[GreenKeys] Model 15 Selectors

[Jim Haynes]

I have seen a military machine with pulling magnet selector and a decal
on the copy holder saying the magnet coils could be wired in series or
parallel for 20 or 60 ma operation.  Issue 6 of the Model 15 parts book
shows only 177M magnet coil, 105 ohms so I don't know whatever happened
with the magnets used in the Signal Corps machine.

There is mention in the Teletypewriters for the Deaf book of Model 15s
with low-voltage selector coils of 1.4 ohms resistance, operating on
600ma.

The original purpose of the holding magnet selector, according to Walt
Zenner who invented it, was to allow operation with a loop voltage of
48 volts.  The reason was to protect TWX switchboard operators who might
accidentally contact the switchboard plugs where 130 volts could be 
lethal.

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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