|STANDARD SWITCHBOARD FOR 20 to 160
METALLIC-CIRCUIT SUBSCRIBERS' LINES
No. 664 shown pictured to the right.
Fitted with jack and indicator for each line. For connecting the lines to each other pairs of plugs and cords are provided, and a three-position combined ringing and speaking key in connection with each pair. When the lever of this key is polled towards the operator (in which position it will remain until released), the latter is in the circuit and can speak to the subscriber; when the lever is pressed away from the operator (it only remains in this position while held there), generator current goes out on the calling cord, the right-hand one of each pair. In the normal position of the key the two lines are through to each other, and the operator is entirely out of the circuit. Two keys T are provided for listening on either one of two lines independently of the other, two keys 1 do the same for ringing, and two keys B are provided for ringing with battery instead of alternating current. These six keys can only be used with the combined key in the forward or listening position.
A hand-generator is provided, but this can be put out of circuit by means of a key M, if it is found more convenient to use a machine-driven generator. This is to be recommended for all switchboards of fifty lines and upwards, where the calls are anything like frequent.
A hand micro-telephone is provided for operating, and terminals for generator (Genr.), ringing battery (R B), earth (E), operator's speaking battery (M B), and extension bell (E B).
Facilities are also provided for making a rough test of the lines.
Last revised: October 11, 2019