generally fall into two types, which has something to do with the way the field
coil is coupled.
A, field coil has one end connected to the live brush, regulation is done between the
other end and chassis
type: One end of field coil connected to chassis, regulation is done
between other end and the live brush.
Polarity is a matter of magnetizing correct.
required, a piece of wire and a voltmeter.
the wires from the dynamo
range: 20 Volt dc
one lead to chassis, the other to D on the dynamo
the engine, but do not exceed fast idle.
the piece of wire, connect F to chassis.
you measure 6 volt or more, you have a type A dynamo
If you measure 0 volt, connect F to
If you now measure 6 volt or
more, you have a type B dynamo.
you still measure 0 (or 1 - 2 volt) you probably have a defective dynamo.
to check that you have the correct polarity
voltmeter can be replaced by a bulb with two wires, but it is first to be
connected when the field coil is connected, as the bulb will "eat" the
small amount of electricity that should get the dynamo started
British bike from 50 60s are type B with chassis plus. Early Brits can be
chassis minus. Germans and Russians, Puch and Nimbus are type A, except DKW and
MZ, and some Jawas which are type B, all with negative chassis, although some
old Russians have been seen with positive chassis.
Davidson from '32 onwards use type B, negative chassis, while Americans
fro the 20s use type A, when converted fro three to two brush system.
remember the human factor, some clever guy may have decided to couple the dynamo
to suit him.