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The enamel wire can be heat-stripped. Place a small amount of
solder (a "blob") on the end of your soldering iron, then insert the clipped
end of the wire into the hot solder. If the iron is hot enough, you should
see the insulation bubble after 4 to 6 seconds. Add more solder and feed
more of the wire into it as the enamel melts. Continue tinning the wire up
to slightly past the edge of the core, then slowly pull the wire out of the
solder. If any enamel remains on the lead, scrape it away using your
fingernail. You can also burn the insulation off by heating it with a
butane lighter for a few seconds, then use sandpaper to remove the
residue. If you scrape the insulation off with a razor blade, avoid nicking
the wire.
Strip the leads of L4 as described above. Remove the enamel from
the leads up to the edge of the core (see Figure 16).
Tin L4's leads. If the solder on the leads looks dull or is not adhering
very well, remove any residual enamel and re-tin the lead.
Install L4 vertically as shown by its component outline. Pull the
leads taut on the bottom of the board.
Solder the leads of L4. When soldering, make sure that the solder
binds well to the leads.
If the lead appears to be an "island" in a pool
of solder, it is not making good contact;
remove the toroid and
prepare the leads as described above.
(For further information, look for
"Soldering Tips" on our web site.)
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Do not apply adhesives or fixatives of any kind to toroids.
Using your DMM on a low resistance scale, check for continuity
between L4's pads (not the leads) on the bottom of the board. If the
reading is over 1 ohm, re-strip the leads.
Note:
Your DMM probes will
have some residual resistance. Short them together to measure this
amount, and subtract it from your continuity readings.
The other low-pass filter toroids are shown in the photos at right
(Figure 18). Wind each of these toroids using the indicated powdered-
iron cores, either
RED
(T50-2) or
BLACK
(T50-10). All are wound
using
#22
enamel wire. Use the wire length and number of turns shown.
Prepare the leads of these toroids as you did for L4.
__ L1: 27 T,
RED
__ L2: 25 T,
RED
22" (56 cm) 21" (53 cm)
__ L5, 16 T,
BLK
__ L6, 16 T,
BLK
__ L7, 11 T,
BLK
14" (36 cm) 14" (36 cm) 10" (26 cm)
__ L8, 10 T,
BLK
__ L10, 9 T,
BLK
__ L11, 8 T,
BLK
9.5" (24 cm) 9" (23 cm) 8" (20 cm)
__ L12, 8 T,
BLK
__ L13, 21 T,
RED
__ L14, 20 T,
RED
8" (20 cm) 18" (45 cm) 17" (43 cm)
Figure 18
