The schematic that's out there is a good way to build one, but it did have a flaw, the output wires where reversed, so the red was the negative and the black was positive. If you build one, just make sure you test the output with a multitester, it will show if anything is messed up.
I am using the radio shack transformer using the 12.6 volt secondary output. My multi tester shows exactly 12 volts DC and 14 AC with this transformer. The DC loses a bit of voltage because the full wave rectifier makes the DC output pulsed which is not a issue for a etcher, you can add a capacitor to smooth the output and that will bring it back to almost the full output.
For my test I used a old schrade + stainless blade that has a crack and 1 cup of hot water with 4 tablespoons of salt. You might read on the web that you need special electrolytes to do stainless, but the saltwater worked really well on this. I think a lot of the people that built these had the output wrong, the etch pad has to be on the negative DC output and the positive gets clipped to the work piece, if you do it the other way around it does nothing. With AC it does not matter but DC it certainly does. I made a crude stencil of a T with black electrical tape and stuck it to the blade, then dipped a Qtip in the salt water and blotted it so it was just damp, not dripping wet and then just slowly rubbed the qtip on the inside of the stencil, if it's working the end of the qtip will become black as the metal is removed from the blade and deposited in the qtip as black oxide. Considering this was a crude stencil, it came out really well and pretty darn sharp, it even etched the fine lines on the corners from the razor blade. After I etched on DC for about 30 seconds I switched to AC and that is how you blacken the mark.
(scroll down for images of the unit I built)
