For sale is a rare vintage RCA Type 56E MI-4162A passive analog equalizer. In good shape and working as it should. The RCA Type 56-E Line Equalizer was been designed to equalize the non linear characteristics of either one or two telephone lines, and it consists of two separate and complete variable equalizers mounted on a single panel. Any amount of equalization from zero to 40 db may be obtained in steps of approximately 3 db. The 56-E does not include line transformers or master attenuators. If you are going into a transformer device like a tube compressor the output does not need a line transformer. If you are going into the EQ with a tube mic or line preamp you don't need a input transformer. If you are using an unbalance in and out, it's best to add a 1:1 line transformer. Two separate and completely variable equalizers mounted on a single panel. The EQ needs to see a source impedance of 600 ohms to operate properly. Insertion loss is 7db or more The entire filter can also be switched out of the line