Fully agree.. SE and PP have slightly different signatures and presentations. You either pick the one that best matches your taste and requirements or better still keep multiple SE and PP amps and rotated them around... 
That makes sense, then, as you are pushing the amps toward grid current. It also confirms the original claim by shoog which was that a well-designed class A PP does have the same general FFT footprint as SE (when not overloaded), although at significantly lower levels of distortion.
My primary complaint about the simulation is the clearly low distortion of even harmonics; the Karna does not show that in practice, but looks like SE to a great degree. Perhaps that is due to real world tube mismatch, but that is part of the benefit to the design, you are less restricted by tube matching.
If the overall argument is one of overload characteristic, then I wonder if all the SE people (I have SE amps, too) go for PP in their preamp stages, since those stages, when properly designed, cannot overload, therefore you get the preferred SE signature but at lower levels. My tendency is to think SE people go SE throughout, but this does not line up with the overload argument. Keep your stages from overloading and you don't have to concern with overload and the higher order terms which are so despised.
I think it's also worthy to note that Olson went to great lengths to design such that well over 90% of the distortion in the Karna is due to the output stage. Input and driver stages are nearly perfect when compared to the output stage. I have confirmed this with my measurements, where it was actually the output transformer (O-Netics) that was contributing the most distortion. Installing a LL-1620 greatly improved high frequency performance, getting as much as 3W RMS out at 10 kHz before significant distortion started in. That's a lot of power for 10 kHz, never going to need that much with my speakers. Not sure about your wattage readings, but at 80-2000Hz, this amp can easily put out 5W (not 1.75) without distortion setting in. I was getting it up to 10W rms before I saw FFT's that had me concerned, but again, due to the OPT this would not hold true at 10kHz.
So my take based on ears and measurements is that since my PP has sufficient power to drive my speakers without overload, I get the pleasant FFT with low order terms, but at significantly lower overall levels. I don't deal with high order terms, as I don't play PA level audio in my house.
a1 or ab1 b1.. is when end tubes work at all times without drawing grid current ( negative voltages, below 0)
2 is when driver must supply some current to tube grids (above zero and positive)
highmu triodes will draw current all the time, medium mu most likely only partially-during positive sinewave halfs
those pesky magnetic domains must rotate in pp iron 180° when signal changes polarity
in se it does not, just more or less magnetized, but still same direction
Choose your PP iron without an air gap and this is not an issue. Toroidals and C-cores do not exhibit these hysteresis effects to a significant degree.
The intrinsic limitations of gapped SE cores far outway the limitations of PP iron.
Another one of the design consideration which most people fail to address when building PP amps.
Shoog
I am not aware of any PP transformers with a homogenous magnetic structure (no airgap). Toroids approach the "gapless structure" but still have a gap. C-cores while tape wound like toroids are very different animals when it comes to the nature of the gap and I fail to see how the two can be lumped together in any general statement of merit.
at the most basic level the amount of hysteresis is a function of the core material, lamination/tape geometry and the nature of the airgap. While both toroids and C-cores are both tape wound cores, the magnetic similarities end there.
Isn't this just saying my choice of compromise is better than yours?
dave
Indeed it is - but I think you will find that on all objective grounds the best PP iron has far fewer compromises. Think about the pathetic amount of H that the SE transformer has as well as its atrociousness HF response.
Shoog
About sums it up really
Maybe overload behavior is more important to SE people ?
Shoog
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I would put that in the "quick 'n' dirty" category, as for an audio strip for a AM/Comm receiver where you're not looking for sonic excellence. You have to consider that you have a pentode final with no NFB. It runs open loop, and will never perform as well as a design that uses NFB correctly.
As for how that will actually sound, no idea here as I never did a design with that final. A lot will depend on what sorts of harmonics appear at the output. Different finals have different sounds depending on what the harmonics actually are. 807s like to make a lot of higher order harmonics. (You can see this with the Twin-T test: the residual after nulling the fundamental looks almost like a picture perfect sawtooth -- lots of h5 and higher.) The open loop sound isn't pleasant, and quickly leads to fatigue.
PP 6V6s and 6BQ6As make mainly h3; open loop, these sound mainly "edgy". They don't need the same level of NFB to clean 'em up.
With that circuit, it's a case of YMMV. I'd like to see some NFB in there.
We stand a far greater chance of agreeing on this: blonde, blue-eyed, long-legged Russian ladies are the best looking ladies in all of the universe, period.
I think they are stating the obvious, from the time when all the best engineers were testing that hypothesis.
Shoog
amorphous iron gaining momentum, big time...in power distribution pole pigs etc !
smaller losses outweight higher price
This thread has just gone to confirm my belief that almost no one has actually fairly compared the best SET amps to the best PP amps. Even when people do compare similar circuits they strangely opt for higher distortion final pentodes in triode strapped mode.
Those who do build fairly comparable designs, with equal high quality finals, report consistently that the PP offers better distortion figures, and generally sounds almost identical or better than their SET efforts. So where the evidence is there (both subjective and objective), the PP consistently delivers on its promises.
That is a stronger conclusion than i would have been prepared to make at the start of this thread - so I suppose I have learnt something
Shoog
Those who do build fairly comparable designs, with equal high quality finals, report consistently that the PP offers better distortion figures, and generally sounds almost identical or better than their SET efforts. So where the evidence is there (both subjective and objective), the PP consistently delivers on its promises.
That is a stronger conclusion than i would have been prepared to make at the start of this thread - so I suppose I have learnt something
Shoog
This also raises the question,
What if the best PP circuits measure worse than the best SS designs?
What then if anyone prefers PP to SS?
Would that make the whole question raised in this thread pointless?
The next question is why would anyone in their right mind build a 211 or 845 SE and why is the audiophile so interested? (They are all nuts!)
But...well..errr...cough...LMAO
Tubes are old, transistors are old OP amps are new etc, they are used in critical applications like military equipment, they are more accurate etc smaller lower power...drone...
So distortion, measurements they are the most important trait of the device..OK why is anyone here?
Regards
M. Gregg
What if the best PP circuits measure worse than the best SS designs?
What then if anyone prefers PP to SS?
Would that make the whole question raised in this thread pointless?
The next question is why would anyone in their right mind build a 211 or 845 SE and why is the audiophile so interested? (They are all nuts!)
But...well..errr...cough...LMAO
Tubes are old, transistors are old OP amps are new etc, they are used in critical applications like military equipment, they are more accurate etc smaller lower power...drone...
So distortion, measurements they are the most important trait of the device..OK why is anyone here?
Regards
M. Gregg
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For me all of this discussion is predicated on zero global negative feedback. Cases of transistor amps with ZgNFB, such as the Nelson Pass F5, can indeed match and better what most valve amps have to offer.
Its not all about the measurements, otherwise we would all be using opamps with massive amounts of gNFB - and last time I tried that the results were ultimately unsatisfactory.
Its the subjective accounts from builders who have pushed the PP envelope which are really compelling to me (and my own personal experience).
I think the builders of Big SE transmitter amps are indulging in bigger is better and look at the size of my amp bravado - I personally think that that whole approach is a dead end and something of a distraction for the metal heads out there.
Shoog
Its not all about the measurements, otherwise we would all be using opamps with massive amounts of gNFB - and last time I tried that the results were ultimately unsatisfactory.
Its the subjective accounts from builders who have pushed the PP envelope which are really compelling to me (and my own personal experience).
I think the builders of Big SE transmitter amps are indulging in bigger is better and look at the size of my amp bravado - I personally think that that whole approach is a dead end and something of a distraction for the metal heads out there.
Shoog
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Precisely, so why is there still seemingly endless debate on which topology works the best on-paper?! (that's why I asked the readers to set aside implementation issues...) By fidelity, I think RDH simply meant that A1 triode push-pull has less distortion as dictated by the triodes' characteristic and the nature of the push-pull operation, period. It did/does not imply anything about how the amp would sound or if one should prefer it over another topology...
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