Elecraft K2 Owner's Manual - Manual (Page 72)

E
LECRAFT ® 71
T2 is wound on the same core type as T1 (FT37-43). Its windings
must be spaced as shown in Figure 6-26(a), with the 3-4 winding
occupying about half the diameter of the core. T2’s 1–2 winding is 12
turns of red enamel wire (13", 33 cm), and its 3–4 winding is 8 turns
of green (9", 23 cm).
Prepare T2’s leads, but leave an extra 1/2" of insulation on leads
3 and 4 (green) as shown in Figure 6-26(a).
Fold the leads of T2's green winding (3-4) down and under the
core as shown in Figure 6-26(b).
Install T2 horizontally, just to the right of Q6. To ensure that the
leads do not contact any adjacent pads or components, T2 should be
mounted so that it is elevated slightly above the board (about 1/16"
[1.5 mm]).
4
3
1
2
4
3
(a)
(b)
Figure 6-26
Transformer T3 is mounted vertically, to the right of T2. The
wires for the two windings must be twisted together before winding
(bi-filar). First, cut two 10" (25 cm) lengths of enamel wire, one red,
and one green. Then twist the wires together over their entire length.
The wires should cross each other once every 1/2" or 1 cm.
Wind the twisted wires onto a 1/2" (12.7 mm) dia. ferrite core
(FT50-43), using exactly 5 turns and covering about 85% of the core.
Figure 6-27 shows how the winding should look. The leads of T3 are
labeled with letters A through D on the PC board to avoid confusing
them with the numbered leads of T2 and T4.
Separate T3’s leads as shown in Figure 6-27. Strip and tin the
leads, being careful not to let the red/green wire pairs short together.
Install T3 vertically as shown by its component outline. T3 must
be seated flat against the PC board, with its leads pulled tight on the
bottom side.
C
(RED)
B
(GRN)
D
(RED)
A
(GRN)
Figure 6-27