[GreenKeys] Stock ticker operation?

[Jim Haynes]

This is why I keep a 1960-ish edition of Encyclopedia Americana.

I'll try to describe how the ticker worked when I was watching it
in person around 1950.  The old tickers had been replaced in stock
market service as too slow around 1930.  Western Union re-purposed
them to transmit baseball scores.  There was one customer for the
service in my home town.  Jack's News Stand had some tables in the
back where a bunch of old geezers sat all day long, playing dominoes
and drinking Cokes.  And, I suspect, betting on the baseball games.
I think they were pensioners from WW-I, or maybe from the 
Spanish-American war.  A teenager was hired to read the ticker tape
and write the developing situations on a chalk board.

There were two electrical circuits, one for the typewheel motor and
the other for the print magnet.  The basis of the typewheel motor
was a pair of discs with triangular-shaped teeth cut into one face
of each, and the two of them facing so that there was a narrow slot
between the two rows of teeth.  A nib on the end of the typewheel
motor electromagnet went into that slot.  The current was polarity
reversals at a frequency of perhaps 20 Hz.  The nib would bear on the
triangular teeth of the motor, each time pushing it a little way
around.

There was a pin projecting from the type wheel shaft.  There was a
part ending in a Y shape projecting from the print magnet.  There
was a worm gear looking thing which guided the Y-shaped part from
side to side.  After a certain number of rotations of the shaft the
pin would engage the Y and that would stop typewheel shaft rotation
even though the polarity reversals continued.  That is how the type
wheels were synchronized on all the printers and with the transmitter.
Just a few seconds of idle time and all type wheels would be held
at the starting position until the print magnet was energized and
disengaged the pin from the Y.  Once released they would all rotate
in synchronism since it was the pulsing current reversals that
caused the motor to turn the shaft.

To print a character the reversals would briefly stop and the print
magnet would be energized, pressing the paper against the type wheel.

Using two wire circuits to run the tickers was probably cheap enough
within a city where wire runs were short and there were many tickers
to be run (in the days of stock market service).  It was costly for
tickers located remotely from the transmitter.  I believe the solution
was to use a single circuit carrying the reversals and pauses, and
then a slow-to-operate relay that would energize the print magnet
circuit when the reversals paused, but was too slow to follow the
reversals.

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 	"Ya can argue all ya wanna, but it's dif'rent than it was."
 	"No it ain't! No it ain't!  But ya gotta know the territory."
 		Meredith Willson, The Music Man