Ni core vs. M6 core

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edcorusa

Active member
Joined
Jan 18, 2006
Messages
39
Location
Carlsbad, NM USA
I have had many comments and questions lately about Nickel core transformers and here are some of the FAQ?s and our comments. EDCOR has been reluctant to stock and use
Ni core material because the cost factor. Ni (80%) costs about 10 times the cost of M6 steel. This equates in the cost of a transformer about 4 times using Ni vs M6.

Now lets? discuss the goods the bad and the fun. Other than the cost what are the real differences. The Ni core has a much higher ac (incremental) permeability. So what! is the effect? The inductance is higher by the permeability factor related to M6. It is the inverse root of the permeability of Ni to M6. Now try to find out what the ac permeability is of either Ni or M6. Tests to us indicate number of about 36 to 50 and the square root is somewhere between 6 and 7. So, the inductance will be 6-7 times more if you use an 80% Ni core instead of M6. The turns equal, of course. Therefore the turns needed to achieve a defined inductance can be 6-7 times less. This is all super secret stuff so don?t mention it to anyone and if you do please don?t mention the source.

Lets? add another factor. Ni and M6 have real different saturation and distortion characteristics. Forgive me, but M6 saturates at about 17,000 gauss and Ni about 5,000 gauss. The 1% distortion levels are at about 14,000 gauss and 4,000 gauss. Now what do you suppose one of the key ingredients is in the determination of primary turns? Walla,
it is the flux density and so as the flux goes down the turns must go up in a direct proportion. The saturation curves look really different on the scope and I am sure they sound really different, like sharp to smooth. Walla, again.

So, where do we go from here? The Ni material is far too expensive for a tube output transformer and the AC input voltage is controlled inversely by the flux density, so M6 is the only acceptable material for a modern day output transformer. Today we cannot purchase Ni material larger than EI75 without committing to large quantity. If we commit to a THD level of 1% the Ni transformer would be 3 times the size of a M6 core and only 12 times the cost, so lets? be practical. Pleeze.

I have tested gapped core (single ended) transformers. The Ni and M6 cores have the same characteristics when gapping the core. Major losses in core efficiency result. That causes a single ended transformer to be about twice the size as a PP. Right! So forget Ni in a SET unless it is low power, low DC current and low input AC voltage.

Where does the Ni core have value? Low input voltage, low power, high inductance, low frequency and they really looks good and sounds good.

EDCOR Electronics now has Ni cores for XSM, WSM and some low power or low voltage transformers, too.

If you have any other information to add please do so. I am always interested in information.
 
Thanks for the essay, and thanks for stocking Ni lams!

Interesting to see that people are asking for Ni output transformers :shock:! I'm sure my WSM600/600s and 2503s would laugh if they could...

On the other hand, if you come up with a nice little nickel core, 1:10 or so, mic-to-grid guy, that would kick ass! :thumb:

Peace,
Al.
 
> Frequency response of Ni lams vs M6?

Lams don't have frequency response; windings do.

Do the thinking. At low-level, Ni needs fewer turns for the same bass inductance, so less leakage inductance and maybe lower capacitance. But at high levels, you need more Ni than M6 to carry a given power, so the situation is inverted, and M6 is "better" even if both metals were the same price.

Every dang thing in a transformer interacts with every other dang thing. There is no silver bullet for a better transformer. Even if cost were no object. Good transformers are made of piles of pencils and stacks of scratch-paper.

> The Ni and M6 cores have the same characteristics when gapping the core.

Thanks for mentioning the "obvious". If you have enough gap to do any good, the iron does not matter. Low perm, high perm, bent perm: the gap has to be big enough to swamp all that iron-stuff. It is all about the air; the iron just holds the copper and couples it to the air-gap. The "best" iron for a gapped core is thin and cheap. Thin because eddy currents are still lossy, and cheap because size is worth much more than magic-metal.

OTOH:

Ni material is far too expensive for a tube output transformer ... 12 times the cost, so lets? be practical. Pleeze.

But modern hi-fi high-end systems are NOT practical. It isn't about the sound, it is about how much you spent. These people need help spending excess wealth. 12 times the cost is not enough, add some gold-flash bellcaps and lots of mark-up.
 
> a nice little nickel core, 1:10 or so, mic-to-grid guy

You can't spec a tranny just by ratio. You need a nominal impedance AND frequency and power level.

I'm sure you are wishing for a 150 or 200 ohm primary. That side is really easy.

But the secondary then comes to about 200H inductance with 200mH and 400pFd maximum parasitics for a hardly-tolerable 20KHz response. We'd actually want much less than 200mH and 400pFd total, counting the hundred or so pFd in a triode's grid.

The capacitance spec leads to a physically very small winding. It helps the pFd to pad-out the winding, not use the whole window, but that hurts the 400H and may increase leakage inductance.

OTOH, a small winding with high inductance means a lot of turns in a small space, which means hyper-fine wire, which takes longer to wind. Longer because of the many turns, and longer still because if you rush, it breaks. Time is money and you pay the piper.

I believe such windings work best on Permalloy-class cores. The very high permeability allows fewer turns of less-skinny wire while allowing overall size to be smallish. The downside of Permalloy is that it saturates if you look at it too hard. But in those situations where a 1:10 is really needed, input levels will be very small. Here the core size is controlled by winding convenience/costs, not power level.

But amplification is cheap. Much cheaper than ever before. The good old tubes have doubled in price while everything else is 5 or 10 times the price it was 40 years ago. We ran input tubes at low current because power filter caps cost money; today big caps are cheap.

Wish for 1:7 or even 1:5. Raise input triode current from ~0.5mA to 3mA; noise will be low. Don't even think of putting 1:10, even 1:5, on a condenser in front of a drum or Fender. For an awful lot of modern close-micing, a 150:600 or even 600:600 input transformer is all you need.
 
Brian, were you the one I talked to yesterday when I ordered those WSM15K:600 transformers to be shipped to Port Huron, MI? It'd be pretty cool if you were. I think it's nice to see a manufacturer willing to deal in ones and twos for individual builders.

I never would've thought, when I started in DIY, that there was so much involved in designing a transformer...
 
So then, if I'm reading this right, a 15K:600 gapped output transformer (like the one you wound for Tamas) could be done on M6 with about the same number of turns? This seems an odd notion to me... But then again, I never gave much thought to the issue of material permeability vs. air gap, since I've dealt mostly with either ungapped single-ended or push-pull transformers to date. But this thread raises interesting points.

This is of particular interest to me since I have a project in the works that could use a few such output transformers (to the same basic specs as we cooked up for Tamas), but nickel-core prices would bust the budget.
 
more on this from Magnequest:

http://www.magnequest.com/diy_lessard_s-240_2a3pp.htm


Nickel needs less excitation current, so in the case of a mic input transformer, you will lose less low level information with Nickel.

Output transformers, with their higher signal levels, will not have to worry as much about core loss and seinsitivity as a mic or line in.

Different alloys will respond to frequency differently.
Cobalt, for instance, is a very heavy molecule that does not swap ends as fast as Ni. Good for bass, but too slow for high end. Thus, it is alloyed with quicker metals, such as Ni and Moly.
 
[quote author="tk@halmi"]Why was Edcor pushing the Ni core on a gapped transformer to me then?
:evil:[/quote]
We did not push a gapped transformer for you. The last transformer that we sent you was not gapped, because the DC current was so low. I am sorry if there was any miss under standing.
 
[quote author="Consul"]Brian, were you the one I talked to yesterday when I ordered ...[/quote]
Yes, I was the one that help you. And the transformers are scheduled you be wound soon.
 
[quote author="NewYorkDave"]So then, if I'm reading this right, a 15K:600 gapped output transformer (like the one you wound for Tamas) could be done on M6 with about the same number of turns?[/quote]

Yes, you could have the same transformer with M6 core, but you would get a lower inductance then with NI. To get the higher inductance you would need to increase the number of turns. By doing that, you would have to see if you can get the higher number of turns in the space that the size of bobbin. That is why NI core is used in some cases, to keep the size of the transformer small.
 
Yes, that's what I thought in the first place: that the lower permeability material would require more turns for a given inductance, regardless of gapped or ungapped. I interpreted what you wrote earlier to mean something different.
 
[quote author="edcorusa"] The last transformer that we sent you was not gapped, because the DC current was so low. I am sorry if there was any miss under standing.[/quote]

OK. I didn't get the memo on that one. Maybe it had no TPS cover sheet.
 

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