Model 28 Teletype

[Redleg130]

I have been looking for a teletype for awhile, and found one that someone just wanted rid of. It looks complete and in decent shape. It still has the last thing it typed, which looks like a news wire. Unfortunately, it does not have the date, which would have been a neat bit of info.

I don't want to turn it on until I am fairly confident I wont damage it, I think this is a model 28 KSR (keyboard send receive) wall mounted model.

I see an extensive collection of manuals at US Navy Radio Communications - 1950's & 1960's (navy-radio.com) and found BULLETIN 216B which seems to be a basic maintenance manual and 217B for adjustments and lubrication.

I don't see any obvious damage on this machine. Ill have to get a ribbon and paper, the ribbon that is in it will probably disintegrate. Any recommendations for things I should check before powering on and attempting to test?


What I hope to do with this machine is mount it on shock mounts in my M35a2 shelter truck and have it as part of my amateur radio setup. I assume I can drive this teletype with a Raspberry PI using software called heavy metal on a serial port. This Rasberry PI is also what interfaces with the radios using FLDIGI software on ICOM 7300 and 7200. Like this it wont be driven directly by incoming signal but I am not sure what other items I would need to interface it, it appears I would need some additional items to drive it directly from on air signals.

Any help in my project to restore this Model 28 and ideas on how to get it in service somehow on amateur radio is welcome. People that visit my station really seem interested in the whole military comms station setup and adding the sounds of a teletype in the background will be a neat addition.

 

[swbradley1]

Does the interface for the Raspberry PI support 20ma loop?

 

[Redleg130]

Very unlikely the Pi outputs that level, I may need some intermediate device. I see several refences to people connecting these to various computers, but have not yet found how specifically. There is a 1/4in plug which I assume was the original interface. It may contain the intermediate driver already in the "electrical service unit" and ill just have to output serial from a computer to that somehow. The Pi has USB, and it is easy enough to adapt USB to serial on RS232, but beyond that I am not sure what magic has to happen between serial and the 1/4in jack, assuming the 1/4in jack is in fact the input output of the teletype.

 

[Redleg130]

More photos of this Model 28 wall mount

Last thing it typed


Maybe a news article?


The inside of the typing area


Keyboard appears sunken in


the electrical service unit


Power and 1/4in audio jack


Empty envelope for spare gear made in 1966, gear isn't in it

 

[swbradley1]

We had some in my region of support when I worked for Harris Computer Systems Div in the 80s. I think ours had an adapter built into the Teletype itself and they had two ports on them. One a military style connector and the other an RS232C. Yes, the USB to RS232C will work off of a Raspberry but you need a converter for the 20ma loop.

Here is a link:

mA to RS232 converter DAT3017I RS232.

mA to RS232 converter DAT3017I RS232. Current to RS232, Current to RS232, Volts to RS232 From Datexel.

www.datexel.com

But that may be too big a solution.

Try this:

BB-232CL9R

Serial Converter, RS-232 DB9 F / 20 mA Current Loop TB

buy.advantech.com

 

[SCSG-G4]

Long ago there was a guy in Texas that had a full comm setup in a shop van. Can't think of his name at the moment. He may have been the one that originally posted "Sarges Katrina Story". Then there is our buddy in Tenn. that has the Unimog Radio setup - he used to come to the GA Rally, and may still be on the site. His wife helped in the kitchen one year. I guess I'm showing my age - having a CRS episode (Can't Remember S**t).

 

[swbradley1]

Tenmogger? @SCSG-G4

 

[SCSG-G4]

Tenmogger? @SCSG-G4

Yep!

 

[swbradley1]

I can't find his name which means I have CRS as well Mike.

 

[Guyfang]

Did the printer ever have a TM? I have a bunch of TM's for this kind of equipment. But the PDF's are only labeled with the TM number, so giving me any other info wont help. Jut TM numbers.

 

[swbradley1]

And Patracy reminded me. It's - Tennmogger

Which makes sense now.

 

[SCSG-G4]

And Patracy reminded me. It's - Tennmogger

Which makes sense now.

Now to remember the guy in Texas, or search for one of his posts. But he is probably working in the motorpool in the sky by now. That fellow was in the Texas State Guard.

 

[Redleg130]

After finding this device, I watched some youtube videos of teletypes interfacing with computers and (incorrectly) assumed interfaces would be straightforward. As swbradley1 pointed out, it is current driven signaling. Modern serial is voltage driven, there is no place to directly interface this teletype (and most/all other teletypes from this era) to a computer. Anyone familiar with teletype will, of course, be thinking to themselves "well duh", I only bring this up if someone else reading this wants to bring a teletype into their collection.

I am still reading and don't have a full understanding yet but I think the interface structure will be:

The radio or some other signaling device (eg wires, like the term news wire) with the audio connected to some signal processing device normally termed a 'Terminal Unit' with an example being the HAL ST-6 and variants made by HAL, which is still in business but no longer makes these - Mainline Solid State ST-6 Demodulator (rtty.com)

The terminal unit then sends current, or switches current from a loop supply to flow on a 'loop' which is where the 'mark/space' (or on/off) signaling is encoded in baudot. I found a good explanation of the terminology that helped me start grasping this at terminal - What protocol do Teletypes use? - Retrocomputing Stack Exchange

These signals are converted into action by electromagnets that kick the mechanical parts around which culminates in the typing or reverse, transmitting keystrokes into baudot out to the terminal unit for conversion to signals to be transmitted out radio or a wire.

While this isnt the model I have, I found this video - Teletype Model 15 - How Does It Work? (youtube.com) a good aid in understanding how mark/space signaling is translated into mechanical action.

So, if anyone reading this is interested in getting a teletype, the Teleprinter (such as the Model 28 I have) is only one part of the whole picture.

In any case, before I even think about turning this on so as not to damage it by aged and exposed wires, or old gummy oil jamming it up, I am cleaning it up and lubricating it. Manuals to do this for a variety of models are found at Teletype Corp. Maintenance, Installation, Operation, and Parts Publications (navy-radio.com) . Disassembling it was shockingly easy, it appears they really thought through maintenance when they designed it.


The typing unit - I have always loved typewriters as fascinating mechanical devices, but the level of detail and precision in engineering and manufacturing this device really is impressive. A beautiful and fascinating machine.


The base and keyboard unit


The electrical service unit - there may be a loop supply (the 20 or 60ma 'loop') on this but I am still slogging through the various manuals and trying to get an understanding of the terminology and determine exactly what all this stuff does.

After I am done cleaning and lubricating it, ill be able to turn it on and see if I get 'local loop', the ability to press keys and have them print on the local teleprinter.

If you do get a teleprinter, there is a very helpful gentleman still selling parts for these at https://www.johnwhitney.com/misc/paul-rtty.htm - RTTY Electronics run by Mr Cembura.

 

[Redleg130]

Did the printer ever have a TM? I have a bunch of TM's for this kind of equipment. But the PDF's are only labeled with the TM number, so giving me any other info wont help. Jut TM numbers.

This seems to be a commercial model, but the military did use this model I think. I did find a gentleman that has paper manuals and other supplies like ribbons and ordered a set of manuals from him - Currently_available_Teletype_SUPPLIES_200602.pdf (w2jc.org) . Mr Cooper, another very helpful teletype vendor.

A massive library of manuals is at Teletype Corp. Maintenance, Installation, Operation, and Parts Publications (navy-radio.com) - it did take me a bit to figure out which ones applied to my device.

Thank you very much for offering