Garrett___ I found this in reference to an earlier explanation of the 5 of 5.
The basic application of a tritone sub is to take any 7th chord
you see and play another 7th chord that occurs a tritone (#4 aka b5),
away from that initial chord, such as playing Db7 over G7.
The reason that this sub works is that 7th chords with a bass note a tritone apart share the same 3rd and 7th.
Here are the notes of those two chords for comparison:
G7 G B D F
Db7 Db F Ab B
As you can see:
· The 3rd of G (B) is the same as the b7 of Db7 (B)
· The b7 of G7 (F) is the same note as the 3rd of Db7 (F)
This is glue that holds the two tritone sub chords together.
Here is how a tritone sub looks on those two chords (G7 and Db7).
Notice that the 3rd and 7th of G7 are the same notes as the 7th and 3rd of Db7 on the fret board.