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Old 11th October 2002, 07:37 PM   #11
tiroth is offline tiroth  United States
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Hmm...I was under the impression that DC saturation was a nonissue with PP provided the design allows sufficient bias adjustment to balance the two halves of the primary. Not true?

Thanks for your input...I have seldom seen any rationale to back up OPT design.
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Old 12th October 2002, 07:07 AM   #12
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Quote:
Originally posted by tiroth
Hmm...I was under the impression that DC saturation was a nonissue with PP provided the design allows sufficient bias adjustment to balance the two halves of the primary. Not true?

Thanks for your input...I have seldom seen any rationale to back up OPT design.
Certainly not true.
A subsonic component of plate current also appears in PP stages due to slightly asymmetrical clipping. This can be called dynamic DC offset.
The operating points of tubes of a PP pair also can drift more or less.
The good PP OPT should tolerate a DC imbalance of at least +-20% of one tube idle current.
Moreover, a small airgap linearises primary inductance.

Denis.
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Old 13th October 2002, 06:06 PM   #13
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Hello

You can interleaving windings on toroidal opts too. With care so do not have a large winding built.

You must Interleaving so that you maximize the contact cooper area between primary and secondary.
With this you garentee a reduction of leakage indutance.

Bifilar windings reduce shunt capacitance.

On toroidal opts all magnetic path is used by the windinds, and that is the reason why you use all bebefits of grain oriented.

On conventional and C cores, the magnetic particles of the non wind magnetic path do not change poles at the same time.
The particles magnetic polarity of the non wind magnetic path has a delay in what concerns the wind magnetic path.
This is the reason why toroidal opts saturate more suddenly than the others.

Regards
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Old 14th October 2002, 07:04 AM   #14
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Quote:
Originally posted by jraraujo
Hello

You can interleaving windings on toroidal opts too. With care so do not have a large winding built.

You must Interleaving so that you maximize the contact cooper area between primary and secondary.
With this you garentee a reduction of leakage indutance.

Bifilar windings reduce shunt capacitance.

On toroidal opts all magnetic path is used by the windinds, and that is the reason why you use all bebefits of grain oriented.

On conventional and C cores, the magnetic particles of the non wind magnetic path do not change poles at the same time.
The particles magnetic polarity of the non wind magnetic path has a delay in what concerns the wind magnetic path.
This is the reason why toroidal opts saturate more suddenly than the others.

Regards
In any case it is impossible to attain the same degree of precision in turns layout with toroidals.

The C cores allow one to utilise the benefits of grain-oriented steel as toroids, but the provide flat and uniform surface for winding. In additional, they possess a natural airgap. It is this latter that makes them saturate rather gradually.

I cannot see why bifilar winding decrase shunt capacitance. It can rather increase it to surely untolerable value. In contrary, the proper interleaving technique with flat layers and rather thick insulation allows one to attain almost any ratio between leakage inductance and shunt capacitance.

And finally, the good OPT must behave equally well over quite wide range of resistive and reactive loads. This requires optimising of the above ratio.

Therefore I'm sure double-C cores are the best.

Denis.
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Old 14th October 2002, 02:26 PM   #15
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[That is true, but you do not need Interleaving 10 layers on toroidal.
4 o 5 primary layers is enoug to reduce leakage indutance to a very low value.

Yes you have a minimum natural air gap and a uniform surface. And it is also true they saturate gradually.
This happens because the windignds do not cover all magnetic path. Like I have exposed.
The portoin of magnetic path not wound, has an intrinsec delay of particles magnetization.
That is why you van not use all benefits of G.O. silicon steel.
With Toroidal you have more conssistent lower full power band. And you have not a increase of indutive reactance at upper band.
On C cores you assist to a progressive degradation of sound at full power lower band.

Easely you can make toroidal ops with a high Quality factor with low Lsp (3 to 10 mH) for a 300 to 500 Henry Prim. Indutance
And values of 500 pF of Efecctive primary capacitante. That makes a QF = 300.000.

I have optimised tranformers in this conditions.

Please refer to "Modern High-End Valve Amplifiers based on toroidal output transformers" from Ir Memnno van der Veen


If you do not see why bifilar windings reduce shunt capacitance, Its very simple, try it like myself.
But if you need teorical expanations, please refer to "Transformer and Inductor Design Handbook" from Colonel Wm. T. McLyman. this is the "bible" of Aeronautical and Spaceships transformers tecnology.

Tehe ratio you refer is the Quality factor of a OPT, do you make it 300.000 with C-Cores?


Double C-cores, simple C-Cores and E I cores are certainly easy to do.

Regards

jraraujo
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Old 18th October 2002, 05:39 AM   #16
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[QUOTE]Originally posted by jraraujo
[B][That is true, but you do not need Interleaving 10 layers on toroidal.
4 o 5 primary layers is enoug to reduce leakage indutance to a very low value.

Yes you have a minimum natural air gap and a uniform surface. And it is also true they saturate gradually.
This happens because the windignds do not cover all magnetic path. Like I have exposed.
The portoin of magnetic path not wound, has an intrinsec delay of particles magnetization.

This is absolutely wrong statement from the viewpoint of physics.
Nonhing to say more.



That is why you van not use all benefits of G.O. silicon steel.
With Toroidal you have more conssistent lower full power band. And you have not a increase of indutive reactance at upper band.
On C cores you assist to a progressive degradation of sound at full power lower band.

What progressive degradation of sound is to be found if an amplifier delivers its full output power at 16 Hz with the same distortion as at 1kHz? The low-level -3db point(when the saturation does not apply) is probably below 1 Hz.

Easely you can make toroidal ops with a high Quality factor with low Lsp (3 to 10 mH) for a 300 to 500 Henry Prim. Indutance
And values of 500 pF of Efecctive primary capacitante. That makes a QF = 300.000.

My double-C OPTs have primary Ll < 1.2 mH and -3dB at 190kHz without observable resonances for an load from open circuit to 2 Ohm. And a perfect symmetry in amplitude and phase response between the halves of the primary.

I have optimised tranformers in this conditions.

Please refer to "Modern High-End Valve Amplifiers based on toroidal output transformers" from Ir Memnno van der Veen

My strong opinion: this book has nothing to do with the design of ultimate audio transformers. It is rather an advertisement for toroidals.

If you do not see why bifilar windings reduce shunt capacitance, Its very simple, try it like myself.
But if you need teorical expanations, please refer to "Transformer and Inductor Design Handbook" from Colonel Wm. T. McLyman. this is the "bible" of Aeronautical and Spaceships transformers tecnology.

But the prop[er interleaving technique and insulation thickness optimisation helps much more. Moreover, the bifilar winding rely solely on wire insulation strength. This is certainly not enough for a tube OPT. One should remember the plate-to-plate votage can exceed 2 x Ep!

Regards

Denis.
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Old 18th October 2002, 03:19 PM   #17
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This is absolutely wrong statement from the viewpoint of physics.
Nonhing to say more.

OK. If you say so!
If have nothing to say, I do not desire arge with you.
But for respect to other people visitor of this forum, yes I have something to say:

Physics is not axiomatic or dogmatic.
Physics is phenomenologic, and due this we have theorical physics.
Physics phenomenon are based on time and space.
There are no instantaneos phenomenon of propagation of magnetic fields or other fields.
From poit "A" to point "B" there is always a "delta t" in what concerns of propagation.
This afirmation is not axiomatic or dogmatic but phenomenologic.
Due this anyone can see why magnetic path of an OPT is not magnetised at the some time.
In other words, core elementary magnets do not realign instantaneosly.
Grain Oriented cores have elementary magnets oriented on direction of magnetic path.
Let your conscious imagination see what's happen on a core when we aply a magnetic force.
Progressively al elementary magnets rotate and align in a specific "delta t".
Now imagine a the movement of magnetic particles due A.C. on a windind.
Only with all magnetic path wond you extract al beneficts of Grain Oriented cores.
In other words you have less hysteresis losses.

The theme of this forum is completely put out of the way of inicial issue: "Double push-pull versus single push-pull"

The originally description of the phenomenon, happens with all types of transformers. Toroidal or Conventional.

And until now, nobody post a satisfactory explanation for the fact.

Regards
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Old 18th October 2002, 04:15 PM   #18
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Hi there,

I would like to put my limited knowledge 2 cents in here, if it would help:

All other things being equal, could it merely be the difference in how two tubes see the primary impedance versus four? I mean, if two tubes need to optimally have a primary impedance of 6K, wouldn't four need a primary impedance of 3K to compensate for the paralleled impedance of the tubes?

Here is why I say this: I have played with just a single pair of pentodes. I connected them straight pentode and UL. I have used 8K primary and 6k6 primary. I find that the 6k6 primary in UL mode sounded more musical, broader soundstage, and sweeter. UL sounded this way (more musical, etc) versus pentode. But UL sounded best with the 6k6 primary impedance. From what I understood about UL, the plate resistance drops. So I chose 6k6 right off, but had the higher impedance ones just to try.

Now, granted, you are actually increasing total plate resistance when you pull out two of the tubes. Which is why the sound changes, IMHO. The single pair may be better matched to the transformers primary impedance.

There should be a difference going from parallel to non parallel, due to this difference in impedance. It is just as when (I have read reviews where they do this) one uses the other taps than the required one for their speakers. " The sound seemed more restricted when I used the 16 ohm taps than the 8 ohm taps..." and the like. This is because, as I am sure you know, the reflected impedance to the output tubes changes, changing the characteristics of the tubes. I would suspect the reverse is true with the tubes and impedance through the transformer.

So if you are using a certain value primary impedance, may I suggest using half the value when paralleling? The impedance curve might make all the difference in sound quality, because then the tubes will be performing within their best plate curve parameters.

Just a thought.

Gabe
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Old 18th October 2002, 06:29 PM   #19
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Hi

Thanks for your post.

I'm using a 2K to 5 Ohms U.Linear transformer.

The four KT88 see 2K Anode to Anode if load = 5 Ohms; or 3200 Ohms if load = 8 Ohms; or 1600 Ohms if load = 4 Ohms.

If my theory is correct, 8 Ohms speakers have 4-5 Ohms at low frequencies.

There also a large amount of feedback (12dB).

I think that values are all right for four KT88 and not correct for only a pair of the same tubes. Don't you agree?

Regards
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Old 19th October 2002, 12:23 AM   #20
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For a single pair, 4K is recommended. So... you have it close.

Perhaps going for a smaller primary? Like 1500?

At this point I would be guessing.

Gabe
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