| 摘要 |
PURPOSE:To attain retention of a private trunk line without special provision of a retention switch to a telephone set by operating an existing function switch during acquisition of the private trunk line to close a retention loop to the private trunk line automatically. CONSTITUTION:When any of function switches, LK1, IK1 and SK is turned on for the service request such as talking by the exchange connection of a master set via a talking line during the operation of a changeover relay LR, the retention relay is operated and the retention loop to the private trunk line is closed. Transistors Q26, Q25 are turned on by changing over a contact hr<1> of a flicker oscillator WKO at the same time, power is applied to a release winding S of the relay LR, the relay is released and the talking circuit is changed over and connected to the talking line. |
