Abstract: An area voice paging feature is provided in a key telephone system wherein key telephone station sets each have a loudspeaker circuit responsive to a d.c. control signal, on an associated signalling path, to audibly reproduce voice band signals superimposed on the d.c. control signal. A page control interface circuit generates a page control signal in response to receiving the d.c. control signal, when the d.c. control signal is directed to the interface circuit on one of the signalling paths, and generates a d.c. biased voltage signal having an a.c. component corresponding to the voice band signals. Page switches each have an output connected in common with a predetermined respective one of the signalling paths and are each responsive to the page control signal to couple the d.c. biased voltage signal to the respective signalling path. Each loudspeaker circuit, in a group as selected by the page switches, receives the d.c. biased voltage signal and produces and audible signal corresponding to the a.c.

Abstract: A hands free answer feature is provided in a key telephone system which includes an intercom lead pair for providing intercommunication between key telephone station sets and a signalling path for providing audible signals via a loudspeaker circuit in the key telephone station sets. The hands free intercom feature is provided by the addition of a hybrid circuit including first and second unidirectional signal paths for coupling a.c. signals between the intercom lead pair and the signalling lead. A d.c. control signal having first and second d.c. signal states is generated on the signalling lead in response to a ratio of amplitudes of signals in the first and second signal paths being greater or lesser than a predetermined ratio. The loudspeaker circuits each include a receive signal path connected to a loudspeaker. A transmit path and path switching circuitry are added to the loudspeaker circuit. The path switching circuitry is responsive to the first and second states of the d.c.

Abstract: A telephone line circuit for supplying energizing current to a telephone line and for providing a voice frequency connection between the telephone line and an associated switching facility includes a transformer having a split primary winding, consisting of n turns, for connection across the telephone line and for connection to a power supply or battery. A first current flows in the split primary winding in proportion to the telephone line load characteristic. A balance winding in the transformer is connected in series with one portion of the split primary winding. The balance winding is counter-wound relative to the split primary winding and consists of more than n turns. A circuit including a current regulator causes sufficient balance current to flow in the balance winding to substantially cancel the d-c flux associated with direct current in the split primary winding.