Tritone substitution: Eb7 can be replaced by A7 (a tritone away). Both chords share the same tritone between the 3rd and 7th, resolving to the same tonic.
The augmented 5th destabilises the triadic core, the minor 7th preserves dominant function, and the major 9th extends the chord. The #5 alteration intensifies chromatic voice leading.
Application
V+ → I in jazz
Altered blues
Passing chords
Voicing & structure
Root position
v1Eb(Eb4)Bass
root
v2G(G4)M3from Eb
v3B(B4)M3from G
v4Db(Db5)M2from B
v5F(F5)M3from Db
Harmony
Compatible scales
All chord tones are contained in these scales — use them for improvisation.