Secondary


The secondary was constructed from a 4.5" OD piece of thick-wall PVC. I cleaned it thoroughly, sanded it to remove any rough patches, and then coated it twice with high gloss polyurethane. Then I mounted it onto a winding jig. The end supports of the winding jig were constructed from pieces of 2x8, with bearings pressed into them to allow easy turning. The PVC piece was bolted onto a threaded rod through holes drilled in endcaps. The rod was then bolted to the bearings. On one end, the rod was fed through the bearing, to allow mounting a pulley. The jig was turned using a DC motor I salvaged from an old reel-to-reel tape recorder. The speed was adjusted with a variac.


Here is a closer look at the winding motor assembly. You can see that I switched to a larger pulley; it provided better speed adjustment. The "belt" is just a very large rubber band. The tension adjuster consists of the original tape tension adjustment bearings from the tape player  mounted onto a larger piece of scrap metal that is screwed to the base and can be turned to change the tension.


The winding jig worked like a charm. Not counting the time I took to snap a few pictures, it took only about 15 minutes to wind 1000+ turns of 22 AWG magnet wire. Then I left the motor running slowly for a few days while I coated the secondary with polyurethane (around 20 coats total). The end result was a very smooth, thick finish.


I made the endcaps from the same HDPE that I used for the primary supports (cutting boards from Wal-Mart). I cut them using the same set-up that I used to make the acrylic cover for the primary. Here is one cap still on the cutting set-up.


The bottom cap has a plug mounted into it for easy attachment of the ground connection. The plug does not project through the cap into the coil form. It is mounted with nylon fasteners and held in place by an additional HDPE piece. It was mounted to the secondary form with nylon fasteners, tapped into the coil form wall.


The top cap was constructed to hold a large nylon bolt, onto which the topload was mounted. Like the bottom cap, it was cut to fit snugly inside the coil form and held in place with tapped nylon fasteners. The large nylon bolt is held in place with a pin drilled through its head and then clamped tight with the two square pieces of HDPE.

Brass washers and small piece of copper pipe that slide over the nylon bolt provide the connection to the secondary wire.