Transformer coupling

[brandon7861]

Does anyone know what the coupling factor is in a typical IF can like those found in cobra and uniden radios? I know some have just the slug and some have ferrite around the top as well, but I just want a ballpark as the K has a significant impact on resonant frequency when external caps are involved. The typical 1/(2pi*sqrt(LC)) only works when the coupling factor is low (loosely coupled).

I have been following along with a few transformer coupling videos modeling them in circuit lab as I watch and I realized that I can't just look at the inductance and associated capacitance to determine frequency, so a place to start would be good if I ever want to rewind one of these cans to suit my needs.

Thanks!

 

[brandon7861]

For example, if I use dual tuned transformer (for lowest loss) and use one in series and one in parallel, a small change in K causes a significant shift in resonant frequency.

If anyone knows the roundabout K value obtained using these small slug-tuned cans, it would be very helpful.

Edit: I know my model is missing a lot, like core loss, magnetizing inductance, uncoupled inductance, parallel capacitance from the windings and interwinding capacitance, I'll add that after I play with this for a while.

 

[19wrc333]

I've got a whole bunch of TOKO transformers here and the numbers on them are not that useful. Same for some existing prints I want to rebuild with transformers on them that are anyone's guess as to what is needed.

So I was at first trying to find more details about the numbers on them - without success, but then have found this: https://www.on1bes.be/toko_tester_en.html
So am considering building that on a bit of test print (atm not going to redraw the print and then send it off) to see if that helps.

It doesn't tell you the K value, but it at least helps you to find the resonant frequency for them.

--
Skyline

 

[brandon7861]

That's a cool circuit. I used to use an oscillator from the bipolar transistor cookbook to check cans. Figure 7 on this page https://www.nutsvolts.com/magazine/article/bipolar_transistor_cookbook_part_5

One thing I want to try but haven't yet is to use a high impedance active probe and hold it close to the can leads while I click a grill igniter or camera flash next to it to try to watch the ringing on the scope. Not sure if it will work with most of it shielded.

 

[unit_399]

Here;s what I could find on toko IF transformers. Hope it helps.

- J.J. 399

 

[19wrc333]

Here;s what I could find on toko IF transformers. Hope it helps.

- J.J. 399

Thanks, I just compared it with what I have on file and this pdf was in the collection, along with a whole bunch of others.

It was surprising to me that TOKO had made so many transformers that you can't find anything about online.

As an example. Among others, I've been gifted 35 toko transformers with description 23721 8049 with an orange coil. There was a whole bunch more in that collection, but haven't been able to ID a single one.
Would be nice to be able to use them.. but so far no idea, couldn't find them.

Anyways, don't want to hijack somebody else's topic.

It's going to be fun to cobble up the tester and see if any of them oscillate and on what frequency. That along with their LC values should hopefully be a start to be able to use them.

--
Skyline

 

[brandon7861]

Anyways, don't want to hijack somebody else's topic.

Please do! It sounds like you have more experience with IF cans than I do. This thread can turn into anything transformer related, it's all very interesting to me. These transformers have always been a mystery to me, so the more info I can get about them, the better.

Here;s what I could find on toko IF transformers. Hope it helps.

- J.J. 399

Thank you!

 

[brandon7861]

Does anyone know of a source of empty ones, just the coil form, the pins, the slug and the can, no windings or internal caps?

 

[19wrc333]

For empty ones I would probably look at AliExpress, but I'm sure there's alternative places.

As for me knowing more about cans, I sincerely doubt it, but I can share the info on TOKO cans that I've found so far.

Here's a huge PDF (187MB)

Toko Coils and Filters Catalog 1993 : Toko America Inc. : Free Download, Borrow, and Streaming : Internet Archive

Toko Coils and Filters Catalogue, for history preservation and vintage equipment service.

archive.org

there's this site:
https://joefreeman.weebly.com/toko-coil-data.html (which has the file from above)
and this one:

Coils, the basic building block

Coils, the basic building block

www.robkalmeijer.nl

Also let me attach the various pdf's I've collected so far.

 

[brandon7861]

I'll have to download those once I get home, thanks!

 

[19wrc333]

Been spending more time on it searching and readon on the web.
Read somewhere that for a custom coil TOKO would put the numbers of the producer on them. Which might explain why I can't locate the cans I have down here. They are probably custom ones.

One thing that's peculiar about those TOKO cans is the color of the core in the coils. As it turns out the color is something you can use to identify the can and what it is intended to be used for.

See also: http://web.archive.org/web/20120225043543/http://hem.passagen.se/communication/ifcan.html

Some other links I located but they are in Dutch and bits of German (sorry about that, browsers should be able to translate some of that)

• https://www.circuitsonline.net/forum/view/102252
• https://on4aol.blogspot.com/2009/04/kleurcodering-mf-spoelen-toko.html
• https://www.transistorforum.nl/forum/index.php?id=89

I'm going to verify those findings against some radio's I have here.

 

[Naysayer]

color of the cores inside of cans, this goes deep.