During the fall of 2011, László Veres (HA7XK), brought to my attention the existence of a Feld-Hell model that was built in Hungary. Note that this is not simply a standard German Hell Feldfernschreiber that was built during World War 2 by a Siemens-Halske subsidiary in occupied Hungary. This model actually dates to the early 1950s! However, the design, including the electronic circuitry and construction, does very closely follow that of the "standard Feld-Hell".
The designator of this model is HTG-1, where "HTG" = Hellschreiber Távírógép = Hellschreiber ticker-tape machine. It was manufactured by the Telefongyár company ("Telephone factory") in Budapest. It is unclear if it was designed there as well. Telefongyár was founded in 1876. As the name suggests, it originally made telephone equipment. From World War I through World War II, they also made electronic components and radios. In 1925, the factory was bought by the I.T.T. conglomerate. In 1992, the company was privatized and became part of Siemens-Hungary.
Two of these machines are in the collection of the Museum of War History (Hadtörténeti Intézet és Múzeum) in Budapest/Hungary (one is exhibited). It is unknown how many machines were built, and how many have survived in private collections.
THE HELLSCHREIBER TÁVÍRÓGÉP HTG-1
Fig. 1: Hellschreiber model HTG-1 (left) and the standard Feld-Hell
(all original unedited HTG-1 photos on this page: courtesy László Veres; used with permission)
Fig. 2: Hellschreiber model HTG-1 (left) and the standard Feld-Hell - paper tray cover opened
The amplifier box shows some major differences with respect to the standard Siemens-Halske Feld-Hell:
- The motor-generator turns at 3840 rpm (vs. 3600 in S-H Feld-Hell).
- The nominal generator voltage is 150 volt DC(vs. 165 in the S-H Feld-Hell)
- There is a volume control for the modulated output pulses, not only for the input signal.
- There is no rectangular bakelite connector block
- There is no 12-pin round connector, but 3 pairs of binding posts (wire or banana plug) - more practical!
- There is a 3-position toggle switch for the interface configuration / operation mode.
- The electronics are based on four tubes of type 6AU6 - instead of the RV12P4000.
- The monitoring/headset output ("Mithören" in the Siemens-Halske Feld-Hell) is not transformer-isolated; instead, it is connected to the anode of the pre-amplifier tube, via a blocking capacitor.
- There is no separate phone jack for a field telephone.
- The push-button to select the range of the voltmeter (battery vs. anode voltage) is a separate switch in the front panel. In the S-H Feld-Hell, the switch is integrated in the bezel of the instrument.
- There is no equipment label with serial number, year of manufacture, etc.
Interestingly, the "battery / power-supply" toggle switch has been retained.
Fig. 3: front of the amplifier box
Fig. 4: front of the amplifier box - annotated
Fig. 5: translation of the labels & legends of the switches and connectors
Hungarian is a difficult language - for foreigners. Basically, signal names and switch positions that begin with a "K" (for "Kemény") have to do with transmitter "keying", those beginning with "M" (Modulált), with modulated tone pulses.
The two diagrams below show the close similarity between the schematics of the standard Feld-Hell and the HTG-1. A detailed schematic of the HTG-1 is provided in ref. 1A.
Fig. 6: simplified schematic of the standard Hell Feldfernschreiber
Fig. 7: simplified schematic of the HTG-1
Fig. 8: top of the HTG-1 amplifier box - tubes, fuse, and toggle switch are easily accessible
Fig. 9: labels next to the vacuum tubes in Fig. 8 above (left to right)
The 6AU6 tube is a 7-pin miniature pentode (RCA, 1947). Ref. 2. It was typically used in AF and RF amplifiers, e.g. in television sets. Equivalents are the CV2524 and EF94, and it is similar to the EF85. Tungsram in Hungary also manufactured this tube (under license). The tube has a large transconductance (4000-5000 μmho, depending on anode voltage), but a relatively low amplification factor of only 36.
- Transconductance is a measure of the change in anode current to a change in grid voltage, with anode voltage held constant; units: mho (old; "ohm" spelled backward), siemens.
- (Static) amplification is gain, expressed as the ratio of the change in anode voltage for a change in grid voltage; units: mu (μ).
Fig. 10: the "6AU6" compared to the "RV12P4000"
The RV12P4000 tube of the standard Feld-hell has a large static gain (4000 max) as well as a large transconductance (2300 μmho). The Royal Hungarian Army (RHA) may also have used Tungsram tubes of type HP1220 in their German Feld-Hells, as a subsitute for the RV12P40000. The HP1220 is a high-frequency pentode with 12 volt heater voltage and 20x10=200 mA heater current.
Other components (capacitors, resistors, potmeters, possibly also the transformers) in the HTG-1 Hellschreiber were made by the company REMIX Radiotechnikai Vállalat [Radio Technology Company] in Budapest/Hungary. The company was founded in 1932 and changed its name to simply "REMIX" in 1937.
Fig. 11: rear of the HTG-1 amplifier box - cover removed
As in the Siemens-Halske Feld-Hell, all components have a small sticker with the component number from the schematic. However, here, the signal numbers are not screen-printed onto the circuit card, but stamped into the card. Resistors and diodes have a plastic sleeve.
As in the standard Feld-Hell, the vacuum tube sockets are mounted in a heavy U-shaped profile, to which the circuit card is also attached:
Fig. 12: the HTG-1 circuit card module, removed from the amplifier box
Fig. 13: the other side of the circuit card, with two audio transformers
Fig. 14: looking into the HTG-1 amplifier box from the rear - circuit card module removed
(the green and blue electrolytic capacitors are modern replacements)
Fig. 15: looking into the HTG-1 amplifier box from the rear - right-hand side of the box
(the blue electrolytic capacitors are modern replacements)
Fig. 16: looking into the HTG-1 amplifier box from the rear - left-hand side of the box
(the green electrolytic capacitors are modern replacements)
Fig. 17: looking into the HTG-1 amplifier box from the top - circuit card module removed
Fig. 18: side of the HTG-1 amplifier box with two connectors for cables to motor-generator & keyboard-drum
(same as standard Feld-Hell, though the latter also identifies each connector (and matching plug) with a colored dot)
Fig. 19: keyboard and printer-head of the Hellschreiber model HTG-1 - same as Feld-Hell
Fig. 20: Close-up of the standard Hell printer module of the HTG-1
Fig. 21: carrying case of Hellschreiber model HTG-1
During WW2, the Royal Hungarian Army (RHA) used standard German Feld-Hell machines, probably with Hungarian legends/labels:
Fig. 22: field telephone exchange unit of the Hungarian army, with "Klappenschrank" switch board and German Feld-Hell machines
(source: ref. 3, 1941)
Overall, the RHA used Hellschreibers from 1939 until 1958. The Magyar Államvasutak (MÁV, Hungarian State Railways) also used the Hellschreiber system, but with commercial "Presse Hell" printers.
- Ref. 1: "A HTG-1 távírógép műszaki leírása és kezelési utasítása" [Technical description and operating instructions of the HTG-1 tape teleprinter], issued by the Hungarian Ministry of Defence, 1954; 98 pp. price: 5 florint. (courtesy László Veres, HA7XK)
- Ref. 1A: HTG-1 wiring diagram (Figure 19 in ref. 1)
- Ref. 1B: "A 39 M. tábori távirógép részletes kapcsolása" [simplified HTG-1 schematic; lit. "Detailed wiring 39 M. of the field ticker tape"]
- Ref. 2: "6AU6 - 6AU6A", Datasheet, Tung-Sol Electric Inc., Electron Tube Division, August 1962, 4 pp.
- Ref. 3: "Bilder von der ungarischen und finnischen Nachrichtentruppe", Pleger, p. 230 in "Deutsche Nachrichtentruppen (Die F-Flagge)" [Zeitschrift für die Nachrichtentruppe und Truppennachrichtenverbände des Heeres, der Luftwaffe und der Waffen-SS - Nachrichtenblatt der Nachrichtenkameradschaften des NS-Reichskriegerbundes], Vol. 17, Issue 7, July 1941
- Ref. 4: "39 M. tábori távírógép műszaki leírása és kezelési utasítása (1942)" [Technical description and operating manual for field tape-teleprinter (1942)], Magyar Királyi Honvéd Híradó Kiképzőtábor Parancsnokság [Signal Corps School of the Royal Hungarian Army], 30 pp., 1942. The cover page of this document is here.
- Ref. 5: "Távírógép a katonai híradásban 1." [Military press tape-teleprinter], Vörös Béla, Haditechnika [Military Technology magazine], nr. 2, 1991
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