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Plumbicon - With a (screwdriver) Twist!

Colour Television

Last Post by Nuvistor 8 years ago

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Anonymous

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Over the weekend I was sorting some Christmas boxes from the garage. 'Spelunking' more like it!

I happened upon a long forgotten box of camera tubes, which I'll share in a future posts. One of the tubes is quite fascinating.

Occiput commented here, message 18, about the English Electric P8400 Lead oxide camera tube. What made it unique was the internal bias light that could be adjusted with a screwdriver to the tiny pot in the tube's base cap.

The tube is completely covered in a black sleeve, except for a window to read the serial number. Most camera tubes have these stamped metal tags inside the glass and thus prevent any 'mistakes' over warranty claims. The outer black sleeve assists in controlling internal reflections from the bias light inside the tube base (typically part of the normal heater/cathode) to give an even backlight to the target. This bias light significantly reduces the build up and lag times, reducing image smearing. It's not the same artifact as comet tails on highlights. Bias lights also increase the dark current, and require further processing in the camera channel electronics to remove the dark current and any target shading. More on this later.

There were other ways to create bias lighting, but the P8400 is the only one that I know of with a screwdriver adjustment on the actual tube.

This tube also has a glass 'anti-halation' window disc on the front, and was the then standard 30mm diameter.