After the surprise, hard-won success of their previous studio album, 1973’s Tres Hombres, the Texas power-blues trio ZZ Top took an odd approach and returned with 1975’s Fandango!: a half-studio/half-live set. “Jailhouse Rock” sounds less like a ‘50s Elvis Presley single than a militant call to revolution. The “Backdoor Medley” is pure ‘70s guitar sludge, one long boogie-number with audience cheers and singer Billy Gibbons egging on the crowd with sassy spoken word and flashy guitar licks. But while the band has always been a formidable live presence, it’s the acute tightness of their studio productions that made their legend and established them as FM radio survivors. It’s what had made Tres Hombres such a revelation, and this album’s finest moments remain the two definitive studio cuts: “Tush” and “Heard It on the X.” In addition, the solid “Blue Jeans Blues” (with its striking guitar tone) goes a long way toward explaining why these guys continue to grace the cover of guitar magazines worldwide.