I'm not if I'm the best to answer this question since I don't play the blues much, but in light of no other posts I'll give it a shot.
For a tab I used
this link. Tabs on the net aren't always correct. Also tabs don't give me rhythm or anything so I used
this youtube video for that. The tab seems to match-up with this and the other youtube video's so I think its right. (also I've never heard this song until I listened to the youtube video which also deturred me from posting).
The first thing I did was try to figure out what scale it's in. As you will see this song doesn't adhere perfectly to the scale. An A blues scale contains: A, C, D, D#, E, G and A. Now I can play song that contains following notes: A, C, D, D#, E, F, G and A, lets call these notes 'My Scale.' If I play a song in A minor and another song in C major the A in one song will sound different than the A in another song, also the C in one song will sound different than the C in the other song and so on. Just say I play a song in A Blues and another song in 'My Scale,' in A note in the first song will be the same as the A in the other song, the G in the first song will sound the same as the G in the other song, and so on. Basically 'My Scale' is the Blues Scale with an F added in, who cares, lets just think of it the A Blues Scale (the whole point of a scale is to let me know what the ccomplexion of the different notes are). With that said lets figure out what scale it's in.
First I looked at the rhythm secion at the bottom, it had 4 Am bar chords and some sort of F major chord and E major chord. I wrote done Am for the Am bar chords, and for the others I wrote down the root and the harmonies within the chord with respect to the root (in ascending order of pitch).
||: Am Am Am Am | F[r,3,b7,r] E[r,3,b7,r] :|| F - F# - |
Looking at that I'm thinking A minor scale (moreso A Blues based of the title)
Then I looked at the beginning of the riff. The first notes are: A, D, E, F, G, A. In terms of intervals compared to A those notes are: Unison, perfect 4th, perfect 5th, minor 6th, minor 7th, Octave.
Lets analyze. I'm gonna try to use words for the complexion of the different notes which will leave much to be desired. Okay, so we're starting on our root, always good. Then we quickly jump up to a perfect 4th which is a nice and solid note, not as solid as a perfect fifth, but its solid in that major thirds and minor thirds aren't. The we go to a fifth then up 1 semitone. (out of scale which may have prompted you to post), going up just one semi tone gave us a nice effect (and that's the best i can describe it, also a minor 6th solid like the fifth, fourth and root, but instead of being solid it gives us more color. Same with minor 7ths, more solid than the minor 6ths and it has some color too. this whole time we've been climbing up the scale, and now we're back to our root, 1 note higher. I bet when the fleetwood make played this the first time he loved, I did when i first heard it. Here we've been climbing up, the 4th and 5th were very stable, then a half step thown in there, a minor 6th and minor 7th less stable, then here up at the top we have this nice resolution, so he plays it twice, and i pled this a bunch of times on my guitar, its such a nice little thing how it does what it does then the root at the top. Anyways, then he vibratos a major 7th and goes back to the root on the 14th fret on the G string, these vibratos and the major 7ths have a nice feel to the them, like the root is real resolving, like i just finished climbing a mountian sort've resolution I'll say for this lick, then the major 7th with, vibrato builds tension tension then the root again but then he jumps back down the scale. I think he plays the minor 6th again and the 4th and (root), but the he jumps way up to a perfect fifth (which a nice and solid note) and so on and so forth.
I wasn't sure exactly what you were looking for, so I hope this is something like it. I couldnt hear any modulation, even when he jumps down the neck he maintains the A as his root. Your question could have been simply answered with you have play strickly the notes in your scale. But anyways, there you go.
If you learn how to play songs, then you learn songs. If you learn how to improvise, then you learn music.
