[GreenKeys] Questions about the M28 Stunt Box & Code Bars

[John Doe]

Thanks to Nick England and Jim Cooper for their replies.

I was under the impression that there might have been a third bank of
non-printing characters. In the brochure they say the first area is
"Letters", the second area "Figures" and the third area is "Select-Non
Print". After reading "Modifying the Model 28 Teletype"* and the brochure
again I now know this is not the case.

If I understand correctly, to have full use of the stunt box, don't bother
with function bars that use the Select/Non-Select ZERO tines because to get
into that mode, you'll waste valuable slots setting up the key sequence to
shift into that mode. As Nick and Jim pointed out to me before, that option
is only really used for Selective Calling. It just didn't click until now.

*RTTY Journal Vol.18, Issue 5 thru 7 by Irvin M. Hoff, W6FFC

Thanks again for the help clarifying the code bar scheme.

Nicholas Gromak.

P.S. I lifted the hook away from the SUPPRESSION bar and straightened the
bent linkage and I can see now how the non printing system works. The stunt
box stays working while the whole front of the machine stays still. It's
just like the brochure says: "The printer is always awake, its stunt box
always riding the line, waiting for information to be directed to it.".

My stunt box is equipped with a FIGS-Blank-H sequence that is supposed to
activate a motor-stop relay and a Blank-Blank sequence that is supposed to
mechanically lock the keyboard - according to the RTTY Journal article by
Hoff.  I don't have the motor-stop relay so the previous owner cut the
wires leading to the contact that sits above 29 and the keyboard lock
function bars need to be installed in 36 - mine have been moved up in the
20's so they don't do anything when activated.


On Sun, Oct 12, 2025 at 4:12 PM Nick England <nick at navy-radio.com> wrote:

> I think pages 16-17 of the brochure give a good example of the primary use
> of suppression and zero code bars, which is in selective calling (sel-cal).
> The “hook” is there so the printer is always active as you’d want it to be
> for local or dedicated use.
>
> There’s also some material in the RTTY Journal stunt box articles.
>
> But I have no experience from back in the heyday of ham RTTY. Hopefully
> some of the guys here who were involved in the autostart nets, playing LF
> tricks on friends, etc. will speak up.
>
> Nick England K4NYW
> Chapel Hill NC
> www.navy-radio.com
>
>
> On Sun, Oct 12, 2025 at 2:51 PM John Doe <jdoe10449 at gmail.com> wrote:
>
>> Hello all,
>>
>> Restoring my M28, I noticed that the SUPPRESSION code bar is permanently
>> hooked in the marking state with its actuator link disabled and the ZERO
>> code bar doesn't have a detent - so is sprung to the marking state but is
>> otherwise free to move. I can see rub marks on the SUPPRESSION actuator
>> links so I know it was operating at some point in the past. I'd like to
>> figure out why it was disabled to restore functionality. Photos attached.
>>
>> The manuals and stunt box brochure explain how they work, but not many
>> practical examples. I'd like to know more about the SUPP. and ZERO code
>> bars before I go on the hunt for shift forks, pawls, function bars, etc.
>>
>> Any help appreciated.
>>
>> Thanks,
>>
>> Nicholas Gromak
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