ECC8100 (System I and II, version i6)

This tube is one of the latest developments before the tube area ended!
This tube copes quite high frequencies when used in cascode configuration. The lower triode has in addition a special feature to reduce the plate-to-grid Miller capasity, which is a special screen between the grid and the plate. This screen covers the gris spars only, while there is a rectangular window in the screen where the electrones shall fly to the plate. It seems like the Miller cap in triodes is mostly caused by the spars, and less by the grid wires itself. With this special screen, the Miller cap is reduced dramatically (factor 3 or so) while the gm of the triode is weakened only slitely. A quite impressive Engineering-work!
Note the macro picture of the ECC8100 construction at the end of this page.

ECC8100SI.i6 spice model

ECC8100SII.i6 spice model