How does this motor speed control circuit work?

[maxhifi]

This is a single phase induction motor circuit, from a USSR made record player (circa 1977). This type of motor is known as a permanent split capacitor type. More common in European equipment versus our shaded pole induction motors.

R16 is used for fine speed control. I can't make sense of this circuit, why the diodes are there, etc. and I have never seen it done this way anywhere else. It looks like a strange form of non variable phase angle control, but I don't know what is the function of R14.

And more to the point, can I increase the resistors to make this thing work on 60Hz, or is it better to machine the pulley down?