Here's how to play a diminished 7th chord on the bass. The diminished 7th chord is a diminished triad and a fully diminished 7th. Which is also the 6th not of the major scale. Using G as our example, we'll use G as our root, B flat as our flat 3rd, D flat as our flat 5th, and now E as our fully diminished 7th which brings us back to G. We can also think about this as 4 minor thirds. G to B flat is a minor 3rd, B flat to D flat, D flat to E, and then E back to G. Here is the diminished 7th chord in 2 octaves.