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 [T typ 72 "GL"]     [T typ 73 "AGL"]     [Literature/references]

The Siemens-Hell Streifenschreiber T typ 72 "GL" was used for teleprinting via regular telecom networks (unlike telex). E.g., by police and fire department, banks, stock- and commodity-market exchanges, weather services, and railway systems.

Starting 1955/56, the Deutsche Bahn (DB, German national railway system) began to replace their 6000 Morse-telegraphy stations with 1300 Hellschreibers model T typ 72 "GL", T typ 73 "AGL", and printer-only model T empf 39 "L". This allowed DB to reduce the workforce of their teleprinter service ("Fernschreibdienst") by 400, and save 80 thousand Morse-code training days per year - combined about 1 million DM per year (ref. 12, 16). Hellschreiber communication was done via the existing private, automated telephone network of the DB: the Bahnselbstanschluß-Netz. The BASA-Netz was in established in the mid-1930s by the Reichsbahn, the predecessor of the DB. It connected all railway stations, controls posts, and offices, and over the decades grew to some 120 thousand terminals. The DB used Hellschreibers throughout the1980s (ref. 24) and at least until 1991 (see printout towards the bottom of this page). The last DB service regulations that mention Hellschreiber are from 1983 (ref. 19).

T TYP 72 "GL"  The Hellschreiber T typ 72 was introduced ca. 1952. It expands the printer-only Hellschreiber T empf 39 "L" with a "Geber", i.e., a keyboard and character-drum. Hence T typ 72 is also known as model "GL". There are three variants: 72a, 72b, and 72c. Their minor differences can be seen in the respective circuit diagrams (ref. 20-24).

      
Siemens-Hell-Schreiber T type 72 "GL“

The equipment plate of my 72 "GL“

(note that this tag  does not indicate whether it is a model 72a, 72b, or 72c; the "L" in the serial number "2L0095" means that it was built in Siemens-year "L", which is 11 years after 1945="A")

The character-drum of the "GL" consists of a set of disks that are stacked onto the shaft of the drum. Each character-disk has notches that represent the character pixels.

Principle diagram of the "GL" character-drum and keyboard mechanism
(source: Figure 3 in ref. 4)

The figures immediately above and below show that there is a separate notched disk to generate the start-pulse.

Notched disks for the letter "E" and for the start-pulse
(source: page 7 in ref. 8)

The photos below have been down-sampled. Full size, print quality, jpg files are available from Frank N4SPP

The AC-motor of the "GL"

Note that the keyboard of my "GL" has rounded rectangular plastic keys. See photos above. According to Siemens-Halske documentation, the "GL" variants 72b and 72c have round keys, with a metal ring (ref. 6, 7, 14).

My "GL" has a standard German QWRTZ keyboard-layout. However, the two signal lamps on the front of the unit are marked in French: "Secteur" (mains power, "Netz") and "Marche" (run, "Bereit"). My machine was a generous donation from Hans, PA0CX/DJ0SA. Here are my notes from Hans' account on the background of this particular "GL" machine:

That would certainly explain the French labels on the signal lamps.

Signal lamps with French label

The "GL" keyboard has a repeat-key ("Dauer-Taste") on the far right. On "GL" machines with a German keyboard, this key is marked "....". This is a standard feature on many teleprinters; if one of the keys is depressed, and then the repeat-key is depressed, then the selected character is repeated as long as the repeat-key is depressed. The repeat-key by itself only repeatedly sends the (blank) space character. Apparently, there are "GL" machines with both a French keyboard (AZERTY layout), and signal lamps with French labels. In this case, the repeat-key is marked with "cont". It has been suggested that French "GL" machines may have been provided to France as part of post-war reparations...

In the Feld-Hell font, the first column is always blank (does not contain any data). The "GL" includes a start-pulse in this first column. It has a duration of 8 pixels (out of the 14 pixel column), but is not printed. As a consequence, the spacing between printed characters is reduced.

This roots of transmitter-receiver synchronization at character level date back to 1869 (start-pulse patent by Ludovic Guyot d'Arlincourt in France) and the early 1900s (e.g., US patent 1,286,351 filed in 1910 by Howard Krum; ref. 13). Ref. 17. During the 1920s, the Creed, Siemens, and Lorenz companies developed so-called "start-stop" teleprinting machines ("Springschreiber"). They transfer characters as 5-bit codes (Baudot, ITA, or Murray). Each 5-bit code is preceded by a start-pulse, and followed by a stop-pulse. Both sending and receiving machine have a continuously running motor. The pulses are used to (de-)energize an electro-mechanical clutch. Using a clutch avoids the need for a motor with a very high starting-torque (very short spool-up time).

The "GL" Hellschreiber achieves synchronization without using a stop-pulse. In some start-stop machines, a stop-pulse is sent some fixed amount of time after the start-pulse. So it actually provides no information whatsoever, and is not needed for synchronization. Like the start-stop machines, the "GL" machine has a start-pulse tone-detector that drives the electro-magnetic clutch. This clutch couples the continuously running electric motor to the spindle and paper transport mechanism. After a fixed delay time (6 spindle revolutions), the clutch disengages: both the spindle and the paper tape stop. No need for a stop-pulse! The start-stop mechanism significantly reduces paper tape consumption: the paper tape only moves when text is transmitted or received. This also means that the "GL" can be used for unattended operation. Note that the paper tape of the Feld-Hell machine moves continuously, independent of whether or not text is transmitted or received.

As with the Feld-Hell, the motor of a "GL" transmitter and receiver are completely asynchronous and their speed will always be different. With the Feld-Hell, these speed differences cause printed text lines to be slanted upward or downward. As the "GL" has synchronization at character-level, accumulated slant is reset for each received character. Text lines of a "GL" are never slanted, only characters.

Slant of printed text: asynchronous (left) vs. start-stop (right)
(for same speed difference between transmitter and receiver)

Hence, there is no need for the receiver to print two parallel text lines. So, the thread of the printer spindle only has a single turn (vs. two in the Feld-Hell), and the paper tape is narrower (9.5 mm vs 15 mm in the Feld-Hell).

           
Hell "GL": 1-turn spindle                                Feld-Hell: 2-turn spindle

Obviously, having a start-stop mechanism implies that noise can cause false starts, and missing of real starts. This characteristic has led the amateur radio use of "GL" to primarily take place on VHF.

Print-out of the "GL" character set
(ruler scale is in cm)

The "GL" basically uses the same typeface as the Feldfernschreiber, without the pause-character, but expanded with . , ' = ( ) : and some modifications to the E, K, Q, = and ?. The binary form of the "GL" font is here (courtesy Heinz, DL4CL; also see p. 55 in ref. 6). To hear what the "GL" character set sounds like: click here.

The font of the Hell 72 "GL" (start pulse in first column)

A map of the notches of the Hell 72 "GL" font

(click here or on the image to get full-size)

 
Pulse sequence of the character "8" (left)                    Contact-bounce at the start of a pulse

Here is a summary of the characteristics of the Hell "GL": 

	Keyboard: as for the Feld-Hell, the "GL" keyboard is also upper-case only. However, it is expanded with additional punctuation marks . , : ' ) ( as well as = . Instead of a space-key, there is a conventional space-bar. There is no pause-character key.
	Font: same 7x14 as Feld-Hell, hence, compliant with minimum 2 pixel height. First column contains a start-pulse (line numbers 5-12).
	Transmission rate: 6.13 characters per second (vs. 2.5 cps in Feld-Hell), i.e., 368 per minute.
	Shortest pulse (for Hell font): 3 1/3 msec (300 baud) vs. 8.16 msec (122.5 baud) in Feld-Hell).
	Duty cycle: worst-case 47% (character "8", with a total of 46 bits out of 7x14=98); note that although the font is basically the same as that of the Feld-Hell, each character has a start-pulse of 8-bits (out of a 14-bit column). The comma and quote have the lowest duty cycle: 15% (14 bits total). The file with the binary format of this font includes the bit-count for each character.
	Modulation: single-tone ASK. Keyed output tone (and center frequency of the associated input bandpass filter) is switchable between 1000 and 3000 Hz tone frequency. This corresponds to the standard 25-2400 Hz lower-band (telephone) and 2700-3400 Hz upper-band (teleprinter) of public and private telecommunication networks. Line bandwidth permitting, the 3000 Hz setting could be used at the same time as a voice channel on the same line. Siemens-Halske made upper- & lower-band interface units for 2-wire telephone lines and for 4-wire telephone lines or radio transmitter/receivers ("Hell-ÜT", ref. 7).
	Size of printed characters: 2.5 x 4.5 mm (WxH).
	Paper tape width: 9.5 mm (3/8 ").
	Printer helix: single-turn.
	Ink roller: same as Feldfernschreiber and Hell-80.
	Motor: 220 Vac (vs. 12 Vdc in Feld-Hell).
	Nominal motor speed: 3000 rpm (vs. 3600 of the Feld-Hell). speed control is done with a 125 Hz tuning fork; there is a stroboscope disk on the printer's main shaft.
	Input bandpass filter: center frequency selectable between 1000 and 3000 Hz (switches at the same time as the tone frequency). Filter bandwidth is 700 Hz.
	Line impedance: 600 ohm (standard POTS telephone land-line).
	Communication channel bandwidth: 450 Hz recommended (300 Hz minimum)
	Allowed signal path attenuation: 35 dB / 4 neper (vs. 46 dB / 5.3 Np for Feld-Hell); note that reliable voice communication is not possible at this level of attenuation.
	Minimum input signal: 23.4 mV into 600 ohm ( -30 dB / -3.5 Np)
	Output signal: I measured ≈75 Vpp at the "Mh" ("Mithören") output (left side of the unit).
	Character drum: separate notched ring for each character (vs. rings of embedded conductive patches in Feld-Hell).
	Tubes (valves): EF80 (pre-amp), EL83 (final amp / solenoid driver), and ECC81 (double triode, one used for remote-control tone oscillator, the other as tone-detector). Rectifier and suppression diodes are solid-state.
	Current-loop: 18-45 mA.
	Detectors for tone and start-pulse: separate 4-diode full wave rectifiers (vs. one 2-diode full wave rectifier tone detector in the Feld-Hell).
	Tolerance to transmitter-receiver motor speed difference: ±2% (vs. ±5% for Feld-Hell)
	Paper tape speed: 1.1 m per minute (vs. 0.47 m/min for Feld-Hell).
	Dimensions: 43x43x26 cm (WxDxH, ≈ 17x17x10").
	Weight: 26 kg (just under 58 lbs: about the same as the Feld-Hell machine in its case).
	Power: 220 Vac, 40-60 Hz, 100 W.

I have also captured the above list and the schematic into a single document "Characteristics and Circuit Diagram of the Hellschreiber Model 72b/c "GL". It is available here.

T TYP 73 "AGL"  A slight variation of the Siemens-Hell-Schreiber 72b/c "GL" is the T typ 73 "AGL". The "AGL" is a "GL", expanded with a punch tape reader attachment ("GL" + "Angebauter Lochstreifensender" = "AGL"). As you can imagine, full utilization of the 368 characters per minute capability is only possible via punch tape operation. Ref. 15. For the complete circuit diagram of the  "AGL", see ref. 18.

The Siemens-Hell-Schreiber T typ 73 "AGL"
(source: “Technical Collection from Dr. Rudolf Hell” in Kiel e. V.)

T typ 73 "AGL" - without cover - of the Deutsche Bundesbahn

(source: Bild 2 in ref. 12)

The following Hellschreiber telegram (note: from 1991 !!!) is a "Bahndienstfernschreiben", i.e., a telegram of the national German railway company ("Deutsche Bundesbahn"). It was printed with a T typ 72, T typ 73, or a "printer-only" T empf 39 (cf. Bild 3 in ref. 12).

1991 Hell "L" or "GL" telegram of the Deutsche Bahn

(source: courtesy B. Rothe)

1954 Hell 72 "GL" printout  - message of the  Seewetterdienst des Deutschen Wetterdienstes (DWD; Marine Weather Service) in Hamburg

(source: "Einleitung", p. 5 of Das Hell-Jahrhundert: Lothar Deckert berichtet über Dr.-Ing. Rudolf Hell und seine eigenen Tätigkeiten in der Firma",  Lothar Deckert, Verlags- und Druckhaus Schmidt & Klaunig KG, 2007, 180 pp.)

My 3D/stereoscopic photos of the Hell-72c "GL" are here.

	Ref. 1: "Hell op de twee-meter-band in alle modes", by Hans, PEØHGD, Electron, February 1978, pp. 82-83
	Ref. 2: "Hellschreiben: Nostalgie oder Realität?", by Helmut, DL1OY, Funkschau, Sonderheft Spezial, November 1990, pp. 58-61
	Ref. 3: "RTTY-Funkfernschreiben nach dem System-Hell", Peter Stolzenberg, DC9XD, QRV - Amateur Radio, Vol. 29, 1975, pp. 562-571 [courtesy Gerard Wolthuis, PA3BCB]
	Ref. 4: "Der Siemens-Hell-Schreiber", Siemens & Halske A.G., Siemens Fernmelde Technik, SH 8354. 443. TT1, 1943 [courtesy Siemens Corporate Archives, München]

	Ref. 5: “Siemens-Hell-Schreiber „GL““ T typ 72 c – Beschreibung“, St Bs 1211/2, October 1955, 31 pp. + schematics , Siemens & Halske AG, Wernerwerk für Telegrafen- und Signaltechnik, T Werb 2880 R GN, 956.0,2 (courtesy Heinz Blumberg, DC4GL)  [52 MB].
	Ref. 6: "Siemens-Hell-Schreiber „GL“" T typ 72 c – Betriebs- und Bedienungsanleitung mit Teileverzeichnis", St Ba 1211/2, December 1956, 56 pp. + schematics, Siemens & Halske AG, Wernerwerk für Telegrafen- und Signaltechnik (courtesy Heinz Blumberg, DC4GL)  [48 MB]
	Ref. 7: “Siemens-Hell-Schreiber „GL“ T typ 72 c” [brief description & characteristics], Siemens & Halske AG, Wernerwerk für Telegrafen- und Signaltechnik, SH 4057, KB T App 15, 7591. T FS 3, 2 pp., 1975? (courtesy Arie van Oijen, PE1AQB)
	Ref. 8: "Hell-72 "GL" Start-Stop-Sender, Start-Stop-Empfänger", Siemens Hell-Technik, T Ausbildung S-Hell/8, Änderung 1, pp. 7-8, SuW 2957 R, 559.0,2 (courtesy Arie van Ooijen PE1AQB)
	Ref. 9: “Hell”, Reflecties door PA0SE, Dick Rollema (PA0SE), Electron, nr. 7, July 1977, p. 349 (courtesy Gerard Wolthuis, PA3BCB)
	Ref. 10: “Hellschrijven met autostart” , Reflecties door PA0SE, Dick Rollema (PA0SE), Electron, nr. 5, May 1979, p. 313 (courtesy Gerard Wolthuis, PA3BCB)
	Ref. 11: "Hellschrijven wint terrein", Dick Rollema (PA0SE), Electron, nr. 2, February 1983, pp. 73-76  (courtesy Gerard Wolthuis, PA3BCB)
	Ref. 12: "Die Fernmeldetechnik als Hilfe bei der Rationalisierung der Eisenbahn", W. Leitenberger [Hellschreiber use in German railroad system is described in Section 3: "Modernisierung des Eisenbahnbetriebes"], ETR: Eisenbahntechnische Rundschau, Nr. 4, April 1966, pp. 139-146
	Ref. 13: "History of Teletypewriter Development", R.A. Nelson, K.M. Lovitt (ed.), Teletype Corporation, October 1963
	Ref. 14: "Siemens-Hell-Fernschreiber „GL“ T typ 72b – Bedienungs- und Wartungsanleitung St Wa 1211/11", Siemens-Halske A.G., Wernerwerk für Fernmeldetechnik, SH 2915, 10530.5 T, ca. 1955, 6 pp.
	Ref. 15: "Siemens-Hell-Fernschreiber „AGL“ T typ 73 – Bedienungs- und Wartungsanleitung für den angebauten Lochstreifensender", Siemens-Halske A.G. Wernerwerk für Telegrafen- und Signaltechnik, Fs Wa 1233/4, SuW Bln 05, 559.0.2, January 1959, 4 pp.
	Ref. 16: "Rationalisierung im Bauwesen der Deutschen Bundesbahn", Albert Dobmaier, pp. 58 in "Jahrbuch des Eisenbahnwesens", W. Teigeler, 1958
	Ref. 17: "Synchronisierung mit dem Start-Stop-verfahren", Fritz Schiweck, Section 3.5, pp. 90-95, Band 9 of "Lehrbücher der Feinwerktechnik", 4th ed., C. F. Winter'sche Verlagsbuchandlung, 1962, 894 pp.
	Ref. 18:  "Stromlaufplan des vollst. Gerätes  9 St Str 1233/7" [73 "AGL" schematic] (courtesy Heinz Blumberg, DC4GL)
	Ref. 19: "Vorläufige ergänzende Bestimmungen zur Fernschreibvorschrift (für den Wählbetrieb, den Betrieb von Hellschreibern und das fernmündliche Zustellen und Aufgeben von Fernschreiben), Deutsche Bahn, Dienstvorschrift  476 b, 1 February 1953 (addendum to DV 476); reprinted 1983.
	Ref. 20: "Complete schematic of the Siemens-Hell-Schreiber T typ 72a" (courtesy B. Rothe)
	Ref. 21: "Complete schematic of the Siemens-Hell-Schreiber T typ 72b" (courtesy B. Rothe)
	Ref. 22: "Complete schematic of the Siemens-Hell-Schreiber T typ 72c" (courtesy B. Rothe)
	Ref. 23: "Complete schematic of the Siemens-Hell-Schreiber T typ 72c - 9 St Str 1211/2" (with some annotations by Hans, PAØCX); here in jpg format.
	Ref. 24: p. 46 "Hundert Jahre Bahn-Telekommunikation", Rainer Knewitz, Signal und Draht (Zeitschrift für das Signal- und Fernmeldewesen der Eisenbahnen), Vol. 98, Nr. 1 + 2, 2006, pp. 38-54
	Ref. 25:"Siemens-Hell-Schreiber "GL" T typ 72 a", Beschreibung St Bs 1211/8 [description and schematic], June 1954, Siemens Fernschreibtechnik, Siemens & Halske AG, Wernerwerk für Fernmeldetechnik, 33 pp. (courtesy B. Rothe)

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