At very high magnetic field settings the electrons are forced back onto the cathode, preventing current flow. At the opposite extreme, with no field, the electrons are free to flow straight from the cathode to the anode. There is a point between the two extremes, the critical value or Hull cut-off magnetic field (and cut-off voltage), where the electrons just reach the anode. At fields around this point, the device operates similar to a triode. However, magnetic control, due to hysteresis and other effects, results in a slower and less faithful response to control current than electrostatic control using a control grid in a conventional triode (not to mention greater weight and complexity), so magnetrons saw limited use in conventional electronic designs.
at very high magnetic field settings the electrons are forced back onto the cathode preventing current flow at the opposite extreme with no field the electrons are free to flow straight from the cathode to the anode there is a point between the two extremes the critical value or hull cut-off magnetic field (and cut-off voltage) where the electrons just reach the anode at fields around this point the device operates similar to a triode however magnetic control due to hysteresis and other effects results in a slower and less faithful response to control current than electrostatic control using a control grid in a conventional triode (not to mention greater weight and complexity) so magnetrons saw limited use in conventional electronic designs