10W HF Linear PA kit assembly
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to identify which pairs of wires have DC continuity.
Now if windings A and B refer to the identified as the bifilar windings, and C is the primary winding,
install the wires in the PCB as per the diagram. Note that the orientation of the core matches the
silkscreen print on the PCB.
Make sure that C is the primary winding
– you can ensure this because it is only wire on each side
which is not tightly twisted bifilar wire. A and B are bifilar; C is the single wire.
Now test the DC continuity again between all three sets of wires (A, B, C) BEFORE soldering, to
make sure that there are no mistakes.
Also make sure that there is NO continuity between A, B and C wires, which would indicate a
short-circuit somewhere in the wiring, perhaps caused by a break in the enamel insulation.
When completely happy, cut the wires to 2mm below
the PCB and solder them, allowing 10 seconds of
heat to burn way the enamel. Inspect the joints with a
jeweller’s loupe or magnifying glass.
Finally do a continuity test, testing for continuity
between the “IN” and “GND” pads of the PA PCB,
holding the black and red probes as indicated by the
black and red circles respectively, in this diagram.
If there is no continuity, it indicates a problem with the
soldering of the primary windi
ng which we called “C”.
Next test for continuity across the pads of R203, which is
winding “B”, and DC continuity across the pads of R204,
which is winding “A”. If either of these tests reveals no DC
continuity, then go back and check the soldering of the
appropriate T201 transformer winding.
