Asimov wrote:
. . .
There is also power
HEXFETs which are something amazing with extremely low ON resistances
in the milli-ohm range. These might be more like a triode on steroids.
These come in pretty high voltage versions which seem to me more
suitable to replace a 6CW4 with some bias voltage adjusting of course.

Have you compared the capacitances of the 6CW4 and Hexfet? Note also
that the FET capacitance is highly nonlinear, varying greatly with
reverse junction voltage.

Roy Lewallen, W7EL