Koss T-5 Headphone Speaker Junction Box - Speaker / Headphone Connector in Box - It was utilized in the 1960s to connect headphones to Tube Amplifiers that did not have 1/4" connectors. Has two (left and right) 1/4" jacks and two level (right/left) controls. So headphones have to have similar to utilize. Please see all photos. Obviously this is a used but still working item.
Note: Please see photo of the schematic and terminal strip on bottom of the unit. This schematic depicts the proper hook up.