Besides the Hell company and Siemens-Halske, there have been other manufacturers of teleprinter machines that use the Hellschreiber principle. Presented below are the ones that I am aware of. Some manufacturers may have filled the void caused by interruption during WW2 of exports from Germany to countries outside the German/Axis influence sphere, and it taking 2-3 years after WW2 for war-torn German companies to resume production.

• [L.M.T. (France)]
• [Teletype (USA)]
• [EMA (Switzerland)]
• [P.T.W (Austria).]
• [RFT (East Germany)]
• [TTK/Sony (Japan)]
• [Toho Denki K.K. (Japan)]
• [RCA (USA)]
• [FIApT (Italy)]
• [US Signal Corps]
• [GRETAG (Switzerland)]
• [FACIT (Sweden)]
• [Thomson (France)]
• [US Secret Service]
• [British Army Lightweight "Telewriter"]
• [British General Post Office]
• [British Y-Service]
• [Creed (UK)]
• [British "Daily Express"]
• [References]

By January 2019 this page had grown to 250 photos and diagrams. It had become rather large (ca. 24 MB download size), which caused long download times for some users. I decided to group the manufacturers listed above into two separate pages of roughly equal size: one for manufacturers in the UK (five of those listed above), and one for the rest of the world. This should be almost transparent to you. Please use the (unchanged!) list of manufacturers above to get to them, and update your bookmarks - if necessary.

©2004-2022 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: August-October 2022 (expanded the British Army Telewriter section with ref. 43M1-43M5 43P, ref .43H, associated text, and video at the end).

Previous updates: January 2020 (added info about a fourth surviving "Telewriter"); October 2019 (uploaded ref. 7V about the NVA/RTF Feld-Hell, updated associated text and added fig. E14), September 2019 (added ref. 7W).

BRITISH ARMY PORTABLE PRINTER / KEYBOARD-SENDER "TELEWRITER" YB.02251

In August of 2011, I received a message from David H. Jones in England. He recalled examining a rare start-stop Hellschreiber variant late 1945, while he was working at the General Post Office (GPO) Research Station at Dollis Hill (north London). Ref. 43N. He was kind enough to write down his quite detailed memories (ref. 43A). The machine was portable, British-made, had a 3-row keyboard (no figure-keys), and an electrochemical Hellschreiber printer mechanism. The machine appeared to have been part of a small batch of pre-production prototypes. Many years later, in April of 2018, the plot finally thickened when I was contacted by Peter Prest - owner of a machine that appeared to match David Jones's description, though adapted to series production and with a 4-row keyboard. Subsequent research has turned up two additional machines. Peter made a nice video (at the end of this section) of the quest to unravel the Telewriter mystery, covering the material presented below from several angles.

Figure R1: Telewriter - case opened

(source original unedited photo: Science Museum in London, inventory nr. 1968-586)

Figure R2: Telewriter - case closed

(source original unedited photo: Science Museum in London, inventory nr. 1968-586)

The equipment label on the carrying case in the photo above shows the following information:

• YB.02251: this is the part number. "YB" refers to the section "Signal Stores, Automatic Telegraph, Line Transmission Equipment and Cryptographic Equipment" of the British Army Ordnance Store catalog. I.e., it is a military teleprinter.
• Telewriter is the model designator.
• G.T.L.: this may be the identification of the manufacturer. "G.T.L." does appear on WW1 and WW2 rifle grenades (e.g., "No. 24", "No.35", and "No. 68") that were manufactured by Gestetner Ltd. in London. This company was founded as Gestener Cyclograph Company in 1881 by the Hungarian David Gestetner. He is the inventor of, among other things, the "stencil duplicator" office copying machine and the associated Neo Cyclostyle Pen stylus. The Gestetner Works were established in 1906 in Tottenham (north London, about 12 km southwest of GPO at Dollis Hill). Per ref. 43M4 (1940) the Telewriter could be manufactured by "non-specialist firms" (see Fig. R4 below).
• Serial № 28.

Ref. 43M1-43M5 (GPO War Diaries, not declassified until 2019!) clearly suggest that this is the Army Lightweight Telewriter developed for the British Army during 1940 by the Research Branch of the Engineering Department of the General Post Office (GPO) at Dollis Hill, north London (ref. 43N). The five 1940/1944 diary entries that are related to the telewriter, do, however, only mention the printer part - not the required sender.

Figure R3: July 1940 entry in the GPO War Diaries

(source: ref. 43M1)

Figure R4: December 1940 entry in the GPO War Diaries

(source: ref. 43M4)

The machine shown in Fig. R1 above is one of four known to still exist. It is in the collection of the Science Museum in London. It was donated to the museum in 1968 by B. Robertson, ref. 43K. The second machine carries serial nr. 109, and is in the collection of the Signals Museum RAF in Henlow/UK. The third machine is mounted on a board, rather than in a numbered carrying case. It is in the private collection of Peter Prest. In his 2018 analysis (ref. 43J), Peter construes that the machine was probably conceived in 1940, based on the operating instructions dating from the end of 1945 (ref. 43B), and assuming standard product development and procurement processes. The existence of a fourth machine was brough to my attention late 2019. It has been in a private collection in the UK since 1984 and has serial number 25:

Figure R5: the label on the case of Telewriter Nr. 25

(source: courtesy F. Brown, used with permission)

Figure R6: Telewriter

(source: left - adapted from Fig.1 in ref. 43B; right - unedited original photo: ©2018 Peter Prest; used with permission)

Note the hinged clear plastic hood to the left of the paper tape spool in Fig. R1 and R6. Most likely, its purpose is to protect the fragile printer wheel and the distributor rotor. Such hoods are not uncommon for conventional teleprinters of the same era, where they may also provide some noise reduction. The storage spool for the paper tape can be swung outward to the right, to remove or replace it.

The unit is actually quite compact: including the case, it measures a mere 13½x6½x10¾ inch (WxHxD, ≈34x16½x27 cm), per ref. 43B (1945). Ref. 43P (1944)states 13x6x19 inch. The case is made of dark brown paxolin (one of the trade names for phenolic resin bonded paper laminate, like pertinax). Combined, the machine and case weigh 24½ lbs (≈11 kg) per ref. 43B; 23 lbs per ref. 43P.  It is powered by 12 Vdc, provided by two 6 Vdc / 16 Ah batteries.

Detailed operating, maintenance and repair instructions are provided by ref. 43H.

A regular Hellschreiber printer uses a spinning helix (spindle) to generate an inked point that continuously sweeps across the width of a paper tape. The moving tape is tapped against the inked spindle, in the rhythm of received pixel pulses. See the "Printing Hellschreiber signals" section of the "How it works" page. The Telewriter uses a different approach: it creates such a sweeping point with a printer wheel (a.k.a. "pecker wheel"). It has 5 tangential springs that are evenly spaced. At the end of each spring tab, there is a small chisel-shaped "pecker". It measures approximately 0.3 x 1 mm. See the photo below. This suggests that printed characters are about 5 mm wide (twice as wide as standard Hellschreiber). Such a printer wheel prints a single line of text, unlike standard 1930s/1940s Hellschreiber spindles (see the "Synchronization" section of the "How it works" page). This is consistent with the Telewriter using a start-stop system to synchronize sending and receiving machines, whereas standard Hellschreibers of that era use no synchronization.

The Telewriter does not use ink. Instead, it uses an electro-chemical process. A water container is inserted into the left hand side of the machine. Chemically impregnated paper tape passes over the wet wick in the top of the water container. This moistening "activates" the paper, just before it reaches the printer wheel. The tape has to be moist, so as to conduct electrical current.

Reference 43M5 implies that the Telewriter actually used potassium iodide-starch-glycerine as a the chemical compound that was used to impregnate and/or coat the paper tape:

Figure R7: March 1944 entry in the GPO War Diaries

(source: ref. 43M5)

Electrolysis of potassium iodide causes the formation of iodine, which colors the white starch dark violet.

Figure R8: Close-up of the printer head - a multi-stylus "pecker wheel" with five spring-loaded tips

(source unedited original photo: ©2018 Peter Prest; used with permission)

Note that the five tipped springs leafs are evenly spaced, but only around a part of the circumference of the printer wheel, almost as if a sixth one is missing:

Figure R9: Principle of the Telewriter's electrochemical paper tape printer

The original reels of Telewriter paper tape carried the British Army Ordnance Store number YB 03858 (ref. 43K). Width of the paper tape is 11/16 inch (≈ 17.5 mm). This is slightly wider than the 15 mm standard Hellschreiber tape for printing two identical parallel lines of text, and much wider than the 9.5 mm tape used in single-line start-stop Hellschreibers that were made by Hell/Siemens-Halske. The paper tape transportation drum below the printer wheel has a diameter of 1.25 inch (≈ 3.2 cm).

The Telewriter keyboard has a 4-row 38-key QWERTY layout with the keys A-Z, 2-9, space, + - / and "." The letter "I" is also used for "1", and the letter "O" for zero. For legibility of the print-outs, only capital letters are used. The presence of the space key implies that the Telewriter is a start-stop teleprinter system: the sending and receiving machine are asynchronous. They are (momentarily) synchronized for each character, by a start pulse that is sent as part of the each character. Synchronous Hellschreiber machines do not have (nor need) a space character: they are not start-stop systems. Instead, they rely on sufficiently equal motor speeds, combined with always printing two identical parallel lines of text, one above the other. One line is always legible, even if speed differences cause the slanting of the printed text. Start-stop systems (esp. over radio, with noise, fading, and multi-path echoes) are vulnerable to false (or omitted) start-pulse detection.

Figure R10: Four-row keyboard layout of the Telewriter machine

(source unedited original photo: ©2019 Frank Brown; used with permission)

The letter type on the keys closely resembles that of a 1930s portable typewriter of the British Oliver Typewriter Company. The keys are metal-rimmed, which is typical of typewriters of that era (Remington, Bar-Lock, Underwood, etc.).

The Telewriter uses the following bit-map font:

Figure R11: The font of the Telewriter - 5x5 pixels in an 8x7 field

(source: based on by signal tracing in a Telewriter machine by Peter Prest)

Per ref. 43B (1945), the motor speed is set at the factory such that the print wheel rotates at 160 rpm, allowing a maximum typing speed of 23 words per minute (wpm). This is equivalent to 115 characters/min (= 1.9 chars/sec), using the standard 5 characters/word conversion factor. Note that ref. 43P (1944) states a maximum typing speed of 20 words/min, and uses a non-standard factor 6 to equate this to 120 chars/min = 2 chars/sec. In the table below, I have used 23 wpm.

Figure R12: Comparison of Telewriter with standard Hellschreiber fonts and speeds

As with all pre-1970s keyboard teleprinter systems (i.e., pre Hell-80), the machine has an electro-mechanical font "memory". It comprises an individually coded key bar for each key of the keyboard, a set of 30 thin cross-wires installed just below the key bars (see Fig. R13 and R14), and a scanning rotary switch with 56 contact studs (one for each pixel of the 7x8 font matrix, see Fig. R15). The special contact wires are made of "silver phosphor bronze". Ref. 43H, §62 (d) (iii). This is very resistant to stretching, and silver oxide is conductive.

Figure R13: Bottom view of the Telewriter machine

(source unedited original photo: ©2018 Peter Prest; used with permission)

Figure R14: Fixation and tensioners of the keyboard cross-wire ends (same on the right hand side of the keyboard)

(source unedited original photos: ©2018 Peter Prest; used with permission)

Figure R15: The rotary distributor of the Telewriter machine - before cleaning the corroded contacts

(source unedited original photo: ©2018 Peter Prest; used with permission)

The "scanning switch" distributor, with it turned brass studs embedded in black thermoplastic, may have been made by Painton & Co. Ltd. of Kingsthorpe/Northampton (est. 1935). Ref. 43A.

Figure R16: Painton & Co. Ltd. "Winkler" switch wafer and 1952 advertising

The 7x8 font matrix shown in Fig. R11 above, shows that first two columns are identical for all characters. These columns contain the start pulse of 8 pixel durations. This leaves a 7x6 sub matrix for printed character pixels. The last column is always blank, and provides the required spacing between printed characters. Of the remaining 7x5 sub matrix, the top pixels (row 7) are also always blank. The reason for this is unclear, as a start-stop Hell-printer does not need this: it only prints a single line of text, not two identical lines that require spacing between lines. In the end, the font memory only accommodates a 6x5=30 pixel sub matrix. This is why there are 30 cross-wires installed below the key bars of the keyboard. Note, however, that the five pixels of the bottom row are not used in the actual font of Fig. R11. Most likely, these pixels (and associated cross-wires) were reserved for making the font more legible at some point in the future - as was done in the "real" Hell fonts.

Figure R17: Going from full character encoding to "keyboard selector + rotary distributor" implementation

Each of the 30 cross-wires is connected to the corresponding contact stud of the rotary distributor:

Figure R18: Connections between keyboard cross-wires and rotary distributor

(distributor wiper shown at the rest position = stud 4; note: on the machine, stud 9 is at the top)

The contact studs that correspond to the start pulse pixels are hard-wired to the electrical "common" of the local key board and printer mechanism, and to the "L1" terminal of the 2-wire line that is connected to a remote Telewriter machine.

Each keybar has key-specific protrusions:

Figure R19: Keybar for the letter "E"

When a key is engaged by pressing it, the protrusions make contact with (only) the cross-wires that correspond to the pixels of that particular character. As in Creed teleprinters (in particular Creed model 3X), the keybar is perforated to save weight.

When the machine is turned on, the motor is running continuously. When a key is pressed, the wiper of the rotary distributor makes exactly one revolution at a speed that is equivalent to 120 rpm. Each time the wiper passes a stud contact that is connected to "common" via the cross-wires and the selected key bar, a DC voltage pulse causes a pixel dot to be printed by the local printer and simultaneously by the connected remote printer. When the distributor wiper transitions from one stud to the next, the contact is "make before break" (i.e., both studs are briefly connected). While printing a character, the paper tape smoothly advances over the width of a character and then stops, like the rotary distributor.

Figure R20: 12 Vdc motor of the Telewriter machine in situ - with 90° gearing (left) and centrifugal governor (right)

(source unedited original photo: ©2018 Peter Prest; used with permission)

The motor has a centrifugal governor that is mounted on one of the two motor shafts. As visible in the photo above, the black disk of the governor has two slip rings on the shaft side. Two spring-loaded carbon brushes ride on these rings. Inside the governor, the rings are connected to the two contacts of the centrifugal switch. The governor has a diameter of 5 cm (2 inch).

Figure R21: The centrifugal governor with its cover - for comparison, the governor of a 1930s Creed 7B teleprinter

(source unedited original photo: ©2018 Peter Prest; used with permission; source photo Creed governor: ref. 43E)

The manufacturer of the motor is unknown. Another such motor, known to be of WW2 vintage, has Air Ministry markings (embossed "crown + AM"), as well as "Type CM3 12 V" marked on one end bell of the housing. The motor draws about 0.8 A (ref. 43P).

Figure R22: The 12 Vdc shunt field motor of the Telewriter machine - with the 90° gear box attached

(source unedited original photo: ©2018 Peter Prest; used with permission)

Figure R23: Top view of the drive mechanism

(source unedited original photo: ©2018 Peter Prest; used with permission)

Figure R24: Drawing of the top view of the drive mechanism

(note: lever L2 does not interact with the drive mechanism; possibly it was used to hold coaxial shaft E during assembly of the machine)

Most of the driven shafts are supported by "Oilite" type bearing bushings (UK: bushes). The bearing sleeves are made of sintered porous bronze and are impregnated with oil, which makes them self-lubricating.

Figure R25: Drawing of the front of the mechanical drive unit with printer and distributor

Figure R26: Interaction of keyboard bar 2 and slip clutch A

(photo and original drawing: ©2018 Peter Prest, used with permission)

The fixture F1 (green), the Bar 2 Follower (orange), and springs Sp2 and Sp3 are also visible in Figure R27 below, through the bottom cut-out in the rear panel.

Figure R27: Rear view of the mechanical drive unit

(source original unedited photo: ©2018 Peter Prest, used with permission)

Peter Prest analyzed the motion sequence of the machine with the help of a low-speed motor drive that replaced the original DC motor. Let's go through the mechanical drive sequence for local operation only. Refer to Figures R23 - R27 above, and the schematics in Figures R28 - R30 below:

• The machine is in the powered down state (Master Switch "off"):
• A 12 volt /16 Ah battery is connected to the + and - terminals.
• Terminals R1 and R2 are not bridged (they are only strapped for line operation, with one or more remote machines).
• The machine is turned on with the Master Switch, which is a 4PDT switch (four simultaneous toggle switches, MS1-MS4):
• The contacts of MS1-MS4 toggle (see circuit diagram in Fig. R29 below, which shows switch positions for Master "off").
• The motor starts and runs continuously (switch MS4 is closed).
• The motor speed is regulated by the centrifugal governor switch S3 (see Fig. R21), which is placed in series with the DC motor's armature. The motor's field winding is energized permanently (as opposed to permanently energizing the armature and using the field winding for speed regulation).
• Via a small 90° gear box (see Fig. R20, R22), followed by skew gears A and B, shaft A (located in Compartment 1) is now driven continuously. Ref. Figure R20.
• At the far left end of shaft A (i.e., in Compartment 2), gear E permanently drives gear F. Hence, shaft D is also driven continuously.
• Note that the coaxial hollow shaft C (colored red in Fig. R24) does not rotate yet! It is prevented from turning with shaft A, as slip clutch A is held by Catch A. Hence, shaft B (of the rotary distributor) does not rotate either.
• Likewise, coaxial shaft E (colored green in Fig. R24) is at rest. It is prevented from turning with shaft D, as slip clutch B is held by Catch B. Hence, shafts F ( = printer wheel) and G ( = paper tape transport) do not rotate either.
• Switch MS3 is closed, so the printer system is enabled.
• The drive system remains in this idling state until one of the keyboard keys is pressed:
• The hinged keyboard Bar 1 is installed across the front of the keyboard mechanism (see the left hand image of Fig. R10), and passes underneath the SPACE key. If a key is pressed, the entire Bar 1 pivots, and its lower edge moves towards the front of the machine, away from the keyboard.
• The movement of Bar 1 pulls keyboard Bar 2 (the orange item in Fig. R26) also towards the front of the machine ( = to the left in Fig. R26). This causes the Bar 2 Follower to pull on the lower end of the Catch A Arm (blue in Fig. R26), such that Catch A releases Slip Clutch A (red in Fig. R26). As Bar 2 moves forward, the bend in the upper branch of Fixture 1 forces the Bar 2 Follower forward and downward. Spring Sp2 ensures that this follower follows the curved contour of Fixture 1.
• Shortly after Slip Clutch A is released and now rotates with Shaft A, the Cam B follower of Lever L1 (yellow in Fig. R14) drops off the vertical edge of Cam B, as the lever is pulled by Spring Sp1. The lower end of this lever moves towards the front of the machine until it is stopped by Peg 1 that is mounted on Bar 2. The force of the spring is such that Bar 2 is kept in its forward position, and thereby Bar 1 in its downward pivoted position. Therefore, the pressed key remains pressed for the duration of the motion sequence, while preventing all other keys from being pressed. The forward motion of Bar 2 causes its follower to slide past the bottom end of the Catch A Arm. The latter then pops back against the adjustable Catch A End-Stop of Fixture 1, as it is pulled by Spring Sp3. This re-arms Catch A, for disengaging Slip Clutch A from Shaft A again at the end of the drive sequence.
• The keybar (see Fig. R19) of the pressed key descends onto the 30 keyboard cross-wires (see Fig. R13, R14, R18). Each keybar has key-specific protrusions that touch a subset of these wires, and connect them electrically to keyboard "common". This wire subset corresponds to the pixels that make up the character that is selected with the pressed key (Fig. R17, R18). Each of the 30 cross-wires is connected to one of the 56 studs of the distributor (though wires nr. 26-30 are held in reserve and are not used). Via the keybar protrusions, only the key-specific pixels are enabled.
• As soon as, and as long as, Slip Clutch A is released, the coaxial shaft C rotates with the continuously turning shaft A. Via skew gears D and C, shaft B ( = rotary distributor) now also turns. The distributor wiper (which was at rest at distributor stud nr. 4) rotates clockwise (looking at the front of the machine), and in sequence, makes contact with each of the 56 pixel studs.
• The rear part of Shaft B carries Cam A. When idling, the follower of the cam-driven contact S1 rests in the notch of Cam A and S1 is connected to terminal R1 (see Fig. R24-R26). As shaft B starts to turn, S1 leaves the notch, is disconnected from R1, and makes contact with the 500 Ω resistor. At this point in the drive sequence, the distributor wiper passes "start pulse" studs nr. 5-12. These studs are hard-wired to keyboard "common". Hence, the electro-magnet is energised via switch MS3 and cam contact S2. This causes the spring-loaded Catch B to release Slip Clutch B
• Soon after the motion sequence starts, the cam briefly actuates cam contact S1 (see Fig. R20, R25, R26). This briefly connects one side of the two series-connected solenoids of the electro-magnet to +12 volt: via the 500 ohm resistor, cam contact S1, switch MS3, and cam contact S2.This connects the lower side of the solenoids to the negative terminal of the 12 volt battery. The resulting energization pulse causes the spring-loaded armature of the electro-magnet (see Fig. R23) to pull Catch B, which releases Slip Clutch B. In turn, this enables coaxial shaft E (green in Fig. R20) to rotate with the continuously turning shaft D. As shaft E rotates, Cam C changes the state of cam-driven contact S2. This causes the electro-magnet to be de-energised. I.e., the electro.magnet is only energised by a short pulse. Catch B is re-armed as soon as the solenoid energization pulse subsides. However, this catch cannot disengage Slip Clutch B until the end of the drive sequence.
• The two solenoids of the electro-magnet are marked "500" in the original circuit diagrams (Fig. R24, R25). In the machine of Peter Prest, these components are actually marked "580 Ω" and "ST.39362 A". The buzzer relay is a British Post Office type, marked "4671 ACF W43.1", and its metal cover is embossed "AN".
• Coaxial shaft E drives shaft F ( = printer wheel) via gears G and H. It also drives shaft G ( = paper tape transport) via worm gear I and worm wheel J (see Fig. R24, R25). During the drive sequence, the printer wheel makes one revolution, whereas the paper tape transportation drum is rotated over the width of a printed character.
• During the remainder of the drive sequence, the wiper contact of the rotary distributor touches contact studs nr. 14-56 followed by nr. 1-3. Based on the pressed key, specific contact studs are connected to keyboard "common", via the protrusions of the associated keybar. Each time the distributor wiper passes over such a "pixel" contact, the scanning "pecker" of the printer wheel creates a blue pixel on the paper tape.
• Near the end of the drive sequence, the Cam B follower of Lever L1 is lifted again by Cam B (see Fig. R26). This causes the bottom of the L1 lever arm to move towards the back of the machine. This allows the keybar spring to push Bar 2 also backward, and release the pressed key by letting Bar 1 pivot back to its default position. At the same time, the rounded edge of the Bar 2 Follower rides over the bottom of the Catch A Arm (momentarily pushing the back end of Bar 2 downward), before reaching its initial position again.
• Catch A was already re-armed, shortly after starting the drive sequence. It will disengage Slip Clutch A from Shaft A when the Catch grabs the notch of that Slip Clutch again, at the end of the latter’s revolution. Likewise, Catch B disengages Slip Clutch B from Shaft D.
• Both of the cam-driven switch contacts (S1 and S2) are also back in their starting state.
• This terminates the drive sequence, and the machine idles until the next key is pressed.

The video/audio clip below goes throuhg the entire character set:

The sequence of the recorded 38 characters follows the Telewriter keyboard rows from left to right: Q through P, A through /, + through •, 2 through 9. Note that the Telewriter uses bursts of DC pulses, not tone pulses. For illustration purposes, the DC pulse sequences were converted to tone pulses with a tone frequency of 1500 Hz.

Below are three video clips that show the motion of the distributor wiper, the printing wheel and paper transport drum below it, upon pressing one of the keyboard keys. To be able to show the entire drive sequence in slow motion, the original DC motor was replaced with a (whining) stepper motor.

When two Telewriter machines are connected, the following overall system circuit diagram applies:

Figure R28: Telewriter circuit diagram - two machines interconnected

(note: switch contacts MS1-MS3 shown for Master Switch MS in "ON" position; MS4 is in the motor circuit - not shown)

The above diagram is based on the official complete circuit diagrams shown in Fig. R29 and R30 below. To make it easier to follow and understand the power and signal flows, the motor circuitry is not shown and the layout has been rearranged. The diagram shows two Telewriter machines in the "line operation" configuration: in both machines, the terminals R1 and R2 have been strapped, and the two machines are interconnected via their L1 and L2/E terminals.

Let's assume that one machine is powered up and idling, whereas the second machine is powered off. Each machine has a "call buzzer". In both machines, the buzzer is normally "off". In the idling machine, this is because switch contact MS2 is open (Master Switch is ON), as is relay contact a₁. The associated buzzer relay cannot be energized, because switch contact MSN1 is open (Master Switch is ON). In the second machine, switch contact MS2 is closed (Master Switch is OFF), and relay contact a₁ is open. Each time a key is pressed on the idling machine, it will go through a drive sequence as detailed above. Each time its rotary distributor makes a revolution, the start-pulse contact studs and the pixel contact studs of the pressed character (none for SPACE) cause the minus terminal of the 12 volt battery to be connected to the L1 terminal of the operating machine. Via the line wire, this terminal is connected to the L1 terminal of the "sleeping" machine, and the lower side of its buzzer relay. The plus 12 volt terminal of the operating machine is connected to upper side of the buzzer relay in this "sleeping" machine (via the L2/E line, the R1-R2 strap, and the closed MS1 contact). So, each pulse of the rotary distributor in the operating machine energizes the buzzer relay in the sleeping machine and briefly activates the buzzer. The buzzer pulses will prompt the operator of the "sleeping" machine to turn that machine on, which disables the buzzer (MS2 is open). At that point, the system configuration is basically that of two idling machines. Standard operating procedure after turning the machine on, is to advance the moistened tape from the water container wick to the printer wheel, by pressing any key a sufficient number of times (ref. 43B). At the same time, this would signal "ready to receive message" to the operator of the calling machine, as we will see next.

When a key is pressed on either of the two idling machines, that sending machine will go through a complete drive sequence:

• The start pulse in the sending machine will cause the solenoids of the local electro-magnet to be briefly energized.
• The solenoids in the receiving machine are energized simultaneously. They are effectively connected in parallel with those in the sending machine: via the L1 and L2/E line connections, the R1-R2 strap, the (still closed) cam-driven S1 contact, switch contact MS3, and the cam-driven S2 contact. The energization pulse causes Catch B to release Slip Clutch B. The printer drive mechanism in this machine (Slip Clutch B, all downstream gears and shafts, the printer wheel and the paper tape transport) will go through the standard drive sequence.
• In the receiving machine, no key is pressed. Hence, its Slip Clutch A is not released and the rotary distributor remains at rest! Only the printer mechanism is activated!
• The motor in the receiving machine is powered by the local 12 volt battery, but the current for its electro-chemical printer comes from the battery of the sending machine, via its distributor.
• Upon completion of the drive sequence, both machines are in the idling state again.

Figure R29: Telewriter circuit diagram - aluminum placard on the machine

(source unedited original photo: ©2018 Peter Prest; used with permission)

The circuit diagram shown in the 1945 instruction manual is slightly different (and improved):

Figure R30: Telewriter circuit diagram - from the Work Instructions (manual)

(source: Fig. 5 in ref. 43B)

In Fig. R30, compared to Fig. R29, the "pecker wheel" is called "printing wheel", the 56 studs of the rotary distributor have been renumbered, all switch and relay contacts are labeled ("MS" refers to the 4DPDT On/Off Master Switch, whereas S1 and S2 are cam-driven), correct symbology is used for those contacts, the buzzer is connected between the battery and the motor's RF choke inductors, and switch MS1 and buzzer relay contact A1 are swapped (Figure R30 reflects the actual wiring).

According to ref. 43H (table of contents), the buzzer is a 24 volt model that is operated at 12 volt, and (§40) the note (tone) of the buzzer can be adjusted with a smal screw in the center of its armature, after removal of the buzzer cover.

Figure R31: Top of the "incoming call" buzzer, made by Sun Electrical Co. Ltd., and 1918 SunCo advertising

The 30 ohm resistor in series with the printer wheel provides current limiting, in case the printer mechanism is inadvertently operated without paper tape while the machine is configured for line operation. I.e., R1 and R2 are strapped, there is no line resistance, and only the 250 mA fuse and the series resistor provide protection.

To the right of the printer/distributor drive unit, there is an interconnection panel with the main switch:

Figure R32: Panel with main switch, fuse, and terminals for phone line & batteries

(source unedited original photo: ©2018 Peter Prest; used with permission)

The panel has two phone line terminals that are labeled "L1" and "L2 or E". Communication between machines was via a 2-wire phone line, or a single-wire phone line with return via ground/earth ("E"). This could be a point-to-point or an "omnibus" circuit (a.k.a. "party line", where the line is shared by multiple parallel terminals). As signaling was done with DC pulses, the phone lines could not include transformers. Up to four additional 1.5 volt cells (of an 8-cell battery) could be connected to the machine, to boost the line voltage so as to obtain sufficient signal current in the remote receiving machine(s) when operating with a line resistance above 1000 ohms (ref. 43B). Line signal-current is about 5 mA (ref. 43P).

When no additional cells are used, the terminals marked "EXTRA CELLS" are bridged. A 250 mA fuse is in series with the additional cells. The fuse holder is made by Belling & Lee and has a "10H/9613" military stores part number. The terminals marked "R1" and "R2" are to be bridged for line operation. See the schematics (Figs. R29 & R30 above) and the operating manual (ref. 43B). Note that the "+" of the 12 volt battery is connected to L2/"earth", not to L1! This is why the operating instructions (ref. 43, §2(g)) state "Do not use a negative earthed 12V battery".

The water container measures 3.5x2.75x1.09 inch (WxDxH, ≈ 8.9x7x2.8 cm). It is made of six separate pieces of yellowish celluloid-like translucent plastic. The material is about 0.085 inch thick (≈ 2.2 mm). The top and bottom pieces are L-shaped, see photos below. The side is a single strip that was softened and formed into the outline of an "L", and is sandwiched between the top and bottom pieces. The ends of the strip overlap by about half an inch (≈ 1⁺ cm), and are glued together. There are three strengthening pieces installed on the outside of the container: a round piece underneath the circular base of the wick holder, a rectangular one underneath the spring-loaded container retaining clip, and a small round piece for the cap chain retainer. The first piece and metal base are fixed from below with four brass screws that are cut off and filed flat on the outside. The retaining clip is fixed with two brass screws and nuts. The screw cap and wick holder are made of nickel plated brass. The flat wick is about 0.7 inch wide (≈ 18 mm). The wick holder base holds a round plate with two projections that prevent the plate from turning. The plate holds a retaining clip with ends that are folded upward. The wick is passed upward on one side of the clip, across it, and down again on the opposite side of the clip, back into the container. The wick is long enough such that both ends lie on the bottom of the container. The plate can be pulled out, to refill the container with water, or to replace (or adjust) the wick. The wick is actually a long rectangular strip of coarse cotton-like cloth, folded over lengthwise, with the open edges sewn to form a long, closed flat envelope. The envelope is filled with a long strip of material, possibly felt.

Figure R33: Top and bottom of the water container with screw cap - note the wick holder and the coarse cloth wick

(source unedited original photo: ©2018 Peter Prest; used with permission)

Figure R34: The water container, with the wick holder cap screwed on

(source unedited original photo: ©2018 Peter Prest; used with permission)

In Figure R25 above, note that the just-moistened paper has to travel a certain distance to the printer wheel. Probably the width of a dozen or so printed characters. This is why the Working Instructions (ref. R43B, §6) state that before actually using the machine, the operator must "depress any key several times until the damp part of the paper reaches the peckers."

Figure R35: Setting up instructions - placards on the machine's paper stand (see Figure R6)

(source unedited original photo: ©2018 Peter Prest; used with permission)

Clearly, digging up all the information presented above, and putting the pieces of the puzzle together, has been a real quest! Peter Prest has made a wonderful video presentation of it:

GENERAL POST OFFICE (GPO)

In the British Empire, the 1904 "Wireless Telegraphy Act" granted full monopolistic control of radio waves to the General Post Office (GPO). The GPO licensed all senders and receivers (telegraph, telephone, radio, teleprinter). It also owned, operated, and maintained all transmitter installations, including the punch-tape senders for Hellschreiber and regular teletype/teleprinter broadcast service. Since 1935, the GPO had already been providing the actual Hellcasts for Reuters news agency. The London Press Service (LPS) was inaugurated in August of 1945 as one of the "gray" propaganda services that was operated by the Central Office of Information (COI, successor to the war-time Ministry of Information, MOI), ref. 30. It was the COI who, with technical backing from the GPO, proposed to introduce a Hellschreiber service for the LPS. Until then, LPS only had Morse telegraphy broadcast service.

In 1947, the GPO issued a request for tender on behalf of the Colonial Office of the Foreign Office for a new Hell-printer and a "thermionic relay" contract. Ref. 19A, 20C. The "relay" is an electronics box with vacuum tubes ("thermionic valves") for a Hellschreiber-tone-pulse detector and a printer-solenoid driver amplifier. The request included full specifications and all official design drawings (including for the printer motor, specified to the Klaxon Company Ltd). The GPO designs must have come from the GPO Engineering Research Station at Dollis Hill in North London (ref. 43N).

The GPO obtained a tender from three companies in December of 1947 (ref. 19A):

• Communications Division of Marconi's Wireless Telegraph Company Ltd. in Chelmsford/Essex. Marconi had been merged into Cables and Wireless Ltd. in 1929 (shortly thereafter renamed Cable and Wireless Ltd.), and was taken over by the English Electric company in 1946. Cable and Wireless (so, probably Marconi) had performed Hellschreiber transmission/reception experiments and signal bandwidth measurements in 1938/39. Ref. 28A, 29. Marconi already negotiated Hellschreiber patent licenses in 1935 with Siemens & Halske via Telefunken Gesellschaft für drahtlose Telegraphie m.b.H. (Telefunken for short). Ref. 36. Siemens was 50% owner of Telefunken, until bought out by joint-venture partner Allgemeine Elektricitäts Gesellschaft (AEG) in 1941. Marconi and Telefunken had general "exclusive territory" agreements.
• Post Office Factories Department. The factories generally covered the assembly and manufacture, repair and reconditioning of all Post Office equipment and machinery. Until 1941, the factories were under control of the PO Stores Department.
• Coventry Gauge and Tool Company Ltd. The Coventry tender included a "relay" from Pye Telecommunications Ltd. in Cambridge. The latter company was created early 1944 as a subsidiary of Pye Ltd.

Both Marconi and Coventry Gauge & Tool / Pye were awarded a contract. As stated above, this was a "new" contract. So there was a preexisting contract: printers from Coventry Gauge & Tool, and "relays" from Pye (ref. 19A). Early-model GPO-procured printers were also supplied to Reuters' news agency, when the supply from Siemens-Halske in Germany was interrupted when WW2 started (ref. 12A, 23A). As printers for both 12-line and (newer) 7-line Hell-font were required, the printer helix ("print wheel", "printer wheel", "marking wheel") could easily be exchanged (ref. 12A).

In total, at least 73 printer/relay sets were ordered under the "new" contract. Of these, 50 were from Coventry Gauge & Tool / Pye, and 3+20 from Marconi (ref. 19B, 20B, 23B). The Coventry units were intended for Europe and the Middle East, the Marconi units for India and the far East (ref. 20A). In November of 1948, acceptance of the 20 Marconi sets was delayed, pending implementation of a "considerable" list of necessary modifications. Marconi agreed to recall, modify, and improve the 20 printers that were on hold at the GPO, and replace a few old model printers that were already fielded (ref. 18D).

The Marconi printer and relay were Marconi-design. The printer was compatible with the GPO-designed relay, but the Marconi relay was not compatible with the GPO-designed printer. I.e., Hell-equipment sets from Marconi and from Coventry Gauge & Tool / Pye were incompatible! The Marconi relay was actually an off-the-shelf general-purpose model for high-speed telegraphy (ref. 20C). Note that both Hell-printer suppliers were obliged to use the GPO-specified motor from Klaxon Co. Ltd. Ref. 19A, 20A.

The following diagram illustrates the relationships between the government and industry partners involved in the GPO contract for Hell-equipment:

Figure K1: Relationships between British government agencies and industry regarding Hellschreibers and Hell-casts

(sources: ref. 12A, 18A, 19A, 23C, 23D)

The table below shows the prices for the various equipment items:

Figure K2: 1948 prices of British Hell-equipment

(sources: 1 = ref. 18A, 2 = ref. 19B, 3 = ref. 19D, 4 = ref. 19E, 5 = ref. 23E)

To put these prices in perspective: in 1946, the average salary in the British "metalworking, engineering and shipbuilding" industry was £22.40 per month (US$98.56 in 1946), ref. 27. Based on general inflation data (ref. 21), this would be equivalent to ca. £806 in 2016 (ca. €930 and US$1005). A Morse operator made about £300-400 a year in 1949 (ref. 23F). So, at the time, a Hell-printer represented several months’ salary of an average worker – as did German Hell-equipment in Germany. A teletype/teleprinter set, including "adaptor" [ = 2-tone filter unit], cost £350 (ref. 26A, 27A), which is significantly more than a set of Hell equipment. For pricing data on German and Swiss Hell-equipment, see the "Hell equipment prices 1937-1952" page.

The GPO-printer is, of course, a British "clone" rendition of the original and ubiquitous German Siemens-Hell Hellschreiber printers for news casts. The design and specification most likely came from the GPO's Research Station (part of the Engineering Dept. of the GPO's Radio Branch) at Dollis Hill in northwest London (near Willesden). Ref. 31. Dollis Hill is also where the GPO tested the Siemens-Hell system (both 12-line and 7-line) in 1934 (ref. 12A) and where the famous "Colossus" code-breaking computers of Bletchley Park were built (1943/44).

According to a 1947 manual of the GPO (ref. 12B), three Hell-printer versions were developed, and produced in significant numbers (i.e., not prototypes):

• No. 1 Mark 1 (serial nr. 7-47).
• No. 1 Mark 2 (serial nr. 49-73).
• No. 1/T Mark 2 (serial nr. 74 and above).
• Note: GPO engineers evaluated a Marconi printer (pre-dating the “new” model) with serial nr. 322 (ref. 20A); the highest serial nr. that I have documented is 229.

The referenced manual states that printers with serial numbers 1 to 6 and 48 "are of German origin, or are obsolete models". Apparently, there either was no model "1/T Mark 1", or few or none were produced...

Note that per ref. 43M2 (GPO War Diary), GPO already constructed a "Hell type helix printer" during 1940, with "results as good as normally obtained with the standard Siemens Hell printer".

The "T" indicates that printer components were treated or selected for operation in the hot-and-humid Tropics. A fair amount of motor insulation failures were observed in tropical climates (ref. 23A), but the motor design was not under control of the printer manufacturers. Note that the "relays" also needed to be fully tropicalized. E.g., by using capacitors with higher voltage rating, and sealing of transformers to avoid water absorption (ref. 19C). GPO engineering concluded that the Coventry printer was tropicalized "as much as possible and to a slightly greater extent than the examined [ = pre-new] Marconi model" (ref. 20A).

The following photos are of the label on an "early model" GPO-printer (ref. 12A, 12D). There is no model designator (e.g., "N^o 1") marked on the label: it reads "HELL PRINTER G.P.O. SERIAL .."

Figure K3: Label on an early model GPO Hell-printer - only "Hell printer" and "G.P.O. Serial" indicated

(source: Fig. 3 in ref. 12A, Fig. 12.38 & 12.39 in ref. 12D)

Serial nr. 31 has model "N^o 1/T" marked on its label, though based on the serial nr., it should be a model "N^o 1 Mark 1". Possibly, it is a regular model no. 1 that was modified by Marconi to be suitable for operation in tropical climates (ref. 18D). Serial nr. 192 and 229 are model "1-T", not "1/T", but those designators may have been interchangeable.

Figure K4: Equipment labels of three GPO Hell-printers

All GPO/Foreign Office combined, there were three versions of the Marconi printer (ref. 18D):

• Ca. two dozen printers per the GPO design and specification.
• Ca. 20 printers, based on that GPO design, but incorporating some of Marconi's own improvements.
• A "new" model (ref. 23C, 24C). Announced changes (in response to Reuters’ experience and field experience at British overseas Posts, compared to the original GPO design, and corresponding GPO engineering assessment (ref. 24C):
• Strengthened ink roller supporting arm, and this roller now has a double-race ball bearing [not considered a problem area by GPO].
• Self-aligning bearing on the drive shaft of the tape feed [not considered a problem area by GPO].
• Improved position-locking of the pinch-roller spring of the tape feed [not considered a problem area by GPO].
• Motor governor resistor changed from screw-in type to clip-in type [actually a GPO suggestion, also implemented by Coventry].
• Wiring to the motor cleaned up [also implemented by Coventry].
• Access to motor brushes improved by moving other components [can only be marginal, as the GPO design fixes the motor location close to the front panel].
• Finer motor speed control of the motor (1½% vs. 4% per notch) [motor manufacturer Klaxon Co. Ltd. is unwilling to make the change. Note: the motor of the German Hell-printers has a superior, continuously variable centrifugal speed regulator, i.e., no incremental notches. The GPO considered it too complex for use in the GPO printer].
• Printer magnet assembly improved, to avoid shorts experienced with the original G.P.O. design.
• Mounting of the top cover plate of the printer module was changed to avoid distortion.
• Added clearance between top & front cover plate of the printer module [also implemented by Coventry].
• “Oilite” bearing [ = porous bronze plain/journal/sleeve bearing] on the printing spindle shaft and on the driven tape feed roller, to avoid seizing [GPO has no experience with such bearings in the tropics, and they may be less accurate].
• Detection of remote-control start/stop tone pulse made more robust to inadvertent starts & stops when receiving noisy signals [not considered very important by the GPO].
• To provide satisfactory ventilation, louvers are incorporated in the back of the unit and air inlet holes in the bottom.
• The holder for 4 inch diameter paper tape rolls has not been adapted to 5½ or 8 inch rolls, as this is not practical with the GPO-specified attachments points [Note: a 4 inch roll suffices for 2 hrs of continuous printing; at the time, the longest Hellcasts of the London Press Service were 1½ hrs, ref. 20A].
• All printers are now tested for speed control, and correct printing of received Hellschreiber signals.

Figure K5: Front view of an early model GPO Hell-printer - cover of the printer module removed

(source: Fig. 12.39 in ref. 12D)

Below are photos of GPO printers with serial number 12, 31, 32, 192, and 229. I have not been able to determine whether they were manufactured by Coventry Gauge & Tool or by Marconi, though most likely by Marconi. There are no manufacturer identification markings on the outside of the units, nor on the inside of the unit that I was able investigate with the cover removed. Also, based on the common GPO design, the Coventry and Marconi printers were "practically identical" with "no serious advantages on either side" (ref. 20A).

The photos below are of a 1943 GPO Hell Printer:

Figure K6: Front view of G.P.O. Hell-printer model 1 with serial nr. 12

(source: ref. 40)

Figure K7: Front view of G.P.O. Hell-printer model 1 with serial nr. 12

(source: ref. 40)

Figure K8: Top view of G.P.O. Hell-printer model 1 with serial nr. 12 - cover removed

(source: ref. 40)

Figure K9: Bottom view of G.P.O. Hell-printer model 1 with serial nr. 12 - cover plate removed

(source: ref. 40)

Figure K10: Front view of Hell-printer model 1/T with serial nr. 31 - cover of printing module removed

(this printer is in the collection of the Science Museum in London, photos with permission)

The printer "box" measures ca. 28.8x20.2x17 cm (WxHxD, 11.25x8x6.75 inch), excluding the protrusions (printer module, paper tape holder, tape feed mechanism, toggle switch, etc.). The holder for the roll of paper tape is copied directly from the 1934 Siemens-Hell printer model T.empf.12b. Compared to the German original, the GPO-printer has a paper tape feed mechanism with three rollers instead of two. As the German arrangement works flawlessly, the reason for adding a third roller is questionable. The printer uses standard 15 mm wide Hellschreiber paper tape. In the photo above, the retainer spring to the left of the printer solenoid (the dark orange component at the center) is missing - compare to the black & white photo above. The ink roller above the printer spindle is also missing.

Figure K11: Right-hand view of GPO Hell-printer model 1/T serial nr. 31 - cover removed

(at center: the horizontally installed motor with the slow/fast speed regulator knob)

Figure K12: Left-hand view of GPO Hell-printer model 1/T serial nr. 31 - cover removed

In the photo above, the jack marked "DC input" is connected directly to the solenoid of the printer mechanism. On the left is circuitry for remote on/off control - also copied from the 1930s/40s Siemens-Hell Presse-Hell printers models T.empf.12 and T.empf.14. The components marked "B" and "A-TH" are electromechanical relays. The "TH" stands for "thermal", to indicate that relay "A" is the thermal time-delay relay. A tone pulse of at least 0.5 sec would turn the motor on, whereas a tone of about 10 sec (8 sec in Siemens-Hell printers) would turn the motor off. Remote control operation is active when the main switch is in the "start stop" position. Note: this is only start-stop for the motor, and is not related to start-stop synchronization of sender and printer.

Figure K13: Toggle switch for selection of motor operation

Figure K14: Rear view of Marconi Hell-printer model 1/T serial nr. 31 - cover removed

(the component with four gray disks on the left is an L.T. (low tension) selenium bridge-rectifier)

Figure K15: Top view of GPO Hell-printer model 1/T serial nr. 31 - cover removed

Figure K16: Bottom view of GPO Hell-printer model 1/T serial nr. 31 - cover removed

The long green component in the photo above is the speed governor resistor, rated at 30 watts. It is screwed into a small light bulb socket. Per ref. 23A, its power rating was insufficient and it tended to overheat. It was replaced with a clip-on type resistor in Marconi's "new" printer model.

The model 1-T with serial number 192 and 229 both have a 10-start printer spindle. Adjacent helix-starts overlap by 50%. The actual spindle hub is slid onto the spindle shaft. This makes it easy to exchange spindles, for compatibility with both the 7-line and the 12-line Hell font (ref. 12A). In the German Hell-printers, the spindle hub is an integral part of the shaft, and not easily exchanged. The GPO spindle hub, excluding the spindle threads, has a diameter of 22 mm. The threads of the spindle have a height of about 1.5 mm.

Figure K17: Close-up of the printer spindle of model 1/T serial nr. 31

Figure K18: 3-prong power plug of Hell-printer model 1/T serial nr. 31

The printer's mains power plug fits into a switched power outlet at the lower right-hand corner of the front of the type W11 printer amplifier:

Figure K19: Printer detector/driver-amplifier "thermionic relay" model W11, serial number 1038

(this item is in the collection of the Science Museum in London, inventory nr. 1978-146, photo with permission)

The above "relay" measures ca. 42x26x26.5 cm (WxHxD, 16.5x10.5x10.25 inch). The inventory documentation of this unit does not indicate if it was manufactured by Marconi or Pye. There are no manufacturer identification markings on the housing. See ref. 37 for a description of types W1 through W8 (1938-1943). The latter types were designed by the Wireless Branch ("W. Branch") of the GPO, for "a variety of uses on radio circuits": keying a radio transmitter, operating electromechanical telegraph recorders (incl. Hellschreibers), as well as for "singing suppressors and voice-operated switches" on certain radio telephone circuits. It is reasonable to assume that types W9-W11 were designed by W. Branch as well. The first type (W1 ?) was developed around 1931. Type W8 comprised four tubes (valves; types V.T. 200 and V.T.196, two each), and was the first type that specifically intended for operating Hellschreiber printers. It was a table model with a DC output current of 20 or 45 mA (into a 500 ohm load), could provide both 110 Vac and 110 Vdc to the printer, and could also be used as a tone-signal amplifier. Audio input could be passed directly to the tone detector (full-wave rectifier with two solid-state diodes) or via an audio input bandpass filter with a 900 Hz center frequency and a 600 Hz bandwidth. Alternatively, the W8 could be used as a DC-pulse amplifier.

The next three photos show another GPO amplifier. The W-type is unknown. It only has a 110 Vdc output (on the front), so it does not appear to be a type W-8.

Figure K20: Front view of a GPO printer amplifier (W-type unknown)

(source: ref. 39)

Figure K21: Front view of a GPO printer amplifier (W-type unknown) - cover flipped up

(source: ref. 39; the toggle switch to the left of the empty tube socket is for selecting 20 vs. 45 mA DC output current)

Figure K22: Bottom view of a GPO printer amplifier (W-type unknown)

(source: ref. 39)

Below is a photo of the inside of serial nr. 32. Note the differences compared to the top view of serial nr. 12 above.

Figure K23: Top view of GPO printer 1/T with serial nr. 32 - cover removed

(source: ref. 38)

Figure K24: Front of model no. 1-T Hell-printer with serial nr. 192 (ink applicator roller missing)

(source of 1-T SNR 192 photos on this page: ©2013 Tony Radio Collection, used with permission)

Note the different shape of the paper tape roll holder, compared to the printers with serial number 31 above, and 229 shown further below.

Figure K25: The inside of the printer module of model 1-T serial nr. 192, with the electro-magnet

Figure K26: Close-up of the printer spindle of model 1-T serial nr. 192

Figure K27: Paper tape transport mechanism (left) and down-gearing for the spindle & paper transport (serial nr. 192)

Figure K28: Printer model no. 1-T Hell-printer with serial nr. 229 - ca. 1944

(this printer is in the collection of the Science Museum in London, inventory nr. 1978-145, photos taken with permission)

Note the slightly different paper tape roll holder above compared to the one of serial nr. 31 and 192 further above.

Figure K29: Close-up of the paper tape feed mechanism and printer module of 1-T Hell-printer with serial nr. 229

As noted above, the printer model with serial nr. 31 had overheating problems. Its housing is fully closed. The model with serial nr. 229 has a screened ventilation hole (ca. 6 cm diameter) in the top of the housing, a group of ten holes (ca. 14 mm diameter each) in the bottom cover plate, and ventilation louvers at the back.

Figure K30: Bottom cover of model no. 1/T Hell-printer with serial nr. 31 (left) and model 1-T with serial nr. 229

In the photos above, note the different placement of the retaining screws of the bottom cover. Also, in serial nr. 229, the jack for "DC" (input to the printer magnet) on the left-hand side of the unit is placed much closer to the front panel than the "DC Input" jack of serial nr. 31.

The motor in the GPO-printers is made by The Klaxon Co., Ltd. As the name clearly suggests, Klaxon's primary product was car horns (i.e., claxons). The company was founded in 1909. It had the telegraphic address "Klaxonet, London". In the exhibitors listing of the 1937 British Industries Fair, the following Klaxon products are listed: fractional-H.P. motors and geared motor units, generators, regulators, relays, transformers, grinding machines, industrial signals and sirens, fire and burglar alarms, staff locators, electric and hand operated horns, push buttons, electric sign flashers. A 1938 Klaxon catalog lists "air-raid warning devices for internal and external situations", gongs, sirens, whistles, and other sound- emitters". In 1961 it was listed as a manufacturer of fractional-HP motors, warning signals and windscreen wipers.

Figure K31: The motor of the GPO model 1-T serial nr. 192, including 25:1 down-gearing from 2500 rpm

(photo source: ©2013 Tony Radio Collection, used with permission)

There are several addresses associated with the company: Klaxon Co. of Birmingham, 36 Blandford Street, London, W1, and Klaxon Ltd., 201 Holland Park Avenue, London, W11. The latter may have been just an import registration address, e.g., for foreign subsidiaries. This address also appears on fractional-HP motors, geared motor, and synchronous motors. The GPO-designed motor model EK5GB1-W3 is a series-wound AC/DC type.

Even though the initial order was only for 50 motors, Klaxon had large problems delivering them. Due to non delivery of the motors (a mere £5 item), the printers from Coventry Gauge & Tool were delayed. In turn, London Press Service was forced to delay its transition to Hell-service to Europe and the Middle East by at least six month, to the end of 1947. This became a political issue (due to the missed savings for the government), and the GPO even looked into getting motors from Germany (ref. 26D, 26E)! In March of 1947, Mr. Gentry, Sales Manager of Klaxon, blamed the delays on the company being inundated with orders [for their automotive motors & horns], the order from new customer (Coventry Gauge & Tool) being placed late (in August of 1946 = 6 months ago...), Klaxon prefers to provide motors to long-time client Marconi [ = competing printer], but Klaxon is willing to support any other company to make the motors. Ref. 26A, 26B.

Further delays were incurred mid-1947, when Coventry Gauge & Tool requested Klaxon to make modifications, as the delivered prototypes did not comply with the required wiring standards (ref. 26C). Another change was made at some point: the motor speed governor had two (carbon)brushes in the Mark 1 model, but only one in the Mark 2 machines (ref. 12B).

In August of 1947, Mr. Gentry (meanwhile General Director) blames all delays on the production output being limited by "government interference and fuel supply restrictions". As to producing a mere 50 motors, he states: "Can’t do it! Just can’t do it!" (ref. 26B).

Note that Pye also had delays in deliveries of their relays/amplifiers, but those were due to labor shortage and sickness (ref. 26F).

The following photo shows a GPO "Hell Sender". The actual model/type is unknown. On the left hand side, there are two outputs: "7-line" and "12-line". The latter has a plug in it. These outputs correspond to the 7-line and 12-line Hellschreiber font. Also on the front are two exchangeable notched disks and associated switch contacts. The front disk appears to capture the pixel sequence of three characters, which could be a station identifier. From the available photo, it is unclear if the disk in the rear also captures several characters. Possibly one disk is for characters in 7-line format, and the other in 12-line format. This sender is for continuously sending a fixed character sequence. The unit has three toggle switches on the front, for "space mark", "Motor on", and "osc[illator]". The latter implies that the unit had a built-in tone oscillator.

Figure K32: GPO "Hell Sender" with serial number 47

(source: ref. 41)

Y-SERVICE

The German Wehrmacht started using the Hellschreiber system in 1935 (wired and wireless). The British radio interception service appears to have been oblivious to this until late 1940 or early 1941 (§1.3 and 1.7 in ref. 32, ref. 33). Even when the signal type was correctly identified, there was no suitable printing equipment available: the standard commercial Hellschreiber operated at a different speed. There were two radio-interception stations that specialized in teletype/teleprinter and Hellschreiber traffic: the Foreign Office (FO) station at Knockholt (near Sevenoaks, in the countryside, about 30 km southeast of the City of London), and the Metropolitan Police (MePo) station at Denmark Hill in Camberwell (about 5 km southeast of the City).

A "satisfactory universal Hellschreiber machine" was designed and manufactured in small numbers during the spring of 1942 (ref. 12C, §2.7 in ref. 32). It is unclear by which organization. It is also unclear if there was just one such development initiative, or multiple in parallel: early 1943, the Foreign Office research department (also) decided to build a universal machine that was to cover all speed ranges (ref. 22A). The latter had a printing mechanism that was copied form the German commercial machines. The universal-DC motor with "complicated centrifugal speed governor" was replaced with a type of synchronous AC-motor that was normally used in teleprinter equipment of Creed & Company Ltd., with an adjustable speed regulator comprising a pair of friction disks.

The Metropolitan Police Y-station at Denmark Hill had equipment workshops in West Wickenham at least as early as 1939 (§2.6 in ref. 32). At some point, the FO's Knockholt station was expanded with an equipment research & development operation (laboratory and workshop). However, this may not have been until 1943 (ref. 22A). This later became the Foreign Office Research & Development Establishment (FORDE).

During 1942-44, RAF 192 Squadron (§9.3 in ref. 32) and the British/American Noise Investigation Bureau (NIB, ref. 34A) investigated a special format of Hellschreiber signals that were transmitted by the Luftwaffe's rotating radio-navigation beacons of type "Bernhard". The FO's Knockholt facilities assisted 192 Sq with subject knowledge and the required tone-filter.

No photos or detailed descriptions of these universal Hell-printers are available.

If you have any information about this "universal Hell-printer", please contact me!

CREED & COMPANY

The transceiver (sender/printer) was Creed Model TR.105. Its successor, model TR.105/1, basically had redesigned electronics and no manual gain control.

Figure P1: Creed Transceiver Model TR.105

(source: ref. 16B)

On the sending side, a message is hand-written on a segment of 3/4 inch wide Teledos tape. The height of the written message is 5/8 inch max. This tape has an enameled surface. Writing is done with a regular pencil, not harder than HB-grade. The pencil-written message is pulled between the spinning stylus and the (curved) platen. The tips of the 4-pointed stylus sweep across the moving tape. As the revolving stylus scans the moving tape, its electrical resistance to earth/ground varies according to whether the points are touching blank tape or message markings. The resulting pulses are transmitted to a second machine via phone lines.

Figure P2: Stylus and curved platen

Note that this method actually dates back to 1864! The patented "copying telegraph" of Bernhard Meyer had a scanner/sender that used a metal tablet on which text was written with non-conductive ink (Creed's Teledos tape and conductive pencil "ink" is actually the opposite). Scanning was done with a swinging platinum stylus. Meyer's electro-chemical printer used paper tape and a 1-turn spindle.

At the receiver, a blank Teledos tape is passed under the stylus. The incoming message pulses from the (phone) line are amplified into voltage surges at the recording stylus. These surges are high enough to burn through the lacquer of the blank tape and leave dark markings on its surface. These markings are identical with the pencil markings on the transmitter tape. Electrical contact with the stylus is maintained via a slip-ring. This is, in effect, a thermal printer that uses "dry-electrolytic action".

Creed Model TR.105 has separate motors for the stylus and tape feed. At the receiver, the motors are started automatically when tone pulses are received. "Black" is represented by a keyed tone of 5000 Hz (+/- 200 Hz). Bandwidth was 2500-7500 Hz. This is too much for a standard analog public telephone network but a local network would be fine. Tape is fed at 1 inch/sec (≈1.5 m/min). Equivalent scanning resolution is 100 lines/inch (≈4 lines/mm).

Figure P5: Functional schematic of Teletape Transceiver Model TR.105

(source: appendix A of ref. 16E)

For the given tape feed speed (1 inch/sec), this implies a stylus speed of 1500 rpm. Model TR.105/1 has four vacuum tubes: CV2136, CV491, 6AU6, and CV1535. The unit operates on 110-145 or 200-225 Vac, 50 Hz (selectable in steps of 5 volt AC). Power consumption is 28 W (standby) - 90 W (sending). Life expectancy of the stylus was sufficient for one roll of Teledos tape. Ref. 16B.

Figure P6: The inside of Teletape Transceiver Model TR.105 (rear view)

(source: ref. 16B)

Figure P7: The inside of Teletape Transceiver Model TR.105 (view from right-hand side)

(source: ref. 16B)

BRITISH "DAILY EXPRESS" PRINTER

During World War 2, the British "Daily Express" newspaper used a British-made Hellschreiber Printing Unit to monitor the Hellcasts from the German news agency DNB. Ref. 42. The manufacturer of the machine and the associated amplifier is unknown.

If you have any information about this printer, please contact me!

Figure S1: The Daily Express "Hellschreiber Printing Unit" and associated amplifier

(source: ref. 42)

Figure S2: Close-up of the printer - lid removed from the felt ink roller and from the paper tape holder

(source: ref. 42)

Figure S3: Close-up of the printing mechanism and tape

(source: ref. 42)

REFERENCES

• Ref. 1: Le Matériel Téléphonique (L.M.T.)
• Ref. 1A: "L.M.T. Laboratories 7-Frequency Radio-printer", L. Devaux, F. Smets, in "Electrical Communication" (quarterly journal of International Standard Electric Co.), Vol. 17, No. 1, July 1938, pp. 22-34
• Ref. 1B: "Der 7-Frequenz-Funkschreiber der Les Laboratoires L.M.T.", L. Devaux, F. Smets, in "Elektrisches Nachrichtenwesen" (German edition of "Electrical Communication" of International Standard Electric Corp.), Volume 17, Nr. 1, December 1938, pp. 22-34
• Ref. 1C: "Radio Teleprinting" [7-tone L.M.T. system], in "The Wireless World", 9 March 1939, p. 294.
• Ref. 1D: "Der 7-Frequenzen-Schreiber" [7-tone printer], pp. 166-167 in "Fernmeldetechnik", Band 9 of "Lehrbücher der Feinwerktechnik", Fritz Schiweck, 1^st ed., 1942, 526 pp., C. F. Winter'sche Verlagsbuchandlung
• Ref. 1E: "Der 7-Frequenzen-Schreiber", Fritz Schiweck, Section 9.5.5, p. 378 in Band 9 of "Lehrbücher der Feinwerktechnik", 4^th ed., C. F. Winter'sche Verlagsbuchandlung, 1962, 894 pp.
• Ref. 1F: "Description de système radiotélégraphique imprimeur décomposée de Laboratoire LMT", L. Devaux, F. Smets in "L'Onde électrique : Revue mensuelle de la Société des électriciens, des électrotechniciens et des radioélectriciens", Vol. 17, Nr. 197, 1938, pp. 217-246
• Ref. 1G: Sheet 8 in "Transmitter - Receiver Sets", Section 2.2, A.L. No. 55, 49809-1(8), 21 January 1946, SubCommittee for the Investigation of German Electronic and Scientific Organisation (SIGESO Reports Vol. 4, Part-2). Source: cdvandt.org
• Ref. 2: Teletype (documents 2E-2T are courtesy Jim Haynes (W6JVE), used with permission)
• Ref. 2A: "Grundlagen der Springschreibertechnik" (Part 1-5) [start-stop synchronization], F. Schiweck, Telegraphen-, und Fernsprech-Technik, Jg. 25, Nr. 3, March 1936, pp. 53-57, Nr. 4, April 1936, pp. 91-97, Nr. 6, June 1936, pp. 139-144, Nr. 9, September 1936, pp. 245-250, Nr. 11, November 1936, pp. 307-313 – 31 pp. total; also: Fernmelde-Technik, 1937, Siemens & Halske A. G., Wernerwerk, Berlin-Siemensstadt, 26 pp. ; also: SH. 6623, 1939, 26 pp.
• Ref. 2B: "The Teletype Story", Teletype Corp., 1957, 38 pp. [hires pdf, 21 MB] [low-res pdf, 4 MB]
• Ref. 2C: "History of teletypewriter development", R.A. Nelson, K.M. Lovitt (ed.), Teletype Corp., October 1963; source: rtty.com
• Ref. 2D: "A brief history of the Morkrum Company", Howard L. Krum, ca. 1925; source: rtty.com.
• Ref. 2E: Specification S-5226 "Description of Teletype Model 17 Radio Printer System Using 7 Line Character Pattern" Issue 1 of 1939, Teletype Corp., 5 pp.
• Ref. 2F: Specification S-5186 "Adjustment of the Radio Distributor (Model 17)", Issue 1, October 1938, Teletype Corp., 9 pp.
• Ref. 2G: Specification S-5286 "Description and Adjustments of the Teletype REC17 Rectifier", Issue 1, January 1941, Teletype Corp., 2 pp.
• Ref. 2H: Specification S-5287 "Instructions for Mounting an REC-17 Rectifier on an SXT-1 Table Using the 101485 Set of Parts", Issue 1, January 1941, Teletype Corp., 1 pp.
• Ref. 2J: Specification S-5288 "Lubrication Supplies and Directions for Use", Issue 1, January 1941, 2 pp.
• Ref. 2K: Specification S-5298 "Instructions for Adjusting, Lubricating and Preparing Model 17 Radio Printers for Operation", Issue 1, March 1941, Teletype Corp., 16 pp.
• Ref. 2L: Bulletin No. 1096: "Parts, Scanning Distributor (Model 17)", Issue 1, July 1942, Teletype Corp., Teletype Corp., 24 pp.
• Ref. 2M: WD-1747 "Wiring Diagram - Table for 17 Type Printer System", Issue F, March 1941, Teletype Corp.
• Ref. 2N: WD-1902 "Wiring Diagram - 17 Type Rectifier Amplifier" (power supply), Issue A, April 1941, Teletype Corp.
• Ref. 2O: WD-2004 "Wiring Diagram - Transmitter X-12 Type 17 Printer System", Issue A, December 1940, Teletype Corp.
• Ref. 2P: WD-2012 "Wiring Diagram of Facsimile Syn. Motor", Issue C, March 1941, Teletype Corp.
• Ref. 2Q: WD-2014 "Actual and Schematic Wiring Diagrams of REC17", Issue A, January 1941, Teletype Corp.
• Ref. 2R: WD-2036 "Wiring Diagram for 17 Type Printer Transmitting Table", March 1941, Teletype Corp.
• Ref. 2S: D-2039 "Wiring Diagram of Receiving Station Cable Connections between Apparatus Units. 17 Type Printer System", March 1941, Teletype Corp.
• Ref. 2T: Instruction Manual No. 6 "Teletype Model 17 Radio Printer Systems" [only lists applicable documents], March 1941, Teletype Corp., 1 p.
• Ref. 2U: Catalog of Copyright Entries. Part 4. Works of Art, Etc., 1938, New Series, Volume 33, No. 1; No. 4, 1938, Classes H-K; Library of Congress. Copyright Office; p. 229: "Teletype model 17 mobile radio printer" (reference only, no images or text).
• Ref. 3: Correspondence of & between EMA, the Dutch P.T.T., and the Dutch news agency ANP, about commercial aspects (pricing, conditions, etc.) of EMA Hell-printers, Hell-sender, accessories, and supplies; source: Nat'l Archives of The Netherlands, catalog ref. nr. 2.9.212, inventory nr. 360, 370, 379:
• Ref. 3A: 17-May-1946 - letter (in German), from EMA to the ANP news agency in The Hague/The Netherlands; price quotations for EMA Hellschreiber printer
• Ref. 3B: 21-April-1947 - declaration from the ANP news agency in The Hague/The Netherlands (Gen. Director Mr van de Pol) to the Dutch P.T.T. about sale to the P.T.T. of Hell-printers and Hell-senders from EMA via N.V. Handelsmaatschappij G. Halbertsma (representative of EMA in The Netherlands)
• Ref. 3C: 5-December-1947 - internal document of the ANP news agency in The Hague/The Netherlands; list of conditions to impose when ordering Hellschreiber equipment from EMA in Meilen/Switzerland.
• Ref. 3D: 18-May-1949 - letter (in Dutch) from the Dutch P.T.T. to the ANP news agency in The Hague/The Netherlands (Mr van der Kallen), requesting when & how the 2 Hell-printers destined for Aneta/Indonesia were paid to the P.T.T., when the 5 Hell-printers destined for ANP correspondents in Willemstad/Curacao and Paramaribo/Surinam, will be paid, and were the 13 remaining Hell-printers are, that were returned to the EMA factory.
• Ref. 3E: 2-June-1948 - note (in Dutch) from the ANP news agency in The Hague/The Netherlands (Dir., Mr van de Pol) to the board of the Dutch P.T.T. in The Hague/The Netherlands, confirming intent to order 2 Hell-senders from Siemens (for the Dutch P.T.T. in Dutch Indonesia), cancelling order of equipment from EMA in Meilen/Switzerland, who have scandalously let the ANP down.
• Ref. 3F: 2-June-1948 - note (in Dutch) from the ANP news agency in The Hague/The Netherlands (Dir., Mr van de Pol) to N.V. Handelsmaatschappij Halbertsma in Utrecht/The Netherlands (representative of EMA/Switzerland; Mr. Smidt) about unconditional return of malfunctioning Hell-printers to EMA.
• Ref. 3G: 28-October-1948 - letter (in Dutch) dated , from the accounting dept. of the Dutch P.T.T. to ANP news agency in The Hague/The Netherlands; unpaid down-payment for two Hellschreiber senders and two printers.
• Ref. 3H: 1949 - billing/invoice from the ANP news agency in The Hague/The Netherlands to the Dutch National Radio and Telephone Service (Lands Radio- en Telefoondienst) in Willemstad/Curacao for various Hellschreiber equipment (EMA and Siemens)
• Ref. 3J: 21-February-1949 - price quote from EMA to the ANP news agency in The Hague/The Netherlands, for spare parts and supplies.
• Ref. 3K: 11-July-1949 - final billing (in Dutch) from the ANP news agency in The Hague/The Netherlands, to the Dutch P.T.T., per agreement of 21-April-1947. Debit: EMA Hellschreiber senders, EMA Hellschreiber printers. Credit: used EMA Hellschreiber printers.
• Ref. 3JL: 21-November-1949 - telex message from EMA to the ANP news agency in The Hague/The Netherlands; quoting pricing for EMA Hell-printers.
• Ref. 3M: 22-December-1949 - billing/invoice from the Dutch P.T.T. (Head office Telegraphy, Telephony, and Radio) to ANP news agency in The Hague/The Netherlands; for EMA Hellschreibers.
• Ref. 3N: 5-January-1950 - final billing/invoice from the Dutch P.T.T. to the ANP news agency in The Hague/The Netherlands (Mr van der Kallen), for EMA Hell-printers and Hell-senders sold by ANP to the P.T.T., and Hell-printers sold by the P.T.T. to ANP.
• Ref. 3O: 18-January-1950 - billing/invoice from the Dutch P.T.T. to the ANP news agency in The Hague/The Netherlands (Mr van der Kallen), for an EMA Hell-printer delivered to the Dutch newspaper "De Waarheid".
• Ref. 3P: 21-November-1951 - price quote from EMA to the ANP news agency in The Hague/The Netherlands, for the EMA Hell-printer model HPr4.
• Ref. 4: 1950 average income in The Netherlands
• Ref. 4A: "Inkomens van natuurlijke personen 1925-1973", Table 2 in a 1979 study; title unknown, author unknown.
• Ref. 4B: p. 54 in "Meer auto voor minder geld", pp. 54-58 in "Kampioen", ANWB (Dutch Automobile Association), November 1992
• Ref. 5: non-commercial correspondence about EMA Hellschreibers between EMA, the Dutch PTT, the Dutch news agency ANP, and ANP-intern; source: Nat'l Archives of The Netherlands, catalog ref. nr. 2.9.212, inventory nr. 360, 370, 379:
• Ref. 5A: 20-January-1948 - letter (in German), from EMA in Meilen/Switzerland to the ANP news agency in The Hague/The Netherlands; notification to ANP of excessive bearing friction, and retrofit.
• Ref. 5B: 7-June-1948 - letter (in German) from EMA in Meilen/Switzerland to the ANP news agency in The Hague/The Netherlands; response to letter from ANP to EMA, dated 4-June-1948. EMA does not accept ANP claims beyond contractual agreement, for modifications and improvements. Two printers returned to EMA have been adjusted and now work flawlessly. EMA refuses to take the units back and refund ANP. EMA declines responsibility for delays regarding the sender equipment by a company in Rome (sub-contractor to Siemens).
• Ref. 5C: 5-August-1948 - letter (in German) from EMA in Meilen/Switzerland to the ANP news agency in The Hague/The Netherlands: mentions EMA Hellschreiber printers operational at Sportinformation Zürich, Agence Cosmographique, Zürich (stock market news), and the Swiss PTT in Bern.
• Ref. 5D: 8-December-1948 - note (in Dutch) from the ANP news agency in The Hague/The Netherlands (Mr. Lysen) to the Dutch P.T.T. in The Hague/The Netherlands, about 20 EMA Hell-printers: 18 still being upgraded at the factory in Switzerland, 2 of which ready for shipment by EMA; 2 of 20 transferred to Aneta news agency in Batavia (Dutch East Indies), 1 of which already covered by adjusted billing.
• Ref. 5E: 17-December-1948 - internal document (in Dutch) of the ANP news agency in The Hague/The Netherlands; report about visit of the EMA company in Meilen/Switzerland, including test of EMA Hell-printers with signals from Reuters on longwave and shortwave; sensitivity (printer amplifier gain) on shortwave considered insufficient.
• Ref. 5F: 23-December-1948 - internal document (in Dutch) of the ANP news agency in The Hague/The Netherlands; report of tests with EMA Hellschreiber printers; radio receiver gain plus printer amplifier gain insufficient for weak signals - additional amplifier stage to be built into the EMA printer; after 10-12 hours of operation, the speed has drifted so much, that the speed regulator could no longer compensate; problem with burned-out 125/145/220/250 volt transformer.
• Ref. 5G: 10-January-1949 - internal note (in Dutch) from the Chief telegraphist (Mr. H. Mater) of the ANP news agency in The Hague/The Netherlands; EMA printer only works with strong signals, ink-roller shaft has too much friction and roller often does not turn freely; printer often needs to run 15 minutes after power-up before it prints properly. After printing a long time, impossible to adjust speed for straight printing.
• Ref. 5H: 10-January-1949 - Internal document (in Dutch) of the ANP news agency in The Hague/The Netherland; summary of correspondence between ANP and Hellschreiber manufacturer EMA of Meilen/Switzerland, including quality/performance problems.
• Ref. 5J: 10-January-1949 - 7 pages of Hell-tape, printed with an EMA HS-125 by the Dutch news agency ANP.
• Ref. 5K: 3-February-1949 - letter (in German) from EMA in Meilen/Switzerland to the ANP news agency in The Hague/The Netherlands; notification that two Hellschreiber senders have been built (despite lack of cooperation from Siemens and Radiar) and are being endurance-tested; 4 Hellschreiber printers were shipped on 26-january, six more are about to be shipped, six more to be shipped with the two senders in 10 days.
• Ref. 5L: 14-February-1949 - report (in German) from the Chief telegraphist (Mr. H. Mater) of the ANP news agency in The Hague/The Netherlands, about 4 EMA Hellschreiber printers received on 11-Feb-49. Two were working, one needed a tube replaced, one could not be made to print straight. These printers had an additional amplifier stage built in, and are much more sensitive. The promised thermo-relays were not built in, so the printers will probably not run smoothly in the tropics.
• Ref. 5M: 24-Feb-1949 - letter (in German) from EMA in Meilen/Switzerland (Mr. Diemer) to the ANP news agency in The Hague/The Netherlands (Gen. Director Mr. van de Pol); EMA will make a compact printer model (as presented to Mr van de Pol during his visit of EMA) available for evaluation by ANP.
• Ref. 5N: print-outs made with an EMA Hellschreiber of a Reuters transmission.
• Ref. 5O: 18-March-1949 - internal letter (in Dutch) of the ANP news agency in The Hague/The Netherlands (from Mr. B. Veltman to Mr. van den Bogaert); 6 modified EMA Hell-printers received (serial nr. 57-59, 63-65) from EMA. Serial nr. 57, 59, 63, 64 work OK, smoothly, good printing quality; serial nr. 66 runs too slow - speed regulator disassembled, reassembled & adjusted, then ran fine; serial nr. 58 does not run at all - several resistors detached; resistors reconnected, then ran fine. Tested all machines for 1 week, 15 minutes a day - with few exceptions, all printers ran fine right away. In general, these machines are less reliable than Siemens printers, and should not be operated for extended periods. OK for intermittent operation, each time after 10 minutes running before using.
• Ref. 5P: 19-April-1949 - internal note (in Dutch) of the ANP news agency in The Hague/The Netherlands (Mr van der Kallen), reporting satisfactory test transmissions with an EMA Hell-sender at facilities of the Dutch P.T.T.
• Ref. 5Q: 23-May-1949 - first page of letter (in German) from EMA in Meilen/Switzerland to the ANP news agency in The Hague/The Netherlands in response to a letter from the ANP news agency in The Hague/The Netherlands, of 11-May-1949, that reports dissatisfaction of the Dutch P.T.T. with the EMA Hellschreiber senders not being able to send figures/numbers. EMA claims it has pointed this out to the P.T.T., as Reuter news agency never transmits figures/numbers as such, only numbers written out in full (to avoid mistakes). Also, EMA can implement a lever mechanism, to interrupt the punch-tape transport, to simplify the insertion of such tape.
• Ref. 5R: 31-May-1949 - internal note (in Dutch) from the Chief telegraphist (Mr. H. Mater) of the ANP news agency in The Hague/The Netherlands, about the EMA printers in the ANP radio rooms in Amsterdam and Rotterdam. In total 21 EMA Hell-printers: 6x model HSG-2 (serial nr. 104, 111-115, all OK, 2 missing ink-roller), 6x model HS125 with additional amplifier stage (serial nr. 57-59, 63-65, all OK), 2x model HS125 without additional amplifier stage (serial nr. 60, 62; nr. 60 with bad transformer and broken fuse holder, nr. 62 OK). Of these 21, 2 (1x HS125 1x HSG2) will go to Batavia/Dutch East Indies, 4 to Dutch West Indies, 14 are in the radio rooms, 1 with printer module missing and to be returned to EMA . In total 4 Siemens Hell-printers: 3 old model printers for long wave European traffic (news agencies DPD, CTK, NTB), 1 new model for short wave traffic (TASS), 1 new model in Amsterdam and 1 in Rotterdam; no replacement ordered yet for the new printer shipped to Curacao. Still awaiting ink rollers ordered from Siemens (as is ANETA in New York). Still awaiting replacement transformer from EMA for HS125 nr. 60, various parts for HSG2 nr. 111 and HSG-2 schematic. Questions what to do with the present EMA printers, and if EMA will add an amplifier-stage to HS125 serial nr. 62.
• Ref. 5S: 4-June-1949 - note (in Dutch) from the ANP news agency in The Hague/The Netherlands (Mr van der Kallen), to the Dutch P.T.T., that 2 of the 20 EMA Hell-printers are now at the Aneta news agency in the Dutch East Indies, 4 are at the "Lands Radio & Telefoondienst" [national radio & telephone service] in Willemstad/Curacao (Dutch West Indies), and 14 are in storage. Final billing will be done shortly, including for the 2 recently delivered EMA Hell-senders.
• Ref. 5T: 16-June-1949 - letter (in Dutch and German) from Halbertsma N.V. (representative of EMA in The Netherlands) to the ANP news agency in The Hague/The Netherlands, with request to return 2 EMA Hell-printers model HS125 (serial nr. 61 & 62), for replacement of transformer and building-in of an additional amplifier stage; the requested parts for printer type HSG2 will be shipped to ANP shortly.
• Ref. 5U: 16-July-1949 - letter (in German) from EMA in Meilen/Switzerland (Mr. Diemer) to the ANP news agency in The Hague/The Netherlands (Gen. Director Mr van de Pol); follow up to letter from 24-February-1949; EMA will provide compact Hell-printer late August/early September for evaluation.
• Ref. 5V: 18-July-1949 - note (in Dutch) from Halbertsma N.V. (representative of EMA in The Netherlands) to the ANP news agency in The Hague/The Netherlands, about shipment of the final EMA Hell-printer model HSG2, and postponed visit of EMA (Mr. Freund) to ANP.
• Ref. 5W: 22-November-1951 - internal note (in Dutch) of the ANP news agency in The Hague/The Netherlands (Chief Engineer Mr Mater to Gen. Dir. van de Pol) about Hell-service. Hell-reception on shortwave requires a good antenna, stable communications receiver, Hell-amplifier, Hell tape-printer. Tape-printer is preferred over sheet-printer, as the latter loses synchronization during signal fading, leading to lost or incorrectly printed text. Amplifier and tape-printer from Siemens, as EMA equipment is not robust enough (e.g., EMA printer hammer-blades; spare parts hard to get from EMA). For shorter distances (e.g., within Europe) and on longwave, sheet-printers can be used, and are less expensive for large texts. The Minerva company in Austria makes a receiver with built-in amplifier for Hell-printer, but was temporarily not available due to currency exchange issues.
• Ref. 6: EMA brochures, manuals, and schematics
• Ref. 6A: HSG2 schematic, dated 17-December-1945
• Ref. 6B: 2-page operating instructions (in English) for EMA Hell-printer model HSG2
• Ref. 6C: "EMA Hell-Printer Type 125", 2-page manual (in German), 1-page component list, 1-page schematic dated 12-March-1947.
• Ref. 6D: EMA brochure for Hell-printer model HS125, in English, French, and German, 4 pages.
• Ref. 6E: "Gebruiksaanwijzing EMA Hellschrijver", 3-page manual for the HS125 (in Dutch)
• Ref. 6F: "Hell-Schreiber für direkte klarschrift drahtloser Nachrichtensendungen" [Hell-recorder for direct-printing of wireless news messages], 4-page EMA brochure (in German) for printer models HPr3 and HPr4.
• Ref. 6G: "Hell System tape Printer for the direct recording of wireless messages in plain characters", 4-page EMA brochure (in English) for printer models HPr3 and HPr4. Same content as ref. 6F.
• Ref. 7: Hellschreiber models built by RTF
• Ref. 7A: "Funkstation kleiner Leistung FK 1 und FK1a", Gerd Balg, 3 pp.  [pdf]
• Ref. 7B: "Der KVP / NVA Feldfernschreiber FSS.02-00001", Bernd Rothe (SK), V2.3, 23-Jan-2013, 26 pp.; used with permission.
• Ref. 7C: "Abtast-Telegrafen" [incl. Presse-Hell, Feld-Hell, 7-tone], chapter IV in "Taschenbuch für Fernmeldetechniker", H.W. Goetsch, Oldenbourg Verlag, 1940, pp. 411-427 of 787
• Ref. 7D: "Rundfunk- und Fernmelde-Technik" [wikipedia, in German]
• Ref. 7E: "Methodische Anleitung zur Ausbildung am Fernschreiber und Feldfernschreiber", Dienstvorschriften Kasernierte Volkspolizei DV-KVP 14/5, Entwurf (draft), 1955, 106 pp. Available at Bundesarchiv in Freiburg/Germany, Archivsignatur DVW 1-DRUCK/616.
• Ref. 7F: pp. 3, 82-85 in "Beschreibung und Bedienungsanweisung der Funkstation FK 1a", DV-44/14, Deutsche Demokratische Republik - Ministerium für Nationale Verteidigung; Berlin, 1956, 142 pp.
• Ref. 7G: personal account of Bruno Schwedler (frmr. ATF instructor at the Signal school in Halle-Saale), Dessau-Roßlau/Germany, 2012.
• Ref. 7H: "Bedienungsanleitung für den RFT-Abtast-Fernschreiber ATF-0001", 1-page operating manual from the inside of the lid of the ATF carrying case; courtesy B. Rothe (SK)
• Ref. 7J: "Der Stimmgabelgenerator", in "Funk-Technik - Zeitschrift für das gesamte Elektro- Radio- und Musikwarenfach", Nr. 5, March 1948, p. 114
• Ref. 7K: schematic of the ATF-0001
• Ref. 7L: blank "Fernschreiben, Fernspruch, Funkspruch" (telegram, radiogram) forms of the NVA: VD-J 13a, Fbl. 203 FS-ST, Fbl. GST 101 Na, Fbl. NVA 40 803, Fbl. VD-I 13, Fbl.
• Ref. 7M: "Repairing vibrators for DC to DC convertors"; source unknown.
• Ref. 7N: "Elektronischer Ersatz für elektromechanische Zerhacker" [electronic replacement for electromechanical choppers], Jochen Jirrmann, DB1NV, in "Funkamateur", FA 9/10, 2010, pp. 936-937  See note 1 at bottom of page.
• Ref. 7P: "Alternative Spannungsversorgung zu Anodenbatterie oder Zerhacker" [replacing electromechanical choppers with series of DC-DC converters], Bernd Beckmann (DJ9PE), in "Funkamateur", FA 6/18, p. 537  See note 1 at bottom of page.
• Ref. 7Q: "Der Zerhacker W Gl 2,4a und MZ 60001", in "Funk-Technik - Zeitschrift für das gesamte Elektro- Radio- und Musikwarenfach", Nr. 6, March 1948, pp. 146, 147, 150
• Ref. 7R: "Die Wechselrichter und Umrichter, ihre Berechnung und Arbeitsweise" [Zerhacker], Walter Schilling, 27 May 1940, R. Oldenbourg Verlag., 160 pp., OCLC Nr. 6139075
• Ref. 7S: "Nachrichtentechnik der Nationalen Volksarmee", Teil 1: "Funkmittel und Antennen 1956 - 1990", Günter Fietsch, Verlag für Technik und Handwerk, 1993, 432 pp.
• Ref. 7T: "Gruß aus der NVA an Oppin" in "Funkamateur", Nr. 10, 1957, p. 27
• Ref. 7U: article in (East-German) "Funkamateur", Nr. 9, 1961
• Ref. 7V: "Felddienst der Fernschreiber - Teil II: Feldfernschreiber (Entwurf)"  [File size:69 MB; a good-but-lower-resolution file is here 25 MB], Dienstvorschriften Kasernierte Volkspolizei DV-14/10a, draft, Tgb.-Nr. VII b/53/55, 1955, 80 pp. + schematic.
• Source: Bundesarchiv Freiburg, archive file nr. (Signatur) BArch DVW 1-DRUCK/640, used in accordance with "Erstinformation für Ihren Besuch im Bundesarchiv in Freiburg, Stand Juni 2016".
• Ref. 7W: "Wo steht der Wechselrichtertechnik?", H.-J. Wilhelmy, pp. 3, 4 in "Funkschau", Vol. 12, Nr. 1, 1 January 1939. Retrieved 12 September 2019. [pdf]
• Ref. 7X: "Fundamental principles of vibrator power supply design", P.R. Mallory & Co., Inc., 1^st ed., 1947, 135 pp. Source: tubebooks.org, accessed 8 october 2021 [pdf]
• Ref. 7Y: "Zerhacker (Wechselrichter/Wechselgleichrichter) Type 51, Type 80", datasheet/Datenblatt, VEB Elektro-mechanik (EMB), Berlin-Pankow, Bp 11/56 15, November 1956, 1 p.
• Ref. 7Z: "Zerhacker für Hoch- und Niedervolt-Wechselrichter" ["Chopper for high- and low-voltage rectifier inverter], Werner W. Diefenbach, in "Helios - Fach-Export-Zeitschrift für Elektrotechnik und Funktechnik" ("Radio-Helios") , Vol. 16, 1939, Nr. 23, pp. 1405-1407.
• Ref. 8: Tokyo Tsushin Kogyo / Sony
• Ref. 8A: "Oral-History: Nobutoshi Kihara" (interview with Sony engineer), IEEE Global History Network, People and Organizations, January 2009.
• Ref. 9: Toho Denki K.K. / Matsushita
• Ref. 9A: "Chinese language becomes a bit faster”, Chris Moss, in "New Scientist", Vol. 77, February 1978, pp. 418-420
• Ref. 9B: "Oriental approach to transpacific transmission", Donald K. deNeuf (WA1SPM; SK), pp. 16, 18 in "Proceedings of The Radio Club of America, Inc.", Vol. 51, Nr. 1, March 1977
• Ref. 9C: "Hellschreiber - Nostalgie oder Realität?", Helmut Liebich DL1OY, in "Funkschau", 11/1990
• Ref. 9D: "Japan Devises New Facsimile System", p. 31 of 11 August 1968 in "Tri-City Herald" newspaper in Kennewick, Pasco, Richland, WA
• Ref. 9E: "The Hellschreiber System", pp. 11.1-11.3 in "Teleprinter Handbook", A. G. Hobbs (G8GOJ), E. W. Yeomanson (G3IIR), Arthur C. Gee (G2UK), Radio Society of Great Britain, 2^nd ed., 1983, 350 pp., ISBN 0900612592
• Ref. 10: RCA
• Ref. 10A: "Tape-Facsimile System", pp. 766, 777 in "Facsimile", R.E. Mathes, Section 20 in "The Radio Engineering Handbook", Keith Henney (ed.), 3^rd ed., McGraw-Hill Book Co., 1941, 964 pp.
• Ref. 10B: "Tape facsimile: historical and descriptive note", Young, C.J., pp. 264-269 in "Radio facsimile - Volume 1", A.N. Goldsmith, A.F. Van Dyck, C.W. Horn, R.M. Morris, L. Galvin, (eds.), RCA Institutes Technical Press, 1938, 353 pp.
• Ref. 10C: "Tape Facsimile Synchronizing Systems", H. Shore, J.N. Whitaker, pp. 270-283 in "Radio facsimile - Volume 1", A.N. Goldsmith, A.F. Van Dyck, C.W. Horn, R.M. Morris, L. Galvin, (eds.), RCA Institutes Technical Press, 1938, 353 pp.
• Ref. 10D: "Practical applications of tape facsimile systems", J.N. Whitaker, F.C. Collings, pp. 284-293 in "Radio facsimile - Volume 1", A.N. Goldsmith, A.F. Van Dyck, C.W. Horn, R.M. Morris, L. Galvin, (eds.), RCA Institutes Technical Press, 1938, 353 pp.
• Ref. 10E: "A Wax-Paper Kymograph", Ralph Gerbrands, John Volkmann, pp. 498-501 in "The American Journal of Psychology", Vol. 48, No. 3, July 1936, pp. 498-501.
• Ref. 11: F.I.A.T.
• Ref. 11A: "List of parts for F.I.A.T. Hell Printer", part of "Hell Printer - Operating and Maintenance Instructions", Issue 2, July 1944, Document M 9501 (Tg), Office of the Engineer-in-Chief, Post Office Engineering Dept. (Radio Branch) GPO, London; courtesy British Science Museum, Blythe House inventory item 1974-190, used with permission.
• Ref. 12: British Post Office
• Ref. 12A: "Reuters' Wireless Services", W. West, in "The Post Office Electrical Engineers’ Journal", Vol. 39, July 1946, pp. 48-52
• Ref. 12B: Hell printers Nos. 1 and 1/T - spare parts", Issue 1, 16 January 1947, 2 pages in "Hell Printer - Operating and Maintenance Instructions", Issue 2, July 1944, Document M 9501 (Tg), Office of the Engineer-in-Chief, Post Office Engineering Dept. (Radio Branch) GPO, London, EC1 [note discrepancy between dates on both documents]
• Ref. 12C: page (which refers to ref. 12D) in Chapter 7 of "Colossus: Bletchley Park's Greatest Secret", Paul Gannon, Atlantic Books, 2007, 588 pp. Source: Paul Gannon Books.
• Ref. 12D: "Hellschreiber Code", and "Hell Telegraph Instruments", pp. 14, 15 and pp. 514-518 in Chapter 12 "Morse and Hellschreiber Instruments" in "Telegraphy", J.W. Freebody, 1^st ed., Sir Isaac Pitman & Sons, 1959, 773 pp.
• Ref. 12E: components lists for Hell Printers No. 1 and 1-T: PO document M 9502 (Tg) and M 9508 (Tg) respectively.
• Ref. 13: US Signal Corps
• Ref. 13A: "Tape Facsimile Equipment RC-58-B" [109 MB; a low-res version is here (66 MB)], War Department Technical Manual TM 11-374, 23 February 1944, 145 pp. (courtesy Louis Gonzales, F5LG).
• Ref. 13B: "RC-58 Facsimile Equipment" [BC-918] in "Surplus sidelights", Gordon E. White, in "CQ: Amateur's Radio Journal", Vol. 24, nr. 3, March 1968, pp. 106-110
• Ref. 13C: "Un Convertisseur RTTY de surplus - le BC 908B" [modification of the BC908B (amplifier/filter unit of the RC-58B system) for RTTY], J.P. Vauchelle (F5QE), in "Radio-REF", November 1969, pp. 729-733.
• Ref. 13D: "Amerikaans Hell system", in "Reflecties door PA0SE" column by Dick Rollema (PA0SE), in "Electron", nr. 7, July 1980, p. 382 (courtesy Gerard Wolthuis, PA3BCB)
• Ref. 13E: "Facsimile Equipment RC-58-( )", Section V in "Installation of Radio and Facsimile Equipment in Shelter HO-17 ( )", US War Department Technical Manual TM 11-2737, May 1945, 20 pp. (courtesy Gary Lynch, KJ6EFH)
• Ref. 14: GRETAG
• Ref. 14A: "Movies by Television - Swiss Used Film of Oil for Theater-Size Image", Joseph Israels, in "Popular Science", January 1946, p. 94
• Ref. 14B: "What is Eidophor? Details on CBS's color system for theater TV viewing, as recently unveiled in New York", Radio & Television News, August 1952, p. 30
• Ref. 14C: "The History of the Eidophor Large Screen Television Projector", Heinrich Johannes, Gretag AG, 1989
• Ref. 14D: "Der Eidophor - Ein Grossbildprojektionssystem zwischen Kino und Fernsehen 1939–1999", Caroline Meyer, vol. 15 of " Interferenzen – Studien zur Kulturgeschichte der Technik", Chronos Verlag, 2009, 416 pp., ISBN 978-3-0340-0988-1
• Ref. 14E: "Anordnung zur Aufzeichnung von Impulsen mittels eines umlaufenden Schreibrades und einer Schreibleiste" [arrangement for printing of impulses with a revolving typewheel and piston], Joseph Lorbach (Hell company), Reichspatentamt, Patentschrift Nr. 732623, 27 Feb. 1941
• Ref. 14F: "Hitlers letzte Maschinen" chapter 2.17 in "Codeknacker gegen Codemacher - Die faszinierende Geschichte der Verschlüsselung", by K. Schmeh, W3L Verlag, 2^nd edition, 2007, 414 pp. [pdf]
• Ref. 14G: "Die Geschichte der "Hagelin-Cryptos"", Boris Hagelin, Crypto AG, lE 720, 1979, 64 pp.; source:www.cryptomuseum.com
• Ref. 14H: "The teletype ETK - Univocal combination teletype", Ingenieurbureau Dr. E. Gretener, Projekt lo9a, Akten-Nr. 188, 12 April 1945, 9 pp.
• Ref. 14J: "An Improved Telegraphic Printing System", Edgar Gretener, UK Patent 639241, filed 20 December 1947
• Ref. 14K: "ETK-R-Fernschreibanlage Mod. 55" [description and schematic], Funktionsbeschreibung Nr. 501-2 & 502-2, Dr. Edgar Gretener A.G., 44 pp.; source: www.armyradio.ch
• Ref. 14L: "Illuminated announcement and display signal", Frank W. Wood, United Sates Patent Office, patent nr. 974943, filing date 17 June 1908
• Ref. 14M: "Der Krypto-Funk-Fernschreiber KFF - Kurzbeschreibung und Bedienungsanleitung" [KFF-58], Reglemente der Schweizerischen Armee, 58.134d, 1960, 36 pp.; source:www.armyradio.ch
• Ref. 14N: "Die Endgeräte vom Morseschreiber bis zum Laptop", Rudolf J. Ritter, Vol. 14 of "Das Fernmeldematerial der Schweizerischen Armee", Merker Verlag, 2007
• Ref. 14O: "Die ETK-Fernschreibstation", Reglemente der Schweizerischen Armee, 58.122d, 1953
• Ref. 14P: "Das Telekryptogerät «TC 53» - Bedienungsanleitung; L'appareil télécrypto «TC 53» - Instruction de service", Dr. Edgar Gretener AG, 50 pp.; source: www.armyradio.ch
• Ref. 14Q: "Analysis of Swiss ETK Teletypewriter", C.P. Seymour, L.B. Rosenberg, W.S. Dwinell, Wright Air Development Center (WADC) Technical Report (TR) 52-266, AF-WP-(S)-O-31 Jul 53 65, RDO No. 102-22, September 1952, 36 pp.
• Ref. 14R: website of the Stiftung Historisches Armeematerial Führungsunterstützung (HAMFU) and Interessengemeinschaft Übermittling (IG Uem)
• Ref. 14S: website of armyradio.ch (here in English)
• Ref. 14T: pp. 2 and 3 of description of the TFFA modem
• Ref. 14U: "Stromlaufplan TFA-Gerät ohne Automatik GR PS 22/3a" [schematic of the ETK47 modem], 1948
• Ref. 14V: "Der Krypto-Funk-Fernschreiber KFF 58: Grundlagen, Funktionen, Betriebstechnik, Simulation", Walter Schmid (HB9AIV), self-published, 2008, 269 pp.
• Ref. 15: FACIT
• Ref. 15A: "FACIT 4552 Strip printer - Technical description", 4552.13.01.Eng.10M.9.71, 12 pp, 1971 (courtesy Arie van Oijen, PE1AQB)
• Ref. 15B: "Facit 4552 Alphanumeric Strip Printer" [brochure], 4552.02.03 Eng 10M.12.72, 2 pp., 1972 (courtesy Arie van Oijen, PE1AQB)
• Ref. 15C: "Facit 4553 alphanumeric serial page printer" [sheet printer], 4553.02.03 Eng 5M.7.74, 4 pp., 1974, (courtesy Arie van Oijen, PE1AQB)
• Ref. 16: Creed
• Ref. 16A: "Creed and Company Limited - The First 50 Years", Alan G. Hobbs (G8GOJ, SK), Spring 1962 "Golden Jubilee" issue of "Creed News"; also reprinted in the Summer 1997 issue of "BARTG Datacom".
• Ref. 16B: "Creed model TR.105/I Teletape transceiver – part list no. PL.105", 2^nd ed., March 1960, Creed & Company Ltd., 24 pp.
• Ref. 16C: "Western Union Teletape Facsimile", L.G. Pollard, in "Western Union Technical Review", Vol. 2, Nr. 3, July 1948, pp. 93-98
• Ref. 16D: "Recording on TELEDELTOS Electrosensitive Paper -- Type L48 and L39", J. H. Hackenberg, F. L. O#Brien, in "Western Union Technical Review", Vol. 16, No. 2, April 1962, pp. 84-92
• Ref. 16E: "Teletape Transceiver Model TR. 105/1", Instruction Book FAX.105, Issue 2 of Booklet MB. 105, Creed & Company Ltd. (I.T.T.), January 1960, 71 pp.; includes full schematics.
• Ref. 16F: "Faksimile-System – Faksimile-Streifenschreiber TR 105 – Montage- und Wartungsanweisung, Einstellvorschriften", Standard Elektrik, 10 pp.
• Ref. 17: Thomson
• Ref. 17A: "Le Hellschreiber", Bernard Pauc, in "Radiofil Magazine", No. 42, Jan/Feb 2011, pp. 34-37.
• Ref. 18: copy of items in file ref. IOR/L/I/1/1210; File 464/26B(iii) "London Press Service: installation of Hellschreiber equipment (1947-1949)" Items are in the collection of the British Library; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 18A-18E.
• Ref. 18A: Letter from S.G. Pennells to Miss M.R. Bruce (Treasury Chambers, London), dated 12^th June 1948, 1 page.
• Ref. 18B: Letter from Mr. M. McLoughlin (Central Office of Information, London) to Mr. K. Jowers (British Information Services, Karachi, Pakistan), dated 29^th July 1948, 1 page.
• Ref. 18C: Letter from Lt. Col. R.N. Bobb (British Information Service, New Delhi, India) to Mr. Ralph Hall (Commonwealth Relations Office, London), dated 2^nd August 1948, 1 page.
• Ref. 18D: Report to Mr. Lovell, Chairman of the Technical Working Committee of an interview with Mr. Cole, Manager of the Marconi Communications Division, dated Friday 10^th November 1948, 3 pages.
• Ref. 18E: Extract of report on the performance of Marconi equipment in India and Pakistan, in letter from Mr. M. McLoughlin to F.H. Raynes (Engineer in the Chiefs Office of the General Post Office (G.P.O.) Telegraph Branch), dated 30^th November 1948, 2 pages.
• Ref. 19: copy of items in file ref. IOR/L/I/1/1213 File 464/26B(vi) "Hellschreiber tests (1948)". Items are in the collection of the British Library; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 19A-19M.
• Ref. 19A: Letter from R.E. Hughes (General Post Office, Overseas Telecommunications Dept., London) to Mr. M. McLoughlin (C.O.I., London), dated 20^th December 1947, 2 pages.
• Ref. 19B: First page of letter from Mr. M. McLoughlin (C.O.I., London) to Mr. G.F. Crawley (C.R.O. Information Dept., London), dated 2^nd February 1948, 1 page.
• Ref. 19C: List of London Press Service long & shortwave frequencies, 3 pages.
• Ref. 19D: Letter from Mr. M. McLoughlin (C.O.I., London) to Mr. G.F. Crawley (CRO Information Dept., London), dated 8^th March 1948, 3 pp.
• Ref. 19E: Letter from Mr. M. McLoughlin (C.O.I., London) to Mr. G.F. Crawley (CRO Information Dept., London), dated 6^th April 1948, 2 pages.
• Ref. 19F: Letter from Kenneth Jowers (Director, British Information Services (BIS), Karachi, Pakistan) to Mr. M. McLoughlin (Central Office of Information (C.O.I.), London), dated 17^th April 1948, 3 pages.
• Ref. 19G: Letter from Mr. M. McLoughlin (C.O.I., London) to Mr. R.W. Bishop (Palace Electrical Co. Ltd., London), dated 22^nd April 1948, 1 page.
• Ref. 19H: Letter from Mr. Jowers (BIS, Karachi/Pakistan India) to Messrs. M. McLoughlin (COI, London) and Crawley (CRO, London), dated 21^st July 1948, 2 pages.
• Ref. 19J: Letter from Mr. D.D. Condon (Editor in Chief, BIS, New Delhi, India) to Mr. G.F. Crawley (CRO, London), dated 23^rd July 1948, 5 pages.
• Ref. 19K: Letter from Mr. Kenneth Jowers (Director at BIS, Karachi/Pakistan) to Mr. Howe, dated 31^st July 1948, 1 page.
• Ref. 19L: Letter from Mr. Kenneth Jowers (Director at BIS, Karachi/Pakistan) to Mr. G.F. Crawley (CRO Information Dept., London), dated 8^th September 1948, 2 pages.
• Ref. 19M: Letter from K. Jowers (BIS, London) to Mr. M. McLoughlin (COI, London), dated 10^th September 1948, 1 page.
• Ref. 20: copy of items in file ref. IOR/L/I/1/1214 File 464/26B(vii) "Hellschreiber Working Committee minutes (1948)". Items are in the collection of the British Library; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 20A-20C.
• Ref. 20A: Minutes of 3^rd meeting of the C.O.I. Hellschreiber Working Committee, 11^th February 1948, 5 pages.
• Ref. 20B: Minutes of 4^th meeting of the COI Hellschreiber Working Committee, 13^th April 1948, 7 pages.
• Ref. 20C: Part of the Minutes of 5^th meeting of the C.O.I. Hellschreiber Working Committee, 30^th June 1948, 4 pages.
• Ref. 21: sources of Pound Sterling inflation data (general cost of goods and services changes over time): thismoney.co.uk, bankofengland.co.uk, inflation.stephenmorley.org; accessed 21-March-2017.
• Ref. 22: copy of an item in file HW 14/70 "Directorate of Gov’t Code & Cypher School, WW2, EWT to NY with details of German Hell system (1943)". Item is in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 22A.
• Ref. 22A: Letter entitled "Hellschreiber", from Travis (Directorate of Gov’t Code & Cypher School) to Mr. Bayly (in New York), dated 18^th March 1943, 3 pages.
• Ref. 23: copy of items in file INF 12/419 "Hellschreiber Working Committee, technical reception arrangements (1948/49)". Items are in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 23A-23E.
• Ref. 23A: Letter entitled "Experiences of Reuters with Hell Printers and Relays provided through Post Office Channels", from E. Davis (Reuters) to Mr. Perkins (Post Office, Chief of Communications), dated 27^th February 1948, 3 pages.
• Ref. 23B: Extract from a personal letter from Angus Malcom (Head of Chancery, London) to Mr. Alan Dudley (British Legation, Mexico City), dated 30^th January (1948), 1 page. “We are still battling with Hellschreiber but I wish you’d take the bloody thing away.”
• Ref. 23C: Letter entitled "Marconi printer", by C.P. Hayter on behalf of Contracts Manager of Marconi’s Wireless telegraph Co. Ltd., to Mr. David St.J. Jones (Director of Contracts, Foreign Office, London), dated 1^st April 1948, 2 pages.
• Ref. 23D: First page of letter from Foreign Office to Mr. McLoughlin (Central Office of Information), dated 20^th July 1948, 1 page.
• Ref. 23E: Letter entitled "Orders & estimated cost of Hell Equipment", from M. McLoughlin (Central Office of Information), dated 20^th November 1948, 1 page.
• Ref. 23F: "London Press Service: Transfer to Hellschreiber working – Statement by the central Office of Information", dated 23^rd March 1949, 4 pp.
• Ref. 24: copy of items in file CO 875/40/1 "London Press Service: Hellschreiber machines; CO PR Dept., CFC (1948)". Items are in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 24A-24D.
• Ref. 24A: Letter from M. McLoughlin (Central Office of Information, London) to O.J. Whitley (Colonial Office, Information Dept., London), dated 23^rd January 1948, 1 p.
• Ref. 24B: "Supply Position on Hell Printers and Relays", date unknown [1948], 1 page.
• Ref. 24C: "Notes on new model Hell Printer being supplied by Marconi W.T. Co. under Contract 51504", date unknown [1948], 1 page.
• Ref. 24D: London Press Service "Notes for Information Officers on the installation, working and general maintenance of [Hellschreiber] printers for reception of the London Press Service"; date unknown [1948], 11 pp.
• Ref. 25: copy of items in file CO 875/40/2 "London Press Service: Hellschreiber machines; CO PR Dept. (1949)". Items are in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 24A.
• Ref. 25A: Invoice from Central Office of Information to the Accountant of the Crown Agents for the Colonies, for Hellschreiber equipment for Post at Mauritius, Accra, Seychelles, Lagos; dated 1^st March 1949, 1 page.
• Ref. 26: copy of items in file INF 12/139 "Hellschreiber working committee, March-December 1947". Items are in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 26A-26G.
• Ref. 26A: "Notes of a meeting held in Mr. Lovell’s room, Central Office of Information, on 27^th March, 1947 to consider the relative merits of Hellschreiber and Teletype working as far as the London Press Service is concerned", by Mr. M. McLoughlin, 3 pp.
• Ref. 26B: "Report on visit to Messrs Klaxon Limited by Wing Commander Jowers of the Foreign Office and Mr. McLoughlin of the Central Office of Information on 28^th March 1947", dated 3^rd April 1947, 2 pp.
• Ref. 26C: Letter from Mr. Perkins (General Post Office, Telecommunications Dept., London) to L.H. Lovell (General Post Office, London), dated 5^th June 1947, 1 p.
• Ref. 26D: "Notes of a meeting held in Mr. Lovell’s room, Central Office of Information, on 26^th June, 1947 to consider the supply of Hellschreiber instruments, fix a new target dated to commence working, and examine the possibility of extending the service to the Americas at an earlier date", dated 30^th June 1947, 4 pp.
• Ref. 26E: "Supply of Hellschreibers", internal note from Mr. Lovell (Central Office of Information) to Mr. Routh, dated 30^th June 1947, 2 pp.
• Ref. 26F: Internal note from Mr. McLoughlin (COI) to Mr. Gore, dated 15^th August 1947, 2 pp.
• Ref. 26G: "Particulars of Posts in connection with the introduction of Hellschreiber [by London Press Service]", date unknown [mid-1947], 2 pages.
• Ref. 27: "Wage trends and wage policies: various foreign countries", Bulletin No. 934, US Dept. of Labor, Bureau of Labor Statistics, March 1948, 60 pp. [pdf]
• Ref. 28: ITU conference 1938; "Propositions transmises au bureau de l'union, pour être soumises à la conference" [proposals to be submitted to the ITU conference], Vol. 1 of "Documents de la Conférence internationale des radiocommunications di Caire (1938)", International Telecommunications Union (ITU), Bern; no English version available; source: ITU
• Ref. 28A: pp. 218, 219: proposal nr 392 R by C.I.N.A - "Considérations générales sur la largeur de bande des émetteurs de t.s.f. modulés par signaux Siemens-Hell" [general considerations about the bandwidth of radio transmitters that are modulated with Siemens-Hell signals]; at 5 chars/sec (punch tape operation), the 12-line Hell-font with a shortest pulse of 2 msec and shortest pause of 3.12 msec has a shortest cycle of 5.12 msec, hence a max cycle rate of 195 Hz, and 97.5 Hz with manual/keyboard operation at 2.5 chars/sec. Tests by Siemens-Halske, Cable & Wireless (UK), and the German Central Postal Authority (R.P.Z) have concluded that a applying a low-pass filter with a corner frequency of 230 Hz at the transmitter is sufficient, and results in 390 Hz occupied bandwidth.
• Ref. 29: "Bandbreitenfragen bei Anwendung der Siemens-Hell-Fernschreibtechnik" [signal bandwidth issues with A2 and A3 modulation], Rudolf Zimmermann, 7 pp., Technische Mitteilungen des Fernmeldewerks, Siemens & Halske A.G., Wernerwerk, Abteilung für Telegrafengerät, Berlin-Siemensstadt, May 1940, SH 7998, 1. 8. 40. T T1.
• Ref. 30: pp. 44-45 in "Organising the Propaganda instrument: The British Experience", by John B. Black, Martinus Nijhoff Publ., 1975, 116 pp.
• Ref. 31: "Research in the British Post Office", J. of the IEE, Vol. 75, issue 452, August 1934, pp. 133-151.
• Ref. 32: pp. 512-516, 524 in "Activities at Knockholt", J.A. Reeds, Appendix B in "Breaking Teleprinter Ciphers at Bletchley Park - General Report on Tunny with Emphasis on Statistical Methods (1945)", 1^st ed., I.J. Good, D. Michie, G. Timms (J.A. Reeds, W. Diffie, J.V. Fields, eds.), John Wiley & Sons, IEEE Press, 2015, 735 pp.
• Ref. 33: p. 85 in "COLOSSUS: The Secrets of Bletchley Park's Codebreaking Computers", B. Jack Copeland et al (eds.), Oxford University Press, 2006, 480 pp.
• Ref. 34: copy of items in file AIR 14/3577 "Signals investigation on 27 to 35 Mc/s "Windjammer" (1943/1944)". Items are in the collection of The National Archives; material with UK Crown Copyright, used in accordance with the Open Government License [pdf].
• Summary of the contents of ref. 173A-173E.
• Ref. 34A: "'Windjammer" observation", by R.A. Fareday (Noise Investigation Bureau [Electronic Intelligence], N.I.B., London), dated 20^th June 1944, 1 page.
• Ref. 34B: ""Possible "Windjammer" transmissions", report by Flight Lieutenant Douglas of 192 Sq., dated 16^th December 1943, 1 page.
• Ref. 34C: "192 Squadron Flight report No. 215/43" by F/Lt Robinson to Squadron Leader Burtler, dated 15^th November 1943 (actual report by P/O G.F. Evans of 13^th November 1943), 6 pages.
• Ref. 34D: "Windjammer – Arcachon", letter from Air Ministry A.I.4. [intelligence branch section supervising RAF Y Service] to Commanding Officer of 192 Squadron, dated 16^th July 1943, 1 page + 1 aerial photo.
• Ref. 34E: "The windjammer and Dreh-Elektra", by 192 Squadron Leader J. Whitehead, dated 18^th June 1943, 1 page.
• Ref. 35: "The Hut Six Story - Breaking the Enigma Codes", Gordon Welchman, M & M Baldwin Publ., 6^th ed., 2011, 263 pp.
• Ref. 36: "Siemens – Hellschreiber / Marconi", internal memo of Telefunken Ges.f.drahtl.Telegraphie m.b.H., 21 May 1935, 1 page; source: corporate archives of DTM Berlin, part of file nr. I.2.060C-02427.
• Summary (in English) of the contents of ref. 36.
• Ref. 37: "Thermionic Relays (Trigger Type): Types W1 to W8", A. Cook, L.T. Arman, P.R. Hutton-Penman, General Post Office Engineering Department Radio Report No. 1276, Copy No. 18, 1938-1943, signed 14th January 1945, 11 pp.; BT Digital Archives, document ref. TCB 226/1276. This documents was obtained via The BT Digital archives search engine and is used in accordance with the terms of the non-commercial Creative Commons Licence CC BY-NC-SA, © Coventry University.
• Ref. 38: "Printer, Telegraph Hell No. 32", 1944. This photo was obtained via The BT Digital archives search engine (Finding Nr. TCB 417/E 12959) and is used in accordance with the terms of the non-commercial Creative Commons Licence CC BY-NC-SA, © BT Heritage.
• Ref. 39: "Hell amp and trigger apparatus. 21 January 1942". These photos were obtained via The BT Digital archives search engine (Finding Nrs. TCB 417/E 12134, 12135, 12136) and are used in accordance with the terms of the non-commercial Creative Commons Licence CC BY-NC-SA, © BT Heritage.
• Ref. 40: "Telegraph Tape Printer. 1943". These photos were obtained via The BT Digital archives search engine (Finding Nrs. TCB 417/E 12508, 12509, 12510, 12511) and are used in accordance with the terms of the non-commercial Creative Commons Licence CC BY-NC-SA, © BT Heritage.
• Ref. 41: "Hell Sender. 7 January 1945". This photos was obtained via The BT Digital archives search engine (Finding Nr. TCB 417/E 13260) and is used in accordance with the terms of the non-commercial Creative Commons Licence CC BY-NC-SA, © BT Heritage.
• Ref. 42: "The "Daily Express" Hellschreiber - A Short Description of an interesting High-Speed Recorder", pp. 104-106 in "Short Wave News", Vol. 1, No. 4, April 1946.
• Ref. 43: G.T.L. Telewriter:
• Ref. 43A: "A Portable Hellschreiber Variant", personal correspondence, David H. Jones, October 2011, January 2014, and April 2018, 4 pp.
• Ref. 43B: "TELEWRITER Working Instructions", YB 04159, The War Office, Whitehall, December 1945, 10 pp., printed by Fosh & Cross Ltd., London. Courtesy L. Meulstee.
• Ref. 43C: "Improvement in Electro-chemical telegraphs", Robert Smith, Alexander Bain, United States Patent no. 6837, 30 October 1849, 5 pp.
• Ref. 43D: "Use of electrochemical recording in medical instruments", N.K. Golobokii, pp. 70-73 in "Biomedical Engineering", Vol. 6, Issue 2, March 1972; accessed 18 November 2018. [pdf of pp. 70, 71] [original article appeared in "Medistinskaya Tekhnika", nr. 2, March-April 1972, pp. 8-13].
• Ref. 43E: p. 2.3 in "Teleprinters", chapter 2 in "RSGB Teleprinter Handbook", A. Hobbs, E. Yeomanson. A. Gee, RSGB, 2^nd ed., 1973. [pdf]
• Ref. 43F: pp. 478, 479 in "The Royal Corps of Signals - A History of its Antecedents and Development", R.F.H. Nalder, 1958, Royal Signals Institution (publ.), London, 672 pp.
• Ref. 43G: pp. 160, 161 in "The History of British Army Signals in the Second World War: General Survey", R.F.H. Nalder, 1953, Royal Signals Institution (publ.), London, 377 pp.
• Ref. 43H: "TELEWRITER - First Echelon Work (Draft E.M.E.R. Tels T 223/1)", Signals Research and Development Establishment (S.R.D.E.; Somerford, Christchurch/Hampshire), S.R.D.E. Pamplet No. 568,  March 1945, 30 pp. Courtesy L. Meulstee.
• E.M.E.R. = Electrical & Mechanical Engineering Regulation; TELS = EMER Group = Telecommunications, T = Section = Telephony; 22 = Equipment Designator = ???; 3 = Part Number; /1 = Mark.
• This document refers to "E.M.E.R. Tels. T 222/1" for a general description of the machine, to "E.M.E.R. Tels A 424/1" for "full details of adjustment", and to "2nd - 4th Echelon Work" for a jig to hold the machine. If you have a copy of any of these documents, please contact me.
• Ref. 43J: "Telewriter Procurement", Peter Prest, December 2018, 5 pp.
• Ref. 43K: "Letters from B. Robertson to the Science Museum in London, offering to donate his Telewriter", February/March 1968, 3 pp.
• Ref. 43L: Sheet 4 (pdf p. 8) in "Method of and apparatus for electrically recording and producing sound or other vibrations", Merle Duston, US Patent 2,030,973; Filed 13 August 1931, 12 pp.
• Ref. 43M: "Research Branch Secret War Diary", W. Gordon Radley, Dollis Hill General Post Office (GPO). Source: British Telecom (BT) Archives - The Dollis Hill war diary; two volumes: Volume 1 of 2, 216 pp. [file size 43 MB; a much smaller transcript file is here],  Volume 2 of 2, 144 pp. [file size 25 MB; a transcript file is here].
• Ref. 43M1: "Design and Construction of simple Telegraph Printer", diary entry for 9 July 1940, p. 41 in Volume 1 of 2.
• Ref. 43M2: "Design of a Simple Telegraph Printer", diary entry for 21 September 1940, p. 55 in Volume 1 of 2.
• Ref. 43M3: "Design of a Simple Telegraph Printer", diary entry for 27 November 1940, pp. 65/66 in Volume 1 of 2.
• Ref. 43M4: "Simple Telegraph Printer for Army Use", diary entry for 11 December 1940, p. 69 in Volume 1 of 2.
• Ref. 43M5: "Electrolytic paper strip for Army Lightweight Telewriter", diary entry for 16 March 1944, p. 232 in Volume 2 of 2.
• Ref. 43N: "Research is the Door to Tomorrow': the Post Office Engineering Research Station, Dollis Hill, 1933-1958" [key words: Colossus, telephone history, history of technology, Dollis Hill, Post Office Research Station, General Post Office, research and development, telecommunications, state-sponsored science], Rachel Boon, PhD thesis at The University of Manchester, December 2020, 286 pp. Source: manchester.ac.uk, retrieved September 2022. [pdf]
• Ref. 43P: "Telewriter - YB 02251", Appendix Z to "Signals Monthly Liaison Notes No. 7", 15 January 1944, 2 pp. Courtesy L. Meulstee.
• Ref. 44: CIA Hellschreiber printers:
• Ref. 44A: "RS-13 Tests", 30 April 1956, 7 pp., document nr. CIA-RDP78-03330A000800130007-8 (sanitized / declassified / released 13 January 2014). Retrieved 25 March 2019.
• Ref. 44B: "ATP-3 Printer, Power-Pack, and Tape Magazine Layout", 1 pp. outline drawing, 6 June 1957, document nr.: CIA-RDP78-03330A004100080037-4 (sanitized / declassified / released 14 February 2012). Retrieved 25 March 2019.
• Ref. 44C: "Radio Set RS-13", Peter McCollum, 2017, source: militaryradio.com; retrieved 25 March 2019.
• Ref. 44D: "Commentary on the use of the AR-2 motor in the RS-13 radio set", 16 March 1956, 3 pp., document nr. CIA-RDP78-03330A000800130013-1 (sanitized / declassified / released 9 January 2014). Retrieved 25 March 2019.
• Ref. 44E: "Preliminary Evaluation of TP-3, Hellschreiber transistorized printer", 19 December 1957, 2 pp., document nr. CIA-RDP78-03330A004100080068-0 (sanitized / declassified / released 14-Feb-2012). Retrieved 10 March 2019.
• Ref. 44F: "Trip Report – AS-3 Tests", 23 April 1959, 4 pp., document nr. CIA-RDP78-03330A000900070004-7 (sanitized / declassified / released 30-Apr-2014). Retrieved 10 March 2019.
• Ref. 44G: "RS-6 Spy Radio Set", source: cryptomuseum.com. Retrieved 14 March 2019.
• Ref. 44H: "The Father of Modern Spy Radios - Allen S. Clarke" [pdf], Terry O'Laughlin, pp. 14-21 in "Popular Communications", June 2009. Retrieved 25 March 2019.
• Ref. 44J1: "Agenda - meeting no. 51 Research, Development and Production Review Board", 4 pp., 7 December 1955, document nr.: CIA-RDP78-05462A000100040018-2 (sanitized / declassified / released 16 February 2010). Retrieved 27 March 2019.
• Ref. 44J2: "Agenda Meeting No. 57 Research, Development and Production Review Board" [page 3: five ATP-3 printers completed], 13 June 1956, 6 pp., document nr.: CIA-RDP78-05462A000100040009-2 (sanitized / declassified / released 27 April 2001). Retrieved 18 November 2020.
• Ref. 44J3: "Agenda - meeting no. 57 Research, Development and Production Review Board", 9 pp., 13 June 1956, document nr.: CIA-RDP78-05462A000100040009-2 (sanitized / declassified / released 16 February 2010). Retrieved 27 March 2019.
• Ref. 44K: "June progress report governed speed D.C. motor" [TP-3 printer], date removed, 2 pp., document nr.: CIA-RDP78-03424A002000070003-1 (sanitized / declassified / released 19 September 2001). Retrieved 18 November 2020.
• Ref. 44L1: "Monthly Report 1 September 1956 - 30 September 1956" [R&D Branch, Engineering Div., R&D Lab.; page 3: 6 volt and 12 volt ATP-3 facsimile printer], 30 September 1956, 4 pp., document nr.: CIA-RDP78-02820A000100080003-9 (sanitized / declassified / released 27 April 2001). Retrieved 18 November 2020.
• Ref. 44L2: "Monthly Report 1 December 1958 - 31 December 1958 - Research, Development and Production Review Board", 7 pp., 31 December 1958, document nr.: CIA-RDP78-02820A000400040068-9 (sanitized / declassified / released 3 August 2000). Retrieved 27 March 2019.
• Ref. 44M: "Development of a Miniature DC Motor for the TP-3 Printer", 3 pp., 30 December 1958, document nr.: CIA-RDP78-03424A002000070001-3 (sanitized / declassified / released 19 September 2011). Retrieved 27 March 2019.
• Ref. 44N1: "Trip and Progress Report, ATP-3, Investigating the Use of Sand Castings - Arlington Bronze & Aluminum Corporation, Baltimore, Maryland", 2 pp., 29 August 1956, document nr. CIA-RDP78-02820A000100080022-8 (sanitized / declassified / released 27-April-2011). Retrieved 5 July 2019.
• Ref. 44N2: "Trip and Progress Report, ATP-3, Investigating the Use of Investment Castings", 6 pp., 29 August 1956, document nr. CIA-RDP78-02820A000100080025-5 (sanitized / declassified / released 27-April-2001). Retrieved 5 July 2019.
• Ref. 44N3: "Trip Report - TP-3 Motor Development with ... (sanitized)", 1 p., 30 October August 1959, document nr. CIA-RDP78-03424A002000070002-2 (sanitized / declassified / released 20-September-2011). Retrieved 5 July 2019.
• Ref. 44P: "title sanitized" [ATP-3: cost quotations from 4 suppliers for investment/die casting parts (case, cover, frame, clapper arm, pesure role holder, ink-roll holder, cradle, bearing block, magnet clamp, access port door) for 65 units], 29 August 1956, 4 pp., document nr.: CIA-RDP78-02820A000100080024-6 (sanitized / declassified / released 16 July 2001). Retrieved 18 November 2020.
• Ref. 44Q: "Conference Report Radio Station AS-3", 2 pp., 27 May 1957, document nr. CIA-RDP78-03330A004200010007-3 (sanitized / declassified / released 28-April-2014). Retrieved 5 July 2019.
• Ref. 44R: "Shipment of ATP-3x and RR/AA-11 to ... (sanitized)", 2 pp., 26 August 1957, document nr. CIA-RDP78-03424A002400090018-9 (sanitized / declassified / released 20-September-2011). Retrieved 5 July 2019.
• Ref. 44S: "TP-3 Motors", 2 pp., 19 November 1957, document nr.: CIA-RDP78-03330A004100080074-3 (sanitized / declassified / released 14-Feb-20012). Retrieved 5 July 2019.
• Ref. 44T1: "Contract RD-122, AS-3 - rest of title sanitized" [report on March 1958 supplier monitoring visit, equipment weight, design improvements, TP-3 printer for RR/D-11 receiver], 27 March 1958, 3 pp., document nr.: CIA-RDP78-03330A004100080072-5 (sanitized / declassified / released 14 February 2012). Retrieved 18 November 2020.
• Ref. 44T2: "Contract RD-122, AS-3 - rest of title sanitized" [report on May 1958 supplier monitoring visit, TP-3 printer], 26 May 1958, 2 pp., document nr.: CIA-RDP78-03330A004100080071-6 (sanitized / declassified / released 14 February 2012). Retrieved 18 November 2020.
• Ref. 44U: "Engraving designations, printer case cover" [TP-3], 12 June 1957, 1 p., document nr.: CIA-RDP78-03330A004100080036-5 (sanitized / declassified / released 14 February 2010). Retrieved 17 November 2020.
• Ref. 44V: "RS-13", Chapter 85 in "Wireless for the Warrior", Vol. 4, Supplement, Chapter 85, V1.03, Louis Meulstee, October 2017, 2 pp. Source: wftw.nl, retrieved 17 November 2020.
• Ref. 44W: "Final research and development report for governed speed 12-volt-DC motor" [TP-3 printer], 28 January 1959, 17 pp., document nr.: CIA-RDP78-03424A002000070004 (sanitized / declassified / released 19 September 2001). Retrieved 18 November 2020.

External links last checked: January 2016, unless stated otherwise.

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