It is incredibly easy to wind those yokes, (fingers get sore after awhile) Jenn probibally has done a hundred of them already, 100 turns of 24ga. Magnet wire, I do wonder where the math comes from however, it seems rather generic, and currently running some tests with a induction meter,, (and comparing some notes with Radiation Laboratory...however it does work, and those boards are the real deal...Not only Ampliphone clones but upgraded to drive larger tubes, With a smaller footprint...Yes that is worthy of some chuff😁