From Analogman Mike - This fuzz pedal is a blueprinted version of the old Sola Sound / Colorsound / VOX tonebenders that had three germanium transistors and a TONE knob. These are known as MK-III and MK-IV versions, also known as "thin case" Tone-Benders. The grey one (MK-III) was made in 1973 and can be seen on some live pictures with Jimmy Page. Some RotoSound and Park fuzz pedals also used this circuit. We own three original versions of these pedals which we studied to make ours. The rare yellow MK-IV model was sent to us from a customer in Germany who LOVED the sound but wanted a smaller, more reliable clone that was made and sounded EXACTLY the same. That led us to the R & D which we used to make our production pedal after we made his custom exact clone.