This set is basically a wall
version of the 410 2-line desk set.
There was apparently not a formal model number assigned to a 2-line
wall set in the 300 series.
(The 500 series 2-line wall set is a 558. Photo here.)
Photos and the following description were provided by Fred, N4YQT
and are used with permission. (All rights reserved.)
2-line set or for use with KTS 1A, 1A1, and 1A2 systems, turn-switch on
bottom right corner of the dial. Key can be wired for
2-line pickup or one line pickup with extension cut-off, ringer cut-off
or headset control. Push button for signaling. The
hookswitch has the capability of A-lead control.
Added components include the
line switch (turnkey with pushbutton for signaling) and 44A terminal block to
Note the 2 extra screw heads on
the back for mounting the line switch.
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