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