The Valcom and 25 volt speakers can share a common audio source but cannot share a common power source. First I would make sure all the Valcoms are working correctly with one pair coming from the 24 volt power supply that is large enough to power the number of speakers you have. That is the biggest mistake that is made, a power supply that doesn't have enough units to power all the speakers. When connecting a 70 volt source to Valcom paging you should use PN v-1095. This single gang expansion module allows a Valcom system to be connected anywhere on 25/70/100 volt line without straining the the existing amp.

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