I search a schematics of farfisa intercom, that have an "anti-LARSEN" circuit to eliminate antilocale effect between microphone and loudspeaker. Have you? Thanks.

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Hello Albert

If you dismantle some of them you will get the needed experience and things will be much easier thereafter. Of course is a difficult task, but nevertheless worth to know it and use this knowledge especially for repairing costly (or vintage) equipment.
The laminations, although it seems impossible to remove them, can be removed. The problem is to remove the first two or three of them and then the core is not so tight and makes things easier. On the other hand, not all the cores are impregnated. In many of them you will see only the laminations without any enamel substance gluing them.
The usual structure of the core is using the so called E and I laminations. Anyway I will try to present all of it in a new article.
For the time being just keep in mind that nothing is impossible. There are alternatives in most of the cases (talking about technical matters of course).
No, it is not difficult to make a transformer as it was before its failure. It is more difficult to make modifications instead.
The heating of the core is mostly applicable to switching transformers as they are always glued. Another inherent difficulty with them is to secure the air gap if needed, at the reassembly phase. I have never heated a classic core in order to dismantle it.
And yes, during heating there is always a bad smell present and you need to work in a very good ventilated environment, most preferably in open space.
Finally I will try to follow your advice, for which I give you my thanks as well.

Best Regards

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No need to hurry dear Paris! Of course I will read it as soon as it gets published.
I think one of the clues will be that the lineair transformer core exists out off two identical halves? At least that sounds a lot easier than dismantling every laminated plate apart. Todays modern transformer cores are toroidal sized. And even those are made by winding machines. Taking apart and reassembling the core with all the glue on it will require some skills and the right equipment I guess? I hope your article will explain how to do the at first almost impossible.

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Thanks, Paris. I consider you a good friend also.

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Yes Albert “Der Grosse”.

Not everything is about electronics in life…And it seems that I and Robert have something more in common than only liking to dismantle burned transformers and rewind them…Don’t you agree? (You don’t interrupt at all anyway)…
I have all the calculations for the Farfisa transformer ready in a new article. I will send it tomorrow to Jestine, after a final review. I hope that it will answer the questions you have so far.
Next I will prepare another one including all what is needed about the topic. And it will be dedicated to you in order for you to have all the answers you need about the topic!

Greetings to you

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You Guys are Funny! Not everything is about Electronics!
Don't let me interrupt your conversations (LOL).
Cheers.

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Thanks Paris! You make modifying or disassembling an old Lineair - as you called the 50/60 Hz - transformers, sounding very easy! Most big square transformers I know are even if they are pre-heated almost impssible to seperate because of the thin laminated glued together plates. And of course because of the glued Windings around them. As you say the classic one with the laminated core can be dismantled and repaired or modified to give a different output than the original. That would most likely be the case if I would try such an enterprise (LOL). It is more difficult to make it identical to the original I guess. I don't know of any examples of people who documented this dissasembling a transformer core part into clear detail. And doing this heating a glued core until it is open thing won't be very healthy either. So I wouldn't want you to feel obligated to undertake such a task on my account! So please stay healthy and do the less impossible repairs. Thanks!

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Hi Albert
First of all you don’t need to feel sorry about anything. Feel free instead to express your opinion or put your questions even though they are lengthy.
Apart from that, any transformer end especially the classic one with the laminated core can be dismantled and repaired or modified to give a different output than the original. There is no problem at all with excessive eddy current losses as compared to the original magnitude of them, as long as the core laminations are tightly hold together, as they originally were. This is the reason that usually the cores are impregnated with a special substance which works both as insulating and at the same time as gluing material.
As regards the specific transformer I ordered, I had given the constructor beforehand the exact info about nominal voltages and currents of the windings at 254V input voltage. Therefore I practically received an exact copy of the original.
And yes, Robert seems to be very familiar with this task…(And I like that)!
Now about the fuse of the 12V winding: this not only is not a problem at all, but it also means that the winding can tolerate much higher current. Practically the fuse puts the upper current limit, but the winding works in a more relaxing mode in terms of temperature development on it.
You know, as I keep on answering you I realize that you were right proposing me to write a relevant article. I have the feeling that more questions will pop-up in your mind as I go on with it…So, I guess I’ll try to organize it so that you along with anyone else interested in this topic can have a clear picture of it.

Best Regards

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PS: About mentioning the Fuse being 1.6A while the Transformer calculated to be 3.5A is no problem I guess? Because it is always better to have a larger transformer to compensate for any peak currents. So you still could have used that information while looking for a suitable replacement transformer?

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Thanks again Paris for your very informative answer! And sorry if my previous post seemed a bit long. I completely understand why you had to do it in the way you did solve it. But I myself never had the confidence to try and repair or destillate the old transformer the way you did it.
And I noticed that also Robert is more experienced in the field of making a new transformer. But I guess the laminated core (to reduce the field energy losses in the core which produce heat) never can be opened afterwards like he mentioned earlier? Did you however manage to find a primary transformer core that still was suitable up to 254 Volt AC? Thanks !

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