To see what I mean, play this two-note shape [Ex. 1]. In the eleventh position, this tritone implies C7. If it doesn’t sound like a C7 chord to you, that’s probably because it doesn’t have a root. Add a C note below it and your ears will likely recognize the tritone as part of the chord. The cool thing about this interval is that in order to convert it into F7’s tritone, all you need to do is slide it back a fret. And to get G7’s tritone, simply slide it up a fret.
A fun thing to do with this shape is incorporate it into your lead lines. Here’s how I often play it over a I-IV-V progression [Ex. 2]. Remember to mix and match these licks and, once you get them down, change ’em up however you like so the moves stay fresh—perhaps like this [Ex. 3]. Or add a pull-off [Ex. 4]. I often use this stuff over a fast I-IV-I-V progression—i.e., a C7-F7-C7-G7 song form where each chord lasts a full measure—but you can, of course, take any one of these moves and apply it to a static vamp on its corresponding chord.