Major 6th chords are common in jazz because they are a good substitute for major chords. The formula for Maj6 chords is as follows: Root-3-5-6. In a key of F, this would be spelled F, A, C, and D. In the key of C it would be C, E, G and A. Practise spelling major sixth chords for the other ten keys. Notice that some of these voicings require you to dampen an inside string. If a string is marked with an "x" in the fingering, it should not be sounded. For instance, in the first voicing below, you can use 4 to dampen to fifth string. The only other solution is to fingerpick instead of strum. There are dozens and dozens of possible voicings. A good chord book can be a handy eference to have, but do try to come up with some voicings of your own. This will reinforce your knowledge of chord theory.
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Minor 6th Chords
In jazz, minor 6th chords (min6) are common replacements for minor chords. After you learn some of these voicings, play any song you know and try using them in place of the minor chords you would ordinarily use. The 6th adds a beautiful element to the minor quality.
The formula for min6 chords is: Root-3-5-6. In the key of GMajor, this would be G, Bb, D, and E. In DMajor it would be D, F, A and B. Practise spelling the min6 chords in the remaining keys. Here are some sample voicing:
