Why hybrid CCS?

[leadbelly]

Background: I am searching for my next input stage for my EL84M PP, which right now consists of paralleled 6922 triodes in a long tailed pair with a MOSFET CCS. So I was looking at things like a cascoded long tailed pair and various forms of CCS's as a "step up".

So in Morgan Jones' book I do see some hybrid CCS's, basically shown as SS CCS's on the cathode of a pentode such as and EF184, in which the combination of SS and tube is used as a CCS for the cathode of a driver tube. What does this improve over just using the SS portion alone?

 

[EC8010]

Prettier and higher voltage compliance; an EF184 can dissipate 2.5W and operate with 250V across it.

 

[ray_moth]

Or, why not ust the pentode alone? If you look at the plate curves of a good small signal pontode, they're almost horizontal at low currents with a suitable screen voltage.