North American Ferrite core supplier for prototypes

Lower capacitive coupling between the windings is the main reason for the split bobbin.

Best regards, Spehro Pefhany

Hello Spehro,

Yes, like the PT Cruiser. I am more of a purist when it comes to tubes and other oldie designs. Only components from the era. When there was no choice I tried hiding modern stuff, especially in restoration projects. One of the radios still contained a Ducati capacitor even though their biz moved to motorcycles decades before. Hidden inside was a new Philips cap.

Regards, Joerg

Do you need the split bobbin for safety ? With small cores margins take up too much room. Using triple insulated wire make more sense.

Graham

Do you need one in your case though ? Split bobbins can be hard to find.

Graham

No, actually it was about six years ago.

The Farnell cat show a wide range of ferrite cores in stock, from Ferroxcube and Epcos. Quite a few low-profile possibilities (4-8mm) from both, either as low-profile RM or E-E cores. Can't see any split bobbins though.

Carpenter is one of the big guys, but steel suppliers are a major PITA to deal with. A few years ago it was a $500 minimum, probably more now. Maybe you can sweet-talk them into giving you some samples.

Many years ago some outfit in the UK had transformer "kits" with the primary pre-wound, you just have to add the secondary. Don't know if they're still available. I bought a few from Maplin.

Best regards, Spehro Pefhany

Hello Graham,

At Kaschke that is a regular catalog item, at least for pot cores.

Regards, Joerg

BTW, does anybody know where I can buy small amount of _transformer steel_ EI lamination? Its not such a difficult thing to find ferrite, iron powder or similar core but I can't find transformer steel anywhere... I want to wind several (4-8) _output_ transformers for tube amplifiers. I can't find any ready-made transformers that suit my needs and all those custom-wound ones are helluva expensive. I would've even try to rewind some surplus ones but they are all varnished that makes such a task next to impossible :((

Hello Sergey,

Other than buying a few cheap transformers and taking them apart I wouldn't know off hand. That is usually how I did it. You could start a separate thread about it so more people would see it.

Regards, Joerg

Hello Spehro,

That was also one of the advantages of taking apart existing transformers. Preferably some with lower voltage secondaries because it was less work to unwind those. Then you had the primary already there,

But Sergey wants to create tube amp output transformers and that would almost certainly require a complete rewind. Unless one would find the perfect match where the primary shows just the desired impedance and a

If I were in his shoes I'd seriously consider one of the hi-perm ferrites. Preferably some huge pot core for easier winding. These materials have come a long way since the days of tube amps. I believe you could get a lot more fidelity out of them. Also, the round bobbins allow to fix them to an electric drill chuck and wind'em up at slow speed. I never really succeeded doing that with square bobbins but in those days the only way to slow down a drill was via a variable transformer and then it would sputter at very low speeds.

Regards, Joerg

Hello Thomas,

Interesting. And they state that it is from current production runs, not old stock. It looks like it is from Ducati-Energia. I don't know about how the companies are linked these days but they are in Bologna just like the motorcycle manufacturer. Plus there are lots of other products under that name, parfumes etc.

Regards, Joerg

There are/were recently still caps being made under the Ducati name. See

Thomas

I have used these people for prototype quantities, they are knowledgeable and responsive, and the products are solid and ready to mount. Why wind it yourself?

The E-I laminations used in a power transformer aren't ideal for an audio output transformer of any fidelity.

The laminations in an audio output transformer should be thinner ( higher frequency eddy current losses ) and ISTR that the preferred matereial grade differs too.

That probably explains the higher costs ( not to mention small quantities ).

You might fare better with a toroidal core ( thinner material anyway and I think it's generally higher quality ). You'll need more turns/Volt than at power line frequency too since you'll want the thing to work down to 20Hz I assume.

Graham

The famous Williamson audio amplifier specified the use of "dynamo grade laminations". Iron losses were not seen as a problem for power output transformers and 0.015" lams in 4% silicon steel were often used.

Low level transformers would need the higher permeability provided by nickel-iron cores (to avoid excessive turns count), and probably using thinner laminations.

The biggest problem with a lamination transformer at audio frequencies was the hf rolloff due to the leakage inductance. Toroidal transformers send most of that problem away.

Hello Tony,

While I also prefer toroids, the large number of turns required for a tube output transformer would entice me to use a pot core with bobbin in this case.

Regards, Joerg

You'ld need something rather larger than a pot core ! ;-)

Graham

What a wimp.

No doubt my 600kHz 10kV paralleled-U-core transformer rates up among the biggest out there in dilettante land, but it's no more massive than an old 60Hz 1kW plate transformer. Get a grip man!