DR Strings PHR9 Pure Blues Nickel Round Core Electric Guitar Strings. 9-42 PURE BLUES Electric Guitar Strings are constructed with a pure nickel wrap wire on a round core wire to produce a distinctive warm and balanced sound with rich overtones and a vintage vibe. They create the unmistakable tone and feel of classic American rock and blues with chords that ring out sweet and round, while leads have more punchiness and sustain. They feel smooth and playable with a remarkably responsive touch.