I was only looking at permeability along the DC magetization curve as a comparison between M-6 and powdered cast iron. Sure, you can look at the incremental permeability of M-6 and see that mu is ever decreasing in an application where a significant gap and DC bias are present. But the same holds true for powdered cast iron where incremental permeability will fall to a ridiculously low and useless value (not to mention that excitation current for cast iron is many times higher than M-6). Look, the core is being designed for an amplifier using parallel single ended 813's and I was using a comparison between relative values of readily available data to show that the number of turns of wire required to make such a monster work is tremendous.
John
John,
Are you sure the curve your looking at isn't powdered ferrite. Powdered ferrite is almost universally referred to as powdered iron in the literature. And why wouldn’t it be as ,with the rare exception, “iron powder” cores available today are in fact iron ferrite. Something to consider…cold rolled steel has very similar magnetic characteristics to cast iron (in a dc magnet circuit anyway), it would be a logical jump to assume Si-steel would be similar to Si-iron. If your data is showing you that they are wildly different, I would be suspicious.
Just a thought
Casey
Are you sure the curve your looking at isn't powdered ferrite. Powdered ferrite is almost universally referred to as powdered iron in the literature. And why wouldn’t it be as ,with the rare exception, “iron powder” cores available today are in fact iron ferrite. Something to consider…cold rolled steel has very similar magnetic characteristics to cast iron (in a dc magnet circuit anyway), it would be a logical jump to assume Si-steel would be similar to Si-iron. If your data is showing you that they are wildly different, I would be suspicious.
Just a thought
Casey
jlsem said:
There was a guy from Italy who did air cored outputs where he was able to get 1hy of inductance from a large diameter form. I bet if he placed this form in a pan of the brake shavings that number might jump to 20 or even 50hy.
a first simple experiment would be to take say 100 turns of wire with say a 6 inch diameter and measure the inductance, then dunk it in a vat of shavings and see how it changes. then apply DC until you can get it to saturate. simply dividing the Air cored inductance by the iron cored inductance will tell you the "relative perm" which is the number we need anyways. then further design decisions could be made.
i'd try this with just the shavings at hand as a starting reference so some sort of standard exists, then you could see the progress of each step.
on a slightly different line of thought, does anybody know why the powdered cores saturate at such low flux densities???
dave
dave
All I can tell you is this: Mo-Permalloy has maximum permeabilities up to 400,000 in tapewound toroids. Sintered powder Mo-Permalloy cores for loading communications cables have a permeability of 125. Pure powdered iron (and I mean INCREDIBLY pure) formed in the manner similar to what Valveitude proposes has a mu of about 8. A pan full of cast iron filings probably has a mu of more than one.
What is the DC resistance of the one Henry air core inductor?
John
jlsem said:
Depends on how thick you build it. Using 12AWG wire in a size of oh, 8" o.d., maybe 2 or 3" thick winding (just SWAGging here on the value, might come close), it might have a resistance suitable for near an ampere. (Note that plain 12AWG is rated for 10 to 20 amps in any other situation.)
Tim
I'm flabbergasted at the lengths some will go to to build a ridiculously inefficient output transformer. Why don't you move in the other direction and design a parallel feed arrangement with a wideband choke of a constant permeability material like Isoperm and a Mumetal output transformer of sufficient size for AC power required for low, low distortion? Hell, I could spend the hours wasted on these proposals flipping burgers and come up with enough cash to do just that.
John
John
Allrighty then....I see the quality of input to this thread deteriorating again…sigh. Don’t get me wrong I appreciate constructive criticism, it forces me to re-analyze.
But this?…
Well lets see….tantalum capacitors are more efficient than oil capacitors, PP is more efficient than SE, class C is WAY more efficient than A etc.etc ad naseum . I hope you see my point. If “Efficient” was the bar, I’d get me one of them thar digital amps.
Now onto the debate…
I won’t get into which cast iron your considering it, there are several, each with there own properties. I’m working with “gray”.
Carbon Silicon Manganese Sulfur Phosphorous
Percent (%) 2.5-4.0 1.0-3.0 0.2-1.0 0.02-0.25 0.02-1.0
First lets look at the E-E-V-I-I-L-L-E carbon . It is not alloyed into the metal, it is dispersed throughout the metal as little carbon graphite pockets, separate and unto themselves. In fact you could say (accurately) its between 97.75% to 99.76% pure (depending on the percentage of the other trace elements) Si-Fe peppered with graphite. In steel, this isn’t the case, in cast iron it IS. So what does this carbon do? At first I thought that it simply took up space. I was wrong…
According to the abstract of a paper titled “Magnetomechanical effects in iron and iron-carbon alloys”
http://www.iop.org/EJ/abstract/0022-3727/4/7/322
“For annealed,low carbon content materials in a small magnetic field, the magnetization-stress curves are unsymmetrical with respect to tension and compression. In the applied fields and stresses used, the asymmetry becomes less pronounced both for increase in residual internal stress and for increase in carbon content until, for cold-worked, high carbon content materials, curves are obtained that are sensibly symmetrical”
Hmmm….
I may just do it…if nothing else it would put the “1000 times more turns” meme to bed. It will have to wait until the weekend at least…I need to finish my ball mill.
Casey
But this?…
Well lets see….tantalum capacitors are more efficient than oil capacitors, PP is more efficient than SE, class C is WAY more efficient than A etc.etc ad naseum . I hope you see my point. If “Efficient” was the bar, I’d get me one of them thar digital amps.
Now onto the debate…
I won’t get into which cast iron your considering it, there are several, each with there own properties. I’m working with “gray”.
Carbon Silicon Manganese Sulfur Phosphorous
Percent (%) 2.5-4.0 1.0-3.0 0.2-1.0 0.02-0.25 0.02-1.0
First lets look at the E-E-V-I-I-L-L-E carbon . It is not alloyed into the metal, it is dispersed throughout the metal as little carbon graphite pockets, separate and unto themselves. In fact you could say (accurately) its between 97.75% to 99.76% pure (depending on the percentage of the other trace elements) Si-Fe peppered with graphite. In steel, this isn’t the case, in cast iron it IS. So what does this carbon do? At first I thought that it simply took up space. I was wrong…
According to the abstract of a paper titled “Magnetomechanical effects in iron and iron-carbon alloys”
http://www.iop.org/EJ/abstract/0022-3727/4/7/322
“For annealed,low carbon content materials in a small magnetic field, the magnetization-stress curves are unsymmetrical with respect to tension and compression. In the applied fields and stresses used, the asymmetry becomes less pronounced both for increase in residual internal stress and for increase in carbon content until, for cold-worked, high carbon content materials, curves are obtained that are sensibly symmetrical”
Hmmm….
I may just do it…if nothing else it would put the “1000 times more turns” meme to bed. It will have to wait until the weekend at least…I need to finish my ball mill.
Casey
Sorry, I was mostly referring to the Italian guy with the air core OPT. I had seen it on the web some time ago and was not impressed. I haven't run across anyone else who has repeated the experiment.
You will notice, however, that I was able to come up with a source that has some information on powdered iron cores pressed together with a plastic binder. They have a mu of 8.
John
John,
You have either found a really bad audio core, or a really good if/rf core.
I suspect the later.
Coincidentally enough, the chart on this page...
http://www.ee.surrey.ac.uk/Workshop/advice/coils/mu/#mui
...shows a materiel called “Ferrite U 60” that has a relative permeability of 8 ,as well as the fact the 99.8% pure iron powder has a relative permeability of 5000. I believe the silicon should effect the iron in “gray iron” in a similar fashion to the iron in steel, ie., raising permeability and saturation limits. My minimum target of an effective permeability of 200 , after air-gap losses, seems reasonable. Naturally more would be nice, but 200 is very do-able.
Now, if I end up with a tranny that’s twice the size but of equivalent performance of a laminated one, I would still be ahead in the diy game. But I feel the potential is greater than that, or I wouldn’t be doing it.
Casey
You have either found a really bad audio core, or a really good if/rf core.
I suspect the later.
Coincidentally enough, the chart on this page...
http://www.ee.surrey.ac.uk/Workshop/advice/coils/mu/#mui
...shows a materiel called “Ferrite U 60” that has a relative permeability of 8 ,as well as the fact the 99.8% pure iron powder has a relative permeability of 5000. I believe the silicon should effect the iron in “gray iron” in a similar fashion to the iron in steel, ie., raising permeability and saturation limits. My minimum target of an effective permeability of 200 , after air-gap losses, seems reasonable. Naturally more would be nice, but 200 is very do-able.
Now, if I end up with a tranny that’s twice the size but of equivalent performance of a laminated one, I would still be ahead in the diy game. But I feel the potential is greater than that, or I wouldn’t be doing it.
Casey
Valveitude,
This is amazing. Continue the excellent work. This is beyond DIY into the realm of the garage/backyard/attic experimentor. A great deal of our modern day knowledge has been gained through people such as yourself. Also take note that most have had a sizeable group of naysayers. This doesn't mean your idea will work, but it certainly shows that just because conventional wisdom says it isn't possible doesn't mean it's right.
I will continue to watch this thread and anticipate your results with great enthusiasm.
This is amazing. Continue the excellent work. This is beyond DIY into the realm of the garage/backyard/attic experimentor. A great deal of our modern day knowledge has been gained through people such as yourself. Also take note that most have had a sizeable group of naysayers. This doesn't mean your idea will work, but it certainly shows that just because conventional wisdom says it isn't possible doesn't mean it's right.
I will continue to watch this thread and anticipate your results with great enthusiasm.
Well I see this thread has been brought back from the dead 
I'm afraid I have given up for now. I still am not convinced I couldn't reach a mu in the low hundreds, but my best efforts before shelving it was no where near that.
It was filthy hard work getting as far as I did, and I decided my hobby time was supposed to have some joy in it. Currently I have been working on a Teres-like (with possible improvements )turntable. If interested you can see it here...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=67089
Thankx to eveyone in this thread for participating.
Casey
I'm afraid I have given up for now. I still am not convinced I couldn't reach a mu in the low hundreds, but my best efforts before shelving it was no where near that.
It was filthy hard work getting as far as I did, and I decided my hobby time was supposed to have some joy in it. Currently I have been working on a Teres-like (with possible improvements )turntable. If interested you can see it here...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=67089
Thankx to eveyone in this thread for participating.
Casey
Hey, I want to make my own OPT's, and I am reinventing the wheel.
I want trifiliar primarys (for 3 parallel output tubes), a dc bias coil to offset the se bias, and multiple taps for output impeadance.
But what I seek is a source of EI laminates without resorting to buying microwaves from Wallmart for disection.
I can put together a gearhead motor with a rev counter and a former and I can find the formulas to get me in the ballpark, If I can source the laminations.
I want trifiliar primarys (for 3 parallel output tubes), a dc bias coil to offset the se bias, and multiple taps for output impeadance.
But what I seek is a source of EI laminates without resorting to buying microwaves from Wallmart for disection.
I can put together a gearhead motor with a rev counter and a former and I can find the formulas to get me in the ballpark, If I can source the laminations.
trifiliar primarys / EI laminates
Hi
The only EI laminates i could buy where from a Danish import company, and they would only deliver when buying between 800 - 1100kg of ion
So my OPT is made of scrap.. Remember that you will need some space for trifilar primarys. Mine is bifilar primarys for SE parallel Tubes , and the cores is stuffed!
Best regards Kim Olesen
www.micro-io.dk
Hi
The only EI laminates i could buy where from a Danish import company, and they would only deliver when buying between 800 - 1100kg of ion
So my OPT is made of scrap.. Remember that you will need some space for trifilar primarys. Mine is bifilar primarys for SE parallel Tubes , and the cores is stuffed!Best regards Kim Olesen
www.micro-io.dk
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