Winding L1/L2, the interstage coupling transformer, is the most complicated part of this project. However, it's not at all hard to do.

We'll begin by winding this transformer.

The transformer is wound on a T-50-2 toroidal core. L1, the primary winding, has 43 turns; L2, the secondary, has five turns.

Note that one pass through the center of the core counts as one turn.

Here are the winding steps:

1. Using magnet wire, wind the 43-turn primary, being careful not to let turns cross over one another.
2. Count the turns to make sure you've wound the right number.
3. Using the plastic-coated wire, wind the five-turn secondary. Be sure to wind in the same direction as used for the primary.
4. Trim the leads to about an inch in length.

That's it! Now set the transformer assembly aside.