Watch the Ham's Boogie in A 1 online guitar lesson by TrueFire from Acoustic Guitar Explorations
Lesson Source: David Hamburger's Fingerstyle Blues Factory
This tune is written out as a 24-bar blues. All that really means is that we're spending twice as much time on each chord; once you get it into it, it will feel pretty normal because all of the phrases are proportionally the same as they would be in a 12-bar form. This first chorus is built around a series of call-and-response phrases. We start with a bluesy melodic phrase in measure 1-2, then answer that with the "Magic Sam" rhythm figure in measures 3-4. Measures 5-6 are a variation on measures 1-2, which are answered again with the "Magic Sam" figure in measures 7-8.
Because of the 24-bar form, we then have four measures on D7, measures 9-12, which are then answered with 4 bars of Magic Sam in measures 13-16. Finally, we spend two bars on the V (E7) and two bars on the IV (D7) before wrapping up with a four-bar turnaround in measures 21-24.