Cascoded mu-follower

[jnb]

Has anyone tried this? I mean, a cascode whose upper triode has an active load? Or in other words, a mu-follower that is driven from the cathode of the lower triode, so there are three triodes on top of each other?

[Bandersnatch]

hey-Hey!!!,
I have built an active load from a triode and a pentode. Since the pentode is much like a pair of triodes in cascode...

Anyway, feeding a 12B4 amplifier triode, a high-gm/medium mu triode with a video pentode stacked on top of it. The sticky issue was the voltage references to separate the elements. It turned out not such an issue after I solved it. The output taken from the triode's cathode gave me a nice low output Z to drive any cable I've put behind it.
cheers,
Douglas

[KaDe]

Doede Douma calls his design " DOUBLE MU "

Please read his words on this pages:

MU article

http://www.dddac.de/

[coresta]

And with output on the upper point of R22 ?

[Bandersnatch]

hey-Hey!!!,
One could also connect C6 to the lower triode's cathode. Anyhoooo, it is another solution to the creation of stable voltage reference required to separate the two active devices. Not quite the same as can be achieved, but on the right path...
cheers,
Douglas

[jnb]

This is what I was thinking. Cover the lower triode and it's a mu-follower, cover the mosfet and it's a cascode.

The mosfet is just one option I had drawn when I posted this. I tend to consider it as a cascode more than anything else.

Not sure how to tell whether it would be stable or over-sensitive in some way.