It's in a double-wide black enameled Hubbell box with a standard = Teletype 110VDC connector on one end next to a ceramic cable entry. = Inside are 4 hi-wattage resistors and a barrier strip connected to them. = The schematic inside the lid says "151A1 TTY Resistance Unit". What is this used with and for? 73, Don Merz, N3RHT