1. Finding Manuals and Wiring Diagrams
2. Terminology
3. Procedure I Used in Restoration
4. Interfacing With Your Teletype
5. Finding Consumables and Parts
6. Links

Since my setup is approximating a 50s-60s era military communications shelter, a natural addition is a teletype. The military used these extensively until the mid/late 90s, and without the modern digital systems we have today, it was great way to send bulk text at least vs sending over voice communications. My unit in the 91 Gulf War used teletype for brigade <-> battalion communications over long distances. While adding a teletype device does improve a setup that is going for a military appearance, there is an extensive learning curve for someone not familiar with these devices.

When looking for a device, I really didn’t know what I was getting into. While I still do not know much, I did want to share some terminology and knowledge from ‘Greenkeys’ that I picked up.

Greenkeys is a mailing list and you can find info on reading the archives of it and joining at Greenkeys@qth.net. Greenkeys is referring to the green keys of the Teletype Corporations keyboard of the Model 15

The Greenkeys group is the most helpful technical group I have ever been involved with. There is an ocean of experience and knowledge that they are willing to share, which is great since electromechanical devices really don’t have any modern equivalents so people coming from GenX and later won’t have much of a frame of reference for these devices.

Finding Manuals and Wiring Diagrams

To understand a device, there really is no escaping reading, and reading quite alot. For Teletype Corporation devices, and I assume other manufacturers, there are several variations in a model family so looking at the correct document is a challenge, and even then finding specific things I found to be a challenge. Almost every document can be found at US Navy Radio Communications – 1950’s & 1960’s – the Navy in the name of the website does not limit the scope of the documentation, it includes most models in commercial and military use. To find a document specific to your device, look for the data plates on the assemblies – as an example, I have a Model 28 KSR wall mount, and the keyboard/base assembly data plate shows:

My keyboard/base is an LK type, found in the code portion of the data plate. I can then find the specific documents and wiring diagrams by searching for “LK” in the directory of Teletype Corporation documents:

For wiring diagrams, it seems that Teletype Corporation consolidated several variations of diagrams in a single document, so you will have to refer to the bottom right corner of the diagrams to match your specific model to the document:

I received this very helpful summary guide to navigating documents from John, a Greenkeys member:

Short course on docs.
Original Teletype bulletins 0 to 999 Description, theory, adjustments, lubrication in general, later version were simply a listing of the BSPs that contained the information.
More bulletins 1000 to ?  Parts manuals

Military manuals contain everything in one document.  sometimes hard to find the right place in it for your information.  I only got there if I can't find it elsewhere.

BSP (Bell System Practices), my preferred sources.
573-000-000, index of 28 series
573-115-100 description of printer
573-115-400 wiring diagrams
573-115-7xx adjustments and lubrication
573-115-800 parts
873-116-xxx keyboard etc.

Last 3 digits can go all over the place for exceptions to the general case
e.g. parts for LESU-72 are in 573-133-804 (IIRC) instead of the generic -800

Also a TC suffix mean Teletype Corporation issued BSP rather than through the chain of command to Bell System.  Sometimes you'll see both on navy-radio with slightly different issue date. 

Terminology

Teleprinter terminology is unique, many concepts and terms have no modern equivalents.

Term		Examples
Teleprinter	A device that prints characters to/from a transmission medium such as radio or wire	There are several, some made by the Teletype corporation, like the Model 28 series Teletype Model 28 – Wikipedia and the Model 15 series, but there are other manufacturers. Teletype is a corporation name, teleprinter is the term for these devices regardless of manufacturer
ASR	Automatic Send Receive – Large machines with facilities for paper tape to store and send text. They key feature of ASR is the ability to send a message repeatedly using a paper tape with punched holes that encoded the text	Model 28 ASR – TELETYPE MODEL 28 ASR COPYING ITTY – MUSEUM OF COMMUNICATIONS – SEATTLE – YouTube
KSR	Keyboard Send Receive – relatively compact machines that can print received text and send text via a human operated typewriter like keyboard	Model 28 KSR – kb8ojh.net – Station Information – Teletype
Baudot	Data transfer protocol used in many teleprinter devices, it is a 5 bit encoding of various character sets	Baudot code – Wikipedia
Baud	Measurement of data transfer speed used for Baudot 45.45 baud, or 60WPM is common, with 75 baud at 100WPM is also in use. There are a small handful of other baud rates around as well	Baud – Wikipedia
Loop	The part of a circuit that carries the required current to drive the selector electromagnets	Current loop – Wikipedia
Terminal Unit (TU)	Device that converts audio into electromagnetic pulses that the teleprinter can use to set code levers to represent characters in Baudot	There are several, but the HAL ST-6 is a common model – HAL ST-6
AFSK	Audio Frequency Shift Keying, a common method of encoding teleprinter data for transmission	Frequency-shift keying – Wikipedia Not Black Magic: AFSK
RTTY	Radio Teletype, sending encoded characters over a radio transmission medium	Radioteletype – Wikipedia
ITTY	Internet Teletype, sending an audio stream over the internet to be decoded by a terminal unit	Internet Teletype Teletype News Services New York Times News Wire
Running open	a teleprinter will repeatedly strike a blank character when not connected to a loop
Mark Space	“Mark” is generally identified with the binary digit “1” and “space” with the binary digit “0”. (From Wikipedia)	Mark and space – Wikipedia

Procedure I Used in Restoration

When looking at a teleprinter it may be tempting to plug it in and see if it works, but you may want to do some checks before you do this. When I first got the Model 28 KSR, I referenced the manuals and disassembled the major components. The Model 28 is surprisingly easy to get apart for maintenance. My primary goal was to look for obvious damage and thoroughly inspect wiring for brittle or shattered insulation to ensure there were no shorts. Either the model I got was stored well, or it was just made to be durable (or both), but all the wiring was in good shape. I did find some rubber parts that didn’t hold up well, but nothing that would cause damage if powered on. I found some rubber on Amazon and cut some replacements for these parts where I could. Fortunately the platen was in good shape since I would not be able to DIY such a thing.

To clean, multiple people recommended Simple Green degreaser, and it was quite effective. Avoid saturating electrical items (eg the motor), but for the mechanical items I placed the assemblies in a large plastic tub and sprayed liberally. I used a soft bristle toothbrush to gently scrub stubborn dried oils, or a toothpick to get the really set in grime. Avoid tools that will scratch. I rinsed thoroughly with water and set in the sun to dry. When it was dry I used penetrating oil to give a light coat of oil to prevent corrosion. Using the manual, Adjustments and Lubrication series, I used machine oil and a silicone grease to get the machine lubricated.

Once you are confident the machine will not be damaged by powering on, you can plug it in and see where you are at with it. At least with the Model 28, it will be normal to power on and immediately start repeatedly striking blank characters (called running open) if the unit is not connected to a ‘loop’ or signal source. Some models have a test mode if you want to power this up and test it without connecting a loop. In test mode, you can type on the keyboard to see if the keyboard and printing mechanism is working properly.

My machine had a broken part which took awhile to figure out. Having no experience with these machines it took a lot of reading referencing the documentation to see how all the mechanical parts interacted. The people from Greenkeys were a key part of pointing me in directions or things to look at. I did have to manipulate each part and gain an understanding of its purpose and function to finally get to a resolution. It took a few weeks in my case, so if you run into this situation, be patient and methodical. It may have been a benefit to have to run down this problem since it compelled me to get a basic understanding of the mechanical part. There is a lot going on with these devices, with a myriad of necessary functions, all relying on mechanical actions to do them. It really is impressive that the engineers of years past were able to accomplish all these complex actions in a device that still functions decades after it was made.

Interfacing With Your Teletype

To summarize – you cannot directly plug a teleprinter to a computer.

When I was looking for a teletype, I assumed that a standard serial port would be sufficient to send and receive data from the device. I was vaguely aware that some sort of translation from ASCII to Baudot would need to be done, but I was fairly sure connecting the device would be straightforward. This assumption was quite incorrect.

The actual interface these devices used was known as a current loop. Signaling is based on the presence of current, or no current, cycling on/off to represent Baudot code. This current kicks around electromagnets (directly or indirectly) to set mechanical levers that ultimately represent the bits mechanically.

Explanation from W6IWI

Teletype stuff uses a current loop (normally 60 ma, but sometimes 20 mA)
at a voltage of about 100 volts. The selector magnets in the printer
detect the current (mark) or lack of current (space). So, that's different
from RS232 which is a voltage (typically -12V for Mark, +12V for space)
instead of a current. Further computers normally work with ASCII (7 bit
characters) instead of Baudot (5 bit characters). Finally, most USB to
serial converters will not go down to 45.45 bits per second (the baud rate
for 60 words per minute).

The common cable used for current loop teleprinters are Tip/Sleeve and Tip/Ring/Sleeve cables. One of my devices requires a Tip/Sleeve cable, while another requires Tip/Ring/Sleeve. Musical instruments and other audio applications still use these cables, so finding them is possible.

The youtube channel Deramp5113 does an excellent job of explaining the concepts of how current loops set mechanical code levers in the video series https://www.youtube.com/playlist?list=PLB3mwSROoJ4JoPgcLzZ3kMKmQI5eN-4No

From a practical perspective, there is no modern equivalent to the current loop interface in common use, some industrial systems use similar concepts for signaling, but there is no way to -directly- connect a teleprinter to a computer.

There are two options that I am aware of, get a vintage terminal unit or one of the recently created interface devices.

Terminal units come up for sale from time to time, but you will have to research your teleprinter to discover what type of signaling it requires as there is variation. 60 milliamp current loop is common, but there are 20 milliamp machines. I ended up with an iRL FSK-1000, which I am still researching before use. Reading the manuals of these devices thoroughly is encouraged as they throw fairly stout voltages/currents around and misconfiguring them can damage things (or hurt you). What a terminal unit does for you is convert audio AFSK, from any audio source like radio (RTTY) or any other audio stream (such as ITTY) and pulse Baudot to the current loop which in turn prints whatever has been sent.

A helpful comparison of various Terminal Units can be found at RTTY Terminal Unit Comparison by W6IWI.

A handful of hobbyists have made interface boards that emulate a terminal unit. One device, specifically made for the Teletype Model 15, but adaptable to the Model 28 is made by DeRamp and can be found at Model 15 Interface

The DeRamp device takes either standard computer serial input, via a DB-9 to RJ11 conversion cable, or from any audio source (ITTY, radio) and sends Baudot pulses to its current loop output. A microprocessor performs the signal processing needed to accomplish this, along with providing some helpful utilities like inserting carriage return/line feed at intervals you can define, and ASCII to Baudot character conversions/substitutions to accommodate characters available in ASCII that are not available in Baudot.

There are other hobbyists making interface devices, one would be W6IWI DSP TU Part Two and a handful of others.

Finding Consumables and Parts

Teleprinters use paper and ink ribbon, and fortunately these consumables can be found, but they may take some searching. The ink ribbons I have were made in the 70s and still print clearly, quite impressive for something 50ish years old.

I found the unusual paper my machine uses (8 1/2×11 tractor feed, which isnt standard) at Label Printing & Shipping | Label Outfitters Label Outfitters. They were very helpful in confirming I was ordering the correct thing before expensive shipping. Another vendor appears to be 8 7/16″ White Bond Paper Roll, 12 rolls/case POS Supply.

Currently_available_Teletype_SUPPLIES_200602.pdf – Mr Cooper, W2JC has various new old stock supplies and is very helpful.

For parts – Mr Rtty has a huge inventory and is very helpful.

Links

Amateur Radio Teletype (RTTY) – General information and ITTY feeds

US Navy Radio Communications – 1950’s & 1960’s Navy Radio with extensive documentation and information on teleprinter and related equipment, commercial and military. It isn’t limited to Navy equipment

W6IWI RTTY Notes – W6IWI’s notes on his teleprinters

Model 15 Interface, deramp5113 – YouTube – Information on older computer systems, including teleprinters

kb8ojh.net – Station Information – Teletype – Notes on the Model 28

Restoring a Teletype Model 15 – Notes on the Model 15

Greenkeys@qth.net – Greenkeys is a very helpful group (mailing list) focused on teleprinters. They have extensive archives to search where you may find information related to question you may have

When I got my teleprinter working, I was immediately faced with the problem of what to print. One source are the Audio Frequency Shift Keying (AFSK) Internet Teletype (ITTY) audio steams from various sources:

• Teletype News Services (60 and 100wpm)
• Internet Teletype (60wpm)
• New York Times News Wire (60 and 100wpm)

The first thing I printed was the Gettysburg Address text copied from some website, which would not have worked without the feature of the interface I happen to have that automatically carriage return line feeds (CR/LF) at a column defined in its settings. Without that feature it would have stopped at the end of line and just typed the same spot over and over. Even with the feature, the formatting was not perfect. In fact, formatting text is a bit of an adventure, particularly if you don’t have software inserting CR/LF at the end of the typing line on your machine.

Unlike modern word processing software, type width is fixed and lines do not “wrap”, meaning the CR/LF has to be placed reliably at the last printable column, which appears to vary from machine to machine. I am using 70 characters per line.

For demonstration, I wanted a military document and I found Operation Atropian Iron at PAVILION Example OPORD_202102 copy. For people who have done military staff exercises, you should be familiar with the “fictional” nations of Atropia, Gorgas, and Donovia. Besides the operations order format, the typical formatting of a TTY message that may have been sent between military teletype machines would be 16-line message format – Wikipedia.

The document below is the operations order in 16 Line format, but assuming software inserted CR/LF. If you don’t have this feature, you can use Notepad++ to insert the CR/LF, which actually would look better since words won’t break in the middle at the end of line.

I have seen the RYRYRY sequence from time to time and wondered what that would be for. The sequence of The quick brown fox jumps over the lazy dog – Wikipedia is something I am familiar with, being every letter in the alphabet, to test type. The RYRYRY sequence is to test and toggle each bit in the electromechanical parts that represent Baudot – RY (test signal) – Wikipedia. From that article – “The characters R and Y are “01010” and “10101” in 5-bit ITA2 code”. So sending the RYRYRY sequence then alternates the mechanical levers that determine the letter to be printed every character. This is useful if you want to test the device, lubricate the assembly, or just exercise it. I made an RYRYRY file and include it below, a 69 column file with alternating RYs.

I am using a Deramp interface board to send text. Using putty to paste text does not seem to work, I am using TeraTerm – Tera Term Open Source Project – to send text as file, using File/Send File, using the binary option, and 110ms delay per character. Large text files seem to overrun the teleprinter without the delay.

While waiting for a serial interface (DB9 to RJ11) so I can use the Deramp interface board (Model 15 Interface) I have been chasing down some occasional screeching noises. These noises were loudest when cold, then smoothed out, returning on occasion. There are a handful of ball bearings in the typing unit and I used silicon grease in each. The grease turned orange after some use, so I cycled grease until it stayed clean looking. This and plenty of oil in all the places the manual calls for did not silence the squeals. I finally found the source, the motor.

There are ball bearings in the motor, but they aren’t very easy to reach. The motor manual (Bulletin 295B) does show that there are oilers for these bearings

You press down on the 4 (2 on each side) ball seals and drop oil in there to lubricate the bearings, but if the old grease is polymerized (like old cosmoline) it wont help a bit, shown in the picture below.

Getting the motor apart was not too bad, there are two long bolts holding the motor together, I marked how everything was oriented so I wouldn’t put it back together incorrectly. The old grease was stiff like a tough wax and I had to pick it all out with a tough plastic pick. I used a Rothco gun cleaning pick set I found at the Fort Riley Post Exchange. There are two bearings and I cleaned both, then repacked with modern grease. The bearings seemed fine, no play when moving them and they spin much better now. This service quieted the squealing sounds and hopefully this machine will keep on clacking away.

I have never seen or heard of this sort of thing, besides the Skillcraft government clocks that you find in almost every government installation, a clock purpose built for army use. The Chelsea clock company is still in business but this particular example was made in the 40s sometime before brass was limited as a strategic material and Chelsea converted to a Bakelite type of case. Chelsea made a large number of clocks for Navy use and some for army message centers where logging times of message traffic is important.

Before futzing around with this clock, as I did find these are fairly rare, I decided to take it to a professional and found that KC Clock in Overland Park, KS ( Kansas City Watches and Watch Repair – KC Watch | Overland Park, Kansas ) has someone familiar with the Chelseas. He stated it was in good shape internally and to leave it be as it is. I would have polished the brass, but apparently there is a coating on this that would be damaged if I had done that. I also would have been tempted to repaint the illuminated spots on the face, but KC Clock discouraged that as well to preserve its original state and I will take their advice. If I do need it worked on, I will definitely take it to KC Watch as they were very helpful and willing to share their knowledge on this clock.

This clock is completely mechanical, powered by an internal spring wound with a key seen to the right using the shaft on the numeral 6. Time is set with a dial on the left side. I wound it a few turns and was very surprised to find it lasted at least a week and held time the entire cycle. Ill have to wind it fully and see what its endurance is, but I suspect quite awhile.

I will have to build the wooden carrying case that it would have been issued with, but it will be a neat addition to my overall communications shelter setup.

I fully assembled the Model 28 and it looks great. It is working in ‘test’ mode, where the device ignores the signal loop and behaves like a typewriter. It is a bit loud, however.

When I got it, there were foam panels stuck inside the housing, but the foam had thoroughly disintegrated. This foam was there to deaden some of the noise this machine makes when operating. Replacing this isn’t straightforward, since these haven’t been made in decades, and these likely wouldn’t have been a part offered by Teletype in any case.

Cleaning the interior of the housing was quite a chore. The foam was easy to remove as it turned to powder when touched, but the adhesive was some tough stuff. I used citrus oil based GooGone which was effective, but needed significant soak time to soften the adhesive, then quite a bit of scrubbing to remove it. It took a couple of cycles of this to remove most of the old adhesive. To finish, I scrubbed with dawn dish soap to remove the citrus oils, then finished with simple green.

I thought through some ways to replace this material, such as quilting something. It occurred to me that carpet squares may be just the material for this. They are light, somewhat rigid, and I was able to find a decent color approximation.

Making the templates from scratch paper and cutting the carpet is fairly straightforward, but the adhesive on the carpet squares isn’t sufficient for a vertical installation. They do offer a spray adhesive with the carpet squares that seems highly effective. When using it, it sticks quite firmly very quickly so placement has to be accurate. These carpet squares should be durable and dampen the noise of the machine without looking out of place.

Next project is the loop interface to a computer provided by Deramp – Model 15 Interface. It will take quite a bit of assembly, so I don’t anticipate a fast build, but with a signal loop I’ll be able to use this close to its original purpose.

You can see a video of this machine working at Model 28 Typing (odysee.com)

This thing is quite complicated mechanically, and it took a bit of doing to find the manuals, find what manuals applied, how to find things in the manuals, then learn the terminology, and so on. The problem turned out to be a broken part that needed replaced. The broken part was responsible for resetting the keyboard after a key was pressed, so you could press a key once, then manually had to reset the code bars to press a key again.

Doing this required disassembling the major components, then disassembling the ‘signal generator’, which is the assembly attached to the large geared shaft

This assembly has a bunch of tiny parts and I am surprised I didn’t lose anything. Reassembly took quite a bit of fiddling with adjustments, fortunately the manuals run though these and I got a better understanding of what all this stuff does.

While I had it apart, I did disassemble the main drive gears to determine the speed of this machine. The nylon (ivory color) gear in the center is one gear that determines speed, but the part number isn’t visible when assembled. Disassembling this permitted me to pack the roller bearings with grease and find the part number – 195997 found in 573-116-800TC-iss3-7012. The speed of this machine is 100WPM.

Now that it is working mechanically, I can start trying to figure out how to interface this with a computer. 100WPM is not common on amateur radio, so getting this to work directly on the air wont be practical, but I can use it indirectly with fldigi and send text to it as a way to print text. This does get me interested in a machine that I can use directly on the air, maybe a Teletype Model 15 at some point.

Simple Green concentrate and a soft toothbrush cleaned up the Teletype really well. Stubborn oil residue came off with a fingernail or toothpick. There are several springs that probably could come loose with vigorous scrubbing so I was careful to use light pressure. I set these subcomponents in a plastic tub and sprayed and scrubbed for awhile, then rinsed and set them in the sun. There are small spots of rust sheen here and there, but ill very lightly coat surfaces with oil.

Disassembly of the subcomponents was surprisingly easy. Just a small handful of fasteners, two electrical disconnects and the typing unit and base/keyboard unit came out without a fuss. Now that it is clean and I am confident there are no exposed electrical contacts, I can reassemble and test after lubrication according to the manual – Teletype Bulletin 217B

Before I plug this in, I need to inspect the machine to ensure it won’t be damaged or gummed up as it begins to operate. A helpful person that sells parts for these machines recommended simple green as a gentle degreaser, followed with lubricating according to the manual. Manuals can be found at Teletype Corp. Maintenance, Installation, Operation, and Parts Publications (navy-radio.com) although getting familiar with the terminology will take a bit

This machine is gummy and dusty, but as far as I can tell there is no mechanical damage or electrical burns on it. Wires all appear intact. The primary motor that gets everything moving spins freely and moves the internals around quite a bit in what I think is correct operation.

Looking at the manual, it appears that there were two paper feed mechanisms, and I have the ‘sprocket feed’ type. Modern term seems to be ‘continuous form’ paper, which if the dimensions are the same, appears to be readily available. Its been decades since I have seen this type of paper though. The sprockets are a fascinating mechanism, the teeth retract as they rotate to only be out when needed to pull paper, and retract when they would get in the way of the mechanism. It appears to be working smoothly.

I will have quite a bit of cleaning ahead of me as there are many places gummy residue is hiding, but I am fairly optimistic that this is in good shape and will be either working or repairable.

Ill have to interpret what connections 5 and 15 are and that should move me towards understanding the input output of this device. Using some sort of serial connection isn’t possible directly, it requires a fairly stout (likely 60ma) current to drive it.

The AN/PRC-9 sets was disappointing to miss out on, but I did get one item I have been after, a teletype.

Last time I saw a teletype in service was mid 90s, email and other electronic communications made these unnecessary since you could print what you needed and discard the rest without wasting consumables. Like the Remington typewriter I have, these mechanical devices are fascinating and the distinctive sound they make should be nostalgic for anyone visiting the station that worked with teletype when they were in service.

It appears to be in good condition, with no obvious damage, but getting this hooked up to something to drive it will be a challenge. Goal will be getting it cleaned up, operational, and able to type things I send it from a Raspberry Pi using FLRIG and FLDIGI. Actual RTTY seems fairly rare these days but I should be able to send text from any digital mode, or really any text that I want a printed copy of.

Edit – FairRadio ran out of stock before my order, so I wont end up with these. There really aren’t many places that have these either so I may have missed my window. Disappointing but ill keep looking and hopefully get lucky sometime.

Following the SCR300 radio, the Army acquired the PRC-8 (Armor)/9 (Artillery) /10 (Infantry) series of radios. These radios were in service for the 50s and early 60s. I previously have taken an unsalvageable PRC-9 as a housing for a modern radio set, but I got a couple of additional salvageable radios which I intend to make operational mostly as issued. The batteries are no longer made, so I wont be able to use those, but there are some alternative power sources I have found that others have come up with.

The PRC-9 that I used gave me a bit of familiarity with the innards and the parts that weren’t corroded I kept. This should give me some spares, a few of the tubes seemed to be in decent shape.

From an amateur radio use perspective, the PRC-10 (38.0 to 54.9 MHz) covers the 6m band and the PRC-9 (27.0 to 38.9 MHz) covers the 10m band. I selected this model because it was the Artillery version, not for its frequency coverage, but it appears that I got lucky, 10m seems more active to me than 6m over the years I have been listening to the amateur bands. The PRC-8 (20.0 to 27.9 MHz) would have been a good selection too, covering the 15m and 12m bands.

I have been wanting a deeper understanding of radio for quite awhile, and this project should do just that. I did work on tuning 12 series radios (the RT-524) in the late 90s full time, but that was just following a script more than understanding fundamentally what I was doing. My basic understanding is that antennas pick up tiny voltage differences and amplify them but the roles of the various components I am not familiar with. Ill just have to start at the beginning, take this in steps, and slog through the math. The math part I am not really enthusiastic about, but I won’t gain an understanding if I skip that part.

I also have a second Transoceanic 3000 that needs repair that I can explore after this project, which should be an interesting comparison of differing receiver designs.