Two cases here:
- lindser: You'd need to find the matching motor-pulley version for 50 Hz.
- Nadav: No problem. A priceworthy step-up/-down transformer will do the job.
Generally speaking, the problematic cases always are models with an AC motor that's pretty directly mains-powered (with "pretty directly mains-powered" meaning either directly mains-powered or that the mains voltage is merely down-transformed or reduced via a resistor in series, at which a certain share of the mains voltage is dropped...), so that the motor speed depends on the mains frequency. Such designs will hence require either a matching motor-pulley version or alternatively some form of electronic frequency-generator box.
Whereas the unproblematic cases are DC-based designs - i.e. basically all models that either work with a DC motor anyway or alternatively an AC motor in combination with some form of an electronic frequency generator.
So, if one is confronted with such a problem and not yet aware, how exactly one's turntable actually works, one would ideally first have a look at the service manual and parts list.
For example, in Nadav's case the schematic of the DP-300F shows that the incoming mains power/voltage is immediately rectified to DC after transformation - so it's a DC-based design. And in addition the parts list shows that there are three transformer variants (for 100 V, 115 V and 230 V), according to the schematic all with just a single secondary winding, so that there's no chance for an internal reconfiguration (unlike in case of designs with two secondary windings, that could be either wired in parallel for 230 V or in series for 115 V). So in this case there's no way around a suitable step-up/-down transformer.
Whereas lindser's case is a bit more complicated, as according to the service manual there are at least two motor versions (2- and 4-pole) and also at least two configurations (with/without voltage selector) - so that one would first have to determine, what the particular exemplar actually is equipped with. But I fear that finding a source for the correct 50 Hz pulley variant will be problematic anyway - whereas voltage reconfigration wouldn't be that difficult, even if the particular exemplar isn't equipped with a voltage selector.
Greetings from Munich!
Manfred / lini