Tested and working well, good used condition as pictured. 
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The Alberta is a low-gain overdrive, designed to add a little extra sizzle to your sound, making your notes fly off the fretboard with a bit more personality and feel. It´s a very musical and pleasing tone, that countless players have used as a “sound enhancer”, not just a great sounding overdrive.

It was actually designed for boosting the amp SRV-style (gain down, level up), so it´s lower gain and less strident than Stevie´s pedal.