Abstract
This chapter discusses beam-current-induced dark current in Plumbicons. The Plumbicon is a television pick-up tube with a lead oxide photoconductive sensor. Its high sensitivity, linear transfer characteristic, low lag, and good resolution have made it the preferred tube for broadcast color television. Another feature of the Plumbicon is its very low dark current. In normal conditions of use, values of the order of 1 nA are encountered. This small dark current is, moreover, only very little temperature dependent, as the major part of it is not “intrinsic” dark current, but because of other causes, such as stray light from the thermionic cathode. With the 1 inch Plumbicon, type XQ 1080, in anticomet-tail operation, the very large beam current used during line fly back causes some dark current. When the beam current is set, at 150 μA, measured in the mesh lead as is sufficient in most cases for proper operation, this dark current is usually 1 to 1.5 nA. The range of high lights, which can be handled now, without undue comet, tails, and blooming, extends to about 5 lens stops. It is possible to enlarge this range by using higher beam currents.
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