Originally Posted by: stephen82I have been playing Tequila by the champs for a while now and when I played the notes for the main section, they roughly followed the Cm pentatonic.[/quote]

Fun tune!

Originally Posted by: stephen82So I play an improvised solo over this section based pretty much on the Cm pentatonic and it all sounds good to me. However the chords are F and Eb. Therefore, I thought I was really playing the Eb pentatonic. But that didn't make sense to me. I assumed the key was F.

The song is in the key of F. But the melody is modal, meaning that it follows the mixolydian mode more than the major scale notes. That's really just one note changed, the E natural (major 7th) to E-flat (minor 7th). This is very typical for bluesy tunes. :)

The main chord progression is clearly in a mixolydian modal F:

F (I) - Eb (bVII) repeat

The B section or chorus goes to a form of the IV chord, then the II & V before returning to F (I) to start again.

F dim (functioning as a B-flat b9 IV) - F (I) 3X

G (II or V of V) - C (V)

The melody as played by the sax makes use of the minor 7th so it's very modal sounding.

c - f - f - e-flat - g - e-flat - f -c

Not all melodies start on the root note of the key. This one happens to start on the 5th degree of the scale (c is the 5th of F major). So, it just happens to coincide with what looks like the C minor pentatonic scale.

To make matters a little more confusing, the B section has the note a-flat! This is from the F minor scale. It helps to give the melody even more bluesy tension. It's from the F dim or B-flat b9 chord.

If you want to solo over this tune you would do well to learn the sax melody first. Then approach it as if it was a blues in F. Play lots of F major pentatonic with the minor 7th. Then play F pentatonic minor (blues scale!) but add the major 3rd!

[quote=stephen82]

Can anyone give me an explanation of the mixolydian scale/key.

Mixolydian is the 5th mode of the major scale. If you start playing any major scale on the 5th note, then play up an octave you get this particular set of intervals.

1st - 2nd - major 3rd - 4th - 5th - major 6th - minor 7th - 1st

So, it's similar to the major scale except that the 7th scale degree is minor instead of major.

I cover the modes of the major scale in this tutorial.

https://www.guitartricks.com/tutorial.php?input=370

There are 2 ways of looking at & using modes: structurally or ornamentally.

1. Structural: each mode relates to a parent scale. So you are always in one key (A major for example) and the various modes are just ways of playing the A major scale, but giving each note of the scale a chance to start the pattern. Often this is used to stay in one key, but play over the chord changes within the key.

2. Ornamental: You just play whichever mode you like the sound of at the time regardless of the key. This requires that you know & apply the scale or mode interval formula. This is most often how you get bluesy melodies like Tequila.

I have another tutorial that is aimed at using modes ornamentally.

https://www.guitartricks.com/tutorial.php?input=770

Hope that helps! Please ask more if necessary. Have playing that tune! :)