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 back to the early 1950s! However, the design, including the electronic circuitry and construction, does verz 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 As the name suggests, it originally made telephone equipment.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.
   

Hellschreiber model HTG-1

(all original unedited HTG-1 photos on this page: courtesy László Veres)

Hellschreiber model HTG-1, paper tray cover opened

The amplifier shows some major differences with respect to the standard S-H Feld-Hell:

	motor-generator runs at 3840 rpm (vs. 3600 in S-H Feld-Hell).
	the nominal generator voltage is 150 VDC (vs. 165 in the S-H Feld-Hell)
	there is a volume control for the modulated output pulses, not only for the input.
	interfaces: 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 S-H 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.

The front of the amplifier box

Hungarian is a difficult language - for foreigners. Basically, signal names and switch positions that begin with a "K" (Kemény) have to do with "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.

Simplified schematic of the standard Hell Feldfernschreiber

Simplified schematic of the HTG-1

Top of the HTG-1 amplifier box - tubes, fuse, and toggle switch are accessible
(tubes left-to-right: előerősitő = pre-amp, végerősitő = power-amp, szabályzó = regulator, oscillátor = tone generator; toggle switch: akku. = battery, E.ir. = egyenirányító = DC power supply)

The 6AU6 tube is a 7-pin miniature pentode (RCA, 1947). Ref. 3. It is 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 (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), siemens.
	(Static) amplification is gain, expressed as the ratio of the change in anode voltage for a change in grid voltage; units: mu (μ).

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). During WW2, the Royal Hungarian Army (RHA) used standard German Feld-Hells, probably with Hungarian legends/labels. 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.

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 the signal numbers are not screen-printed onto the circuit card, but stamped into the card. Resistors and diodes have a plastic sleeve.

The HTG-1 circuit card module, removed from the amplifier box

Reverse of the circuit card

Looking into the HTG-1 amplifier box from the rear, circuit card module removed

Looking into the HTG-1 amplifier box from the top, circuit card module removed

Side of the HTG-1 amplifier box with connectors for cables to motor-generator & keyboard-drum

Keyboard and printer-head of the Hellschreiber model HTG-1 - same as Feld-Hell

Printer-spindle of the Hellschreiber model HTG-1 - same as Presse-Hell

Carrying case of the Hellschreiber model HTG-1

Field unit of the Hungarian army, with "Klappenschrank" switch board and German Feld-Hell

(source: ref. 3, 1941)

Overall, the RHA used Hellschreibers from 1939 until 1958.

Note that the Magyar Államvasutak (MÁV, Hungarian State Railways) also used the Hellschreiber system, with a printer resembling the "Presse Hell" printer.

	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)  (courtesy László Veres, HA7XK)
	Ref. 2: "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. 3: "6AU6 - 6AU6A", Datasheet, Tung-Sol Electric Inc., Electron Tube Division, August 1962, 4 pp.
	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
	Ref. 5: "Távírógép a katonai híradásban 1." [Military press tape-teleprinter], Vörös Béla, Haditechnika [Military Technology magazine], nr. 2, 1991

©2011 F. Dörenberg. All rights reserved worldwide. No part of this publication may be used without permission from the author. It has taken considerable effort to create these pages. If you "borrow" content from them, at least reference the source.

   top of page