Watch the Applying the Chord Arrangement Principles online guitar lesson by Fareed Haque from Solo Guitar Handbook

At 3:24, note that I say A7 but actually play C#dim7. Going back to our diminished chord discussion in the Chord Embellishment section, C# dim7 is spelled C#-E-G-Bb. A7b9 is spelled A-C#-E-G-Bb; C#dim7 is the same notes just without the A.