I am modding my old F2-B today. I often use it for recording various instruments, using it one day for bass and the next a Fender Rhodes, etc. Anyway, I usually take pictures of it and other gear so I can repeat my settings later on if needed (yes I am too lazy to take complicated notes of all my settings). I do this a lot. However the F2-B sits in a rack under a shelf, which means I can't get a usable straight on shot to show how it's set because the knobs only have reference lines on their sides. This morning I removed the knobs and used my TAIG/Unimat micro lathe and mill to drill small reference spots in the tops of the knobs to fix the problem.
The overall shot shows the F2-B pulled part way out of my rack to work on it.
