4-Channel Switchboard Main Station - 5-channel X 10 station assignment matrix, no speaker - with built-in 2-amp power supply, rack mount (2RU) SB-704 includes all of the features of the MS-704, with a 4 x10 assignment matrix in place of the internal speaker (external speaker required for station monitoring). The station features a ten-position slide switch matrix that allows assignment of any of the ten intercom lines to any of the four intercom channels, to an isolated separate party-line, or to an off position.