The Locrian Mode is the name given to Notes 7 to 14 of a Major Scale (the seven note one ‘do re mi’ etc) or notes 2 to 9 of a Natural Minor Scale(the relative minor scale of the ‘do re mi’ one).
If you extract its root triad ( taking notes 1, 3 and 5) you’ll notice that the 5th note is flattened by comparison to that of a normal minor triad i.e. the D minor scale tonic triad = D F A but the D Locrian Mode root triad= D F Ab.
If you combime D and Ab you get a really dissonant harmony which medieval Christians declared to be the Diabolus in Musica (the devil in music) and censored its usage…..do you remember Tippa Gore and her PMRC trying this approach ? Too bad her Hubby lost the elections.
The flat 5th interval is the foundation of many bands sound e.g Slayer use it to get there creepy sounding passages.
The flat 5th is also the note which is added to a Minor Pentatonic scale in order to create a Blues Minor Scale…..D F G A C becomes D F G Ab A C D
For soloing you can either site it one fret below wherever you have put your Major scale or 2 frets above your Natural Minor or Minor Pentatonic/Blues scale.
You can of course experiment with putting it in place of the Minor scale.
By Guy Pople, our 7 String Guy