Hello
Accordionist since the age of 7, then guitarist at 14 and
keyboard at 18 and today at 66 years old, I can neither play accordion,
nor play guitar well. But when it comes to chords and piano,
there is no problem.
So let's start at the beginning.
An Eb chord is three notes ..Eb G and Bb . (without any reversal)
To make Eb 7 you
add a Db the eighth of Eb
would be Eb (the octave)
A chord being formed of the root (Eb)
and its third G
and its fifth Bb
7b5 means 7th
with diminished fifth
To decrease the fifth is to decrease by a semitone the note
Bb which becomes A
So the Eb7b5
It's the notes
Eb G A Db
I leave the rest of the answer to the accordionists for the
keys of the basses and chords.
Lionel