Just to expand on BENGO's excellent reply.
The usual configuration for a DC (dynamo) armature commutator, is a cylinder divided into strips...each has to be insulated from the others ( imagine a straight-sided beer barrel where the staves have a strip of insulation between them)
The brushes are spring-loaded carbon -copper blocks with bonded-in leads(AKA 'tails') Because of the size of the windings and the required output, dynamic balance, cooling and structural integrity against centrifugal (centripetal?) force are major issues. brush-size and pressure against the rotating drum of segments is also an issue..insulated holders are needed to ensure accurate alignment between brushes and segments as the windings pass the pole-shoes, too much pressure causes drag and premature-wear in the Com. segments...too little and there's excessive sparking (with attendant R.F. interference) burning and erosion of Com. and brushes.
The Alternator rotor only has a single coil wound on itin the same rotational axis. balance and dynamic stresses are minimal,,the two ends of the coil can terminate in slip-rings which, as each one has a brush pressing on a smooth, continuous track,carrying only "field" current, are lighter and far longer-wearing than the brush-system on dynamos.
The fixed coils in the stator, being external, are much easier to construct and cool, no balancing required ,minimal mechanical anchoring. the outputs are normally diode-rectified...these solid-state devices are maintenance-free and have very high efficiency.
I struggle to find anything good to say about a dynamo when compared to an alternator. They are heavier and need a higher rotational speed to start generating, compared with an Alternator.they're mechanically more complex have more to wear and are less reliable....and, yes, AC transmission-losses are lower and the induction of currents in ajacent wires is less of a problem.
all sorts of odd things can happen when you get bundles of uncsreened conductors together!,