?
Take a look at the stabdards please. It could be designed even for one digit + - shift 20Hz 20KHz.
,
I was talking a device electrical specifications. And measurements.
They are also standard. Not subjective... But tube folks wants to mistify the things always...
.
It was not about moving the speakers around the room.
.
What has left and right speaker channel with electrical specs of stand alone unit?
Please... 🙁
.
Zoran,
At 79 years old, and at least 1/2 worn out, I wish I had the time and energy to write a book about phase shift and group delay (specifically for Audio Fans).
And, I would also include info about all the comb filter effects of real stereo playback systems caused by so many recording techniques.
Some are not observable by those with 2 good ears, but are very easy to hear by those with only one ear (2 ears often allows the brain to fill in the comb filtering effects).
If you have a specified time delay through an amplifier or playback system, that simply means that the number of degrees of phase shift is higher for high frequencies, and lower for low frequencies, as they relate to the input to the amplifier or playback system.
A time delay can be caused by a low pass filter, such as the Miller Effect of a single stage.
Or,
An output transformer.
Etc.
The result is a different number of degrees at different frequencies.
If you have one loudspeaker at one distance, and another loudspeaker at another distance, the far loudspeaker has a lagging phase versus the close loudspeaker.
One engineer of Tektronix TV measurement products division, and his Tektronix product . . . proved that a manufacturer's video player was delaying one of the two sections of a video field (The interleaving was offset).
Guess what . . . it was not visually detectable, only special test equipment could prove it.
Why do I use that video example . . . I reminded me of an early CD player.
The early CD player was designed to use only One DAC. That "saved" money, which allowed the use of a more expensive precision DAC.
The DAC ran at 88.2k: 44.1k for Left, and 44.1k for Right.
A switch alternated the DAC output to the Left and Right channels.
So, the Relative L and R phases were offset by 90 degrees at 22.05kHz.
Did anybody hear that 90 degree phase shift? NO.
At 1080 feet per second, 90 degrees at 22.05 kHz figures out to 0.012244898 feet, which is 0.146938776 Inches.
Are the relative distances of the left speaker to your left ear, versus the right speaker to your right ear accurate enough so that they are within
0.15 inches of each other. (or plus 0.075 inches of one ear, and minus 0.075 inches of the othe ear)
If not, your listening position is suffering from a 90 degree phase shift from left to right (yes, at 22.05kHz).
A 90 degree phase shift at 22.05 kHz, is a 9 degree phase shift at 2.205kHz, and a 0.9 degree phase shift at 220.5 Hz.
Are we concerned?
Do we hear that error?
I am a nutty audio fan, I admit that.
I worry less about phase shift than the average audio fan.
I do not use global negative feedback, and not even use secondary to output tube cathode negative feedback.
Poor phase shift numbers? Probably not always a problem.
Instability? Instability can be a Major problem.
Relative phase shift is one thing.
I do not normally read the diyAudio full range, and multiway threads.
But I bet there discussions at multiway threads that talk about Group Delay.
My work with Group Delay had to do with such things as Radars, and Microwave Spectrum Analyzers.
Nothing Audio about that.
There is a book written about Absolute Phase, it is called "The Wood Effect".
Other than mentioning it, I will probably never discuss it on diyAudio.
I am tired already, so that is all on this subject tonight.
$0.03
adjusted for inflation
PS
The phase shift and group delay of both an amplifier, a loudspeaker, and loudspeaker unequal distances, and many recordings can be a problem.
A single item of the above, or 2 or more of the above, affects the performance of a Playback System.
Key Word: System
Musician and microphone, all the way to the listening ear and the brain is a . . . System.
How many great system designers have I met at my many jobs over the dacades . . . only a few.
At 79 years old, and at least 1/2 worn out, I wish I had the time and energy to write a book about phase shift and group delay (specifically for Audio Fans).
And, I would also include info about all the comb filter effects of real stereo playback systems caused by so many recording techniques.
Some are not observable by those with 2 good ears, but are very easy to hear by those with only one ear (2 ears often allows the brain to fill in the comb filtering effects).
If you have a specified time delay through an amplifier or playback system, that simply means that the number of degrees of phase shift is higher for high frequencies, and lower for low frequencies, as they relate to the input to the amplifier or playback system.
A time delay can be caused by a low pass filter, such as the Miller Effect of a single stage.
Or,
An output transformer.
Etc.
The result is a different number of degrees at different frequencies.
If you have one loudspeaker at one distance, and another loudspeaker at another distance, the far loudspeaker has a lagging phase versus the close loudspeaker.
One engineer of Tektronix TV measurement products division, and his Tektronix product . . . proved that a manufacturer's video player was delaying one of the two sections of a video field (The interleaving was offset).
Guess what . . . it was not visually detectable, only special test equipment could prove it.
Why do I use that video example . . . I reminded me of an early CD player.
The early CD player was designed to use only One DAC. That "saved" money, which allowed the use of a more expensive precision DAC.
The DAC ran at 88.2k: 44.1k for Left, and 44.1k for Right.
A switch alternated the DAC output to the Left and Right channels.
So, the Relative L and R phases were offset by 90 degrees at 22.05kHz.
Did anybody hear that 90 degree phase shift? NO.
At 1080 feet per second, 90 degrees at 22.05 kHz figures out to 0.012244898 feet, which is 0.146938776 Inches.
Are the relative distances of the left speaker to your left ear, versus the right speaker to your right ear accurate enough so that they are within
0.15 inches of each other. (or plus 0.075 inches of one ear, and minus 0.075 inches of the othe ear)
If not, your listening position is suffering from a 90 degree phase shift from left to right (yes, at 22.05kHz).
A 90 degree phase shift at 22.05 kHz, is a 9 degree phase shift at 2.205kHz, and a 0.9 degree phase shift at 220.5 Hz.
Are we concerned?
Do we hear that error?
I am a nutty audio fan, I admit that.
I worry less about phase shift than the average audio fan.
I do not use global negative feedback, and not even use secondary to output tube cathode negative feedback.
Poor phase shift numbers? Probably not always a problem.
Instability? Instability can be a Major problem.
Relative phase shift is one thing.
I do not normally read the diyAudio full range, and multiway threads.
But I bet there discussions at multiway threads that talk about Group Delay.
My work with Group Delay had to do with such things as Radars, and Microwave Spectrum Analyzers.
Nothing Audio about that.
There is a book written about Absolute Phase, it is called "The Wood Effect".
Other than mentioning it, I will probably never discuss it on diyAudio.
I am tired already, so that is all on this subject tonight.
$0.03
adjusted for inflation
PS
The phase shift and group delay of both an amplifier, a loudspeaker, and loudspeaker unequal distances, and many recordings can be a problem.
A single item of the above, or 2 or more of the above, affects the performance of a Playback System.
Key Word: System
Musician and microphone, all the way to the listening ear and the brain is a . . . System.
How many great system designers have I met at my many jobs over the dacades . . . only a few.
Last edited:
I'm also a one-eared guy, are we missing something? Or can we test the equipment better?
The brain has correction circuitry to compensate for sounds reaching our ears at different times. Historically it helped with detecting the predator sneaking up from behind, but modern man finds it detrimental to speaker placement. Being deaf in one ear bypasses that correction circuitry.
What is the Damping Factor of a common 2A3 SE amplifier?
How did you arrive at that number for DF?🙂
jhstewart9,
and interested parties,
1. My varioius SE 2A3 amplifiers had a damping factor of about 2.5 to 4.5.
For many, that is nothing to write home about (sorry for the american trite expression).
I measure the small signal damping factor.
Starting with a 1kHz signal applied to the input volume control, and with the secondary Un-loaded, I set the volume control until the amplifier secondary output is 1VRMS.
Then, I connect a non-inductive 8 Ohm load resistor across the secondary and measure the loaded output RMS voltage.
If the loaded Volts rms is 0.8V, than the amplifier's internal voltage is divided 0.2V across the amplifier's output impedance, and 0.8V across the 8 Ohm load..
0.8V/0.2V = 4.0
The damping factor, referred to an 8 Ohm load is 4.0.
2. A builder used a 2A3 at 60mA, the plate impedance, rp, is 800 Ohms to drive the transformer he wound himself.
He wound a turns ratio of 20. 20 squared is 400. And 8 Ohms x 400 = 3200 Ohms
He expected the damping factor to be 4.0, according to 3200 Ohms / 800 = 4.0.
But it was less than 4.
He forgot to account for primary DCR of 5% of 3200, and secondary DCR of 5% of 8. The DCR total: 5% + 5% = 10%.
The effective primary impedance is is 3200 Ohms + 320 Ohms = 3,520 Ohms.
The effective secondary impedance is 8 Ohms + 0.4 Ohms = 8.4 Ohms.
The result is that the 800 Ohm 2A3 plate is driving a winding of 3200 Ohms, that is in series with an effective DCR of 320 Ohms (3520 Ohms total)
But that will cause a loss of voltage into an 8 Ohm load resistor; 90.9% versus a lossless transformer.
The transformer loss at 1kHz is about -1dB.
And the damping factor is about 3.6.
I hope my late night calculations were done correctly.
3. Some will object at my small signal method of measuring and calculating damping factor.
But a 2A3 at maximum plate current of say 120mA, the rp is perhaps close to 700 Ohms.
And a 2A3 at minimum plate current of say 5mA, the rp is perhaps close to 2400 Ohms.
As you can see, the large signal damping factor is Non-Symmetrical, as it goes through the complete 1kHz sine wave.
I have talked about the much more Symmetrical damping factor of push pull amplifiers; especially in Class A.
In Class AB, the damping factor is still symmetrical, but it varies by 2:1 with both tubes on, versus when one tube is off;
as the 1kHz sine wave changes from one alternation to the other (alternating which tube is off).
and interested parties,
1. My varioius SE 2A3 amplifiers had a damping factor of about 2.5 to 4.5.
For many, that is nothing to write home about (sorry for the american trite expression).
I measure the small signal damping factor.
Starting with a 1kHz signal applied to the input volume control, and with the secondary Un-loaded, I set the volume control until the amplifier secondary output is 1VRMS.
Then, I connect a non-inductive 8 Ohm load resistor across the secondary and measure the loaded output RMS voltage.
If the loaded Volts rms is 0.8V, than the amplifier's internal voltage is divided 0.2V across the amplifier's output impedance, and 0.8V across the 8 Ohm load..
0.8V/0.2V = 4.0
The damping factor, referred to an 8 Ohm load is 4.0.
2. A builder used a 2A3 at 60mA, the plate impedance, rp, is 800 Ohms to drive the transformer he wound himself.
He wound a turns ratio of 20. 20 squared is 400. And 8 Ohms x 400 = 3200 Ohms
He expected the damping factor to be 4.0, according to 3200 Ohms / 800 = 4.0.
But it was less than 4.
He forgot to account for primary DCR of 5% of 3200, and secondary DCR of 5% of 8. The DCR total: 5% + 5% = 10%.
The effective primary impedance is is 3200 Ohms + 320 Ohms = 3,520 Ohms.
The effective secondary impedance is 8 Ohms + 0.4 Ohms = 8.4 Ohms.
The result is that the 800 Ohm 2A3 plate is driving a winding of 3200 Ohms, that is in series with an effective DCR of 320 Ohms (3520 Ohms total)
But that will cause a loss of voltage into an 8 Ohm load resistor; 90.9% versus a lossless transformer.
The transformer loss at 1kHz is about -1dB.
And the damping factor is about 3.6.
I hope my late night calculations were done correctly.
3. Some will object at my small signal method of measuring and calculating damping factor.
But a 2A3 at maximum plate current of say 120mA, the rp is perhaps close to 700 Ohms.
And a 2A3 at minimum plate current of say 5mA, the rp is perhaps close to 2400 Ohms.
As you can see, the large signal damping factor is Non-Symmetrical, as it goes through the complete 1kHz sine wave.
I have talked about the much more Symmetrical damping factor of push pull amplifiers; especially in Class A.
In Class AB, the damping factor is still symmetrical, but it varies by 2:1 with both tubes on, versus when one tube is off;
as the 1kHz sine wave changes from one alternation to the other (alternating which tube is off).
This is the visual field... There is diferent rules thn in audio domain.
Please not speak in the hearing and listening domain?
With complex system include many other separate things.
this is an experiment not in the electrical system but in the medical, social, and other...
Ehwre the tool is only equipment and sublect to the test are people.
Test is about people not about the phase and elecrical specifications...
.
Why do we just listen to the pocket radio units if the thing is so relative and not important?
Where is the border line of subjectivism abused by the relativisation?
.
People are convinced trough the pleasent photographies, personal testimonies that very affirmative?
And if some argumented debate starts - then everybody are ennemies? Like how dare You to say that when John Smith said different...
.
I am trying to say that we can design a electrical unit that can be better in bandwidth, phase, driving posibilities.
With:
1. more suitable value of pot as the first step regarding to the dynamic capacitnace of input tube.
When I spot 1Meg ohm or 470K or even 100K, POT value first in the circuit I emediately know, that the amp is not measured, that other cmponents values will be wrong, that the allover design will be poor. That is for more than 40 year rule that was close to the 100% true.
2. Good choice of working point for the specific tube. And appropriate choice of the load.
3. adjusting the RC constants, in the active circuit, C at Vb, Ck if existed and output C in the respect to the next stage Rg
.......
Manu people simple dont know that -3db@20HZ-20KHz is not correct.
the correct value is about -0.25db@edges of the BW, thus -3db will be @ 1.6Hz and 131KHz...
Morgan jones was once gave the formula for calculating the BW in N Stages of amplification,
in Electronics World, March 1996 issue, page 190, article "Designing valve preamps"
Phase will follow that. A target phase at the electric circuit that we can obtain with simple given components,
is about +-8.5deg or less, but we can tolerate up to 15deg. Phase shift is in direct conn. with BW.
.
If the Output transformer is a no 1 factor for BW in amplifiers, that does not mean that other limitations should fit that?
Just oposite. it should be designed for wider BW anf less phase shift. (group delay us a function of phase)
.
Sorry if I maybe was not showed, more clearly, enough respect for the experience, work amd effort.
Now I am saying - I respect all of the senior members.
Not huge. It mainly depends of Rdc of secondary layers.
The problem is that we often dont have suficient space in transformer core window, to choose the higher diameter wire to lower Se. Rdc and to lower DF.
.
But there is one solution: another output transformer after the Main OT. that additional transformer will be working only with AC signal, witout DC magnetization component, smaller gap needed. And wider diameter of wire can be used.
.
I tried once long time ago 1:1 trafo after between the tube SE amp and speakers. Was bigg diferece in sound.
Infact the additional AC trafo should be taken from geometric mean of current ratio transformation. Most of the tube loads from 3K to 10k and wider, gravitate to 200 ohm value. As intermediate load and transformation ratio point...
So the aproximate ratio example wil be say (3500 : 200) (200 : 8) ohms
.
You can try it just for test, with power 1:1 transformer. But first You can simple measure DC resistance of secondary, at the speaker terminals off-course power off amp...
I agree, it is nice to have wide bandwidth, lower phase differences, and lower group delay in an amplifier.
But, we have to consider that the most perfect amplifier can not solve all the System problems of a playback signal source, amplifier, and loudspeaker.
Think of an Onion. Do we clean the outside, or at least remove the first two layers, before we cut the Onion and put it into our stew?
A Hi Fi or Stereo playback system is very much like an Onion. First, attack the most offending layers, before working on the smaller problems.
Start with the waveforms in the Terman excerpt in Post # 72.
The waveforms show a fundamental plus a 3rd harmonic.
The 3rd harmonic is either in-phase, or is out-of-phase with the fundamental.
The power of the fundamental in those 3 waveforms are the same.
The power of the 3rd harmonic in those 3 waveforms are the same.
But the Peak amplitude of those 3 waveforms are not the same.
Those constant power of the fundamental, and constant power of the 3rd harmonic are what activate the different nerve cells: according to the nerve cells that detect the fundamental frequency, and the different nerve cells that detect the 3rd harmonic frequency.
But note that whichever waveform is present, the nerve cells always detect the same amplitude in their frequency range, no matter which of the waveforms is present.
But, the real difference in the waveform shapes is the Peak amplitudes:
When the fundamental is at 90 degrees, and at the same time the 3rd harmonic is at 90 degrees, we see the pointy shaped waveform. The point is a relatively large peak amplitude.
In the other case, when the fundamental is at 90 degrees, and at the same time the 3rd harmonic is at 180 degrees, we see the two Smaller peaks in the waveform. The two smaller peaks are at relatively small peak amplitudes.
For a full range loudspeaker, the peak cone excursion is larger for the single large amplitude peak waveform,
The larger peak excursion will drive the speaker to be less linear, versus . . .
The peak cone excursion which is smaller for the double peak waveform . . . where the loudspeaker is more linear with lower excursion.
Please do not forget that the amplitudes of the fundamental and the amplitude of the 3rd harmonic did not change . . .
But the Peak amplitude of the complete waveform did change.
Now, you see how the full range driver is driven by different waveforms that change the performance of the driver.
Our ear is also Non-Linear. The mechanical system of the ear produces its own harmonic distortion.
The larger singfle peak of the one waveform will cause more harmonic distortion in the ear, versus the smaller double peak waveform.
If you can follow and understand all of what I wrote above, you are better than I am.
Or, please write up your own explanation of those effects.
$0.03
adjusted for inflation
But, we have to consider that the most perfect amplifier can not solve all the System problems of a playback signal source, amplifier, and loudspeaker.
Think of an Onion. Do we clean the outside, or at least remove the first two layers, before we cut the Onion and put it into our stew?
A Hi Fi or Stereo playback system is very much like an Onion. First, attack the most offending layers, before working on the smaller problems.
Start with the waveforms in the Terman excerpt in Post # 72.
The waveforms show a fundamental plus a 3rd harmonic.
The 3rd harmonic is either in-phase, or is out-of-phase with the fundamental.
The power of the fundamental in those 3 waveforms are the same.
The power of the 3rd harmonic in those 3 waveforms are the same.
But the Peak amplitude of those 3 waveforms are not the same.
Those constant power of the fundamental, and constant power of the 3rd harmonic are what activate the different nerve cells: according to the nerve cells that detect the fundamental frequency, and the different nerve cells that detect the 3rd harmonic frequency.
But note that whichever waveform is present, the nerve cells always detect the same amplitude in their frequency range, no matter which of the waveforms is present.
But, the real difference in the waveform shapes is the Peak amplitudes:
When the fundamental is at 90 degrees, and at the same time the 3rd harmonic is at 90 degrees, we see the pointy shaped waveform. The point is a relatively large peak amplitude.
In the other case, when the fundamental is at 90 degrees, and at the same time the 3rd harmonic is at 180 degrees, we see the two Smaller peaks in the waveform. The two smaller peaks are at relatively small peak amplitudes.
For a full range loudspeaker, the peak cone excursion is larger for the single large amplitude peak waveform,
The larger peak excursion will drive the speaker to be less linear, versus . . .
The peak cone excursion which is smaller for the double peak waveform . . . where the loudspeaker is more linear with lower excursion.
Please do not forget that the amplitudes of the fundamental and the amplitude of the 3rd harmonic did not change . . .
But the Peak amplitude of the complete waveform did change.
Now, you see how the full range driver is driven by different waveforms that change the performance of the driver.
Our ear is also Non-Linear. The mechanical system of the ear produces its own harmonic distortion.
The larger singfle peak of the one waveform will cause more harmonic distortion in the ear, versus the smaller double peak waveform.
If you can follow and understand all of what I wrote above, you are better than I am.
Or, please write up your own explanation of those effects.
$0.03
adjusted for inflation
In my post # 73 (above), I forgot another important concept.
Take a 2 way loudspeaker, with a 2kHz, 24db per octave crossover.
Then take those two waveforms.
Suppose the fundamental is at 1 kHz. Therefore, the 3rd harmonic is at 3kHz.
Only 1 kHz reaches the woofer.
Only 3 kHz reaches the tweeter.
The woofer excursion, and the tweeter excursion, do not change with the two different waveforms . . .
The waveform with the single large peak voltage, or the waveform with the small double peak voltage.
The Loudspeaker System does not "know" the difference between the two different waveforms.
And there gentlemen and ladies, is another difference between a full range speaker, and a 2 way speaker.
YLEMV . . . Your Listening Experience May Vary
$0.03
adjusted for inflation
Take a 2 way loudspeaker, with a 2kHz, 24db per octave crossover.
Then take those two waveforms.
Suppose the fundamental is at 1 kHz. Therefore, the 3rd harmonic is at 3kHz.
Only 1 kHz reaches the woofer.
Only 3 kHz reaches the tweeter.
The woofer excursion, and the tweeter excursion, do not change with the two different waveforms . . .
The waveform with the single large peak voltage, or the waveform with the small double peak voltage.
The Loudspeaker System does not "know" the difference between the two different waveforms.
And there gentlemen and ladies, is another difference between a full range speaker, and a 2 way speaker.
YLEMV . . . Your Listening Experience May Vary
$0.03
adjusted for inflation
Last edited:
Please try to understand that:
1. Amplifier is pure electrical system. (with addition of magnetic materials properties for transformers...)
2. Loudspeaker is electro, magnetic, mechanical and acoustical system.
3. Ear is electro-chemical, mechanical, acoustical, neurological and psychological system. (Incorporated in more complex cluster of other senses with own reception, perception and cognitive mechanisms...)
.
These are completely and totally different systems...
It is too coplex and naive to blend each one into "something"...
.
I suggest that we stand on most simple one that covering electrical field?
🙂
1. Amplifier is pure electrical system. (with addition of magnetic materials properties for transformers...)
2. Loudspeaker is electro, magnetic, mechanical and acoustical system.
3. Ear is electro-chemical, mechanical, acoustical, neurological and psychological system. (Incorporated in more complex cluster of other senses with own reception, perception and cognitive mechanisms...)
.
These are completely and totally different systems...
It is too coplex and naive to blend each one into "something"...
.
I suggest that we stand on most simple one that covering electrical field?
🙂
It is actually a good example of phase shift?
(BTW, FR does not have it... With no added complex elements in the electrical network. And it is not primary property of the amplifier to consider the shape of complex impedance line which is different in so many ways in massive range of speakers...)
.
But it is not like this 1st and 3rd example, yes if it is a single tone generating signal.
It is never like this. We have very large number of 1st harmonics and their residuals in the signal of music material.
AND they "happening" in the same time. And they are not the same length of harmonic content.
Plus, they are in different frequency positions in the bandwidth.
.
So again, this is fact of the input content.
The goal is to have same distribution as possible of amplifying signal on the whole BW. Or as much as we can.
Not deliberately narrow it and ruin it at the very input of the device and again after the first stage tube, because we "cant hear it" or OT does not capable to reproduce, or loudspeaker cant cope with it, whatever...
There are different and not insignificant issues but not addressed directly to the amplifier or preamplifier.
Mr. Nestorovic of McIntosh fame ( MI-350 / MC-3500 amp ) had different opinion on narrowing the bandwith at input but with the caveat that the design from the beginning must be excellent before doing this at the end.
He wrotte an lenghty article/complete project on this, laboratory 20 Watt amplifier, EL34 PP in Triode Class A2, but unfortunately it is not in english and is a way to big to be uploaded.
That response on a double EE quiz would get you a fail.
You did not answer the questions asked. But in response went into a long harangue about God knows what.
People in the real World need prompt & concise answers. Period.🙄
jh9stewart "What is the Damping Factor of a common 2A3 SE amplifier?
6A3sUMMER "I only know the damping factors of my 2A3 SE amplifiers, I do not know if they are the same DF as other's common 2A3 SE amplifiers."
jhstewart "How did you arrive at that number for DF?"
6A3sUMMER "Measure the output impedance of the amplifier. I list my damping factors in reference to an 8 Ohm load. 8 Ohm load / output impedance = damping factor; my method of calculation."
Some will use other loads, and other secondary output taps, and may want to refer DF to loads of 4 or 16 Ohms, etc.
Can I get a better grade now, please?
6A3sUMMER "I only know the damping factors of my 2A3 SE amplifiers, I do not know if they are the same DF as other's common 2A3 SE amplifiers."
jhstewart "How did you arrive at that number for DF?"
6A3sUMMER "Measure the output impedance of the amplifier. I list my damping factors in reference to an 8 Ohm load. 8 Ohm load / output impedance = damping factor; my method of calculation."
Some will use other loads, and other secondary output taps, and may want to refer DF to loads of 4 or 16 Ohms, etc.
Can I get a better grade now, please?
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First of all, I didn’t ask for your results, but rather how you would get the DF result in a general way. And then,’How did you get that estimate’.
Early in the study of vacuun tube electronics, most of the text books of that era would take us thru the calculation of the maximum power available from a triode. And the resultant distortion. For the case using an OPT the max efficiency is ~25%. Need to be careful the loadline is not too steep.
Damping Factor is Rl / rp. So DF of about 3 is possible at max output. The distortion can be reduced quite a bit by choosing a higher Rl, say 4-5rp. This leads to the interesting conclusion that the DF of all triodes is the same under similar conditions of load vs rp. Rp can be lowered by increasing cathode current, but there is a limit to that.
In a practical application the circuit will need a matching device to the load, most often a transformer. Now there is resistance (& other) in the path to the load. This will lower the DF still further no matter what the quality of the OPT. Spend your money wisely.
Many of the common triode SE amps we see here have a DF of about 3. Or less. And that is OK, it is what produces the kind of sound people expect to hear from their system. Often referred to as ‘not to tight’. Like a NFB amp!
Your buddy Matt Kamna made some interesting observations with reference to the 7199 back in 1996. Off the top I’m thinking folks were using the 6AN8 by then instead. And had been elevating the heater supply to something like 25-30 volts. Either with a voltage divider or picked off the output tube(s) cathode. I did both.
Where are all those amplifiers you have built & tested? I’ve only ever seen two references to them, one in Joe Roberts Sound Pratices Magazine of 1996. The other more recently here on DIY.
I get the sense you are on DIY 24/7. But I could be wrong, any family, wife & kids to keep you busy?
