The term "Hyperlinear" referes to the feedback loop from the cathode follower back to the input pentode’s screen grid (g2). Due to this feedback loop the input pentode is more or less working in triode mode, but the connection between plate and g2 is extended to include the cathode follower. This reduces the overall distortion and lowers the output resistance of the CF.
Some measurements with 6SJ7G and EBC33:
(c) Jan Erling Veiset, 27-MAY-2008 - E-mail: valhalla[at]mikke-mus.com
Akersora 2
N-6600 Sunndalsora
Norway