A key assumption is some models of radio source evolution is that the magnetic field in the hotspots is always equal to the equipartition value and that this value is proportional to the jet energy flux. This assumption is tested by following the evolution of the magnetic field in the turbulent hotspot flow via a series of three dimensional, time dependent and fully nonlinear calculations of MHD turbulence in the hotspots. Turbulent amplification of the magnetic field is examined for a variety of energy spectra that might occur in the hotspots. It is found that equipartition is reached in the time required only for a subset of possible initial conditions and only reliably on the smallest turbulent scales. Amplification to equipartition on all turbulent scales usually takes 30 or more large scale eddy turnover times, and this time may well exceed the dwell time of the fluid in the hotspot unless special conditions are imposed.