This is a cool little DC-AC converter to allow operation of the 117-x power supply and tube-type Swan rigs to operate from a 12vdc source. It converts 12vdc to 12vAC, feeds it into the 117x filament winding, and powers the 117x supply in that way. After working with this, I'm sure the 14c could be used on some Heathkit rigs, and other tube sets. Here's a few pics and a video...