The vidicon tube (1) of a television camera has a uniform glass envelope and a semiconductor storage readout array (4) at the end face. External deflecting and focussing coils (15,16) are provided and an electron optical system with four internal grids (10 to 13). The first grid (10) is provided with two beam-defining apertures of different sizes with a deflecting electrode (19,20) between it and the cathode and which is employed to steer the beam through either of the holes. The tube can operate with alternative line-frequencies and thus may be set for optimum beam dimensions in the readout system. ADVANTAGE - Has application over a wide range of line-frequencies.
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