Besides the Hell company and Siemens-Halske, there have been other manufacturers of teletype machines that use the Hellschreiber printer principle. Presented below are the ones that I am aware of. Some manufacturers may have filled the void caused by interruption during WW2 of exports from Germany to countries outside the German/Axis influence sphere, and it taking 2-3 years after WW2 for war-torn German companies to resume production.

Latest page update: 2 November 2018

©2004-2018 F. Dörenberg, unless stated otherwise. All rights reserved worldwide. No part of this publication may be used without permission from the author.

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The French company Le Matériel Téléphonque (L.M.T.) was created in 1889 by G. Aboilard & Cie., who in 1900 became a licensee for telephone patents of the American Western Electric Company (WECo). WECo was a wholly owned subsidiary of American Telephone & Telegraph (AT&T).


1933 L.M.T. advertizing

Ca. 1920, L.M.T. became a subsidiary of the American International Telephone & Telegraph (I.T.T) group, that was created by the Puerto Rico Telephone Company (Ricotelco) in 1920. From 1922 through 1925, ITT acquired all overseas subsidiaries of Western Electric, and a number of European telephone companies through its subsidiary C. Lorenz AG in Germany. This included Standard Telephones & Cables Ltd (STC) in Britain, Standard Elektrik Lorenz (SEL) in Germany, Bell Telephone Manufacturing (BTM) in Belgium, and Compagnie Générale de Constructions Téléphoniques (CGCT) in France. L.M.T-ITT was acquired by Thomson-CSF in 1976, by Alcatel-Cit in 1986, Nokia in 1987, and Semi-Tech in 1996. In 1925, L.M.T. moved from Paris to nearby Boulogne-Billancourt, on the banks of the river Seine. They co-developed the national PTT public telephone network, in which they introduced the Rotary exchange switch (originally a Western Electric product). They also provided private exchanges to large companies such as Renault and EDF (the French national electrical power company). In 1937 they built and installed a very high-power transmitter on top of the Eiffel tower. During the 1930s they also made radio sets, car radios TV sets, vacuum tubes/valves (under license; incl. thyratrons), and arc lights (also under license).


The L.M.T. labs in Paris

In the mid-1930s, the R&D labs of L.M.T. developed a 7-tone teleprinter system. Like the Hellschreiber system, it is based on transmitting pixel stream that are printed in real-time, without encoding. The L.M.T. system uses a character font that comprises 7 rows of 10 pixels (max, excluding space between characters).


Some examples of the LMT 7-line font

(source: Figure 1 in ref. 1A, 1B, Fig. 2 in ref. 1F)

For a standard 46 character alphabet (letters, numbers, punctuation marks), the font consisted of 39 different elemental row-patterns of 10 pixels each:


The 39 elemental line patterns

(source: Figure 2 in ref. 1A, 1B, Fig. 2 in ref. 1F)

Of these 39 patterns, several are the combination of two other such patters. E.g., pattern 16 is the combination of pattern 2 and 7. This allowed the number of required elemental line patterns to be reduced to 23. Hence only these 23 were "programmed" into memory, in the form of 23 continuously turning notched disks (cam wheels) - just like what had already been common practice for years in Hellschreiber-senders of the Siemens-Halske company.


Notched-disk are the mechanical memories of the 23 pixel line-patterns

(source: Fig. 3 in ref. 1F)

The rows are transmitted and printed simultaneously, like the original Hellschreibers with electrochemical and carbon-ribbon printers. Effectively, this means that there are seven character-line transmitters, that translate the charter selected via a keyboard into seven pulse sequences. This is done by keying seven separate tone oscillators: 600-2040 Hz with 240 Hz spacing. The tones are "normally on", so keying of the tones is actually "off-on", rather than the standard "on-off". That is, the row-tone is turned off for black pixels (p. 24 in ref. 1B).

The receiver comprises seven parallel narrow bandpass filters, each followed by a dedicated rectifier/detector. Unlike the Hellschreiber with its helix printer, there are seven individually actuated printer "pins" (needle, stylus), each actuated by a separate solenoids (electro-magnet) and associated driver tube. Printing is done onto paper tape, with a carbon-paper ribbon between the paper tape and the styluses. Obviously the resulting equipment is rather complex.


Principle of the 7-frequency L.M.T. printer

(source: Fig. 297 in ref. 1E)

The L.M.T. keyboard sender is a rather complicated device. This is driven by the fact that the font was reduced to 23 elemental line-patterns, and a complex electro-mechanical "sequencer/re-combiner" (including a 1-character deep buffer between the keyboard and the character generator) was required to generate the 7 simultaneous pixel streams.


Keyboard sender (without the 7 tone oscillators)

(source: Fig. 3 in ref. 1A, 1B; click here to get full size)

The photos below show that the equipment was impressive in size. Note that the equivalent Siemens-Halske equipment was no bigger than the keyboard-unit and printer-unit attached to the large cabinets in these photos!


L.M.T. sender/printer unit (left) and receiver/printer unit (right)

(source: Fig. 11 & 12 in ref. 1A, 1B)

Transmission is 5 characters per second. That is, 200 msec per character. Each character-line comprises at most 10 pixels. Hence, the shortest pulse is 20 msec, and the telegraphy speed is 50 Baud (25 Hz pixel rate). The system uses start-stop synchronization. A start-pulse is generated by temporarily suppressing the "normally on" tones of lines 1, 3, 5, and 7. Audio bandwidth is well over 2000 Hz, as the highest tone frequency is 2040 Hz.


Ernst Eduard Kleinschmidt, born in 1875 in Bremen/Germany, emigrated to the USA in 1883. At that time, his name was changed to Ernest Edward. During the period 1910-1920 he as well as Charles and Howard Krum developed major aspects of a new type of electromechanical printing telegraph: the start-stop teleprinter ("Springschreiber"). It had a start-stop mechanism that was an improvement of the one invented in France by Goyot d'Arlincourt (1869), combined with the multiplex system invented by Donald Murray in New Zealand in 1901. The trademarked product name "Teletype" was first applied to one of their machine models in 1921. A patent battle ensued between Kleinschmidt Electric Company and the Morkrum Company. The latter was founded in 1906 by Joy Morton and Charles & Howard Krum for the purpose of developing printing telegraph systems. The battle resulting in merger of the two companies into the Morkum-Kleinschmidt Company in 1924/25. The company name was simplified to Teletype Corporation in 1928. Ref. 2A-2D. Teletype became a subsidiary of the Western Electric Company (the manufacturing arm of AT&T) in 1930. In 1982, the Teletype Corporation became AT&T Teletype, when Western Electric was fully absorbed into AT&T as part of a settlement between the US Department of Justice and AT&T.


In 1930 (about a year and a half after Rudolf Hell filed his principal patent), Kleinschmidt filed a rather long patent (37 pages) for a "Facsimile printing telegraph system and apparatus":

Patent number Patent office Year Inventor(s) Patent owner(s) Title (original)
2046328 US 1930 E.E. & E.F. Kleinschmidt Teletype Corp. Facsimile printing telegraph system and apparatus

This is a two-fold patent. One part proposes a method for optically scanning a text message that is written, typed, or printed on a segment of tape. The pulses from the scanner are transmitted to a device that uses those pulses to directly reproduce the original message on sensitized paper, photographic film, or by chemical means. The printer creates two identical lines of text, one above the other. The second part proposes the equivalent of a Hellschreiber sender and printer. A sender that reads the message from a punch tape that is prepared with a standard keyboard perforator. The sender comprises a stack of notched "code disks". One disk for each character in the character set. The proposed character field has 18 columns of 25 pixels. The bottom three rows and the first three columns are left blank for character spacing. A "3-pixel rule" is applied (compared to Hell's "2-pixel rule"): black and white line-segments have a length of at least three pixels. Printing is done with a multi-start spindle onto paper tape, with a carbon tape or ink ribbon between the paper tape and the spindle. An electromagnet actuates the knife-edge hammer of the printer. The motor has a speed governor based on a tuning-fork.


Elements of Kleinschmidt's facsimile printing telegraph

(source: US patent 2046328)

Kleinschmidt is behind the late 1930s development of Teletype Corp.'s Model 17 teleprinter. Ref. 2E-2T. Based on its characteristics, it should be fully compatible with the ubiquitous Siemens Hell-Feldfernschreiber that entered military service in Germany in 1935. Model 17 transmits from a 5-bit punch tape.

  • The sender has a character-drum ("distributor") comprising a stack of 55 notched disks ("code disks"), one disk for each character of the character set (letters, figures, punctuation marks). Two different sets of disks were available:
  • 7-line characters (5x7 pattern - like the military Feld-Hell)
  • 12-line characters (9x12 pattern - like the original "Presse Hell" for news agencies)
  • Shortest pulse of ca. 4 msec (4.08 msec in the Feld-Hell)
  • Transmission rate of 122.5 Bd (same as the Feld-hell)
  • The tone frequency is 1000 Hz (vs. 900 Hz of the Feld-Hell - but that does not prevent complete interoperability).
  • Printer mechanism with a large-diameter 2-turn spindle ("scanning wheel"), 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 1800 rpm (vs. 3600 rpm in the Feld-Hell - but that is just a design choice). The motor is a 1/40 HP (25 watt) synchronous 110 volt / 50 Hz (!) AC-motor from GE
  • Paper tape transport is automatically stopped if no signal is received for about 10 sec. The sender transmits a motor-start pulse at the beginning of each message.


The sender of Teletype Model 17 - front view (ca. 1945)

(source: The Henry Ford Collection; used in accordance with Creative Commons license BY-NC-ND)


The sender of Teletype Model 17 - rear view (ca. 1945)

(source: The Henry Ford Collection; used in accordance with Creative Commons license BY-NC-ND)


The printer of Teletype Model 17 (1938)

(source: ref. 2E)


The printer & sender of Teletype Model 17 with a keyboard perforator on an SXT-1 table (1937)

(source: ref. 2E)


The Swiss company Fabrik für Electrische Mess-Apparate A.-G. (EMA) was founded in 1945. As the name suggests, their primary products were measurement instruments for voltage, current, power factor, resistance, and grounding. In November of 1947, the company moved to 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 ceased its operations in 1988. These days, there still exists at least one (new) company named EMA in Meilen (Engineering für Mikrotechnologie + Antriebstechnik GmbH), but they are not related.

EMA logo

EMA built four Hellschreiber printer models, from late 1945 through the early 1950s: HSG2, HS125, HPr3 and HPr4. War-torn companies Siemens and Hell did not resume operations until ca. 1948, so their was a market opportunity for other companies to service the large Hellschreiber user-base.

One of EMA's major Hellschreiber-customers was the Schweizerische Bundesbahnen (SBB, Swiss Railway Co.). EMA Hell-printers were also used by the Sportinformation sports news agency in Zürich (a subsidiary of the Swiss general news agency Schweizerische Depeschenagentur, SDA), Agence Cosmographique (a Swiss financial & commercial news agency), and the Swiss P.T.T. in Bern. Ref. 5C. EMA Hell-printers were also acquired by the Dutch P.T.T. and the Dutch news agency ANP (ref. 3A-3P, 5A-5W), as well as the Dutch newspaper De Waarheid (ref. 3M)

EMA logo

EMA logo

EMA also built and marketed at least one model Hell-sender, early 1949. The development of this punch-tape sender was apparently difficult, due to lack of cooperation by Siemens in Germany and RADIAR S.A.I. in Rome/Italy. Ref. 5K. The Dutch news agency ANP successfully tested an EMA Hell-sender at transmitter facilities of the Dutch P.T.T. in April of 1949. The Dutch P.T.T. was, however, dissatisfied by the fact that (unlike Siemens Hell-senders), the EMA senders cannot send figures/numbers. EMA's response: Reuters only sends numbers written out in full. In May of 1949, EMA proposed to ANP/P.T.T. to include a lever mechanism, to interrupt the punch-tape transport, to simplify the insertion of such tape. Ref. 5S.

EMA hellschreiber

Hell-message from EMA to the ANP news agency, announcing the EMA Hell-sender ("EMA Geber")

(February 1949, ref. 5K)

EMA hellschreiber

Label on EMA Hell-printer model HSG2 , serial nr. 113

EMA Hell-Schreiber HSG2 was designed late 1945 (ref. 6A). I do not know what the "G" in "HSG" stands for, or whether an HSG1 was ever produced. HSG2 had the following characteristics and interfaces (ref. 6A, 6B):

  • Two pairs of "Input" jacks on the front panel, for audio from a radio receiver. Selectable on the front panel are 4 kΩand 800 Ω inputs. The inputs are transformer-coupled. The 4 kΩ input is for connecting to a standard high-impedance headphone output of a radio. The 800 ohm input is for connecting to a standard 600 Ω phone line.
  • This suggests a mismatch, but keep in mind that a "600 Ω" phone line only has a 600 Ω impedance at one single frequency: around 1300-1400 Hz. I.e., only in the center of the voice-passband. At the standard Hellschreiber tone-frequency of 900 Hz, a "600 Ω" phone line actually has an impedance of 800 Ω.
  • Required audio input power: about 100 mW.
  • Tone filter: selectable for 900 Hz, 1500 Hz, and Off.
  • "Headphones" output jacks on the front panel, for connecting a headset.
  • Printing speed: 2.5 characters per sec.
  • Paper tape: width 15 mm.
  • Felt ink roller, with an inside diameter of 16 mm.
  • Mains switch / volume control.
  • Power: selectable 110/125/145/220 volt AC; the "Pilot Light" indicates if the unit is powered on.
  • AC-motor with centrifugal speed governor.
  • "Speed Regulator" knob: adjusts the position of the electrical contacts of the speed governor.
  • "Start/Autom./stop" switch: to turn the motor on/off manually, and enable remote on/off control with a long tone pulse at the beginning and end of message (as in the Siemens-Hell "Presse Hell" machines).
  • Paper tape speed: 44 cm/min.

This printer is fully compatible with the 1935-1945 Siemens Hell-Feldfernschreiber.

This model has three vacuum tubes/valves: an EF13 pentode (pre-amplifier), an AL4 pentode (printer-magnet driver amplifier) and an AZ1 (power-supply rectifier). Ref. 6A.

EMA hellschreiber

Front-view of EMA Hell-printer model HSG2, serial nr. 113

(original HSG2 photos: courtesy Heinz Blumberg, DC4GL, 2011)

EMA hellschreiber

Top-view of EMA Hell-printer model HSG2, serial nr. 113

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.

EMA hellschreiber

Bottom-view of the chassis of EMA Hell-printer model HSG2, serial nr. 113

EMA hellschreiber

Rear-view of the chassis of EMA Hell-printer model HSG2, serial nr. 113

(center: disk of centrifugal motor speed control, far right: motor on/off relay)

EMA hellschreiber

Motor (below the capacitor block) and disk of the centrifugal speed regulator

EMA hellschreiber

Printer-solenoid of EMA Hell-printer model HSG2, serial nr. 113

EMA hellschreiber

EMA Hellschreiber HS-125 was designed in 1947 (ref. 6C). It is a simplified version of the HSG2. HS-125 had the following characteristics and interfaces (ref. 6C, 6D, 6E):

  • Four input jacks on the rear panel, for inputting the audio signal from the primary or secondary side of the radio receiver's output transformer (10 kΩ and 5 Ω respectively), or to a standard 600 Ω phone line.
  • Tone filter: selectable for 900 Hz ,1500 Hz , and Off.
  • "Headphones" output jacks on the front panel, for connecting a headset - to verify the audio signal from the radio receiver.
  • "Writing Control" knob - to adjust the gap between the printer-spindle and the knife-edge hammer of the printer-magnet.
  • "Volume Control" - to adjust the current through the printer-magnet.
  • A neon lamp illuminates when the unit is powered up, and blinks in the rhythm of the received tone pulses.
  • AC-motor with centrifugal speed governor.
  • "Speed Regulator" knob: adjusts the position of the electrical contacts of the speed governor.
  • Printer speed adjustable from 2-5 characters/sec.
  • "Start" & "Stop" pushbuttons - to manually turn the motor on/off.
  • "Automatic On/Off" - to enable turning the machine on/off via remote control with a long tone pulse at the beginning and end of message (as in the Siemens-Hell "Presse Hell" machines)
  • Paper consumption 1 m per minute at 5 chars/sec.
  • Power: selectable 110/125/145/220/250 volt AC, 65 watt (30 watt on stand-by).
  • Size: 39x22x27 cm (LxWxD; ≈15.4x8.7x10.6 inch)
  • Weight 14 kg (31 lbs)
  • Cabinet: dark-brown oakwood.

The HS-125 is compatible with the 1935-1945 Siemens Hell-Feldfernschreiber and the 1933 & 1940 Siemens "Presse Hell" models.

As on model HSG2, the legends on the front and rear are in English. The unit only has two vacuum tubes/valves: an AZ1 dual-diode rectifier in the power supply, and an EBL21 in the amplifier. The EBL21 is a rare dual-diode audio-output pentode. Ref. 6D.

EMA hellschreiber

EMA Hell-Printer Type 125

(source: ref. 6D)

EMA hellschreiber

Front-panel of the EMA Hell-Printer Type 125, serial nr. 63

(original HS125 photos: courtesy Remmelt-Jan Warries, PAØRJW, SK)

EMA hellschreiber

Top-view of the EMA Hell-Printer Type 125, serial nr. 63

EMA hellschreiber

Bottom-view of the EMA Hell-Printer Type 125, serial nr. 63

EMA hellschreiber

Connections on the rear of EMA Hell-Printer Type 125, serial nr. 63

The Dutch news agency ANP and the Dutch P.T.T. encountered major design and quality problems with this EMA model, and actually tried (unsuccessfully) to return the 21 purchased units to EMA. EMA itself also announced some problems.

  • Excessive friction in the bearings of the Swiss-built motors, affecting a batch of printers, and requiring refurbishment ("product recall"). Ref. 5A.
  • Radio receiver gain plus printer amplifier gain is considered insufficient for weak signals, esp. on shortwave. An additional amplifier stage must be built into the HS-125 printers. Ref. 5E, 5F, 5G.
  • After 10-12 hours of operation, the speed has drifted so much, that the speed regulator could no longer compensate. Ref. 5F.
  • Burned-out 110/125/145/220/250 volt transformer. Ref. 5O, 5T.
  • Ink-roller shaft has too much friction and rollers often do not turn freely. Ref. 5G.
  • Printer often needs to run 15 minutes after power-up, before it prints properly. Ref. 5G.
  • One brand new printer ran too slowly; ANP had to disassemble, reassemble and adjust the speed regulator. Ref. 5O.
  • One brand new unit did not work at all: several resistors were detached. Ref. 5O.

A chronological summary from ANP's point of view is provided in ref. 5H. Ref. 5J shows several pages of print-outs of a Reuters newscast, that were made by ANP on 10-January-1949 with an HS-125 printer.

General conclusion from ANP and P.T.T: these machines are less reliable than Siemens printers, and should not be operated for extended periods. OK for intermittent operation, each time after 10 minutes running before using. Ref. 5L states that the HS-125 units that were upgraded by EMA with a second amplifier stage, performed satisfactorily.

According to EMA advertizing, Hell-Printer HPr3 was "primarily designed for use in the diplomatic service" (ref. 6F, 6G). The main characteristics and interfaces are:

  • Input jacks on the rear panel, for inputting the audio signal from the primary or secondary side of the radio receiver's output transformer (7 kΩ and 7 Ω respectively), or to a standard 600 Ω phone line (700 Ω).
  • Required audio input power ("sensitivity"): 6 volt (!) at 7kΩ - unclear if this is volt peak, peak-peak, or rms. Anyway, it confirms the reported insensitivity.
  • No volume control - audio signal volume has to be adjusted at the radio receiver!
  • No tone filter.
  • Printer speed is 5 chars/sec.
  • "Start" & "Stop" pushbuttons - to manually turn the motor on/off.
  • Optional: automatic motor start-stop, for remote control.
  • Paper speed 1 m/minute.
  • Power: 110-250 volt / 50 Hz / ca. 60 W.
  • Size: 28x20x12 cm (WxHxD; ≈11x8x4.7 inch)
  • Weight ca. 8 kg (17.5 lbs)

The unit has two vacuum tubes/valves. Like the HS-125, it has a single-stage amplifier with an EBL21 dual-diode audio-output pentode (deemed insufficient by the Dutch P.T.T. and news agency ANP, as discussed above for the HS-125). The rectifier diode in the power supply is an AZ21 rather than an AZ1. The photo below shows that the EBL21 is readily accessible at the top right-hand corner of the unit (partially hidden by the roll of paper tape). This suggests that the EBL21 was not particularly reliable, and needed frequent replacement, hence easy access.

EMA hellschreiber

EMA Hell-printer model HPr3

(source: ref. 6F, 6G)

According to EMA advertizing, Hell-Printer HPr4 was "particularly suitable for commercial use" (ref. 6F, 6G). The main characteristics and interfaces are:

  • Input jacks on the rear panel, for inputting the audio signal from the primary or secondary side of the radio receiver's output transformer (10 kΩ and 5 Ω respectively), or to a standard 600 Ω phone line.
  • Required audio input power ("sensitivity"): 20 mV at 600 Ω - much better than the HS-125 and HPr3!
  • Volume control
  • A neon lamp illuminates when the unit is powered up, and blinks in the rhythm of the received tone pulses.
  • Tone filter: 900 Hz (400 Hz bandwidth)  / Off.
  • Printer speed is 5 chars/sec.
  • "Start" & "Stop" pushbuttons - to manually turn the motor on/off.
  • Automatic motor start-stop, for remote control.
  • Paper speed 1 m/minute.
  • Power: 110-250 volt / 50 Hz / ca. 60 W.
  • Size: 36x23x15 cm (WxHxD; ≈14x9x6 inch)
  • Weight ca. 12 kg (126.4lbs)

Like the HSG2, but unlike the original HS-125 and the HPr3, the HPr4 has three vacuum tubes/valves. The two-stage amplifier comprises two Philips 18040 pentodes. The photo below shows that these two tubes are readily accessible at the top of the unit (above the roll of paper tape).

EMA hellschreiber

EMA Hell-printer model HPr4

(source: ref. 6F, 6G)

The photo below shows HPr4, serial number 5219. Note: this does not mean that over 5000 units were built: the first digit(s) of the serial number often indicated the version or modification status. Compared to the unit shown above, it has an additional headphone output at the top of the front-panel, and what appears to be a push button at the top right-hand corner:

EMA hellschreiber

HPr4 VARIATION, SLIGHT headphone jacks at front, different paper tape roll holder

(original photo: courtesy Miklós, HA5CMB, used with permission)

This printer can be seen in action in the video clip below:

EMA Hellschreiber printer in action

(source: YouTube; Miki András, HA5CBM/HA5KDR)

As mentioned above, customers of EMA included the Dutch news agency ANP (Algemeen Nederlands Persbureau) and the Dutch P.T.T. Early 2015, I located archived correspondence between these three parties in the National Archives of The Netherlands in The Hague. I visited the Archives in August of 2015, and copied about 75 documents. A number of them include price quotations and invoices (ref. 3A-3P), including taxes, import duties (12-30%!), and shipment. I have summarized this is the table below. I have added my estimates of what the equivalent prices would be in today's money (2015), based on historic statistics on general inflation ("buying power") and exchange rates. Note that inflation for specific industrial products such as telecommunications equipment, does not necessarily track that general "consumer price index" inflation.

EMA prices

Pricing of EMA Hellschreiber printer models, parts, and accessories

(source of Swiss inflation data: fxtop.com)

The estimated equivalent equipment prices in 2015 may seem excessive. However, when considering what the original 1946-1951 prices were, in terms of average salaries at the time, they may not be all that unrealistic... As a reference, in 1950, the average gross income in The Netherlands was DFL 3030, and an average car cost DFL 5000 (only 1 in 75 people owned a car). Ref. 4A, 4B. Source for historic DFL to Euro conversion data: Internationaal instituut voor sociale geschiedenis. Source historic Euro inflation rates: global-rates.com.


The Post- und Telegraphen Werkstätte (P.T.W., factory of the P.T.T) in Salzburg/Austria built at least one type of Hellschreiber printer: model HS1.


It prints at the same speed as the Siemens-Halske T empf 14 "Presse Hell" (5 characters/sec), The printer mechanism and associated levers are also the standard Siemens-Halske items, so it may have been built under license. The unit measures 21x38x14 cm (HxWxD, ≈8¼x15x5½"). Shown below are the machines with serial number 319, 323, and 331. It is unknown exactly in which period they were built - most likely not long after WW2.


Front-view of HS1 Hellschreiber serial nr. 331

(original photos of serial no. 321: courtesy H. Blumberg (DC4GL), used with permission)

The photo above shows that the HS1 has a standard Siemens-Hell printer module. Note: the blank metal sheet to which to printer module is fixed, is original!


Front-view of HS1 Hellschreiber serial nr. 331 - roll of paper tape removed

(round cover-plate to the right of the printer: access to one of the carbon brushes of the generator)


Rear-view of HS1 Hellschreiber serial nr. 331

(round cover plates: access to one of the carbon brushes of the generator, and a grease point of the gear box; top right-hand: operating voltage selector)

A very interesting design aspect of the HS1Hell-printer, is that is is constructed around the motor-generator of the Siemens Hell-Feldfernschreiber ("Feld-Hell") of WW2! Contrary to the Feld-Hell machine, here the motor-generator is installed horizontally! The top of the motor (which is the manual speed adjustment cap) sticks out of the right-hand side of the HS1:


The manual speed adjustment cap of the Feld-Hell motor-generator protrudes from the right hand side of the HS1


Front-view of HS1 serial nr. 331 - housing removed; horizontal installation of the Feld-Hell motor is clearly visible

(this particular HS1 has a Feld-Hell motor-generator that was built in 1941)


Top-view of HS1 serial nr. 331 - housing removed

This 12 Volt motor is powered by a 110/125/150/220 to 12 Volt transformer, followed by a bridge rectifier. The metal rectifier consists of 4+4 large disks, that are either selenium or copper-oxide rectifiers. A single selenium rectifier has a reverse voltage of ca. 20 volt (hence 4x20 = 80 volt), compared to ca. 6 volt for cuprous oxide (hence 4x6 = 24 volt). So, most likely, they are the latter. There is no filtering capacitor for the 12 VDC.The centrifugal speed regulator of the Feld-Hell motor has two centrifugally actuated contacts: one for nominal speed, one for overspeed.In the HSI1, it appears that the overspeed contact is not used, and the nominal speed contact is simply hard-wired to 12 VDC.

In the Feld-Hellschreiber, the generator part of the motor-generator provides the anode voltage for the Feld-Hell's four tubes (valves). In the HS1 Hellschreiber, there are no tubes, so there is no need for an anode voltage source. This also means that an external Hell printer-amplifier must be used, as is the case with all Siemens "Presse Hell" printers. For some reason, the carbon brushes of the generator are easily accessible from the outside of the HS1 housing...


Rear-view of HS1 serial nr. 331 - housing removed

The photo above and below clearly show that the gearbox is also "borrowed" from the Feld-Hellschreiber! The gearbox includes a notched disk (lower right-hand in photos below). It is used in the Feld-Hell when transmitting the special "pause" character. The HS1 does not have an integrated keyboard-sender, so the notched wheel serves no purpose (other than retaining the shaft of the paper tape transport).


The gear box of the HS1 (left) is the same as the one in the Siemens Hell-Feldfernschreiber (right)

There is an additional gear stage between the Feld-Hell motor and the Feld-Hell gearbox. It has a capped grease point (see photo below). The printer is set up for the speed of the "Presse Hell" system: 5 characters/sec. This is twice the speed of the Feld-Hell, so a 1:2 gear stage is required between Feld-Hell motor and the gear box.


Intermediate gear stage with a grease point (cap removed)


P.T.W. Hellschreiber type "HS1" - 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 "HS1" - serial number 323

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


Ca. 1952, a Hellschreiber was developed in the German (not-so) Democratic Republic (frmr. "East Germany"). It went into service with the Kasernierte Volks Polizei (KVP - Barracked People's Police) in 1954/55. The KVP was established in 1952 and was the predecessor to the Nationale Volks Armee (NVA - National People's Army, 1956-1990). This Hellschreiber was decommissioned towards the end of the 1950s, during standardization of communications equipment in the Warsaw Pact countries. Ref. 7A, 7B.

The Hellschreiber is referred to as Abtast-Fernschreiber (ATF, lit. "scanning teleprinter"), probably so as to avoid using the Hellschreiber name that was associated with the war-time Wehrmacht. The term "Abtastfernschreiber" was actually not new: Hellschreibers were referred to as "Abtast-Telegrafen" at least as early as 1940 (ref. 7C).

The ATF was manufactured by Rundfunk- und Fernmelde-Technik (RFT, Radio & Telecommunications Technology). RFT was a collective of electronic equipment and component manufacturers that had ended up in Soviet-occupied "East Germany" at the end of WW2. It was founded in 1946, and continued in the Democratic Republic (GDR/DDR, established 1949). Ref. 7D.


Not counting experimental prototypes, there are two basic versions of the ATF. Based on labels on the machines, they are:

  • ATF-00001
  • FSS.002-0001, simply referred to as "ATF-Schreiber" by KVP/NVA instructors and operators, and as "Feldfernschreiber" in the official military documents (ref. 7E, 7F, 7V).

The ATF was made for field operation, in combination with an FF 53 field telephone and Morse telegraphy key, over telephone "land" lines and via radio. The units also include a telegraphy relay, for direct-keying of a CW transmitter (or DC-pulse telegraphy).

The ATF was directly based on Siemens-Hell Feld-Fernschreiber ("Fed-Hell") technology. One of the surviving ATF model FSS.002 machines actually has a motor built by the Hell company. No doubt "procured" in the facilities of the Hell company in Berlin, that were abandoned at the end of World War 2. Knowledgeable staff of the Hell company must also have been available in the area.

The ATF are actually start-stop Hellschreibers, just like the Siemens-Hell models of the early/mid-1950s: the T typ 39/40/44 (printer-only), and T typ 72/73 (keyboard sender + printer). All these start-stop Hellschreibers use a start-pulse that is embedded in the (normally blank) first column of the characters of the Feld-Hell font. To send a start-pulse, the character-drum of the Hell-sender must be expanded. The Siemens-Hell start-stop senders have a character-drum that consists of a stack of notched disks. Here, the start-pulse is simply generated with an additional notch on the shaft of the drum. The ATF Hellschreibers used the same type of character-drum as the Hell Feldfernschreiber: a smooth drum with a ring of conductive metal patches for each character. In this case, a patch must be added at the beginning of each ring. This can be implemented as a conductive strip across the entire drum.

The photo below shows the evolution of the character-drum, from the Hell Feldfernschreiber to the ATF. From top to bottom:

  • Standard Siemens Feld-Hell, model T typ 58.
  • Siemens Feld-Hell, expanded with a start-pulse.
  • EXperimental prototype ATF, the XATF.
  • ATF model FFS-002.


Evolution of the character-drum, from Feld-Hell to ATF

The second character-drum in the photo above was probably used as a "proof of concept" prototype for the ATFs. It belongs to a factory-new Hell Feldfernschreiber with such a modified character drum that re-emerged in Berlin during the early 1990s. The professionally modified Feld-Hell drum has a flush metal strip across it. The width of the strip corresponds to a start-pulse with a duration of 4 pixels (out of a 14-pixel column), i.e., about 16 msec. The Feld-Hell drum is 20.4 cm long, with a diameter of 49.5 mm (8x2 inch), and 41 character-rings. Unlike the synchronous Feld-Hell and "Presse-Hell" systems, a start-stop system requires a "space" character. So there is an additional modification to this character drum and the associated keyboard: the "?" has been re-labeled "Zw" for "Zwischenzeichen" ( = "space"). Most likely, the white pixels of the corresponding ring of the character-drum (3rd ring from the right) would also have had to be removed, e.g., by lacquering them over.


The modified keyboard and character drum

The third drum belonged to an eXperimental prototype ATF, the XATF. It has a length of 23.6 cm and a diameter of 2.9 cm. This drum is the only surviving part of an XATF machine, besides a few components marked "XATF" in the regular ATFs. On the outside, the XATFs were identical to the FSS.002 ATFs. Obviously, the drum and associated mechanisms were different (ref. 7G). The XATF may have been model FSS.001. The fourth drum in the photo shows the ATF drum. It measures 23.6 by 3.95 cm and has 45 character-rings. It is narrower and longer than the 41-character Feld-Hell drum.

The photo below shows that the start-pulse strip of the XATF is interrupted for the last character - the "pause" character. This character was only used in the Siemens Feld-Hell, and was used to occupy a phone line and during motor speed adjustments between two Feld-Hell stations. With start-stop operation, this speed coordination is actually not necessary. Also, the ATF machines have a stroboscopic ring mounted on the motor shaft. It enables visual adjustment of the motor speed, with the aid of a tuning fork. I.e., without needing another station.


Character-drum of the XATF - no start-pulse for the pause character

The peeling black lacquer on the above XATF-drum reveals an all-metal drum cylinder underneath. The non-conductive lacquer is used for the "white" pixels of the font. This construction is different from the (heavy!) Feld-Hell drums that consist of a stack of notched disks with a hard insulating filler between the notches. The pixel-pattern on the XATF and ATF drums may have been made with a photo-chemical process. The photo above suggests that the cylinder was metal-plated. The metal patches of the Feld-Hell drum were nickel-plated, for durability and corrosion protection.

The basic characteristics of the ATF Hellschreibers are (ref. 7B):

  • Tone frequency: 900 Hz (same as the Siemens Feld-Hell)
  • Font:
  • standard Hell-font
  • 5 font-columns of 14 pixels
  • Hell's 2-pixel rule is applied (minimum black and white pixel-pulse duration = 2 pixels)
  • 1 preamble column of 14 pixels, with a 9-pixel start-pulse
  • 2 blank postamble columns of 14 pixels each (actually 28.5 pixels total)
  • Telegraphy speed:
  • 4 characters/sec = 250 msec per character (vs. 2.5 char/sec of the Siemens Feld-Hell, and 5 chars/sec of the Siemens "Presse Hell")
  • single pixel duration = 250 msec / (14 + 98 + 28.5 pixels) = 2.222 msec
  • shortest pulse duration = 2 pixels = 4.444 msec
  • telegraphy speed = 1000 / 4.4444 = 225 Baud
  • Power: 12 volt DC
  • As the ATFs are start-stop Hellschreibers, only a single line of text is printed.

PC-software is available here for sending to characters to an ATF machine.

The ATF-0001 was developed for the KVP in 1952. Only 2 units are known to still exist (2013): one in the Military History Museum of the German Armed Forces in Dresden, and one in the collection of the University of Applied Sciences in Mittweida (50 km west of Dresden).


Label of ATF model ATF-00001 with serial number 51


Cover of the ATF carrying case - wood panels with metal edges


The ATF machine - the printer (to the left of the keyboard) has a cover to reduce printing noise


Front of the amplifier & interface module of the ATF-0001

The controls on the front of the panel are (left-to-right): toggle-switches for "Empfang/Senden" (transmit/receive), and "Motor Ein/Aus" (motor on/off), two rotary switches for selection of "Schreiben/Sprechen/Morsen" (teleprinter/phone/"Morse" telegraphy), and "Aus/Bereit/Ein" (off/standby/on), and a potentiometer for "Verstärkung" (amplifier gain). When the middle rotary power-switch is in the "Bereit" (standby) position, only heater voltage is supplied to the tubes, and the green signal light is on. This is exactly the same as the main switch and red signal light of the Hell Feldfernschreiber. A one-page condensed operating manual is provided in ref. 7H.


Rear of the amplifier & interface module of the ATF, with a "Zerhacker" (vibrator power "chopper") at the center


Top of the amplifier & interface module of the ATF - the three tubes were of type RV12P2000


Character-drum and motor of the ATF-0001

(note the stroboscopic ring attached to the motor shaft, for checking and adjusting the motor speed with a 170 Hz tuning fork)

The ATF machines have a stroboscopic ring mounted on the motor shaft, see photo above. It enables visual adjustment of the motor speed, with the aid of a tuning fork. I.e., without communication with another ATF machine. The motor speed is checked by tapping the tuning fork to bring it to resonance. The vibrating fork is then held across the stroboscopic ring of the spinning motor. If the correct number of strobe spots is visible between the teeth of the fork, then the speed is correct. ATF-0001 used a 170 Hz fork, whereas ATF model FSS.002 used a 125 Hz fork. The adjusted motor speed was kept constant with a centrifugal regulator (like the Feld-Hell machines). A small tuning fork could also have been used to adjust the motor speed automatically (ref. 7J). However, this would have made the very simple electronics of the ATFs (ref. 7K) significantly more complicated.


There is a 150:1 down-gearing between the motor and the gearbox of the printer-spindle and paper-tape transport.


Hellschreiber printer module of the ATF-0001


Label of ATF model FFS.002-00001 with serial number 12275 and 12320

The ATF model FSS-002.001 was built in 1954/55. The NVA operated these machines until ca. 1958. Only 11 machines are known to still exist (2013). Five of them have been accessed: serial numbers 8009, 8018, 12232, 12275, and 12320. Two of these have been returned to a fully operational state. Machines with serial numbers in the "80" series may have been the first production series (XATF machines). Based on the serial numbers, it is estimated that at least 400 XATF and ATF machines were built.


ATF Hellschreiber model FFS.002-00001

The printer-keyboard unit is hinged into the case, and can be folded up into it. Below the printer module (lower left-hand corner in the photo above), there is a curved window in which the stroboscopic ring on a drive shaft is visible. It is used for checking the motor speed with a 125 Hz tuning fork. The speed is adjusted with a potentiometer to the right of the window. Note the tuning fork on the back wall of the carrying case, between the amplifier module and the cover of the compartment for the paper tape roll. The motor actually also has a stroboscopic ring on its shaft (see photo below). A spare "Zerhacker" is stored just above and to the right of the tuning fork. There is a lever below the printer module, for selecting Hellschreiber vs. Morse telegraphy operation.


The printer/keyboard/drum unit of ATF FFS.002 Hellschreiber

(source original photo: Heinz Blumberg (DC4GL); used with permission)

The photo below shows the printer module of the ATF FFS.002. Note the large diameter of the printer spindle (helix). Also note the plastic ink-transfer roller between the spindle and the felt ink-roller. Allegedly, its purpose is to reduce wear on the felt ink roller.


Close-up of the ATF FFS.002 printer

Shown below is a print-out of a fictitious message, made with an ATF FFS.002. As with the Feld-Hell and "Presse Hell" prints, they were cut up into segments and glued onto telegram forms (ref. 7L)


Print-out from an ATF FSS.002 Hellschreiber

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

The printer of an ATF FFS.002 Hellschreiber in action

The control & interfaces module is located at the top of the carrying case. On the front panel, there are controls for selection of "Empfang/Sendung/Leitung" (receive/transmit/phone-line), "Tonsieb Ein/Aus" (tone filter on/off), and "Betrieb/Bereit/Aus" (on/standby/off). Unlike the ATF-00001, there is no potentiometer for manual adjustment of the audio input volume. There is a volt meter for checking the 12 volt power and the anode voltage of the tubes/valves (just like in the Siemens Feld-Hellschreiber). There are jacks for a telephone and a headset. There are 2-wire binding posts for a telephone, "Morse" telegraphy key, the contacts of a telegraphy relay for keying a CW-transmitter, and a phone line.


Front of the amplifier/interface module of the ATF FFS.002 Hellschreiber


Top of the amplifier/interface module of the ATF FFS.002 Hellschreiber

The photo above shows the top of the ATF's amplifier and interface module. There are two sets of three tubes visible. The three in the back are secured in place with a bracket. These are the active tubes. There is no bracket for the three tubes in the middle. This is a set of spare tubes. The photo below shows that they are not wired. The two rectangular silver-grey metal boxes at the far left are telegraphy relays of type Rls 0373. 001. 51218. The one on the right is a spare, and is not wired.


Bottom of the amplifier/interface module of the ATF FFS.002 Hellschreiber

The sockets for the spare tubes are at the the center of the photo above shows. Clearly, they are not wired. At the bottom right is the full-wave bridge rectifier of the tone-pulse detector, comprising four Siemens "Sirutor" diodes.


Keyboard and character-drum module of the ATF FFS.002 Hellschreiber


The character drum of the ATF FSS-002 Hellschreiber

(original photo: Heinz Blumberg (DC4GL), used with permission)


The 7x14 Hell-font of the ATF Hellschreiber

(9-pixel start-pulse in the first column)

The nominal motor speed of the ATF is 3750 rpm. Some of the motors in ATF machines were actually produced before the end of the war by the Hell company in Berlin. Later, "East German" motors were used, built by "VEB Elektromotorenwerk Hartha" in Hartha, about 50 km west of Dresden. The original Hartha company "Alfred Oemig und Co., A.G.", was founded in 1922 by the merchant Sander and cigar manufacturer Oemig, as a factory for small electric motors. In October of 1946, the company was confiscated by the Soviet occupation authorities. The factory almost completely dismantled and shipped to Russia. In 1948, the Oemig-company became state-owned, and resumed operation as "VEB Elektromotorenwerk Hartha".


Labels on motors of two ATF FSS-002 Hellschreibers

The three tubes in the amplifier & interface module of the ATF are for the pre-amplifier, final amplifier (printer solenoid driver), and tone oscillator. The tubes are standard American "metal can" pentodes: two of type 6SH7, one of type 6SJ7. Original American tubes were used, as well as "East-German" copies from the "Werk für Fernmeldewesen". This company was originally founded in July of 1945 as "Labor-Konstruktions-Versuchswerk Oberspree" (LKVO), an engineering company founded by the Soviet occupation authorities. It was housed in the (confiscated) AEG-Telefunken tube factory Röhrenfabrik Oberspree (RFO) on the Spree river in Berlin-Oberschöneweide. Mid-1946 LKVO was renamed to "Oberspreewerk" (logo: OSW) and changed to a Soviet corporation. In 1951 it was renamed to "Werk für Fernmeldewesen", and tubes were stamped with the logo "HF" (as in the photo below). In 1953/54 it was absorbed into the the RFT conglomerate. Tubes were stamped with the logo "WF" starting in 1955. In 1960 it changed to "VEB Werk für Fernsehelektronik, and retained the "WF" logo.


Tubes in the ATF FSS.002 Hellschreiber: 2x 6SH7 and 1x 6SJ7


VEB "Werk für Fernmeldewesen" HF in Berlin- Oberschöneweide,

(source photo: Bundesarchiv Bild 183-57649-0002; 1958)

Unlike in the Hell Feldfernschreiber, the 150 volt DC anode voltage for the tubes is not supplied by a motor-driven generator, but with a "Zerhacker" (12 Volt model 1188.001 – 10174 (Typ 51)). This is an electromechanical vibrator "chopper" for DC-DC conversion (ref. 7M-7R).


An EMB "Zerhacker"

The manufacturer of these Zerhacker was the VEB Elektro-Mechanik of Berlin-Pankow (EMB). This company made a variety of other products, such as sirens, Geiger-counters, power supplies, electric and electronic demonstration models for schools (frmr. products of the company Erwin Pahl KG (DEPA), and electric heaters ("DDR Heitzgerät").


Some components in the ATF machines are marked "XATF"

The ATF was used with transceivers such as the "FK 1a", and later the "FK 5". Ref. 7A, 7F. The "FK 1a" is a portable low-power HF transceiver set: 0.3 W AM, 1.2 W CW. It covered the frequency range 1475-5025 kHz in two bands. Ref. 7S. The set was built by C. Lorenz A.G. in Leipzig-Plagwitz. It was used by the KVP from 1952 to 1956, and from 1956 to 1970 by the youth organization GST (Gesellschaft für Sport und Technik) for training of radio operators.


"Funkstation FK 1a" transceiver + battery unit and ATF FSS-002 Hellschreiber in field operation

(source photo right: ref. 7B)


ATF FSS-002 Hellschreibers in a KVP class room

(source: ref. 7T)

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. 8A. 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 TTK/Sony 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.


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. 9A). 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).


Hellcast in Chinese: "... was appointed as government official of the Republic of China [ = Taiwan]"

(source: ref. 9B)


Hellcast in Chinese: "The destination is important. The maintenance manual shall be visible"

(source: ref. 9C)

Chinese Hell print-out

Hellcast in Chinese - recorded from a Beijing station on 14040 kHz (late 1970s/early 1980s)

(source: Fig. 11.1.f in ref. 9E, courtesy RSGB; used with permission)

The Toho Denki Kabushiki Kaisha company (Eastern Electric Ltd.) in Japan made Hellschreiber systems for the Japanese and Chinese markets (ref. 9B). Their machines were used by Chinese news and meteorological services, and Japanese news services. Shown below is a Hellschreiber printer built by Toho Denki. It has a 110 VAC motor, made by Bodine of Chicago/USA. It has a two-stage amplifier.


A Hellschreiber built by Toho Denki K.K.

(source: Steve Pazar (W6SPP); used with permission)


The label of the above TDK Hellschreiber printer

The label reads (top to bottom, line 1-5, lit. translation):

  • "TDK-type tape character transmission apparatus"
  • "Receiving machine unit"
  • "Production number 154"
  • "Showa era, 26th year, 10th month" (i.e., October 1951)
  • "Toho Denki Kabushiki Kaisha"

Toho Denki K.K. was a fax equipment manufacturer, and became part of Matsushita Graphic Communication Systems Inc. in 1962. Note: this TDK is not to be confused with the TDK company that is known for its magnetic materials products (incl. magnetic tape).


(source: ref. 9D)


1968 TDK fax machine model LDI-3

(source: National Science Technology Museum, Taiwan)


During the late 1930s, RCA also developed some tape facsimile machines (ref. 10A-10D). The printers used a "rotating spiral", per the Hellschreiber-principle. This was probably under license from Siemens-Hell (ref. 10A). On the sending side, text was typed on a paper tape and subsequently optically scanned with 60 scanning strokes per second (60 Hz / 110 volt AC synchronous motor). The same method can, of course, be used for scanning and transmitting handwritten text. RCA also conducted experiments between aircraft and a ground station (ref. 10C).


Principle of the RCA tape facsimile scanner

(source: adapted from Fig. 2 in ref. 10C)

RCA investigated three ways to deal with asynchrony between the motor of the scanner/sender and of the receiver/printer:

  • The standard "quasi synchronous" Hellschreiber solution: a two-turn printer spindle, printing two identical parallel lines.
  • Connection to a common AC power-grid (basically limited to "same building" or "same city block").
  • The use of a synchronization pulse at the end of each scanned line, i.e., in the margin of the scanned paper tape. Hence, RCA refers to those pulses as "marginal pulses".

The RCA printers were regular Hellschreiber printers. RCA experimented with carbon paper, typewriter ribbon, colored paper with white wax coating and a heated stylus (kymograph, stylograph; ref. 10E). They eventually settled on a soft inking roller, just like the Hell company had done about a decade earlier...


Samples of non-synchronous & synchronous tape facsimile recordings, and a transition between the two

(source: Fig. 1 & 13 in ref. 10C)

The printers had the following characteristics:

  • Printer helix:
  • 2 windings (two lines of text), total stroke 1/4 inch (6.35 mm)
  • 60 rps (3600 rpm)
  • Tape: standard ticker tape (width = 3/8 inch, 9.5 mm).
  • Height of each printed text line: 1/8 inch (3.2 mm).
  • Tape speed: 40 inch/min (1 m/min).
  • Scanning resolution:
  • 90 lines per inch (lpi) of input tape.
  • 16 pixels across the full width of the input tape, 10 pixels for the height of the characters on the input tape.
  • Telegraphy speed: 60 words per minute (5 characters/sec, same as Siemens-Hell "Presse Hell").
  • Keying frequency ("Punktfrequenz"): 480 Hz, hence a "necessary bandwidth" of 3x480 = 1440 Hz.
  • Single motor for helix and paper feed.


Early RCA portable tape facsimile recorder (operated on 12 volt DC) and a later desktop model

(source: Fig. 2 in ref. 10B and Fig. 3 in ref. 10C = Fig.4 in ref. 10D)

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. Going through the schematic from left to right, we see a standard transformer-coupled input and a pre-amplifier tube with volume control. This is followed by a full-wave rectifier tube and a limiter-amplifier tube, for squaring the received sine-wave signals. Unlike the standard single driver-amplifier tube for the printer solenoid, there are two tubes in a push-pull configuration. The same pulses that are used to actuate the printer solenoid, are fed to the special commutator on the shaft of the printer spindle. The numbers of commutator bars is determined by the nominal rpm of the motor and the number of starts of the the printer spindle. RCA used a 6-start spindle: the spindle has six separate threads that are shifted by 360°/6 = 60°. The bars of the commutator are aligned with the six starts. The end of each spindle-thread corresponds to the "marginal pulse" of a single scanned column. The motor speed has to be adjusted until the received marginal pulses and the commutator bars coincide. I.e., until the motors of the sender/scanner and receiver/printer are iso-synchronous: same speed and same phase. RCA refers to this as "synchronizing" and "framing". The output pulses from the commutator are fed to the control-grid of an oscillator with a nominal frequency of 60 Hz. The actual frequency varies with difference between the frequency of the received "marginal pulses" and of the commutator pulses. The oscillator signal is amplified in two stages, and then a push-pull amplifier drives the synchronous motor. Note that the "marginal pulses" method was also used in the airborne bearing-printer of the "Bernhard/Bernhardine" radio-navigation system of the Luftwaffe in WW2.


RCA tape-fax printer amplifier, including dynatron oscillator and motor-drive amplifier

(source: Fig. 12 in ref. 10C)


Towards the end of World War II, Hellschreiber printers were made by the "Fabbrica Italiana Apparati per Telecomunicazioni" [FIApT, Italian Factory for Telecom Equipment]. They had an office located at Via Ausonio 3, in Milan. To date, I have not been able to trace this company. Note: FIApT is not be confused with the FIAT automobile company from Turin (Fabbrica Italiana Automobili Torino). FIApT made at least 50 Hellschreiber printers for the Reuters news agency (ref. 11A). The Hell-printer is FIApT teleprinter model R-46.


Equipment label on FIApT Hellschreiber-printer model R-46 with serial-number 17


Front view of FIApT Hellschreiber-printer model R-46 with serial number 17

(this printer is in the collection of the Science Museum in London, inventory nr. 1974-190, photos with permission)

There are four controls on front: a toggle switch for mains power, a toggle switch for turning the motor on/off, a potentiometer for audio volume ( = gain of the audio amplifier in the tone-pulse detector circuit), and a mechanical speed adjustment knob.

The input for the audio input from a radio receiver is located at the bottom of the left-hand side:


Left-hand view of the FIApT printer


Right-hand view of the FIApT printer

There are two voltage selectors located at the bottom of the right-hand side of the unit:


Voltage selectors on the right-hand side of the FIApT printer - here set to "10" and "230"

The top view of the unit shows the mains AC power transformer (for motor voltage as well as filament and anode voltage of the tubes), the motor and adjustable belt-drive for the printer spindle, and three radio tubes (valves). Per ref. 11A, the tubes are of type 5Y3 (full-wave rectifier), 6K7 (pentode), and 6V6 ( = VT-107; power pentode). However, in his particular machine, there is a 6X5GT tube (dual-diode full-wave rectifier) on the left and a metal-can VT-87 (heptode) on the far right. I do not know what type the third tube is. All of these are tube types from the USA that were introduced in the mid-1930s. Additional passive electronic components (9 capacitors, 4 resistors, 1 "inter-valve" transformer) are located below the chassis. The electro-magnet of the printer module comprises two 1000 Ω coils in parallel.


Top view of the FIApT printer - cover removed

The speed adjustment for the printer spindle is completely mechanical. The photo above and below show two "meshed fingers" gear wheels, made of brass. One gear wheel is mounted on the motor shaft. The amount of mesh can be adjusted during production and maintenance, but not during normal operation. Hence, this gear wheel has a fixed diameter. A second such gear wheel is mounted on the spindle shaft. A belt transfers the motor speed to this second gear wheel. Its "fingers" that point to the rear of the machine are fixed onto the actual spindle shaft. The fingers that point to the front of the machine are mounted an a shaft that can be moved forward (towards the front of the machine) and backward by turning the "Speed" knob on the front panel. This changes the amount of mesh between the fingers. Due to the shape of the fingers, this changes the diameter of this gear wheel. Hence, the pair of gear wheels has a continuously variable transmission gear ratio.


Close-up of the drive system of the FIApT printer

The paper tape transport shaft is driven by the motor shaft via two worm gears, with a drive shaft in between. In the photo above, the latter shaft is seen crossing horizontally below the spindle shaft, almost up against the front panel.

The motor is a single-phase 160 volt / 60 Hz (!) induction motor, model IM 1/6. It was made by LESA of Milan, Italy. The LESA company was founded in 1929 as "Laboratori Elettrotecnici di Luigi Massaroni", named after its founder, Luigi Massaroni. In 1930, it incorporated as "Lavorazioni Elettromecchaniche S.A". Until the end of WW2, its focus was on small AC motors for record-players, sewing machines, film projectors, etc., and potentiometers. Later it also made a variety of small domestic appliances. The serial number of this particular motor (22143) suggests that it was an off-the-shelf mass-produced model.


Label on the LESA motor and the LESA factory ca. 1950s

The printer spindle is a 2-start ( = 2 threads) type. The one in this particular machine appears to be rather worn and made of low grade steel.


Close-up of the printer spindle of the FIApT printer


In the British Empire, the 1904 "Wireless Telegraphy Act" granted full monopolistic control of radio waves to the General Post Office (GPO). The GPO licensed all senders and receivers (telegraph, telephone, radio, teleprinter). It also owned, operated, and maintained all transmitter installations, including the punch-tape senders for Hellschreiber and regular teletype/teleprinter broadcast service. Since 1935, the GPO had already been providing the actual Hellcasts for Reuters news agency. The London Press Service (LPS) was inaugurated in August of 1945 as one of the "gray" propaganda services that was operated by the Central Office of Information (COI), ref. 30. It was the COI (successor to the war-time Ministry of Information, MOI) who, with technical backing from the GPO, proposed to introduce a Hellschreiber service for the LPS. Until then, LPS only had Morse telegraphy broadcast service.

In 1947, the GPO issued a request for tender on behalf of the Foreign Office / Colonial Office for a new Hell-printer and a "thermionic relay" contract. Ref. 19A, 20C. The "relay" is an electronics box with vacuum tubes ("thermionic valves") for a Hellschreiber-tone-pulse detector and a printer-solenoid driver amplifier. The request included full specifications and all official design drawings (including for the printer motor, specified to the Klaxon Company Ltd). The GPO obtained a tender from three companies in December of 1947 (ref. 19A):

  • Communications Division of Marconi's Wireless Telegraph Company Ltd. in Chelmsford/Essex. Marconi had been merged into Cables and Wireless Ltd. in 1929 (shortly thereafter renamed Cable and Wireless Ltd.), and was taken over by the English Electric company in 1946. Cable and Wireless (so, probably Marconi) had performed Hellschreiber transmission/reception experiments and signal bandwidth measurements in 1938/39. Ref. 28A, 29. Marconi already negotiated Hellschreiber patent licenses in 1935 with Siemens & Halske via Telefunken Gesellschaft für drahtlose Telegraphie m.b.H. (Telefunken for short). Ref. 36. Siemens was 50% owner of Telefunken, until bought out by joint-venture partner Allgemeine Elektricitäts Gesellschaft (AEG) in 1941. Marconi and Telefunken had general "exclusive territory" agreements.
  • Post Office Factories Department. The factories generally covered the assembly and manufacture, repair and reconditioning of all Post Office equipment and machinery. Until 1941, the factories were under control of the PO Stores Department.
  • Coventry Gauge and Tool Company Ltd. The Coventry tender included a "relay" from Pye Telecommunications Ltd. in Cambridge. The latter company was created early 1944 as a subsidiary of Pye Ltd.


Both Marconi and Coventry Gauge & Tool / Pye were awarded a contract. As stated above, this was a "new" contract. So there was a preexisting contract: printers from Coventry Gauge & Tool, and "relays" from Pye (ref. 19A). Early-model GPO-procured printers were also supplied to Reuters' news agency, when the supply from Siemens-Halske in Germany was interrupted when WW2 started (ref. 12A, 23A). As printers for both 12-line and (newer) 7-line Hell-font were required, the printer helix ("print wheel", "printer wheel", "marking wheel") could easily be exchanged (ref. 12A).

In total, at least 73 printer/relay sets were ordered under the "new" contract. Of these, 50 were from Coventry Gauge & Tool / Pye, and 3+20 from Marconi (ref. 19B, 20B, 23B). The Coventry units were intended for Europe and the Middle East, the Marconi units for India and the far East (ref. 20A). In November of 1948, acceptance of the 20 Marconi sets was delayed, pending implementation of a "considerable" list of necessary modifications. Marconi agreed to recall, modify, and improve the 20 printers that were on hold at the GPO, and replace a few old model printers that were already fielded (ref. 18D).

The Marconi printer and relay were Marconi-design. The printer was compatible with the GPO-designed relay, but the Marconi relay was not compatible with the GPO-designed printer. I.e., Hell-equipment sets from Marconi and from Coventry Gauge & Tool / Pye were incompatible! The Marconi relay was actually an off-the-shelf general-purpose model for high-speed telegraphy (ref. 20C). Note that both Hell-printer suppliers were obliged to use the GPO-specified motor from Klaxon Co. Ltd. Ref. 19A, 20A.

The following diagram illustrates the relationships between the government and industry partners involved in the GPO contract for Hell-equipment:


Relationships between British government agencies and industry regarding Hellschreibers and Hell-casts

(sources: ref. 12A, 18A, 19A, 23C, 23D)

The table below shows the prices for the various equipment items:


1948 prices of British Hell-equipment

(sources: 1 = ref. 18A, 2 = ref. 19B, 3 = ref. 19D, 4 = ref. 19E, 5 = ref. 23E)

To put these prices in perspective: in 1946, the average salary in the British "metalworking, engineering and shipbuilding" industry was £22.40 per month (US$98.56 in 1946), ref. 27. Based on general inflation data (ref. 21), this would be equivalent to ca. £806 in 2016 (ca. €930 and US$1005). A Morse operator made about £300-400 a year in 1949 (ref. 23F). So, at the time, a Hell-printer represented several months’ salary of an average worker – as did German Hell-equipment in Germany. A teletype/teleprinter set, including "adaptor" [ = 2-tone filter unit], cost £350 (ref. 26A, 27A), which is significantly more than a set of Hell equipment. For pricing data on German and Swiss Hell-equipment, see the "Hell equipment prices 1937-1952" page.

The GPO-printer is, of course, a British "clone" rendition of the original and ubiquitous German Siemens-Hell Hellschreiber printers for news casts. The design and specification most likely came from the GPO's Research Station (part of the Engineering Dept. of the GPO's Radio Branch) at Dollis Hill in northwest London (near Willesden). Ref. 31. Dollis Hill is also where the GPO tested the Siemens-Hell system (both 12-line and 7-line) in 1934 (ref. 12A) and where the famous "Colossus" code-breaking computers of Bletchley Park were built (1943/44).

According to a 1947 manual of the GPO (ref. 12B), three Hell-printer versions were developed, and produced in significant numbers (i.e., not prototypes):

  • 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)
  • Note: GPO engineers evaluated a Marconi printer (pre-dating the “new” model) with serial nr. 322 (ref. 20A); the highest serial nr. that I have documented is 229.

The referenced manual states that printers with serial numbers 1 to 6 and 48 "are of German origin, or are obsolete models". Apparently, there either was no model "1/T Mark 1", or few or none were produced...

The "T" indicates that printer components were treated or selected for operation in the hot-and-humid Tropics. A fair amount of motor insulation failures were observed in tropical climates (ref. 23A), but the motor design was not under control of the printer manufacturers. Note that the "relays" also needed to be fully tropicalized. E.g., by using capacitors with higher voltage rating, and sealing of transformers to avoid water absorption (ref. 19C). GPO engineering concluded that the Coventry printer was tropicalized "as much as possible and to a slightly greater extent than the examined [ = pre-new] Marconi model" (ref. 20A).

The following photos are of the label on an "early model" GPO-printer (ref. 12A, 12D). There is no model designator (e.g., "No 1") marked on the label: it reads "HELL PRINTER G.P.O. SERIAL .."


Label on an early model GPO Hell-printer - only "Hell printer" and "G.P.O. Serial" indicated

(source: Fig. 3 in ref. 12A, Fig. 12.38 & 12.39 in ref. 12D)

Serial nr. 31 has model "No 1/T" marked on its label, though based on the serial nr., it should be a model "No 1 Mark 1". Possibly, it is a regular model no. 1 that was modified by Marconi to be suitable for operation in tropical climates (ref. 18D). Serial nr. 192 and 229 are model "1-T", not "1/T", but those designators may have been interchangeable.


Equipment labels of three GPO Hell-printers

All GPO/Foreign Office combined, there were three versions of the Marconi printer (ref. 18D):

  • Ca. two dozen printers per the GPO design and specification.
  • Ca. 20 printers, based on that GPO design, but incorporating some of Marconi's own improvements. 
  • A "new" model (ref. 23C, 24C). Announced changes (in response to Reuters’ experience and field experience at British overseas Posts, compared to the original GPO design, and corresponding GPO engineering assessment (ref. 24C):
  • Strengthened ink roller supporting arm, and this roller now has a double-race ball bearing [not considered a problem area by GPO].
  • Self-aligning bearing on the drive shaft of the tape feed [not considered a problem area by GPO].
  • Improved position-locking of the pinch-roller spring of the tape feed [not considered a problem area by GPO].
  • Motor governor resistor changed from screw-in type to clip-in type [actually a GPO suggestion, also implemented by Coventry].
  • Wiring to the motor cleaned up [also implemented by Coventry].
  • Access to motor brushes improved by moving other components [can only be marginal, as the GPO design fixes the motor location close to the front panel].
  • Finer motor speed control of the motor (1½% vs. 4% per notch) [motor manufacturer Klaxon Co. Ltd. is unwilling to make the change. Note: the motor of the German Hell-printers has a superior, continuously variable centrifugal speed regulator, i.e., no incremental notches. The GPO considered it too complex for use in the GPO printer].
  • Printer magnet assembly improved, to avoid shorts experienced with the original G.P.O. design.
  • Mounting of the top cover plate of the printer module was changed to avoid distortion.
  • Added clearance between top & front cover plate of the printer module [also implemented by Coventry].
  • “Oilite” bearing [ = porous bronze plain/journal/sleeve bearing] on the printing spindle shaft and on the driven tape feed roller, to avoid seizing [GPO has no experience with such bearings in the tropics, and they may be less accurate].
  • Detection of remote-control start/stop tone pulse made more robust to inadvertent starts & stops when receiving noisy signals [not considered very important by the GPO].
  • To provide satisfactory ventilation, louvers are incorporated in the back of the unit and air inlet holes in the bottom.
  • The holder for 4 inch diameter paper tape rolls has not been adapted to 5½ or 8 inch rolls, as this is not practical with the GPO-specified attachments points [Note: a 4 inch roll suffices for 2 hrs of continuous printing; at the time, the longest Hellcasts of the London Press Service were 1½ hrs, ref. 20A].
  • All printers are now tested for speed control, and correct printing of received Hellschreiber signals.


Front view of an early model GPO Hell-printer - cover of the printer module removed

(source: Fig. 12.39 in ref. 12D)

Below are photos of GPO printers with serial number 12, 31, 32, 192, and 229. I have not been able to determine whether they were manufactured by Coventry Gauge & Tool or by Marconi, though most likely by Marconi. There are no manufacturer identification markings on the outside of the units, nor on the inside of the unit that I was able investigate with the cover removed. Also, based on the common GPO design, the Coventry and Marconi printers were "practically identical" with "no serious advantages on either side" (ref. 20A).

GPO Hell-printer model 1 with serial nr. 12

The photos below are of a 1943 GPO Hell Printer:


Front view of G.P.O. Hell-printer model 1 with serial nr. 12

(source: ref. 40)


Front view of G.P.O. Hell-printer model 1 with serial nr. 12

(source: ref. 40)


top view of G.P.O. Hell-printer model 1 with serial nr. 12 - cover removed

(source: ref. 40)


bottom view of G.P.O. Hell-printer model 1 with serial nr. 12 - cover plate removed

(source: ref. 40)

GPO Hell-printer model 1/T with serial nr. 31


Front view of Hell-printer model 1/T with serial nr. 31 - cover of printing module removed

(this printer is in the collection of the Science Museum in London, photos with permission)

The printer "box" measures ca. 28.8x20.2x17 cm (WxHxD, 11.25x8x6.75 inch), excluding the protrusions (printer module, paper tape holder, tape feed mechanism, toggle switch, etc.). The holder for the roll of paper tape is copied directly from the 1934 Siemens-Hell printer model T.empf.12b. Compared to the German original, the GPO-printer has a paper tape feed mechanism with three rollers instead of two. As the German arrangement works flawlessly, the reason for adding a third roller is questionable. The printer uses standard 15 mm wide Hellschreiber paper tape. In the photo above, the retainer spring to the left of the printer solenoid (the dark orange component at the center) is missing - compare to the black & white photo above. The ink roller above the printer spindle is also missing.


Right-hand view of GPO Hell-printer model 1/T serial nr. 31 - cover removed

(at center: the horizontally installed motor with the slow/fast speed regulator knob)


Left-hand view of GPO Hell-printer model 1/T serial nr. 31 - cover removed

In the photo above, the jack marked "DC input" is connected directly to the solenoid of the printer mechanism. On the left is circuitry for remote on/off control - also copied from the 1930s/40s Siemens-Hell Presse-Hell printers models T.empf.12 and T.empf.14. The components marked "B" and "A-TH" are electromechanical relays. The "TH" stands for "thermal", to indicate that relay "A" is the thermal time-delay relay. 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 printers) would turn the motor off. Remote control operation is active when the main switch is in the "start stop" position. Note: this is only start-stop for the motor, and is not related to start-stop synchronization of sender and printer.


Toggle switch for selection of motor operation


Rear view of Marconi Hell-printer model 1/T serial nr. 31 - cover removed

(the component with four gray disks on the left is an L.T. (low tension) selenium bridge-rectifier)


Top view of GPO Hell-printer model 1/T serial nr. 31 - cover removed


Bottom view of GPO Hell-printer model 1/T serial nr. 31 - cover removed

The long green component in the photo above is the speed governor resistor, rated at 30 watts. It is screwed into a small light bulb socket. Per ref. 23A, its power rating was insufficient and it tended to overheat. It was replaced with a clip-on type resistor in Marconi's "new" printer model.

The model 1-T with serial number 192 and 229 both have a 10-start printer spindle. Adjacent helix-starts overlap by 50%. The actual spindle hub is slid onto the spindle shaft. This makes it easy to exchange spindles, for compatibility with both the 7-line and the 12-line Hell font (ref. 12A). In the German Hell-printers, the spindle hub is an integral part of the shaft, and not easily exchanged. The GPO spindle hub, excluding the spindle threads, has a diameter of 22 mm. The threads of the spindle have a height of about 1.5 mm.


Close-up of the printer spindle of model 1/T serial nr. 31


3-prong power plug of Hell-printer model 1/T serial nr. 31

The printer's mains power plug fits into a switched power outlet at the lower right-hand corner of the front of the type W11 printer amplifier:


Printer detector/driver-amplifier "thermionic relay" model W11, serial number 1038

(this item is in the collection of the Science Museum in London, inventory nr. 1978-146, photo with permission)

The above "relay" measures ca. 42x26x26.5 cm (WxHxD, 16.5x10.5x10.25 inch). The inventory documentation of this unit does not indicate if it was manufactured by Marconi or Pye. There are no manufacturer identification markings on the housing. See ref. 37 for a description of types W1 through W8 (1938-1943). The latter types were designed by the Wireles Branch ("W. Branch") of the GPO, for "a variety of uses on radio circuits": keying a radio transmitter, operating electromechanical telegraph recorders (incl. Hellschreibers), as well as for "singing suppressors and voice-operated switches" on certain radio telephone circuits. It is reasonable to assume that types W9-W11 were designed by W. Branch as well. The first type (W1 ?) was developed around 1931. Type W8 comprised four tubes (valves; types V.T. 200 and V.T.196, two each), and was the first type that specifically intended for operating Hellschreiber printers. It was a table model with a DC output current of 20 or 45 mA (into a 500 ohm load), could provide both 110 Vac and 110 Vdc to the printer, and could also be used as a tone-signal amplifier. Audio input could be passed directly to the tone detector (full-wave rectifier with two solid-state diodes) or via an audio input bandpass filter with a 900 Hz center frequency and a 600 Hz bandwidth. Alternatively, the W8 could be used as a DC-pulse amplifier.

The next three photos show another GPO amplifier. The W-type is unknown. It only has a 110 Vdc output (on the front), so it does not appear to be a type W-8.


Front view of a GPO printer amplifier (W-type unknown)

(source: ref. 39)


Front view of a GPO printer amplifier (W-type unknown) - cover flipped up

(source: ref. 39; the toggle switch to the left of the empty tube socket is for selecting 20 vs. 45 mA DC output current)


Bottom view of a GPO printer amplifier (W-type unknown)

(source: ref. 39)

GPO Hell-printer model 1/T with serial nr. 32

Below is a photo of the inside of serial nr. 32. Note the differences compared to the top view of serial nr. 12 above.


Top view of GPO printer 1/T with serial nr. 32 - cover removed

(source: ref. 38)

GPO Hell-printer model 1-T with serial nr. 192


Front of model no. 1-T Hell-printer with serial nr. 192 (ink applicator roller missing)

(source of 1-T SNR 192 photos on this page: ©2013 Tony Radio Collection, used with permission)

Note the different shape of the paper tape roll holder, compared to the printers with serial number 31 above, and 229 shown further below.


The inside of the printer module of model 1-T serial nr. 192, with the electro-magnet


Close-up of the printer spindle of model 1-T serial nr. 192


Paper tape transport mechanism (left) and down-gearing for the spindle & paper transport (serial nr. 192)

GPO Hell-printer model 1-T with serial nr. 229


Printer model no. 1-T Hell-printer with serial nr. 229 - ca. 1944

(this printer is in the collection of the Science Museum in London, inventory nr. 1978-145, photos taken with permission)

Note the slightly different paper tape roll holder above compared to the one of serial nr. 31 and 192 further above.


Close-up of the paper tape feed mechanism and printer module of 1-T Hell-printer with serial nr. 229

As noted above, the printer model with serial nr. 31 had overheating problems. Its housing is fully closed. The model with serial nr. 229 has a screened ventilation hole (ca. 6 cm diameter) in the top of the housing, a group of ten holes (ca. 14 mm diameter each) in the bottom cover plate, and ventilation louvers at the back.


Bottom cover of model no. 1/T Hell-printer with serial nr. 31 (left) and model 1-T with serial nr. 229

In the photos above, note the different placement of the retaining screws of the bottom cover. Also, in serial nr. 229, the jack for "DC" (input to the printer magnet) on the left-hand side of the unit is placed much closer to the front panel than the "DC Input" jack of serial nr. 31.

The Claxon Company Ltd.

The motor in the GPO-printers is made by The Klaxon Co., Ltd. As the name clearly suggests, Klaxon's primary product was car horns (i.e., claxons). The company was founded in 1909. It had the telegraphic address "Klaxonet, London". In the exhibitors listing of the 1937 British Industries Fair, the following Klaxon products are listed: 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. A 1938 Klaxon catalog Iists "air-raid warning devices for internal and external situations", gongs, sirens, whistles, and other sound- emitters". In 1961 it was listed as a manufacturer of fractional-HP motors, warning signals and windscreen wipers.


The motor of the GPO model 1-T serial nr. 192, including 25:1 down-gearing from 2500 rpm

(photo source: ©2013 Tony Radio Collection, used with permission)

There are several addresses associated with the company: Klaxon Co. of Birmingham, 36 Blandford Street, London, W1, and Klaxon Ltd., 201 Holland Park Avenue, London, W11. The latter may have been just an import registration address, e.g., for foreign subsidiaries. This address also appears on fractional-HP motors, geared motor, and synchronous motors. The GPO-designed motor model EK5GB1-W3 is a series-wound AC/DC type.

Even though the initial order was only for 50 motors, Klaxon had large problems delivering them. Due to non delivery of the motors (a mere £5 item), the printers from Coventry Gauge & Tool were delayed. In turn, London Press Service was forced to delay its transition to Hell-service to Europe and the Middle East by at least six month, to the end of 1947. This became a political issue (due to the missed savings for the government), and the GPO even looked into getting motors from Germany (ref. 26D, 26E)! In March of 1947, Mr. Gentry, Sales Manager of Klaxon, blamed the delays on the company being inundated with orders [for their automotive motors & horns], the order from new customer (Coventry Gauge & Tool) being placed late (in August of 1946 = 6 months ago...), Klaxon prefers to provide motors to long-time client Marconi [ = competing printer], but Klaxon is willing to support any other company to make the motors. Ref. 26A, 26B.

Further delays were incurred mid-1947, when Coventry Gauge & Tool requested Klaxon to make modifications, as the delivered prototypes did not comply with the required wiring standards (ref. 26C). Another change was made at some point: the motor speed governor had two (carbon)brushes in the Mark 1 model, but only one in the Mark 2 machines (ref. 12B).

In August of 1947, Mr. Gentry (meanwhile General Director) blames all delays on the production output being limited by "government interference and fuel supply restrictions". As to producing a mere 50 motors, he states: "Can’t do it! Just can’t do it!" (ref. 26B).

Note that Pye also had delays in deliveries of their relays/amplifiers, but those were due to labor shortage and sickness (ref. 26F).

GPO Hell Sender

The following photo shows a GPO "Hell Sender". The actual model/type is unknown. On the left hand side, there are two outputs: "7-line" and "12-line". The latter has a plug in it. These outputs correspond to the 7-line and 12-line Hellschreiber font. Also on the front are two exchangeable notched disks and associated switch contacts. The front disk appears to capture the pixel sequence of three characters, which could be a station identifier. From the available photo, it is unclear if the disk in the rear also captures severeal characters. Possibly one disk is for characters in 7-line format, and the other in 12-line format. This sender is for continuously sending a  fixed character sequence. The unit has three toggle switches on the front, for "space mark", "Motor on", and "osc[illator]". The latter implies that the unit had a built-in tone oscillator.


GPO "Hell Sender" with serial number 47

(source: ref. 41)


The German Wehrmacht started using the Hellschreiber system in 1935 (wired and wireless). The British radio interception service appears to have been oblivious to this until late 1940 or early 1941 (§1.3 and 1.7 in ref. 32, ref. 33). Even when the signal type was correctly identified, there was no suitable printing equipment available: the standard commercial Hellschreiber operated at a different speed. There were two radio-interception stations that specialized in teletype/teleprinter and Hellschreiber traffic: the Foreign Office (FO) station at Knockholt (near Sevenoaks, in the countryside, about 30 km southeast of the City of London), and the Metropolitan Police (MePo) station at Denmark Hill in Camberwell (about 5 km southeast of the City).

The British "Wireless Interception" service (WI-service, phonetically abbreviated to "Y" service) was responsible for monitoring of enemy radio transmissions. The radio-intercept stations were known as Y-stations. The service dates back to WW1, and was run by the Royal Navy: Naval Intelligence department I.D. 25, also known as "Room 40". In 1920, the service was transferred from the Navy to the Foreign Office, and "Room 40" was renamed to Government Code and Cipher School (GCCS). In 1939, the GCCS moved to Bletchley Park (BP) in Milton Keynes/Buckinghamshire, and was renamed to Government Code Head Quarters (GCHQ). Ref. 35.

During WW2, the Y-service covered radio-telephony, Morse telegraphy, and Non-Morse (NoMo) transmissions, whether encrypted or not. NoMo traffic included teletype/teleprinter and Hellschreiber. The Y-stations were operated by a number of government agencies (the branches of the armed forces, the Metropolitan Police, and the General Post Office) and the Marconi company. Some stations only had direction-finding (D/F) capability.

During the course of WW2, the service grew from a few Y-stations, to a global network of small and large stations. They were located in the UK, the Middle East, Far East, North Africa, mainland Europe, and offshore. Intercepted encrypted signals were either analyzed locally, or transferred (by dispatch riders on motorcycle or via teleprinter) to BP. Sometimes BP is referred to as "Station X" (i.e., station nr. 10), though that actually appears to only refer to a small MI6 wireless station that was temporarily located at BP.

A "satisfactory universal Hellschreiber machine" was designed and manufactured in small numbers during the spring of 1942 (ref. 12C, §2.7 in ref. 32). It is unclear by which organization. It is also unclear if there was just one such development initiative, or multiple in parallel: early 1943, the Foreign Office research department (also) decided to build a universal machine that was to cover all speed ranges (ref. 22A). The latter had a printing mechanism that was copied form the German commercial machines. The universal-DC motor with "complicated centrifugal speed governor" was replaced with a type of synchronous AC-motor that was normally used in teleprinter equipment of Creed & Company Ltd., with an adjustable speed regulator comprising a pair of friction disks.

The Metropolitan Police Y-station at Denmark Hill had equipment workshops in West Wickenham at least as early as 1939 (§2.6 in ref. 32). At some point, the FO's Knockholt station was expanded with an equipment research & development operation (laboratory and workshop). However, this may not have been until 1943 (ref. 22A). This later became the Foreign Office Research & Development Establishment (FORDE).

During 1942-44, RAF 192 Squadron (§9.3 in ref. 32) and the British/American Noise Investigation Bureau (NIB, ref. 34A) investigated a special format of Hellschreiber signals that were transmitted by the Luftwaffe's rotating radio-navigation beacons of type "Bernhard". The FO's Knockholt facilities assisted 192 Sq with subject knowledge and the required tone-filter.

No photos or detailed descriptions of these universal Hell-printers are available.

If you have any information about this "universal Hell-printer", please contact me!



The 1943/44 tape facsimile system RC-58-B of the US Signal Corps was developed for "faxing" handwritten text messages during mobile operation (hence 12 Vdc power; configurable for 24 VDC). The main equipment items of this system are:

  • Scanner-printer unit RC-918-B. This unit combines the recording ( = Hellschreiber-printing) of incoming messages on paper tape, and the tape-scanning of outgoing messages. It includes an automatic start-stop circuit that starts the drive motor when an incoming signal is received, and when a signal is being sent out from the scanner.
  • Amplifier unit BC-908-B. This unit converts black and white pulses from the optical scanner of the BC-918-B into tone pulses of 1650 Hz and 1150 Hz respectively (2-tone FSK). The tone pulses are sent to the amplifier unit of another RC-58-B station, via phone lines or radio. Conversely, it converts 1650 Hz and 1150 Hz tone pulses received from another RC-58-B station to keying-pulses for the 2-coil electro-magnet of the printer module in the BC-918-B.
  • Writing-tablet MC-308B
  • Spare parts chest CH-108-B

Combined, the BC-908-B and BC-918-B contain 15 vacuum tubes. The system was probably manufactured by RCA (ref. 13B). Detailed descriptions are provided in ref. 13A. I do not know if an RC-58-A system ever existed. Surplus BC-908-B amplifier/filter units were modified by radio amateurs in the 1960s, for use with RTTY teleprinters (ref. 13C).


Scanner-amplifier BC-908-B (left) and recorder-scanner BC-918-B, on their respective shock-mounting

(source: Fig. 2 & 3 in ref. 13A)



Recorder-scanner BC-918-B on shock mounting FT-328-B

(cover of the optical system removed)

The BC-918-B scanner-printer unit measures approximately 11.6x10x11 inch (≈29.4x25.3x28 cm), and weighs 35 lbs (15.8 kg).


The right-hand side of the BC-918-B unit is the paper tape compartment

A phosphor-bronze strip is clipped to the inside of the cover of the paper tape compartment. It has the width of the paper tape (¾ inch), is 0.02 inch thick (0.5 mm), and has a bent tip. It is used for cleaning lint and paper dust out of the paper tape passages.


The inside of the cover of the paper tape compartment - with a phosphor-bronze strip for cleaning paper tape passages


The rear and the left-hand side of the BC-918-B


The inside of the opened BC-918-B - top view (left) and bottom view

The diagram below illustrates the optical system. Light from an incandescent light bulb enters through an opening into the optical system on the front of the unit. The light then passes through two lenses, a rotating hexagonal prism, a fixed prism, and then through one more lens. The spinning of the hexagonal prism causes a small spot of light to sweep across the paper tape that is passed underneath it. The light that is reflected off the paper tape (that has a message written on it), and is concentrated onto the photo-cell by two curved mirrors. The brightness of the reflected light appears at the output of the photo-cell. This allows distinction between dark/black and light/white reflections. The output of the photo-cell is connected to a frequency-modulated oscillator in the BC-908-B amplifier unit, via a black-vs-white discriminator. For "white" signals, this oscillator outputs a signal with a frequency of 56.15 kHz. For "black" signals, this changes to 56.65 kHz. This 2-tone signal is mixed with the signal from a second oscillator. The latter has a fixed frequency of 55.0 kHz. Hence, the output of the mixer is an audio tone of 56.1 - 55.0 kHz = 1150 Hz for "white" signals, and 1650 Hz for "black" signals. This audio signal is sent to the printer of another RC-58-B station via radio or phone lines (as well as to the local printer, as in the Siemens Feld-Hell machines).


Path of the light beam through the optical system

(source: adapted from Fig. 16 in ref. 13A)

The hexagonal prism spins at 600 rpm. As the a prism has six sides, the paper tape is scanned 600x6 = 3600 times per minute. As the paper tape advances 50 inch/minute (127 cm/min), each lineal inch of the paper tape is progressively scanned 3600/50 = 72 times (72 lpi). I.e., a scan-swath of 1/72 inch (0.35 mm). The scanner and printer mechanism are driven by a single 12 volt DC / 3600 rpm motor made by Signal Electric Mfg Corp. and by RCA.

The light beam always enters and exits the hexagonal prism via two parallel surfaces. Hence, the light beams that enter and exit that prism, are also always parallel:


The spinning prism creates a light-spot that continuously scans across the paper tape

(source: adapted from Fig. 18 in ref. 13A)


Photo-cell type JAN-927 made by RCA

The printer of the BC-918-B is a standard Hellschreiber printer, with a 6-start spindle and a felt ink roller.


Close-up of the printer module with the 6-start helix and a felt ink roller

The "writing stand MC-308-B" is a flat metal box with a hinged cover. It contains one roll of paper tape. The tape is passed through a writing-guide window across the top of the top of the tablet. There is a saw-edged knife blade at the left of the window, for tearing off paper. Spare-parts kit CH-108-B holds extra rolls of paper tape (7 inch diam.), fuses, vacuum tubes, and a mechanical pencil with replacement leads. The box measures 14¾x8¾x9 inch (LxHxW, 37x22x23 cm), and weighs 9 lbs (4 kg).


Writing tablet MC-308-B and spares chest CH-108-B with rolls of paper tape and vacuum tubes



During the 1930s, the Swiss Dr. Edgar Gretener (born 1902) headed up the telegraphy (incl. teleprinters) development department at Siemens-Halske in Berlin. In 1943, he founded an engineering company near Zürich/Switzerland. It developed and built electromechanical systems and lighting technology. The company name was named after him: "Dr. Edgar Gretener AG".

In 1939, Gretener's compatriot Prof. Friedrich ("Fritz") Fischer and his team at ETH-Zürich university, invented an impressive large-screen video projection system, suitable for movie theaters: the "Eidophor" (ref. 14A-14D). A working prototype was presented in 1943. Fischer died in 1947, at which time Gretener took over the development and commercialization. It came to market ca. 1952, via Gretag. In the USA, it was marketed by CBS and Twentieth Century Fox Film Corp. Image quality (incl. color) and performance were enhanced over the following years. Production ceased in the late 1990s.

Upon Dr. Gretener's death late 1958, the company became a subsidiary of the Swiss industrial giant Ciba-Geigy, at which time it was renamed to "Gretag AG". A buy-out by Gretag management occurred in 1990. Around that time, the crypto activities of Gretag were spun off to AT&T and became "Gretag Data Systems AG". It was sold to another US company in 1995, and renamed to "Gretacoder Data Systems AG", and subsequently to "Safe Net data Systems AG" in 2002. It ceased operation late 2004. Gretag Imaging became a leading manufacturer of photo-finishing equipment. 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 Edgar Gretener and Rudolf Hell. Obviously there is the common 1930s connection via the telegraphy department of Siemens-Halske in Berlin. This may be where Gretener was exposed to the Hell teleprinter system. The ETK printer mechanism also shows some similarities with a 1941 Hell company patent about a spring-loaded printer hammer (ref. 14E).

"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, which is actually a Hagelin-C52 crypto machine built in license. The famous crypto-machine builder Boris Hagelin also developed crypto machines for/with Rudolf Hell; see ref. 14F and p. 30 in ref. 14G. The Swede Hagelin developed his first cipher machine in 1921. He spent WW2 in Switzerland, and co-developed a crypto machine with Gretener around 1949-1951, before founding his own company ("Crypto AG") in 1952 in Zug/Switzerland.

Hell co-invented the video camera tube in 1925, and was very active in the field of typesetting, color scanning and printing technology. Gretener also developed color-separation technology.

Ca. 1946, the Gretener company started to develop teleprinters. The Gretener teleprinters are not true Hellschreibers. However, just like Rudolf Hell's invention of 1929, they are based on the decomposition of text font into basic elements. And, also like the Hell-printers, the Gretener machines are "direct printing": individual character-elements are printed immediately, as they are received - the machine does not collect all elements of a received character, and then decides which character to print. Besides that, they are interesting electro-mechanical machines of and by themselves.

Note that "direct printing" of each individual character-element (segments, in the case of Gretener, pixels in the case of Hell), makes the system more robust against interference, signal fading, etc.: 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). This makes the system suitable for use with encryption systems via radio. However, as shown below, the Gretener-font is made up of a lot less elements than the 5x12=60 pixel Hell-font (not counting the first & last column & row of the 7x14 font, as they are blank). The latter has a significantly higher level of redundancy.

Edgar Gretener decomposed characters into letter-segments. He defined a set of 14 such basic elements:


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

(source: Fig. 1 in ref. 14H)


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

(source: based on Fig. 2 in ref. 14K)


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

(source: Fig. 2 in ref. 14J)

Each character of Gretener-font can be expressed as a combination of no more than five of these elements. Several elements partially overlap. E.g., elements number 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 the figure "8". A figure "8" could also be composed with elements number 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 number 13 and 14. The alphanumeric character-set of the Gretener system comprises 41 characters:


The character set - 41 characters (pre-1947)

(source: Fig. 1 in ref. 14H)


Additional characters possible with the elemental sets

(source: based on Fig. 2 in ref. 14XXXXXX)

The use of segmented characters was not new or original: it dates back at least to 1908, when a 9-element numeric indicator was patented:


Multi-segment numeric indicators - incandescent backlighting

(source: Fig. 1 & 2 in ref. 14L; 1908)

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.


"Modern" 16-segment alphanumeric LED display indicator

Gretener-characters are transmitted as a pulse sequence of 14-bits: 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.

Initially, transmission speed of the Gretener teleprinter system was 2.5 characters per second (400 msec/character), as with the "Feld-Hell" machine. In 1947, this was increased to 5 characters/sec (200 msec/character), as with "Presse Hell".

THE SENDER OF THE GRETENER TELEPRINTER. 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 Hellschreiber-senders, 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. 14K)

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).


Pulse sequence for the character "R"

(source: Fig. 3 in ref. 14H; 400 msec timing implies pre-1947 definition)

Timing of the 400 msec character pulse sequence is as follows (ref. 14H):

  • 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. 14K)

  • 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. 14M):

  • 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 1000/10.8 = 93 baud.

THE PRINTER OF THE GRETENER TELEPRINTER. 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 Gretener printer 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 printer

(source: Fig 11. in ref. 14J)

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. The large 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 in the ETK, absence of a tone signals receipt of an active element-bit. The smaller cam wheel (item 25) provides actuation of the spring-loaded printer hammer (if the latter is enabled by the same solenoid).


The ETK printer mechanism

(source: adapted from Fig. 2 in ref. 14H)

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 inch). 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 (bits 1, 2, 6, 7 & 8 )

(source: Fig. 2 in ref. 14H)


Left: the individual elements for "R". Right: those same five elements printed in sequence

(source: Fig. 3 in ref. 14K)


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

(source: adapted from Fig. 1 in ref. 14J)

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. The opposing ends of these two shafts are 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: Fig. 6 in ref. 14J)

The following printer models were developed and manufactured by Dr. Edgar Gretener AG:

  • ETK 47 - in two versions: a tape printer and a sheet printer.
  • ETK 50, an upgrade of ETK 47 - sometimes referred to as the 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.

ETK stands for Einton-Kombinationsschreiber, i.e., a "single-tone combination printer". ETK 47 and 50 use "Ein-Ton-Telegraphie" (ETT), literally "single-tone telegraphy". I.e., Amplitude Shift Keying (ASK): a tone is keyed on/off. Here, the tone is 1500 Hz tone. "Combination printer" refers to the Gretener printing system described above, where several character-elements are combined into a complete character.

Model ETK 47 was developed ca. 1942-1947 and manufactured 1947-1950. The Swiss army bought 250 units, with a first order for 50 units placed in 1947. ETK 47/50 remained in service until 1971. Ref. 14N, 14O. 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. 14P; also developed and manufactured by Gretener).

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 (≈18¼x13¾x11½ inch) 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 volt DC or 220 volt AC. 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. 14H, 14J, 14Q-14S.


ETK 47 in its case - all legends are in German and French

(unless noted otherwise, all original unedited Gretag equipment photos: courtesy Walter Schmid (HB9AIV); used with permission)


ETK 47 - keyboard-printer in operating position

The keyboard has 50 keys. A special key at the lower left-hand corner is marked KZ ("Kennzeichen"), for sending a programmable callsign. Depending on the ETK 47 version, three keys are not used and are blank.


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

The keyboard of the ETK 47 has 50 keys, three of which are not used. A special key at the lower left-hand corner is marked KZ ("Kennzeichen"), for sending a programmable callsign of up to six characters. These characters are generated with a motorized stack of notched disks. This stack is located in a separate unit, the TFAA ("Trägerfrequenzanschlußgerät mit Automatik"). Ref. 14S, 14T. This unit is also used for remote control of another ETK station that is also equipped with a TFFA. The "A" ("automatic") part of the TFFA listens for the incoming ring-signal from an incoming call via the public or private phone system. In Switzerland, the phone system applies a 25 or 50 Hz ring signal of 25-90 volt RMS at the receiving terminal. Around the world, this ring signal varies from 15-70 Hz, and 25-150 volt RMS at the terminal. The TFFA uses this signal to "wake up" the local ETK unit: the heating voltages of the vacuum tubes is turned on, as is the motor. When ready, the receiving ETK station replies with a 1500 Hz tone. The calling ETK station can push the "WERDA" key on the keyboard (equivalent to the "WHO IS" key of telex teleprinters). The receiving ETK station responds by sending its callsign. The TFFA disconnects when no signals are received for 1-2 minutes.


ETK 47 page-printer and the associated "TFFA" modem (ref. 14S, 14T)


Equipment label on the ETK 47 page-printer (left) and on the modem (right)


The inside of the ETK 47 modem with optional callsign generator (right)

The modem comprises a motorized callsign-generator ("Namengeber") with 14 notched disks, six of which are "programmable" for the 6-character callsign.


Close-up of the optional callsign generator in the modem - similar to the notched character drum of Hellschreiber senders

Tape-printers such as the Gretener ETK 47 and the Siemens Feld-Hell and Presse-Hell machines, print on paper tape. The printed tapes were either transcribed with a typewriter, or cut up into segments and glued onto telegram forms. This is a disadvantage, especially compared to the competing "telex" type teleprinters that printed on sheets. Gretener developed a sheet-printer version of the ETK 47, introduced in 1947, just like the ETK 47 tape printer. Rudolf Hell and Siemens obviously faced the same sheet-printer competition for the Hell-system. Hell already foresaw a sheet-printer Hellschreiber in his 1933 patent 668821. Hell patented and developed his sheet printer in 1948: Hell model "P" (Siemens-Hell model 9 T empf 1b).


ETK 47 tape-printer and ETK 47 page-printer


ETK 47 page-printer


ETK 47 page-printer - with printing revolver on a carriage (top left of the photo)


ETK 47 page-printer - close-up of the printing revolver on a carriage


Test print-out of an ETK47 page-printer

The ETK 50 is basically an ETK 47 with an improved keyboard mechanism, so it is full compatible with the ETK 47. As stated above, the ETK 47/50 used 1500 Hz ASK modulation.

ETK 50 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 inch) and the set weighs 27½ 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 volt DC or 110-250 volt AC. Ref. 14H, 14K, 14Q-14R.

Gretener teleprinter models ETK 47 and 50, use "single-tone" ASK modulation, with a 1500 Hz tone. This can be transmitted via phone lines (2- and 4-wire) and radio. 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. 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). 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.

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. 14M, 14R, 14S, 14V. The synchronization method is based on using crystal-based clocks in the sending and receiving system. These 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).

Later on, the TC 61 was develeopd - same function and operation as the TC 53 and TC 58, but adapted to work with a Siemens T100 terminal.

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


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 also 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 a gear-wheel with the teeth set at an angle. It is a many-start printer helix.


The FACIT printer mechanism

(source: ref. 15A)

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.


Hell-style font rasterization (left) and FACIT-font examples

(source: ref. 15A-15C)



The British Creed & Company was founded in 1912 and its name shortened to "Creed & Co." in 1916. In 1924, they entered the teleprinter market and were absorbed into the International telegraph & Telephone Corp. (ITT) in 1928. Ref. 16A.

Late 1950, Creed 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. 16B). 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 the receiving (printing) side.

The transceiver (sender/printer) 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

(source: ref. 16B)

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 pencil-written message is pulled 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 transmitted to a second machine via phone lines.


Stylus and curved platen

Note that this method actually dates back to 1864! The patented "copying telegraph" of Bernhard Meyer had a scanner/sender that used a metal tablet on which text was written with non-conductive ink (Creed's Teledos tape and conductive pencil "ink" is actually the opposite). Scanning was done with a swinging platinum stylus. Meyer's electro-chemical printer used paper tape and a 1-turn spindle.

At the receiver, a blank Teledos tape is passed 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 that uses "dry-electrolytic action".

The Creed Teletape system appears to be a direct retake of the late 1940s Teletape system developed by Western Union (ref. 16C, 16D). Western Union's electro-sensitive tape was called Teledeltos rather than Teledos, and printing was also electro-thermal. The stylus is identical in both cases. The Western Union' stylus spun at 1800 rpm.


Scanning-stylus of the Western Union Teletape system

(source: ref. 16C)


Western Union Teletape transceiver with built-in amplfier & control unit

(source: ref. 16C)

Creed 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). Bandwidth was 2500-7500 Hz. This is too much for a standard analog public telephone network but a local network would be fine. Tape is fed at 1 inch/sec (1.5 m/min). Equivalent scanning resolution is 100 lines/inch.


Functional schematic of Teletape Transceiver Model TR.105

(source: appendix A of ref. 16E)

For the given tape feed speed (1 inch/sec), this implies a stylus speed of 1500 rpm. Model TR.105/1 has four vacuum tubes: CV2136, CV491, 6AU6, and CV1535. The unit operates on 110-145 or 200-225 Vac, 50 Hz (selectable in steps of 5 volt AC). Power consumption is 28 W (standby) - 90 W (sending). Life expectancy of the stylus was sufficient for one roll of Teledos tape. Ref. 16B.


The inside of Teletape Transceiver Model TR.105 (rear view)

(source: ref. 16B)


The inside of Teletape Transceiver Model TR.105 (view from right-hand side)

(source: ref. 16B)


In 1892, Thomson-Houston (founded in 1879 by Messrs. Thomson and Houston) and the Edison General Electric Co. merged into General Electric (GE). Shortly thereafter, GE formed a French subsidiary: the Compagnie Francaise Thomson-Houston (CFTH). CFTH merged with Hotchkiss-Brandt in 1966, and the electronics business of Thomson-Brandt merged with the Compagnie Générale de Télégraphie Sans Fil (CSF, "General Company for Wireless Telegraphy") to form Thomson-CSF. In 1982, Thomson-Brandt and Thomson-CSF were nationalized and merged into Thomson SA. The company went through a number of spin-offs and mergers from 1983 through 1987. Before the re-privatization in 1999, the defence and the consumer electronics businesses were split into Thomson Multimedia (later Technicolor SA) and Thomson-CSF (later Thales Group).

Sometime during the late 1950s or early 1960s, Thomson built Hellschreiber machines that are compatible with the Siemens Feld-Hell machines. Two of these machines are known to exist. They are believed to be prototypes made for the French armed forces. They are attributed to Thomson, France's prime defence contractor, but there is no official confirmation of this: there is no name plate or manufacturer marking on the equipment.


The Thomson Hellschreiber

This compact unit measures 38x33x19 cm (LxWxH, 15x13x7½ inch), comes in an army-green case, and operates on 12 volt DC. Ref. 17A.


The top view of the Thomson machine - cover removed

(original unedited photo: courtesy Jean-Claude Prat (F5PU); used with permission)


The rear side of the Thomson machine - cover removed

(original unedited photo: courtesy Jean-Claude Prat (F5PU); used with permission)

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.


Front & back of circuit card nr. 1 with transformer coupling, diode-bridge rectifier, two amplifier transistors


Front & back of circuit card nr. 2 with two transistors


Front & back of circuit card nr. 3 with 1 transistor

The Thomson Hellschreibers are solid-state ( = fully transistorized). Several transistors are GE-made, at least one is marked "Thomson". There are five transistors of type 2N43. The 2N43 is a Germanium PNP transistor, intended for (relatively) high-gain (hFE = 30) low-power (300 mW) AF applications. "More modern" equivalents the AC128, AC152, and 2N2706. 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 a "lady's top hat". Early versions have a pinched top. See photo below. Based on gain, manufactured transistors where screened into three categories, and labeled 2N43, 2N44, and 2N45. Parts that exceeded the highest specified gain of the 2N43 or were below the lowest specified 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 (Raytheon, RCA, Sylvania, Mullard, and... Thomson).


The GE "2N43" transistor

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.L.T was founded in 1920 - with Thomson-Houston as a major shareholder. International Western Electric acquired a minority interest in the company in 1922. Starting in 1927, L.L.T. made iron-dust cores for transformers and paper capacitors; polystyrene capacitors started in 1938. In 1978 it became a wholly owned subsidiary of Thomson CSF.


1955 L.T.T. advertizing


Close-up of the printer module with its 2-turn spindle

The Thomson machine has a character drum ("tambour"). 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. The Feld-Hell drum is 20.4 cm long, has a diameter of 49.5 mm (8x2 inch), and weighs 970 grams (2+ lbs)! The Thomson drum looks like a cylinder of a coarse cloth material that is impregnated with some sort of resin. Copper traces and pads are stitched onto the drum. 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, which is not the case in the Thomson machine.


Close-up of the Thomson character-drum

The font of the Thomson machine is very similar to that of the Siemens Feld-Hell. However, the audio output of the machine is not an on/off-keyed 900 Hz tone. Instead it is 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.


Character set of the Thomson

(printed with IZ8BLY Hell-software; slant of the text lines is due to speed offset of the Thomson machine)

Note the start-pulse in the first column of each character:


Start-pulse in the first column of the character matrix

It is only a rather short pulse: 2/14 of a character column, whereas it is 8/14 of a column in the Siemens Hell-39/40/44/72/73. This suggests that the Thomson machine is more susceptible to inadvertent start-pulse detections when receiving noisy signals.

Here is a recording that I made of the audio output of the Thomson machine:

Audio recording of the Thomson Hellschreiber (2x character set)


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

(in FFT plot: blue trace = "space" tone only; yellow trace = "mark" & "space" during character transmission)

The Thomson machine uses "start-stop" synchronization, like the Siemens Hell models 39/40/44, 72/73 and 80. The motor turns continuously, and both the character drum and the printer spindle are engaged via a clutch mechanism, as in the aforementioned Siemens-Hell models.


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

Paper speed is about the same as that of the Feld-Hell machines (about 47 cm/min nominal), but the manual speed adjustment of the Thomson machine appears to have a much wider range. It is a simple centrifugal speed regulator that is mounted on the motor shaft. The regulator has three so-called "fly-ball" weights (here, though they are stubby steel disks 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 flange 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 flange 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 flange touches the brake pad. 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, especially if the brake pad is not kept slightly lubricated.


Top-view of the centrifugal speed regulator (note the three governor weights, flange and and brake-pad)

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. "MASSE" is of course simply "ground/earth". There does not appear to be a PTT output, but I don't know yet what "SUP" ("suppression") and "PED" mean.


The interconnect panel on the back of the unit.

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"). The "START-STOP"/"CONTINU" switch probably has the same function as with the Hell-80: the unit can operate in the asynchronous/quasisynchronous Feld-Hell mode (ignoring received start pulses), or in the synchronized start-stop mode.


Controls and fuse on the front of the unit


In August of 2011, I received a message from David H. Jones in England, who recalled examining a rare start-stop Hellschreiber variant at the end of 1945. He was kind enough to write down his memories and allow me to post them here. The machine was portable, British-made, had a keyboard, and used an electrochemical printer (like the 1929 Hellschreiber prototype). A small batch of these machines may have been built.

If you recognize this machine, and have any additional information or documentation on it, please contact me.

A Portable Hellschreiber Variant

"In 1945 I was working at the Post Office Research Station, Dollis Hill (in north London) [FD: where the GPO Hell Printer No. 1 was developed]. In the latter part of the year we began to see many examples of former enemy communication equipment, including a military Hellschreiber. It was the first time I had ever heard of the system. It was very solidly built in typical military style, and though it was less than half the size of a teleprinter, it was still a large and very heavy piece of equipment.

I was impressed by it; a simple printing system which could work over a very noisy channel using visual judgment to decide whether or not a character remained legible through the noise. I also admired the way it avoided the need for synchronism by increasing the width of the printing head so that when timing errors displaced the line of print, at least one line of characters was always visible.

Shortly after that I was searching a shelf in an annex to the telegraph lab, where I found a plastic-cased portable instrument with a three-row typewriter keyboard. Nobody I could ask knew anything about it, or even that it was there.

The case was made of paxolin [pertinax], with metal angle along the edges and a webbing carrying handle. When opened, the shallow part formed the base with the machine fixed to it. The mechanism was very lightly built, with nickel-plated brass plates and round pillars. All parts of the mechanism were open.

The printing mechanism was immediately behind the keyboard, with the paper tape running from right to left. Beneath the tape path was a small D.C. motor, a short gear train and a one-revolution clutch released by an electromagnet. The one-revolution shaft turned a rotary stud switch, a hub with five radiating flat springs with small contact domes near their tips and the tape feed roller. The springs were not radial, but tangential to a circle concentric with the shaft and their tips trailing the direction of rotation.

About 15 thin bare wires (I did not count them) were stretched beneath the keyboard, with tension springs at one end, and spacing combs. They formed contacts with the bottom edges of the key levers which were notched to set up some sort of code.

The feed roller drew paper tape from a reel, passing over a wick in the neck of a flat plastic liquid container, and then over a flat plate where contact points at the ends of the flat springs swept across the width of the tape. A cam held the tape clear of the wick when the mechanism was not running. I believe another cam locked the keyboard when the mechanism was turning, although I am not quite certain of this.

After examining it, I could see how it worked. On depressing a key, one contact wire served by all keys switched the electromagnet and the mechanism made one turn. The rotary switch scanned the other contact wires and so transmitted the code selected by that key. It must have connected to the transmitter keying circuit, and very likely to the local printer as well. I could not follow the wiring in enough detail to be sure of that, and had no opportunity to operate it under power.

A signal from the receiver operated the clutch magnet and was connected to the rotating springs. During their single turn, the five springs swept across the tape in succession, marking the tape wherever the spring was energised, by electrolysing the liquid and releasing a dye. In this way it built up the characters exactly like a Hellschreiber.

Although I could easily see how it worked, I was puzzled by the application. It did not fit any of the Post Office services, so it must be military, yet it seemed poorly designed for that. The German army Hellschreiber in the next room showed the way the Military liked it; portable, yet rugged to withstand abuse and rough conditions. This piece of clockmaking would not stand up to such treatment for a moment. It carried no name or type number, but certain details showed it was British manufacture.

The choice of other details was eccentric, to say the least. The electrochemical printing system was a long-forgotten idea from the distant past, but what possible advantage did it have to justify reviving it here? Why synchronise the instruments with a start-stop action when the Hellschreiber solved the problem so easily by avoiding the need for synchronising altogether?

Recently my son, who is interested in old radio equipment, was telling me about a very small lightweight battery-powered World War 2 transceiver he had seen. It was intended for clandestine operations, and while discussing it I remembered the start-stop Hellschreiber I had seen. We wondered if they could have been used together. I saw it made such good sense, it was probably true. Every feature which seemed such a poor choice for most purposes, offered real advantages in that application.

A secret agent may have to operate in all manner of locations – in the open, in forests, in small buildings, in hideouts in dense urban areas – and wherever he is, he must draw no attention to his presence or activities. To send messages with a radio transmitter, the easiest means is speech, but besides being difficult to use over a very noisy channel, he is necessarily audible – and not only the microphone might hear him. The usual answer to those problems was a Morse key, but that required training. Agents were difficult to train; they had much to learn in a short time which had nothing to do with radio techniques and acquiring Morse skills was a burden which extended the training time.

That start-stop Hellschreiber could solve both these problems. Its immunity to noise at least equals Morse, while the typewriter keyboard is easy to use. The standard Hellschreiber has a fixed transmission cycle, and keying in step with it demands fair typing skill, but by changing to start-stop operation, even the one-finger non-typist can pick out a short message.

For clandestine operations, such a machine must be small and light to make it easy to carry and conceal, operate silently, run from radio batteries consuming very little power and be compatible with the radio inputs and outputs.

This machine meets all these requirements. Even the cumbersome electrochemical wet printing system was the best choice from those available at that time for it was silent, and no kind of impact printer could provide that. It could even operate from an audio tone output of a few volts from the radio.

I have never heard any mention of such an instrument, so what was its history? At least one such machine existed, because I saw it, and it gave the appearance of being made as a small batch rather than a one-off, yet it could not have been used in large numbers because its details were not designed for quantity production.

I would be interested in any comments you may have, and I would like to hear of any record or memory that such a machine was ever used in service."

David H. Jones, October 2011

Post script, January 2014:

"I can add a little more now. It had a 3-row keyboard with the usual typewriter layout (3-row with double shifts were usual on portable typrwriters at that time). However, the feature that confirms it was British, is the scanning switch, which I recognised. It was a standard component made by Painton. It was a high quality version of the wafer switch.

Manually operated wafer switches, which were very widely used in radio and electronic instruments, were assembled from a twelve-position indexing mechanism and any number of contact discs (wafers). The wafers were stamped from laminated plastic with contact clips riveted on.

Painton produced a much better made version with many more than 12 positions, used in high grade instruments and some professional sound equipment. The contacts were turned metal studs, moulded into a thermoplastic (bakelite?) wafer. The obvious reason for choosing it for this machine was the need for more than 12 positions. Only the wafer was used, mounted on top with the printing mechanism.

The keys with their levers were probably typewriter parts, modified by cutting notches along their lower edges to match the code. The contact wires beneath them were very thin, tensioned with coil springs at one end. The wires appeared to be made of brass. The scanning operation was as you suggested. Do not rely too much on the number 15; it fits my impression, but I am not certain I counted them.

The whole mechanism was very open. The framing of the machine certainly did not form a box. It fitted in a carrying case made of panels of laminated plastic (paxolin) joined by external strips of brass, angle srewed along all the edges. One sheet was hinged with the machine fixed to it and forming the base when it was in use.

The liquid container was like a flat bottle laid on its side, with an offset neck. It was transparent and appeared to be moulded, which I now realise was unusual. At that time, what mouldable transparent plastics were there? The container laid beneath the print mechanism and extended most of the width of the machine."

Many years later, in April of 2018, the plot finally thickened! When the puzzle has been solved, the entire story will be posted here.

under construction


Telewriter - case opened

(source original unedited photo: Science Museum in London, inventory nr. 1968-586)

The unit is quite small: the case measures about 32x12x20 cm (WxHxD, 12.7x4.8x7.8 inch). The case is made of dark brown bakelite or paxolin (resin bonded paper, like pertinax).


Telewriter - case closed

(source original unedited photo: Science Museum in London, inventory nr. 1968-586)

Equipment label:

  • Part number: YB.02251
  • Model designator: "Telewriter"
  • Manufacturer: G.T.L.
  • Serial number: 28

"YB" refers to section "Signal Stores, Automatic Telegraph, Line Transmission Equipment and Cryptographic Equipment" of the British Army Ordnance Store catalog. I.e., it is a military teleprinter.

Manufacturer "G.T.L.": unknown.

Serial number: one of three known to exist (Science Museum in London (nr. 28), Signals Museum RAF in Henlow/UK (nr. 109), private collection - unit not in numbered carrying case).


Close-up of the "pecker" wheel with its six spring-loaded tips

(source unedited original photo: ©2018 Peter Prest; used with permission)


During World War 2, the British "Daily Express" newspaper used a British-made Hellschreiber Printing Unit to monitor the Hellcasts from the German news agency DNB. Ref. 42. The manufacturer of the machine and the associated amplifier is unknown.

If you have any information about this printer, please contact me!

Daily Express

The Daily Express "Hellschreiber Printing Unit"  and associated amplifier

(source: ref. 42)

Daily Express

Close-up of the printer - lid removed from ink roller and from paper tape holder

(source: ref. 42)

Daily Express

Close-up of the printing mechanism and tape

(source: ref. 42)


External links last checked: January 2016

Note 1: due to copyright reasons, this file is in a password-protected directory. Contact me if you need access for research or personal study purposes.

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