The U87 output transformer is historically a
BV13-style step-down transformer with a ratio
of 10:1, that is the voltage on the primaries will
be 10 times higher than the voltage on the
secondaries.
Consequently, we can also deduce by Ohm’s
Law that the resistance on the primaries must
be higher than the resistance on the
secondaries.
~ Example ~
You may stumble upon a scenario where you are
unsure as to which wires belong to the primaries or
secondaries of your transformer. Some may even be
wired incorrectly from the factory! Therefore,
checking the resistance on the windings can be a
useful method for determining the correct wiring.
Once you have the resistance readings from both
sides, compare the values to determine the primary
and secondary sides of your transformer.
In our case, the transformer provided in the kit has
its primaries denoted by black wires and its
secondaries denoted by yellow wires.
19
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Pro Tip!
Transformer Windings
