Frank's N4SPP Hellschreiber page

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Most recent updates on this page:

	21-July-2010: added photos of spare carbon brushes etc.
	18-June-2010: moved photos of Waffenamt and other markings to this separate page.
	6-March-2010: added photos of inside of Feld-Hell electronics box).
	1-March 2010: added photo of original connector of audio patch cable.
	12-Feb-2010: added photo of Hell Morseschreiber with document reference.
	20-Oct-2009: added perspective photos of drive shafts.
	22-Sept-2009: added dimensional drawing of the Tornister (carrying case).

[photos of my Feld-Hell machine]          [video clips]         [historical photos]

[3D photos of my Feld-Hell are here ]      [photos of my Hell 72c "GL" are here]

        ©2007-2009 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. Look, but don't steal!

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These photos have been down-sampled.
All photos are available in full size, high-resolution jpg files. Contact me.

Front view of the Hell Feldfernschreiber
(paper supply drawers slightly pulled out)

Printer/keyboard and electronics units removed from the case

Electronics unit partially pulled out of the case

Top view of the printer/keyboard unit of the Feldfernschreiber
- cover of the character drum removed -

The character-drum is 20.4 cm long and has a diameter of 2.4 cm (≈ 8x1")

Rear view of the printer/keyboard unit of the Feldfernschreiber
- cover of the character drum removed -

Rear view of the Mechanical Unit with the Keyboard-Drum Unit removed

Left side of the motor-generator

Top part of the motor-generator with regulator cap and scale removed

The contact plate of the speed regulator

Top part of the motor-generator with contact plate removed, centrifugal weight mechanism visible

The centrifugal speed regulator disk

Top of the motor-generator - centrifugal regulator removed, ball bearing visible

Here is a diagram that I made it to illustrate the construction of the motor-generator, and to guide its disassembly and reassembly (see the "maintenance" page). It is available as a high-resolution jpg file here (2.3 MB).

The following diagram illustrates the installation of the various drive shafts in the Feld-Hell's gearbox. The diagram will be included in the overhaul manual for the gear train.

Top view of the drive shafts installed in the Gearbox
(worm drives of the input drive shaft are located below the ball bearing shown at the center)

Perspective view of the drive shafts installed in the Gearbox
(also available as red/green anaglyphic stereoscopic ("3D") photo here)

Front view of the Mechanical Unit with the Keyboard-Drum Unit and motor-generator removed

A look into the gear-box of the Feldfernschreiber from the rear of the unit
- cam wheel at lower right is for the pause character key; several gears are molded or machined out of Harex® or Turbax® (ref. 1) -

Spur gear (1, 2), bevel gear (3), helical My great-grandfather and his
gears (4), worm-gear (5) and pinion ( 6) bevel-gear-driven chainless bicycle, ca. 1914

Bottom of the motor-generator, with tappet of the pin-coupling to the gear-box
(note red alignment lines on the tappet and the base ring)

Top of the gear-box, with tappet of the pin-coupling to the motor-generator
(note red alignment lines on the tappet, base ring, and link for coupling pin from motor-generator tappet)

Generator carbon brush (left):

– 5 x 6.4 x 15 mm (HxWxL)

– turned head: 2 mm

– spring length: 25 mm (1”)

Character drum carbon brush (right):

– 3.9 x 3.9 x 15 mm (HxWxL)

– turned head: 2 mm

– spring length: 25 mm (1”)

Click here for some general information on carbon brushes.

Carbon brushes of the generator (left) and the character drum (right)
(shown with carbon brush holder caps)

Original cardboard strip with spare carbon brushes for the motor and drum

Original cardboard strip with spare fuses, carbon brushes for the generator, and lamp

Keyboard of the Feldfernschreiber

Note the special "pause character" key to the right of the "P" key (similar to "E") - it is unique to the Feld-Hell! The "green dot" key on the far left is the "Morse" telegraphy key. The blank key at the bottom right is the "space" key.

Keyboard-Drum Unit, removed from the Mechanical Unit

Bottom view of the keyboard

Paper trays pulled out of the unit

Printing mechanism of the Feldfernschreiber
(spindle (electro-magnet is in the small box below it), ink roller, paper transport rolls)

Printing mechanism without cover

Spindle-magnet box removed

The spindle-magnet box viewed from the equipment side

The inside of the spindle-magnet box
(electro-magnet, spring-loaded armature, various adjustment points)

The only "Hell" markings (4) that I have found so far, are inside the printer

The hammer moves up about 0.4 mm when the electro-magnet is energized

The electro-magnet is marked "0,06 CuL", "4090", and "15000". That is: 0.06 mm Ø "lackisolierter Kupferdraht" (enameled solid copper wire), 15000 windings, 4090 ohms (I measured ≈ 4075 Ω).

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The Hell Co. also produced "Schnellmorseschreiber" (high-speed Morse printers, up to 500 wpm!). Here type "MS 5". The printer has parts in common with the Feld-Hell machine. The printer spindle resembles a gearwheel with the teeth set at an angle.
Ref.: "Der Schnellmorseschreiber System Hell", G. Ege,
Ref.: "Der Schnellmorseschreiber als Funkempfangsgerät", H. Haberland
pp. 22- and 26-31 and respectively in "Hell - Technische Mitteilungen der Firma Dr.-Ing. Rudolf Hell - Gerätentwicklungen aus den Jahren 1929-1939", Nr. 1, May 1940

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Front panel of the electronics unit of the Feldfernschreiber

Top of the electronics unit of the Feldfernschreiber
(6 amp fuse and switch between two 12 V power sources (via round front connector); note that the tubes can be replaced without opening the unit, and that the pins of the tubes are accessible with a voltmeter)

Top of the electronics unit of the Feldfernschreiber with the tubes removed
- the tubes (considered to be the least reliable components) can be replaced without opening the unit ! -

Rear of the electronics unit of the Feldfernschreiber
- the white numbers next to solder lugs correspond to numbered points in the schematic; also each component has a small round sticker on it, with a number that corresponds to the component number in the schematic - takes the guesswork out! -

Left side of the electronics unit, with connectors for the cables to the printer/keyboard
(connectors are keyed differently and color coded)

Top of the electronics unit, top & rear covers removed

Bottom of the electronics unit, top with circuit board removed

Top and circuit board of the electronics unit
(upside down, two tubes removed; shield box removed from transformer Ü17 (SÜ) in foreground)

Bottom view of circuit board and top cover of the electronics unit

Front side of the circuit card and top cover of the electronics unit (upside down)

Left side of the circuit card of the electronics unit

Right side of the circuit board of the electronics unit

The concept of "design re-use" is as sold as the art of engineering itself. The photo below shows the electronics box of a Hell Schnellmorseschreiber, model MS3a (upto 300 wpm). The front panel is very similar to that of the Feld Hell. The unit has two RV12P4000 tubes (see the schematic). It operates on 110/220 Vac or 12 Vdc. In the latter case, the required anode voltage is not provided by a motor-generator, but by a so-called "Wechselrichter" (a.k.a. "Zerhackerpatrone"): an electro-mechanical chopper. Tone frequency is 900 Hz or 1500 Hz (selectable).

Electronics unit of a Hell Schnellmorseschreiber type "MS3" from 1940
(courtesy G. Schulte; used with permission)

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The Feldfernschreiber was designed for (mobile) field operation. So it needed to be carried around - on the back of soldiers. The complete unit weighs in at 27 kg (5.7 kg for the electronics unit, 14.6 for the motor + printer + keyboard unit, and 6.5 for the case + lid; 60 lbs total), so this must not have been easy (but then again, there are more serious downsides to field operation and war). The case has attachment points (on top and at the bottom of the side panels) for a leather harness to carry it as a backpack ("Tornister"). The enhance the carrying pleasure, the back of the case has two vertical tracks for inserting a cushion to protect the back of the soldier who had to lug the unit. The bottom of the case has two strips that run front to back (1 cm thick turbax/harex®, a cotton-reinforced thermosetting phenol-formaldehyde (PF) laminate). Probably served to protect government-issue desk tops! The closed unit measures 45½ x 39 x 24 cm (HxWxD, ±17 x 15 x 9 inch).

Outline drawings of the Feld-Hell "Tornister" carrying case (ref. 5)

The front and back of the Feldfernschreiber case
- inside the case: tracks + latch at the bottom, for the mechanical unit; tracks at right & top for the electronics unit, with nut for the mounting bolt of that unit at the center/left; small L-bracket above it, prevents the two connectors on the left side of the electronics unit to become unplugged when that unit is mounted in the case -

The cover and side of the Feldfernschreiber case

The case of this 1938 model is made of aluminium. As the war years progressed, this strategic material became scarce and cases where made out of wood. The word "Feldfernschreiber" is barely legible on the cover. The cover of some Feld-Hells used in the Spanish Civil War (1936-1939) had the label "Tele-inscritor" ( = "Fernschreiber) on the lid. I'm not sure whether those were used by the Spanish military, or by the German Legion Condor (English: Condor Legion) - who obviously wouldn't need Spanish labeling...

The cover of an other Hellschreiber case (1944) - text more legible

Bottom of the printer/keyboard unit - part of latching mechanism on the right
(cover plate of the lower paper tray removed; top of the image shows spring-loading of the trays)

15 mm wide Feld-Hell paper rolls
(a original 250 meter (820 ft) roll suffices for 9+ hrs of operation (82k characters); originally, paper was used that was lightly gummed on the side not printed - per item 12c on p. 6 of the 1941 manual, this was a moisture protection). More on Hellschreiber paper tape on this page.

Round plug for the front-connector
(home-brew insert with pins for the Hellschreiber's transmitter keying output)

Original connector of audio patch cable
(photo courtesy John Alexander Wilson)

The original 12 Vdc plug that came with the Hellschreiber

Plug for the La-Lb/E phone jack

A Wehrmacht transformer-rectifier unit that matches the Feld-Hell
(I am still trying to locate and acquire one of these power supplies)

Ref. 1: Turbax is a brand name dating back to Jaroslaw's Erste Glimmer-Waren Fabrik (Jaroslaw's First Mica Products Factory) of Berlin-Weißensee in the 1930s, for a "Hartgewebe" ("hard fabric"); here: a cotton-reinforced laminate of a particular thermosetting polymeric resin (phenol-formaldehyde, PF). PF is the basis of bakelite®, a moldable sawdust-reinforced PF that was invented in 1907 and patented in 1909 by the Belgian Leo Bakeland (1863-1944), who emigrated to the USA at the age of 26; his patent expired in 1927. PF patents date back to the late 1890s. In sheet form, the equivalent of turbax is often referred to as Harex®, a trademark of Resopal® Werk H. Römmler GmbH (founded 1935). Turbax/harex is still used today for gears due to its flexible and quiet-running properties. This material can be machined like wood and metal, or be molded. Novotext, Tenazit, Thesit, Taumalit, Esconit, Bernit, Resinol, Resitex, Tenatext, Trolitan, Tufnol, Celeron, and Micarta are (registered) brand names for similar materials of other manufacturers. Later on, an other polymer replaced PF for many applications: polyepoxide ("epoxy"); it was patented in Germany in 1939 by I.G. Farbenindustrie, a company that became infamous for other chemicals during WWII.

"TURBAX Hartgewebe. Aus Gewebe und Kunstharz", Jaroslaw, 1938, 8 pages, 15 x 21 cm.

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Historical photos

1944 Feld-Hell Fernschreiben (telegram) from General Wenck to Major-General Wisch, congratulating the latter with his promotion *
(courtesy and © M. Lippl; click on image or here to get full size. * General Wenck was Chief of Staff of the 1st Panzer Army and youngest general in the German Army during WWII; Major-General Wisch was Commander of 1st SS Division "LSSAH")

Hell Feldfernschreiber (ref. 4)

Feldfernschreiber in field operation (ref. 5)
(with standard-issue army Feldfernsprecher 33 (FF33) field telephone set on top of it)

Feldfernschreiber communication in a teleprinter station

Radio shack with Hellschreiber from a scene in the 2008 comedy movie "U-900" (ref. 3)
(note the US-made tuning unit in the corner!)

The joy of collective listening to a portable radio

	Ref. 3: source: website of the Association of Friends and Sponsors of the “ Dr. Rudolf Hell Technical Collection”
	Ref. 4: Figure 29. in Chapter VIII "Equipment" of "Handbook on German Military Forces", 15 March 1945, War Department Technical Manual TM-E 30-451
	Ref. 5: photo courtesy Helge Fykse, LA6NCA; also see his WWII German radio website
	Ref 6: “Der SH-Feldschreiber“, author ??, Siemens-Halske AG, Berlin-Siemensstadt, SH 7535. 1.2.39. TT1., 11 pp. (courtesy Siemens Corporate Archives, München).

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©2004-2009 F. Dörenberg N4SPP

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