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The gain for a cathode biased triode with bypassed cathode resistor and a CCS load is the mu of the tube (assuming ideal (infinite impedance) CCS. If your goal is to eliminate the plate impedance from the gain equation you can implement a half mu stage. It looks like an SRPP with equal cathode resistors and triodes and the output is taken off the lower tubes's plate. Disadvantages are a rather high output impedance and a low PSRR.
"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln
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"Had the output been taken at..."
Omnes feriunt, ultima necat.
"Simple variation of a grounded cathode amplifier"
I feel that is over simplified.
Taking the output off the plate of the bottom tube or taking the output off the cathode of the top tube, the top tube is still acting as a high impedance plate load for the bottom tube. Kind of like a poor CCS.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
There's no push-pull action anyway unless the output is driving a very low impedance. If that's not the case, this circuit offers no benefit over a simple grounded cathode in most applications.
"No push-pull action anyway unless the output is driving a very low impedance".
Omnes feriunt, ultima necat.
!
The Mind has No Firewall~ U.S. Army War College.
You mean CCS as in active load?
The top tube of a SRPP is already an active load, no?
You can read the reply #4 through the given link. It has mentioned that CCS in SRPP.
"You can use a choke for the upper cathode resistor in an SRPP configuration, making it a mu follower with fewer parts and no capacitors. My experience is that it sounds good but a C4S sounds better"
I think Paul meant using a C4S instead of the top tube.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
...mean what Tre' said.
I thought the C4S had no low output Z capability?
For sure, put a single MOSFET in place of that triode, and it can still have the source/cathode output. Make it even 'harder' by adding a second in cascode. With the advent of 1kV depletion-mode 'FETs, the 10M90 is not needed anymore...LOL
Or build a cascode with a triode on bottom and a pentode on top. Couple voltage ref's to separate them by enough voltage to do the job and give it a BIG 'R-set' resistance... :)
cheers.
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
My mistake; I was only considering taking the output from the lower plate. Some 20+ years ago, we decided that sounds better than the mu follower, and I haven't re-visited that conclusion since.
So, the mu follower current source is a moderate current source, and the solid-state current sources are by and large superior - if the output is taken from the lower plate. The half-mu stage with a choke at the upper cathode does have two available outputs, as does the full mu-follower. The choke does not have to be large, since its inductance is effectively multiplied by mu.
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