The typical JT coil is wound bifilar, two windings at the same time. Winding the wire at the same time makes it easier, and it’s electrically the same as if two separate windings were wound. I often use 24 AWG wire and wind the coil bifilar. But I also wind it using four pieces of wire, I’ve seen this called quadrifilar winding. The advantage is that the wire can be smaller, and easier to wind. And the resultant four windings can be connected as if they are bifilar, or as in the case of the drawing, three of the windings can be in parallel for the primary, and the fourth used as the feedback winding. The advantage is the three windings have a lot less DC resistance than a single winding, and a lot less loss due to that resistance.
2013-03-11 Quadrifilar Winding A Joule Thief Coil
