Check the listing for details. SONIFEX TB-6R Intercom rackmount 6-way. Condition: Used. Listed at 550.00 USD. The TB-6D/R intercoms use ‘phantom’ or ‘common-mode’ DC signalling, where a ground is placed on the centre-tap of a transformer, to communicate, so are compatible with many of the other talkback systems in use. A sending station places an earth on the centre-tap; this is detected by the receiving unit, which then un-mutes (and provides a DC signal to dim local monitors if required). Each station has a single listen line input and six outputs. When any of the talk buttons is pressed, outgoing talkback and signalling is sent to the selected line. The ‘send’ circuits to a single receiving unit are simply connected in parallel to the input of the receiving unit. Since sending impedance is quite high, and receiving input is quite low, the effect is to mix any incoming talkback signals. Housed in a 2U rack-mounting case, this is similar to the TD-6D. The external microphone input XLR is on the front panel, as is the speaker grille.