red-blue line


The prime manufacturer of the Hellschreiber was Siemens-Halske. Not surprisingly, most of the components are also from Siemens-Halske and carry the entwined S-H logo. But there are also components from other manufacturers. The sections below provide a description of the components and their manufacturers. The RV 12 P 4000 vacuum tube of the Feld-Hellschreiber is discussed extensively on this page. The electronics box of the Feld-Hell was also manufactured by the Mende company, and some motor-generators carry the Mende logo.


Fig. 1: logos of the companies involved with the design and manufacturing of the Feld Hell


Rudolf Hell invented the Hellschreiber in 1929.  That same year, he licensed the rights to the Siemens &Halske (S-H) company for 13,000 Reichsmark. The "Telegraphen Bau-Anstalt von Siemens & Halske" ("The Telegraph Construction Company of Siemens & Halske") was founded in 1847 in Berlin. A nice overview of the very interesting corporate history can be found in ref. 1A, 1B, 1C.


Fig. 2: the 1847 company letterhead of Siemens & Halske

The next chart illustrates 150 years of corporate development of the Siemens-Halske company:


Fig. 3: simplified historical structure of the Siemens company


Fig. 4: company logos - left-to-right: 1899, 1925, 1928, 1936, 1973

(source: Siemens Corporate Archives, Munich)

The Feldfernschreiber was manufactured at the Siemens-Halske "Fernmeldewerk" (Telecommunications Plant). This was one of the factories at the Wernerwerk complex in Berlin-Siemensstadt. "Siemensstadt" (lit. "Siemens Town") was the new name given to the Nonnenwiese area in Berlin in 1914. Siemens-Halske settled here around 1900, starting with its Kabelwerk Westend factory. This area of roughly 2½ x 2½ km (1½ x 1½ mi), is located on the west side of downtown Berlin, just north of the Spree river, between Berlin-Spandau, Berlin-Charlottenburg, and Berlin-Tegel (airport). It is part of the Spandau-borough. A listing of Siemens-Halske factories in the south and the west of Germany at the end of WWII is given in ref. 1D.


Fig. 5: a coaster from the Siemens cafeteria and a stamp commemorating Werner von Siemens

Operations at this factory started on 1 April 1905. At one point, some 14.000 people worked at the Siemens complex! The "Fernmeldewerk" was also known as "Werk für Fernmeldetechnik", "Werk für die Fernmeldegerätefertigung", "Wernerwerk F", "WWF", "Werk F Funktechnik", and "Gebäudegruppe 1". The name "Wernerwerk" (initially "Werner-Werk"), refers to the founder of the Siemens company: Werner von Siemens (1816-1892), ref. 1E.


Fig. 6: early 1900s postcards of the "Fernmeldewerk F" (left) and  of "F & W" (right)

For a while, after 1928, all S-H sites (domestic and overseas) had a Wernerwerk-designator, later replaced by a "Gebäudegruppe" (building-group) number. By 1970 there were over one hundred Wernerwerke worldwide. The "Fernmeldewerk" made it through WWII relatively unscathed, which cannot be said for other parts of the S-H Siemensstadt facilities. Note that Siemens (as was Brown Boveri) had no close ties with US companies. Their production sites where the specific target of Allied bombing raids. The A.E.G., Telefunken, and C. Lorenz companies did have such affiliations, notably with International General Electric (IGE) and International Telegraph & Telephone (ITT). Their facilities were not bombed, other than accidentally. They were actually on American "do-not-bomb" lists, as were Ford facilities. Ref. 1F.


Fig. 7: "Die Siemensstadt um 1930" (Berlin Siemens Town, ca. 1930) - the Fernmeldewerk is highlighted

(source: Sammlung Siemens Berlin; oil painting by Anton Scheuritzel (1874-1954), view in northerly direction)

The "Fernmeldewerk" was located in the area outlined in yellow in the picture above. It is bounded by Nonnendamm (to the north), Wernerwerkdamm (to the south), Ohmstraße (to the east), and Reisstraße (to the west). Johann Philipp Reis invented the telephone and gave it that name in 1861 (ref. 1G); his German patent application was officially declined, as it was considered a useless invention. Graham Alexander Bell patented an improved version in 1876 (ref. 1H). The  "Fernmeldewerk" was torn down in 1981/1982.


Fig. 8: Berlin-Siemensstadt - at the center of the triangle Spandau-Charlottenburg-Tegel

(map source: ©2008 Michelin)


The Feldfernschreiber carries the name or logo of the Siemens-Halske company on part-number labels on the rear of the motor and of the keyboard unit. The "entwined S-H" monogram of the company logo appears on the face of the voltmeter, on various capacitors and resistors, on the sockets of the four vacuum tubes, and as a boss on the bottom of the drawers for the paper tape rolls.


Fig. 9: S-H logo on "teerie" (tar-filled) capacitors from Feld-Hell motor-generator and the volt meter


Fig. 10: S-H boss on the bottom of the light metal drawers for the paper tape

The 12-pin connector on the front of the Hell Feldfernschreiber has a Bakelite insert. Some of these inserts have the "entwined S-A" logo of Siemens-Apparate- und Maschinenbau (SAM). Some of the Bakelite inserts have the logo of Siemens' Luftfahrtgerätewerk Hakenfelde GmbH (LGW). The aluminum die-cast shell of the matching 12-pin plug also has a SAM logo, or the S-H and LGW logo.


Fig. 11: S-H, S-A, and LGW logos on connector shells and inserts

The Feld-Hell motor-generator includes filter inductors for noise suppression. They are similar to the clear plastic Sirufer ("Siemens Rundfunk Eisen") powdered iron (Fe) core coils illustrated below. Ref. 2A, 2B.


Fig. 12: "Sirufer-Rollenkerne" inductor cores

(source: Fig. 19 in ref. 2B)

Siemens-Halks and other component manufacturers continued to supply the civil markets during WW2:


Fig. 13: Siemens-Halske advertising of 1942 - electronic components for hobbyists

(source: ref. 2C)


The signal detector of the Feld-Hellschreiber is a full-wave diode rectifier that comprises two "Kupferoxydul-Gleichrichter": cuprous-oxide-on-copper diodes. Note that in those days, the word "diode" was reserved for vacuum tubes with two electrodes. Solid-state diodes were referred to as "dry" rectifiers ("Trockengleichrichter"), as opposed to "wet" mercury rectifiers. These semiconductor diodes often came with one or two pairs in the same package (ref. 3A, 3B, 3C, 3D).


Fig. 14: a two-diode Kupferoxydul-Gleichrichter (left) and the two tubular Sirutor diodes of my Hellschreiber

(the two-diode "blockform" rectifier is also called a "Maikäfer", i.e., maybug beetle, for its buggy look)

This type of metal-oxide diode was invented around 1922 by Lars Grondahl and Paul Geiger (ref. 3E; their 1925 U.S. Patent (ref. 3F) only lists the name of the prior). Ref. 3S. They are made by heavily oxidizing copper plate on one side, in order to form black cupric oxide (CuO, called tenorite in mineral form). Subsequent heat treatment (annealing) causes the formation of red cuprous oxide (Cu2O, called cuprite in mineral form) between the copper and the cupric oxide. The latter is etched off, leaving a semiconductor PN-junction of Cu2O and Cu. Ref. 4A-4S provide an exhaustive scientific treatise of these early semiconductors. These diodes are quite suitable for detectors: they have a forward voltage (a.k.a. "knee" or "turn-on" voltage) of only 0.2-0.3 V, and a relatively linear forward I-V curve. This is similar to germanium diodes (as compared to 0.5-0.7 V for silicon diodes). Reverse voltage is only 6 volts. With larger dimensions, they were also used for rectifiers in radio power supplies (ref. 3G, 3H), and high power applications. Due to their inherent capacitance, they are not effective above several 100 kHz.


Fig. 15: I-V characteristics of various diode types

Note that asymmetrical conductivity was already discovered in lead-sulfide some 50 years earlier, by Ferdinand Braun (1874). From the early 1900s on, this was used for so-called "cat's whisker" signal detectors in crystal set radios. Braun also invented the cathode ray tube ("Braun'sche Röhre"). Walter Schottky (1886-1976) was head of the Siemens-Halske semiconductor research labs around 1930 (ref. 3J, 3K). He was the founder of barrier-layer semiconductor theory (ca. 1938), discoverer of shot noise and the Schottky effect, and inventor of the screen-grid tube, the tetrode, and the superheterodyne receiver (Schottky filed the associated patent mid-1918, some six months before Edwin Armstrong in the USA, who developed it independently and to whom it is usually - but incorrectly - attributed. Ref. 3L).

The diodes in the Hellschreiber are marked Sirutor. This is short for "Siemens Rundfunk Detektor" ( = broadcast detector). It is a so-called "Kupferoxydul-Pillengleichrichter". Siemens-Halske started to produce these small-signal detector diodes around 1930. The 1940 list-price was 3.75 Reichsmark a piece (ref. 3B); this is roughly equivalent to an estimated 2 Euros in 2015. This diode comprises a small plastic tube in which a number of cuprous-oxide-on-copper "pills" are stacked (2 mm diameter). Diodes were made with 1 to 10 or even 15 pills. The standard diode has 5 pills, and the tube is marked with a "5" (or "5b") accordingly. The Hellschreiber has two of these. Small copper disks are added to both ends of the stack as fillers, as necessary. One end of the stack has a contact-spring, the other a small filler rod. The ends of the plastic tube are threaded; end-caps are fitted to these ends. The Sirutors in my Feld-Hell have a conical cap on both ends; others have one conical and one straight cap (see below). There appears to be a small dab of soft metal (lead?) on each pill, probably to ensure proper contact with the next pill. Note: some Sirutors had a ceramic tube body.


Fig. 16: the parts of a Sirutor "5" diode - sold individually packaged

(color coding: white, orange, blue, ... depending on the number of diode-pills)

Each diode-pill has a relatively small reverse-voltage: about 6 volt. So a number 5 Sirutor has a reverse-voltage of about 30 volt (at 0.1 mA). See ref 73B, 3C, 3M, 3N. This is why the Hellschreiber diodes are marked "30V" in some original schematics. The forward voltage of the Sirutor 5 is about 5x0.25=1.2 volt.

The Sirutors themselves are marked with a "+" at one end. Note that well into the 1950s (DIN standard 50700), the polarity of the symbol for semiconductor diodes was not fully standardized. As the 1931 warning below shows, this caused confusion (and probably lots of blown components). The polarity issue has to do with the fact that the physical direction of an electron flow ( = negative) is opposite to the that of the current flow (= positive). The anode of a polarized device is always the electrode through which electrons flow into that device - independent of the type of device and its operating mode. This means, by the way, that the anode of a (re)charging battery is opposite to that of a discharging battery. Note that the same polarity issue happened with the battery symbol (also around 1939-1941), where the long bar used to be the negative terminal (e.g., corresponding to the long terminal on the classical flat 4.5 volt batteries).

Siemens-Halske also screened Sirutor diodes to higher voltages. They are marked with a yellow band ("Kennstreifen"). They are not used in the Feld-Hell. As Sirutors are more robust, much lighter and smaller than vacuum tube diodes, they were also used in the three ring-modulators of the guidance and control control computer of the A4 ("Aggregat 4") missile. (ref. 3P, 3Q, 3R). For propaganda purposes, the A4 was dubbed "Vergeltungswaffe 2" ("revenge weapon" V2) upon its deployment in the fall of 1944.

In the 1930s, other manufacturers also made copper-oxide rectifier diodes. For instance, Westinghouse made "metal rectifiers": the "Westector". Westectors had either one copper-oxide pill (WX1), four (W4, WS4), or six pills (W6, WS6), providing a reverse voltage of 1x6=6, 4x6=24 and 6x6=36 volt respectively, with a maximum current of 0.25 mA. The W-series was suitable for frequencies up to about 200 kHz, the WX-series up to ca. 1.5 MHz. Their construction was basically the same as that of the Sirutor. The WM-type Westectors (WM24, WM26) are full-wave rectifiers, combining two half-wave rectifiers (WS4, WS6). In 1933, UK prices for Westectors were 7 shilling and 6 pence for WS, and 10 shilling for a WM.


Fig. 17: Westector type WX6

(size: 40x9 mm, almost 50% larger than a Sirutor; a WX1 is only 15 mm long)


The printer module has a "HELL" marking on several of its parts, implying that they were manufactured by the "Dr.Ing. Rudolf Hell" company:

  • "HELL 1505" on the inside of the cast housing of the printer module
  • "HELL SM3 A40" on the die-cast mounting bracket of the printer solenoid. "SM" probably stands for "Schreibmodul" ( = printer module).
  • "HELL SM3 A41" and "A42" on the die-cast parts of the mounting and adjustment yoke of the printer-spindle.


Fig. 18: "HELL 1505" and "HELL SM3 A40" markings on the inside of the Feld-Hell printer module


Fig. 19: "HELL SM3 A41" and "HELL SM3 A42" markings on the spindle mounting & adjustment yoke

As discussed on the "Design evolutions" page, the design of the printer module was changed around 1939/40. The new design does not have one, but two solenoids. They carry Siemens-Halske manufacturing markings. Also, there are no more "HELL" markings on the die-cast parts.


Several capacitors and resistors in the amplifier box of the Feld-Hell are marked HOGES, which means that they were made by Hochohm Gesellschaft mbH of Berlin-Schöneberg and Berlin-Adlershof. HOGES manufactured vacuum tubes and passive components, especially resistors (as the name suggests). They also marketed components from other manufacturers under their own label. The HOGES resistors are typically dark green, as opposed to Siemens-Halske grey. There are also some HOGES capacitors in the motor-generator. E.g., the yellow filter capacitors numbered C70 and C71 in the Feld-Hell schematic (200 pF, 10%, 1500 V). Hochohm's earliest patent dates back to 1927 (Reichspatentamt, Nr. 565176).


Fig. 20: a HOGES filter capacitor from the motor-generator


Fig. 21: cover of a HOGES resistor catalog and a capacitor catalog, both from the 1930s

(source: ref. 5A, 5B)

The capacitors are marked with both operating voltage ("Betriebsspannung", Bsp. or Betr.-Sp.) and test voltage ("Prüfspannung", Psp.) or max/peak voltage ("Spitzenspannung", Spitz.-Spg). Typically 250/750, 500/1500, or 750/2250 volt. Some electrolytics are 25/30. Typical operating temperature limit is 70 ºC (160 ºF). Resistors have 5% tolerance.


The electrolytic capacitors in the motor-generator are made by Richard Jahre GmbH of Berlin (hence: JAHRELYT). These particular capacitors are actually packaged inside a small cardboard tube that measures 40x12 mm (length x diameter; ≈1.6x0.5 inch).


Fig. 22: a JAHRE electrolytic capacitor from my Feld-Hellschreiber's motor-generator


Fig. 23: JAHRE catalog from 1938 and a Jahre advert

(source catalog: ref. 6A)


Fig. 24: JAHRE advert from 1936 (left) and 1942 (right)

(source: ref. 6B, 2C)

Richard Jahre GmbH Kondensatoren & Induktivitäten (in Wilhelmshafen) is still a capacitor manufacturer today, still specialized in mica ("Glimmer") capacitors. Mr. Jahre founded the "Apparate- und Modellbau" company in November of 1919, at the age of 24, originally to develop and manufacture demonstration devices for university physics courses. During the early 1920s, as radio became increasingly popular, he recognized the market for series production of components (e.g., capacitors, inductors, detectors) and test equipment (decades, precision reference components, wavelength meters, etc.); the name changes to "Radioapparatebau". Jahre's first patent dates back to 1931 (Reichspatentamt nr. 587098). In 1965, Jahre sells the company to the Roederstein group (ROE). In 1977, the company moves to Wilhelmshafen. Richard Jahre died in 1994 at the age of 99. Ernst Roederstein Spezialfabrik für Kondensatoren GmbH started out in Berlin, and moved to Landshut (Lower Bavaria) in 1958. In 1993, Roederstein was acquired by Vishay (a leading global manufacturer of discrete semiconductor components and passive components).


Fig. 25: listings in the "Kondensatoren" (capacitors) section of the Berlin telephone & address books

(source: Berliner Adreßbuch 1799-1943 - 1929 (Part II, p. 418) and 1943 (Part II, p. 371))


As an interesting side note: in 1979, the Jahre company acquired the mica capacitor manufacturer Scherb & Schwer Glimmertechnik (mica) of Berlin-Weißensee. In the early 1940s, this company was called "Scherb & Schwer Elektro- Glimmer- und Preßwerke". In 1941, Scherb & Schwer had acquired Jaroslaw's Erste Glimmer-Waren Fabrik (lit. Jaroslaw's First Mica Products Factory), also of Berlin-Weißensee. The Jaroslaw's company dates back at least to 1923, based on its advertising for mica, Mikanit, and Turbonit, in the "Jahrbuch der Drahtlosen Telegraphie und Telephonie" (yearbook of wireless telegraphy and telephony) of that year.


Fig. 26: listings in the "Kondensatoren" (capacitors) section of the Berlin telephone & address books

(source: Berliner Adreßbuch 1799-1943 - 1940 (Part II, p. 300), 1941 (Part II, p. 309), 1943 (Part II, p. 371))

In the 1930s, Jaroslaw's had been one of first manufacturers of "Hartgewebe" (lit. hard cloth): a cotton-reinforced laminate of a particular thermosetting polymeric resin (phenol-formaldehyde, PF). Ref. 7A, 7B. Note that, whereas Hartgewebe was (and is) usually cotton-based, there were also linen-based versions. Jaroslaw's used the trade name "Turbax" for their PF-laminate. Jaroslaw's was confiscated by the German government in 1940, for ethnic reasons. This laminate material is still used today for small gears, e.g., in the automobile and motorcycle industry. For good reason: it is very durable, lightweight, quiet-running, can be machined like wood and metal, and can also be press-molded ("Schichtpreßstoff"). The Hell Feldfernschreiber contains a small block of Hartgewebe in the centrifugal speed regulator, and several gears are made of it, as are the tracks on the bottom of the unit.


Fig. 27: book covers

(source: ref. 7C(Turbax) and 8A (Bakelite))

Phenol is a by-product of coking coal, and formaldehyde is obtained by converting aldehyde, e.g., by oxidizing vaporized methyl alcohol (methanol - highly toxic, unlike ethanol). The latter is also known as "wood alcohol", as it is a by-product of the distillation of wood. Both coal and wood were in plenty supply. PF-related patents actually date back to the late 1890s, though it was Adolf Baeyer (later changed to von Baeyer; not to be confused with Friedrich Bayer, founder of chemical giant Bayer) who had already discovered in 1872 that formaldehyde and phenols can be processed into a hard resin. Baeyer did not commercialize his discovery. PF reinforced with sawdust filler is usually referred to as "Bakelite". Ref. 8A, 8B. It was invented in 1907 by the Belgian Leo Baekeland (1863-1944), who emigrated to the USA at the age of 26. He filed patents in the USA in 1909; they expired in 1927. Hans Lebach of Knoll & Co. filed patents in Germany for a virtually identical material ("Resit"), several months before Baekeland did so in the USA - though with a different hardening process. Extensive patent litigation ensued (ref. 8C). In the end (May 1910), Baekeland, Knoll & Co., and Rütgerswerke (the exclusive Bakelite-licensee for continental Europe since 1909) founded the Bakelite GmbH company near Berlin.

Note that Bakelite is not a cheap or inferior material! The customized molds are very expensive, as are the molding presses. However, Bakelite was competitive, as durable items with complex shapes could be mass produced - accurately (ref. 8D), without post-molding machining such as drilling, grinding, sanding, turning, or polishing (though a shiny surface was not required for military products). Also, the wood dust filler is not a cheap ingredient at all, given the required fineness of the powder. Towards the end of WW2, good wood dust became scarce, and the quality of the Bakelite products declined.


Fig. 28: letterhead of the Jaroslaw company

There are no manufacturer's markings on the Hartgewebe parts of the Feld-Hellschreiber. However, the official 1941 manual (ref. 7D, 7E) mentions "turbax", which was a trade name of Jaroslaw.


Fig. 29: Jaroslaw brochure from 1938 and a 1935 product overview

(source: ref. 7F, 7G)

An equivalent of Turbax is HAREX (though typically in sheet form). This is a trademark of Hermann Römmler GmbH. Römmler was founded in 1867 in Spremberg, some 80 km (50 mi) to the southeast of Berlin. In 1921 they obtained license-free access to the Bakelite patents. Römmler had a background in the processing of textiles (e.g., cotton flocks for shellac gramophone records), which facilitated the step to cotton-reinforced PF. One of their molding materials (a "Hartpapier-Preßstoff", paper-reinforced laminate), had the trademark HARES (registered ca. 1908), derived from the phonetic German pronunciation of the company logo "HRS" (the initials HR of the company founder and S for the town of Spremberg; ref. 7H, 7J). HARES has many applications, including entire doors of the 1935/36 F5 car made by DKW (part of Auto Union). Ref. 7K. The body of the 1939 DKW F8 was almost entirely made of molded phenolic laminate.

I have contacted the Römmler company early 2010, to find out of there is a similar phonetic explanation for "HAREX", but they had no info on this. In 1938, Römmler became a wholly-owned subsidiary of Brown, Boveri & Cie (BBC). BBC was established in 1891 in Baden/Switzerland, as a major player in the field of large electrical motors, electrical power generation and distribution; it merged with the Swedish ASEA company in 1988 to form ABB. Based on the success of their Resopal Schichtpreßstoff (a laminate, dating back to the early 1930s), the Römmler company name was expanded to Resopal Werk H. Römmler GmbH in 1971. It is located in Groß-Umstadt.


Fig. 30: letterhead of the Römmler company

Numerous other manufacturers produced similar Hartgewebe materials with registered brand names such as Novotext, Tenazit, Thesit, Taumalit, Esconit, Bernit, Resinol, Resitex, Tenatext, Trolitan, Trolitax, Tufnol, Biratex, Celeron, and Micarta.

Another well-known PF-laminate is "Hartpapier" (lit. hard paper), i.e., a paper-reinforced laminate (a.k.a. synthetic resin-bonded paper). The most well-known brand name is pertinax (not related to the 2nd century Roman emperor with that name). It was widely used for electronic circuit boards in the early days. Related brand names are Paxolin, Lamitex, Jarax, and Vetronit. This material is yellow to dark brown, brittle, not mechanically resistant, and it is hard to bond copper to it. Before the introduction of PF-resin, pertinax was apparently made with bovine blood as a binder...

Later on, an other polymer replaced PF for many applications: poly-epoxide (a.k.a. "epoxy"); it was patented in Germany in 1939 by the giant chemical conglomerate Interessen-Gemeinschaft Farbenindustrie AG ("I.G. Farben" for short). I.G. Farben originally comprised other well-know companies such as Bayer, BASF, Hoechst, and AGFA.


Practically all resistors and capacitors in the Feld-Hell machine have the Siemens-Halske (S-H) logo on it. Resistors are typically carbon type (only resistor nr. W5 is wire-wound). No color coding is used: component values are printed on the component. However, in the electronics box of some Feld-Hell machines, we find resistors from an other manufacturer. The photo below shows a Dralowid-N resistor from a 1939 Feld-Hell electronics box made by Mende. In that box, resistors nr. W45, W48, and W49 are made by Dralowid. These type -N resistors are wire-wound.


Fig. 31: Dralowid-N resistor from a Feld-Hell


Fig. 32: part of the Dralowid-N page of a Dralowid hobbyist catalog

(source: ref. 9A ca.1938)

The history of Dralowid goes back to 1926, when the company Steatit-Magnesia A.G. (STEMAG, Berlin & Nürnberg) decided to manufacture resistors that were not wire-wound, but carbon resistors ("Kohleschichtwiderstände" = carbon deposited on porcelain). That is, these were leadless (wire-less) resistors: drahtlose Widerstände. Hence the product and company name Dralowid. Obviously they still had leads (connecting wires) - Surface Mount Device (SMD) technology was not developed until the 1950s. Originally a pilot plant was set up in Berlin-Tempelhof, but the commercial production started in the Dralowid-Werk in Berlin-Pankow. Later on, they also made wire-resistors, wound on porcelain tubes.


Fig. 33: logo of the Dralowid company and its products

The STEMAG company was created in 1921, as a combination of four companies: Steatit A.G., Vereinigte Magnesia-Co. & Ernst Hildebrand A.G. (specializing in industrial insulators and ceramic parts for gas lights), Jean Stadelmann & Co. and J. von Schwarz A.G. (both manufacturers of spark-plug insulators). Their roots go back as far as the mid-1800s. In 1929, STEMAG merged with the Porzellanfabrik Teltow GmbH, a manufacturer of industrial porcelains and products made of melalith (a mix between porcelain and steatite, ref. 9B). Teltow's porcelain production was fully ramped down in 1931 and the kilns were torn down in 1934. Dralowid's manufacturing gradually transitioned to this factory in Berlin-Teltow during 1932-1935.


Fig. 34: Dralowid advert from 1942

(source: Funk-Technische Monatshefte (FTM) of 1942, ref. 2C (right))

Some other trademarked "Dralo..." products of STEMAG are "Draloperm" (HF iron powder cores, "Draloston" (gramophone records) and "Dralofon", all made by STEMAG's Dralowid subsidiary. Dralowid also manufactured electronic components such as mica capacitors ("Mikafarad"), electrolytic capacitors, "Potentiator" variable resistors, and "Kombinator" (small bakelite boxes with several capacitors and resistors), ref. 9C. Dralowid components were used by all major equipment manufacturers such as Siemens-Halske, AEG, Telefunken, Lorenz, Saba, Blaupunkt, and Mende. Dralowid also made movie (film) projectors.


Fig. 35: Dralowid advertizing - general, 8 mm film projector (1936), and company magazine (1933)


Some of the Feld-Hellschreibers - in particular the ones with an electronics box made by the Mende Co. - contain capacitors that are marked "NSF". NSF was founded in 1897 as "Nürnberger Schraubenfabrik und Façondreherei Carl Göbel G.m.b.H." (factory for screws and custom turned parts). The founder left the company two years later, and his name was dropped from the company name. In 1920, the company expanded to Berlin, where it started to started to develop and produce radio parts in 1923, including "cats-whiskers" detectors and banana-plugs. The the radio parts activities were moved to a separate factory ("Werk II", "Elektrowerk") in Nürnberg in 1927.


Fig. 36: NSF advertising from ca.1930 and the cover of a catalog

During the mid-1930s, the company already began to support military activities. The UK subsidiary British NSF was founded in 1932 in Croydon/UK, and was destroyed during a bombing raid in 1940. In 1938, the jewish owner of the company was forced to relinquish ownership for ethnic reasons. It was sold to the newly founded Nürnberger Schraubenfabrik GmbH. In September of 1940, the name was changed to "N.S.F. Nürnberger Schraubenfabrik und Elektrowerk G.m.b.H", to better reflect the company's activities. The Elektrowerk was acquired by AEG Telefunken in 1942. In 1960, the name changed once again, this time to "Nürnberger Schwachstrom-Bauelemente Fabrik G.m.b.H.", which later became a production site of "Telefunken Microelektronik GmbH".

As the name suggests, the company had its roots in Nürnberg (Nuremberg). The area around Nürnberg became a major center for military production. Well-known names are Maschinenfabrik Augsburg-Nürnberg (M.A.N.; diesel engines, U-boot engines, Panther tanks), Zünder- und Apparatebaugesellschaft (Zündapp; detonators and equipment), "Süddeutsche Telefon-Apparate, Kabel- und Draht-Werke A.G." with the telegraph address TeKaDe (electronic components such as radio tubes, telecom equipment, cable & wire), Siemens-Schuckert, Nürnberger Aluminiumwerke (Nüral), and Diehl (ammunition, detonators, bombs). Well over a hundred additional companies in the region also contributed.


The wire-wound volume control potentiometer of the Feld-Hell amplifier box was made by "Kabi": Karl Biermann, a small manufacturer of electro-mechanical components in Berlin-Johannisthal during the latter half of the 1920s, through WWII. It is not related to the "Fa. Karl Biermann" radio repair & sales shop, established in 1933 in Bünde (320 km west of Berlin) - still in existence today (2016).


Fig. 37: the "Kabi" potentiometer of the Feld-Hell and "Kabi" advertising


Fig. 38: entries in the Berlin phonebook for Karl Biermann (top to bottom: 1925, 1926, 1932, 1939-1943)

(source: Berliner Adreßbuch 1799-1943)


The Feld-Hell has a 2 watt light bulb for its signal lamp (Ba9s bayonet-base). It was made by OSRAM. OSRAM is the contraction of Osmium-Wolfram. Wolfram is also know as tungsten, from the Swedish for "heavy stone". OSRAM is the alloy used for the helical filaments of incandescent light bulbs. An other alloy used for filaments at that time was Wotan: Wolfram-Tantalum. Early 1906, OSRAM was registered with the imperial patent office in Berlin as a trademark for "Elektrische Glüh- und Bogenlichtlampen von der Auer-Gesellschaft" (electrical incandescent & arc lights of the Auer Co.). The "Auer Gesellschaft" (Auer von Welsbach) was also referred to as the "Deutsche Gasglühlicht-Anstalt" (the German Gaslight Establishment). In 1919, the Auer company, Siemens-Halske, and AEG, founded the OSRAM G.m.b.H. & KG (Kommanditgesellschaft = limited partnership), to combine their light bulb manufacturing activities. They adopted OSRAM as their brand name. The first OSRAM logo (see below) is from the same year. In 1929, during the Great Depression, the International General Electric Company (subsidiary of GE USA), acquired an interest in OSRAM. During WWII, a number of production sites were moved from the Berlin area to the eastern part of Germany. Some remained in east-Berlin. After the war, the sites located in the Soviet occupied zone were dispossessed, and OSRAM lost its foreign subsidiaries and trademark rights. The OSRAM G.m.b.H. KG was converted to OSRAM G.m.b.H Berlin/München in 1956, with the same shareholders as the original KG. During 1976-1978 Siemens AG became sole shareholder. Ref. 12A, 12B.


Fig. 39: first OSRAM logo (1929) and advertising for dial lights and regular light bulbs (1941)


Fig. 40: blue "air raid" or "blackout" light bulb - low power (typ. 8 watt) and instructions


Siemens-Halske (or the Heereswaffenamt) outsourced the manufacturing of some Feld-Hell parts and subassemblies. Outsourcing may have been to optimize production capacity utilization at both small and large companies, or geographical distribution to reduce vulnerability during a potential war situation. Note that the Heereswaffenamt (and the Technische Amt of the Reichsluftfahrtministerium (RLM), the German Air Ministry) fully controlled contract awards to prime suppliers ("Leifirmen", "Lieferer") and their sub-contractor/supplier companies ("Unterlieferanten"). This covered development and production, system assembly, subassembly, spares parts production, and manufacturing under license. Ref. 94. Licensee companies received all required design documentation, and paid license fees. The fees typically amounted to 1.5% of the product's list price, and were typically reduced or even eliminated after several years of production. During the war, the RLM regularly assumed the fees. Ref. 13A.

As shown in Fig. 41 below, some of the Feld-Hell electronics boxes were made by Radio H. Mende & Co. GmbH in Dresden (ref. 13B, 13C). This is indicated by the triangular Mende logo to the right of the serial number. In my database, the earliest Feld-Hell with a Mende-built electronics box, has serial number 0053 and dates back to 1935. Ca. 1939, company logos and names began to be replaced with anonymous "Herstellercodes" (manufacturer codes). The code for Mende is "bl" (see right-hand image in Fig. 41). Other codes are, e.g., "cmw" for the Hell company, "dms" for NSF, and "gyz" for the Dralowid-Werk. Ref. 13D.


Fig. 41: Mende logo and manufacturer's code on the plate of Feld-Hell electronics boxes


Fig. 42: colored Mende logo above the front plate of a 1941 Feld-Hell motor-generator

(note: there is no serial number or year of manufacturing on this plate!)

The Mende company was founded late 1923 by Otto Hermann Mende and Rudolf Müller as the general partnership "Offene Handelsgesellschaft H. Mende & Co." Early 1938, the company structure changed to a limited partnership ("Kommanditgesellschaft", KG). By then, they had sold a million household broadcast radio receivers, some under license from Philips N.V. Some broadcast receivers were used by the military, e.g., installed in submarines such as the U432. In 1935, Mende started production of teleprinters, transmitters, receivers for the army (Heer) and bomb fuses for the Luftwaffe. This included the Hell Feldfernschreiber, Feldfernsprecher (field telephone), and Feldverstärker (field phone line amplifiers). By the end of the war, it had also produced some 25000 Tornister-Empfänger "b" (Torn.E.b.) receivers. Ref. 13B.


Fig. 43: the 1930s letterhead of Radio H. Mende & Co. G.m.b.H.


Fig. 44: various Mende logos

Mende's in-house capabilities covered everything required - other than radio tubes - for the manufacture of wired and wireless telecom equipment: tool & die making, machine building, coil winding (inductors, relay solenoids, transformers, motors), compression molding (e.g., Bakelite parts, and mipolam (a trade name for PVC, which was invented at Chemische Fabrik Griesheim (CFG) in the early 1900s) cases for type 2B38 lead-acid batteries), etc. Ref. 13E. Mende hardly engaged in product development.

The Russian occupational forces dismantled the factory during 1945-46 (ref. 13F, 13G), and moved it to Russia. In 1947, the founder's son, Martin Mende, created North German Mende Broadcast GmbH in Bremen, later renamed to NordMende. It manufactured household electronics. See ref. 13H, 13J.


Fig. 45: a "NordMende" label


Practically all Feld-Hell motor-generators that I have seen, have the Siemens-Halske drawing number "11 T typ 58 6" as a boss on the bottom of the aluminium die-cast base. Here, "T typ 58" is the Siemens-Halske designator for the Feldfernschreiber. Figure 46 below shows the bottom of a Feld-Hell motor-generator that does not have that Siemens-Halske designator. Instead, it has a "Nüral" boss:


Fig. 46: a "Nüral" boss on the aluminium die-cast base of a 1943 Feld-Hell motor-generator

(source original unedited photo: eBay)

Nüral is the trade name (esp. for engine pistons) of the Nürnberger Aluminiumwerke GmbH, which was founded in 1924. In 1962, it merged with Aluminiumwerke Göttingen GmbH, to form Alcan Aluminiumwerke GmbH. During the 1990s, it was absorbed into US-based Federal-Mogul.  Ref. 14A.


Fig. 47: advertising for Nüral engine pistons & blocks (1940 and 1947)


One of my Feld-Hell machines has a  motor-generator that was made in 1942. The light-metal base has an "EC" boss. This is the logo of the manufacturer: Elektronmetall Cannstatt.


Fig. 48: Elektronmetall Cannstatt - logo bossed on the bottom of a Feld-Hell motor-generator

Ca. 1919, Hellmuth Hirth founded Versuchsbau Hellmuth Hirth (VHH) in Stuttgart-Bad Cannstatt. That same year, Hirth starts the Elektronmetall Cannstatt GmbH (EC) company. In 1920, he hires Hermann Mahle. Two years later, brother Ernst Mahle joins the company. In the company's early years, they used Elektron material from ompany Chemische Fabrik Griesheim-Elektron (CFGE). Elektron-metal is an alloy that consists of ±90% magnesium and ±9% aluminium. The rest is manganese (for corrosion resistance), zinc, and silicon. CFGE later became 50% partner in VHH. Ca. 1925, Hirth sells his share of the company to IG Farben (CFGE was a 9.6% parther of the IG), and in 1932 the Mahle brothers acquired EC. For production capacity reasons, the die-casting factory moved to Fellbach (near Stuttgart) and named Mahle Werke GmbH. A factory was added in Berlin-Spandau, for engine pistons and other aircraft parts. In 1938 the company is renamed Mahle K.G. Mahle became one of the largest non-iron/steel metal processing companies in Germany. The IG Farben became holder of the trademark name "Elektronmetall".


Fig. 49: Elektronmetall Cannstatt - 1936 advertising


The Feld-Hell machine contains eleven ball bearings. The purpose of ball bearings is to support rotating parts and reduce rotational friction. The basic ball bearing consists of two concentric rings: the outer ring and the inner ring. Each ring has a so-called race (raceway) that is concave and spherical. The outer ring has one on the inside, the inner ring on the outside. The steel bearing balls roll between these races. A cage cage (or retainer or separator) distributes the balls evenly around the raceways, and prevents them from scuffing against each other. This reduces drag, but also reduces the load capacity (since fewer balls can be installed) and the tolerance against misalignment of the races. The bearing is lubricated to minimize friction and frictional heat, reduce wear, and provide protection against corrosion and ingress of contaminants.


Fig. 50: An open deep-groove ball bearing and its parts

The modern precision ball bearing goes back to the company Kugelfabrik Fischer A.G. (FAG). Ref. 15A. Friedrich Fischer in Schweinfurt/Germany was the son of Philipp Fischer, co-inventor of the pedal-powered bicycle. Friedrich was owner of a sales & repair shop for sewing machines and bicycles since 1872. He invented the ball bearing grinding machine in 1883. This made it possible to produce perfectly round hardened-steel bearing balls on an industrial scale. Before this invention, such balls were only cast or turned on a lathe - with low precision.


The machine was further developed by Fisher's co-worker Wilhelm Höpflinger, and patented in 1890. Around that time, Höpflinger started his own ball bearing company, also in Schweinfurt, together with another co-worker: Engelbert Fries. A court case resulted in Fischer being the patent owner and Höpflinger being granted license-free right of use. To raise funds, their private Fries & Höpflinger company went public in 1896, as Deutsche Gussstahlkugelfabrik A.G. vormals Fries & Höpflinger. After a merger with Deutsche Rollkugelwerke A.G., the name was simplified to Deutsche Gussstahlkugelfabrik A.G.. A year later, they founded the German American Steel Ball Company in Camden/NJ. In 1897, Fisher's company also went public, as Erste Automatische Gußstahlkugelfabrik, vorm. Friedrich Fischer A.G. ("Kugelfabrik Fischer", "Kugelfischer", or "Kufi" for short). Ref. 15P. Fischer's business stagnated, and was acquired by Georg Schäfer & Co. in 1909, to be merged with the latter's own 1904 ball bearing factory. In 1941, it was transformed into Kugelfischer Georg Schäfer & Co. After a hostile take-over in 2001, FAG became part of the German automotive supplier Schaeffler Group. A third early ball bearing company in Schweinfurt was the Schweinfurter Präcisions-Kugellagerwerke Fichtel & Sachs, established in 1895 by Karl Fichtel and Ernst Sachs. Sachs invented the freewheel hub for bicycles (D: Freilaufnabe) in 1903. The three companies, FAG Kugelfischer, Fries & Höpflinger, and Fichtel & Sachs established Schweinfurt as the center of the German ball bearing industry. The city of Schweinfurt with its bearing industry was a major target of Allied bombing raids from August 1943 to April 1945 (once a month, on average).


Fig. 51: Advertising from Fischer, Fichtel & Sachs, and Fries & Höpflinger

A major competitor to the German ball bearing industry was the Swedish company Aktiebolaget Svenska Kullagerfabriken (SKF). Ref. 15B. SKF was founded in Göteborg in 1907, to industrialize the self-aligning bearing that was invented by Sven Gustaf Wingqvist. His single-row version was patented in 1906, followed by multi-row in 1907. SKF started an automotive branch in 1915, AB Volvo, to build test vehicles. It was spun off in 1936. During the period 1937-1943, the Swedish ball bearing industry increased its exports to Germany from 10% to 65% of its total exports (ref. 15C). Note that in 1937 alone, the world-wide automotive industry used some 173 million ball bearings! Ref. 15B.


Fig. 52: A self-aligning bearing (inner ring turned 90°) and a commemorative postage stamp of its inventor

In 1929, six German ball bearing companies were combined under SKF into the Vereinigte Kugellagerfabriken AG (VKF, "United Ball Bearing Factories") with about 9000 employees (ref. 15D):

  • Two in Schweinfurt:
  • Deutsche Gussstahlkugelfabrik AG vorm. Fries & Höpflinger
  • Schweinfurter Präcisions-Kugellagerwerke Fichtel & Sachs
  • Two in Berlin:
  • Riebe Kugellager- und Werkzeugfabrik(in Berlin-Weißensee; part of Riebe-Werke A.G)
  • Deutsche Waffen- und Munitionsfabriken AG (DWF; named Berlin-Karlsruher Industriewerke AG (BERKA) during the inter-bellum period 1922-36; DFW had already established a foothold in the USA in 1904: Hess-Bright Manufacturing Co. in Philadelphia/PA)
  • One in Stuttgart/Bad-Cannstatt: Norma-Compagnie GmbH. SKF already became major shareholder in 1914.
  • One in Düsseldorf: Maschinenfabrik "Rheinland" A.G. (RHL)

The VKF head office was originally located in Berlin, but was moved to Schweinfurt in 1931. VKF was later expanded with Präzisions-Kugellager-Werke Friedrich Hoffmann A.G. in Wetzlar, and Berliner Kugellagerfabrik G.m.b.H. A. Riebe in Berlin-Wittenau. There were many others ball bearing manufacturers in Germany, e.g., Berliner Kugellagerfabrik G.m.b.H. (BKF; in Leipzig), Roebert Kling (in Wetzlar), Kugellagerfabrik Georg Müller (RKW, in Nürnberg), Nordeutsche Kugellagerfabrik (NKF, in Berlin), Präzisionswerke G.m.b.H. (PWB, in Bielefeld), Universal-Kugellagerfabrik G.m.b.H. (UKF, in Berlin), and Deutsche Kugellagerfabrik (DKF, in Leipzig-Plagwitz and Leipzig-Böhlitz-Ehrenberg).

The Feld-Hell machine contains eleven ball bearings:


Fig. 53: Ball bearings installed in the Feld-Hell machine

(note: basic modern ISO designators have a 5-parameter designator and can have numerous suffixes)

The designator scheme for these bearings is simple:

  • First digit - type of bearing construction
  • 1 = two-row self-aligning ball bearing
  • 6 = single-row deep groove ball bearing
  • Second digit - bearing robustness ( = load handling = cross-section of the rings & ball size)
  • 2 = light
  • 3 = medium
  • Third digit - bore size (inner diameter)
  • single-digit size is in millimeter (e.g., 6 or 7)
  • Suffix - design variants (cage design, shields, seals, accuracy, materials, lubrication, ...)
  • none = open (i.e., no integral shields or seals)

Note that modern bearings have the same standard dimensions as before WW2. Two of the Feld-Hell shafts (printer spindle and paper transportation drive) do not have greased ball bearings. Instead, they simply have an oiled sleeve bearing (bushing) at both ends. The two cam-followers of the character drum look like type 604 ball bearings (12 mm outer diameter, 4 mm inner diameter). However, they too are sleeve bearings, and are oiled (per the Feld-Hell manual). The bearings in my machines appear to be made by FAG and SFK.


Fig. 54: some ball bearing terminology in several languages

As stated above, all ball bearings in the Feld-Hell machine are "open". That is, they do not have integral metal shields or rubber/neoprene seals. However, metal shielding is added in all cases. This is required, to keep the bearing grease inside the bearing, and to keep dirt and other abrasive contaminants out. In the Feld-Hell, the shielding takes several forms (see Fig. 53 below):

  • a thin (0.2 mm) metal disk with a diameter that is slightly smaller than the outer diameter of the bearing. If such a washer is installed between the bearing and the shoulder on the drive shaft, it has an inner diameter that is slightly larger than the bore of the bearing. If it is installed at the very tip of a shaft, it has a hole that is suitable for an M3 screw that is fastened into the shaft tip. These thin disks only serve as shields.
  • 1.5 mm thick metal washers that have a diameter that is about 50% larger than the outer diameter of the bearing. These washers not only serve as shield, but also to mount the bearing.
  • the bearing is mounted in a housing (or a thick/deep mounting flange) that has a bore with a stepped inner diameter, such that it is only in contact with the outer ring of the bearing, and has a hole that is slightly smaller than the outer diameter of the bearing.


Fig. 55: several examples of bearing shields in the Feld Hell machine

The original bearings of the Feld-Hell can be can be replaced with same-size modern bearings that have non-contact metal shields. Such bearings have a small gap (typically less than 0.125 mm, 0.005") between the inside diameter of the shield and the bearing's inner ring. They are spot-pack greased for life. Depending on the manufacturer, 30-50% of the space is filled with solid grease. "Solid" means that the grease has special compounds and has been processed so as not to be runny; hence it should not leak from the bearing during normal operation. Excessive packing causes overheating and loss of lubrication. There is a small gap (typically less than 0.125 mm, 0.005") between the inside diameter of the shield and the bearing's inner race. As it does not touch the inner race, it is referred to as "non-contact". The shield is non-removable if it is permanently staked to the outer ring of the bearing. A removable shield is kept in place with a C-ring, D-ring or a spring wire. Once the ring or spring is removed (with special pliers), the shield can be removed and the bearing cleaned and re-greased. Yes, non-removable shields can be removed – once, as typically the shield is destroyed. Note that a shield is not a seal! A seal is a synthetic rubber washer, often with a steel core. The seal is fixed to the outer ring and touches the inner ring: this provides higher protection against contamination, but also more friction.

Most bearings are of the standard "single-row deep-groove" type. "Deep groove" simply means that the groove in the races is deep with respect to the diameter of the balls. This enables the ball bearing to simultaneously handle both radial and axial loads. In the Feld-Hell machines, one or more self-aligning bearings may be found. These bearings typically have two rows of balls. They share the raceway in the rings of the bearing. During normal operation, these bearings can accommodate a couple of degrees of angular misalignment between the outer ring of the bearing, and the shaft. Such misalignment occurs when a shaft has a bearing at both ends, and the bores into which the bearings are installed are not perfectly concentric ( = coaxially aligned). In this case, a self-aligning bearing should actually be used at both shaft ends. Self-aligning bearings can only support about 70% of the radial load of a regular bearing, and only about 30% of the axial load. However, their friction factor is about 20% lower than that of same-size deep-groove bearings (ref. 15E). This is important on the shaft with the highest speed: the gear-box input shaft (3600 rpm). Especially, given the fairly low power of the Feld-Hell motor. Obviously such bearings are more expensive...

During installation, self-aligning bearings can handle much more than just a couple of degrees of misalignment. This is quite convenient when putting the multi-shaft gear box of the Feld-Hell back in! The character drum drive shaft has a large steel gear wheel on the outside of the gear box. It meshes with a similarly large gear wheel on the shaft of the character drum. There is bearing behind the latter gear wheel. It can be adjusted up and down, to adjust the meshing. This means that both bearings on the shaft of the character drum are forced to be misaligned in their socket, or a misalignment force is applied to the inner ring of the bearing. This is why some Feld-Hells have one or two self-aligning bearings on the character drum. On this shaft, the original bearings in my 1938 Feld-Hell are not self-aligning, and their fit into the bores is rather loose. Sometimes the drive shaft of the printer spindle also has self-aligning bearings (or has been retrofitted with them). But not in my machine. Given the trouble that I had removing and reinstalling this shaft, it is not a bad idea....

Have you ever wondered how ball bearings are made? Here is a 5-minute video that explains it all:

How ball bearings are made


The electronics box ("Verstärker- und Anschlußsatz") of the Feld-Hellschreiber has a one-piece die-cast chassis. The chassis of the Feld-Hell's bottom unit (gear-box, base below the keyboard) is also die-cast. These chassis are  most likely made of "Elektron" metal - a magnesium alloy. Ref. 16A. Other parts of the machine (in particular the base and housing of the motor-generator) are made of aluminium ("Leichtmetall"). Ref. 16B. The Hell Feld-Morseschreiber is of the same vintage and has the same construction.


Fig. 56: the die-cast box, all components removed

Elektronmetall (Elektron-metal) is an alloy that consists of ±90% magnesium and ±9% aluminium. The rest is manganese (for corrosion resistance), zinc, and silicon. Over the years, "Elektron" has become a generic name for this type of alloy, with varying composition. It is about 30% lighter than aluminium, and 75% lighter than steel. Elektron was widely used in optical devices (microscopes, binoculars), for structural elements in airplanes and airships, motor cycle frames, engine pistons, compressor rotors, landing gears, and all sorts of equipment frames and housings. Cast Elektron and magnesium parts were also used in automobiles. E.g., Prof. Ferdinand "Ferry" Porsche included some 27.5 kg (≈60 lbs) in the Volkswagen "Käfer" (Beetle) design. Ref. 17G. Note that this VW was actually based on the complete designs "borrowed" from Josef Ganz, a jewish automobile journalist and designer. Ref. 17A.

Elektron was well-suited for "Druckguß" parts manufacturing: compression molding (UK: moulding), a.k.a. die-casting. The die-casting process consists of quickly (less than 5-100 msec) forcing molten metal under high pressure (400 – 4000 tons) into a re-usable steel mold called a “die”. The basic technology dates back to the mid-1800s, when it began to displace low-pressure "gravity-feed" casting. The original application was for machine production of printing type (letters). Die-castings are characterized by a good surface finish (very smooth, by casting standards) and dimensional accuracy. The dies can be designed to produce castings with very complex shapes. "Druckguß" is also referred to as "Preßguß", "Fertigguß", and "Spritzguß". However, these days, the latter terminology is exclusively reserved for injection molding of plastic parts. Today, the term  "Druckguß" is used for what used to be called "Spritzguß" during the middle of the 1900s.

In April of 1909, the company Chemische Fabrik Griesheim-Elektron (CFGE) registered the first patent for this magnesium alloy as a construction material. CFGE presented the alloy under the name Elektron at the first ILA (Internationale Luftfahrt-Ausstellung, International Air Transport Fair). This ILA took place in 1909 in Frankfurt/Main and lasted 100 days! Ref. 17B. This is the world's oldest commercial air show.

The Frankfurter AG für landwirtschaftlich chemische Fabrikate was founded in 1856 in the town of Griesheim (on the river Main, some 30 km (20 mi) southwest of Frankfurt/Main). An 1863 entry in the trade register lists this company as Chemische Fabrik Griesheim am Main (CFG). In 1892, CFG and partners founded the Chemische Fabrik Griesheim-Elektron (CFGE), to exploit the technology of electrolysis of caustic soda. CFG and CFE merged in 1898 as Chemische Fabrik Griesheim-Elektron (CFGE). Ref. 17C, 17D. Later on, factories were added in Mainthal, Küppersteg, Spandau, Rheinfelden, and Bitterfeld. The latter is vast center of chemical industry, 130 km southwest of Berlin. Ref. 17E, 17F. The location was chosen for its availability of cheap lignite (brown coal, used in electricity plants) and transportation infrastructure (railways, waterways). CFG became world-famous for electrolysis technologies, inventions such as autogenous welding & cutting (1902), and PVC plastic (1912). One of its electrolysis by-products, hydrogen, was used to fill Zeppelin and Parseval dirigibles.

CFG produced magnesium by electrolysis of molten carnallite (a form of magnesium chloride). Other sources of magnesium are seawater, dolomite, and magnesite. Commercially viable production of magnesium was invented by the German chemist Robert Bunsen (yes, of the famous Bunsen burner, but also discoverer of the chemical elements caesium (cesium) and rubidium, co-inventor of the spectroscope (with Gustav Kirchoff, of the famous voltage & current laws), etc.) From the 1880s until the middle of World War I, Germany was basically the world's only magnesium producer. Ref. 17G. In 1938, it still accounted for over 2/3 of the world production (ref. 17H). The local supplies of carnallite made the German magnesium production entirely independent of foreign raw material. Near the end of WWII, aluminium (and, hence, associated alloys) became a scare strategic material and much heavier zinc was used in many die-cast products. Ref. 17P.


Fig. 57: logos of the Mahle and the CFGE company

An other big name in magnesium alloy products, and connected to CFGE, is "Mahle". Ca. 1919, Hellmuth Hirth founded Versuchsbau Hellmuth Hirth (VHH) in Stuttgart-Bad Cannstatt. In 1920, he hires Hermann Mahle. Two years later, brother Ernst Mahle joins the company. That same year, Hirth starts the Elektronmetall Cannstatt GmbH (EC). In the company's early years, they used Elektron material from CFGE. CFGE later became 50% partner in VHH. Ca. 1925, Hirth sells his share of the company to IG Farben (CFGE was a 9.6% parther of the IG), and in 1932 the Mahle brothers acquired EC. For production capacity reasons, the die-casting factory moved to Fellbach (near Stuttgart) and named Mahle Werke GmbH. In 1938 the company is renamed Mahle K.G. Mahle became one of the largest non-iron/steel metal processing companies in Germany. The IG Farben became holder of the trademark name "Elektronmetall".

Ca. 1928/1929, Mahle and the Lorenz company co-developed precision die-casting of Elektron and aluminium modular housings and chassis structures for (military) radio equipment. Ref. 17J, 17K.

In Germany it was determined early on, that magnesium and associated alloys were strategic materials. In the US, magnesium production was insignificant, until the government rapidly ramped it up in 1939, primarily with technology licensed from the gigantic German conglomerate IG Farben, via their consortium with ALCOA/AMC and Dow Chemical. The situation in the UK was very similar. Production was negligible until the second half of the 1930s. Up to 1930, the UK imported nearly 60% of the entire German magnesium production. It was used in engines and transmissions for busses. The Magesium Elektron, Ltd. (MEL) company was founded in 1934/35 by F.A. Hughes & Co., and started magnesium production in 1936, as an IG Farben licensee for the British Commonwealth. MEL still exists today (2016). The German capability was (publicly) recognized in the UK and US, even during WWII. Ref. 17G, 17L, 17M, 17N, 17P.

Note that there are no markings on the cast parts of the Feld-Hell machines that allow definitive conclusions as to whether they were made by the Mahle or the Griesheim company. The aluminium die-cast base of some Feld-Hell motor-generators was definitely made by the Nüral company.

The rear of the electronics box has a simple removable cover. Removing this cover exposes a two-row pertinax circuit card, with point-to-point wiring. Note that single- and multi-layer printed-circuit technology dates back to the very early 1900s (ref. 16C), but it was not used until the 1960s. All components on the Feld-Hell's circuit card and the vacuum tube sockets have a small round sticker on them, with a letter + number. This identifier corresponds to that of the same component in the schematic. Very helpful during manufacturing, troubleshooting and repair! Likewise, all the solder lugs on the pertinax circuit card and the interconnect blocks have a number printed on them or next to them (or embossed next to them). This number corresponds to that of a signal line in the schematic.


Fig. 58: rear of the electronics box - cover removed

(note that all the wires/signals are numbered on the circuit board; all components have a sticker with a number)

The circuit card is in fact part of a larger assembly: it is attached to the top cover of the electronics box, as are the four tube sockets, an audio isolation transformer, the fuse holder, and the battery/power-supply toggle switch.


Fig. 59: front-view of the circuit card & vacuum tubes module

The wire bundles in the Feld-Hell are laced. Lacing is a method of using thin wax-impregnated cotton twine or linen cord, to tie a wire bundle with a series of knots and stitches. In the Feld-Hell, continuous running lock-stitches are used (a.k.a. Marline-hitches, single-hitches).


Fig. 60: one of the cable harnesses in the Feld-Hell electronics box

This technique is traditionally used (to this date) in military, telecommunications, marine, and aerospace systems. It is more time-consuming than using fasteners such as cable ties (a.k.a. zip ties, Ty-Rap®, wire ties). However, unlike cable ties, lacing will not crush or cut into insulating sleeves of the wiring, does not create obstructions along the bundle, and can conform to bundle shapes other than ellipses. Ref. 16D.


Note 1: due to copyright reasons, this file is in a password-protected directory. Contact me if you need access for research or personal study purposes.

External links last checked: April 2016

red-blue line

©2004-2016 F. Dörenberg, unless stated otherwise. All rights reserved worldwide. No part of this publication may be used without permission from the author.