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SRPP: adifferent perspective

hi all

enclosed an SRPP equivalent circuit.
Maybe, someone will find it easier to understand.
maybe not.

the inductors are to be considered of infinite value ,i.e. CCS.
 

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Hi docali,

No, the circuit reported from you is
an SRPP variant that, as I have read, works very well
if correctly implemented.

I have not proposed a working circuit,
but a theoretical circuit (on the right) equivalent to the SRPP.
Its performances (freq. resp, harmonic distortion, etc.)
are identical to those of the standard SRPP (on the left).

It is only a different view of the same circuit.
Maybe someone, by looking at this non operative
circuit will find some good ideas.
or will reach a better understanding
of the SRPP circuit.

I don't know.

bye
Federico
 
I do not see the two circuits being equal...
The circuit on the right is not in series and does not get the benifiets of the circuit on the left...Cirsuit on Right is a Common cathode direct coupled to a cathode follower...
The inductor in the cathode does not seem to have any advantage...possibly a disadvantage...
SInce the output impedance of the follower is dominated by the impedance looking into the cathode....and that is in parallel with the L which could introduce capacitance and loss of highs......

Chris
 
The inductor in the cathode does not seem to have any advantage...possibly a disadvantage... SInce the output impedance of the follower is dominated by the impedance looking into the cathode....and that is in parallel with the L which could introduce capacitance and loss of highs......

Only at very high frequencies or with a poorly chosen choke, yes, but putting a choke with a CF is not inherently a bad (or a new idea) idea. It is generally desirable to make the cathode load of a CF stage have a very high AC impedance, and a choke has advantages in this role. If a choke's capacitance is a problem interacting with the low resistance of the cathode in a CF, then that same choke would behave even worse (lower roll-off frequency) working against the higher plate resistance in a common cathode stage, where we see it more commonly. In either case, series resistors are often used to set DC operating points, only serving to further isolate shunt capacitance, and to prevent possible oscillation in CFs.
 
cerrem said:
I do not see the two circuits being equal...

Ahh, but they are!

The circuit on the right is not in series

No, but for theoretical work you assume I1 = I2 anyway.

The inductor in the cathode does not seem to have any advantage...possibly a disadvantage...

Oh, it has advantage, namely of removing any loading resistance. This allows you to see the only impedance at the 2nd triode's grid (and cathode) is the preceeding tube's plate resistance.

Of course it isn't a perfect cathode follower, rather only bootstrapped, so the 2nd cathode has a loading effect too, depending on output load impedance. That is why this circuit is imperfect; an infinite AC impedance in the 2nd cathode would decouple output nicely from the 1st triode, allowing constant current operation of the bottom triode, while providing classy CF output.

SInce the output impedance of the follower is dominated by the impedance looking into the cathode....and that is in parallel with the L which could introduce capacitance and loss of highs...[/B]

Huh? Whatchoo talkin' bout there? From what I see, this circuit goes well into the UHF range.

Parasitic circuit elements are for engineers, not theorists ;)

Tim
 
Hi

Of course it is not identical to a SRPP for DC.

why not? same DC currents, same DC voltage.

but this is not the point.
The point is: Does such a circuit suggest you something? No?
Nor to me but,...

I think that it is a good thing to have our brain working and
searching.

For instance look at the following buffer circuit (left pic)
It is a variant of the White cathode follower.

Now looks on the right. This circuit is equivalent but
it can be simplified by removing upper res. and cap.
(there is a little change in the working point but it is not important).
The cost is in the floating supply.

bye
Federico
 

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This thread is very interesting, I'm following it closely, I can see how the two circuits in the first post are similar, and how they would both behave in a similar manner, It would be interesting if someone were to build the two in somethign like circuitmaker and show us some figures for both circuits. I'd do it myself but i dont really have the experience.
Owen
 
why not? same DC currents, same DC voltage.

Yes, but only for static conditions if the anode of the first tube is always exactly half of the supply voltage. For instance if one of the resistors are changed the circuit is not valid anymore as there will be current drawn from the V/2 sources.

Maybe I am nitpicking but I like models to be accurate also for DC sweep.

Regards Hans