Watch the Limehouse Blues online guitar lesson by Andreas Oberg from Gypsy Jazz Duets

Over the B7, Andreas uses a B7 altered scale, one which omits the 5. Ending on the B leads in well to the E minor chord as it is its 5th. Over the E minor, we can improvise with the Dorian or melodic minor scale, both imparting a bebop feel to the progression.