THE FOLLOWING INFORMATION IS NOT NEW JUST RE-STATED WITH THE DOTS CONNECTED.  IT ALSO IS NOT IN FINISHED FORM AND ANY SUGGESTIONS FOR CLARITY ARE WELCOME.  BEING A WORK IN PROGRESS IT WILL CHANG OVER TIME.    

The following photos are of a standard 8122 and a 4662 which is a ruggedest 8122.

Note, the only obvious difference is the cathode in the 4662 is a flat surface and the 8122 is a wire matrix.  The Barium and Strontium oxides applied to the cathode are delicate and can be dislodged with vibration.  The filament in both is approximately half the diameter of the cathode and not visible.

NOTE:  If you should decide to dissect any tube using an oxide coated filament, beware the Barium oxide is incredibly caustic.  You don't want to get the dust on your skin or breath it.

The first photo is an 8122 and visible are the cathode (wire matrix with the screen and control grids overlapping each other.

The second photo represents the cathode, control and screen grids.  Expand it to view the wording and pointers.  

The third photo is the 4662.  Note the solid cathode and the precision alignment of the CG and SG wires.

The alignment of the CG and SG wires hide the CG from the plate and the SG from the cathode. The result is the dynamic CG to plate capacity is significantly reduced and the screen current is reduced.

MORE INFO TO FOLLOW: