10W HF Linear PA kit assembly
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3.5 Wind and install transformer T201
T201 is wound on a BN61-2402 binocular core (two of these
are in the small internal zipped bag). Again, use a drill bit,
twisted by hand in each end of each of the binocular core
holes, to remove any rough edges which could cut into the
wire enamel.
T201 has a primary consisting of 6 turns, and the secondaries
are made up of 3 bifilar turns. First use a drill bit twisted by
hand, to gently remove any rough edges to the holes, that
could cut into the wire.
Un-wind the thinnest wire. The best way to un-wind it, without
tangling it up, is to think of what the kit-packing person that
wound it up did. Then reverse his steps. So, first unwind the tightly wrapped part in the middle
where the end of the wire has been secured.
Then, open out the spool of wire so that it is a circle.
Then unwind the spool, around your fingers, reversing the process of the person winding it in the
first place. Straighten the wire carefully and make sure there are no kinks.
Cut the thinnest wire into 4 equal pieces. Take ONE of those
pieces, bend it in the middle (do not cut it yet), and twist it into
bifilar-style wire. There are many ways to do this. You could clamp
one end and twist the other in a VERY LOW-speed drill or using an
electric screwdriver. Or just apply twists by hand, this is the method
I use.
The number of twists is not critical, and it will not be the end of the
world if it does not look perfectly neat.
Wind 3 turns of this bifilar wire on the core, remember that one “turn” goes through BOTH holes,
so in the end all the wires come out on the same side of the toroid.
Now take ONE more of the pieces of thinnest wire, and wind it through 6 turns. Remember, one
turn means the wire goes through BOTH holes of the toroid.
It is difficult to get the 6 turns through. It takes a great deal of patience. It can help to use a
wooden toothpick to poke in the holes, to move the existing wires to one side, to make space for
you to push through the new wire. Do not use anything metallic for this (such as a screwdriver)
which would scratch the enamel of the wire.
Be assured that it IS possible, I have wound many of these to prove it!
At the end of it, you have a transformer like the
picture, with 6 wires coming out of it. Two pairs
of wires will be the bifilar windings. Untwist
these ends but don’t remove the kinks from the
wire. This is how you can identify the primary
winding: since it was never twisted into bifilar
wire.
Now it is necessary to identify the wires of the
bifilar winding. So, tin the ends (by scraping
enamel off, or holding the wire ends in a blob
of molten solder for 10 seconds). Use a DVM
