ruffrecords

Laminations and Bobbins
« on: May 25, 2019, 06:35:07 PM »
The cryptic part numbers for transformer bobbins and laminations make no sense to me (never mind the differences between the opposite side of the Atlantic). Is there a simple guide to the standard types and how they go together?

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'


volker

Re: Laminations and Bobbins
« Reply #1 on: May 26, 2019, 03:51:03 AM »
Metric: EI 84, long side is 84mm long. Tongue is always one third, so 28mm. For the smaller laminations (30-60) you will typically only find one bobbin size, for the larger ones, like EI 84 there are two: EI 84/29,5 and EI 84/43,5 (often also called a and b). Where the number will indicate the thickness of the lamination stack in mm. For bigger sizes there are even more, EI 96 has three sizes, and so on.

Imperial: the number directly gives the tongue width.

Re: Laminations and Bobbins
« Reply #2 on: May 26, 2019, 04:16:36 AM »
Metric: EI 84, long side is 84mm long. Tongue is always one third, so 28mm. For the smaller laminations (30-60) you will typically only find one bobbin size, for the larger ones, like EI 84 there are two: EI 84/29,5 and EI 84/43,5 (often also called a and b). Where the number will indicate the thickness of the lamination stack in mm. For bigger sizes there are even more, EI 96 has three sizes, and so on.

Imperial: the number directly gives the tongue width.

Good Information, thanks!

ruffrecords

Re: Laminations and Bobbins
« Reply #3 on: May 26, 2019, 04:50:59 AM »
Metric: EI 84, long side is 84mm long. Tongue is always one third, so 28mm.
Excellent. Loads of info in that one sentence. Thank you
Quote
For the smaller laminations (30-60) you will typically only find one bobbin size, for the larger ones, like EI 84 there are two: EI 84/29,5 and EI 84/43,5 (often also called a and b). Where the number will indicate the thickness of the lamination stack in mm. For bigger sizes there are even more, EI 96 has three sizes, and so on.
I am trying to get my head around how to have a low profile output transformer made. It fits on a PCB (but can have flying leads) and must be no more than 27mm tall. Width and length are not restricted. It is a 2:1 step down which needs to be able to handle 20V rms at 20Hz on the primary without saturation. CJ kindly came up with a design using a standard bobbin that just about fits. But the number of turns needed to handle the 20V rms means the wire is rather thin which raises the dcr and the insertion loss. I would like to lower the dcr which means thicker wire. The only way I can think of to achieve this is to use extended tongue laminations which is where I again come unstuck in trying to find the right lam/bobbin combination
Quote
Imperial: the number directly gives the tongue width.
What about tongue length?

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'

volker

Re: Laminations and Bobbins
« Reply #4 on: May 26, 2019, 05:31:44 AM »
> What about tongue length?

The length is also a function of tongue width/overall size. Two EI lams are stamped out of one rectangle, the two Is lie in the middle of the two Es. This is called scrapless or waste-free lamination because there is nothing left over. Another type is low waste lams with increased tongue length, but these aren't as widespread, and I think mostly for higher power appliations, bigger sizes.

There is also the M lamination, which is square instead of the rectangular EI, so it gives more winding space. But they are not quite as common as EI and are/have been phased out of production for a large part. I think they don't exist in imperial sizes at all.

My3gger

Re: Laminations and Bobbins
« Reply #5 on: May 29, 2019, 04:04:46 PM »
> What about tongue length?

The length is also a function of tongue width/overall size. Two EI lams are stamped out of one rectangle, the two Is lie in the middle of the two Es. This is called scrapless or waste-free lamination because there is nothing left over. Another type is low waste lams with increased tongue length, but these aren't as widespread, and I think mostly for higher power appliations, bigger sizes.

There is also the M lamination, which is square instead of the rectangular EI, so it gives more winding space. But they are not quite as common as EI and are/have been phased out of production for a large part. I think they don't exist in imperial sizes at all.

Two years ago a friend was using newly made European Fe M laminations for line OTs. Iirc longer side was ~48mm, thickness ~0,335mm. I can ask him more about specifications and source if it still exists (please use pm if interested).
Here is a bit of reading although from 2002, wish i thought about interlaving for parafeed and stock some lams.

MatthisD

Re: Laminations and Bobbins
« Reply #6 on: June 21, 2019, 09:10:17 AM »
I am trying to get my head around how to have a low profile output transformer made. It fits on a PCB (but can have flying leads) and must be no more than 27mm tall. Width and length are not restricted. It is a 2:1 step down which needs to be able to handle 20V rms at 20Hz on the primary without saturation.


What is the highest DCR and the minimum inductance of the primary winding that would be acceptable for this transformer ?

CJ

Re: Laminations and Bobbins
« Reply #7 on: June 21, 2019, 03:13:11 PM »
87 EI  (US)  = .875 tongue,  50 EI = 1/2" tongue, 125 EI = 1.25" tongue  etc...

http://www.laminationspecialties.com/products.htm
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

ruffrecords

Re: Laminations and Bobbins
« Reply #8 on: June 21, 2019, 06:13:19 PM »

What is the highest DCR and the minimum inductance of the primary winding that would be acceptable for this transformer ?

Apologies for the delay in replying. Don't know how I missed your post.

Anyway, both good questions. The design CJ came up with I have had made by a local manufacturer. The measured params are inductance 32H at 100Hz, primary DCR was 178 ohms and secondary dcr was 90 ohms. This design performs pretty well when driven by the actual tube circuit and loaded with 600 ohms so I would like the primary inductance to be no less than 32H. If the pri and sec DCR can be reduced that would be nice but not essential. The one key parameter is that the height of the transformer above the PCB is no more than 26mm.

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'

MatthisD

Re: Laminations and Bobbins
« Reply #9 on: June 22, 2019, 11:34:10 AM »
It seems like you have a solution. Out of interest, what type of core is it using...an EI lamination or other ?

There are a few Lundahl C-core transformers which are quite compact at 21mm in height.


ruffrecords

Re: Laminations and Bobbins
« Reply #10 on: June 22, 2019, 12:18:57 PM »
It seems like you have a solution. Out of interest, what type of core is it using...an EI lamination or other ?

There are a few Lundahl C-core transformers which are quite compact at 21mm in height.

The current design uses an EI core but it is too tall. So I am looking a a UI39 core as a possible alternative as this would give a 25mm high transformer.

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'

MatthisD

Re: Laminations and Bobbins
« Reply #11 on: June 23, 2019, 10:26:06 AM »
This might be a stupid question, could you have a cut-out in the circuit board which one side of bobbin could pass through as is common with 500 series modules?

ruffrecords

Re: Laminations and Bobbins
« Reply #12 on: June 23, 2019, 12:20:45 PM »
This might be a stupid question, could you have a cut-out in the circuit board which one side of bobbin could pass through as is common with 500 series modules?
Not stupid. The answer is yes and no. None of the PCB mounting bobbins I know of are compatible with a hole in the PCB. So you would need to use a flying lead bobbin and mount using hole sin the laminations. However, the distance from the top of the PCB to the edge of the module is 3.87mm so we could probably gain at most 3mm but that is definitely worth having.

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'

MatthisD

Re: Laminations and Bobbins
« Reply #13 on: June 26, 2019, 11:57:16 AM »
I can see how difficult it is to find something 'off the shelf'. Do you need a continued supply of this transformer or just a handful for a project?

ruffrecords

Re: Laminations and Bobbins
« Reply #14 on: June 27, 2019, 03:29:24 AM »
I can see how difficult it is to find something 'off the shelf'. Do you need a continued supply of this transformer or just a handful for a project?

This will be the standard output transformer for my Mark 3 rube mixer design so I would need a continued supply.

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'


 

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