Tips on power chords

Ever think of what a power chord is?  Well it is believed and accepted as a chord that is composed of the root and the 5th note above.

There is a combination of terminology here.  A chord composed of the root and the 5th is not necessarily a complete chord, therefore the name sits on tone quality more so than on harmonic principles.

We have all played them and still do.  Especially if you grew up in the grunge era and were trying to play "Come as you are" or something of that matter...power chords are good friends that add quality to our compositions and playing.

Now, talking a bit about how these relate to music theory, there is an issue with one particular power chord in ANY key.

The VII chord in any key will not technically produce a legitimate power chord the way we like for it to align with musical theory.  There is an alteration here.  The 5th in the VII chord of ANY key will not belong to the scale in question.  Therefore, we may need to adjust it by playing a diminished 5th (or augmented 4th).

Example:
In the key of C major, the VII chord is B...the power chord of B is B5 as we know it :)
B5 will get played usually by placing your 1st finger on the 7th fret 6th string and your 3rd finger on the 9th fret 5th string.
Problem: the last note played 9th fret 5th string is F#...and as we know, we are in the key of C major here, and there are not F#'s in the key of C major.
Adjustment: if it sounds funny and you want to make the sound more cohesive, then adjust the F# by lowering your 3rd finger by one fret.  Thus, playing a natural F with your 2nd finger instead.

However, always remember that sound is king, so if you are looking for that F# sound then go for it as it creates a nice tritone interval agains the key center.  On the other hand, the F itself will create a tritone as well against the root of the chord.