"Ian Iveson" wrote in message
...
Two arguments, take your pick. Easiest for Yves' simple CC with CCS
at anode.

I'm most familiar (such that I am) with a mu-follower.. which I presume
could be done with a CCS in place of the resistor between the two tubes.

In the case where the load is placed on the top tube's cathode, above
the R/CCS, the load develops a voltage across the resistor, causing
a stronger voltage at the bottom tube's plate, which is coupled to
top's grid, which acts as a CF, bootstrapping out the load impedance.
This is my understanding.

If you vary the load, you vary the current robbed from the CCS and
therefore the current arriving at the cathode. This results in
series nfb from the unbypassed resistor.

But the CCS (top tube you mean?) ensures a CC into the bottom tube, by
supplying additional current to the load, if loaded down.

Naturally there will be a bit of voltage change on the cathode resistor,
but nothing is perfect.

The signal cannot go
up the CCS so for a low output impedance Ra and Rk must be kept low.

Ah, but it does, for what else is that coupling cap doing?

Rk is effectively multiplied...can't remember the formula and too
tired to work it out. You know it anyway.

Uhm... notes are downstairs. But yes I have it.

The problem is not so bad for the mu-follower, because a returning
signal does not see a CCS in either direction. But still the bottom
Ra is part of the path to ground, and the bottom valve is
responsible for the gain, so the resistor makes a significant
difference.

Are you referring to the CC w/ CCS load mentioned earlier? Or a mu stage?
Your post didn't specify too well :-\

Tim

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