letters ("kana") can be transmitted. Both the use of this equipment, the information of stock market, news, etc., can be transmitted to the subscriber on private lines. Machines have been tested and approved by the Ministry of Communication, and the Ministry of Transportation.

Photo and information: courtesy of Mr. Fumiko Okudera, Planning & Archive Group, Sony Corp., Tokyo.

If you have any information or documentation on Hellschreiber machines from this company, please contact me.

Chinese and Japanese have written languages that are based on thousands of pictographic characters. Obviously it is inconvenient to enter such characters with a keyboard (ref. 1). However, the Hell printer system has no problem with such characters. Also, the character-scanning concept of the Hell system has no problem with such characters. Rather than using a "keyboard plus character-memory", a character-entry system can be used that optically scans hand-written text. Examples of this are the ZETFAX of the Hell company, the RCA Tapefax, and the RC-58B system of the US Army (WWII).

The Toho Denki Kabushikigaisha company (Eastern Electric Ltd.) in Japan made such Hellschreiber systems for the Japanese and Chinese markets (ref. 44). Toho Denki K.K. was a fax equipment manufacturer, and became part of Matsushita Graphic Communication Systems Inc. in 1962. Their machines were used by Chinese news and meteorological services, and Japanese news services..

(source: ref. 1; the text reads "Appointment of the post of the Republic of China [= Taiwan] is notified" or something to that effect - to be confirmed)

Print of an other Chinese hellcast

(source: ref. 2)

	Ref. 1: "Chinese language becomes a bit faster”, Chris Moss, New Scientist, Vol. 77, February 1978, pp. 418-420
	Ref. 2: "Oriental approach to transpacific transmission", Donald K. deNeuf (WA1SPM; SK), pp. 16, 18 in "Proceedings of The Radio Club of America, Inc.", Vol. 51, Nr. 1, March 1977
	Ref. 3: "Hellschreiber - Nostalgie oder Realität?", Helmut Liebich DL1OY, Funkschau, 11/1990

During the late 1930s, RCA also developed some tape facsimile machines. The printers used a "rotating spiral", per the Hellschreiber-principle. On the sending side, text was typed on a paper tape and subsequently optically scanned with 60 scanning strokes per second (60 Hz / 110 Vac synchronous motor). RCA investigated three ways to : 1) a two-turn printer helix, 2) synchronous AC motors at the sending and receiving station, connected to a common AC power supply grid (a within-the-same-building solution), and 3) the use of synchronization pulses. The latter consisted of "marginal pulses" that were transmitted at the end of each line of scanned tape at the transmitter. As illustrated by the schematic below, the associated sync pulse recovery and motor-drive circuitry was not simple, and required a motor with an additional commutator. Telegraphy speed was 60 WPM, paper tape width 3/8 inch (≈9.5 mm) with a character height of 1/8 inch. Like the early Hell prototypes, the printers used carbon paper tape between paper tape and spiral.

Tape facsimile scanner

(adapted from Fig. 2 in ref. 2)

Samples of asynchronous and synchronous tape facsimile recordings

(source: Fig 1 and 13 in ref. 2)

Early RCA portable tape facsimile recorder

(source: figure 2 in ref. 1)

The printer shown above had the following characteristics:

	printer helix: 2 windings (two lines of text), total stroke 1/4 inch (6.35 mm) 60 rps (3600 rpm)
	height of each printed text line: 1/8 inch (3.2 mm)
	tape width: 3/8 inch (9.5 mm)
	tape speed: 40 inch/min (100 cm/min), resulting in 90 lpi scanning resolution
	telegraphy speed: about 60 wpm
	keying frequency ("Punktfrequenz"): 480 Hz, hence a "necessary bandwidth" of 1440 Hz
	single motor for helix and paper feed

For their printers, RCA experimented with carbon paper, typewriter ribbon, colored paper with white wax coating and a heated stylus (kymograph, stylograph; ref. 4). They eventually settled on a soft inking roller, just like the Hell company had done about a decade earlier...

RCA tape facsimile recorder

(source: figure 4 in ref. 2)

(source: second reference below)

	Ref. 1: "Tape facsimile: historical and descriptive note", Young, C.J., pp. 264-269 in "Radio facsimile - Volume 1", Goldsmith, A.N., Van Dyck, A.F., Horn, C.W., Morris, R.M., Galvin, L. (eds.), RCA Institutes Technical Press, 1938, 353 pp.
	Ref. 2: "Tape Facsimile Synchronizing Systems", Shore, H., Whitaker, J.N, pp. 270-283 in "Radio facsimile - Volume 1", Goldsmith, A.N., Van Dyck, A.F., Horn, C.W., Morris, R.M., Galvin, L. (eds.), RCA Institutes Technical Press, 1938, 353 pp.
	Ref. 3: "Practical applications of tape facsimile systems", Whitaker, J.N., Collings, F.C., pp. 284-293 in "Radio facsimile - Volume 1", Goldsmith, A.N., Van Dyck, A.F., Horn, C.W., Morris, R.M., Galvin, L. (eds.), RCA Institutes Technical Press, 1938, 353 pp.
	Ref. 4: "A Wax-Paper Kymograph", Ralph Gerbrands, John Volkmann, pp. 498-501 in "The American Journal of Psychology", Vol. 48, No. 3, July 1936

Towards the end of World War II, Hellschreiber printers were made by the "Fabbrica Italiana Apparati per Telecomunicazioni" [F.I.A.T., Italian Factory for Telecom Equipment]. They were located at Via Ausonio 3, in Milan. To date, I have not been able to trace this company, or any with similar name... This F.I.A.T is not be confused with the automobile company from Turin, that has the same abbreviated name.  

F.I.A.T made at least 50 Hellschreiber printers for the Reuters news agency.

F.I.A.T. Hell-printer

(original unedited photo: courtesy Science & Society Picture Library of the Science Museum in London; used with permission; in the lower left-hand corner of this photo, I have edited out a distracting item)

Ref. 1: "F.I.A.T. Hell Printer"; courtesy British Science Museum, Blythe House item ', used with permission.

During World War II, the British General Post Office (GPO) made its own Hellschreiber printers, primarily for Reuters' news agency (ref. 3). They are referred to as "Hell Printer No. 1". These printers were used by the GPO and other entities, including radio operations of the British Home Office. They may have been developed and manufactured at the GPO's Engineering Department and Research Station at Dollis Hill in Northwest London (near Willesden). Dollis Hill is also where the GPO tested the Siemens-Hell system (both 7-line and 12-line) in 1934, and where the "Colossus" code-breaking computer was built.

Three versions were developed, and produced in significant numbers:

	No. 1 Mark 1 (serial nr. 7-47)
	No. 1 Mark 2 (serial nr. 49-73)
	No. 1-T Mark 2 (serial nr. 74 and above; at least 229 units)

Model no. 1-T contains components that were specifically treated for use in tropical climates.

PO Hell-Printer

(source: Figure 3 in ref. 3)

Label on the British Post Office Hell-Printer model 1-T

(all original photos of serial no. 192 on this page: ©2013 Tony Radio Collection, used with permission)

Front of the British Post Office Hell-Printer model 1-T (ink applicator roller missing)

Front of the British Post Office Hell-Printer model 1-T

Top view of the printer module of the British Post Office Hell-Printer model 1-T

Note that this printer has a many-start spindle ("printing wheel"), see photo below. It has ten threads. This allows the spindle to turn at 1/10 of the nominal speed. The latter is 1050 rpm for 7-line Hell-font at 2.5 characters/sec. The Feld-Hell machine has a two-start spindle that turns at 1050/2=525 rpm. The printers could be used for both the 12-line and the 7-line Hell system, by simply changing the spindle (ref. 3). The motor speed governor included a slip-ring arrangement.

Close-up of the printer helix

The inside of the printer module, with the electro-magnet

Paper transport rollers

Holder for a roll of paper tape

The GPO Hell-printer included a remote control function for unattended operation (an optional function in Siemens-Hell "Presse Hell" printers). A tone pulse of at least 0.5 sec would turn the motor on, whereas a tone of about 10 sec (8 sec in Siemens-Hell) would turn the motor off. "START STOP" position of the toggle switch?

Main switch

Gearing between the motor, printer helix, and paper tape transport

"The Klaxon Co., Ltd."

As the name suggests, Klaxon' primary product was sirens and car horns

Klaxon Co. of Birmingham of 36 Blandford Street, London, W1.

1909 Company founded.

1937 Listed Exhibitor - British Industries Fair. Fractional H.P. Motors and Geared Motor Units. Generators. Regulators. Relays. Transformers. Grinding Machines. Industrial Signals and Sirens. Fire and Burglar Alarms. Staff Locators. Electric and Hand Operated Horns. Push Buttons. Electric Sign Flashers.

Telephone: Welbeck 8367/8/9. Telegraphic Address: "Klaxonet, London". (1937)

1961 Electrical engineers and manufacturers of fractional H.P. motors, warning signals and windscreen wipers.

vs. Klaxon Ltd., 201 Holland Park Avenue, London, W11  = their Import Reg (eg one of the US subsidiaries? vs motor labe " british made") was Holland Park London W1.

1938: Klaxon Limited, of 201, Holland Park Avenue, London, W.ll, has published an illustrated catalogue of air-raid warning devices for internal and external situations. These are of various types, such as gongs, sirens, whistles, or sound- emitters

1941 KLAXON, LTD., 201, Holland Park Avenue, London, W II. ; fratcionalonal H P. and Geared Motor, Synchronous Motors -nted range. Unique features. • 25 years' leadership G OPERATED All sizes

twin wipers by Klaxon,

Klaxon advertising - September 1938

Speed regulator side of the motor

Speed adjustment knob

PO Hell-Printer No. 1-T - serial nr. 229

(original unedited photo: courtesy Science & Society Picture Library of the Science Museum in London; used with permission)

This model has a speed regulator knob that is different from S/N 192 above.

Front of the PO Hell-Printer No. 1-T

(original unedited photo: courtesy Science & Society Picture Library of the Science Museum in London; used with permission)

This model has a 10-start spindle that is not machined, unlike S/N 192 above. The spindle of this PO printer is not machined out of a single piece of metal: the threads appeared to be soldered onto the spindle hub, between two flanges.

The spindle of PO Hell-Printer No. 1-T

	Ref. 1: 2 pages from "Hell Printer - Operating and Maintenance Instructions", Issue 2, July 1944, Document M 9501 (Tg), Office of the Engineer-in-Chief, Post Office Engineering Dept. (Radio Branch) GPO, London
	Ref. 2: components lists for Hell Printers No. 1 and 1-T: PO document M 9502 (Tg) and M 9508 (Tg) respectively.
	Ref. 3: “Reuters' Wireless Services”, W. West, The Post Office Electrical Engineers’ Journal, Vol. 39, July 1946, pp. 48-52

RC-58-B is the designator of a US Signal Corps tape facsimile system from the early 1940s. It was developed for "faxing" handwritten and typed text messages during mobile operation (hence 12 Vdc power; configurable for 24 Vdc).

The main equipment items of this system are:

	Recorder-scanner BC-918 (with covers BG-118-B and mounting FT-328-B)
	Amplifier BC-908 (with covers BG-128-B and mounting FT-318B)
	Writing-stand MC-308B
	Paper tape M-298
	Spare parts chest CH-108-B.

Text to be transmitted is handwritten onto paper tape. This is done with a writing stand. It has a separate roll of paper tape that is passed through a ⅜ inch (9½ mm) high window (i.e., half the width of the tape). During the writing process, the tape moves at 18 inch per minute (≈ 45 cm/min, close to the paper transportation speed of the Hell Feldfernschreiber). The tape with the written (or typed) message is subsequently passed through the optical scanner of the BC-918. The scanner has a resolution of 72 lines (columns) per lineal inch of tape (≈ 0.35 mm/column). Scanning and transmission speed is 50 inch/minute (about 1.27 m/s, almost three times as fast as the Hell Feldfernschreiber). Assuming ¼ inch per character, these speeds are equivalent to a telegraphy speed of about 15 wpm for writing, and 42 wpm for scanning, transmitting, and printing.

Optical progressive-scanning principle and mechanism

(source: Figure 16 in TM 11-374)

The analog (brightness) output of the scanner is passed from the photocell and pre-amplifier in the BC-918 recorder/scanner unit, to the BC-908 amplifier unit. The later converts the brightness pulses into an FSK audio output signal with a 500 Hz shift (1150 Hz for white, 1650 Hz for black). As with all Hellschreibers, the RC-58-B can be used for communication via radio and over phone lines.

The BC-908 amplifier unit passes received FSK signals through a discriminator/detector. The resulting signal is amplified and drives the solenoids of the printer in the BC-918.

The "recorder" is a regular Hellschreiber printer with a 6-start spindle. Each spindle-thread makes 1/3 of a full winding, so adjacent spindle-threads overlap by 50%. Hence, it prints two identical, parallel lines of text onto paper tape. The tape is ¾ inch wide (19 mm). Own-machine's transmissions can be printed simultaneously on the local printer, for monitoring purposes (as with Hellschreibers).

The 6-start printer helix

(source Figure 21A in TM 11-374)

If you have any additional information or documentation on these machines, please contact me.

See the ZETFAX of the Hell Co. for another example of a tape fax system with optical scanning.

BC-918-B Facsimile Recorder/Scanner

BC-918-B Facsimile Recorder/Scanner

(source: collection of the Museum Jan Corver (Museum voor Radiozendamateurisme) in Budel / The Netherlands).

Recorder-scanner BC-918-B and mounting
(Figure 3 in TM 11-374)

	"Tape Facsimile Equipment RC-58-B", War Department Technical Manual TM 11-374, 23 February 1944, 145 pp. (courtesy Louis Gonzales, F5LG). This file is 109 MB! Lower-res file (66 MB) is here.
	"Un Convertisseur RTTY de surplus - le BC 908B" [modification of the BC908B (amplifier/filter unit of the RC-58B system) for RTTY], J.P. Vauchelle (F5QE), Radio-REF, November 1969, pp. 729-733.
	“Amerikaans Hell system”, Reflecties door PA0SE, Dick Rollema (PA0SE), Electron, nr. 7, July 1980, p. 382  (courtesy Gerard Wolthuis, PA3BCB)
	"RC-58 Facsimile Equipment" [BC-918] in “Surplus sidelights”, Gordon E. White, CQ: Amateur's Radio Journal, Vol. 24, nr. 3, March 1968, pp. 106-110
	"Facsimile Equipment RC-58-( )", Section V in "Installation of Radio and Facsimile Equipment in Shelter HO-17 ( )", US War Department Technical Manual TM 11-2737, May 1945, 20 pp. (courtesy Gary, KJ6EFH)

In the late 1950s, the Creed company (ref. 4) developed “… a simple facsimile transceiver, designed to exchange, with an identical machine over relatively short distances, brief messages written and recorded on Teledos tape“ (ref. 1). It is indeed closer to a direct-printing black & white fax system, then a Hellschreiber in the strict sense. However, it does use a spinning "stylus" (from the Latin word for "pointed implement") at both the sending and receiving (printing) side.

The transceiver was Creed Model TR.105. Its successor, model TR.105/1, basically had redesigned electronics and no manual gain control.

Creed Transceiver Model TR.105

On the sending side, a message is hand-written on a segment of 3/4 inch wide "Teledos" tape. The height of the written message is 5/8 inch max. This tape has an enameled surface. Writing is done with a regular pencil, not harder than HB-grade. The penciled message is drawn between the spinning stylus and the (curved) platen. The tips of the 4-pointed stylus sweep across the moving tape. As the revolving stylus scans the moving tape, its electrical resistance to earth/ground varies according to whether the points are touching blank tape or message markings. The resulting pulses are fed to the (phone)line.

Stylus and curved platen

At the receiver, a blank Teldos tape is fed under the stylus. The incoming message pulses from the (pone)line are amplified into voltage surges at the recording stylus. These surges are high enough to burn through the lacquer of the blank tape and leave dark markings on its surface. These markings are identical with the pencil markings on the transmitter tape. Electrical contact with the stylus is maintained via a slip-ring. This is in effect a thermal printer, using "dry-electrolytic action".

Functional schematic of Teletape Transceiver Model TR.105

(source: appendix A of ref. 1)

Model TR.105 has separate motors for the stylus and tape feed. At the receiver, the motors are started automatically when tone pulses are received. "Black" is represented by a keyed tone of 5000 Hz (+/- 200 Hz), i.e., not suitable for operation over regular phone lines. Tape is fed at 1 inch/sec (1.5 m/min). Equivalent scanning resolution is 100 lpi. For the given tape feed speed (1 inch/sec), this implies a stylus speed of 1500 rpm. Model TR.105/1 has four tubes: CV2136, CV491, 6AU6, and CV1535. The unit operates on 110-145 or 200-225 Vac, 50 Hz (selectable in steps of 5 Vac). Power consumption is 28 W (standby) - 90 W (sending). Life expectancy of the stylus was sufficient for one roll of Teledos tape.

The inside of Teletape Transceiver Model TR.105

The inside of Teletape Transceiver Model TR.105

	Ref. 1: "Teletape Transceiver Model TR. 105/1“, Instruction Book FAX.105, Issue 2 of Booklet MB. 105, Creed & Company Ltd. (I.T.T.), January 1960, 71 pp.
	Ref. 2: "Faksimile-System – Faksimile-Streifenschreiber TR 105 – Montage- und Wartungsanweisung, Einstellvorschriften”, Standard Elektrik, 10 pp.
	Ref. 3: "Creed model TR.105/I Teletape transceiver – part list no. PL.105“, 2nd ed., March 1960, Creed & Company Ltd., 24 pp.
	Ref. 4: "Creed and Company Limited - The First 50 Years", Alan G. Hobbs (G8GOJ, SK), Spring 1962 "Golden Jubilee" issue of "Creed News"; also reprinted in the Summer 1997 issue of BARTG Datacom.

If you have any additional information or documentation on these machines, please contact me.
 

Philippe, F2TV, brought to my attention the existence of solid-state machines that are compatible with Feld-Hell machines. Two of these machines are known to exist. They are believed to be prototypes made for the French armed forces in the late 1950s or early 1960s.

They are attributed to the French company Thomson, but this there is no official confirmation of this: there is no name plate or manufacturer marking on the equipment. The original Thomson-Houston company was founded in the USA in 1879. The French subsidiary was created in 1892. Eventually it merged with the Brandt company and then in 1968 with the CSF company ("Compagnie Générale de Télégraphie Sans Fil", the "General Company for Wireless Telegraphy") to form Thomson-CSF.

This compact unit measures 38 x 33 x 19 cm (L x W x H, 15x13x7½"), comes in an army-green case, and operates on 12 Vdc.

Front view of the Thomson Hellschreiber

(original unedited photo: courtesy Jean-Claude, F5PU)
 

Top view of the Thomson Hellschreiber

(original unedited photo: courtesy Bernard, F9ZB)

This machine uses the same paper tape as the Feld-Hell and Hell-80: 15 mm width. However, the printer spindle only measures 5 mm in diameter, compared to close to 10 mm for the Feld-Hell and Hell-80, and 6 mm for the Hell-72. The spindle has two windings, like the Feld-Hell and Hell-80, but it is a 1-start helix; the Feld-Hell spindle is a 2-start ("double") helix, which allows it to turn at half speed. Like the Feld-hell, transmission speed is 2.5 characters per sec.

Close-up of the printer

(photo: Frank Dörenberg, N4SPP)

Paper speed is about the same as that of the Feld-Hell (46.7 cm/min nominal), but the manual speed adjustment appears to have a much wider range. Speed regulation is done with a simple centrifugal speed regulator that is mounted on the motor shaft. The regulator has three so-called "fly-ball" weights (though they are stubby steel cylinders rather than balls). Each weight is mounted on a strip of spring metal. One end of the strips is fixed to the motor shaft, the other to a flywheel-disk that can move freely on the motor shaft. As the motor speed increases, centrifugal forces move the weights radially away from the motor shaft; in turn, this pulls the flywheel disk towards the motor. The speed set point is changed with a knob at the top of the unit. This knob changes the position of a lever arm. At the end of the lever arm, there is clamp with a small rod of hard leather. This is simply a brake pad, with a manually variable position. The motor speeds up until the flywheel disk touches the leather brake. The faster the motor turns, the harder the disk pushes against the brake pad, the more friction builds, which slows down the motor, which reduces the friction, etc. In other words: a feedback control loop. This same mechanism is used in old gramophone record players. However, as it is friction based, it is also temperature dependent, and the speed set point drifts rather noticeably over time. This is rather inconvenient, as it forces the receiving machine to continuously adjusts its local motor speed in order to follow the drift of the transmitting machine; like all Hellschreibers, the transmitting machine also prints its own text, but that is always perfectly horizontal, independent of the local motor speed.

Note that the centrifugal regulator in the Feld-Hell is not friction-based: the position of its fly-weight opens and closes an electrical contact, that switches a vacuum tube on/off, whose anode current controls the current in the governor windings of the motor. Its speed remains stable to within a fraction of a percent!

Close-up of the centrifugal speed regulator

The Thomson machine has a character drum. However, it is much smaller (9.5 cm long, 3.4 cm diameter) than that of the Feld-Hell and appears to be very lightweight. It looks like a cylinder of a coarse resin-impregnated cloth material, onto which copper traces and pads are stitched. Each track has a wire spring-contact that is permanently engaged. This is mechanically much simpler than in the Feld-Hell machine, where only the contact of the selected character is engaged. Of course, in the Feld-hell machine, the drum turns continuously.

Close-up of the character-drum

The Thomson machine uses "start-stop" synchronization, like the Hell-72 and Hell-80. I still have to confirm if & how this is affected by the position of the "start-stop"/"continu" switch on the front of the unit. Maybe it is selectable, as with the Hell-80. Inspection of the three circuit cards in the machine shows a 4-diode rectifier bridge for detection of the pulses to drive the printer, but no separate start-pulse detection circuit... The motor turns continuously, and both the character drum and the printer spindle are engaged via a clutch mechanism, as in the Hell-72/73.

Close-up of the start-stop cams on the shaft of the character drum

The start-pulse is 2/14 of a character column, whereas it is 8/14 of a column in the Hell-72. This suggests that the Thomson machine is more susceptible to inadvertent start-pulse detections when receiving noisy signals.

Start-pulse in the first column of the character matrix

The font of the Thomson machine is very similar to that of the Feld-Hell. However, the audio output of the machine is not an on/off-keyed 900 Hz tone. Instead it appears to be a 2-tone FSK signal, with a 1325 Hz "space" and a 1225 Hz "mark" tone. Hence, 100% duty-cycle. To print this signal with a Feld-Hell machine or equivalent software, the detector must be set to something close to the "mark" frequency, not close to the (near-constant) "space" tone. Printing can also be done with software in Hell FM105/245 mode, with the detector set to the "space" tone. Hell PSK mode also works. A recording of the audio output of the Thomson machine is here  (10 MB .wav file, 2x full character set).

Character set of the Thomson, with IZ8BLY software in Feld-Hell mode ("mark" tone)

(slant is due to speed offset of the Thomson machine)

Character set of the Thomson, with IZ8BLY software in FM105 mode ("space" tone)

Character set of the Thomson, with IZ8BLY software in FM245 mode ("space" tone)

Audio spectrum of the output of the Thomson machine - waterfall display

(click on image or here to get full size)

Audio spectrum of the output of the Thomson machine - FFT display

(blue: "space" tone only; yellow: "mark" & "space" during character transmission)

The rear side of the Thomson machine - cover removed

(original unedited photo: courtesy Jean-Claude, F5PU)

As mentioned, the machine has three circuit cards and solid-state circuitry: five transistors of type 2N43. The 2N43 is a Germanium PNP transistor, intended for (relatively) high-gain (h(FE) = 30) low-power (300 mW) AF applications. "Modern" equivalents are 2N2706, AC128, and AC152. The four basic transistor manufacturing processes are point-contact, grown- or rate-grown-junction, alloy- or fused-junction, and diffused-junction. The 2N43 is an alloy-fused junction, the first junction transistor developed by General Electric in 1953, to a US military specification. The transistor is housed in a hermetically-sealed can, referred to as "lady's top hat". Early versions have a pinched top. Based on gain, manufactured transistors where screened into three categories, and labeled 2N43, 2N44, and 2N45. Parts that exceeded the highest spec gain of the 2N43 or were below the lowest spec gain of the 2N45, were rejected. In 1955, GE started selling the rejects to the civil market, as 2N107. The 2N4x was manufactured in license by several manufacturers (Ratheon, RCA, Sylvania, Mullard, and... Thomson).

General Electric transistor of type 2N43

(the "pinched top" can on the lower right is an early model)

The three circuit cards in the Thomson machine are simple pertinax cards, with point-to-point wiring on the back. This suggests that the machine is a prototype.

The tone-detector / solenoid-driver circuit card

(diode bridge at the center)

Back of the tone-detector / solenoid-driver circuit card

The second circuit card

The third circuit card

The large rectangular capacitors (2-in-a-can), inductors and transformers are made by the "Transmissions - Composants" division of the French company ”Lignes télégraphiques et téléphoniques" (L.T.T.). L.L.T was founded in 1920, and had a history similar to and coinciding with that of Thomson. International Western Electric acquired an minority interest in the company in 1922. Starting in 1927, they made iron dust cores for transformers, paper capacitors; polystyrene capacitors started in 1938. In 1978 it became a wholly owned subsidiary of Thomson CSF.

1955 LTT advertising

(original unedited photo: courtesy Jean-Claude, F5PU)

(original unedited photo: courtesy Bernard, F7ZB)

The interconnect panel on the rear of the unit.

Interfacing to telephone lines or a radio transceiver is done via the interconnect panel on the rear of the unit. There are four banana plug jacks for connecting to a phone line (far left in the above photo). Not sure if this accommodates 2- and 4-wire interfacing. The eight jacks on the right are for transceiver interfacing. "EMIS" ("emission") is the audio output to the transmitter. "RON" is short for "ReceptiON", hence, the input for audio from the receiver. Don't know yet what "SUP" ("supplementary"?) and "PED" mean. "MASSE" is of course simply "ground/earth". There does not appear to be a PTT output.

A 3-position switch on the front panel is used to select between RON, TEL, and EM. This suggests manual switching between the telephone line and the transceiver interface (makes sense), and also between transmission and reception, if the radio interface is selected.

The "M" / "A" toggle switch simply turns the machine on and off ("Marche" / "Arrêt").

Controls and fuse on the front of the unit

The "Facit" company was established in Stockholm in 1918 to build a line of hand-operated calculators. Later (mid-late 1960s) they built electrically powered mechanical desktop calculators, and electronic desktop calculators. The company ventured into computer and tape printer and sheet printer products in the 1970s.

The FACIT 4452 printers print on pressure sensitive paper tape. The actual printer is basically a Hellschreiber-type spindle-and-hammer mechanism. The hammer is, of course, actuated by an electromagnet. The spindle (marked "cam" in the diagram below) looks like gear-wheel with the teeth at an angle. It is a many-start printer helix.

The FACIT printer mechanism

(source: ref. 1 below)

This is an asynchronous system, i.e., it uses start-stop synchronization. The spindle shaft has a 1-notch cam wheel on one end, and an optical encoder with 7x5=35 positions. The encoder is mounted on the drive shaft via a slip-clutch disk. The notch of the cam wheel corresponds to the start position of the spindle. When the release solenoid is energized, the cam can turn freely. When the release solenoid is energized, the cam will stop and be held at the start position ("spoke-in-the-wheel" clutch). The release solenoid is driven by a sync pulse detector, in combination with the optical encoder.

Maximum printing speed is about 15½ characters per second. The pressure-sensitive paper tape is 17.5 mm wide (same as 11/16” telex punch tape). Transfer of a single column takes 6.9 msec. This is equivalent to a pixel duration of close to 1 msec, or 1000 strokes of the printer hammer per second. There is a dwell time of 2.8 msec after each of the first four columns. Hence, each character takes 5x6.9 + 4x2.8 = 45.7 msec. Dwell time between characters is about 21 msec, equivalent to 3 columns.

Characters are 7x5 dot matrix. Height of the printed characters is 3.2 x 2.5 mm (1/8 x 0.1 inch). These printers have a digital input (serial or parallel) and were not used with radios; some models had a built-in character generator. FACIT model 4553 is a continuous-form sheet line printer, where the printer helix is mounted on a carriage that traverses back and forth underneath the paper. It is the equivalent of a "needle" or "comb" printer head. Depending on the model, signaling is serial (pixel-by-pixel) or parallel (column-by-column). This system was not intended for use via radio.

 
(source: ref. 1 below)

(source: "Product Profile," Computer, vol. 6, no. 1, pp. 57, Jan./Feb. 1973)
 

	Ref. 1: “FACIT 4552 Strip printer - Technical description”, 4552.13.01.Eng.10M.9.71, 12 pp, 1971 (courtesy Arie van Oijen, PE1AQB)
	Ref. 2: “Facit 4552 Alphanumeric Strip Printer” [brochure], 4552.02.03 Eng 10M.12.72, 2 pp., 1972 (courtesy Arie van Oijen, PE1AQB)
	Ref. 3: “Facit 4553 alphanumeric serial page printer” [sheet printer], 4553.02.03 Eng 5M.7.74, 4 pp., 1974, (courtesy Arie van Oijen, PE1AQB)

SUMMARY. Compared to the Hellschreiber, the ETK teleprinter system has the following basic characteristics:

	It is based on decomposing text characters into basic elements (here: letter-segments, instead of Hellschreiber pixels).
	The elements of the characters are sent as a fixed-length series of tone-pulses (here 14, instead of the Hell-font with 7x14 pixel pulses).
	Characters are selected with a keyboard, and the pulses are generated with a character-drum (stack of notched disks). The keyboard has a locking mechanism to ensure that a key can only be depressed when the drum is at the start position of a character sequence (like Hellschreiber keyboard-senders).
	Initially, transmission speed was 2.5 characters per second (400 msec/char, as with Feld-Hell). In 1947, this was increased to 5 characters/sec (200 msec/char, as with "Presse Hell").
	Direct printing (like Hellschreiber): each of the received pulses is printed immediately, without interpreting the complete pulse sequence that makes up the character. This makes the system robust against interference, as an incorrectly received pulse ("bit-flip") causes the printed character to be distorted but not wrong (which would be the case with standard "telex" teleprinter systems). Hence, the system is suitable for use with encryption systems (as was Hellschreiber).
	The printer does not use an inked helix that is so typical of the Hellschreiber. Instead, it uses a revolving printer-head with 14 type-stamps. The printer-head does use a felt ink roller, like Hellschreibers. The printer reconstitutes the received characters by combination of the selected basic elements. Hence the name "combination printer" ("Kombinationsschreiber").
	Text is printed on (gummed) paper tape, like the Hellschreiber.
	The character-pulse generating mechanism of the sender and the printer-head of the printer must be synchronized. This is done with a start-stop system, as with asynchronous Hellschreibers. A start-pulse precedes each 14-bit pulse sequence. There is an implicit stop-pulse ("rest bit") after the pulse sequence.
	The keyboard-printer terminal is powered by a single universal-motor (AC/DC), with a centrifugal-switch governor (like the Hellschreiber).

THE CONCEPT. As stated above, the ETK is based on decomposing text characters into letter-segments. Edgar Gretener defined a set of 14 such basic elements. Each character of the ETK-font can be expressed as a combination of no more than five of these elements. Several elements partially overlap. E.g., elements 1 and 8, 5 and 8, 4 and 12, and 5 and 12. The 13th and 14th element were changed over time. Initially, the set comprised 3 vertical, 3 horizontal, 4 diagonal, 2 angled elements, and "8". The figure "8" could be composed with elements 1, 2, 3, 4, and 5, but maybe the resulting character was initially considered as being too similar to the letter "B". Later versions of the set of the basic elements have different elements 13 and 14:

The 14 character-elements - set nr. 1 (pre-1947)

(source: figure 1 in ref. 1; also consistent with figure in ref. 4)

The 14 character-elements - set nr. 2 (intermediate)

(source: based on figure 2 in ref. 6)

The 14 character-elements - set nr. 3 (post-1947)

(source: figure 2 in ref. 4, also consistent with fig. 11 in ref. 6)

The alphanumeric character-set of the ETK comprises 41 characters:

The character set - 41 characters (pre-1947)
(source: figure 1 in ref. 1)

Additional characters possible with the elemental sets

(source: based on figure 2 in ref. 6)

Characters are transmitted as a 14-bit pulse sequence: one bit for each of the 14 basic elements. Bit 1 represents element 1, bit 2 represents element 2, etc. The receiving printer evaluates each received bit by itself, and determines if the associated element needs to be printed. Clearly, this can only work if the printer knows when the sender starts a pulse sequence. Also, sender and printer have to operate at the same speed. This is easy in a single-motor sender-printer terminal (local printer). However, a remote printer needs to be signaled that a new sequence starts. This is done by sending a conventional start-pulse before sending the 14 data bits. An implicit stop-bit is added at the end. It serves as a pause between characters, to get ready for the next start-pulse, and to add margin for the difference in motor speed between sender and remote printer.

The use of segmented characters dates back at least to 1908, when a 9-element numeric indicator was patented. This type of indicator made a comeback in the 1960s, in the form of multi-segment numeric and alphanumeric indicators that use incandescent/filament, gas plasma, cold-cathode neon ("nixie" tube), vacuum fluorescent, LED, or  LCD technology.

Multi-segment numeric indicators - incandescent backlighting

(source: fig. 1, 2 in ref. 4; 1908)

"Modern" 16-segment LED display indicator

THE SENDER. The function of the sender is to translate keyboard selected characters into a fixed-length, 16-bit pulse sequence (14 elemental bits, start-bit, stop-bit). Each key of the keyboard is attached to a selector bar that has 2-6 tabs. The tabs correspond to the start-pulse, and up to five basic character elements that make up the associated character. The keyboard mechanism has 15 switch contacts (start-pulse, 14 basic elements). The switches are actuated by the tabs of the selector bar of the depressed character-key. As with Hellschreibers, the keyboard has a lock-out mechanism such that the selected key remains latched; no other key can be depressed as long as the selected key is being sent. The keyboard has a self-locking repeat key (as found on standard telex terminals and Hell start-stop machines).

Generation of a tone-pulse sequence
(source: adapted from fig. 1 in ref. 6)

One side of each switch is connected to a dedicated segment of the stator of the sender. The switches are "normally closed" ( = "tone on"). Switches that are actuated by a tab of the selector bar are "open" ( = "tone off"). The other side of all the contacts is connected to a common point.

Depressing any key starts the transmission sequence. Via a clutch mechanism, the main driveshaft of the sender-printer terminal is engaged and makes one revolution. A copper brush is connected to the tip of a lever that is attached to the drive shaft. The brush is connected to a slip-ring on the drive shaft.

A tone oscillator is connected to the common point. Its constant tone passes via all closed switches to the associated stator segments. As the shaft turns, the brush scans all segments of the stator. The tone is output for all segments for which the corresponding switch contact is closed. The contacts for the elements of the selected character are open. They cause the tone to be turned off for the duration of the segment.

That is, the pulses are actually created by off-keying the tone. This is the opposite of Hellschreiber (and most other telegraphy systems). Early ETK-models (ETK 47 & 50) use "Ein-Ton-Telegraphie" (ETT, single-tone telegraphie),  with keying of a 1500 Hz tone (ASK modulation). It can be transmitted via phone lines (2- and 4-wire) and radio. Model ETK-R 55 can also use two-tone frequency shift modulation (FSK), with mark and space frequencies of 1145 Hz and 1255 Hz respectively (1200 Hz +/- 55 Hz, 110 Hz shift). This increased robustness of the start-stop synchronisation. The receiver circuitry of this ETK model could also evaluate the second harmonic of the tone frequency (i.e., 2400 Hz +/- 110 Hz), to improve print quality during radio propagation conditions with selective fading.

Pulse sequence for the character "R"
(source: figure 3 in ref. 1; 400 msec timing implies pre-1947 definition)

Timing of the 400 msec character pulse sequence is as follows (ref. 1): 

	start-pulse: 25 msec
	14 element-pulses, each 25 msec (hence 14 x 25 = 350 msec total)
	stop-pulse of 25 msec. The stop-pulse is actually "tone on", unlike the start-pulse and activated element-pulses. It is generated separately from start- and element-pulses.

Timing of the 200 msec character pulse sequence is as follows (ref. 6): 

	start-pulse of 20 msec
	14 element-pulses, each 10.8 msec (hence 14 x 10.8 = 150 msec total)
	stop-pulse of 20+9 = 29 msec (the main drive shaft stops 9 msec after element 14; the stop pulse continues for another 20 msec, via a cam wheel).

Timing of the 197 msec character pulse sequence is as follows (ref. 11, KFF-58/61/68): 

	start-pulse of 25 msec
	14 element-pulses, each 10.85 msec (hence 14 x 10.85 = 152 msec total)
	stop-pulse of 20 msec (the main drive shaft stops 9 msec after element 14; the stop pulse continues for another 20 msec, via a cam wheel).

A data-bit length of 10.8 msec implies a telegraphy speed of 93 baud.

The ETK sender uses a 14-element mechanism. It appears to be impractical to expand this to the 98-pixel sender of the Hellschreiber (the Hell-font has 7 columns of 14 pixels). As usual, appearances are deceptive.  It can be done - and has been done! Amateur Hellschreiber enthusiast  Martinus Rooth (PA0MPR, SK) used a stator disk with 98 segments and a turning brush contact. He added a switch to each key of a typewriter keyboard. Via diodes, each switch fans-out to the stator segments that are associated with the specific character (±800 diodes in total). Ref. 10, early 1990s.

98-segment stator with revolving brush contact in homebuilt Hellschreiber sender of M. Rooth
(source: ref. 10; the stator disk is clearly visible left of center)

THE PRINTER. At the heart of the printer is a revolving type-wheel ("Typenrevolver"). The wheel has 14 type-stamps that are distributed around its circumference. Each stamp has the type of one specific character-element on its striking face. So, the revolver of the ETK is not a six-shooter, but a Swiss 14-shooter! The type-stamps are spring-loaded, and can only move parallel to the axis of rotation of the wheel.

Type-wheel of the ETK-R-55
(source: fig 11 in ref. 6)

There are two cam wheels on the drive-shaft of the revolver (items 25 and 47 in the diagram below). Both have notches all around their circumference. One cam wheel (item 47) enables the printer-hammer if 1)  a recessed notch of this cam wheel passes by the printer solenoid (item 42), and 2) the solenoid is not energized at that time. Recall that absence of a tone signals receipt of an active element-bit. The second cam wheel (item 25) provides actuation of the spring-loaded printer hammer (if the latter is enabled by the solenoid).

The ETK printer mechanism

(source: adapted from figure 2 in ref. 5)

Upon receipt of a start-pulse, the drive shaft begins to make one revolution. At the start of the revolution, the type-stamp of the first basic element appears in front of the paper tape. If at that time no tone is received from the sender, then the hammer is enabled and actuated. This taps the type-stamp against the paper, and the basic element is printed. The type-stamps are kept inked with a felt ink roller. The ETK prints on paper tape that is 9.5 mm wide (3/8"). That is the same width as used by start-stop Hellschreibers (models 39, 40, 44, and 72, 73) of the 1950s. Gummed tape could be used, to facilitate gluing the tape onto telegram forms.

The drive-shaft of the sender and the (local or remote) printer move in lock-step. One by one, the 14 type-stamps rotate by the paper tape, as the 14 bits are received. The diagrams below show how the characters R, A, and E are recomposed with a sequence of basic character-elements.

Re-composition of the character "R" onto paper tape
(source: figure 2 in ref. 1)

Left: the individual elements for "R". Right: those same five elements printed in sequence
(source: figure 3 in ref. 6)

Pulse-sequence and re-composition of the characters  "A" and "E"

(source: figure 1 in ref. 5)

The drive-train of the sender-printer contains an interesting coupling mechanism: a spring-coupler ("Federkupplung"). The driving shaft and the driven shaft are of equal diameter and coaxially aligned. One end of each shaft is inserted into a cylindrical spring. One end of the spring is permanently attached to the driven shaft. When the opposite end of the spring is not attached to the driving shaft, the spring spins freely about the driving shaft, with insignificant friction. The driving shaft has a collar with a snubber. When the snubber is activated, it holds the spinning end of the spring firmly against the driving shaft. This causes the spring to tighten up around both shafts, and rigidly couples the shafts almost instantaneously.

Principle of the spring-coupling

(source: figure 6 in ref. 6)

ETK MODELS. The following ETK models were developed and manufactured by Gretag AG (founded in 1943 as Dr. Edgar Gretener AG, renamed Gretag AG in 1946):

	ETK 47 and its upgrade, the ETK 50; sometimes referred to as ETK 47/50.
	ETK-R 55,
	the combined ETK/crypto-machine KFF-58, and its upgrade, the KFF 68; sometimes referred to as KFF-58/68.

The two-digit number in the model designator generally refers to the first year of manufacturing.

Model ETK 47 was developed ca. 1942-1947 and manufactured1947-1950. The Swiss army bought 250 units, with a first order for 50 units placed in 1947. ETK 47/50 remained in service until 1971. It was also used commercially, over public telephone lines. In military service, it was used in combination with the 12-wheel electro-mechanical tele-crypto machine TC 53 (ref. 7; also developed and manufactured by Gretag AG).

ETK 47 comprises a sender/printer terminal unit, and an amplifier/detector unit, housed in a carrying case.  Like the Hell Feldfernschreiber, the terminal unit is pulled out of the case during operation. The case measures ca. 30x35x45 cm (≈ 18¼ x 13¾ x 11½ ") and the set weighs 26 kg (≈ 56 lbs). Like the Feld-Hell, anode voltage is provided by a generator that is attached to the motor of the terminal (standard "dynamotor" arrangement). The circuitry of the amplifier/detector unit is very straightforward, and uses three tubes of type DLL21 (Philips dual-pentode). The unit can be powered with either 12 Vdc or 220 Vac. Communication is half-duplex over phone lines, and uses 1500 Hz "Ein-Ton-Telegraphie" (ETT). That is, ASK modulation of a 1500 Hz tone. Ref. 1, 2, 5, 12a, 12b.

ETK 50 is basically an ETK 47 with an improved keyboard mechanism, so it is full compatible with the ETK 47.

ETK 47 in its case - all legends are in German and French
(all original unedited Gretag equipment photos: courtesy Walter Schmid, HB9AIV)

ETK 47 - keyboard-printer in operating position

Printer-head and stator of the sender of the ETK 47

The printer mechanism of the ETK 47

Close-up of the ETK 47 printer revolver - one type-stamp engaged
 

Schematic of the amplifier unit of the ETK 47
(source: figure 13 in ref. 2)

As stated above, the ETK 47/50 used 1500 Hz ASK modulation. Not surprisingly, this was insufficient for robust detection of the start-pulse when communicating over shortwave radio - in particular during poor signal-to-noise conditions and fading. This prompted the development of model ETK-R 55. The "R" stands for "Radio". ETK-R 55 retains the 1500 Hz ASK modulation, but only for operation over telephone lines.  Two-tone frequency-shift keying (FSK) modulation was added for radio communication. The mark and space frequencies are 1145 Hz and 1255 Hz respectively (1200 Hz +/- 55 Hz; 110 Hz shift). The amplifier/detector circuitry of this ETK model could also evaluate the second harmonic of the tone frequency (i.e., 2400 Hz +/- 110 Hz). This improved print fidelity during radio propagation conditions with selective fading.

ETK 47 comprises a sender/printer terminal unit, and an amplifier/detector unit, housed in a carrying case.  Like the Hell Feldfernschreiber, the terminal unit is pulled out of the case during operation. The case measures ca. 30x36x48 cm (≈ 12 x 14¼ x 19 ") and the set weighs 27.5 kg (≈ 60 lbs). The amplifier/detector unit uses five tubes of type DLL21 (Philips dual-pentode) - two more than ETK 47/50. The unit can be powered with either 12 Vdc or 110-250 Vac. Ref. 1, 2, 6, 12a, 12b.

Model ETK-R 55 was developed 1953-1954 and manufactured 1956-1957. The Swiss army bought 90 units in 1957. ETK-R 55 remained in service until 1980.

ETK-R 55 - keyboard-printer removed from case

Electronics box of the ETK-R 55

ETK 47/50 and ETK-R 55 were used with the crypto unit TC-53. ETK-R 55 did significantly improve the robustness of the start-stop synchronization. However, loss of sync still occurred during high-noise conditions. Obviously this caused problems when communicating encrypted messages. Therefore, Gretag AG developed an ETK sender/printer model with a new synchronization method, and a matching real-time crypto encoder/decoder: the Kryptofunkfernschreiber KFF 58 (crypto radio-teleprinter) and the télécrypto TC 58, respectively. Ref. 3, 11, 12a, 12b. The synchronization method is based on using crystal-based clocks in the sending and receiving system. Clocks are aligned by both systems entering the "SYN" mode. The sender continuously sends a special sync character, and the printer operator adjust the local sync setting until the printed sync character received from sender overlays a locally generated (and also printed) sync character. Once synchronized, the two units remained in sync for at least 15 minutes without needing a re-sync. Contrary to its predecessor ETK-R 55, the KFF 58 only used 1500 Hz ASK modulation, not FSK.

The particular transmission and printing processing of the KFF 58 required a buffer for two 14-bit characters. This was implemented with electromechanical components (relays). During a technology refresh in 1968, this was replaced with solid-state circuitry. The model number was bumped to KFF 68 (fully compatible with the KFF 58).

Model KFF 58 was developed 1956-1958 and manufactured 1958-1962. The Swiss army bought 441 units. KFF-58 remained in service at least until 1987. The Austrian army also bought a number of units.

The set is not exactly "light weight": the teleprinter terminal  weighs 69 kg and the crypto unit 26 kg - almost 100 kg total (220 lbs)!

The KFF-58/68 sender/printer terminal with crypto unit TC 58 on top

To hear what the FSK signal of the KFF sounds like: click here (Stiftung HAMFU / Verein IG Uem).

PERSON & COMPANY. The ETK was developed by the Swiss Dr. Edgar Gretener (1902-1958). During the 1930s, he headed up a development department at Siemens in Berlin. In 1943, he founded a engineering company near Zürich/Switzerland, for electromechanical systems and lighting technology. The company name was "Dr. Edgar Gretener AG", renamed to Gretag AG in 1946.

In 1939, Gretener's compatriot Prof. Friedrich ("Fritz") Fischer and his university team invented an impressive large-screen video projection system: the "Eidophor" (ref. 13-16). A working prototype was presented in 1943. Fischer died in 1947, at which time Gretener took over the development and commercialization. It came onto the market ca. 1952, via Gretag. Image quality (incl. color) and performance were enhanced over the following years. Production ceased in the late 1990s.

The Gretag group became a subsidiary of the Swiss industrial giant Ciba-Geigy in the late 1950s, until a buy-out by Gretag management in 1990. Gretag Imaging then became a leading manufacturer of photofinishing equipment. Also ca. 1990, the crypto activities of Gretag were spun off as "Gretag Data Systems AG". It was renamed to "Gretacoder Data Systems AG" in 1995, and to "Safe Net data Systems AG" after a foreign takeover. Late 2000, the share price of Gretag Imaging collapsed, and it was sold off to the Dutch reprographic specialist Océ. Two years later, Gretag Imaging went out of business.

Dr. Gretener held about 350 patents in Europe, the USA and Canada; primarily in the field of film and image technology (e.g., color separation), lighting, and cryptology.

There are some interesting links between Dr. Gretener and Dr. Hell. Obviously there is the common connection via Siemens in Berlin. This may be where Gretener was exposed to the Hell teleprinter system. It may also be a coincidence that the Zürich-based EMA company built Hellschreibers during WW2... The ETK printer mechanism also shows some similarities with a 1941 Hell company patent about a sping-loaded printer hammer (ref. 19). "Crypto" is an other common area. In 1944, Dr. Hell developed the "Hell-Geheimschreiber" crypto machine. He obtained over a dozen crypto-patents during the period 1952-1976. In 1954, Hell built the Hell 54 crypto machine, actually a Hagelin C52 crypto machine built in license. Boris Hagelin also developed crypto machines for/with Rudolf Hell; p. 30 in ref. 17. Hagelin spent WW2 in... Switzerland. Hell co-invented the video camera tube in 1925, and was very active in the field of color scanning and printing technology - before Gretener developed his color-separation technology. I do not know if they knew each other personally...

REFERENCES:

	Ref. 1: "The teletype ETK - Univocal combination teletype", Ingenieurbureau Dr. E. Gretener, Projekt lo9a, Akten-Nr. 188, 12 April 1945, 9 pp.
	Ref. 2: "Analysis of Swiss ETK Teletypewriter", C.P. Seymour, L.B. Rosenberg, W.S. Dwinell, Wright Air Development Center (WADC) Technical Report (TR) 52-266, AF-WP-(S)-O-31 Jul 53 65, RDO No. 102-22, September 1952, 36 pp.
	Ref. 3: "Der Krypto-Funk-Fernschreiber KFF 58: Grundlagen, Funktionen, Betriebstechnik, Simulation", Walter Schmid (HB9AIV), self-published, 2008, 269 pp.
	Ref. 4: "Illuminated announcement and display signal", Frank W. Wood, United Sates Patent Office, patent nr. 974943, filing date 17 June 1908
	Ref. 5: "An Improved Telegraphic Printing System", Edgar Gretener, UK Patent 639241, filed 20 December 1947
	Ref. 6: "ETK-R-Fernschreibanlage Mod. 55" [description and schematic], Funktionsbeschreibung Nr. 501-2 & 502-2, Dr. Edgar Gretener A.G., 44 pp.
	Ref. 7: "Das Telekryptogerät «TC 53» - Bedienungsanleitung; L'appareil télécrypto «TC 53» - Instruction de service", Dr. Edgar Gretener AG, 50 pp.
	Ref. 8: "Die Endgeräte vom Morseschreiber bis zum Laptop", Rudolf J. Ritter, Vol. 14 of "Das Fernmeldematerial der Schweizerischen Armee",  Merker Verlag, 2007
	Ref. 9: "Die ETK-Fernschreibstation", Reglemente der Schweizerischen Armee, 58.122d, 1958
	Ref. 10: p. 4, 5 in "Hellschrijver voor zelfbouw (deel 1-5)", (description of home-built Feld-Hell of Martinus Rooth (PA0MPR) and A. Rooth-Beems (PA0ARB)), Bastiaan Edelman (PA3FFZ), CQ-PA, 2/1994, pp. 32-34, 3/1994, pp. 63-64, 4/1994, pp.  97-98. 5/1994 , pp. 121-122, 12/1994, pp. 322-325
	Ref. 11: "Der Krypto-Funk-Fernschreiber KFF - Kurzbeschreibung und Bedienungsanleitung" [KFF-58], Reglemente der Schweizerischen Armee, 58.134d, 1960, 36 pp.
	Ref. 12a: website of the Stiftung Historisches Armeematerial Führungsunterstützung (HAMFU) and Interessengemeinschaft Übermittling (IG Uem)
	Ref. 12b: website of armyradio.ch (here in English)
	Ref. 13: "Movies by Television - Swiss Used Film of Oil for Theater-Size Image", Joseph Israels, Popular Science, January 1946, p. 94
	Ref. 14: "What is Eidophor? Details on CBS's color system for theater TV viewing, as recently unveiled in New York", Radio & Television News, August 1952, p. 30
	Ref. 15: "The History of the Eidophor Large Screen Television Projector", Heinrich Johannes, Gretag AG, 1989
	Ref. 16: "Der Eidophor - Ein Grossbildprojektionssystem zwischen Kino und Fernsehen 1939–1999", Caroline Meyer, vol. 15 of " Interferenzen – Studien zur Kulturgeschichte der Technik", Chronos Verlag, 2009, 416 pp., ISBN 978-3-0340-0988-1
	Ref. 17: "Die Geschichte der "Hagelin-Cryptos"", Boris Hagelin, Crypto AG, lE 720, 1979, 64 pp.
	Ref. 18: "Hitlers letzte Maschinen" chapter 2.17 in "Codeknacker gegen Codemacher - Die faszinierende Geschichte der Verschlüsselung", by K. Schmeh, W3L Verlag, 2nd edition, 2007, 414 pp.
	Ref. 19:"Anordnung zur Aufzeichnung von Impulsen mittels eines umlaufenden Schreibrades und einer Schreibleiste" [arrangement for priniting of impulses with a revolving typewheel and piston], Joseph Lorbach (Hell company), Reichspatentamt, Patentschrift Nr. 732623, 27 Feb. 1941,

Allegedly, "Q", the gadget-guru of Her Majesty's secret service, provided James Bond with a wrist-watch Hellschreiber in the 1977 movie The Spy Who Loved Me. It is an "upgraded" Seiko model 0674.
 

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