• [Introduction]
• [Parts of the tube]
• [Glass tube construction]
• [Tube sockets]
• [Molding marks]
• [Waffenamt & other markings]
• [RV12P4000 tube manufacturers]
• [Video clips about tube manufacturing]
• [References]

Photos of all my RV12P4000 tubes and their markings are on this separate page. 3D/stereoscopic photos of my my RV12P4000 tubes (and Hell-equipment) are on this page.

©2004-2023 F. Dörenberg, unless stated otherwise. All rights reserved worldwide. No part of this publication may be used without permission from the author.

Latest page update: Aprlil 2023 (added ref. 87T)

Previous upates: September 2022 (added Fig. 68B ,68C, added text about "BA" and "W.ab" acceptance stamps, ref. 114A/B); 2 May 2021 (added Siegmund Loewe's multi-valve/tube patents, ref. 87L-87S); March 2020 (added ref. 87K); February 2020 (added ref. 113), 24 September 2019 (added ref. 87H & 87J).

INTRODUCTION

Vacuum tubes are thermionic "valves" in british English. "Tube" refers to the tubular shape of the device, whereas "valve" refers to the function of a simple diode tube. Up to the mid-1930s, the German military used civil vacuum tubes for their mobile amplifiers, receivers and transmitters. Those tubes had actually been developed for civil commercial broadcast radios and stationary telecommunication equipment of German government agencies and authorities ("Behörden"). E.g., the national postal system (who had the monopoly in all matters of  telephone, telegraphy, radio), police, and railroads. These agencies had tubes specially made, screened, or simply just marked for them. In some modern publications, they are generally referred to as "Behördenröhren". However, this term was actually only used by the marketing & sales department of one tube manufacturer (Telefunken), in order to distinguish them from regular commercial broadcast tubes (ref. 110).

Civil and and other non-military tubes types were nonetheless deemed to be usable by the military, e.g., based on screening to tighter tolerances. They received additional markings ("Kennung"). Typically, an additional letter was appended to the tube type, to indicate their suitability for army or airborne radio applications ("Wehrmachtsverwendbarkeit" or "Flugfunktauglichkeit, respectively). Ref. 1. Still, for several reasons, they were not robust enough for general military mobile and field operation:

• Tube characteristics and performance were sensitive to temperature, vibration and shock (incl. microphonic effect), low atmospheric pressure, as well as to variations in filament voltage.
• Seating of the tubes in their sockets was unreliable (electrical contact, retention in the socket).
• They were too big (hence, large equipment volume).
• They were not easy to replace in situ (in darkness, in cold with gloves, under battle conditions).
• There was too much variability of the electrical characteristics of same-type tubes. A major consequence was that replacement of tubes impacted the function and performance of the equipment (frequency, power, amplification, sensitivity).
• The upper limit of the operating frequency was limited to HF (due to inter-electrode capacitance, capacitance in the base and between lead-in wires, etc.)
• Unreliable for orientation other than upright.
• Not powerful enough (esp. transmitter tubes).
• Too many different tube and socket types (lack of standardization). Ref. 95.

The Wehrmacht (and its predecessor, the Reichswehr) had a special agency, the Heereswaffenamt: the Army Ordnance Office. Its main responsibilities included the research and development, specification, testing, industrialization (procurement, logistics), and acceptance of weaponry, ammunition, and equipment, as well as the assessment of enemy weaponry. Ref. 2, 3, 94, 97, 99. The office was dissolved at the end of April 1945. Heereswaffenamt is usually abbreviated to He.Wa.A, HWA, WaA, Wa. A, or Wa.A.

After in-house pre-development, the Heereswaffenamt instructed Telefunken (TFK) in 1933/34 to start the development and production of a series of tubes, specifically for military applications. They had to be suitable for compact, powerful, mechanically and electrically robust telecommunications equipment. These, and subsequently developed tubes, are collectively referred to as Wehrmachtröhren (sometimes spelled "Wehrmachtsröhren"). Ref. 4, 5.

Among the first Wehrmachtröhren were two similar receiver pentodes (1935):

• RV 2 P 800 - for battery-operated portable equipment. It is directly heated (i.e., heater filament = cathode). The filament is designed for operation with a single-cell lead-acid battery ("Bleiakkumulator", such as the 2B38 with 38 Ah capacity, ref. 6), i.e., 2 volt nominal. RV 2,4 tubes such as the RV 2,4 P 800 (ref. 7), have a filament voltage adapted to lightweight rechargeable two-cell nickel-cadmium (NiCd) and nickel-iron (NiFe) batteries. The latter were also used in the A4 missile (a.k.a. "V2").
• RV 12 P 4000 - for field and mobile equipment, incl. trucks, armored vehicles, and tanks (ref. 105). It is indirectly heated (separate heater and cathode), with a 12.6 volt heater (standard 6-cell lead-acid battery). Here, 12.6 is the nominal value: the required range was 10.8 - 14.5 volt, to accommodate operation in both tanks and aircraft (ref. 1, p. 28).

For readability purposes, RV 12 P 4000 will be denoted below as RV12P4000, without spaces. The first series production of this tube was a batch of 5000, in the fall of 1935 (ref. 8). Starting in 1937, other tube manufacturers were forced to also manufacture Wehrmachtröhren, including those developed by Telefunken (ref. 9). Valvo ( = Philips), and TeKaDe (TKD, Telefonapparate-, Kabel-, und Drahtwerke AG),  produced the RV12P4000 and other types in Nürnberg (Nuremberg in English, sillily copying the French language in which there can be no "n" before a "b"). The RV2P800 was produced by the same companies, and by Lorenz AG.

Fig. 1: the "RV 12 P 4000" vacuum tube

Ca. 1938/1939, the Technisches Amt (TA, Technical Office) of the Reichsluftfahrtministerium (RLM, the Air Ministry of the Reich, 1933-1945) began its own development and procurement of tubes, specifically for airborne applications (including missiles). This was primarily done due to the particular environmental conditions (e.g., temperature range, accelerations). This led to the "Wehrmachtröhren" being separated into "Heeresröhren" (army tubes) and "Luftwaffenröhren" (air force tubes; in some literature referred to as "Luftfahrtröhren", i.e., aviation tubes). Each group had its own numbering / designator scheme (ref. 5, 10, 11, and tables below). Prior to 1938, the RV12P4000 tube had the designator NF4 (ref. 12) and the RV2P800 was MF2. In the latter, the first letter designates the heater type and voltage (M = 1.9 volt, indirectly heated, N = 12.6 volt, directly heated). The second letter indicates the tube type (F = pentode). Ref. 13.The Kriegsmarine (Navy) had very few specific "Spezialröhren".

Note that this does not mean that army tubes could not be used by the air force, or vice versa. E.g., the universal RV12P2000 pentode tube was widely used in army radios, and also in airborne communication & navigation radios. Ref. 1, 8, 14, 15, 16, 17, 18, 19, 20, 104. This includes the A4 ("V2") missile, at least in the A4 prototypes that were remote controlled via the "Ortler"/SEUK radio set. Regular A4's electronic boxes typically had metal can tubes ("Stahlröhre", incl. civil types). The P2000 is one of the early miniature-pentodes ("Zwerg-Pentoden"). It is the military version of the 1936-1937 civil/commercial NF6 tube (ref. 16, 110). The latter was based on the 12 volt version of the 1935-1937 SF1 and SF1A. These  had a very similar shape and size, but different anode (plate) arrangement. The P2000 was readied for production and produced by Telefunken starting mid-1937. Ref. 21, 110. An estimated total of about 16 million of this universal pentode was manufactured from 1937 to 1956 (ref. 22, 23). It was produced as late as 1965 at the RFT Neuhaus factory (Röhrenwerk Neuhaus (RWN) in then-East-Germany, and in Japan until 1979 (with the designator RE 3, ref. 110).

During 1943 and 1944, the annual production volume of Wehrmachtröhren rose to an estimated 16.9 and 17.8 million tubes respectively (ref. 24; note that the 1945 tube production volume of Britain was about 30 million; ref. 25).

The tables below explain the predominant numbering scheme (basically Telefunken). Note that other manufacturers, such as Philips-Valvo and GEMA, had additional numbering schemes. Pre-1934 numbering schemes are discussed in ref. 26 and 27.

Fig. 2: numbering scheme of the "R" Wehrmachtröhren

(source: ref. 13)

Note: some "R" tubes have a 6^th designator-field, such as "A" to indicate a version without base, or a lower-case letter with running numbering to indicate a new variant, sometimes followed by a figure to indicate a different base.

Fig. 3: numbering scheme of the "Luftfahrtröhren" (aviation/Luftwaffe Wehrmachtröhren)

Some tubes have a type-designator with the suffix "V", or a separate stamp "Verluströhre". These are not special versions of the tube: they were functional, but did not pass production screening. They were used in one-shot applications (torpedoes, weather balloons, etc.).

Following the above numbering scheme, the RV12P4000 tube designator stands for:

• R: "Reichsheer" = Army, or "Reichswehr" = Army/Navy
• V: "Empfangs-Verstärkerröhre" = receiver amplifier tube
• 12: average heater voltage
• P: type = pentode
• 4000 = maximum static amplification factor μ.

(source: ref. 28 data sheet)

Fig. 4: pin-out of the "RV12P4000"

Fig. 5: characteristics of the "RV12P4000" tube

(source: ref. 29)

There has also been an "RV 12 P 4000X", but I do not know what the "X" stands for, nor to what extent its characteristics were different:

Fig. 6: a rare  "RV 12 P 4000X"

(source: U. Radtke; used with permission)

The RV12P4000 is a pentode. The pentode was invented in 1926 by the Dutchman Bernard Tellegen (1900-1990), at the Philips Research Labs (Philips Natuurkundig Laboratorium, NatLab) in Eindhoven/The Netherlands. He also invented the gyrator (ref. 30). The Tellegen Theorem still is one of the most powerful theorems in network theory and in the analysis of complex networks (electrical circuits, biological and metabolic networks, pipeline flow networks, chemical process networks, etc.). As the name suggests, the pentode has five electrodes - one more than the tetrode, which was invented by Walter Schottky (1886-1976; head of the Siemens-Halske semiconductor research labs around 1930). The tetrode has four electrodes: anode (a.k.a. "plate"), cathode, control-grid, and a screen-grid (a.k.a. shield-grid). The applied control-grid voltage causes plate current to vary, whereas the screen-grid effectively isolates the control-grid from the plate. This reduces the so-called Miller Effect that limits the tube's high-frequency gain. The pentode expands the tetrode with a suppressor-grid between the plate and the screen grid. This suppressor-grid eliminates secondary-emission current: stray electrons that bounce off the plate and cause an undesirable negative-resistance characteristic. Ref. 31, 32.

As stated above, the electronics of the Feld-Hell machine only comprises tubes of type RV12P4000. The tables in Fig. 5 above appear to suggest that the nominal anode current is only 3 mA. Note that the typical/intended application of RV-tubes is an amplifier. So this 3 mA current value is for the normal tube operating point - as an amplifier. The RV12P4000 has typical pentode characteristic curves. See the blue lines in Fig. 7 below. The maximum anode current is actually a little over 10 mA!

Fig. 7: characteristic anode voltage & current curves of the "RV12P4000"

The anode dissipation has to remain below 1.5 watt. The red curve in Fig. 7 shows that at that, at the maximum current level of ≈10 mA, the anode voltage must remain below +150 volt. The anode voltage in the Feld-Hell machine is provided by a motor-generator ("dynamotor"). It generates +165 volt DC nominal, with an acceptable operating range of +150 to +185 volt. Yes, this is is above the stated +150 volt limit. But it is not a problem: the printer-solenoid is placed between the anode and the generator voltage. See Fig. 8. One side of the solenoid is always connected to the generator voltage, the other side can be pulled down to a low voltage via the tube.

Fig. 8: anode circuitry of the tube that drives the Feld-Hell's printer solenoid

The solenoid of the Feld-Hell's printer has a nominal DC-resistance of 4090 Ω. When energized, the voltage drop across that solenoid is 10 mA x 4 kΩ = 40 volt. Hence, for the generator voltage range of +150 to +185 volt, the anode voltage of this driver-tube is actually only +110 to +145 volt (+125 volt nominal, see the orange dot in Fig. 7). Perfect! Turning the printer-solenoid current on/off is a switching function, not an amplifier. So the solenoid-driver tube does not have to be operated at the normal amplifier operating-point (the magenta dot in Fig. 7). Note that the standard printer-solenoid current of Hell-printers of the era was not 10 but 20 mA. So, a special solenoid had to be developed for the Feld-Hell printer.

It was common practice in Wehrmacht telecommunication equipment, to use only a single type of tube in all stages of most receivers (ref. 33): the "Einheitsröhre" ( = standard tube) concept. Ref. 96. For instance, the circuitry of the Hell-Feldfernschreiber comprises four RV12P4000 tubes. The table below lists additional examples. This standardization had its advantages: lower cost (larger production volume) and improved logistics (fewer part numbers to stock, fewer spare tubes to stock per equipment, fewer specific test equipment) The down side of such standardization is the inherently sub-optimal use of the component in question. Using the same type of tube for AF-through-RF applications, often implied the need for more complicated circuitry to work around the generic characteristics of the tube or operation in a sub-optimal region of its characteristics. Sometimes a pentode is wasted by using it as a simple diode, etc.

Fig. 9: examples of German WK2 military radios with a uniform tube configuration

(the equipment may have other tube types, in addition to those listed; for the Ukw.E receiver and matching 20W.S.c transmitter, see ref. 114A, 114B.)

During WW2, tubes for civil radios (commercial and amateur) became scarce. Towards the end of the war, electronic equipment suppliers still had significant stocks of military tubes, and the Wehrmacht even hid radio equipment and spare parts at various locations around the country. After the war, several Wehrmacht tubes continued to be built (or copied) outside Germany - until at least the early 1970s! Surplus Wehrmacht tubes were used in home-built radio projects, and in "civil" broadcast receivers until ca. 1949 (ref. 34, 35, 36, 37, 38, 39) - often the original bakelite base was replaced with a "civil" base. These makeshift radios are referred to as "Notradios". Some examples of such commercial radios are:

• Grundig Radio-Werke G.m.b.H. in Fürth/Bavaria (Radio-Vertrieb, RVF Elektrotechnische Fabrik G.m.b.H.): "Heinzelmann Model A" (Long Wave (LW), Medium Wave (MW), Short Wave (SW); RV12P2000/2001 + RV12P2000/2002). This was a small, inexpensive kit that was sold without the required tubes. This way, Grundig cleverly bypassed both the ban by the Allied military government on the manufacturing of radio sets ("A radio without tubes is not a radio - but a toy"), and the ration-coupon based economy of that time.
• Blaupunkt-Werke GmbH in Berlin: model 5GW646 (LW + MW + SW, 5x RV12P2000, 2x RV12P2001, 1946-1947). Blaupunkt (Ideal) was part of Robert Bosch GmbH, in Stuttgart. In 1929, Bosch founded the Fernseh AG, together with Baird Television Ltd., Radio AG D.S. Loewe, and Zeiss Ikon AG. Since 1932, and to this day, Blaupunkt makes car radios.
• The Sachsenwerk in Radeberg (near Dresden): model 463W (LW + MW; incl. 2x RV12P4000, 1946-1947). Sachsenwerk ("SW" until 1926, "ESWE" thereafter) dates back to 1903 Sachsenwerk Licht- und Kraft-Aktiengesellschaft. Around 1930/1931 AEG becomes majority shareholder. At the height of the Great Depression (1932) the company goes bankrupt, but resumes operation in 1935 as part of the re-armament and makes grenades, fuses, telecom equipment, and weapon control systems.
• G. Schaub Apparatebau-Gesellschaft mbH in Pforzheim: model 2K-47 (LW + MW; 3x RV2P2000, 1947-1949; C. Lorenz AG took over Schaub in 1940, on government orders).
• Lembeck & Co. Gerätebau und Vertriebsgesellschaft ("Lembeck-Radio") in Braunschweig: model L147W (LW + MW + SW, 3x RV12P4000,1947-1949). Lembeck produced communications equipment for the Wehrmacht during WWII, and built radios until 1954.
• Atlas-Werke AG in Bremen and Munich: model Ra2 (MW + KW, 3x RV2P2000, 1947-1948). Atlas was involved with shipbuilding (incl. U-Boats and mine-sweepers), and related equipment such as depth gauges, active and passive sonar. Their Maschinenfabrik manufactured parts of the famous Enigma encryption system (also ref. 40, 41, 42). One of their sonar systems built in Bremen comprised 52 tubes of type RV12P2000. Their stock was used after the war for the Ra2, built at their factory in München. The same tube was also used in a tabletop model hearing aid that Atlas sold 1946-1948 (ref. 43).
• Telephon- und Telegraphenfabriks-AG Kapsch & Söhne in Vienna/Austria: model 247G and 248B (MW, 2x RV12P800, 1947)
• Signalbau AG, Dr. Erich F. Huth ("Huth Signalbau AG") in Berlin and Hannover: model 12P (LW + SW; 5x RV2P2000, 1945-1946). During the 1920s, Telefunken and Lorenz became major shareholders of Huth. Model 12P was built in Hannover for Lorenz. Huth was also a small tube manufacturer.

As a side note, the Soviet Military Administration in Germany temporarily banned the use in (new) radios of Wehrmachtröhren, in a part of their occupation zone during 1946. Ref. 44.

Fig. 10: covers of 1946 magazines with articles about using "Wehrmachtröhren"

(source: ref. 34, 37)

Fig. 11: several configurations of a pair of "RV12P2000", to substitute a VCL11

(source: Fig. 3 & 4 in ref. 34)

Fig. 12: 1946 adverts that offer schematics and other services for using surplus Wehrmachtröhren

(source: "Funkschau", Vol. 18, Nr. 1, June 1946, inside of front & rear cover page)

PARTS OF THE RV12P4000 TUBE

The actual glass tube ("Glasskörper", "Kolbe") of the RV12P4000, is mechanically protected and electrically shielded by a perforated metal cylinder. This was initially made of extruded aluminium tubing. The holes are for ventilation/cooling purposes. Later on during the war, this strategic material became scarce and thin tin-plated steel sheet metal was used (0.3 mm "Weißblech"). The RV12P4000 (like the 4 mm narrower RV12P800 and the RL2P3, ref. 7) was nicknamed "Lockenwickler", i.e., "hair curling roller", as it resembled the personal-care paraphernalia of that era.

Fig. 13: cross-section of the "RV12P4000"

(length: 10.9 cm (≈4¼"), 2.95 cm Ø perforated sleeve, 3.25 cm Ø Bakelite base, weight: ≈50 gr)

As you can see in the photo above, I have taken one of my RV12P4000 tubes apart. The disassembly starts with removal of the Bakelite knob at the base of the tube. The knob  ["Sockelknopf"] is used for extracting the tube from its socket.

A color-coding scheme was used for about 16 commonly used Wehrmacht-tubes, the wrappers of their cardboard packaging, and a marking in or on the sockets. See ref. 45, 46, 47. This was done to avoid mistakes when replacing tubes in the field. This color is green for the RV12P4000, blue for the RV12P800, and white for the RV2P2000. For the RV12P4000, the color is applied to the manufacturers logo insert of the extractor knob. The insert of two of the four original tubes (those made by Telefunken) in my Feld-Hellschreiber are medium green; one of my Valvo spares has brighter green logo in its knob, as does my TeKaDe tube. My other Valvo tube has a green dot.

Fig. 14: the top of two Telefunken RV 12 P 4000 tubes

(note the different TFK logos in the knob; the octagonal logo was used from 1926 until mid-1937; it was trademarked March/April of 1937)

Fig. 15: the top of two Valvo "RV12P4000" tubes

Fig. 16: green dot marker on a Valvo tube and top of a TeKaDe "RV12P4000" tube

Fig. 17: blue color coding on the extractor knob of several "RV2P800" tubes

Fig. 18: white triangle on the base of an "RV12P2000" and an "RV12P2000" with the knob screwed into base

Removal of the RV12P400's extractor knob requires folding back four metal lugs that are inserted through the knob. The knob can then be pulled off the Bakelite base.

Note that RV12P4000 tubes made by Telefunken ca. 1935 had a single-piece white ceramic base and knob. They are a very rare collector's item. Contrary to the two-piece Bakelite bases, the wires from the tube are soldered on the outside of the base. Possibly, the ceramic material is Calit, an iron-free magnesium silicate (stetatite) ceramic, made by the "Hescho" company: Hermsdorf-Schomburg-Isolatoren-Gesellschaft, founded in 1922 by Porzellanfabrik Kahla AG and Schomburg AG. Hescho was a world-leader in ceramic components for RF (HF) applications.

Fig. 19: rare Telefunken "RV12P4000" with white ceramic base

(source: Jogis Röhrenbude; used with permission of the tube owner/photographer; note manufacturing date: week 46 of 1935)

Fig. 20: base of the tube after removal of the retractor knob

Removal of the knob exposes a small ceramic tuning capacitor ("Abgleichkondensator"), with a capacitance of several pF. It is connected in parallel with the tubes inherent output capacitance:

Fig. 21: placement of the tuning capacitor across the tube's output

(source: Fig. 2 in ref. 48A)

The capacitor is formed by two crescent-shaped areas of silver deposit on a ceramic (originally mica) disk. Ref. 48. Some literature claims that the disk is fully metallized on the other side (e.g., p.38 in ref. 1); this seems unlikely, given the through-disk riveting of the leads.

After installation into the base of the tube, the capacitor was trimmed during manufacturing by scraping off part of the metal deposit until the desired output capacitance value was obtained for that particular tube. This was done to make the tuning of the circuit in which the tubes were used, independent of the individual tube (e.g., after replacement of the tube in the field)! I.e., independent of production variations.

Fig. 22: both sides of the capacitor

The capacitor's disk has an outer diameter of 14.5 mm, inner diameter of 4 mm, and it is 1 mm thick. It is easily removed, by de-soldering its leads from the pins of the tube. The next part to remove is a Bakelite insulating disk ("Isolierplatte"). The disk is held firmly in place by the four lugs that also retained the knob. Part of these lugs is peened over onto the disk, to hold the latter firmly in place. This also provides additional stability of the Bakelite base of the tube, and prevents the actual glass tube from moving down.

Fig. 23: the inside of the retractor knob, and the bottom of the tube after removal of the capacitor

The Bakelite disk has a so-called "Pressmarke". This small round marking identifies the factory and the material. See the discussion further below.

Fig. 24: both sides of the Bakelite "Isolierplatte"

A rubber cushion ("Gummi Puffer") is placed between the Bakelite disk and the glass base of the tube. It is a piece of thick black rubber tubing (9 mm OD, 3 mm ID, 8 mm long).

Fig. 25: rubber cushion and glass base of the tube are exposed after removal of the "Isolierplatte"

The photo below shows how the four lugs are riveted to the Bakelite base of the tube:

Fig. 26: the Bakelite base of the tube, with the riveted lugs

Once the lead-wires of the tube are de-soldered from the pins of the base, the bottom end of the tube is ready for removal of the glass tube. We now have to dismantle the top-end of the tube. The disk at the top of the tube is made of brown Bakelite, except for my 1940 tubes made by Telefunken and Valvo. Those have a white disk, possibly made of Calit (fired magnesium silicate).

Fig. 27: top of the "RV12P4000 "

My two 1937 Telefunken tubes have grid pin (nr. 7) with pointed shape. All my other tubes (Telefunken and Valvo, 1940-1943, TeKaDe) have a rounded pin. I have measured pin length varying from 11.5 to 13.2 mm.

Fig. 28: the shape of the grid pin

The first item to remove is a one-hole disk ("Lochscheibe") through which the grid pin protrudes. It has an OD of 28.5 mm and is 1.8 mm thick, with a 3 mm raised edge. The disk is usually made of Bakelite, though there are also white plastic disks. The center hole is not a tight fit for the grid pin, so this disk is merely a cover plate. The disk is removed by folding back six lugs that are part of the perforated metal sleeve of the tube. With some effort, the disk can then be pulled out.

Fig. 29: the Bakelite top disk (bottom side shown)

The next item is the so-called "Abgleichscheibe": a tuning disk. This is a slightly cupped spring washer that is pressed all the way down onto the grid pin. As discussed above, the RV12P4000 has a small capacitor for tuning the output capacitance. The capacitance of the input of the tube is also tuned.

Fig. 30: placement of the tuning disk across the tube's input

(source: Fig. 2 in ref. 48A)

Tuning was done by installing metal disks of various sizes until the desired capacitance was obtained. Ref. 48. This washer is not easily removed.

Fig. 31: top of the tube after removal of the 1-hole disk (left) and the tuning disk

The retention washer sits on top of a 4-hole Bakelite disk. Note that the grid pin is not press-fit into this (brittle) disk, but the disk is molded around it (see cross-section photo towards the top of this page). The disk is relatively thin. It does not provide much hold for the grid pin when force is applied to it, e.g., when inserting the tube into, and pulling out of its socket. So, the function of the retention washer probably is to immobilize the grid pin, and distribute contact forces over the disk. The grid lead-wire that comes out of the top of the glass tube, is soldered into the grid pin. This disk is also tightly fit into the perforated metal sleeve of the tube. The grid lead-wire is either de-soldered or broken off while removing the disk.

Fig. 32: the 4-hole Bakelite disk with grid pin (left) and the top of the tube after removal of that disk

At this point, we can see the very tip of the glass tube peaking through the hole in the black rubber (or synthetic rubber) stopper ("Gummi Hülse"). The concave side of this vibration damper rests on top of the glass tube.

Fig. 33: the rubber vibration damper

This rubber piece is 18 mm high, and is simply pulled out. The upper third part of the glass tube is shielded with a sheet-metal sleeve ("Metall Hülse"). It is 18 mm high and 0.2 mm thick. Both this sleeve, and the perforated outer sleeve of the tube, are connected to the same contact at the base - with a thin multi-strand copper wire.

Fig. 34: the metal shielding sleeve

The glass tube is now pushed out the top of the outer sleeve. There are no markings whatsoever on this glass tube.

Fig. 35: the actual glass tube of the "RV12P4000"

Fig. 36: relative size of the "RV12P4000" (left) and "RV12P2000"

The bottom of the glass tube was resting on another vibration damper: a blue rubber band ("Gummi Ring"). it measures 5 mm in height and is 1.7 mm thick, with scalloping on the inside.

Fig. 37: the blue rubber band

The perforated metal sleeve is fixed to the Bakelite base of the tube in six places: holes into the sleeve are pressed into slightly larger holes in the Bakelite base. After drilling out these holes with a 3.2 mm bit, the sleeve can be pulled off the base. As clearly visible in the photo immediately below, the tin-plated sheet-metal sleeve of this TeKaDe tube, has a longitudinal seam that is soldered. All my other RV12P4000 tubes have a perforated sleeve made of seamless aluminium tubing.

Fig. 38: the perforated sheet metal sleeve of an "RV12P4000" made by TeKaDe - note the soldered seam

Fig. 39: tubes with a perforated metal sleeve were also made in England in the 1930s

(source: p. 41 in "Popular Science", November 1933; don't try this at home!)

Fig. 40: the Bakelite base

Fig. 41: the "RV12P4000" - disassembled

(click here to get full size)

Fig. 42: another decomposition of the "RV12P4000"

(source: Fig. 1 in ref. 48A)

Fig. 43: the "RV12P4000", "RV2P800", and "RV12P2000" - all to the same scale

GLASS TUBE CONSTRUCTION

Tubes like the RV12P series (4000, 2000, 800) represent a major transition in tube construction and manufacturing technology. They have a button-stem rather than a pinch-stem. The pinch-stem is also known as "pinched stem", "crimped stem", and "press stem" (D: "Quetschfuß", NL: "kneep"). The stem is the bottom part of the glass tube, where the lead-in wires are passed through to the electrodes. The conventional pinch stem was - and still is - the standard for regular incandescent light bulbs, gas discharge lamps, and halogen lamps. As tubes were originally developed from incandescent light bulbs (both have metal filaments and external connections, contained in an evacuated or gas-filled vessel), it is logical that the same manufacturing technology was used. Light bulbs had already been mass-produced for many years.

Fig. 44: stem making machine - showing lead wires being fused into a pinched stem

(source: "Brimar Valves" company advertising in "Wireless World", March 1943)

A pinch-stem (a.k.a. "electrode support tube") is made by a sequence of basic manufacturing steps (ref. 49, 50, 51, section 42.2 in ref. 52):

• The end of a section of glass tubing is heated while being spun.
• A wide cone is inserted into the soft end of this tube, to create a flange ("flare") with the diameter of the final vacuum tube.
• The lead-in wires are placed into a jig, to hold them into position.
• The wires are then inserted into and through the flanged tube.
• A small glass tube is inserted between the wires (for later attachment of a vacuum pump).
• The entire assembly is heated until soft.
• Metal jaws squeeze the molten glass around the wires, to fuse them.
• Air is blown into the small tube, to create a hole through the stem.

Some video clips about making vacuum tubes are shown on this page.

Fig. 45: parts of a pinched stem in various stages of assembly

(source: p. 6 in ref. 50)

A highly simplified sequence of tube manufacturing steps is as follows:

• The tube's electrodes are spot-welded to the lead-in wires at the top of the pinch-stem. The electrodes sub-assembly, with mica spacers - if necessary, is also referred to as the "system". The combined stem plus system is called the "mount".
• The mount is inserted into the tube's glass envelope ("vessel", "globe"; D: "Kolbe") until the flange of the stem touches the tube. A grid wire may stick out of the top.
• While turning, the tube's edge is fused to the flange of the glass stem.
• While turning, the top of the the tube heated until it forms the dome shaped top of the top. The small protrusion where the dome is closed is called the "nub".
• The tube is evacuated via the small glass tube in the stem, which is then melted shut.
• The lead-in wires are connected to the pins of the base (D: "Sockel"), and the base is fixed to the tube.

Annealing (heat treatment) steps throughout the manufacturing process ensure that strains and stressed in the glass are removed. To retain the vacuum seal, the lead-in wires (or at least the part that is fused into the glass) must adhere to the glass and have the same thermal expansion coefficient and expansion rate as the glass. Copper-clad wire made of a nickel-iron alloy has the required properties. Cf. section 42.2. in ref 52. This is called "dumet" wire, for "dual metal". It was developed ca. 1911, and can be used for wires up to 0.5 mm in diameter (≈ 1/64 inch). Related alloys are "cunife", made of copper (Cu), nickel (Ni), and iron (Fe), and "fernico", made of iron, nickel, and cobalt (Co). For lead wires through quartz glass (gas discharge lamps, neon lamps), molybdenum wire or strips are used instead.

Fig. 46: pinched stem ("Quetschfuß") glass tube base

(source left & center: Fig.2 in ref. 53, source right: ref. 54)

Clearly, with the pinch-stem construction, the wiring between the contacts and the electrodes of the tube is relatively long. In the stem, the lead-in wires are parallel and closely spaced - especially so, in a tube with a larger number of electrodes (pentode, heptode, etc.). Each wire has self-inductance that depends on the wire's length. Between the wires (and, hence, between the electrodes) there also is undesirable capacitance. The self-inductance and capacitance limit the operating frequency of such tubes to VHF. Ref. 9, 91, 92. The parasitic capacitance in the stem also depends on the dielectric constant of the glass, which varies with the operating temperature. The lead-in wires are arranged in a straight line at the top of the pinch. This makes the attached system of electrodes mechanically less stable, and more susceptible to vibration and shock, especially in a direction perpendicular to the long side of the pinch.

These limitations were mitigated with the introduction of the button stem (D: "Preßteller"), which was also used in the "Stahlröhren" (ref. 8, 93). A button stem starts out as a pressed glass disk, with small holes that are evenly distributed around the edge of the disk, like a button for clothes. Hence the name. The lead-in wires are passed through the holes and fused to the glass. Button stems are typically at least 1 cm (≈ 3/8 inch) shorter than pinch stems. There are two basic forms of "Preßteller": the "Scheibenfuß", and the "Napfpreßteller" or "Napffuß". The prior is a button that is simply a glass disk, whereas the latter is a button with a raised edge. Ref. 53, 92, 106.

Fig. 47: button stem glass tube bases "Preßnapf" and 2x "Preßteller" (left-to-right )

(source left & center: Fig. 2 in ref. 53, source right: ref. 54)

Initially, the lead-in wires were still connected to contact pins of a tube base. Later on, the tube base (D: "Sockel") was dispensed with altogether, to create the all-glass tube (D: "Allglasröhre"), where heavy-gauge lead-in wires or dumet pins serve as connector pins. Ref. 55, 56.

The RV-series tubes are among the very first  button-stem tubes that were series-produced in Europe. However, button-stem and all-glass technology had already been used in (almost) all-metal tubes ("Stahlröhre"), "peanut" tubes, and "acorn" tubes (D: "Eichelröhre") such as the "955" miniature triode developed by RCA in 1934 (ref. 57, 58, 108A-108D). The latter was suitable up to low-UHF (≈ 600 MHz), and was also used in 1935 by GEMA-Berlin ("Gesellschaft für elektroakustische und mechanische Apparate mbH") in their early radars and radio telephones (ref. 59). The origins of practical miniature tubes go back to the South-African Hendrik van der Bijl in 1919, who further developed his technology in 1923 at Western Electric, to create the 215A "peanut" triode. Ref. 60, 61.

TUBE SOCKETS

The RV12P4000 tubes are inserted "head first" into a so-called "Patronenfassung" - literally a "cartridge socket", probably named so because the sleeve (turret) part made it resemble large caliber ammunition. The sleeve keeps the tube properly aligned during insertion and extraction. The sockets are installed in such a way, that that the tubes can be removed without opening the equipment housing - very convenient for maintenance!

Fig. 48: a bakelite "Preßstoff-Patronenfassung mit Flansch" socket for the RV 12 P 4000

The molded tube sockets of the Feld-Hell's electronics box are made entirely of Bakelite. The socket is installed into the equipment chassis with two screws through the flange at the entrance of the socket. The old plumbers' adage about tightening pipes and screws is appropriate here: "Nach fest kommt ab" (after "tight" (it) comes "off"). Over-tightening of the mounting screws cracked the mounting flange of the socket. This construction with relatively brittle Bakelite was not robust enough for military operation. Later equipment had a socket with a sleeve made of perforated sheet metal, and an adjustable mounting bracket.

Fig. 49: top of the Feld-Hell tube socket, without and with an RV12P4000 inserted

Note that a notch ("Nase" (nose), "Warze" (wart)) protrudes from the side of the base of the tube. The tube can only be inserted fully into the socket and engage the contacts, if the notch is aligned with the corresponding recess in the socket. A simple and effective fool-proofing method.

The Bakelite molded sockets were not suitable for sustained operating temperatures above 150 ºC (300 ºF), such as with transmitter tubes. The Bakelite sleeve was replaced with a . Originally an aluminium-magnesium alloy (such as Elektron), later die-cast zinc (ca. 1944), and in the end (1945) plain steel sheet metal.

Fig. 50: "Patronen-Mantelfassung": perforated aluminium socket for the RV12P4000

In the photo above, one of the retainer springs is visible inside. The springs connect the metal shield of the inserted tube to chassis ground, without the need for additional pins.

Fig. 51: a perforated aluminium socket with (adjustable) mounting flange

Fig. 52: dimensions (in mm) of the perforated sheet metal socket with mounting bracket

According to the Telefunken datasheet for this tube (ref. 28), the socket has part number ("Lieferung-Nummer", "Lg.-Nr.") 1670. Some sources refer to this as T1670 (ref. 29), where "T" probably stands for Telefunken. They also call out other flanged sockets with part numbers "024 b D3487", "024 b D3615", as well as "WG6". There is also an adjustable mounting flange, with Telefunken part number "1795". The Bakelite socket does not require a separate mounting flange, as it has an integrated Bakelite flange. The aluminium socket shown above, does require a mounting flange or bracket. I have not found any part number markings on the Bakelite and aluminium sockets that I have looked at, nor any authoritative literature that specifies the above part numbers. The RL2P3 (a low-power ("QRP") transmitter tube), uses exactly the same socket (ref. 62).

The RV12P4000 - and similar tubes - has conically shaped brass contacts ("Kegelkontakte") that protrude radially from the Bakelite base of the tube. The next generation of Wehrmacht tubes, such as the RV12P2000, dispensed with the perforated metal sleeve, and had cylindrical radial pins ("Seitenstiftkontakte"). See Fig. 36 and 43 above.

Fig. 53: conical brass contacts of the "RV12P4000"

MOLDING MARKS

The RV12P4000 tube and the tube socket contain press-molded parts that are made of a moldable phenolic resin (PF), reinforced with sawdust, paper, textile, etc. This is usually referred to as "Bakelite". Ref. 63, 64. Bakelite was patented in the USA in 1907 by the Belgian Leo Baekeland (1863-1944), who emigrated to the USA at the age of 26; his patent expired in 1927. Hans Lebach filed patents in Germany for a virtually identical material ("resit"), several months before Baekeland did so in the USA. Extensive patent litigation ensued. PF-related patents actually date back to the late 1890s, though it was Adolf Baeyer (later changed to von Baeyer; and 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. 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, 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 the war, good wood dust became scarce, and the quality of the Bakelite products declined.

Fig. 54: Bakelite - made in Germany

(source: cover page of ref. 63)

Bakelite parts of the RV12P4000 tube, as well as the Bakelite tube socket, carry small round embossed molding marks. They are so-called "Preßmarken", "Prägezeichen", or "Prägemarken".

Fig. 55: Siemens-Halske logo and material marking on tube sockets of one of my Feld-Hell machines

The entwined S-H on the left is the standard Siemens-Halske logo marking of that era. The second one is a "Kunststoffkennzeichen", a German industry standard marking for molded items. It comprises a two-digit code (either two figures, or one letter + one figure) to identify the "Preßwerk" - the factory where the material was molded, and a letter or number to identify the actual material. Ref. 65-68. The molding mark codes are placed within the stylized initials "MP", which stands for "Material" and "Prüfung" (testing).

Fig. 56: The MP molding mark with its press-works and material identifier codes

In the "34 S" molding-mark above, the factory code "34" denotes Siemens-Schuckertwerke, Abteilung Isolierstoffe, in Berlin-Siemenststadt. The "S" denotes "Phenolharz mit Holzmehl als Füllstoff". This is a phenolic resin, reinforced with sawdust filler. The material code "Z2" appears on the inside of the rear-cover of my T.empf.14 "Presse Hell" machine. This code refers to "Phenolharz (Bakelit) mit Zellstoff als Füllstoff" - Bakelite with cellulose filler (e.g., shredded paper).

Fig. 57: Press-mark on the Bakelite rear-cover of my Presse-Hell printer

The material molding marks were issued by MPAD, the "Staatliche Materialprüfungsamt zu Berlin-Dahlem" - the State Materials Testing Institute at Berlin-Dahlem. The institute was founded in 1904, as a merger of three royal testing institutes: the "Königliche Mechanisch-Technische Versuchsanstalt" (M.T.V.), the "Königliche Prüfungsstation für Baumaterialien", and the "Königliche Chemisch-Technischen Versuchsanstalt". Most of the building shown below still exists today, and is home of the "Bundesanstalt für Materialforschung und -prüfung" (BAM), the Federal Institute for Materials Research and Testing.

Fig. 58: Materialprüfungsamt, Berlin-Dahlem, 1904 - as seen from Potsdammer Chaussee

(source: Fig. 46, in ref. 69)

Fig. 59: the "Materialprüfungsamt der Technischen Hochschule", in Berlin-Dahlem, 1904

(source: fold-out in ref. 69)

The industry standard dates back to 1924, when it was established by the members of the "Technische Vereinigung der Hersteller typisierter Preßmassen und Preßstoffe" (T.V.) - the "Technical Association of Manufacturers of Standardized Molded and Compression Molded Materials". In 1938, this association was later changed into "Technische Vereinigung der Fabrikanten gummifreier Isolierstoffe e.V." - the "Technical Association of Manufacturers of non-rubber insulating materials". Also see ref. 107.

The MPAD molding marks were used until ca.1960. Note that molded material identifier codes made a comeback in 1988, when the Society of the Plastics Industry (founded in the USA in 1937) introduced its Resin Identification Code. It is used worldwide on plastic items, in combination with the universal triangular recycling symbol.

Fig. 60: Marks on Bakelite parts of a Valvo "RV12P4000", an aluminium tube socket, and "RV12P200"

Fig. 61: Mende logo and material marking on tube sockets of one of my Feld-Hell machines

The above markings measure 3 - 5 mm in diameter. On other items, e.g., (field)telephones "(Feld)Fernsprecher", they are 5 - 10 mm.

MPAD "56 31,5", "54 *S", "12 42", and "1380" appear on parts of the 1944 Valvo RV12P4000 that I dismantled (the Bakelite "Isolierplatte", the 1-hole Bakelite disk, the 4-hole Bakelite disk, and the 1-hole Bakelite disk, respectively). MPAD "56 31,5" also appears on the base of a Valvo RV12P2000 in my collection. It has a WaA745 acceptance stamp and manufacturing date 45/44 H. MPAD "54 *S" also appears on the base of post-war RFT RV12P2000. MPAD "W3 *S" appears on bottom (near the hole and contact for grid pin 7) of the perforated-metal tube socket shown further above. The Bakelite inkroller holder of my Feld-Hell machine has two pressmarks: one with the entwined S-H logo, the other with the MPAD mark shown below (manufacturer "34", material "31").

Fig. 62: mark on the bottom of the Bakelite ink roller holder of the Feld-Hell

The inside of the Feld-Hell's 12 volt power plug has an MPAD mark with the manufacturer's code "24", and material code "T1".

Fig. 63: MPAD molding mark on the inside of the 12 volt power plug of the Feld-Hell machine

The following press marks appear inside power-source switching unit ("Steckanschluß Fu.b") of the 5W.S. transmitter: a standard MPAD mark and a mark with the 3-letter manufacturer's code "dbf". The latter belongs to Hoppmann & Mulsow in Hamburg, manufacturer of that switching unit.

Fig. 64: example of another MPAD "T1" mark - without indentification of the press works

The company codes on the above markings are as follows:

• 24: Gebrüder Merten GmbH & Co. KG., Elektrotechnische Spezial-Fabrik. A small manufacturer located in Gummersbach, about 50 km east of Köln (Cologne). They manufactured radio parts made of rubber, Bakelite, and brass (tube sockets, plugs, switches, knobs, etc.) The company still exists to this day.
• 34: Siemens-Schuckertwerke, Abteilung Isolierstoffe, in Berlin-Siemenststadt.
• 54: Ellinger und Geissler Fabrik Elektrotechnischer Bedarfsartikel und Elgesit-Isolier-Pressteilen in Dorfhain (Dresden-Tharandt). Incidentally, Dorfhain is also the birthplace of Hermann Mende, founder of Radio-Mende in Dresden. Ellinger & Geissler was a manufacturer of fixed and variable resistors, switches, and tube sockets. They produced Bakelite under the trade name Elgesit.
• 56: H. Mende und Co. in Dresden, who used the trade name Mendelith for their bakelite.
• W3: is Dralowidwerk der Steatit-Magnesia AG, in Berlin-Teltow (see advertising below)

The associated material codes are:

• S: as stated above, this is "Phenolharz mit Holzmehl als Füllstoff", i.e., moldable phenolic (carbolic) resin that is reinforced with sawdust filler. It is usually referred to as "Bakelite".
• T was used for phenolic resin reinforced with textile, often cotton. It is referred to as "Hartgewebe" (lit. hard cloth), with many brand names such as Turbax and Harex. In Feld-Hellschreiber machines, this material is used for several gear wheels, the slider bars underneath the set, and the 12 volt power plug. The latter has the material identifier T1, which means "short textile fibers", as opposed to T2 "shredded textile cloth" (ref. 65).
• Asterisk or + to the left of the "S": significance unknown.
• 31: rapidly curing Bakelite. Used for about 90% of applications (p. 41 in ref. 65). Resin percentage ranges from 35 - 60%. Bakelite with a higher resin percentage has a higher price, retains glossy surface better, is less hydrophobic (swelling), has higher insulation resistance, and has better chemical resistance. Special blends were made either without ammonia (no ammonia odor, no discoloring of light metals in contact, no discoloring of the scale of instruments with Bakelite housing), without phenols (odor), or that were acid-proof, or suitable for use in tropical environments.
• 31.5: this is a "low voltage" insulator material. It is similar to type 31, but slightly softer and with lower insulating resistance (p. 42 in ref. 65). Color is usually brown; a black version also exist, but has worse electrical properties than brown.
• 12 42: significance unknown; the tube in question has 1944 date codes 11/4 and 13/4.
• 1380: significance unknown.

Fig. 65: 1942 Dralowid advertising

(source: "Funk-Technische Monatshefte" (FTM), 1942

Fig. 66: Letterhead of Ellinger & Geissler (1938)

WAFFENAMT AND OTHER MARKINGS

Wehrmachtröhren are typically marked with several stamps:

• Tube type-designator (here: RV12P4000)
• Manufacturing location
• Date of manufacturing
• Acceptance agency
• Date of acceptance
• "Property of"
• Other

Special thanks go to Werner Thote (DL1VHF), who has provided me with invaluable information regarding tube markings.

Fig. 67: example of manufacturing, acceptance, and property stamps on a Valvo RV12P4000 tube

All weaponry, ammunition, and equipment delivered to the Wehrmacht was subject to pre-delivery testing, inspection and acceptance. This was the responsibility of the Heeresabnahmewesen, the Army Acceptance Organization. Inspections were performed according to detailed guidelines called "Technische Lieferbedingungen", the technical delivery specifications. These were prepared by the respective "Waffenprüfämter" (WaPrüf) - the weapons test departments. The Abnahmewesen comprised a large number of Heeresabnahmestellen (army acceptance / inspection stations, ordnance detachments). The Abnahmestellen were typically inspection stations that each covered multiple equipment suppliers and factories. They were often co-located with the factory of a major manufacturer, but not staffed by employees of that manufacturer.

Note that the acceptance identification number does not represent an individual inspector, nor a specific inspection station. It belongs to a particular chief inspector, and all of his subordinate inspectors used the same number. If he moved to a different location, then the number moved with him. Ref. 70. Each accepted item was marked with an Abnahmestempel, a stamp to indicate both Prüfung (test/inspection) and Übernahme (transfer) by the Wehrmacht. The stamp consists of an eagle-above-swastika symbol, "Wa A" and the identification number.

A more detailed discussion of the Waffenamt organization, its acceptance stamps and other markings on the Hell Feldfernschreiber is on this page.

Fig. 68A: WaA, Wa. A., and Wa.A. stamps on my RV12P4000 tubes

The RV12P4000 tubes in my collection, and those that I have seen "in the wild", carry various WaA acceptance stamps:

• WaA 89 is associated with Telefunken Röhren- und Gerätewerk in Erfurt, a tube factory founded in 1936. Erfurt is in former East-Germany, and after WWII, this factory became the state-owned VEB RFT Funkwerk Erfurt. The "89" stamp was used from 1943-1945 (cf. pp. 42-43 in ref. 15).
• WaA 338 is associated with a central Abnahmestelle in Berlin. It appears to have only been used in 1936-1937, and for a variety of goods from several manufacturers of radio related equipment, including Lorenz AG and Hans Boas Elektrotechnische Fabrik. It is very unusal to find it on tubes, such as my Telefunken RV12P4000s.
• WaA 617 is also associated with an Abnahmestelle at the Telefunken Röhren- und Gerätewerk in Erfurt. It appears to have been used during the period 1940-1943. It can be found on other TFK tubes such as the RV2,4P45, RV2P800, RL2P3, and LS50, as well as TFK radios such as 15W.S.E.a, 80W.S.a, K.W.e., Lw.Ea, UkwEa, and TornFu.d2 (ref. 70).
• WaA 745 is associated with a Heeresabnahmestelle at the Valvo tube factory (Röhrenwerk) in Hamburg. It was used during the period 1939 through early April 1945 on tubes manufactured by Valvo/Philips, and the Studiengesellschaft für Elektronengeräte mbH. The Studiengesellschaft was an R&D and prototyping lab in Hamburg with a a small production capability. It was founded by Valvo/Philips in 1939 and developed special tubes such as "drift tubes", the predecessor of the klystron. This stamp can be found on other Valvo tubes such as the RV2,4P700, RV12P2000, RL2P3, P10, and RL12T2 (ref. 70).
• WaA 836 was used at the Abnahmestelle in Nürnberg for tubes from the Süddeutsche Telefon-Apparate, Kabel- und Draht-Werke A.-G. (TeKaDe, frmr. TKD). It can be found on other TeKaDe tubes such as RV2P800, RV12P2000, RL2T2, RL12T15, and RG12D60 (ref. 70). WaA 836 is also used from 1943-1944 on electrical and electronic products (e.g., "Wechselrichter") from regional companies such as AEG, Nürnberger Schraubenfabrik und Elektrowerk (N.S.F; the electrical part of the company merged with AEG in 1942), Lumophon (radios, telephones; acquired by Grundig in 1951), and Kabel- und Metallwerke Neumeyer AG. The latter was part of the Gutehoffnungshütte Aktienverein für Bergbau und Hüttenbetrieb (GHH) conglomerate, that also included large companies such as Maschinenfabrik Augsburg Nürnberg AG (M.A.N.). See ref. 71. M.A.N. and Krupp financed the ultimate development by Rudolf Diesel of his invention: the ubiquitous "rotational heat engine" that eversince bears his name.

I also have Telefunken RV12P4000 tubes from 1940 without a Waffenamt stamp - which is rather unusual.

An other possible acceptance stamp on Wehrmacht tubes and equipment is "BAL". According to official Luftwaffe service regulations, this stands for Bauaufsichten des Reichsluftfahrtministerium (the Administration for the Supervision of Construction), in short "Bauaufsicht Luft". Ref. 47, 72, 101. Some publications suggest that B.A.L. stands for Bauaufsichten der Luftwaffe", "Bauaufsichts-Leitung", "Beschaffungs-Amt für die Luftwaffe" (air force procurement agency). The BAL stamp comprises the abbreviation "BAL" and the number of the acceptance authority, both placed together inside an octagon. Though fully independent organizations, the BAL and WaA did coordinate their tube acceptance activities. Tubes from Valvo, Lorenz, TeKaDe (TKD) and Telefunken/Erfurt only carry a WaA stamp, whereas tubes from Telefunken/Berlin only carry a BAL stamp, e.g., BAL 716 or 1964. Tubes from Philips/Eindhoven typically also only carry a BAL stamp (BAL 1790), though sometimes they were retested at Philips-Valvo/Hamburg, where they received a second acceptance stamp (WaA 745). The Kriegsmarine (navy) did not have its own acceptance stamps for tubes, as the acceptance of their tubes was handled by WaA and BAL. Tubes and equipment may, of course, be marked with the "Kriegsmarine" property stamp.

Fig. 68B: BAL 1790 stamp on an RV12P4000 tube with location stamp "H"

During the last two years of World War II, the German military was forced to reduce the number of personnel for supervising product quality in the various industries. Therefore, in 1943 the conditions for accepting military goods in industry were changed. Qualified personnel of manufacturing companies themselves were authorized to, and responsible for, acceptance of goods supplied to the Wehrmacht. This was called "Betriebsabnahme" (BA): company acceptance. Each authorised person had an individual BA-number. This is why BA-numbers can have as many as five digits, e.g., "BA 11328". Another kind of acceptance marking is W.ab, without a number. Most likely, this stands for "Werksabnahme" - "factory acceptance". Betriebsabnahme and Werksabnahme basically mean the same thing. However, the latter has only been used by Telefunken/Berlin.

Fig. 68C: Several BA stamps on RV12P2000 tubes and W.ab stamps

Examples of acceptance stamps used on other tubes (pp. 42-44 in ref. 15, ref. 100, ref. 110):

• Telefunken: WaA 716, BAL 716, BAL 964, BA 6933.
• Valvo: WaA 584 (also found on Wechselrichter of the company Baco-Apparatebau of Berlin-Pankow, ref. 73), WaA 801, WaA 4801, BAL 1790, BAL 393 (on tubes made for Valvo bei RT in Paris/France).
• Opta: BAL 913, BAL 2879, BA 2979, BA 11328.
• Lorenz: BA 4721.

As the old saying goes: "The great thing about standards is that there are so many of them." This also applies to the formats used for the date stamps. Most common is a single date-of-manufacturing stamp (D: "Herstellungsdatum"), with a "WW/YY" format. For example "11/40" means week 11 in 1940. However, the same date stamp could also be formatted as "11. 40", "11.40", "11 40", "1140", or "11-40". During 1944, Valvo exclusively used yet an other format: /4 instead of /44.

Some tubes have two date code stamps. They are typically diffeernt: e.g., 42/43 and 47/43, see Fig. 68B above. The second stamp is the acceptance date (D: "Abnahmedatum") - sometimes as much as a year after the manufacturing date. The two dates need not necessarily have the same format, e.g.:

• "47/43" and "15.11.43"
• "12. Juli 1937" and "27/37"

Some tubes made by Lorenz have the date (and other markings) engraved or etched into the glass tube, or engraved into the Bakelite base, rather than stamped. Sometimes the date includes the day as well.

Note that there are documented cases of Wehrmacht tubes where the acceptance stamp actually pre-dates the manufacturing stamp! This may have been done as part of a scheme to show compliance with production targets.

The major tube manufacturers all had multiple manufacturing locations. The date-of-manufacturing stamp is often expanded with an indication of the Röhrenwerk (RöW, tube factory) location. On Valvo/Philips tubes, this is typically "H" for Hamburg, "W" for Wien (Vienna/Austria), "WW" for Weißwasser, "Pg" for Prague/Czechia ("Pg T" for the subsidiary "Tatra" factory, ref. 110), and "E" for Eindhoven/The Netherlands. The letter code is placed after the date code, except for "W", which is typically placed in front of the date code.

Fig. 69: example of Telefunken RV12P4000 tube manufactured in Hamburg

Telefunken had quite a number of Röhrenwerke, e.g., Berlin (multiple Werkstätte factory shops), Erfurt ("E" or /4), Ulm ("U"), Neuhaus am Rennweg ("N" or /2), Lodz/Poland ("L"), Prague/Czechoslovakia - now Czech Republic ("Pr"), Mülhausen, and Rudolstadt. Tubes manufactured at the Neuhaus plant were often accepted at nearby Erfurt.

The Wehrmacht tubes normally carry an "Eigentum" ("ownership" / "property of") stamp, to indicate that it was produced for - and owned by - the Wehrmacht in general, or by a specific branch of the Wehrmacht: Heer, Kriegsmarine, or Reichsluftfahrtministerium (as a proxy for the Luftwaffe). Typically, the stamp is one of the following:

• Wehrmachteigentum
• Wehrm.-Eigentum
• Wehrmacht
• Wehrm.
• Heereseigentum
• Heereseigent.
• R.L.M. Eigentum
• RLM Eigentum
• Eigentum RLM
• RLM
• Kriegsmarine

Fig. 70: Wehrmacht "Eigentum" stamps on some of my RV12P4000 tubes - with & without a box around the text

Fig. 71: an RLM "Eigentum" stamp on one of my RV12P4000 tubes

The stamps are typically black. However, the "Eigentum RLM" stamp on two of my Telefunken RV12P4000 tubes is magenta, which is rather unusual. These tubes also have no Waffenamt stamp...

Two of my RV12P4000 tubes, have the number "2" and "4" stamped directly below the WaA 745 stamp. They were manufactured at Valvo in Hamburg in 1941. I have also seen a 1940 RV12P4000 from Valvo, with a separate "7" stamp below the WaA 745. The number "3" has been used on other Wehrmachtröhren from Valvo. It is not clear what these numbers refer to. Valvo did have multiple manufacturing locations in the Hamburg area (Lokstedt, Stellingen), and a particular site may have had multiple manufacturing lines for the same tube.

Fig. 72: stand-alone "2" and "4" below the WaA stamp

Some tubes have a 4- to 6-digit code stamp in addition to the date-of-manufacturing stamp. Most likely, the first digit refers to a Telefunken manufacturing plant. E.g., "1" implies Berlin, "2" Neuhaus am Rennweg, "4" Erfurt, "5" is for the AEG/Telefunken Röhrenfabrik Berlin-Oberschöneweide/Oberspree (RFO), whereas "8" implies "manufactured for Telefunken by Philips/Valvo". Ref. 13. The rest of the digits are a running serial number ("Fertigungsnummer"). The serial number part of the 5- and 6- digit codes refers to the weekly production run - it was reset every week (ref. 110). The 4-digit codes may have been used for tubes with a modification that had not yet been homologated (early production runs, prototypes).

Fig. 73: examples of 4- and 6-digit code stamps

(two Telefunken RV12P4000 tubes; the tube on the left has date code 31/37, the other 24/40)

RV12P4000 TUBE MANUFACTURERS

RV12P4000 tubes were manufactured by several companies: Telefunken, Valvo/Philips (ref. 74), and TeKaDe. These companies have an interesting history, that is intertwined largely due to leveraging of patents (esp. the Telefunken-owned rights to the famous 1910 Robert von Lieben patent, ref. 75). The worldwide light bulb and radio tube industries were rife with cartels - perfectly legal in most western countries until the mid-1950s - mid-1980s. Ref. 76A-76F.

Fig. 74: logos of Telefunken (pre & post mid-1937), TeKaDe, Valvo and Philips

The Telefunken history dates back to 1903, when Emperor Wilhelm II instructed the Gesellschaft für drahtlose Telegraphie, System Prof. Braun und Siemens & Halske m.b.H. (S-H) and the Allgemeine Elektrizitäts-Gesellschaft (AEG) to form a joint-venture, to pool their patents and R&D efforts against Marconi's monopoly in maritime radio communication. This company was called the Gesellschaft für drahtlose Telegraphie m.b.H., System Telefunken. Ref. 22b, 77. It had the telegraph address TELEFUNKEN, which became the company's trademark and later on its name. As the name clearly suggests, the main activities were initially related to spark transmitters. Based on its many patents, Telefunken was able to establish a monopolistic position in the vacuum tube industry. They developed an estimated 75% of all tubes manufactured in Germany up to 1945. In October of 1941, Telefunken became wholly owned by AEG. Ref. 102.

Telefunken had a number of tube factories in Germany and in occupied areas. In August of 1944, ahead of the approaching Soviet forces, a Telefunken tube factory that was originally moved from Berlin to Litzmannstadt (Łódź/Poland, ca. 115 km southwest of Warsaw), was moved to Ulm in the south of Germany. Production there started in November of 1944. Ref. 109. Despite being destroyed during a bombing raid mid-December, the factory produced over 280 thousand tubes until the US forces halted production late April 1945. Telefunken was fully absorbed into AEG in 1966. Ref. 78. Telefunken AG was one of the last Western manufacturers of vacuum tubes, and ceased production in the mid 1980s. The post-war production volume of their West-German factories totaled some 670 million tubes!

Fig. 75: several Telefunken tube adverts

(source advert at center: ref. 44)

Fig. 76: 1944 Telefunken advertising

(source: "Funk-Technische Monatshefte", 1944, nr. 1, p. 20)

The Radio-Röhren-Fabrik GmbH (RRF) was founded in April of 1924 in Hamburg by C.H.F. Müller AG (a.k.a. "Röntgenmüller"), the sole manufacturer of X-ray tubes in Germany at that time. Ref. 5, 22A, 79, 80, 81. They also manufactured transmitter tubes and receiver tubes (starting 1916 and 1921 respectively). In 1924, the Müller company ran into financial problems: as part of a (hostile) take-over attempt, Siemens-Halske Co. (!) no longer paid its outstanding bills to them. Max Liebermann, owner of Müller since 1909, enters into a bail-out venture with the Dutch company N.V. Philips Gloeilampenfabrieken in 1925. Philips was also an X-ray tube manufacturer, and eager to get access to the German tube and radio market. That same year, Telefunken, unaware of Philips' link with Müller, enters into an agreement with Philips: Philips could only import a limited number of tubes to Germany, and only via direct sales to Telefunken. In 1926, Telefunken enters into an agreement with Müller/RRF, allowing the latter to produce tubes, but only sell the tubes wholesale and retail as spares and replacements, but not to equipment manufacturers. The latter were still obliged to buy their tubes exclusively from Telefunken. In 1926, the brand-name "Valvo" is adopted. The "RRF" in the pointed-circle logo is changed to "Valvo" and trademarked in 1927. Just like the English word "valve", the word "valvo" refers to the Latin "valva": half of a double-door, generalized to any flow controlling device.

Liebermann sells Müller and RRF to Philips in May of 1927 (the same year that Philips bought Mullard Radio Valve Co. Ltd in England). They are henceforth called Philips-Valvo Werke GmbH. It is fully absorbed into Deutsche Philips GmbH in 1932. Towards the end of 1931, Philips, and its direct competitor Telefunken enter into a formal agreement with world-wide coverage, regarding cross-licensing of patents, sales channels, tube types, and production quota; this superseded their 1925 and 1926 agreements. Both Philips and Telefunken had additional agreements with other tube manufacturers (e.g., Lorenz, TeKaDe, Tungsram). Valvo Radio Röhren GmbH becomes a separate company in 1939. Some of the convoluted relationships between the various German and Dutch companies between the World Wars are highlighted in ref. 82.

For its light bulb production, Philips bought the "Glasfabrik Weißwasser GmbH" glasworks in Weißwasser in 1920 -  already a bulb supplier to a number of European lampmakers, including Volt and Pope. The town of Weißwasser is located about 150 km southeast of Berlin, in an area with large deposits of quartz sand (silica). During the economic boom period of the mid-1900s ("Gründerzeit"), there were about a dozen glassworks in the area. The Weißwasser plant later became a Philips/Valvo tube factory. Wehrmacht tubes manufactured in Weißwasser carry the factory location stamp "WW".

In 1938 Valvo/Philips also founded the "Studiengesellschaft zur Erforschung von Elektronengeräte mbH", short the "Studiengesellschaft"(Research Company). It was co-located in Hamburg, and specialized in "drift tubes", the predecessor of the klystron. It had rather limited production capacity, and was dissolved by the British occupational powers in 1946. Ref. 112. Philips/Valvo produced an estimated 6.7 million Wehrmacht-tubes. Ref. 103. May 1951, Philips-Valvo Werke GmbH was renamed back to Deutsche Philips GmbH. Valvo ceased to exist in 1975. Over the decades, Philips bought tube manufacturing companies in many countries, e.g., "Radio Technique" and "Dario" in France.

Fig. 77: advertising by Valvo (1933) and Philips (1939)

(source Philips advert: Funkschau, 1939, nr. 18)

The origins of TeKaDe go back to ca. 1858, when Johann Friedrich Heller opened the first electrical company in Nürnberg: a machine shop for the manufacturing of medical and physics devices, and... door bells. In 1860, his first apprentice was Johann Sigmund Schuckert, who dabbled in telegraphy equipment on the side, and founded "Schuckert & Co. Offene Handelsgesellschaft (OHG)" in 1885. The Schuckertwerke was acquired by Siemens-Halske in 1903, and combined with a Siemens-Halske electrical division to form Siemens-Schuckertwerke GmbH. Heller also expanded his activities to telegraphy equipment, and the company name is changed to "Friedrich Heller, Fabrik Elektrotechnischer Apparate" at the end of 1875.

In 1904 the company became insolvent and was bought by Felten & Guillaume in Köln (Cologne), originally a rope-making company founded in 1826, later a cable and wire company with a cable factory in Nürnberg. In 1912 Felten & Guillaume combine their operations in Nürnberg into the "Süddeutsche Telefon-Apparate, Kabel- und Draht-Werke A.G." (Southern-German Telephone Devices, Cable & Wire Works). The company has the telegraph address TeKaDe. Until August of 1927, their trademark is TKD (pronounced "Tay-Kah-Day" in English = "Te-Ka-De" in German).

In 1916, TeKaDe started its own tube manufacturing, including "multi-valve" tubes ("Mehrfachröhre") for Telefunken. At one point, a patent battle with Telefunken forced TeKaDe to halt its tube manufacturing - other than for Telefunken. In the early 1920s, their product range is expanded with broadcast radios, headsets, radio tubes, as well as cables and line amplifiers for the telephone system, etc. During the late 1920s, their overall monthly tube production volume was about 100 thousand. TeKaDe developed and manufactured mechanical TV sets from 1928-1936, and CRT-based ("Braunsche Röhre") TVs from 1937-1938.

Fig. 78: 1924 TeKaDe advertising

The tube factory in Nürnberg was bombed in January of 1944, and production was moved to Helmbrechts (ref. 111) and Asch (now in the Czech Republic). After the war, TeKaDe made "Ersatz" tubes out of Wehrmachtröhre for a while. For instance, the RV12P4000 was transformed into the 13F7, a substitute for the scarce CF7 tube. This was easy: the perforated metal shield was removed, the grid wire emanating from the top of the tube was shortened and capped, and the Bakelite base replaced with one compatible with the CF7. The nominal heater voltage of the CF7 was close enough that of the RV12P4000 (13 volt and 12.6 volt respectively). Similarly, the RV12P4000 was modified to a 4 volt heater voltage, and dubbed 4F7, a substitute for the AF7.

In 1949, Philips and Felten & Guillaume founded "Felten & Guillaume Fernmeldeanlagen-GmbH" (FGF) for telephone equipment, tubes, radios, and car phones. The latter included the "TeKaDe-B72", developed for the Deutsche Bundespost in 1958 for the - at the time - world's largest mobile phone network in the world, the "A-Netz". The phone weighed 16 kg (≈ 35 lbs) and cost about 16k Deutsche Mark (equivalent to ≈28k Euros in 2014, based on the average Germann inflation rate since 1958). In 1982, FGF was consolidated with other Felten & Guillaume divisions and Philips Data Systems, to form Philips Kommunikationsindustrie AG (PKI), later bought by AT&T.

Besides Telefunken, Valvo/Philips/Studiengesellschaft, and TekADe, there were many other companies involved with development and manufacturing of (specialized) Wehrmachtröhren, e.g. (ref. 1, 83, 84A/B):

• AEG
• Fernseh GmbH; cathode ray tubes (CRT), video cameras (e.g., 441 lines) for remotely controlled bombs, missiles, and aircraft (called "drones" these days, but invented in Germany during WW2).
• GEMA ("Gesellschaft für elektroakustische und mechanische Apparate mbH", Berlin) - sonar and radar specialist (e.g., developed the Freya, Mammut, Wassermann, Seetakt radars); many GEMA tubes were actually manufactured by AEG, Siemens, Lorenz, and Telefunken. Ref. 59.
• Koch & Sterzel (Dresden); magnetrons.
• Lorenz (Berlin); tube laboratories in Auerbach/Thuringia and Vienna/Austria (also a factory), factories in Mühlhausen (primatily acorn tubes) and Oberhohenelbe. Ref. 229R.
• Loewe/Opta (founded 1923 in Berlin; ref .85); radio tubes (incl. the RV12P2000), cathode ray tubes (CRT), magnetrons.
• Contrary to popular belief, "the" integrated circuit (IC) was not invented in the late 1950s by Jack Kilby (Texas Instruments) and Robert Noyce (Fairchild Semiconductor Corp., later founder of Intel). Yes, they did invent and patent miniaturized electronic circuits and a monolithic solid-state (silicon) IC in 1959. However, the monolithic IC concept actually clearly dates back to G.W.A. Drummer of the UK Royal Radar Establishment in 1952; ref. 86. My own definition of an IC is "a discrete electronic device that embodies multiple active and passive components, and their interconnections, in one envelope". Hence, it is actually the Loewe company (Dr. Siegmund Loewe (idea + patent in 1924) and Dr. Manfred von Ardenne (design) who invented and developed the first IC in the early 1920s: the multi-valve tube ("Mehrfachröhre"). For related patents, see ref. 87L-87S. A magnificent example of this is the 3NF tube (not to be confused with Telefunken's NF3 pentode of 1934). The 3NF is a single glass envelope (tube), containing three separate triode mounts, two fixed capacitors and four fixed resistors - enough to build a complete radio receiver by just adding a tuning coil, a variable tuning capacitor, a loudspeaker and batteries. The resistors and capacitors were each sealed in an individual glass tube inside the main tube, to prevent their out-gassing from contaminating the tube's vacuum. Ref. 87A-87J, 87T. The 3NF is a real piece of art, as is the WG33 (2 triodes, 1 tetrode, 3 capacitors, 6 resistors; 1933). The 3NF was the heart of the famous radio receiver "Loewe Ortsempfänger OE333". The motivation for multi-valves was threefold: reduce the production cost of radios, bypass competitor's patents (e.g., Marcony Co.), and reduce radio tax (at the time, Germany had a special sales tax on radios, that depended on the number of tubes). In 1926, the 3NF retailed for approximately ₤0.88 plus ₤0.39 tax (ref, 87K), equivalent to approximately €57 plus  €25 tax in 2018 (≈ US$67 and US$30). Note that multi-triodes were also built in the USA around 1925 and 1930 (e.g., the 6SN7), but they did not include other components.

Fig. 79: a "3NF" with close-up of the capacitors & resistors (center) and of the 3 triodes (right)

(source center photo: © H.-T. Schmidt, used with permission)

• Rectron GmbH (ref. 88, Berlin). As the name suggests, Rectron manufactured rectifier tubes. But also photo-cells, battery chargers, microphones, etc. The company was founded in 1925 in Berlin by Philips of the Netherlands (through their mailbox-company "Rectron", co-located at Philips' corporate headquarters in Eindhoven). Ref. 89.
• Blaupunkt (Berlin), video cameras
• In the 1920s, "Blaupunkt" (lit. "Blue Dot") was one of the tradenames of the company "Ideal-Radiotelefon- & Apparatefabrik GmbH" for some of their radio receivers and loudspeakers. Other tradenames of Ideal were: "Rotstern" (lit. Red Star"), "Grünkreuz" ("Green Cross"), and "Weißkreuz" ("White Cross"; headphones only). During the same period, Ideal marketed Ampladyn, Heliodyn, and Superdyn triodes under the Blaupunkt name (though they were manufactured by Huth/Telefunken, and later by Osram). In 1927, "Blaupunkt" replaced the "Ideal" name. In 1933, the Ideal company became part of Robert Bosch GmbH. Blaupunkt developed the world's first FM "UKW" car radio.
• Elektrizitätsgesellschaft "Sanitas" (Berlin; absorbed into AEG in 1957); "Röntgenrohre" = X-Ray tubes, magnetrons. Sanitas also invented the electric hairdryer in 1900 ("Föhn", registered trademark "Fön" since 1909).
• Siemens & Halske (Berlin, Erlangen, München)
• Hochohm Gesellschaft ("HOGES"; Berlin)
• Stabilovolt (Berlin; abbreviated to STV, StV, Stv, and stv)
• Funkstrahl-Gesellschaft für Nachrichtentechnik mbH, founded 1942 in Konstanz (on the lake of that name) as subsidiary of Julius Pintsch Maschinenfabrik und Beleuchtungs-Gesellschaft of Berlin - manufacturer of searchlight and signalling apparatus, light bulbs, centimeter-wave tubes, torpedo parts.
• OSRAM (Berlin; for AEG/Telefunken)
• Dr. E. F. Huth GmbH (Signalbau Huth, Berlin, Hannover)
• Seddig (Würzburg)
• Zeiss-Ikon (Dresden); cathode ray tubes (CRT)
• Reichspostzentralamt (RPZ, Berlin); drift tubes, klystrons
• Flugfunk-Forschungsinstitut Oberpfaffenhofen (FFO; the founder, Prof. Max Dieckman, was graduation professor of Rudolf Hell)
• Tungsram (ref. 22C, 90, 98); drift tubes, klystrons, magnetrons.
• Preßler
• Physikalisch-Technischen Reichsanstalt (PTR, Berlin); magnetrons

Factories were located in Germany and in German-controlled countries (Austria, Netherlands, Czechoslovakia, Hungary, Italy (e.g., Fabbrica Italiana Valvole Radio Elettriche (Fivre), in Milan). Note that the Heereswaffenamt was initially reluctant to generally involve the German tube industry, due to the fact that many tube companies had tight connections (incl. R&D exchanges) with partners in hostile countries.

Fig. 80: Stabilovolt advertising

(sources: 1939 "Wireless World", 1941 "Funk-Technische Monatshefte", 1955 "Frequenz", 1955 )

Fig. 81: 1930s advertising by Rectron and Huth, and female adoration for a phallic Blaupunkt/Ideal model

(source Blaupunkt/Ideal: G. Pahl, 1930, Bundesarchiv Bild 102-10295)

Fig. 82: mid-1930s Tungsram advertising

(note: the right-hand advert mentions Siemens as the distributor for Tungsram tubes)

REFERENCES

• Ref. 1: "Röhrenhistorie 4: Deutsche Wehrmachtsröhren 1933-1945", Wolfgang Scharschmidt, Funk Verlag Bernhard Hein e.K., 360 pp., ISBN: 978-3-939197-31-7 Highly recommended. [click here [pdf] for a 7 page extract on the publishers website]
• Ref. 2: "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. 3: "Das Heereswaffenamt" [pdf], Claus Espeholt, March 2016
• Ref. 4: "Aus der Entwicklungsgeschichte von Wehrmachts- und Luftfahrtröhren", Gerhard Salzmann, in "Funkgeschichte (Gesellschaft der Freunde der Geschichte des Funkwesens e.V.)", Nr. 56, 1987, pp. 12-14; Teil 2: Nr. 57, 1987, pp. 20-22; Teil 2 (second part 2): Nr.58, 1988, pp. 19-23; Teil 3: Nr. 59, 1988, pp. 20-24; Teil 4 und Schluß: Nr. 60, 1988, pp. 11-13.  See note 1.
• Ref. 5: "Wehrmachts-, Luftfahrt- und Spezialröhren 1936-1945", Gerhard Salzmann, in "Funkgeschichte" (Gesellschaft der Freunde der Geschichte des Funkwesens e.V.), Heft 26, 1982, pp. 128-144  See note 1
• Ref. 6: "Der Sammler 2B38 als Stromquelle für die mobile Funktechnik der Deutschen Wehrmacht" [battery for mobile radios of the Wehrmacht], Max Schindler, update of November 2014, 17 pp. (used with kind permission of the author; other publications of the author are here)
• Ref. 7: "RV 2 P 800 HF-Pentode Technische Daten und Streuwerte", Telefunken data sheet G.R.B. 11 D II (5000), 2 pp. Based on the square Telefunken logo used in this document, it was published after mid-1937.
• Ref. 8: "Spezial- und Wehrmachtsröhren, UKW-Röhren (λ = 10 - 1 m)" [pdf], Gerhard Bogner, Folge 6 of Teil 6 "Zeitraum 1934-1940" of "Entwicklung des UKW-Rundfunks", Funkgeschichte (Gesellschaft der Freunde der Geschichte des Funkwesens (GFGF) e.V.), Nr. 141/2002
• Ref. 9: "Problematik und Entwicklungsbeginn von UKW-Empfängerröhren" [pdf], Gerhard Bogner, Folge 3 of Teil 6 "Zeitraum 1934-1940" of "Entwicklung des UKW-Rundfunks", Funkgeschichte , Nr. 141/2002
• Ref. 10: "All You Ever Needed to Know--and Even More--About European Tube-Numbering Schemes",  [pdf] Martin Faust (DK9QT)
• Ref. 11: "Tube number systems", Frank Philipse; source: "Frank's Electron tube Pages"
• Ref. 12: "NF4 HF-Pentode Technische Daten und Streuwerte", Telefunken data sheet G.R.B. 7 D (5000), 2 pp. Based on the square Telefunken logo used in this document, it was published after mid-1937.
• Ref. 13: "Wehrmachtsröhren", pp. 72-79 in "Röhrencodierungen der 20er und 30er Jahre", Gerhard Salzmann, Vol. 1 of "Schriftenreihe zur Funkgeschichte", Gesellschaft der Freunde der Geschichte des Funkwesens (GFGF e.V.), 1988, Winkler Verlag, 191 pp. ISBN 3-924517-25-8
• Ref. 14: "Wehrmachtröhren", Telefunken data sheet C.R.B. 29 D VII (4000), September 1944, 4 pp.
• Ref. 15: "Zur Geschichte der RV 12 P 2000 - ein nostalgischer Rückblick auf eine legendäre Röhre", Volume 4 of "Schriftenreihe zur Funkgeschichte", Gerhard B. Salzmann, Gesellschaft der Freunde der Geschichte des Funkwesens (Ulm, Germany), Walz Verlag, 1994, 88 pp., ISBN/ISSN: 3-9802576-2-2  See note 1
• Ref. 16: "Die RV12 P 2000 - Story", Joachim Gittel (Jogis Röhrenbude), June 2008. Note: this write-up has not been updated/corrected since then! See ref. 110 for corrections.
• Ref. 17: "Universalröhre: RV 12 P 2000 Kennzeichnung, Bauform, Bauartänderung im Laufe der Entwicklung als Vorkriegs-, Kriegs- und Nachkriegsausführung", Gerhard B. Salzmann, 1997
• Ref. 18: "RV 12 P 2000 HF-Pentode Technische Daten und Streuwerte", Telefunken data sheet G.R.B. 3 D (5000), 2 pp. Based on the square Telefunken logo used in this document, it was published after mid-1937.
• Ref. 19: "55 Jahre RV 12 P 2000", Conrad H. von Sengbush, in "Funkgeschichte" (Gesellschaft der Freunde der Geschichte des Funkwesens e.V.), Heft 75, 1990, pp. 18-20  See note 1
• Ref. 20: "Heute letztmals: RV 2 P 2000", p. 8 in "QRV - Die Zeitschrift der Radio-Amateure", February-March 1947
• Ref. 21: "Die Entwicklung der kleinen Wehrmachtsröhren in der Bauform für Ring- und Patronenfassung (RV12P2000)", Gerhard Bogner, pp. 86-87 in "Funkgeschichte - Mitteilungen der Gesellschaft der Freunde der Geschichte des Funkwesens (GFGF)", Nr. 108, 1996  See note 1
• Ref. 22: "Röhrenhistorie 2: Firmenporträts", Wolfgang Scharschmidt, Funk Verlag Bernhard Hein e.K., 600 pp., ISBN: 978-3-939197-29-4
• Ref. 22A: "RRF Radio-Röhren-Fabrik Valvo HH-Loksted und seine Röhren", pp. 1-38  See note 1
• Ref. 22B: "Ein Jahrhundert Telefunken-Röhren", pp. 46-103  See note 1
• Ref. 22C: "Auszug im original Text aus "The History of Tungsram 1896-1945"", pp. 39-46 (see ref. 98 for complete publication)  See note 1
• Ref. 23: "Receiver and Transmitter Development in Germany 1920-1945", Arthur Bauer (PA0AOB), IEE Int'l Conf. on 100 Years of Radio, London, September 1994
• Ref. 24: "Elektronenröhre", Section 3.2.1. in "Blitz und Anker, Band 1: Informationstechnik - Geschichte und Hintergründe", Joachim Beckh, August 2005, Books on Demand GmbH, 560 pp., ISBN: 3833429968
• Ref. 25: p. 14 "Telecommunications in War", S.A. Angwin, J. of the IEE, Part IIIA: Radiocommunication, Vol. 94, Issue 11, Nov. 1947, pp. 7-15
• Ref. 26: "Röhrenbezeichnungen vor 1934 – Teil 1, Die Kennzeichnungssysteme der großen Röhrenhersteller", Thomas Lebeth, in "Radiobote", Vol. 2, Nr. 8, March-April 2006, pp. 12-14. Source: radiobote.at.
• Ref. 27: "Röhrenbezeichnungen vor 1934 – Teil 2, Die Kennzeichnungssysteme der Marken Triotron, Orion, Sator, und Tungsram", Thomas Lebeth, in "Radiobote", Vol. 2, Nr. 9, May-June 2006, pp. 11-13. Source: radiobote.at.
• Ref. 28: "RV12 P 4000 - Technische Daten und Streuwerte", Telefunken data sheet G.R.B. 12 D II (5000), 2 pp. Based on the square Telefunken logo used in this document, it was published after mid-1937
• Ref. 29: "FUNKSCHAU-Tabelle der Wehrmachtröhren", Ludwig Ratheiser (ed.), Funkschau-Verlag, München, 1944, 39 pp., 1st. ed.; "Autorisierter sonderdruck aus dem “Handbuch der Wehrmachtröhren“, Verlag Walter de Gruyter & Co., Berlin; also in ref. 56  [15 MB]
• Ref. 30: "The gyrator, a new electric network element", B. D. H. Tellegen, Philips Research Reports, Vol. 3, No. 2, Apr 1948, pp. 81-101
• Ref. 31: "Introduction to the Radio Valve" [pdf], F. Langford-Smith, chapter 1 (pp. 1-12) of part 1 of "Radiotron Designers Handbook", Radio Corporation of America (RCA), 4^th ed., 1952, 1482 pp.
• Ref. 32: "Electron Tubes in World War II", J.E. Gorham, Proc. of the I.R.E., Vol. 35 , Issue 3, March 1947, pp. 295-301
• Ref. 33: "German World War II communications receivers; Parts I-IV", Dick Rollema (PA0SE), in "CQ Magazine", 8/1980, 12/1980, 5/1981, 8/1981
• Ref. 34: "RV 12 P 2000 und andere Spezialröhren als Ersatz für normale Radioröhren und für den Neuaufbau von Empfangsgeräten/Neubauschaltungen mit Selen-Gleichrichter", Günter Heine, Rudolf Wollenschläger, Deutscher Funk-Verlag, Berlin, October 1946, Heft 19, 19 pp. (also reprinted in 1995 by Freundlieb Verlag Historischer Technikerliteratur)  [13 MB]
• Ref. 35: "Die universelle Verwendbarkeit von kommerziellen Röhren", H. Zimmerman, in "Hamburger Funk-Technik für den Fachmann und den Bastler", Sonderdruck Nr. 2011, Hamburg, June 1947, 4 pp. (von der Militärregierung genehmigt - published with permission of the military government!)
• Ref. 36: "Guten Empfang bringt die BASTELFREUND-Schaltung", "Bastelfunk - Schaltung 112: Einkreis - 4- Röhrenempfänger für Gleich-, Wechsel-, und Batteriestrom" (Sept. 1940, 4x RV 2,4 P 700, "Bastelfunk - Schaltung 119: Zweikreis - 4- Röhrenempfänger für Allstrom" (3x RV12P2000), "Bastelfunk - Schaltung 120: Zweikreis - 4 - Röhrenempfänger für Allstrom" (3x RV12 P 2000), Alexander Frentzel, München.
• Ref. 37: "Der Rundfunk-Bastler - 7 erprobte Schaltungen. Für den erfahrenen Bastler zum Selbstbau unter Verwendung von Spezialröhren", Richard Grüneberg, Deutscher Funk-Verlag GmbH Berlin, Issue A, 1946, 149 pp; Issue B, new and expanded edition, 1947, 27 pp.  [28 MB]
• Ref. 38: "Moderne Radioschaltungen für Bastler und Werkstatt", 3^rd ed., May 1947, WIJO-Vertrieb, Berlin-Köpenick, 22 pp.
• Ref. 39: "Gerätebeschreibung: Nachkriegseinkreiser mit 3x RV 12 P 2000", Herbert Börner, Funkgeschichte (Gesellschaft der Freunde der Geschichte des Funkwesens e.V.), Heft 48, 1986, pp. 120-122  See note 1
• Ref. 40: "Enigma", D.W. Rollema (PA0SE), in "Wireless World", Vol. 89, Nr. 1569, June 1983, p. 49-54
• Ref. 41: "The Tiltman Break", F.L. Bauer, Appendix 5, pp. 370, 371 in "Colossus: the secrets of Bletchley Park's codebraking computers", B. Jack Copeland (ed.), Oxford University Press, 2006, ISBN 019284055X, 462 pp.
• Ref. 42: "Lorenz and Colossus" [military cryptography], A.E. Sale, Proc. of the 13th IEEE Computer Security Foundations Workshop, (CSFW-13), 2000, pp. 216-222
• Ref. 43: "Die Geschichte der Hörhilfen, Was sie wurden, was sie sind", Aubrey Miller, in "Hörakustik", Nr. 5, May 1995, Median-Verlag, Heidelberg
• Ref. 44: p. 287 in "Bekanntmachung der Abteilung Post- und Fernmeldewesen der Provinzialverwaltung Sachsen", in "VOBI PS", Vol. 2 (1946), Nr. 28, 6 July 1946; referenced on p. 142 in "Zensur und Zensoren - Medienkontrolle und Propagandapolitik unter sowjetischer Besatzungsherrschaft in Deutschland", Strunk, P., Akademie Verlag, 1996, 183 pp., ISBN 978-3-05-002850-71996.
• Image also appeared on p. 179 of "25 Jahre Telefunken - Festschrift der Telefunken-Gesellschaft 1903-1928", 345 pp. Source: nvhrbiblio.nl, accessed March 2020. [pdf, 41 MB]
• Ref. 45: "Some hardly known aspects of German military communications during World War Two", Arthur O. Bauer, lecture at 2008 Autumn Symposium of the Defence Electronics History Society (DEHS), Shrivenham/UK, 16 October 2008, 26 pp.; source: www.cdvandt.org
• Ref. 46: "Wehrmachtsröhren Farbcodierung" [color-coding of Wehrmacht-tubes]
• Ref. 47: "Röhrenfarben der Wehrmacht" [color-coding of Wehrmacht-tubes], source: Museum für historische Wehrtechnik e.V.
• Ref. 48: "Ominöse Lochscheibe in der RV 12 P 4000 [Was hat diese Scheibe in der Röhre zu bedeuten?]", Hans-Peter Bölke, in "Funkgeschichte (Gesellschaft der Freunde der Geschichte des Funkwesens e.V.)", Heft 143, 2002, p. 155  See note 1
• Ref. 48A: (response to 82): "Zweck der Lochscheibe in der RV 12 P 4000", Gerhard Bogner, Funkgeschichte, Vol. 25, Heft 144, 2002, pp. 205, 206  See note 1
• Ref. 49: "The Story of the Valve" [pdf], C. H. Gardner, in "Radio Constructor", 1965, Data Publications
• Ref. 50: "The RCA Radiotron Manual", RCA Technical Series No. R-10, RCA Radiotron Co., Inc., 1932 (1937?), 87 pp.
• Ref. 51: "Manufacture of valves by machinery", Hall, T.F.B., How, A.H., in "Journal of Scientific Instruments", Vol. 16, Nr. 9, September 1939, pp. 277-285
• Ref. 52: "Vacuum Sealing Techniques", Roth, A., American Institute of Physics Publ., 1997, 860 pp. , ISBN-10: 1563962594
• Ref. 53: "Preßglas-Röhren", Reinhard Kretzmann, in "Funktechnische Monatshefte (FTM)", Heft 10, 1941, pp. 156-159
• Ref. 54: "40 Jahre VALVO - Empfängerröhren", E. Schaaff, W. Sparbier, pp. 13-31 in "Valvo Berichte", Band X, Heft 1/2, Sonderheft zum vierzigjährigen Firmenjubiläum, April 1964, 292 pp.  [31 MB]
• Ref. 55: "A new principle of construction for radio valves", P.C. Cath, Philips Technical Review, Vol.1, No.6, 1939, pp.162-166
• Ref. 56: "A New All-Glass Valve Construction", F. Prakke, J.L.H. Jonker, M.J.O. Strutt, The Wireless Engineer, May 1939
• Ref. 57: "Recent developments in miniature tubes", Salzberg, B., Burnside, D.G., Proc. of the Institute of Radio Engineers (IRE), Vol. 23, Issue 10, October 1935, pp. 1142-1157; also published as pp. 292-307 in ref. 67
• Ref. 58: "Electron Tubes - Volume I (1935-1941)", Goldsmith, A.N., Van Dyk, A.F., Burnap, A.S., Dickey, E.T., Baker, G.M. (eds.), RCA, March 1949, 483 pp.
• Ref. 57: "Recent developments in miniature tubes", Salzberg, B., Burnside, D.G., Proc. of the Institute of Radio Engineers (IRE), Vol. 23, Issue 10, October 1935, pp. 1142-1157; also published as pp. 292-307 in ref. 67
• Ref. 58: "Electron Tubes - Volume I (1935-1941)", Goldsmith, A.N., Van Dyk, A.F., Burnap, A.S., Dickey, E.T., Baker, G.M. (eds.), RCA, March 1949, 483 pp.
• Ref. 59: "GEMA: birthplace of German radar and sonar", Harry von Kroge, Taylor & Francis Publ., 2000, 206 pp., ISBN 0750307323; (English translation of the book "Gema -Berlin, Geburtsstätte der deutschen aktiven Wasserschall- und Funkortungstechnik", Harry von Kroge, self-published, 1998, 224 pp., ISBN 3-00-002865-X.
• Ref. 60: "Theory and Operating Characteristics of the Thermionic Amplifier", H.J. van der Bijl, Proc. of the Institute of Radio Engineers (IRE), Vol. 17, April 1919, pp. 97-128; reprinted in Proc. of the IEEE, Vol. 86, No. 12, December 1998, pp. 2455- 2467
• Ref. 61: "The Remarkable Dr. Hendrik van der Bijl", D.J. Vermeulen, Proc. of the IEEE, Vol. 86, No. 12, December 1998, pp. 2445-2454
• Ref. 62: "RL 2 P 3 Pentode für Enstufen u. Sendezwecken Technische Daten", Telefunken data sheet G.R.B. 5 D II (5000), 2 pp. Based on the square Telefunken logo used in this document, it was published after mid-1937.
• Ref. 63: "Bakelite - Seine herstellung und Verwendung" [Bakelite, its manufacture and application], Bakelite Gesellschaft mbH, document 668/3537/Wbr, 1937, 44 pp.
• Ref. 64: "Moulding bakelite materials: the design, production, and use of moulds for synthetic resin compounds", Volume 3 of Machinery's yellow-back series, Machinery Publishing Co., Ltd., 2^nd ed., 1942, 62 pp.
• Ref. 65: "Kunstharzpreßstoffe und andere Kunststoffe: Eigenschaften, Verarbeitung und Anwendung", Walter Mehdorn, Springer Verlag, 3^rd ed., 1949, 354 pp., ASIN: B0000BLFXN [note: the posted file only contains some selected pages].
• Ref. 66: "Liste der Presswerk-Codes der Materialprüfungsanstalt 1938" [listing of Kunststoffkenzeichen]
• Ref. 67: "Isolierstoff-Prägemarken - Stand: 1954"
• Ref. 68: "Bekanntmachung über Kunstharz-Preßmassen für typisierte und überwachte Preßstoffe", pp. 282-284 in "Elektrotechnische Zeitschrift (ETZ)", Vol. 61, Issue 10, 7 March 1940, and p. 303 in Vol. 61, Issue 12, 21 March 1940
• Ref. 69: "Das Königliche Materialprüfungsamt der Technischen Hochschule Berlin auf dem Gelände der Domäne Dahlem beim Bahnhof Groß-Lichterfelde West – Denkschrift zur Eröffnung", Adolf Martens, Manfred Guth (eds.), Julius Springer Verlag, Berlin, 1904, 380 pp.
• Ref. 70: "Abnahmestempel auf Funkgeräten und Bauteilen" [acceptance stamps on radio equipment and components], Werner Thote, in "Radiobote", Vol. 5, Nr. 29, Sept-Oct 2010, pp. 21-27. Source: radiobote.at.
• Ref. 71: "Die MAN: eine deutsche Industriegeschichte", Johannes Bähr, Ralf Banken, Thomas Flemming, 2008, C.H. Beck Publ., 544 pp., ISBN-10: 3406577628
• Ref. 72: "Die Gegenspieler in Europa: Philips und Telefunken" [pdf] in "Radio-Katalog 2: Deutschland, Österreich, Schweiz", Ernst Erb, April 2006, 400 pp., ISBN-10: 3881806520
• Ref. 73: "Die Empfängerwechselrichter", Werner Thote, in "Radiobote", Vol. 5, Nr. 26, March-April 2010, pp. 21-25. Source: radiobote.at.
• Ref. 74: sheet 26-29 in "Philips Valvo Works, Hamburg, including Studiengesellschaft, Stellingen and subsidiary factory at Hornsburg" [incl. production volumes], Section 2.23, A.L. No. 4, 1946, SubCommittee for the Investigation of German Electronic and Scientific Organisation (SIGESO Reports Vol. 4, Part-2). Source: cdvandt.org
• Ref. 75: "The Lieben Valve: a German "universal amplifier"", Oskar Blumtritt, 2004 IEEE Conf. on the History of Electronics CHE2004, Bletchley Park, UK, June 2004, 10 pp. [incl. discussion of the Lieben Consortium]
• Ref. 76: kartels
• Ref. 76A: "Massenproduktion im globalen Kartell - Glühlampen, Radioröhren und die Rationalisierung der Elektroindustrie bis 1945", Günther Luxbacher, Verlag für Geschichte der Naturwissenschaften und der Technik (GNT), 2003, 490 pp., ISBN 978-3-928186-68-1
• Ref. 76B: "Die Gegenspieler in Europa: Philips und Telefunken", in "Radiokatalog - Band 2: Deutschland, Österreich, Schweiz", Ernst Erb, Verlag für Technik, 2006, 400 pp.
• Ref. 76C: "Transnational Corporations in Electrical Industry", Economic and Political Weekly, Vol. 14, No. 3 (Jan. 20, 1979), pp. 103, 105-106
• Ref. 76D: "Die internationale Stellung Telefunkens", Carl Schapira, pp. 52-59 in: "25 Jahre Telefunken 1903 – 1928; Festschrift der Telefunken-Gesellschaft", Fritz Schröter, Ernst Zechel, Otto Nairz (editors), Berlin, 1928, 328 pp.
• Ref. 76E: "Webs of Power - International Cartels and the World Economy", Kurt Rudolf Mirow, Harry Mauerer, Houghton Mifflin Harcourt Publishing Company, 1982, 525 pp., ISBN 0395305365
• Ref. 76F: "Zur Entstehung der elektronischen Technologie in Deutschland und den USA. Der Beginn der Massenproduktion von Elektronenröhren 1912-1918", Hartmut Petzold, in "Sozialgeschichte der Technik", Vol. 13 (1987), Nr.3, pp. 340-367 of "Geschichte und Gesellschaft - Zeitschrift für historische Sozialwissenschaft", Vandenhoeck & Ruprecht Publ.  [28 MB]
• Ref. 77: "Marksteine der Telefunken-Entwicklung von 1903 bis 1945", in "Telefunken-Zeitung", 23. Jg., Heft 87/88, September 1950, pp. 5-8
• Ref. 78: "25 Jahre Telefunken 1903 – 1928; Festschrift der Telefunken-Gesellschaft", Fritz Schröter, Ernst Zechel, Otto Nairz (editors), Berlin, 1928, 328 pp. Source: www.cdvandt.org.
• Ref. 79: "Ein halbes Jahrhundert für die Bauelemente" (50 years Valvo), G. Lorenz, Funkschau Nr. 7, 1974, pp. 219-222
• Ref. 80: "Stationen in der Geschichte des Hauses VALVO", O. Stodemund, pp. 7-12 in "Valvo-Berichte", Band X, Heft 1/2 : "Sonderheft zum vierzigjährigen Firmenjubiläum", Valvo GmbH, Hamburg, April 1964
• Ref. 81: "Visit to C.H.F. Müller A.G., Röntgenstr. 24, Bahrenfeld, Hamburg" (8 Oct 1945), C.G. Lloyd, G.J. Thiessen, Combined Intelligence Objectives Sub-Committee (CIOS) Item No. 21, British Intelligence Objectives Sub-Committee (BIOS) Target Numbers 1/132(e), C7/193, C21/744 (Final Report No. 201), 7 pp. Source: Foundation for German communication and related technologies.
• Ref. 82: "Behavioral Rules in R&D Strategies: German and Dutch Electrical Equipment Enterprises between the Wars", Renato Giannetti, Mauro Lombardi, Business and Economic History, Vol. 24, no. 1, Fall 1995, pp. 206-217
• Ref. 83: "Wehrmacht-Röhren" website by H.-T. Schmidt, including "Farbcode der Wehrmachtröhren" (color coding) [in German]
• Ref. 84A (was 127): pp. 209-218 [pdf]
• Ref. 84B (was 128): pp. 218-229 [pdf]
• Ref. 85: "Ortsempfänger, Volksfernseher und Optaphon: Die Entwicklung der deutschen Radio- und Fernsehindustrie und das Unternehmen Loewe, 1923-1962" ["Ortsempfänger", "Volksfernseher", and "Optaphon": The Development of German Radio and Television Industry and the Loewe Company, 1923-1962"], Kilian J.L. Steiner, Klartext Verlag, 2005, 381 pp., ISBN 389861492.
• A review of this book by P. Jelavich can be found here.
• Ref. 86: "Genesis of the monolithic integrated circuit", p. 45-50 in "A History of the World Semiconductor Industry", P.R. Morris, Vol. 12 of "IEE History of Technology series", 1990, 160 pp., ISBN-10: 0863412270. This book can be accessed via Google books here.
• Ref. 87: Loewe multiple-tubes
• Ref. 87A: "Tubes within Tubes" [Loewe "Mehrachröhre"], G.C.B. Rowe, Radio News, July 1926, pp. 30-31 + September 1926 "Tubes within Tubes", C.G.B. Rowe, Radio News, July 1926, 30-31, plus addendum from "Radio News", September 1926.
• Ref. 87B: "Die Loewe-Dreifach-Röhre", Bruno Wienecke [a personal account by the first employee of Dr. Loewe], in "Funkgeschichte (Gesellschaft der Freunde der Geschichte des Funkwesens e.V.)", Nr. 57, 1987, pp. 29-32  See note 1
• Ref. 87C: "Die neuen Mehrfachröhren", in "Funk Bastler (Fachblatt des funktechnischen Vereins zu Berlin / des deutschen Radioclubs zu Berlin und des süddeutschen Radioclubs zu München), 1926, Nr. 44, pp. 537-540
• Ref. 87D: "Die 3 NF von Loewe", Eduard Steinbach, in "Funkgeschichte", Nov/Dec 1985, p. 211
• Ref. 87E: "Die Loewe Röhre 3NFB – Analyse einer Mehrfachröhre" [pdf], Gerhard Eisenbach, January 2008
• Ref. 87F: "Die Mehrfachröhre", Eugen Nesper, Walter Kunze, Fischer-Druck G.m.b.H., 1928, 99 pp.
• Ref. 87G: "Die Mehrfachröhre und ihre Verwendung im Selbstbau: Vom Erfinder authorisierte Darstellung durch Dr. Funk eingerichtet“, Vol. 4 of "Dr. Funk' s wohlfeile Rundfunktechnik", Rufu-Verlagsgesellschaft m.b.H., 1926, 80 pp.
• Ref. 87H: "Loewe-Dreifachröhre als weltweit erster integrierter Schaltkreis", Martin Steyer (DK7ZB), in "Funkamateur", Nr. 1, 2017, pp. 28-30. Retrieved 9 May 2019. [pdf] See note 1
• Ref. 87J: "The world's first integrated circuit", William A. Gold, in "Electronics Australia", January 1976, pp. 24, 25.
• Ref. 87K: "The Loewe-Radio Company's Exhibit", in "Experimental Wireless & The Wireless Engineer", Vol. III, Nr. 38, November 1926, pp. 654-658.
• Ref. 87L: "Vakuumröhre" [dual valve], Siegmund Loewe, Swiss patent nr. 98671, applied 29 March 1921, awarded 16 April 1923, 6 pp.
• Ref. 87M: "In Widerstandsverstärkerschaltung betriebene Mehrfachröhre" ["multi-tube tube with resistor coupled stages"], Sigmund Loewe, Reichspatent Nr. 614229, applied 13 May 1926, awarded 16 May 1935, 5 pp.
• Ref. 87N: "Mehrfachröhre" ["multple tube tube"] Siegmund Loewe, Reichspatent Nr. 532638, applied 20 July 1926, awarded 20 August 1931, 4 pp.
• Ref. 87P: "Mehrfachröhre mit eingebauter Widerstandsverstärkerschaltung und in Serie geschalteten Kathoden, insbesondere für Netzanschluß", Siegmund Loewe, Reichspatent Nr. 484374, applied 20 July 1926, awarded 3 October 1929, 3 pp.
• Ref. 87Q: "Mehrfachröhre mit eingebauten, aus hochohmigen Widerständen und Kondensatoren bestehenden Kopplungselementen", Siegmund Loewe, Reichspatent Nr. 454530, applied 20 July 1926, awarded 22 december 1927, 3 pp.
• Ref. 87R: "Empfangsanordnung, bestehend aus einer Mehrfachröhre mit Widerstandskopplung und eingebauten Kopplungselementen für Hochfrequenzverstärkung in Verbindung mit einer ebensolchen Mehrfachröhre für Niederfrequenzverstärkung", Siegmund Loewe, applied 6 August 1926, awarded, 7 June 1928, 5 pp.
• Ref. 87S: "Schaltungsweise fuer widerstandsgekoppelte Mehrfachröhren mit eingebauten Kopplungselementen", Siegmund Loewe, applied 27 July 1926, awarded 22 December1927, 5 pp.
• Ref. 87T: "New Radio developments in Germany", S. McClatchie, in "Radio News", Vol. 7, No. 6, December 1925, pp. 782-783, 933. Source: worldradiohistory.com, retrieved April 2023.
• Ref. 88: "Spurensuche zur Identität und Geschichte der RECTRON-Gesellschaft mbH, Berlin", Winfried Müller, pp. 63-68 in "Funkgeschichte - Mitteilungen der Gesellschaft der Freunde der Geschichte des Funkwesens (GFGF)", Vol. 26, Nr. 148, April/May 2003  See note 1
• Ref. 89: "Leserbrief mit Hinweis zum RECTRON-beitrag aus FG 148", Werner Diedrich, pp. 286-287 in "Funkgeschichte - Mitteilungen der Gesellschaft der Freunde der Geschichte des Funkwesens (GFGF)", Vol. 26, Nr. 151, October/November 2003. See note 1
• Ref. 90: "Tungsram's positioning strategies on the world market in the interwar period - Why not Europe? Sources of economic growth", Mária Hidvégi, European Science Foundation / GlobalEuroNet, Summer School 2007
• Ref. 91: "Technical Problems in the Construction of Radio Valves", Th. P. Tromp, pp. 317-323 in "Philips Technical Review", Vol. 6, Nr. 11, November 1941.
• Ref. 92: "Aufbautechnik der Empfänger- und Verstärkerröhren", pp. 44-45 of Chapter 5 in "Das große Röhren-Handbuch", Ludwig Ratheiser, Franzis Verlag GmbH, 1995 (reprint of 1955 ed.), 296 pp, ISBN: 377235064X
• Ref. 93: "Ein Beitrag zur Geschichte der Stahlröhrenentwicklung – Die Abstimmung des Stahlröhrenprogrammes, Teil 2", Thomas Lebeth, pp. 15-17 in "Radiobote", Jg. 5, Heft 25, Jan-Feb 2010. Source: radiobote.at. Part 1 (pp. 9-13 in Vol. 4, Nr. 24, November/December 2009) can be found here.
• Ref. 94: "Das Heereswaffenamt und die KWG im "Drittem Reich" - die militärischen Forschungsbeziehungen zwischen 1918 und 1945" [pdf], Burghard Ciesla, pp. 32-76 in "Gemeinschaftsforschung, Bevollmächtigte und der Wissenschafttransfer - Die Rolle der Kaiser-Wilhelm-Gesellschaft im System kriegsrelevanter Forschung des Nationalsozialismus", Helmut Maier (ed.), Wallstein Verlag, 2007, 613 pp., ISBN-10: 3835301829
• Ref. 95: "The proliferation of tube types", Joachim Goerth, 2004 IEEE Conf. on the History of Electronics, Bletchley Park/UK, June 2004, 17 pp.  [pdf]
• Ref. 96: "Einheitsröhreserie" [standardized tube series], Reinhard Kretzman, in "Funk-Technische Monatshefte (FTM)", Heft 11/12, 1942, pp. 157-160; source: www.cdvandt.org
• Ref. 97: "Inspection of Philips Works at Eindhoven, September 23-26, 1944", Combined Intelligence Objectives Sub-Committee (CIOS); CIOS file No. III-1 (transcribed and annotated by Arthur Bauer; source: www.cdvandt.org
• Ref. 98: "The history of Tungsram 1896-1945", Károly Jeney, Ferenc Gáspár, History Committee of Tungsram, István Harkay (ed.), Erwin Dunay (transl.), 1990, 292 pp. [Tungsram, Philips, INRACO/Phoebus, RCA]. Source: mek.oszk.hu, accessed 7 November 2021. [pdf, 44 MB]
• Also excerpted in German as pp. 39-46 in "Röhrenhistorie Band 2. Firmenporträts", Wolfgang Scharschmidt, ISBN: 978-3-939197-29-4, 600 pp., see ref. 22.
• Ref. 99: Section II "System of Supply within Germany" and Section III "System of Supply of the Field Army" of Chaper VI "Supply, Evacuation, and Movements" in "Handbook on German Military Forces", U. S. War Department Technical Manual TM-E 30-451, 15 March 1945; reprinted by Louisiana State University Press, 1995, 670 pp., ISBN-10: 0807120111
• Ref. 100: "BA-, BAL-, Wa.A.- und W.ab-Stempel auf Röhren" [pdf], Werner Thote, discussion tread in the Forum of Radiomuseum.org, March 2008 - January 2009
• Ref. 101: "Abkürzungen", p. 5 in "Dienstanweisung für die Bauaufsichten (BAL) des Reichsluftfahrtministeriums", Teil 1, "Aufgabengebiet", 1 August 1940 (supersedes issue of 1 April 1937), Luftwaffen Dienstvorschrift 61/1 (L. Dv. 61/1), 33 pp.; source: cdvandt.org
• Ref. 102: "Die Telefunkenröhren und ihre Geschichte", Rukop, H., pp. 114-154 in "25 Jahre Telefunken 1903 – 1928; Festschrift der Telefunken-Gesellschaft", Fritz Schröter, Ernst Zechel, Otto Nairz (editors), Berlin, 1928, 328 pp.
• Ref. 103: "25 Jahre Valvo-Röhren", in "Funkschau", Vol. 21, 1949, Heft 5, p. 77
• Ref. 104: "Verwendung der Telefunken-Röhre RV 12 P 2000", Rudolf Dreibholz, Telefunken Rö.E. (L. Ratheiser), Berlin, 27 pp. Source: lucafusari.altervista.org
• Ref. 105: "Elektronenröhren für Panzerfunkgeräte", Chapter 22.2.4 in "Funk- und Bordsprechanlagen in Panzerfahrzeugen", Band 3 of "Die deutschen Funknachrichtenanlagen bis 1945", H.-J. Ellisen, Marketing & Technik Verlag, 1991, 240 pp., ISBN 3928388010
• Ref. 106: "Aufbautechnik der Empfänger- und Verstärkerröhren", pp. 44-45 of Chapter 5 in "Das große Röhren-Handbuch", Ludwig Ratheiser, Franzis Verlag GmbH, 1995 (reprint of 1955 ed.), 296 pp, ISBN: 377235064X
• Ref. 107: Normblatt DIN 7701 "Kunstharz-Preßstoffe, warmgepreßt" [hot-moulded synthetic plastics)], 1936; Issue 2, 1938 "Kunstharzpreßstoffe, Kunsstoffe" [molded synthetic resin, plastics]
• Ref. 108:
• Ref. 108A: "Development and Production of the New Miniature Battery Tubes", N.R. Smith, A.H. Schooley, in "RCA Review", April, 1940 (also: pp. 375-381 in ref. 67).
• Ref. 108B: "Microwave tube development in Germany from 1920-1945", H. Döring, in "International Journal of Electronics", Volume 70, Issue 5, May 1991, pages 955 – 978“ (original German version of this paper appeared in "Frequenz", nr. 43, 1989, pp. 277–283 and 309–314)
• Ref. 108C: "Reliability in Miniature and Sub-Miniature Tubes", P.T. Weeks, in "Proc. of the Institute of Radio Engineers (IRE)", May 1951, pp. 499-503
• Ref. 108D: "The Design and Development of Three New Ultra-High-Frequency Transmitting Tubes", C.E. Haller, Proc. of the Institute of Radio Engineers (IRE), January 1942, pp. 20-26
• Ref. 109: "Die Röhre in Ulm", Gerhard Bogner, in "Funkgeschichte", Nr. 107, 1996, pp. 63-67  See note 1
• Ref. 110: "Details zur Entwicklung der RV 12 P 2000" [details of the development of the RV 12 P 2000], Heinz Trochelmann, presented at the 25^th annual meeting of the Funkhistorischer Interessenkreis, Eschwege/Germany, 26-29 April 2018.  See note 1
• Ref. 111: "Electronic Valve (Tube) Factories TeKaDe, Helmbrechts and Philips; Minden", Combined Intelligence Objectives Sub-Committee (CIOS); CIOS file No. XXIV-26,27, June 6^th, 1945, 18 pp.; source: www.cdvandt.org. Accessed 10 June 2019.
• Ref. 112: "Philips Valvo Works, Hamburg Hammerwerke (Valve Works), Minden C.H. Müller A.G. (X-Ray Tube Factory) Hamburg", British Intelligence Objectives Sub-Committee (BIOS), Final Report No. 65, 18 pp. Source: Foundation for German communication and related technologies; Accessed 10 June 2019.
• Ref. 113: "Röhren, Rundfunk und kurze Wellen" [tubes,broadcast radio, short wave], H. Rukop, K. Steimelund, H.Rothe, pp. 165-180 in "50 Jahre Telefunken - Festschrift zum 50 jährigen Jubileum der Telefunken Gesellschaft für drahtlose Telegraphy m.b.h. - Gleichzeitig als 100. Ausgabe der Telefunken Zeitung", Vol. 26, Nr. 100, May 1953, 164 pp. Retrieved 19 February 2020.
• Ref. 113: Wehrmacht radios with RV12 and RL tubes:
• Ref. 114A: "Dreistufiger 20-Watt-Sender für das 10-m-Amateurband“ [20W.S.c. used post-war for amateur radio purposes], H. Bürkle, in "Funk-Technik", Nr. 1, January,1950 (January issue 1 of 2), pp. 14-15.
• Ref. 114B: "Ein Empfänger für das 10-m-Amateurband" [7-tube superhet Wehrmacht VHF receiver "Ukw.E" ("Emil") used post-war for amateur radio purposes, 27.2-33.3 MHz (40.3-44.7 MHz for Ukw.E.m), Ukw.E.c1 "Cäsar": 8x RVP12P4000, 1x STV75/15; Ukw.E.d1: 9x RV12P2000], H. Bürkle, in "Funk-Technik", Nr. 14, 1950 (July issue 2 of 2), pp. 428-430.
• Ref. 229R: "Das Auge am Marktgeschehen – Die Lorenz-Röhre und der Sieg nach 1945" ["Watching the market - the Lorenz valve and victory after 1945"], Jakob Tschandl, pp. 45-53 in "Fliegen und Funktechnik - Die Flugzeugfabrik der Luftwaffe Berline-Tempelhof 1933-1945" ["Aviation and radio - The Luftwaffe aircraft factory at Berlin-Tempelhof 1933-1945"], Marcus Popplow (ed.), Beate Winzer (ed.), Universitätsverlag der TU Berlin (publ.), 60 pp. Creative Commons License CC BY 4.0. Retrieved 22 May 2020.

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External links last checked: March 2016, unless noted otherwise.