Well, I hope I can add a post without diminishing this thread.

A diminished seventh chord is very interesting because each note of the chord is a minor third above or below the next. This consistant minor third (three fret) interval between each note means (allowing for inversions) there are really only three such chords.

Any diminished chord may be named after any of the notes it contains since the intervals are all the same. (The choice of name depends on usage.) That is because you use up four evenly spaced notes of the scale playing any particular dim chord. Move your chord up the neck one fret and you have four new notes. Move it up one more fret and you have played all the notes there are. If you move it one more fret up the neck, you have the same four notes you started with.

If my ear (and memory) serves me correctly, Doc Watson plays an A#dim as the second chord of his wonderful rendition of "Deep River Blues." The fingering I use is a thumbed chord but you could skip the thumb and play only the four treble strings.

When chording, I tend to make an A#dim this way. Naturally these forms may all be moved up and down the neck as needed.

      - Mark