I have old amp that has AC 7 volts on its keying line. I would like to use it with my 746 Pro or Yaesu 920 rigs. I do have a Ameritron ARB-704 relay interface (less the paperwork) I am not sure what the jumber set should actually be. Going to see if any info is on the net. Any input on 7 volt keying would be helpful. Thanks Scott