There's a few possiblities to choose the right output transformer when you want to make a good sounding amp.
I find the ideea based on some "old fashion" or "old school" manufactures and said the amorphous and permalloy core isn't that good in sonic terms.Same story with the silver windings on the transformer. Also they look impressive on paper but sonicaly don't have a very good mark.
That thing reminds me about the tone test-mark- of different speakers.Ex:
-look very good on paper but sound flat,without soul,cold,direct (check SEAS) and other (check Altec) with a very good tonal balance and amaizing resolution-details....personally speaking.
What is your subjective oppinion about these "new" output cores?
I find the ideea based on some "old fashion" or "old school" manufactures and said the amorphous and permalloy core isn't that good in sonic terms.Same story with the silver windings on the transformer. Also they look impressive on paper but sonicaly don't have a very good mark.
That thing reminds me about the tone test-mark- of different speakers.Ex:
-look very good on paper but sound flat,without soul,cold,direct (check SEAS) and other (check Altec) with a very good tonal balance and amaizing resolution-details....personally speaking.
What is your subjective oppinion about these "new" output cores?
I haven't listened to any of these exotic material output xfmrs. But a few technical issues that would raise some questions do arise:
The permalloy cores solve an important factor of increased permeability, but sacrifice max. flux level. This would mean less power or bass from a comparable size core versus M6 material (but greatly reduced hysteresis distortion). Increasing the core size to compensate power-wise will increase cost substantially. The increased permeability also leads to DC stauration problems like encountered in toroids, so DC servo's would be a big help. (putting in an air gap cancels out the permeability advantage)
The striped permalloy/M6 core idea appears interesting, raising the permeability for small signal fidelity. But it has an issue of sudden drop off in permeability at some flux level when the permalloy saturates and the M6 takes over. This would be akin to a class AB output stage when one tube cuts off (losing transconducance). So you get class AB like effects even with a class A output stage here. This should be fixable with a low output Z tube stage (see below, but note that the same fix works for M6 alone). DC servo-ing to avoid saturation at idle would be important here too.
The amorphous alloy and micro-crystalline materials cover a large range of characteristics and depend on final heat/magnetic treatments as well. But the most affordable (and most likely used) ones are the type used for utility power transformers to reduce hysteresis losses. Since losses in output transformers aren't really an issue, the main advantage here would be reduced hysteresis distortion. Hysteresis distortion in M6 can be dealt with very successfully by just using a low output Z tube stage (plate feedback schemes or partial CFB or even UL to some extent), so this issue can be overcome by design at lower cost.
So I don't see any compelling reason to pay for exotic materials.
The Berning type (and related switching type) switched ferrite or switched capacitor OTs also can reduce hysteresis effects nicely, but at considerable complexity and risk of HF noise. It has a very steep technical learning curve to successfully apply however, but once overcome, enables easier, low-turn, OT winding and reduced cost (if self implemented with that in mind). For the DIYer making his/her own OTs, these are nice advantages.
Don
The permalloy cores solve an important factor of increased permeability, but sacrifice max. flux level. This would mean less power or bass from a comparable size core versus M6 material (but greatly reduced hysteresis distortion). Increasing the core size to compensate power-wise will increase cost substantially. The increased permeability also leads to DC stauration problems like encountered in toroids, so DC servo's would be a big help. (putting in an air gap cancels out the permeability advantage)
The striped permalloy/M6 core idea appears interesting, raising the permeability for small signal fidelity. But it has an issue of sudden drop off in permeability at some flux level when the permalloy saturates and the M6 takes over. This would be akin to a class AB output stage when one tube cuts off (losing transconducance). So you get class AB like effects even with a class A output stage here. This should be fixable with a low output Z tube stage (see below, but note that the same fix works for M6 alone). DC servo-ing to avoid saturation at idle would be important here too.
The amorphous alloy and micro-crystalline materials cover a large range of characteristics and depend on final heat/magnetic treatments as well. But the most affordable (and most likely used) ones are the type used for utility power transformers to reduce hysteresis losses. Since losses in output transformers aren't really an issue, the main advantage here would be reduced hysteresis distortion. Hysteresis distortion in M6 can be dealt with very successfully by just using a low output Z tube stage (plate feedback schemes or partial CFB or even UL to some extent), so this issue can be overcome by design at lower cost.
So I don't see any compelling reason to pay for exotic materials.
The Berning type (and related switching type) switched ferrite or switched capacitor OTs also can reduce hysteresis effects nicely, but at considerable complexity and risk of HF noise. It has a very steep technical learning curve to successfully apply however, but once overcome, enables easier, low-turn, OT winding and reduced cost (if self implemented with that in mind). For the DIYer making his/her own OTs, these are nice advantages.
Don
I read a discussion based on Hashimoto transformers (japanese forum) some time ago,but I can't remember where.
This mean you are be able to share some of your thoughts (based on your subjective perception) in this issue?THX.
#smoking-amp
Well explained.
After PP,consider to build a SE class A -no feedback based on this schematics.
And...how to do that?
MSL: "The nickel cannot saturate if you design the transformer to operate within the flux capacity of the nickel material by itself. "
Well, yes, but the high permeability of the permalloy will cause most of the flux to build up in the permalloy first, rather than the M6. Could just as well put plastic in instead of the M6. Waisting space in the core (unless the permalloy has special air gapping to equalize its effective permeability with the M6).
Don
Well, yes, but the high permeability of the permalloy will cause most of the flux to build up in the permalloy first, rather than the M6. Could just as well put plastic in instead of the M6. Waisting space in the core (unless the permalloy has special air gapping to equalize its effective permeability with the M6).
Don
smoking-amp said:
If you have a EI-100 by 1" stack---- the flux density at any given drive level and frequency will be uniform if the number of primary turns is kept constant (this to a first approx--- i.e., ingoring for example the magnetic skin effect)----
your imagining that there are two separate cores at work--- but this is not the case. There is only one core--- and the flux density of that core structure will be the same whether we use nickel, M6, or bumper steel or any combination of these three materials. In-other-words the magnitude of the flux density is independent
of the materials which make up that core.
what we have to be careful about is to make sure that the core does not operate at a flux density greater than the material which has the least amount of flux density capacity--- if we do that the core cannot saturate. I.E., different grades of core materials have different maximum flux densities that they can support. Some will saturate easier than others. So we design around the core material which is most easily saturated and make sure that the flux density is less than than maximum that can be supported by that material.
What will vary is the permeability--- the nickel for instance will have greater permeability than the M6. So that given at any given drive level across the coil's primary--- the perm of the nickel will be greater than the perm of the M6. But at any given drive level ALL of the core will be "energized" (i.e., will have the same flux density).
"Pinstriping" cores in audio transformers has been done for more than five decades. The earliest examples that I have seen were made by Peerless. Even some of their small signal input transformers used a combination of both high and low nickel at the same time.
what the pinstriping does for you--- is that at very low drive levels---
especially in the case of M6 (which has a reverse knee in it's bh loop)--- is that at very low flux density levels--- the nickel exhibits greater permeability---- so that it "jump starts" easier than M6.
So that given that nickel has greater perm--- think of perm as an
"inductance multiplier"---- air has a multiplication effect of 1--- magnetic core materials might have a perm of say 5,000 to 50,000 or even higher---- meaning that you will get (as a first approximation) 5,000 to 50,000 (or even more) times the inductance (given a specific set of operating conditions) than if you had no magnetic core at all.
And that is why you might use a few slivers of high perm core materials--- to simply enhance the perm at very low drive levels--- so that the inductive reactance produced by the larger amount of effective L is greater than it would be if you did not use the high perm material as an enhancement.
MSL
Don wrote:
::::The permalloy cores solve an important factor of increased permeability, but sacrifice max. flux level.:::
True.
:::This would mean less power or bass from a comparable size core versus M6 material.... :::
Only partially true. Your mixing two different factors and treating them the same.
For a given size core with a fixed number of turns and at a specific frequency---- M6 can handle a greater amount of voltage across it's primary and stay below it's saturation point--- so from this perspective, yes, M6 can handle greater power than the nickels.
But--- bass response depends also on the amount of inductive reactance that you have--- when you say "less bass" I presume you mean less bass extension as in low frequency response.
For a given level of bass response at a specific power level--- what we need is a core that has enough flux capacity to handle the power at the lowest frequency of interest AND we also need that coil\core combination to be able to develop enough inductance to support that lowest frequency of interest.
But these are two different considerations or factors---- it's possible that we could have enough flux capacity to support X amount of power at frequency Y without saturating the core--- but yet still be lacking the necessary amount of inductance to support that same lowest frequency of interest.
The same core and coil combination made with say all nickel lams--- and operated within it's permissible flux capacity---- i.e., at power levels which will not saturate the nickel---- may very likely still produce a much greater amount of inductance--- which (within it's power range) would permit or extend the low frequency response (i.e., what you call the bass response) much lower than the same core and coil combination built with M6.
Any given low frequency power response capability depends on both flux density (i.e., keeping the core from saturating) as well as the properties of the core\coil combination that results in the production of inductance. You need a sufficient amount of inductance AND you need to keep the core from saturating to deliver a given amount of power at some stated low frequency of interest.
But simply having enough flux capacity--- is not in-and-of-itself sufficient to produce a specific low frequency extension.
::::Increasing the core size to compensate power-wise will increase cost substantially.::::
yes... from a power only point of view--- a nickel core will require a greater core area and\or a greater number of primary turns or some combination of these two---- this is due to the fact that you cannot run nickel nearly as high flux density wise as you can M6.
::::The increased permeability also leads to DC stauration problems like encountered in toroids, so DC servo's would be a big help.::::
this is perhaps awkwardly stated. It is not the perm which limits or provokes dc saturation----
Saturation is produced by demanding of the core more flux capacity than it has.
Since nickel has a smaller magnitude of permissable flux density--- then obviously it can saturate easier than M6.
when a core material saturates--- by definition---- a wholly saturated core would have a permeability of zero.
But the zero permeablity is the effect not the cause. It is not because the material has a high perm that it might be more easily saturable---
for a good example of this--- cobalt has significantly higher permeability than M6 and also has greater flux capacity.
:::
putting in an air gap cancels out the permeability advantage)::::
I want to agree with you on this point---- perhaps "cancels out" if meant entirely is worded too strongly---- but if your point is that an airgap rapidly diminishes the effective permeability of the coil\core combination--- your on pretty safe grounds in making this moreso qualified statement.
MSL
::::The permalloy cores solve an important factor of increased permeability, but sacrifice max. flux level.:::
True.
:::This would mean less power or bass from a comparable size core versus M6 material.... :::
Only partially true. Your mixing two different factors and treating them the same.
For a given size core with a fixed number of turns and at a specific frequency---- M6 can handle a greater amount of voltage across it's primary and stay below it's saturation point--- so from this perspective, yes, M6 can handle greater power than the nickels.
But--- bass response depends also on the amount of inductive reactance that you have--- when you say "less bass" I presume you mean less bass extension as in low frequency response.
For a given level of bass response at a specific power level--- what we need is a core that has enough flux capacity to handle the power at the lowest frequency of interest AND we also need that coil\core combination to be able to develop enough inductance to support that lowest frequency of interest.
But these are two different considerations or factors---- it's possible that we could have enough flux capacity to support X amount of power at frequency Y without saturating the core--- but yet still be lacking the necessary amount of inductance to support that same lowest frequency of interest.
The same core and coil combination made with say all nickel lams--- and operated within it's permissible flux capacity---- i.e., at power levels which will not saturate the nickel---- may very likely still produce a much greater amount of inductance--- which (within it's power range) would permit or extend the low frequency response (i.e., what you call the bass response) much lower than the same core and coil combination built with M6.
Any given low frequency power response capability depends on both flux density (i.e., keeping the core from saturating) as well as the properties of the core\coil combination that results in the production of inductance. You need a sufficient amount of inductance AND you need to keep the core from saturating to deliver a given amount of power at some stated low frequency of interest.
But simply having enough flux capacity--- is not in-and-of-itself sufficient to produce a specific low frequency extension.
::::Increasing the core size to compensate power-wise will increase cost substantially.::::
yes... from a power only point of view--- a nickel core will require a greater core area and\or a greater number of primary turns or some combination of these two---- this is due to the fact that you cannot run nickel nearly as high flux density wise as you can M6.
::::The increased permeability also leads to DC stauration problems like encountered in toroids, so DC servo's would be a big help.::::
this is perhaps awkwardly stated. It is not the perm which limits or provokes dc saturation----
Saturation is produced by demanding of the core more flux capacity than it has.
Since nickel has a smaller magnitude of permissable flux density--- then obviously it can saturate easier than M6.
when a core material saturates--- by definition---- a wholly saturated core would have a permeability of zero.
But the zero permeablity is the effect not the cause. It is not because the material has a high perm that it might be more easily saturable---
for a good example of this--- cobalt has significantly higher permeability than M6 and also has greater flux capacity.
:::
putting in an air gap cancels out the permeability advantage)::::I want to agree with you on this point---- perhaps "cancels out" if meant entirely is worded too strongly---- but if your point is that an airgap rapidly diminishes the effective permeability of the coil\core combination--- your on pretty safe grounds in making this moreso qualified statement.
MSL
If I recall correctly, Permalloy has been around longer than grain oriented silicon steel. As far as amorphous cores go, there are many different alloys available with at least three heat treating methods each but so far it is unclear who is using what in which transformers. Does anyone know, for example, what kind of cores are being used by Tamura, Lundahl, or Intact Audio?
John
MSL: "There is only one core--- and the flux density of that core structure will be the same whether we use nickel, M6, or bumper steel or any combination of these three materials. In-other-words the magnitude of the flux density is independent
of the materials which make up that core. "
The total core flux IS proportional to the voltage drive level, but not the flux distribution in the material. For that, one has to consider the ampere turns around the materials. At any given moment, some level of current will be in the windings, and the amount of flux thru each material type will be proportional to the lamination permeability times the current (divided by path lengths, which I will assume are equal for same size laminations).
[this is a very standard, elementary magnetics calculation]
This means that 100X higher permiability material will develop 99% of the flux, up until it saturates, then the lower perm. material will pick up the flux increase required for the voltage increase.
This, in turn, means that driving a mixed/pinstriped core only up to the permalloy sat. level will have only about a few% of the flux developed in the M6 before the permalloy saturates. (hence my comment about just putting plastic in for the M6)
This discontinuity does not put a kink in the voltage transfer curve if driven from a hard voltage source (since that can handle the suddenly increased magnetizing current at sat. crossover seamlessly). But if driven from a resistive source, a voltage drop will develop (in the source itself) in the transfer as the discontinuity is crossed, due to the increased magnetizing current thru the source resistance.
Because of this phenomena, only using the core up to the permalloy sat. level would be silly and waistful. Using the core fully up to the M6 sat. level will work fine if driven from a low Z source, but so will just plain vanilla M6 alone with low Z drive. The pinstiping idea is another example of a marketing driven poor design. (UL transformer taps at B+ DC are another.)
Don
of the materials which make up that core. "
The total core flux IS proportional to the voltage drive level, but not the flux distribution in the material. For that, one has to consider the ampere turns around the materials. At any given moment, some level of current will be in the windings, and the amount of flux thru each material type will be proportional to the lamination permeability times the current (divided by path lengths, which I will assume are equal for same size laminations).
[this is a very standard, elementary magnetics calculation]
This means that 100X higher permiability material will develop 99% of the flux, up until it saturates, then the lower perm. material will pick up the flux increase required for the voltage increase.
This, in turn, means that driving a mixed/pinstriped core only up to the permalloy sat. level will have only about a few% of the flux developed in the M6 before the permalloy saturates. (hence my comment about just putting plastic in for the M6)
This discontinuity does not put a kink in the voltage transfer curve if driven from a hard voltage source (since that can handle the suddenly increased magnetizing current at sat. crossover seamlessly). But if driven from a resistive source, a voltage drop will develop (in the source itself) in the transfer as the discontinuity is crossed, due to the increased magnetizing current thru the source resistance.
Because of this phenomena, only using the core up to the permalloy sat. level would be silly and waistful. Using the core fully up to the M6 sat. level will work fine if driven from a low Z source, but so will just plain vanilla M6 alone with low Z drive. The pinstiping idea is another example of a marketing driven poor design. (UL transformer taps at B+ DC are another.)
Don
Oh, I don't think so. The Permalloy has a much lower excitation current figure than the M6, which means that for low signal levels it will have some incremental permeability while the M6 is essentially dormant. This only applies to cores with no DC bias such as in a parallel-feed amp or a well-balanced push-pull amp. There are enough laminations present in such a core that it will operate within the linear region of the magnetization curve at low signal levels. I don't know if Peerless ever advertised the Permalloy lamination aspect of their 20-20 Plus series.
John
I agree that the permalloy increases the permeability at low excitation, which is helpful for small signal levels where M6 has poor permeability. An all permalloy xfmr is nicer yet.
The issue I brought up however has to do with somewhat higher signal levels in a pinstriped xfmr, when the permalloy saturates and the M6 takes over. There is a discontinuity in the magnetization current (due to sudden drop of permeability), that is analogous to class AB operation when one tube turns off (sudden drop of gm). This is quite easy to demonstrate too. Just put 5X the plate resistance in series with the tube plates and watch the kink develop on the scope at some intermediate signal level. Or use a spectrum analyzer, much more sensitive.
The cure of course is to use a low output Z stage to drive the xfmr. My 2nd point was that the cure fixes the original problem too. The pinstriping just makes the xfmr more expensive. I would call that a poor engineering solution by most standards. 50 years does not made snake oil more respectable.
Don
The issue I brought up however has to do with somewhat higher signal levels in a pinstriped xfmr, when the permalloy saturates and the M6 takes over. There is a discontinuity in the magnetization current (due to sudden drop of permeability), that is analogous to class AB operation when one tube turns off (sudden drop of gm). This is quite easy to demonstrate too. Just put 5X the plate resistance in series with the tube plates and watch the kink develop on the scope at some intermediate signal level. Or use a spectrum analyzer, much more sensitive.
The cure of course is to use a low output Z stage to drive the xfmr. My 2nd point was that the cure fixes the original problem too. The pinstriping just makes the xfmr more expensive. I would call that a poor engineering solution by most standards. 50 years does not made snake oil more respectable.
Don
I should mention some ameliorating factors for pinstriping to be fair. (ie, its not as bad as it looks)
If the cross sectional core areas of the M6 to permalloy are in the ratio of Mu_perm to Mu_m6, then the effective dropoff of perm. for the full "effective" core can be made to be only 50% (when the permalloy saturates) rather than the alarming 50 to 1 that their Mu ratio alone might lead one to suspect. In other words, one can compensate for the Mu differential by an opposing area ratio. But, again, a 50% drop in "effective" Mu is still of the same order as the 50% drop of Gm for class AB cutoff.
An alternative fix would be to include a small air gap in the permalloy lams so that their reduced effective Mu_perm would then bring them to saturation at the same winding current as the M6 lams. So saturation crossover would be completely avoided. This would have the effect of giving the full core, peak-M6-like Mu throughout the full signal range. But then, that's getting more expensive yet. Some magnetic saparators between the permalloy and M6 would be required also to avoid bypassing the air gap thru the adjacent M6.
Don
If the cross sectional core areas of the M6 to permalloy are in the ratio of Mu_perm to Mu_m6, then the effective dropoff of perm. for the full "effective" core can be made to be only 50% (when the permalloy saturates) rather than the alarming 50 to 1 that their Mu ratio alone might lead one to suspect. In other words, one can compensate for the Mu differential by an opposing area ratio. But, again, a 50% drop in "effective" Mu is still of the same order as the 50% drop of Gm for class AB cutoff.
An alternative fix would be to include a small air gap in the permalloy lams so that their reduced effective Mu_perm would then bring them to saturation at the same winding current as the M6 lams. So saturation crossover would be completely avoided. This would have the effect of giving the full core, peak-M6-like Mu throughout the full signal range. But then, that's getting more expensive yet. Some magnetic saparators between the permalloy and M6 would be required also to avoid bypassing the air gap thru the adjacent M6.
Don
smoking-amp said:
hey-Hey!!!,
I don't think there is a gap term in the AC flux equ'n. Certainly for the DC.
cheers,
Douglas
I am preparing some low level TX testing, and I have in line a design to look at. One version the original vintage, another pinstriped M6 and another new one made with M3...it will indeed be interesting to compare them...
jlsem:
"Correct me if I'm wrong, but where Permalloy begins to saturate and the permeability starts to drop off, the incremental permeability value for M6 is close to that of Permalloy at the midrange signal level in question. "
I won't have access to my magnetics literature for the next month, so I can't check the curves now. But it seems unlikely that a 100 to 1 differential in initial perm. can smoothly blend down to M6 peak. I vaguely recall something like 10,000 perm for M6 peak (will depend on manu. source of matl too). Permalloy can start out at as high as 300,000. Supermalloy can start up in the millions I think. But need to check some real manufacturer's data.
A magnetization current versus applied voltage level test performed on a real pin striped xfmr would give the most definitive results. I don't have one available to test currently.
Magnetic saturation tends to set in fairly abruptly. Tubes in class AB at least have the advantage that gm drops off fairly smoothly with current drop off, which to a 1st approx. is linear ramp (that is, the current drop off).
Bandersnatch:
"I don't think there is a gap term in the AC flux equ'n. Certainly for the DC."
AC and DC should both see an air gap as far as permeability goes.
1/perm. times path length is like magnetic resistance. So you can sum the effective magn. resistances, then divide by total path length and then invert the result to get effective perm. for the total path.
An M6 lam adjacent to an air gapped lam will largely short out the air gap.
The only other design where two very different magnetic materials are used in one core that I am aware off are some HF switchmode toroid cores using ferrite and powdered iron, and the resultant effect is very non-linear. (used as protection for the switches if the ferrite saturates, usually for forward converters where unwanted DC flux can build up)
Don
"Correct me if I'm wrong, but where Permalloy begins to saturate and the permeability starts to drop off, the incremental permeability value for M6 is close to that of Permalloy at the midrange signal level in question. "
I won't have access to my magnetics literature for the next month, so I can't check the curves now. But it seems unlikely that a 100 to 1 differential in initial perm. can smoothly blend down to M6 peak. I vaguely recall something like 10,000 perm for M6 peak (will depend on manu. source of matl too). Permalloy can start out at as high as 300,000. Supermalloy can start up in the millions I think. But need to check some real manufacturer's data.
A magnetization current versus applied voltage level test performed on a real pin striped xfmr would give the most definitive results. I don't have one available to test currently.
Magnetic saturation tends to set in fairly abruptly. Tubes in class AB at least have the advantage that gm drops off fairly smoothly with current drop off, which to a 1st approx. is linear ramp (that is, the current drop off).
Bandersnatch:
"I don't think there is a gap term in the AC flux equ'n. Certainly for the DC."
AC and DC should both see an air gap as far as permeability goes.
1/perm. times path length is like magnetic resistance. So you can sum the effective magn. resistances, then divide by total path length and then invert the result to get effective perm. for the total path.
An M6 lam adjacent to an air gapped lam will largely short out the air gap.
The only other design where two very different magnetic materials are used in one core that I am aware off are some HF switchmode toroid cores using ferrite and powdered iron, and the resultant effect is very non-linear. (used as protection for the switches if the ferrite saturates, usually for forward converters where unwanted DC flux can build up)
Don
A bit more info:
The M6 material develops its maximum perm. in a broad rounded hump around 40 or 50% Bmax. for E lams. A toroid M6 should peak a little sooner (lower B) and sharper I think (also somewhat higher initial and peak perm.) Again, need to check real data for sure.
Since permalloy has about half the Bmax, one might expect it to saturate out near the M6 peak, but this unfortunately won't be the case. Due to the vastly higher initial perm. of the permalloy, it builds up flux much faster than the M6, and so will saturate out down in the low initial perm. area of the M6 (at only a few % of the M6 Bmax). So this crossover is going to be large, abrubt and still at relatively small signal level. Which is not too good.
I don't mean to be sounding like I'm trashing pinstriping, I wish it would work well, but I don't see the physics as supporting that. Exotic measures can maybe fix this, but will be expensive. Probably just going to all permalloy will be the most "economical" (like $1000 premium gasoline).
Don
The M6 material develops its maximum perm. in a broad rounded hump around 40 or 50% Bmax. for E lams. A toroid M6 should peak a little sooner (lower B) and sharper I think (also somewhat higher initial and peak perm.) Again, need to check real data for sure.
Since permalloy has about half the Bmax, one might expect it to saturate out near the M6 peak, but this unfortunately won't be the case. Due to the vastly higher initial perm. of the permalloy, it builds up flux much faster than the M6, and so will saturate out down in the low initial perm. area of the M6 (at only a few % of the M6 Bmax). So this crossover is going to be large, abrubt and still at relatively small signal level. Which is not too good.
I don't mean to be sounding like I'm trashing pinstriping, I wish it would work well, but I don't see the physics as supporting that. Exotic measures can maybe fix this, but will be expensive. Probably just going to all permalloy will be the most "economical" (like $1000 premium gasoline).
Don
Hey don,
It is also interesting to note that alternately stacked EI laminations in groups (ie 4X4) will show this same behavior even if the same material is used.
It makes perfect sense when you consider that alternate stacking essentially creates a core structure with two different gap sizes.
dave
It is also interesting to note that alternately stacked EI laminations in groups (ie 4X4) will show this same behavior even if the same material is used.
It makes perfect sense when you consider that alternate stacking essentially creates a core structure with two different gap sizes.
dave
I only have limited resources at hand, so these permeability figures are along the DC magnetization curve. Permalloy begins to saturate at an induction level of 6000-8000 Gausses. At 6000G its DC permeability is about 50,000 where it begins to drop off rapidly to about 600 at 8000G. At 6000G, M-6 has a DC permeability of about 42,000 and by 8000G its permeability has risen to about 46,000 which is very close to maximum. AC magnetization curves tend to parallel DC curves fairly closely.
John
John
John,
Thanks for the info on the materials. Do you have any info on M6 and permalloy permeability at around 500 to 1000 Gauss? The sat. crossover between the materials will not occur at the same flux density in each one, due to the large initial permeability of permalloy versus M6. For the same current, the permalloy will have much higher flux density than the M6 at low currents. So one would really need an iterative solution to find the crossover point. But I would guess the M6 will be below 500 G when the permalloy begins to saturate. Can only check backwards then from an assumed solution to see if it is indeed consistent with the perms. there. (ie, from permalloy sat. B find ampere turns, from ampere turns find M6 permeability)
From the data you have given though, it is apparent that 300,000 perm has had to drop to 40,000 or so. An earlier ampere turn crossover makes for an even bigger drop (at lower M6 perm.), then a pickup again as the M6 peak is reached. (a saddle shaped curve)
Don
Thanks for the info on the materials. Do you have any info on M6 and permalloy permeability at around 500 to 1000 Gauss? The sat. crossover between the materials will not occur at the same flux density in each one, due to the large initial permeability of permalloy versus M6. For the same current, the permalloy will have much higher flux density than the M6 at low currents. So one would really need an iterative solution to find the crossover point. But I would guess the M6 will be below 500 G when the permalloy begins to saturate. Can only check backwards then from an assumed solution to see if it is indeed consistent with the perms. there. (ie, from permalloy sat. B find ampere turns, from ampere turns find M6 permeability)
From the data you have given though, it is apparent that 300,000 perm has had to drop to 40,000 or so. An earlier ampere turn crossover makes for an even bigger drop (at lower M6 perm.), then a pickup again as the M6 peak is reached. (a saddle shaped curve)
Don
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