The RJ4 was not a complete receiver, but just a box to hold the A & B batteries for the tube and switch taps to set the proper voltages. The tube, either a tubular audion, or later a spherical audion, was mounted on the front of the box. The box and a tube were sold together. The tube output was connected to a set of headphones. Used with the RJ4 detector box would have been a tuner like a ‘loose coupler,’ connected to an antenna, and a set of earphones.
The second version of the RJ4 came out in early 1914. This is the version in The Perham Collection. The filament rheostat was moved to the right-hand side and the switches were built in.
A later version had a tube socket for a spherical audion, and was called the “Improved Type RJ4 Detector.” In 1916 de Forest came out with the RJ-9, which was a panel only and sold for a lower price. By this time, de Forest himself had already sold most of his patent rights.