- [First generation Feld-Hell]
- [Basic characteristics]
- [Sending messages]
- [Printing messages]
- [The motor-generator]
- ["Tornister" carrying-case]
- [Operating instructions]
Latest page update: December 2022 (added Fig. 5B and associated expanded text)
Previous updates: August 2022 (added ref. 10 and associated text about the Feld-Hell predecessor model); 10 January 2019.
©2004-2022 F. Dörenberg, unless stated otherwise. All rights reserved worldwide. No part of this publication may be used without permission from the author.
The Siemens-Hell Feldfernschreiber (Feld-Hell for short) is a self-contained, portable teleprinter system that is based on the Hellschreiber system. The latter, in particular the printer part, was invented by Rudolf Hell in 1929. It was developed specifically for portable field ( = "Feld") operation by the Wehrmacht. Per §2 of the "Wehrgesetz" law of 12 May 1935, the Wehrmacht comprised the German "Heer" (army), "Kriegsmarine" (navy), and "Luftwaffe" (air force) during the period 1935-1945 (the Wehrmacht was officially abolished a year later, 20 August 1946, by "Kontrollratsgesetz No. 34" of the Allied Control Council). The first Feld-Hell machines entered service with the Wehrmacht in 1935 - that is, at the beginning of the official German re-armament. They were used until the end of WW2, primarily for tactical communications (p. 50 of ref. 1).
Fig. 1: front-view of the Hell Feldfernschreiber
(compartment with paper tape rolls closed (left) and drawers slightly pulled out(right))
E.g., Luftwaffe-Vermittlungen, (air force telecom exchanges) were required to have at least one or two Hell Feldfernschreiber at their disposal, to ensure urgent telegram message capability over phone lines, when the conventional teleprinter network was not available (p. 500 in ref. 2).
Fig. 2: German military symbols for motorized radio (wireless) sub-units
(source: ref. 3)
As stated, the Feld-Hell was conceived for mobile military operation in the field. So it is:
- portable and rugged,
- easily maintainable,
- operable from a portable source of electrical power, such as a car battery, and
- has interfaces for a standard (field) phone line, basically any radio transmitter/receiver, and headphones.
Fig. 3: printer/keyboard and electronics units removed from the carrying-case
To be easily maintainable, all parts and items that require regular preventive maintenance (e.g., lubrication) must be easily accessible. Some parts are subject to wear and/or have a limited operating life time (e.g., the vacuum tubes, fuse, felt ink roller). Such components require unscheduled corrective maintenance (repair), and must be both easily accessible and easily replaceable. The unit must also be maintainable by minimally trained personnel, in wartime field conditions, without special tools. It must also be easy to verify correct basic operation of the unit, and perform simple troubleshooting. The above requirements apply to both line-maintenance (in the field) and shop-maintenance (repair shop). The Feld-Hell fully supports all this.
Ease of maintenance is provided in several ways. First of all, the system is modular. It comprises two major line-replaceable units:
- the electronics box (the "Verstärker- und Anschlußsatz" = amplifier and interconnect unit), and
- the mechanical unit, itself comprising four line-replaceable units:
- the motor-generator,
- the keyboard-sender unit,
- the Hell-printer mechanism, and
- the base unit (D: "Unterteil"), with the gearbox and trays for two rolls of paper printer-tape. The above three units are mounted onto this base unit with two or four screws.
Note that the modular design also had advantages for the manufacturing and assembly process. Modules and sub-modules can be built in simultaneously at geographically distributed locations (less vulnerable), tested in a stand-alone manner, and brought together for final assembly and test. What many people consider to be a "modern", post-war concept is now over 80 years old!
All line-replaceable items are easy to identify: they are marked with a red ring around the head of their mounting screws. No other disassembly was allowed during field-maintenance. The screws require only a standard large screwdriver or a coin, or have a large knurled head and can be removed manually. Some Wehrmacht equipment also has items with a blue ring. They allow a further level of disassembly (by qualified staff).
The four vacuum tubes of the electronics unit are early Wehrmacht-tubes of type RV 12 P 4000. They are inserted "head-first" into the top of the electronics box. No need to open the box or do any other disassembly. Using four identical standard tubes simplifies maintenance logistics: only one type to stock. They can also be quickly swapped during troubleshooting. The built-in voltmeter can be used to check the voltage of the external battery or power-supply, and also verify the anode voltage from the motor-generator. Verification at system level is also simple: the Feld-Hell locally prints the text that it sends. This covers almost the entire end-to-end system! All electronic components inside the electronics box (resistors, capacitors, diodes, inductors, transformers, connector pins, etc.) are marked with a number that corresponds to the component or wire number in the schematic. A big help during shop-maintenance! Of course, the extreme simplicity of the Hell-printer system (compared to conventional teleprinters of the era) also contributed to excellent suitability of the Feld-Hell for field-operation.
The standard Feld-Hell set has the Siemens-Halske model designator T.typ.58. The Wehrmacht referred to this set by the designator Tbs 24a-32, where Tbs is short for Typenbildschreiber (another name for Hellschreiber), and 24a-32 is the Wehrmacht Zeichnungnummer. More about this on the "Markings on Feld-Hell" page. The reference of the Luftwaffe's Luftnachrichten (signal corps) used the reference Ln 562 and Ln 5562 for the Feld-Hell set with its peripherals ("Feldfernschreiber Satz"), ref. 13. The basic design of the Feld-Hell was done by the Hell company. The primary manufacturer of the set was the Siemens-Halske company in Berlin, who industrialized the design. However, the Radio H. Mende & Co. GmbH company in Dresden built over 4000 sets - again, see the "Markings on Feld-Hell" page. Note that the Hell company also designed and built its own Feld-Hel machine. It had the Wehrmacht designator Tbs 24b-32, and was similar to the standard Tbs 24a-32, but with some operational refinements. The Hell company's model "MS3" and "MS5" "Feld" Morseschreiber machines are the equivalent Morse-telegraphy printer-only sets of the Wehrmacht.
The Siemens-Halske company also marketed the Feld-Hell to the civil market! In the office (desktop) configuration used by both military and civil customers, the machine was taken out of its carrying case:
Fig. 6: 1942 (!) advertizing in Switzerland for civil use of the Feld-Hell via power lines
(source: ref. 8; the same photo also appears in ref. 9 from 1939)
THE FIRST-GENERATION FELD-HELL
The ubiquitous Feld-Hellschreiber shown and described above, is in fact the second generation! The photo below shows the first generation Feld-Hell, installed in a model Kfz 72 "Funkbetriebskraftwagen" (Fu.Betr.Kw.) military radio truck:
Fig. 4: mobile Wehrmacht station with a "first generation" Feld-Hell
(source: ref. 10)
Two leather straps with a ratchet tension lock ("Halteriemen mit Spannverschluß") keep the Hellschreiber firmly onto a tray with shock absorbers ("gefederter Untersatz"). The radio receiver to the left of the Feld Hell is a 1932/33 portable Telefunken receiver model Spez. 445 Bs . The latter radio was the predecessor of the famous Torn.E.b.
Fig. 5: close-up of the "first generation" Feld-Hell
(source: ref. 10)
The above photos are taken from an early-1936 Wehrmacht Signals Corps instruction document (ref. 10). This implies that this Feld-Hell model dates back at least to 1935, possibly even 1934. Note that there is no compartment below the keyboard module for rolls of paper tape. There are two small reels just above the printer mechanism. Above those reels, there is what appears to be a third reel. The printer mechanism does not seem to have a felt ink roller. This implies that carbon tape was used, as in the 1933/34 model T.empf.12a Presse-Hell printer. The latter also has a 3-reel arrangement: a paper tape reel, a carbon tape reel, and a reel for collecting the used carbon tape. The rotary main switch on the electronics box has five labels, suggesting more switch positions than the three of the "standard" Feld-Hell. There are two volume control knobs instead of one (lower left-hand corner and center top), possibly also allowing the amplitude of the output signal to be adjusted. Above the motor-generator, there is a small compartment with a hinged lid. It may have been used to keep spare rolls of paper and carbon tape, and other spare parts (carbon brushes, light bulb, fuses).
The radio truck is a version of the ubiquitous Kraftfahrzeug Kfz. 72. The were built from 1934-1942 by several manufacturers (Henschel, Krupp, Mercedes Benz, Büssing). The Kfz.72 was based on a standard 3-ton 3-axle type 33 "all terrain" truck chassis: Fahrgestell des mittleren geländegängigen Lastkraftwagens, offen (m. gl. Lkw. (o)). They were equipped with several engine types (gasoline (UK: petrol), diesel), and sizes. There were at least five different types of communication trucks based on the Kfz. 72:
- Funkbetriebskraftwagen (Fu. Betr. Kw.) - radio operations truck.
- Total max payload 1035 kg (i.e., a 2-ton truck in US-English parlance), excluding 2-man crew; 1250 kg total payload incl. 2-man crew with standard kit; total max weight of 8100 kg ≈ 18000 lbs).
- Fernschreibkraftwagen (Fernschr. Kw.) - teleprinter truck
- Fernsprechbetriebskraftwagen ( Fsp. Betr. Kw.) - telephone truck
- Funkhorchkraftwagen a (Fu. Horch Kw. a) - radio intercept truck A
- Funkkraftwagen a und b (Fu. Kw. a & b) - radio truck A/B
Fig. 5A: The Kraftfahrzeug "Kfz. 72" radio truck
Fig. 5B: rear view and side view of the "Kfz. 72" Funkbetriebskraftwagen radio truck
(source: adapted from ref. 10; on the back: two 10 m telescopic antenna masts, each with 4 spools of antenna wire/cable)
BASIC CHARACTERISTICS OF THE FELD-HELL
The basic characteristics of the Hell Feldfernschreiber are as follows:
- Text character font (see the "Hellschreiber fonts" page):
- Special bitmap-font of 7 columns x 14 rows; the first and last column are used for spacing between characters; the top and bottom rows are use for spacing between lines; bottom-up scanning; no start-pulse/bit.
- Font memory technology: electro-mechanical (character-drum with slip-contacts).
- Character set: letters A-Z, figures 0-9, punctuation marks + - ? /, special character: Feld-Hell pause-symbol.
- Character transmission rate: 2.5 characters/sec (150 chars/min); 30 WPM.
- Text entry: keyboard with standard German QWERTZ layout; no punch-tape reader.
- Electronics technology (see "Electronic circuitry and schematics" and "Components & construction" page):
- Amplifiers and tone oscillator: four vacuum tubes of type RV 12 P 4000.
- Tone detector: full-wave rectifier with solid-state Siemens SIRUTOR diodes .
- Vacuum tube anode voltage: generator driven by the motor ("dynamotor").
- Built-in audio bandpass filter (900 Hz center frequency, 150 Hz bandwidth).
- Standard Hell -system spindle printer with felt ink roller.
- The spindle is double-thread/single turn, scanning bottom-to-top with 525 rpm.
- Communication via telephone lines or AM radio: tone-modulated audio pulses ("900 Hz tone off" = white pixel, "900 Hz tone on" = black pixel); the character drum is used to key the built-in 900 Hz tone oscillator.
- Communication via CW-telegraphy radio: unmodulated-carrier-frequency pulses ("carrier off" = white pixel, "carrier on" = black pixel); the character drum is used to directly key the CW/telegraphy transmitter.
- Shortest pulse duration: 1000 / (2.5 x (7x14/2) = 8.16 msec (black or white).
- Telegraphy speed: 1000/8.16 = 122.5 baud.
- Channel bandwidth:
- "Necessary bandwidth" per ITU: 3 x 122.5 = 367 Hz (see the "Bandwidth & duty-cycle" page.
- However, the pixel rate ("Schrittfrequenz", "Bildpunkfrequenz") = 1 / time required for one white + 1 black pixel) = 1000 / (2x8.16) = 61.25 Hz. This implies a necessary bandwidth of 3 x 61.25 < 200 Hz. Extensive 1930s tests by Siemens-Halske, Cable & Wireless, and the German national postal company concluded that bandwidth should be at least 1.2 x 61.25 ≈ 75 Hz and no more than 1.6 x 61.25 ≈ 100 Hz. This bandwidth limitation should obviously be implemented on the transmitter side.
- Duty cycle: average ca. 25% (min 6%, max 39%, depending on the character).
- Mode: (quasi)synchronous only (i.e., not asynchronous/start-stop mode with a start-pulse or bit).
- Phone line interface: standard 2-wire, or 1-wire plus ground (not allowed within 3 km (2 miles) of the front line).
- Radio transmitter/receiver interfaces (see the "Interfaces to a transceiver" page):
- Keying output to a CW-transmitter: max 100 volt or 0.1 mA (1 watt combined max).
- Audio from a radio receiver to the "Empfänger" input.
- Tone pulses to phone line or an AM/SSB transmitter.
- There is no "PTT" output.
- Allowed signal path attenuation: ≈ 43-45 dB end-to-end (5 neper per p. 6 in ref. 4A/B; 5.3 neper per page 11 in ref 5A).
- Power source: 12 volt DC +/- 10% (40 Ah car battery or 12 volt power supply with a rating of 4.5 amp continuous).
- Paper tape:
- Width: 15 mm.
- Speed: 47 cm/min (≈1½ ft/min).
- Length of a roll: 250 or 300 m (≈ 800-100 ft); 9-11 hours of continuous operation.
- Width of printed characters: about 2.2 mm (47 cm/min / 60 sec/min / 2.5 chars/sec / 5 of 7 pixel columns printed per character = 2.24 mm).
- Height of printed characters: about 4.3 mm (10 of 14 pixel rows printed per character, two identical characters printed one above the other, 1.5 mm on the edge of the paper tape is not printed = 10/14 x (15 mm tape width - 2x1.5 mm margin) / 2 = 4.28 mm).
- Dimensions (carrying-case outline): 45½ x 39 x 24 cm (HxWxD, ≈ 17 x 15 x 9 inch)
- Weight (including carrying case): 27 kg total (≈ 60 lbs); 5.7 kg for the electronics unit, 14.6 kg for the motor + printer + keyboard unit, and 6.5 kg for the case + lid.
- Accessories: power cord, spare light bulb, spare fuses, spare carbon brushes (motor + generator), ink bottle + application brush, spare felt ink rollers, 1-page instruction manual. See the "Accessories" page.
- Peripherals: field telephone, headphones, CW-transmitter keying devices, remote control, line attenuator, power supply. See the "Peripherals" page.
- Price: see discussion on the "Hell equipment prices 1937-1952" page.
SENDING MESSAGES WITH THE FELD-HELL
The character-set of the Feld-Hell comprises 41 characters. The characters are captured as a so-called 7-line bitmap font: 7 columns of 2x7=14 pixels. See the "Hellschreiber fonts" page. Rudolf Hell's font is the world's first digital font (ca. 1929).
Fig. 6: the official Feld-Hell font with its 41 characters
Each character has its specific 7-column bitmap pattern. This bitmap is transmitted column by column, as a stream of pixels (bit stream). Tho facilitate this, the columns of each character are arranged head-to-tail. The result is a single sequence of 7x14=98 pixel-bits. In the Feld-Hell, each such sequence is memorized as a ring. Each pixel is captured as a conductive patch. The combined 41 rings form a cylinder that is referred to as the character-drum (D: "Geberwalze"):
Fig. 7: Character drum with a ring of conductive patches for each character
Fig. 8: the character-drum of the Feld-Hell
There are 41 characters of 7 x 14 bits each. Hence, the Feld-Hell's character drum is actually a 4 kilobit electro-mechanical Non-Volatile Read-Only Memory. It weighs about 1 kg (2 lbs)! The character-drum is integrated with the keyboard. It is simply mounted onto the base module of the Feld-Hell with two screws.
Fig. 9: the keyboard / character-drum module of the Feld-Hell (cover removed)
Of course, the Feld-Hell keyboard has a German QWERTZ layout rather than QWERTY (US/UK), AZERTY (France), or other. It only has capital letters A-Z, the figures 0-9, and the characters + - ? / but there is no period or comma. The keyboard does not have a space-bar, but there is a space-key. It is located at the bottom right of the keyboard; it does not have a corresponding track on the character drum, but it is subject to the keyboard enabling/locking mechanism described below. A "Morse" telegraphy key is provided to the left of the Q and A keys. It is marked with a green dot. Besides using it for Morse telegraphy, it can also be used to transmit a constant tone that can be used when tuning a radio receiver (side-tone).
Note the special character key to the right of the "P" key. It is unique to the Feld-Hell and the post-WW2 "T.send.46" and "ATF" Hellschreibers.
Fig. 10A: The Hell "pause" character
It was used during speed adjustments between two stations, and when having to keep a phone line or radio frequency occupied. When the "pause" character key is selected, a feature in the keyboard of the Feldfernschreiber latches that key, and another mechanism ensures that only one out of every four is actually transmitted.
In August of 2017, Marius Spix took the very laudable initiative to submit the Hell Pause Character to the Unicode Technical Consortium (UTC) for inclusion in the Unicode character set (ref. UTC L2017/17222/152-C12, UTC L2/17-151R, U120-2B00). The UTC has accepted his proposal, and in March of 2019, the Unicode revision 12.0 character code set was released. The "Hellschreiber Pause Symbol" has been included as hexadecimal Code Point 2BFF in the "Miscellaneous Symbols and Arrows" block:
Fig. 10B: The Hell "pause" symbol has been included in Version 12.0 of the Unicode Standard
If Unicode 12.0 (or newer) is installed for your browser, the next two characters should be the Hell Pause symbol: ⯿ ⯿.
The drum turns continuously, and each character takes one full revolution. However, transmission of a character must always start at the first pixel position of the sequence (i.e., the bottom of the first column). Hence, the keyboard must only allow a key to be selected during a brief time window just before the start of that sequence. This is done with a lock-out/enable mechanism. This is shown in Figure 11 below. When a key is depressed, the associated spring-loaded slip-contact flips, and makes contact with the associated track of the drum. At the end of the revolution of the drum, the slip-contact flips back and no longer touches the drum. At the same time, the keyboard is once again briefly enabled for selection of the next character to be transmitted. While the pixel sequence of the selected character is being output, no other character can be selected: the keyboard is mechanically disabled (i.e., no "type ahead").
Fig. 11: Illustration of the key locking/enabling and slip-contact (dis)engaging mechanism
(the vertically oriented black lever is the slip-contact associated with the key)
Note that when you keep a key depressed for more than one revolution of the drum, the slip-contact is still released after one revolution and the character is only sent once. To send the same character multiple times in a row, you have to push the key multiple times (section II.a in ref. 5B).
Fig. 12: Details of the Feld-Hell mechanism for key locking/enabling and slip contact (dis)engagement
(source: figure 11 in ref. 4)
All the metal pixel patches of the drum are interconnected. The 41 slip-contacts, one for each ring of drum, are also interconnected. The common point is connected to a separate, continuous ring on the drum. This ring is connected with a carbon brush. If, and as long as, any slip-contact touches a metal pixel patch when the drum turns, the "switch" is closed. This switch can be used to direct key a CW-telegraphy transmitter. It can also be put in series with the constant 900 Hz tone that is provided by the Feld-Hell's tone oscillator. The result is a stream of 900 Hz tone-pulses. This stream can be output to the opposite Feld-Hell machine via phone lines or a radio transmitter. See the "Interfaces to a transceiver" page.
PRINTING MESSAGES WITH THE FELD-HELL
The Feld-Hell has a standard Hell-printer, see the "How it works" page. The Feld-Hell character images (font) consist of 7 pixel-columns, and 2.5 characters are sent/printed per second. That is: 7 x 2.5 x 60 = 1050 columns per minute. If the printer spindle only has one thread, then a spindle speed of 1050 rpm is required. Such a spindle has one helix or spiral, like a regular screw. This is also referred to as single-thread, single-flight, single-start, and 1-start (D: "eingängig"). The Hell-printer must simultaneously print two identical lines of text, one above the other. So, the thread of the spindle must make two turns ( = wound twice around the hub of the spindle). However, the spindle of the Feld-Hell machine runs at 525 rpm, not 1050 rpm! How come? At first glance, the spindle appears to be a regular spindle, with a single-thread that makes two turns:
Fig. 13: the two-turn helix spindle is installed just above and across the paper
However, a closer look at this spindle shows that it is actually a double-threaded worm (double-helix, double-start, 2-start; D: "Doppelspirale", "zweigängige Schnecke"): it has two intertwined windings. They are shifted 180º. Note that each of these two threads only makes one turn!
Fig. 14: the double-thread spindle - each thread is "single-turn"
With 525 rpm, this "double-thread/single-turn" spindle produces the same column-scan speed as a "single-thread/two-turn" worm at 1050 rpm. Hence, a lower motor speed can be used, or the motor can be down-geared (which makes speed regulation less sensitive to load changes). Lower speed also means less wear on ball bearings.
Fig. 15: cross-section of single-thread and a double-thread worm
Figure 16 below shows the complete send-and-print sequence for the character "3". The operator selects a character on the keyboard of the sending Feld-Hell machine. The character-drum of that machine generates the pixel stream for the image of that selected character. This is equivalent to scanning that 7x14 pixel-image column-by-column, scanning each column bottom-to-top. As long as a pixel is active, a 900 Hz audio tone is sent to the receiving Feld-Hell machine. The latter machine receives the stream of tone-pulses. As long as the tone is received, the electromagnet of the printer is energized. This pushes the paper tape against the spinning printer spindle. The spindle is kept wet with ink. The threads of the spindle continuously scan across the paper tape. The length of each printed dot or line segment is determined by the length of the received tone pulse. This recreates the pixel pattern of the character that was selected at the sending machine.
Fig. 16: Complete send/print sequence for the character "3"
(click to start or stop; a dynamic gif file without sound is here)
Fig. 17: ticker-tape with the 7x14 character set of the Hell Feldfernschreiber
Helge Fykse (LA6NCA), demonstrating communication between two Feld-Hell machines
THE MOTOR-GENERATOR OF THE FELD-HELL
The Feld-Hell machine has one motor that is powered by 12 volt DC. The motor is part of a single-rotor motor-generator. The generator provides the anode voltage that is required by the vacuum tubes (valves) in the electronics box. The motor drives the rest of the mechanical system via a gearbox.
Fig. 18: the motor-generator of the Feld-Hell
The motor runs at a constant speed of 3600 rpm. The choice of the motor rpm may be a carry-over from the spindle speed of some older Hellschreiber models: 12 pixel columns per character (12-line font), 5 characters/sec (punch-tape), 60 sec/min = 3600 rpm. The motor-generator weighs 1.5 kg (≈ 3.3 lbs).
According to the data plate on the motor-generator, the motor is rated at 4.5 amps at 12 volt DC (= 54 watt), and delivers 5 watt mechanical power (to the gear box), whereas the generator is rated at 25 mA at 180 volt DC ( = 4.5 watt). Note that the 1941 Feld-Hell manual (ref. 2, line item 93) states that the mechanical dissipation is 4 watt; it also states that the nominal generator voltage is 165 V at 15 mA max (i.e., 2.5 W).
The generator is permanently loaded with two 15 kΩ resistors in parallel, see the "Circuitry and Schematics" page. They are located in the junction box on the back of the motor-generator. They draw 12 / (15kΩ/2) = 22 mA at the nominal generator voltage. Two of the four RV 12 P 400 vacuum tubes in the amplifier box are configured as an amplifier, and draw an average 3 mA. The other two vacuum tubes are configured as a switch, and draw up to 10 mA each when active. Possibly, the generator voltage rating on the data plate is not standard, and indicates the average over and beyond the load by the resistors, rather than a continuous maximum current rating. The purpose of the loading resistors in unclear - possibly, the (relative) load variation is less with the resistors, than without.
The motor of the Feld-Hell machine is a shunt wound DC motor: the field windings are connected in parallel with the motor's armature windings. The governor field compounds the field of the armature windings. When the current through the shunt (governor) field windings is increased, the motor must turn slower in order to produce the same amount of back-EMF. Conversely, decreasing the shunt field current causes the motor speed to increase. This property is used to regulate the motor rpm. The motor speed is kept constant with a centrifugal regulator that is mounted on top of the motor's shaft:
Fig. 19: cross-section of the Feld-Hell motor-generator
As the motor speed exceeds (or falls below) the selected set point, centrifugal forces cause a governor weight to close (or open) a switch contact. This switch contact is in connected in series with the motor's governor field winding. For more details on the speed regulation and control system: see the "Circuitry & schematics" page.
THE GEARING OF THE FELD-HELL
A gear train is used to reduce the 3600 rpm of the motor down to:
- 150 rpm for the character drum (1 revolution per character, 2.5 characters/sec = 150 revs/min)
- 3600 x 3:48 x 72:108 = 150 rpm
- 525 rpm for the spindle (7 columns/character, 150 chars/min, 2-start printer helix = 7x150/2 = 525 revs/min)
- 3600 x 3:24 x 14:12 = 525 rpm
- 12.5 rpm for the paper transport roller. The powered roller has a diameter of 12 mm, which results in a paper speed of close to 47 cm per minute.
- 3600 x 3:48 x 2:36 = 12.5 rpm
Fig. 20: the Feld-Hell gear train
Fig. 21: top view of the gearbox - located directly below the motor-generator
The gear box is located directly below the motor-generator and behind the printer mechanism. The output to the character-drum is the large steel gear wheel at the bottom right in the figure above. This gear meshes with a similarly sized gear on the tip of the shaft of the drum.
Fig. 22: rear-view of the gear-box, cover removed
(the horizontal shaft is the output to the character-drum; bottom-right: timing/interrupter cam-wheel for the pause-character)
The 3-notch cam wheel in the photo above (lower right-hand corner) is mounted on the same driveshaft as the paper transport roller. So it turns at 12½ rpm. The character-drum turns at 150 rpm (150 characters per minute): 12 times as fast. The three notches actuate a contact that is placed in series with the slip-contact of the pause-character key of the keyboard. The contact closes three times per revolution of the cam wheel. Each notch covers 1/12th of the circumference of that wheel. Hence, only 3x1-out-of-12 = 1-out-of-4 pause characters is actually sent.
For more details on the drive shafts and bearings, see the "Design evolutions" page and the "Maintenance & repair" page.
"TORNISTER" BACK-PACK CARYING-CASE OF THE FELD-HELL
As the name "Feldfernschreiber" clearly suggests, this machine was developed for - and used in - military field operation. Like portable German military radios of the era, the Feld-Hell is housed in a rugged carrying-case: a so-called "Tornister" (ref. 6A, 6B, 6C). This backpack was intended to be carried around - on the back of a soldier. The complete unit weighs in at about 27 kg total (≈60 lbs), so backpacking was probably not a pleasure. But then again, there are more serious downsides to field operation and war... The system weight was kept to a minimum, by extensive use of light metals (aluminium and die-cast "Elektron" magnesium-aluminium alloy, see the "Components and construction" page). Note that the standard outfit of a Wehrmacht soldier weighed about 40 kg (≈88 lbs), in addition to the clothes he was wearing: standard backpack, rifle and 30 rounds of ammunition, laudry/clothes pack, water bottle, bread pack.
Fig. 23: outside & inside of the Feld-Hell carrying case
(there are tracks on the back of the case for a lumbar cushion (D: "Rückenpolster", "Rückenkissen"))
The closed unit measures ≈45½x39x24 cm (HxWxD, ≈17x15x9 inch). The empty case weighs 6.5 kg (≈14 lbs).
Fig. 24: outline drawing of the Feld-Hell "Tornister" carrying case
(source: ref. 7; dimensions are in mm)
BASIC FELD-HELL OPERATING PROCEDURES
The operating instructions for Hell Feldfernschreiber are straightforward. A 1-page instruction sheet is framed inside the lid of the carrying-case of each Feld-Hell machine (see further down on this page). The general Feld-Hell manuals (ref. 4A-4D) go into more detail, and also include trouble-shooting and simple field-maintenance steps. The basic instructions are illustrated below.
- Put the machine in the operating position:
- Release the latch at the lower left by pulling the latch lever to the left until it stops. While holding the lever at this position, pull the printer/keyboard unit 1 cm out of the carrying case, and let go of the latch lever. Then pull out the equipment until the latch snaps back to the right.
- In order to remove the printer/keyboard unit completely from the carrying case while it is in the operating position, slide and hold the lever to the left as far as it will go, then push the printer/keyboard unit back into the carrying case until the lever can be slid all the way to the left. Then pull the unit out completely. If the unit was still in the fully pushed-in position, slide and hold the lever to the left as far as it will go, pull the unit out until the lever can be slid all the way to the left. Then pull the unit out completely.
Fig. 25: "Riegel lösen" = "release latch" - a latch-pin moves in a track on the inside bottom of the carrying case
- Ground the equipment: use the ground/earth binding post on the front panel of the electronics unit. Grounding is done to connected radios, external power-supply (if used), or to a ground stake (for 1-wire + ground-return communication).
Fig. 26: the ground/earth binding post is located on the front of the electronics box
- Verify that the needle of voltmeter is at zero.
- Connect a 12 volt car battery or a rectifier unit.
- Ensure correct polarity! Note that the power plug is fool-proofed against reverse polarity.
- Note that "12 volt power supplies" often actually provide 13.8 volt, which is the normal charging voltage for "12 volt" car batteries.
- The "Sammler" / "Netzgleichrichter" switch ( = "Battery" / AC-transformer-rectifier power supply") must be in the "Sammler" position.
- The "Netzgleichrichter" position of the switch is only used in combination with an early model of a Hellschreiber-specific transformer-rectifier power supply unit that had poor voltage regulation with small loads (such as the Feld-Hell in "stand by"). According to the 1941 manual (ref. 4A/B), the switch is not necessarily installed in Feld-Hells that were built later.
Fig. 27: power connection
- Connect a 2-wire phone line to jacks La and Lb/E.
- Connect a field telephone in parallel with the phone line.
- Select the main switch from "Aus" ( = "off") to "Bereit" ( = "ready / standby").
- The red indicator light above the switch will illuminate. Steady-state current is about 750 mA. Note that the circuit for the red light passes through the two carbon brushes and the commutator of the motor. If the red light does not come on, this may be a hint for the cause...
- Wait 1 minute.
- This wait time is necessary, because the vacuum tubes should be allowed to warm up, before turning on the motor-generator. Applying anode voltage to cold vacuum tubes may damage the tubes.
- In standby mode, only the heater filament of the tubes is powered. The voltmeter reads about 10 volts; this is consistent with a 3.8 volt drop from the 13.8 volt power supply due to the 0.75 amp standby current through the 5 ohm resistor that is in series with the supply, when the power source switch on top of the electronics unit is in the "Sammler"/"Battery" position.
- Establish connection with the opposite Feld-Hell station via the field telephone.
Fig. 28: the three positions of the main switch
- Select the main switch to "Ein" ( = "on")
- The indicator light is now turned off
- The battery voltage should be in the red range of the voltmeter scale ( = 11-13 volt). The motor/generator will be turning.
- If the blue button on the voltmeter bezel is pushed, the anode voltage is shown. It should be in the blue range of the voltmeter (150-195 volt). Note: blue was the standard color for voltmeter buttons for anode voltage (ref. 11).
- Steady-state current varies between 3.5 and 4 amp.
Fig. 29: voltmeter readings in "standby", battery voltage & anode voltage when "on"
- While writing/typing, hold finger lightly on key without applying pressure, until key descends. Immediately release the key and actuate the next key.
- Adjust reception for best print quality with the "Verstärkung" ( = "Gain") knob.
- In case of poor text printing due to noisy signals, select the 900 Hz tone-filter from "Ohne" ( = "without / off") to "Mit" ( = "with / on").
- Adjust for straight text lines.
- If text lines are slanted downward, adjust the speed control cap on top of the motor-generator assembly to a higher number. If text lines are slanted upward, adjust speed control to a lower number.
Fig. 30: volume control knob, filter toggle-switch, and speed adjustment cap of the motor
- Check the paper supply.
- Open the paper tray cover by pushing down on the small black pushbutton at the middle of the base of keyboard (between the V and B keys).
- If necessary, insert a new roll of paper tape. Separate the end of the paper tape from the paper roll, and place it on the paper tray such that the roll unwinds clockwise. Feed the paper tape through the guides in the box, twist it 90º (if using gummed paper, the gummy side will be down), feed it through the slit in the left hand side of the paper tray box, while inserting the tray.
- Insert paper from roll into the printer system. Pull up the ink roller lever, pull the paper tape under the printer helix, and feed it between the paper transport rollers. Briefly pull the upper paper transport roller lever to the left; the ink roller will drop back onto the printer helix again
Fig. 31: the two paper trays
- Replace ink roller, if necessary:
- Pull ink roller lever upward and hold; pull off the used ink roller; insert a replacement roller from the spares box. If only replacement felt rings are available, pull the used felt ring off the steel bushing of the ink roller, put an inked replacement felt ring on, and push the roller back on its spinner.
- Immediately re-ink the removed ink roller.
Fig. 32: the felt ink roller ("Farbrolle")
A simple 1-page Feld-Hell operating manual ("Anleitung") is framed inside the lid of the carrying case, behind a sheet of clear plastic/celluloid:
Fig. 33: 1-page manual inside the lid of the Feld-Hell carrying-case
Siemens-Halske manual "T anl 4205/1" from May 1942
(for full size image: click here - 2.6 MB)
Manual "T anl 4205/2" from May 1942
(for full size image: click here - 1.6 MB)
Manual for the Feld-Hell with schematic 24a-32-a2
(for full size image: click here - 1 MB)
Italian manual "T anl 4205/10 it." from May 1942
(for full size image: click here - 1.2 MB)
THE PRICE OF FELD-HELL SETS
Pricing information about the Siemens-Halske Hell-Feldfernschreiber ("Feld-Hell") model T.typ.58 is very limited. I have no German pricing information.
In 1948 (i.e., post-WW2), Siemens in The Netherlands quoted a price of DFL 4295 to the Dutch news agency ANP (ref. 12A) for a Feld-Hellschreiber machine (including taxes, import duties, and shipment; re-import from Siemens/Sweden). In 2015 money, I have estimated this to be equivalent to 19308 Euros (US$ 21688), based on historic general inflation and exchange rate data.
The Swedish army bought both mobile and office Hellschreiber systems. The mobile systems comprised a Hell Feldfernschreiber ("Hellskrivare för fältbruk"), two lead-acid batteries (85 Ah capacity each), and a keying device. The set was referred to as "Sats Tc 33". The set's original stock number was "Tc 90240", later "M3936-105211". The keying device had stock number stock no. "Tc 20033", later "M3936-105219". Feld-Hell systems entered service in the Swedish Army in 1942. They were used with several types of mobile stations: 75 W Tp, 250 W Bl, and the 800 W Bl. See the Feld-Hell "Performance" page. The Hell equipment was decommissioned in the early 1960s and replaced by 5-bitstart-stop teleprinters (Siemens T.typ.68, Swedish designator "Fjärrskrivmaskin M 3").
Early 1941, Siemens-Halske quoted a price of 42400 Swedish Crowns (SEK) to the Swedish Air Force for eight complete Feldfernschreiber systems, similar to the systems already delivered to the Swedish Army (ref. 12B). I.e., 5300 SEK per Feld-Hell set. This is equivalent to an estimated 10537 Euros at the end of 2010 (ref. 12C). The 1944 book price for a complete Feld-Hell system of the Swedish Army was 6100 SEK. Ref. 12D. This is estimated to be equivalent to about €12125 and US$15000 in 2010 (ref. 12C).
The "desktop" office systems comprised a "Handlocher" tape puncher, a "Lochstreifensender" tape reader/sender, and a "Presse Hell" printer. In 1943, a price of 10200 SEK was quoted for each office Hell system (ca. €20280 in 2010). For prices of civil "Presse Hell" equipment, see this page.
If you have any additional pricing information, please contact me.
Note: the provided conversions from historic prices to post year-2010 equivalent prices, are estimates by me, based on historic statistics on general inflation ("buying power") and exchange rates. Inflation for specific industrial products such as telecommunications equipment, does not necessarily track that general "consumer price index" inflation.
- Ref. 1: "Aus der Rüstung des Dritten Reiches (Das Heereswaffenamt 1938-1945); ein authentischer Bericht des letzten Chefs des Heereswaffenamtes", General Emil Leeb (last chief of the Heereswaffenamt), in "Wehrtechnische Monatshefte (Zeitschrift für Wehrtechnik, Wehrindustrie und Wehrwirtschaft, Deutschen Gesellschaft für Wehrtechnik)", Beiheft 4, May 1958,70 pp. [62 MB]
- Ref. 2: various pages of "Drahtnachrichtenverbindungen, Richtfunkverbindungen 1939 - 1945", Part 2 of "Der Weltkrieg", Volume 2 of "Ln- Die Geschichte der Luftnachrichtentruppe", Karl Otto Hoffman, Kurt Vowinckel Verlag, 1973, 762 pp., ASIN: B002N0OROA. Also see Volume 1: "Die Anfänge von 1935 - 1939", 1965, and Volume 2, Part 1 "Der Flugmelde- und Jägerleitdienst 1939 - 1945", 508 pp.
- Ref. 3: p. 124 in "German Military Symbols", Military Intelligence Division, War Dept., Washington, Directorate of Military Intelligence, War Office, London, 1 April 1944, 364 pp.
- Ref. 4: "Der Feldfernschreiber" - original military manuals
- Ref. 4A: "Der Feldfernschreiber", document D 758/1 of the Oberkommando des Heeres, Heereswaffenamt, Amtsgruppe für Entwicklung und Prüfung, Berlin, 1 April 1941, [this is the official original Wehrmacht manual in German for model 24a-32 (a1 and a2)]. Here is another scan of this document, with high image quality. [30 MB]
- Ref. 4B: "The Hell Feldfernschreiber", the above D 758/1 "Der Feldfernschreiber" document, translated into English and annotated by me, Frank Dörenberg; updated 2 May 2009.
- Ref. 4C: "Der Feldfernschreiber", Luftwaffen Dienstvorschriften L.Dv. 702/1 Heft 213, "Luftnachrichtentruppe – Ausbildung am Gerät, Teil 1 - Gerätebeschreibungen", Reichsluftfahrtministerium (RLM), 21 November 1940 25 MB; this is the Luftwaffe Feld-Hell manual; counterpart to the Army manual D 758/1 below]
- Ref. 4D: "Der Feldfernschreiber", LDv 702/1, Heft 213; pp. 8-27 in "Fernschreibmaschinen", Heft 2 of "Fernschreibgerätelehre", Fsg-2, Arbeitsunterlagen für nachrichtentechnisches Unterricht, Luftnachrichtenschule, Halle (Saale), 2. Auflage, July 1943, 107 pp. [high-resolution scan - 400 dpi; 47 MB]
- Ref. 5: "Hell - Technische Mitteilungen der Firma Dr.-Ing. Rudolf Hell - Gerätentwicklungen aus den Jahren 1929-1939", Nr. 1, May 1940:
- Ref. 5A: pp. 2-11 "Die Entwicklung des Hell-Schreibers" by the inventor himself: Rudolf Hell
- Ref. 5B: pp. 11-20, "Der Siemens-Hell-Feldschreiber", by Rudolf Hell's co-workers G. Ege and H. Promnitz
- Ref. 6: German backpack radios
- Ref. 6A: "Die Generationen der Tornisterfunkgeräte (1)", Werner Thote, pp. 20-24 in "Radiobote", Vol. 3, Nr. 18, Nov-Dec 2008, pp. 20-24. Source: radiobote.at.
- Ref. 6B: "Die Generationen der Tornisterfunkgeräte (2)", Werner Thote, pp. 22-26 in "Radiobote", Vol. 4, Nr. 19, Jan-Feb 2009. Source: radiobote.at.
- Ref. 6C: "Die Generationen der Tornisterfunkgeräte (3)", Werner Thote, pp. 20-24 in "Radiobote", Vol. 4, Nr.20, March-April 2009. Source: radiobote.at.
- Ref. 7: "Der SH-Feldschreiber", Fernmeldetechnik, Siemens & Halske A.G., Wernerwerk, Berlin-Siemensstadt, 1940, 14 pp., SH. 7535a, 1.1.40 TT1. N/1069 [note: not the same as SH 7535 from 1939, 11 pp.]
- Ref. 8: p. 4 in "Bulletin technique de la Suisse romande" (Société suisse des ingénieurs et des architectes (Schweizerischer Ingenieur- und Architektenverein, SIA), Vol. 68 (1942), Nr. 8. Source: e-periodica.ch.
- Ref. 9: "Der Betrieb von Siemens-Hell-Schreibern auf Hochspannungsleitungen im Elektrizitätswerk-Nachrichtendienst" [operating Hellschreibers over 60 kV and 100 kV power lines], Fernmeldetechnik, Siemens & Halske, Berlin-Siemensstadt, 1939, SH. 7802, 1,5 9. 39, 4 pp.
- Ref. 10: p. 15-16 in "Beladeplan für den Funkbetriebskraftwagen (Kfz. 72) des schweren Funktrupps b (mot)", Dienst-Vorschrift D-800/4, November 1940 reprint of the 10 February 1936 original issue, 34 pp. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, file nr. (Signatur) RH 8/7711, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
- Associated with D 800/4 is equipment description D 934, supposedly entitled "Der Typen-Bildschreiber". Unfortunately, this is the only missing document in the D 900 - D 1099 series in the collection of the Bundesarchiv-Militärarchiv...
- Note: the 3 March 1942 version of D 800/4 has a slightly different title: "Beladeplan für den Funkbetriebskraftwagen (Kfz. 72) eines großen Funktrupps b (mot)" (BAMA file RH 8/7712). This version does not include the Hell Feldfernschreiber.
- Ref. 11: p. 23 in "Die 5 Watt Sender", Werner Thote, in "Radiobote", Vol. 3, Nr. 17, Sept-Oct 2008, pp. 21-25. Source: radiobote.at.
- Ref. 12: Pricing information
- Ref. 12A: 27-January-1948 - price quote (incl. taxes, import duties 12%) from Nederlandsche Siemens Maatschappij NV in The Hague/The Netherlands to ANP news agency in The Hague, for Siemens-Halske Hell punch-tape sender ("Streifenschreiber") Tsend17, Hell-printers Tempf14, Hell-Feldfernschreiber (Feld-Hell) Ttyp58. Re-imports from (Siemens) Sweden.
- Ref. 12B: "Flygvapnets radiosystem - Del 1. 1916-1945, avsnitt 2" [air force radio systems], Arne Larsson, 13 October 2009, F13/09, 164 pp.
- Ref. 12C: Krona-Reichsmark exchange rate provided by Sveriges Riksbank (Riksbanken), December 2010
- Ref. 12D: 1944 price list of the “Kungl Arméförvaltningens Tygavdelning” (Royal Swedish Arms Dept.), based on personal correspondence with K.-G. Strid, January 2011
- Ref. 13: page 1 and page a (a-f) in "Band Ln Teil 1" of "Anlagebände zu Ausrüstungsnachweisungen der Luftwaffe (Anl.-Bde. Luftw.)", 1 January 1945. Source: Bundesarchiv-Militärarchiv (BArch-MA, BAMA) Freiburg/Germany, Signatur/file nr. RL 2-III/1707; used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016"
External links last checked: May 2016