This is a Century P/N 1D755 Slaving Amp that was recently removed for panel upgrade. It is used with the NSD-360 and NSD-1000 Horizontal Situation Indicator (HSI). Other parts of the slaved HSI system are separately listed, along with some spares I kept on hand. This unit works with either 14 VDC or 28 VDC electrical systems. If you buy other items from me, I will gladly combine shipping.