[GreenKeys] Stock Ticker

[Jim Haynes]

That's quite a find.  Those machines are quite rare and when they do
change hands it's usually for thousands of dollars.

After the stock exchanges went to the more modern start-stop ticker
about 1930, Western Union continued to use the old tickers to transmit
things like baseball scores until 1950 or so.  There was one in my
home town where the customer was a news stand.  There was a space in
the back of the news stand with tables where a bunch of old geezers
played dominoes all day long.  Maybe they were World War I pensioners.
I assume they bet on the baseball games and drank enough Cokes during
the day to pay for the ticker service.  (Dry county, so they weren't
drinking anything alcoholic, at least not visibly.)

There are two circuits, one for rotating the print wheel and the other
for operating the print magnet.  The rotate circuit is bipolar, while
the print circuit is on-off.  When the system is idle the transmitter
sends out reversals on the rotate circuit at about 20 Hz.  This steps
the type wheel around until it latches up at a home position.  To print
a character the transmitter sends a pulse on the print circuit, which
releases the latch and allows the type wheel to rotate in response to
the reversals.  When the wheel gets to where the desired character is
over the tape, the reversals stop momentarily and another pulse on the 
print magnet hammers the tape against the inked print wheel.  Then the
print wheel resumes rotating until another character is printed or until
it latches up against the stop after a few revolutions.

No batteries at the ticker location; the current comes from the
telegraph office and operates a number of tickers wired in series.
For long distance transmission a scheme was worked out to use a single
wire.  The polarity reversals are sent through both a polar relay and
a neutral relay.  The neutral relay is sluggish in operation - what we
would call slow-operate in the telephone biz - so it remains released
while the reversals continue.  The polar relay responds to and repeats
the reversals.  When there is a pause in the reversals the neutral relay
has time to operate and energizes the print circuit.

See also the article by Charles R. Tilghman, "Telegraph History : Some
Early Days of Western Union's Stock Ticker Service, 1871-1910" in
Western Union Technical Review, 15:2, April 1961, p. 75.  (To find
Western Union Technical Review online, google for it.)