How to tune a guitar to true open A tuning. By Ed Dowling of Dowling Sound Labs. This is the tuning I use on my Dobro. Use light gage strings – .011 to .052 max. The 2nd, 3rd and 4th strings will be tuned to a higher tension than a standard tuning. This tuning is great for slide guitar – not so good for fretted music. Open D and Open E are better for fretted guitar playing.