The RCA Selectron -- US Patent 2,558,461 Selectron Electron Optics
Jan A. Rajchman, Radio Corporation of America
Applied: 28 December, 1949
Granted: 26 June, 1951
The '461 patent relates to the electron optics of the 256-bit planar type tube.
'461 describes the geometry of electron emission from the faces of square cathodes.
The beams are then guided along a 45 degree path and then through the addressing bars before becoming orthogonal.
One goal is to use the emission efficiently, not unlike beam forming techniques
used in "beam-power pentode" electron tubes. Another goal is to minimize the "line-of-sight"
between cathode and storage element. This is necessary because the heavy ions and particles of cathode coatings
will travel to the storage elements and destroy their secondary-electron emissive properties.