The Blue Max. I think they were by World Engine Company. Bought as a Semi-kit in about 1975 or so. The cord had a full-size stereo phone plug. I know (pretty sure) I was Buddy-Boxing my cousin before my sons were born, and they turned 30 four days ago. We moved from that location in May 1980.

The 10-channel reed set I had in 1966 did not have the capability.

Ken Erickson, AMA 19352