De Forest RJ4 Detector, 1914

This rare 1914 de Forest Audion Detector Control Box (Wireless) Model RJ4 was sold amateur radio operators and for experimental use. The RJ, or "Radio Junior," was not a complete receiver, but a box to hold the A and B batteries for the vacuum tube and switch taps to set the proper voltages. A spherical (later tubular) audion tube was mounted on the front of the box. The box and tube were sold together. In addition to a set of headphones, the radio operator would also have at hand a tuner connected to an antenna. In 1916, de Forest came out with a lower-priced RJ-9, but ongoing price wars, along with increased war-time federal control over amateur radio production and operation, drove many small companies out of business. Like many others, de Forest would soon sell most of his patent rights to RCA.