Anthon

Choosing lamination grade for audio transformers.
« on: May 15, 2019, 12:44:21 PM »
I wanted to invest in a CNC coil winder and couple of EI lamination stacking machines. I'm using a lot of transformers lately for my projects and DIY kits that I sell, and I think starting making my own would be worth the effort.

But it seems as the stacking machines that I'm interested in can do only 0.5mm laminations or 0.35mm - they can't do both.
This means I have to commit to the grade of lamination before buying the machines.

I want to make power transformers, audio output transformers, and chokes for tube guitar amp projects.
I've done some research, and it seems like M6 grain oriented steel (which is 0.35mm) would be the optimal choice for audio application. So the stacking machine for thinner lamination would be better.
(thinner lamination mean less losses. Also the grain oriented steel is more efficient).

But are the other things worth considering? Could thicker laminations have an advantage too? Besides being less expensive.
It seems like the transformers I have now use thicker laminations. But for example Edcor uses M6 grain oriented steel for their transformers.


ruffrecords

Re: Choosing lamination grade for audio transformers.
« Reply #1 on: May 15, 2019, 12:52:47 PM »
M6 grain oriented is pretty much the goto lamination these days.

Steel supports more flux density than any other material but its distortion is not the best that can be achieved at audio frequencies. For that you need a nickel alloy (like mu metal) but these support much less flux density so you will need a larger core cross section for a given voltage.

So for low level transformers (like mic inputs) nickel alloys are fine but for power everyone use M6.

Cheers

Ian
www.customtubeconsoles.com
https://mark3vtm.blogspot.co.uk/
www.eztubemixer.blogspot.co.uk


'The only people not making mistakes are the people doing nothing'

Anthon

Re: Choosing lamination grade for audio transformers.
« Reply #2 on: May 15, 2019, 02:13:54 PM »
M6 grain oriented is pretty much the goto lamination these days.

Steel supports more flux density than any other material but its distortion is not the best that can be achieved at audio frequencies. For that you need a nickel alloy (like mu metal) but these support much less flux density so you will need a larger core cross section for a given voltage.

So for low level transformers (like mic inputs) nickel alloys are fine but for power everyone use M6.

Cheers

Ian

Ok, thank you. I'll go with M6  grain oriented electrical steel then.
Yes,  I was aware that for mic transformers you should use mumetal for the core, but currently I'm interested in audio output transformers (5-45W) and power transformers for tube guitar amplifiers, so distortion is not a real concern.

CJ

Re: Choosing lamination grade for audio transformers.
« Reply #3 on: May 15, 2019, 07:57:42 PM »
a lot of the older classic tube amp transformers were done on  0.018"   (26 gauge)  laminations.

these were made out of non grain oriented silicon steel.

properties of these laminations are reduced inductance, higher saturation levels, and better magnetic aging.

both the power and output transformers would use this less expensive steel.

you can get fast at hand stacking lams, unless you do 10,000 units a week i see no need for a stacking machine,
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html

Anthon

Re: Choosing lamination grade for audio transformers.
« Reply #4 on: May 16, 2019, 06:45:59 AM »
a lot of the older classic tube amp transformers were done on  0.018"   (26 gauge)  laminations.

these were made out of non grain oriented silicon steel.

properties of these laminations are reduced inductance, higher saturation levels, and better magnetic aging.

both the power and output transformers would use this less expensive steel.

you can get fast at hand stacking lams, unless you do 10,000 units a week i see no need for a stacking machine,

Yes, it seems like the 'vintage style' transformers I have now use thicker laminations.
I guess considering the long lifespan of a tube amp, it's worth taking the aging into consideration.
Also for being true to the classic designs.

I don't know about stacking laminations by hand. I've seen people doing it, it seems like a very tedious process. I would prefer investing in the stacking machines. Time is money, after all.
I guess you could call me lazy  ;D
I need to spend some money for tax write off anyway.
« Last Edit: May 16, 2019, 08:51:44 AM by Anthon »

Anthon

Re: Choosing lamination grade for audio transformers.
« Reply #5 on: May 16, 2019, 12:24:12 PM »
After some consideration maybe it would be wise to stack them by hand for now after all.
The machines only work for a certain thickness and a certain type of EI laminations, which would be a rather limiting factor  ::)

And I see some manufacturers even brag about hand stacked transformers (Edcor for example).

CJ

Re: Choosing lamination grade for audio transformers. New
« Reply #6 on: May 17, 2019, 02:43:48 AM »
get a flat magnet and glue it to the back of some stainless steel for a core stacker ,

this will spread the lams out so you can grab them quickly.

once you grab two or three lams, two or three more will magically creep up the plate for the next lap.

keep your burrs all on the same side of the core, that is, do not flip the lams around at random, you want them oriented the same way they come off the string.

doing butt stacked chokes or transformers? same thing with the I bars, you can feel with your hand which side has the most burr. unless you use stuff from Lamination Specialties which seem to have no burr, they must sharpen their dies in house.

a gapped core will show different inductance depending on how you orient the I bars, if you stack them with the burr on the gap side, inductance will go down due to the fact that the I bars can not get as close to the E lams, this will be less prevalent if using a kraft paper (KP) or Nomex 410 gap.
« Last Edit: May 17, 2019, 02:51:43 AM by CJ »
If I can't fix it, I can fix it so nobody else can!
Frank's Tube Page: www.mif.pg.gda.pl/homepages/frank/vs.html
Guitar Amps: http://bmamps.com/Tech_sch.html


 

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