INSTRUMENT, EXTENSION, CB No. 19

The description includes Case for Extension Instrument, C.B., No. 19; fitted with Coil, Retardation, Type 9A (80 + 80 ohms); Switch, 3-position, Drawing 926; 2 Condensers, metal-cased, 2uf; and Switch spring, 5-point.

Calls from the P.O. Exchange are received on P.O. Telephone, and answered by turning Switch to "Exchange." If an Extension is wanted, the Switch is left in "Exchange" position, Receiver is replaced on hook, and the Extension is called by means of the National Company's instrument in the usual way.

When Extension subscriber replies, he is plugged through to Switch spring on this instrument and the Switch turned to "Extension." When the Extension subscriber clears, his Indicator drops and bell of P.O. Telephone rings. The pegs should then be withdrawn and the Switch restored to normal, the latter operation sending the clearing signal to the P.O. Exchange.

When an Extension subscriber desires to communicate with the P.O. Exchange, his line should be connected to the Switch spring on this instrument and the Switch turned to "Extension"; the P.O. Exchange will then be automatically called.

When the instrument is used in connection with a private wire circuit maintained by the N.T. Company where that is the only extension, teed connections should be taken from the private wire to the right hand terminals A, B. The operating is the same as before, except that no plugging through is necessary.

The position of the apparatus should be in accordance with the wishes of the subscriber.

C.B. Diagram - No. 19.