For short wave listeners, Drake produced the SW-4 receiver in 1967 (and later the SW-4A), which matched the rest of the 4-Line in appearance, was based on the R-4 design, but greatly simplified to be easier for the casual listener to use. It was replaced in 1973 by the SPR-4, a receiver similar in appearance to the R-4C but, again, simplified for ease of use. Its biggest difference, however, was that it was Drake's first all solid state design. It covered a greater portion of the high frequency (HF) and medium wave spectrum than did the SW-4, by using a large set of selectable heterodyne oscillator crystals for selecting the tuning range, each covering a 500 kHz wide segment. The receiver came supplied with 10 crystals and a user could add up to 14 more.