Dynamic beam current reserve margin in television camera tubes necessary for the neutralizing of bright spots, which is accumulated on the camera tube signal electrode during a multiplicity of successive picture field periods after which a signal electrode is scanned by the electron beam during several field periods in interlaced line pattern and the video signal level of the third field is measured. In this measurement, the signal level is below a first predetermined threshold value, the dynamic beam current reserve is sufficient and the procedure is terminated. The threshold is reached or exceeded, the dynamic rise of the beam current is gradually magnified and further cycles of charge and scanning are performed, this time with measurement of the video signal during the second field. So long as the measured video signal remains below a second predetermined threshold value, the limiting of the beam current rise is magnified until the video signal in a further measurement cycle exceeds the second threshold value. The first and second threshold values are typically 110% of the normal video level and 50% of the video level of the first field respectively.