Television camera tube arrangements

In a H.O.P. or A.C.T. television camera tube arrangement including control means for causing electron beams defocussing such that the diameter of the beam covers many scanning lines at the target and for raising cothode potential to a value slightly higher than target potential corresponding to that selected peak value at which a single forward line scan of the beam is effective to reduce the target potential substantially to cathode potential, means for actuating said control means during periods of line flyback whereby to limit target potential in areas of successive scanning in the field substantially to said selected peak value, and means for effecting field blanking to overlap the beginning of each field period, the improvement which comprises:

• additional means for actuating said control means during forward line scan only at the beginning of each field period.

In an H.O.P. or A.C.T. television camera tube arrangement wherein forward line scanning is effective to reduce target poetntial substantially to cathode potential so long as target potential does not exceed a particular peak value, and including means for increasing the intensity of the scanning beam during line flyback periods whereby to limit the target potential in successive lines substantially to said particular peak value, and means for effecting field blanking to overlap at least one line of each successive field, the improvement which comprises:

• additional means operative only during the field blanking overlap of each field period for limiting target potential, at initial lines of each field immediately following such field blanking and which are not overlapped thereby, substantially to said particular peak value.