Can you be more precise. What is the UL driver? The common cathode with bootstrap? What is the driver running the output stage? The cathode follower? What is a single link? You seem to talk another language....
I have already done it and distortion is lower than any driver I have used.
In a modified UL with less than 50% of the turns at the cathode the required driving voltage is less than the McIntosh of comparable output power and the bootstrap effect is higher because the ratio of normal grid swing-to-output late voltage increases. This is elementary because the driver has to develop the normal swing that gets amplified and present at the finals plates and the full voltage that will be produced at the cathodes. If the ratio is already 62.5%-37.5% (which I have done) that's already a significant difference..... and even more if 75%-25%.
You don't like it? Fine but it works. Sorry for shattering your dreams....
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The driver is a cascade that stands before the last.
The distortion of any cascade and even the driver depends on the amplitude of the signal, and this one also works in all textbooks. The lower the signal level in any cascade running in class A, the less distortion. In the driver working in class A is the same! Consequently, in only UL amplifiers and amplifiers with tetrodes at the output, the same driver will lessly introduce its own distortions into the overall contribution of the distortions. In triode circuits and others, for example, the same driver is always more distorted because of the larger signal amplitude.
David Hafler in his patent just patented that it is important to observe a certain ratio of % in the UL tap.
The paradox is that this scheme was proposed much earlier by the British but because they did not find out this main feature of this scheme the scheme did not get proper propagation then. David Hafler also spent a lot of effort to make the scheme a standard. He made a beautiful move in chess, in a correspondence dispute with Williamson, who claimed that his scheme could be the same. David Hafler simply put his transformer in Williamson's scheme, and the point in the dispute was posed once and for all.
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Here is an indipendent opinion in post 34 and results about bootstrapping the plate:
http://www.diyaudio.com/forums/tubes-valves/159177-push-pull-45-a-4.html
Here the output stage is a simple triode PP class AB.
Bootstrapping is often seen in preamps using cathode followers and also here distortion is reduced.
Reading papers and books is and then elaborating strange theories is not reality. I think I don't have anything more to add to this offtopic discussion.
http://www.diyaudio.com/forums/tubes-valves/159177-push-pull-45-a-4.html
Here the output stage is a simple triode PP class AB.
Bootstrapping is often seen in preamps using cathode followers and also here distortion is reduced.
Reading papers and books is and then elaborating strange theories is not reality. I think I don't have anything more to add to this offtopic discussion.
45, Gunfu,
With all respect, but you are hijacking this thread; it's about litz wire, not amplifier circuits.
Open your own thread; the subject is interesting enough (though discussed many times before).
With all respect, but you are hijacking this thread; it's about litz wire, not amplifier circuits.
Open your own thread; the subject is interesting enough (though discussed many times before).
All the ratios are not typical for a particular tubes, they will not be as effective as they can be if% UL is optimal. For example, for KT88 this is 40%. Therefore, the modified UL ratio is 60% / 40% on KT88 or EL34. Other relationships are not UL.
With a ratio of 60% / 40%, the excitation amplitude of such a cascade will be required to be high, almost like in the single McIntosh diagram.
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Announce this Devid Hafler his UL patent apparently all the time worked incorrectly!
I had to raise the issue in this and another branch. Since the cascade on tetrodes never required such a quality that it was worthwhile to apply the Litz. It does not have such low values of distortion and low internal resistance as for example in UL, where does it cost to fight for even higher quality.
The choice of the tetrode scheme for demonstrating the worth of Litz, is doubtful.
I suppose that the effect of using Litz on the UL or with a local cathode bond is more noticeable.
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I had to raise the issue in this and another branch. Since the cascade on tetrodes never required such a quality that it was worthwhile to apply the Litz. It does not have such low values of distortion and low internal resistance as for example in UL, where does it cost to fight for even higher quality.
The circuit was called modified UL because the screen becomes the reference electrode for the ratios (i.e. screen-to-plate voltage and screen-to-cathode voltage). You call it partial cathode follower but it doesn't change anything. It's just a name.....and it WORKs just fine!
I know, but in the cathode winding, for example, for KT88, there will already be 40%
And this means that the voltage on the first grid should be significantly increased compared to the conventional UL scheme. If you are afraid of dumping a lot of voltage on the screen, as if using the EL509 only 140-150 V
It is also a good circuit with the supply of local feedback from the anodes to the cathode driver.
The transformer is simpler, even compared to the conventional UL.
http://www.wowhififever.com/LV_60/Neuman LV60.htm
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Why? The standard Ultralinear itself has not a fixed ratio! The inventor was wrong because he didn't test all tubes. So much so that even tube manufacturers proposed UL with different ratio from 43%. For example, Mullard proposed the EL84 UL with both 43% and 20% tap. Have a look at the Mullard EL84 datasheet. I would pick the 20% with some cathode feedback every time! This subject has been beaten to death. Just use the search function in this forum......
Even so bootstrapping works even with 50-50 ratios in partial cathode followers. It might be a problem with full cathode followers but even there people have found alternative solutions....One just needs to know how it works and do it properly....
You also argued that it doesn't work with triodes and instead I gave you a link with facts (i.e. the real amp + THD measurements) where it has been used in a worst case scenario (i.e. low gain device and bootstrap taken from UL taps).
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This 'what U-L percentage is best' depends on not only the goals, but the operating condition. Note that all of the old U-L data gives the starting point...
Weigh the effects; higher percentage, less power, more capacitance, higher g2 idle voltage, lower plate resistance...
The McIntosh circuit should not need the positive FB on the 12BH7 plates. Install a CCS plate load instead of the 12kOhm resistors. Do away with the loop of global FB while you're at it. Whole lot more pleasant amps in that form. It hurts not at all to do away with the 12AX7/12AU7 pair and use instead a 12AY7 and a 6CG7.
cheers,
Douglas
Weigh the effects; higher percentage, less power, more capacitance, higher g2 idle voltage, lower plate resistance...
The McIntosh circuit should not need the positive FB on the 12BH7 plates. Install a CCS plate load instead of the 12kOhm resistors. Do away with the loop of global FB while you're at it. Whole lot more pleasant amps in that form. It hurts not at all to do away with the 12AX7/12AU7 pair and use instead a 12AY7 and a 6CG7.
cheers,
Douglas
Douglas,
Just curious if you have ever tried the above modifications and documented the performance changes. I think I am getting ready to revamp the driver stage in my UC amp and am thinking things through.
Heath
Just curious if you have ever tried the above modifications and documented the performance changes. I think I am getting ready to revamp the driver stage in my UC amp and am thinking things through.
Heath
Do not invent your own nonsense. Hafler appears to be mistaken аnd with him the US Bureau too. Or maybe you have patents? For each tube there is an optimal UL% and Hafler wrote about it in patent. The cathode feedback also has % and it necessarily sums with UL% if they work in one output transformer. By the type "modfied-ultralinear" 60% / 40%, which you all the time refer to, but you close your eyes to important % numbers.
For KT88 UL40% is the optimum. Look link.
For other tubes and modes, there may be anothers %. But this does not mean that the KT88 work at its maximum opportunity at UL20% or at 50% as in the McIntosh diagram. Because the UL's advantage in the patent Hafler as a low distortion like a triode, or even lower, and at the same time high gain as in tetrodes (pentodes).
Or consider the case for EL34 at 60% or even 50% it's all not UL at all but a fake. And such delusional recommendations not of Mullard too!
The best UL percentage is zero, i.e. regulated voltage between cathode and G2, with zero dynamic resistance. G2 and G1 transfer curves do not match, so apply your feedback between G1 and cathode, and be happy! It is 21'St Century, and you don't need a patent like Haffler did, despite Otto Schade back in 1938 offered the right solution for free. And you don't need to be hypnotized by an "ultralinear" word that in comparison to feedback to G1 is anything but linear.
Fashions, even silly ones, never die...
Fashions, even silly ones, never die...
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Not sufficiently deep cathode feedback, for example, less than 40% in the case of KT88 will not have the same effect as UL.
In UL there is a nonlinear feedback, and the result is clearly visible on the graph (for those who want to see), View attachment 621091
distortions are minimal only with a certain feedback ratio in %, output impedance too. The output power opposite has its maximum but also at this %.
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Amen. Apply the feedback to the electrode that caused the non-linearity and the results will be superior to applying it to some other electrode.
Nothing like this! Not only minor distortions are important, such as for a triode. A whole set, useful properties. Such as a large gain, and the main load resistance, which in the case of UL is less than that of a triode.
In your example, the gain becomes simply less, and the optimum load resistance at which the power will be maximized will have to be determined empirically.
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Here you go:
http://www.clarisonus.com/Archives/TubeTheory/Schade 1938 Beam Power Tubes.pdf
Feedback theory is well described, even for complex systems. Here is the simplest possible case.