RTS' SAP-612 source assign panel independently assigns each of 24 TW channels (12 two-channel TW user station strings) to any one of six busses, communication channels. All channels assigned to a common buss channel can intercommunicate and exchange call signals. One to three TW power supplies (such as models PS-31 or PS-15) may be conveniently connected to the SAP-612 to distribute power to the intercom stations. Alternatively, the SAP-612 may be used with a non-TW power source. Switchable 200 ohm line terminations are built into the SAP-612 for proper line termination when using a non-TW power source. The SAP-612 has two balanced, transformer isolated program inputs. Program 1 is permanently assigned to buss channel 5, and program 2 is permanently assigned to buss channel 6.