Take an ordinary open B7 shape and move it up the fingerboard to the 7th fret and voila! - you have E7.
I have used this chord as the basis of a rock & roll type 12 bar blues in E ( to get a different sound to that at the open position )
The alternating bass on this chord is achieved by moving your 2nd finger from the 5th string to the bottom string and back.
There's then another way to play an A7 chord ( a good one for vibrato or bending slightly )
I use an ordinary open B7 to keep the alternating bass going
followed by the A shape shown below in order to get some melody notes on top.
As the focus here is on chords I have just tabbed out the bare bones of this piece - as always use the shapes but find your own way of fitting them into tunes etc.
The soundfile has one twelve bar sequence
If you want to play along this is a looped version of the soundfile