winding a toroidal pp output

[tubetvr]

But all this difficulties correspond to EI cores as well.

Now I'm trying just to ensure you that problems EI and O cores are the same

I think no one is saying that only O-cores have problems and EI or C-cores not but that there are different problems for each design, however when you are saying that there are the same difficulties with EI and O-cores it is IMHO not 100% correct.

The major disadvantage with for instance EI cores is that they can
not benefit in the same way as C-cores and Toroidal cores when using grain oriented transformer material as some field lines will always be perpendicular to the grain orientation which reduces max allowable flux density.

The difference between C- cores and O-cores are smaller and the allowable flux density is almost the same with some small advantage for O-cores. However C-cores are easy to wind in sections which allow the 2 halfs of a push-pull transformer to be identical, proper sectioning on O-cores is much more difficult and as the winding is not so effective, (there are a lot of unavoidable air pockets between the wires of an O-core) there is a big risk of increased leakage inductance.

A special problem for O-cores is how to take out the connection wires from lower layers, in EI- and C- core type transformers this is easy to do without creating any gaps or extra air pockets but it is a well known problem on O-cores that can create leakage flux, (e.g. very common on mains O-core transformers).

Another advantage of C-cores are that it is very easy to implement a small airgap which allow for a certain degree of DC magnetisation which is almost unavoidable in a push-pull amp. This together with the fact that a C-core transformer is much easier to wind for an amateur than a O-core I think give benefits for using C-cores if you are an amateur.

I think also it is important to realise that one important reason for using O-cores in industrial scale is the lower manufacturering costs compared to C-cores, C-cores are from the beginning manufactured the same way as for O-cores by winding a thin tape of magnetic material into a "donut" shaped assembly but for a C-core this "donut" is cut in two and the ends are polished and need to be assembled using some means of holding it together tight, the cost for these additional steps give a total cost advantage for O-cores in industrial applications and as long as you have the winding machine an O-core transformer will be cheaper to manufacture than a C-core type.

So as a summary IMHO each type of transformer being it EI-, C- or O-core type have their own advantages and disadvantages but they are not the same for each type. Regarding which type is best it depends on your application and what is important for you.

Igormak, if you have succeeded in winding your own O-core transformers that is an admirable achievement but have you compared those transformers to other commercially available types or have you tried making EI or C-core transformers?

Regarding air-gap the fact is that many output transformers using C-cores use a small airgap, (examples Lundahl and Tango), this is not because they need to be manufactured that way but because there are obvious advantages doing this.

I think it is also worth noticing that most comercially available output transformers are C-type including some of the best manufacturers like Tango, Tamura and Lundahl.

Regards Hans

 

[igormak]

Hans, thank's for expanded answer

>So as a summary IMHO each type of transformer being it EI-, C-
>or O-core type have their own advantages and disadvantages
>but they are not the same for each type. Regarding which type
>is best it depends on your application and what is important for
>you.

Yes, it's correct and exactly what i mean. The cost of work I put
outside the brackets. That is not my business.

>However C-cores are easy to wind in sections which allow the 2
>halfs of a push-pull transformer to be identical, proper
>sectioning on O-cores is much more difficult and as the winding
>is not so effective

Who told it will be easy? 🙂 But you can wind O core like C, just
imagine you hold C core... 🙂 It is an answer. I wind lile that.
It is bifillar in each layer. Left and right sides symmetrical - equal
number of turns, and have equal resistance. Connection wires
replaced by pins ( with ceramic base). Isolation... it's long story.
Now I use toilet paper.🙂 Anyway, I don't keep any secrets and
ready explain everything, better by email.

>Igormak, if you have succeeded in winding your own O-core
>transformers that is an admirable achievement but have you
>compared those transformers to other commercially available
>types or have you tried making EI or C-core transformers?

First of all, I compared with Plitron. Even not comparable at all. 🙂
The best is Tamura (best EI). Very close sound, but my
transformers usially for higher power. IMHO it's a benefit.

My main problem is an iron. I can't find different manufactures of
cores. Everybody sale only ready transfomers. 🙁

Igor.