Electron cyclotron wave current startup has been investigated in a wid
e range of toroidal magnetic fields on the CT-6B tokamak. Two kinds of
drive mechanisms of current startup have been identified experimental
ly, according to the dependence of the wave started current on the ver
tical field. Their contributions to the current have been estimated qu
antitatively for different resonance scenarios. The wave started curre
nt may occur at a downshifted resonance frequency even if the resonanc
e layer is located outside the vacuum vessel.