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Old 25-04-15, 14:30
Chris Suslowicz Chris Suslowicz is offline
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Join Date: May 2007
Location: England
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Quote:
Originally Posted by Robert Bergeron View Post
Thank-you David,

Does anyone know what the abbreviations for line and control are ?

Could it be L and Col ?

If so , i think we just resolved a mystery in the Restoration Forum about outside connections in the Wire-5 box.
Er, If those are for the WS19 remote control units then it's two separate pairs (as far as I know) on three terminals. One pair (Exchange Line) is used if you need to connect it to a switchboard for normal telephony use, and you cannot control the set over that (because there may well be capacitors in the way that will block the DC path for the relay and the circuit resistance will also be variable/unknown). The other pair (Control) is used between two control units (only), to operate the set from a remote position (Max 3 miles, I think, more if you add extra batteries for the DC signalling voltage to overcome the extra circuit resistance.)

The exchange line is usually connected to the "Local" control unit.

You may see earlier field telephones with three terminals (marked L, CL and E), but the CL means "Capacitor to Line" and was intended for "piggybacking" a telephone onto a DC telegraph circuit (usually railway lines) to avoid the need to lay lots of cable, especially in remote areas in India, etc. The capacitor blocks the telegraph DC circuit and the telegraph sounder is unaffected by audio frequencies (speech and buzzer calling).

Chris.
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