• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

C-core transformers

Has anyone have an idea on the advantages of C-cores (double C construction) over the conventional scrapless EI laminates and does the computation of turns and capacity for both are the same? I have been to several transformer notes over the net and as we know, the cross section of the winding area of the laminates determine the transformer power and relevant to determining the number of windings and wire size. But then C cores have longer traverse width and has definitely bigger winding window compared to EI laminates. I remember I read in the past that a well designed transformer has its entire winding window and traverse width covered. Will this also be true for double C-cores? I am also seeing tube amps with OPTs using double C cores. Better or not? I would appreciate anyone's take on this as well as links that may be helpful to my questions. Well, I have an ample qty of C cores lying around and has knowhows in constructing transformers. Thanks in advance..

edrel
 
I think that make transformers is simple, make state-of-art hi-fi transformers is an hard job.
For your question, and also for all other factors involved in the "know-how" of this "fine-art", it's important to have a long "chat" with specialized designers.
I know that Bartolucci, for example, made long studies on this.
Visit his web site, and e-mail him for "secret details".
http://www.audiomarketing.net/bartolucci ;)
 
I forgot that the italian magazine "Costruire hi-fi" (it is a magazine of hi-fi DIY) published many super-detailed articles on making transformers and on transformers performances. This Magazine has often many articles with translation in english language also. But I don't remember if this kind of articles had the translation, and I don't remember the numbers and the years of magazines containing this articles. I remember the autors: Francesco Callegari and Paolo Maggiolo.
This is the web-site of magazine: http://www.costruirehifi.net/index.html#
 
C core xfmrs

My exposure to C core xfmrs is limited to prototype-building and adjustable inductor/chokes. I will wind a prototype power transformer by hand using premade Cs and clamp it together with banding material. As a prototype, I don't mind the extra mechanical noise (they can be very noisy) and lower efficiency. It seems that the mating surfaces of the two Cs is very critical to good eff. and low noise. Just my exposure to them.
 
I have been using C-core output transformers extensively for tube amps over the decades. A rough comparison to E-cores is that they can handle about 1.5 times the flux and at lower distortion. In between there are of course grain oriented E-I cores, where the grain lies in the direction of the major legs. This gives somewhat better results than ordinary E-I, but it depends on the type of steel.

In RSA we can get C-cores of M5 type material, with permeability graphs available which are a great help. I design my own transformers according to procedures outlined in "Radio Designer's Handbook" by F Langford-Smith, using data from Crowhurst. I have found these predictable. The Bartolucci products look fine, although I would have expected at least the leakage reactance specs also (hope I did not overlook them!). The equivalent capacitance is also important - this is sometimes rather neglected. (In practice the equivalent capacitance can easily be the significant limitation to high frequency response rather than the more generally quoted leakage reactance.)

Yes, it is advisable to fill the whole winding window to get maximum windings with lowest copper loss. It is difficult to give more specific advice here; I would recommend using them though - locally they are not much more expensive than ordinary cores. I have unfortunately never been able to measure specific distortion or find data on that.
 

TonyTecson

diyAudio Moderator Emeritus
2003-05-29 2:57 am
Maybunga, Pasig City
edrel sison said:
Has anyone have an idea on the advantages of C-cores (double C construction) over the conventional scrapless EI laminates and does the computation of turns and capacity for both are the same? I have been to several transformer notes over the net and as we know, the cross section of the winding area of the laminates determine the transformer power and relevant to determining the number of windings and wire size. But then C cores have longer traverse width and has definitely bigger winding window compared to EI laminates. I remember I read in the past that a well designed transformer has its entire winding window and traverse width covered. Will this also be true for double C-cores? I am also seeing tube amps with OPTs using double C cores. Better or not? I would appreciate anyone's take on this as well as links that may be helpful to my questions. Well, I have an ample qty of C cores lying around and has knowhows in constructing transformers. Thanks in advance..

edrel

the "C" cores are just like torroids except that the doughnut is cut in two, therefore, the coils can be pre-wound on a former before the transformer is assembled,

if you have them and know what voltages they have, you can reverse engineer them. if you can find out the turns per volt of a coil, then certeinly you can use them for audio.

can you post pictures? what are the weights and dimensions of traffos that you have. i too have been making my own traffos for my projects since mid 70's.
 
thanks guys for replies and links. .


i have bare c cores with combined cross section dimensions at 1X 1 1/8 inch for dual C. since i was doing OPTs and power trf using EIs, i would like to try the C core potential whether it can really improve things. i use auto machines for winding. as i have mentioned on my post, there is plenty of room for double Cs. The longer traverse width and the winding window is large as compared to EI. Transfering the same number of turns and same wire size from an EI to double C transformer of the same cross sectional area would only make a half filled double C cored windings which i think is not good. i maybe wrong..

"I design my own transformers according to procedures outlined in "Radio Designer's Handbook""

thanks johan for this info, i will try to grab a copy (if i can find one here in Phils)

tony, doc, the gates, thanks too for your help. i'll try to post pics of my previously completed OPTs later..

edrel
 

TonyTecson

diyAudio Moderator Emeritus
2003-05-29 2:57 am
Maybunga, Pasig City
hi,

with that cross-section, you have the potential to build traffos of around 50va at 60hz according to my transformer calculator!

the bigger window of the c-cores you have allows you to use bigger cross section wires, so the inprovement you will gain will be in the area of lower copper losses, attractive for opt's and power traffos.

you can stack them for bigger cross sections for more power. if you use 2 of them you can have a 190va traffo.

btw, are you selling them, and how much, please email me.

fyi, the radiotron designer's handbook can be downloaded from the net, it was posted here some time back. you will need dsl though, it is quite massive!
 

6NS

Member
2013-11-22 6:20 am
Thailand
I know what you mean, I had a transformer builder from Poland ,that builds both C and EI core, say, overall he prefers EI.
The biggest problem I have is shipping and duty. Here in Thailand there is duty and tax totaling 37% calculated on both purchase price and shipping cost. But from China where I have an account with a favorable ground shipping company, there is no duty or tax at all. There is now a free trade act with all of Asia.
I've been very lucky purchasing from China but haven't found great transformers yet. I'll even settle with GRAIN ORIENTATED annealed SILICONE STEEL.
Any ideas??
 

6NS

Member
2013-11-22 6:20 am
Thailand
These are the best I've found. BEZ tube amplifier
Cut and past.

At least the H10 correlates to transformer steel I've read in papers from worldly transformer building and metal suppliers. I haven't seen anything supporting the quality of the said Z11 steal, and I looked for the data.
From what I feel I know, all transformer steel includes silicone, most are the cheapest (non orientated), orientated being better but more costly. The better steel also gets annealed after being cut which I'm sure most from China do not.
I look for grain orientated, and annealing. If they have both I'm happy. If you notice, Chinese sellers are now stating when there transformers are annealed. Doesn't mean they are though. I'm Canadian and have lived in Thailand for four years now and the truth means nothing here. Very tough to get the straight goods here. I believe most of Asia is like this, excluding Japan maybe.
 

6NS

Member
2013-11-22 6:20 am
Thailand
Forgot to tell you to check out the prices on that site, great aren't they.
I cam post the address of the Poland company who sells annealed transformers I'd like to buy from. I just can't bite off paying the same for shipping and duty as the product costed. I'll look for their site and post it in a bit.
 

6NS

Member
2013-11-22 6:20 am
Thailand
These are the transformers to by I thing,,, for the money. I just don't want to pay double with shipping and duty. There from Poland.

Ogonowski.eu - profesjonalne transformatry do wzmacniaczy lampowych

They don't have the grain orientation though. I think there's a market for a good transformer made in Asia. Grain orientated and annealed with silver or gold plated OCC 7N copper wingdings. I buy silver and gold platted OCC copper ire by the 1000 meter so know it doesn't cost as much more as they all make out it to cost.
 
14753714200805219702.jpg


f2a project ..... c_core double coils .
 
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