The symbol G7 + can be written in several different ways. The most common are G7 +, G7aug (short for augmented) and G7 # 5. When you see this symbol in music you should play a whole-tone scale. This scale is easy to remember because it is made entirely out of whole steps. In reality there are only two different whole-tone scales.
If you play one, and then move up 1/2 step and play another, between the two scales you have played all available combinations. Go up 1/2 step more, and you'll see that you are actually playing the same scale as the first one, just starting in a different place. This is much like playing a chromatic scale; Anywhere you start, you'll be playing the same notes as any other chromatic scale.
The basic chord in a whole tone scale is spelled 1 3 # 5 b7 9 (these numbers are a scale compared to a major chord of 1 3 5 7 9. In other words if I have a 1 3 5 7 9, and sharp the 5th, and flat the 7th it would become a whole tone sound).
Listen carefully how it compares to a major chord. The flat seven is a part of ALL dominant 7th chords, otherwise they would not be dominant 7th! If I see the symbol G7 +, I can play the G whole-tone scale over it. You can hear that the G whole-tone will effectively use ALL of the important sound from the basic chord.
Now, the fun part is that if I see on my music a ii V7 I like this: D-G7 Cmaj7, I can take some liberty with the G7 and change it to a G7 +. The whole point to altering dominant 7th chords is to add more tension. This makes the release even better!
Source by Pete Swiderski