[GreenKeys] Back to Teletypes after many Years!

[Jim Haynes]

On Tue, 1 Dec 2009, Roy Morgan wrote:
>
> I *think* we need more information.  The stunt box is not in the base
> of the ASR, is it?  I don't know diddle (pun intended) about model
> 28's (yet), but I think the stunt box is at the rear of the typing unit.

Right.  And there was a selective calling mechanism that was an option
for the stunt box.  One of the code bars is a print suppression code bar
and when slid to one side stops printing, but allows everything else in
the typing unit to continue.  Another code bar controls whether the
printer is or is not listening for station selection characters, since
you don't want it to respond to selection characters that happen to
occur in the message text.

The CAA/FAA was an early customer for this feature, although it could
also be used on any multistation line to control which printers copy
the message.  On FAA machines there was a solenoid on the left side of
the typing unit that could override the selective calling feature.
This was wired to a local-remote switch on the front of the machine.
Remote meant use the selective calling feature and local meant locally
override it.  This allowed them to keep a spare machine which could be
switched to a circuit using selective calling or to one not using it.
Selective calling was used on for example the circuit that distributes
flight plans, so that only the stations needing flight plan data for
a particular flight would copy it.  Selective calling was not used on
the weather circuits, since all stations were to copy all the weather.

This was fine for FAA stations, where there were always several machines
prnting most of the time.  Other kinds of users in business offices
objected to the machine sitting there making busy noises but not
printing.  To meet this objection there was an electronic stunt box
developed that would monitor the line silently and turn on the printer
when needed.  (This was after I had left the company, so I don't know
much about it.)

>
> I have a Model 28 KSR with extra "stuff" in the base, behind the
> sloping panel that's in front of the operators knees.  I think it's
> Tempest equipment, but have  not investigated yet.  Is that where some
> sort of electronic selective calling system would be put?
>
Probably so.  If you have the tempest model then the selector magnet is
problably inside a shielded box and has shielded wires running to the
stuff in the bottom.  Sometime take a picture of it for us to look at.