When Ricky ditched mainstream country and returned to the bluegrass of his youth nine years ago, he immediately set about building perhaps the fieriest backup band in the genre, Kentucky Thunder. Instrumentals, an 11-track set of, um, instrumentals, naturally throws the spotlight on the astonishing skills of those players—not the least among them Ricky himself, who shines on mandolin and guitar. The relatively laid-back Instrumentals is lacking in the convective heat Kentucky Thunder generates in concert, but there’s enough fleet-fingered fretwork here to satisfy proponents of powerful pickin’.