ELECRAFT K2 - Page 52

ELECRAFT 51
To wind RFC14, cut a 9" (23 cm) length of #26 red enamel-
coated wire, then "sew" the long end of the wire through the core
exactly 10 times. Each pass through the core counts as one turn.
The finished winding should look very similar to Figure 6-15, but
with 10 turns rather than 14.
Verify that the turns of RFC14 are not bunched together.
They should be evenly-spaced and occupy about 85% of the core’s
circumference. If the turns are all bunched together, RFC14’s
inductance value will not be correct. (Unless otherwise specified,
about 80 to 90% of the core should always be used.)
Stripping Toroid Leads
The enamel wire supplied with the kit can be heat-stripped. One
way to do this is to place a small amount of solder (a "blob") on the
end of your soldering iron, then insert the wire into the hot solder
for a few seconds. Another possibility is to burn the insulation off
by heating it with a match or small butane lighter for a few seconds,
then use fine-grain sandpaper to remove the enamel residue. Avoid
scraping insulation off with a razor blade, as this may nick the wire.
Strip and tin the leads of the toroid before you mount it on the
board. As shown in Figure 6-15, you should remove the enamel
from the leads up to about 1/8" (3 mm) from the core. You should
see only bare wire (no insulation) on the side to be soldered.
Install RFC14 vertically as shown by its component outline,
near the front left-hand corner of the board, then pull the leads taut
on the bottom of the board.
Solder the leads of RFC14. When soldering, make sure that the
solder binds well to the leads. If the lead appears to be an "island" in
a small pool of solder, chances are it is not making good contact.
Measure from pad to pad (not wire to wire) using an ohmmeter to
be sure the leads are making contact.
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Do not use adhesives or fixatives of any kind to
secure toroids to the PC board. Toroids will be adequately held
to the board by their leads alone. (T5 is the only exception.)
RFC16 is wound on an FT37-43 core (dark gray) using 16
turns of red enamel wire (12", 30 cm). Wind this inductor in the
same manner as RFC14. Install RFC16 vertically, to the right of
RFC14.
RFC11 is wound on an FT37-43 core using 20 turns of red
enamel wire (16", 40 cm). Wind this inductor and prepare its leads
in the same manner as RFC14.
Install RFC11 horizontally, on the bottom side of the board, as
shown by its component outline (near the center of the board). The
pads for RFC11 are the two that just touch the outline. Pull the
leads taut on the top to keep the toroid secured to the board, then
solder.
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T5 is a toroidal transformer, with two numbered windings.
These numbers are printed next to each pad on the PC board. T5’s
windings are 1–2 and 3–4
.
Locate the large yellow core (T50-6) for use at T5. The core
is 1/2" (12.7 mm) in diameter.
Wind the first winding, 1-2, using 16 turns of red enamel wire
(15", 38 cm). This winding must occupy 85% of the core, and will
look very similar to Figure 6-15. Remember that each pass through
the core counts as one turn.
Carefully strip and tin the leads of T5’s 1-2 winding.