A simple version of an Incandescent Lamp Dimmer would be a very large Rheostat (Variable Resistor).
Since this is a very wasteful method to dim lamps, it is not used very much anymore!
The basic "Solid State" Incandescent Lamp dimmer performs a function, known as "Chopped Wave".
This "Limits" only a portion of an AC wave to flow, which reduces the overall efficiency of the Lamp, and at the same time, reduces the amount of power the Lamp can draw - so it (the Lamp) gets dimmed.
Chopped Wave dimmers cause Lamp fillaments to "Sing" acrossed certain levels.
Another method, which does not incorporate any SCRs or TRIACs (Solid State controls), is an AutoTransformer with a "Wiper" contact.
I am sure there is (or has been) a saturable reactor type dimmer scheme.
I am thinking the "Actual Motor Speed Controllers" which look much like Lamp Dimmers, and are for use with Ceiling Fans (PSC Motors), are either "Pseudo Reactors" , Autotransformers, or Voltage Reducing Solid State types of control, as this is the most likely method used to control PSC and Shaded Pole Motors.
Is there a Variable Frequency type Speed Controller, in the form of the typical wall switch dimmer?
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!