Teletype Model 28 Stunt Box Secrets and Data!
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see above....  Baudot or BCD?   as a console on the DEC  PDP-4
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STUNT BOX MATERIALS for Teletype Model 28 and Model 35 Submitted by David Christ K0LUM1) 

General Description 28 SB Issue 1 (c) 1959 Teletype 28 Stunt Box in color 20 pages. Description of how the stunt box works. 13.7 MB

Download the ULTIMATE Model 28 Teletype Stunt Box  Booklet  - 28stuntBox001


2) 28LP Technical Data Sheet Issue 2 (c) 1959 Send-receive and Receive-only Page Printer Sets 2 color 8 pages. Descriptions of various models and options available. Explanation of model codes. Comprehensive listing including pictures of all parts available for stunt boxes. 4.8 MB

Download  a Great Set of Model 28 Page Printer 8 page glossy Data sheets  - 28LP001


3) Handwritten note from Len Jaguilo on Teletype Corporation note paper attached to item 3. Additional information on selective calling. Undated 152 KB

Download Teletype  Model 35 Selective Call Cover Note - SelCallcovernote001


4) Application of the Model 35 Page Printer to Selective Calling. Memo dated August 9, 1963. Copy of 2 page typescript. 995 KB

Download Teletype  Model 35 Selective Call Model 35 printer to Selective Calling - 35SelCall001


5) Selective Calling Without Using the Zero Code Bar. Memo dated 3-27-63 Copy of 4 page typescript. 1.8 MB

Download Teletype  Model 35 Selective Calling without the Using the Zero  Code Bar  - NonzeroSelCall001


Non-Overline and Automatic CR/LF for the Teletype Model 28

Non-overline fixes that annoying problem when your Teletypeís carriage comes back and overprints a perfectly good line of text after receiving a carriage return but no line feed.

Automatic carriage return / line feed fixes the problem where your Teletypeís carriage continues to print at the extreme right hand side of the platen.




  1. Non-Overline for the Teletype Model 28
  2. On a normal Teletype machine, when someone hits CR, the carriage will automatically come back but will not turn up a new line. This is a nice feature for RTTY Art but a real problem if you are trying to copy a weak signal and you are already receiving partially garbled text.

    Fortunately, the Model 28 machines can be easily converted to avoid overlining. This change requires no new parts and can easily converted back to factory stock in a few minutes.

    Here are the steps to make the change:

    1. Remove the roll of paper
    2. With the motor running, look at the top of the stunt box.

      Hit the CR key and some slot will show activity. This should be slot 5, counting from right to left as you stand in front of the machine.

    3. Hit the LF key and two slots should show activity. These should be slots 38 and 40, counting from right to left as you stand in front of the machine.
    4. Leave slot 40 alone.

    Remove the LP and take out the stunt box (after disabling all power).

    Swap the universal code bars in slots 5 and 38 and reassemble the machine.

    Now, when the CR key is pressed, nothing happens. When the LF key is pressed, both CR and LF occur at the same time.

    You will still have to hit the CR key when you are transmitting. The CR character still needs to be sent to the distant machine. It may seem awkward to type the CR key and have nothing happen. But, the simplicity of this change, the fact that no additional parts are needed and that it works so well are huge benefits.



  3. Automatic Carriage Return and Line Feed


The first step is to check to see that the "0" codebar is already installed. Most, but not all, Model 28s have this feature installed. You can easily check this by looking under the left ribbon spool. There should be 9 code bars and the second from the bottom should be labeled "0". If itís there -- fine. If itís not there, you will need the parts kit needed to add this feature.

Next, look at the right side of the line printer near the piston used to slow the carriage when CR is selected. Look through the spacing drum Ė the round metal object that slowly turns as the carriage spaces across the page. Using a lot of light, look at the 12 oíclock position, through the top inside of the spacing drum to see something that looks like a horse-head. There could be something in the horseís mouth. If it looks like a bit, then you already have mod kit 157514 installed. If not, you need mod kit 157514 installed.

Next check to see if stunt box slots 4 and 39 contain parts. You can check this in the same way that you checked for motion when installing non-overline. Remember, the slots count from right to left when standing in front of the machine. You probably donít have anything in these two slows and will need to obtain two uncoded function bars, part number 153440 and two sets of slot parts, part number 153916..

When you have the needed parts, start the installation by adding mod kit 157514 to the "horseís mouth".

The next step is to remove the stunt box and add the parts to slots 4 and 39. Before you do this, you will need to code the uncoded code bar by breaking off all of the tines except for one. This is going to look like a very strange code bar when you are finished. The one tine that remains is in the zero level, non-selected position. There is a good picture of the function bars and how they are coded along with an overview of the stunt box in the Teletype brochure that you can find here: This will take a while to download. Page 12 of 20 has a good picture of the code bars.

If you donít have access to this document, break off all ten tines at the top of the code bar and three of the four tines at the bottom of the code bar. The one tine that remains is in the upper right quadrant of the four tines that are clustered together.

Once you have the slot parts and the code bar installed, and the stunt box and LP are all back in place, the checkout is pretty easy. First confirm that spacing over to the extreme right hand margin causes an automatic CR and LF. Then go back and count the exact point when this occurs. By standard, you should get 73 characters on a line an automatic return on character 74. If this is set correctly, you are finished.

To adjust the return character, locate the spacing drum and the five bolts holding the front and rear rings to the spacing drum. Going clockwise, you will see that the first, third and fifth are all round-head bolts. The second and fourth are hex-head bolts. You have to slightly loosen, but not remove, the first, second, third and fifth bolts to adjust the right hand margin adjustment. .Take a screwdriver and slightly move the rear ring that is attached to the spacing drum. Move the ring counterclockwise to lengthen the line length. You donít have to move the ring very far so go slowly. Temporarily tighten the bolts that you loosened and try the line length test until you get the desired line length.

Submitted by: Russ - WA3FRP




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