The Skreddy Lunar Module and Skreddy Screw Driver are built to essentially the same schematic, with some different component values and transistor part numbers. This mod transforms an all silicon transistor design to a hybrid MOSFET-Silicon-Germanium design. The advantages of the MOSFET 1st stage are higher input impedance, smoother 1st stage overdrive and the ability to drive the 2nd stage harder. See the attached file for a table of parts changes. Only the parts that change have been listed. The pot values all remain the same. There are two optional parts that get soldered onto the bottom of the board: D1 & C101. D1 provides static protection for Q1's gate and is highly recommended. C101 adds a high-freq power supply bypass. D1 is soldered in parallel with R4 and will clear the pots. C101 is soldered between the + power terminal and the input jack ground terminal (right next to the + terminal) and will clear the pots. There is one more difference that I did not install: The Screw Driver has a 33K in parallel with C14 that alters the Volume pot's taper slightly. C14 is 4.7nF in the Screw Driver, but with the 33K left out, I kept C14 at 2.2nF. I actually used a 2N5210 for Q2, mainly because I have a pile of them. Any high-gain, low-noise NPN will work, including 2N5088, 2N5089, MPS-A18, etc. I always change the LED resistor value because I use violet LEDs in my builds. There is a pic of my Screw Driver in the Build Reports forum.
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