The B alt vamp works very nicely through a G Chord as its notes include a strong II(B) and V(D)part of the chord without playing the rootnote. This riff makes for some simple and easy changes under any major I, V chord progression ,but works most effectively through a C major/G major Combination. This example is based upon all the notes of the C Major Scale, the first phrase notes I,III,V,VI and 8ve, the B alt phrase (2nd phrase) the VII,II,IV notes plus a second use of the VI note.