Whether Jimmy Thackery headlines a festival in South Dakota or jams for hours in one of numerous blues bars that dot the musical landscape, he'll always unleash an intense volley of rockin' blues guitar guaranteed to leave crowds emotionally spent.   He's one of the few blues guitarists who learned first hand from the masters of the blues, not off a blues record or DVD. Though most associate Jimmy with his 15 years as the co-founder of the Nighthawks, he ended his time with them in 1987. Since then, Jimmy has been on the road as a solo musician for 15 years doing nearly 300 shows a year proving each night that he is still the guitar powerhouse in the blues.