Smoking Amp,
Slightly off the topic, but the 'more revered' tubes that have flat pentode plate curves:
Are they more revered in Pentode operation?
Are they also revered in Ultra Linear operation?
Are they also revered in Triode wired operation?
I ask because so many of these amp threads have switches for Triode wired, Ultra Linear, and Pentode operation.
Could be a topic for another thread (anyone)?
Slightly off the topic, but the 'more revered' tubes that have flat pentode plate curves:
Are they more revered in Pentode operation?
Are they also revered in Ultra Linear operation?
Are they also revered in Triode wired operation?
I ask because so many of these amp threads have switches for Triode wired, Ultra Linear, and Pentode operation.
Could be a topic for another thread (anyone)?
The "revered" tubes I mentioned have curved plate curves, not flat ones. That's why I am puzzled by their elevated status. Flat curves would give lower distortion, rather than "warmth" (2nd H) or bass slam I guess (3H). Pentode mode would be where that would be most noticeable, followed by UL mode. All gone in triode mode.
For SE (pentode) mode, the curved over knee regions would lower 2nd H some along a load line, but the cancellation is far from perfect, increasing higher harmonics.
6GN8 pentode (not particularly revered! but looks somewhat similar to 6BQ5) is a good example of really curved over plate curves. So much so that I think they purposely designed it that way, to remove 2nd harmonic from SE operation. But any load line shows substantial 3rd harmonic.
https://frank.pocnet.net/sheets/135/6/6GN8.pdf
https://frank.pocnet.net/sheets/093/6/6BQ5.pdf
For SE (pentode) mode, the curved over knee regions would lower 2nd H some along a load line, but the cancellation is far from perfect, increasing higher harmonics.
6GN8 pentode (not particularly revered! but looks somewhat similar to 6BQ5) is a good example of really curved over plate curves. So much so that I think they purposely designed it that way, to remove 2nd harmonic from SE operation. But any load line shows substantial 3rd harmonic.
https://frank.pocnet.net/sheets/135/6/6GN8.pdf
https://frank.pocnet.net/sheets/093/6/6BQ5.pdf
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smoking-amp,
Thanks!
I Did mix up which shaped curves revered tubes had.
It makes sense when you said the effect would be lessened for UL, and even more for triode wired.
I build and listen to SE and Push Pull amps.
Some of my 2-stage push pull amps have a balance pot in the plates of the cathode coupled driver/splitter circuit to null out the 2nd harmonic. It cancels the total unmatched gain of the driver/splitter, the output tubes, and the output transformer.
The null is very sharp, and easily viewed on the FFT.
Now what I want to do is have positions on the balance pot marked, so I can change the ratios of the 2nd and 3rd harmonics to known values.
That could make for an interesting listening session with some guests.
It could be:
"which setting do you like best"
or "guess which one has larger 2nd, equal 2nd, or larger 3rd harmonic".
Thanks!
I Did mix up which shaped curves revered tubes had.
It makes sense when you said the effect would be lessened for UL, and even more for triode wired.
I build and listen to SE and Push Pull amps.
Some of my 2-stage push pull amps have a balance pot in the plates of the cathode coupled driver/splitter circuit to null out the 2nd harmonic. It cancels the total unmatched gain of the driver/splitter, the output tubes, and the output transformer.
The null is very sharp, and easily viewed on the FFT.
Now what I want to do is have positions on the balance pot marked, so I can change the ratios of the 2nd and 3rd harmonics to known values.
That could make for an interesting listening session with some guests.
It could be:
"which setting do you like best"
or "guess which one has larger 2nd, equal 2nd, or larger 3rd harmonic".
Changing the splitter gain will affect the 2nd harmonic strongly, but that will kick up higher harmonics in class aB or AB, due to the sudden gain change when crossing from one output tube to the other. Class A operation makes that transition smoothly without kicking up high harmonics. This is generalizing to the full amplitude range.
At any fixed amplitude (and like for sine wave only), one can get various harmonic nulls, but they don't generally hold up well for complex waveforms with varying amplitude/power.
At any fixed amplitude (and like for sine wave only), one can get various harmonic nulls, but they don't generally hold up well for complex waveforms with varying amplitude/power.
smoking-amp,
You make me think (good).
Those PP amps I have Do keep the 2nd fairly well nulled throughout the power range, I have tested that. I bet that is only because the output tubes and push pull transformer are well matched and balanced.
But your point is well taken for when the splitter is imbalanced, the amp push pull output will not maintain the 2nd to 3rd ratio when going from A to AB and deep into AB.
I once used a serial splitter, with the 2nd triode taking a voltage-divided sample from the 1st triode. I stopped using that kind of splitter when I thought about the fact that the
1st triode had some 2nd harmonic, but the 2nd triode did not (same triode type, same standing volts and current, same load, but opposite phase).
That meant that the "push" output tube got driven by a signal that Did have some 2nd harmonic.
But the "pull" output tube got driven by a signal that did Not have some 2nd harmonic.
I like the cathode coupled splitter with a current source in the cathode. With a very good current source, and very well matched plate load resistors, and very well matched next stage grid resistors there is no 2nd HD (unless one to the triodes is toast).
You make me think (good).
Those PP amps I have Do keep the 2nd fairly well nulled throughout the power range, I have tested that. I bet that is only because the output tubes and push pull transformer are well matched and balanced.
But your point is well taken for when the splitter is imbalanced, the amp push pull output will not maintain the 2nd to 3rd ratio when going from A to AB and deep into AB.
I once used a serial splitter, with the 2nd triode taking a voltage-divided sample from the 1st triode. I stopped using that kind of splitter when I thought about the fact that the
1st triode had some 2nd harmonic, but the 2nd triode did not (same triode type, same standing volts and current, same load, but opposite phase).
That meant that the "push" output tube got driven by a signal that Did have some 2nd harmonic.
But the "pull" output tube got driven by a signal that did Not have some 2nd harmonic.
I like the cathode coupled splitter with a current source in the cathode. With a very good current source, and very well matched plate load resistors, and very well matched next stage grid resistors there is no 2nd HD (unless one to the triodes is toast).
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