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Scan Converter
Technical details

The PEP400 and PEP 500 Scan-Converter System manufactured by Princeton Electronic Products Inc, New Jersey USA.

The PEP scan converters were based on a tube type analog memory. In the base of the vacuum tube which is the heart of the image memory was a silicon disk that was etched with over 1 million .5 micron square islands that acted as capacitors. The electron beam directed by the magnetic field coils would usually scan the silicon target in a video raster fashion and charge or discharge the capacitors to form the image. The bias voltage on the tube's silicon target would be raised or lowered depending on whether you wanted to read or write. If the power was turned off the image would remain intact for a year or more. With the power on image would degrade after several hours.
The unit was made obsolete when better digital memories became available and the company has since gone out of business.(1)

1. Robert Renner (ex-Princeton Electronic Products Field Service Engineer)