Watch the Blues Power: Ex. 1b online guitar lesson by Andy Aledort from Kings of Blues & Rock Vol. 2: Albert King
This excerpt is played over the second half of a standard 12-bar blues progression, and begins with a brief reference to G major pentatonic (G A B D E) in bar 1, quickly moving right back within the same phrase-to G minor pentatonic. Because Albert's strings were upside-down, it was easier for him to pull down and put a big giant vibrato on the root note G fretted on the high E string. This is much more unnatural when strung normally, so it will take some practice to learn to apply this vibrato to good effect.