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Old 15th February 2005, 04:53 AM   #1
Coulomb is offline Coulomb  England
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Default Toroids VS EI Transfomers

I have done a search and could not find a thread specific to this argument. There is certainly a lot of discussion regarding the topic in assorted threads. If there is some relevant discusions you know of, please post a link here in this thread.

I am starting to get back into tubes after a long haitus and building frenzy with FETs. I find toroids in power supply and choke application to be a God Send in solid state design. I am not happy with the rapidly escalating prices of toroids from top of the line manufacturers like Plitron and certainly not with the price of tube related toroids, output or supply.

Price aside, I would like to see hear some practical discussion on the differences between Toroid and EI style transformers in there applications with tube amps. In solid state it is generally accepted that a good toroid is the best thing going, quite the opposite with tube designs it would appear. Is this just romantiiscm for days past or real Science?

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Anthony
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Old 15th February 2005, 05:03 AM   #2
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My preference for EI's is due to the narrower bandwidth. Why let all the c*r*a*p on the mains in in the first place? Did some measurements in a test lab years back and the inclusion of a huge EI iso tx dropped the dirt from the mains significantly. I also always use electrostatic foil (not another winding) screens wherever possible. None of my system has a torroid PS.

Torroids are only better due to the smaller size and lower radiated field, neither of which are a particular issue in DIY where it doesn't get moved about as much, it can be designed to negate these effects nor usually have to fit in a specified form factor. The power tx's in the MI gear we build are torroids for these reasons, and about 15% or so better price for the torroids I have made from a specific supplier.
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Old 15th February 2005, 05:20 AM   #3
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What Brett said...

Even my next chip amp will use split bobbin EI transformers in preference to toroids. The last thing you want in a power transformer is wide bandwidth.

Edit: the best thing about a toroid is that you can pull the secondaries off a cheap one and wind up your own centre-tapped filament transformers to the exact voltage you need. Good for those 2.5V and 4V valves.
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Old 15th February 2005, 10:28 AM   #4
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Default Re: Toroids VS EI Transfomers

Konnichiwa,

Quote:
Originally posted by Coulomb
Price aside, I would like to see hear some practical discussion on the differences between Toroid and EI style transformers in there applications with tube amps.
The issues are identical to those in Solid State Amplifiers.

Quote:
Originally posted by Coulomb
In solid state it is generally accepted that a good toroid is the best thing going,
It is? I must have missed that.

So you consider a transformer "a good thing" which has the following fundamental flaws:

1) no airgap (an EI Transformer invariably has a distributed airgap even if tiny) and very little iron in the core, leading to early saturation, waveform distortion and high sensitivity to DC offset in the mains and "flattopping" and which in the real world as a result run hot, often hum and are inefficient, unless extensive external circuitry is appended to offset these issues which do not exist in EI Transformers

2) low primary inductance which as a result stores little energy which could be used to "bulk up" the current flow on the rectification peaks (measure the primary current waveform of EI vs. Torroid to see what I mean)

3) Exteremely high coupling capacity between sections which makes sure all mains related junk sweeps right through the PSU and onto the supply rails.

4) Due to construction and the problems around high shunt capacitance and low leakage inductance makes snubbing out the ringing from the reverse switching all the more difficult

Given the drawbacks compared to more traditional shapes of mains transformers it strikes me that the only thing Torroids offer is more profit to the transformer maker and/or equipment maker as they are MUCH CHEAPER to make and in materials than EI Types.

I use torroids where I have no no real choice and fit the required circuits to reduce their drawbacks but would prefer to use EI transformers of suitable construction instead and to just connect them.

Sayonara
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Old 15th February 2005, 11:32 AM   #5
Coulomb is offline Coulomb  England
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Kuei Yang Wang do not beat around the bush, tell us how you really feel!

So if Toroids are cheap to make why are they many times more expensive than conventional designs? Is it because a lot of us fall into the newer is better trap?

With conventional EI and R core transformers who has a global distribution base other than Hammond?

Does Hammond make the best EI transformers or do they have the best marketing?

BTW please post links to your favourite suppliers of transformers if you wish.

Regards

Anthony
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Old 15th February 2005, 11:47 AM   #6
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Konnichiwa,

Quote:
Originally posted by Coulomb
So if Toroids are cheap to make why are they many times more expensive than conventional designs?
They are not in Europe. It seems in the US the market supports a higher pricing for torroids than for EI Transformers, in Asia and Europe this is not the case. If cost/size/weight is a concern you fit a torroidal, if quality is more important R-Core, C-Core or EI types are used.

Quote:
Originally posted by Coulomb
With conventional EI and R core transformers who has a global distribution base other than Hammond?
Hammond is largely unknown outside NA. Many manufcaturers for commercial grade EI transformers exist. Just look into the usual industrial electronics suppliers catalogues.

Quote:
Originally posted by Coulomb
Does Hammond make the best EI transformers or do they have the best marketing?
I think neither. They are non-entities out here. As are Plitron BTW.

Quote:
Originally posted by Coulomb
BTW please post links to your favourite suppliers of transformers if you wish.
I have no preferred supplier per se. I tend to peruse the Catalogues of Farnell, RS-Components and others.

If I want something wound to my own spec I do have links to a number of suppliers, but they are industrial, so don't bother asking for a pair, minimum order on custom designs tends to be 10 - 20 pieces if you supply the full design, more if they design it.

If I need a transformer or two personally I can always drive over to Stevens & Billington on a saturday morning and wind my own, just pay for cores & wire.... ;-)

A company I never ended up dealing with (they quoted way too long delivery time and where impossible to pay when I asked - which was during their startup so should be better now) is Reinhoefer Electronics in (former East) Germany. The guy behind it really knows his ransformers and his designs are reputed very good, but as said no 1st hand experience.

http://www.roehrentechnik.de/

Sayonara
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Old 15th February 2005, 12:04 PM   #7
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Thorsten is right, toroids aren't necessarily more expensive. I thought about getting a Hammond, but I got a larger capacity toroid for around half the cost. So, the reason for using a toroid for me was basically cost and the fact that it fit into the space allocated.
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Old 15th February 2005, 12:21 PM   #8
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The smaller power torroids make very good (and cheap) output transformers for parafeed line stages. I'm even using some as input phase splitters for my current line stage. Their wide bandwidth can be a good thing when used in the right place.
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Old 15th February 2005, 03:56 PM   #9
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Hello all.
Well, if you read throughout this posts you can see why I make my transformers and inductors myself.
Cost? Who cares? I don't!
I'm not an industry I'm a DIY so why I should care for the cost of somenthing. Right the way not to use gold or platinum wires for windings. Let's think... I'm investing many hours a day for making something really unique, a beatifull object, a nice amp, with nice tubes, so, why to worry about few dollars or euros for a transformer? This will be somenthing that will last for decades! Even when I'll be dead it will be working, with the pleasure of the peple who remember the author of such a hard work fruit of patience. So I use the best components regardless off their cost.
What will be the real cost for making an amp? Time. Borrowed time from my life.
Further, I consider the magnetic components of the amp the key for good results from main transformers with shielded primary. Low output resistance high iron weight for low flux density, non magnetic field around and no hum etc... Who will be concerned about a couple or more pound of weight? Is this transportable?
Now, if you aren't sick yet, there cames the answer to toroid or not. I find very difficult to wind toroids myself, meanwhile, I enjoy to wind perfect bobbins, using polypropylene for insulation. I also enjoy to make brass covers bright polished or hand docored and then chrome plated, or even gold plated.
I could'nd do this with a toroid. Who will in turn show all the troubles you all stated in the above posts.
Nevertheless, fine hearing people warship MOS amplifier powered by toroids. But they are a class apart!
Have a nice day!
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Old 15th February 2005, 09:53 PM   #10
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Hi there.....come on Larry.......burning the midnight oil winding EI trannies ain't so bad.....you can think of other things while you are doing it.....Re mains trannies......if you wind the primary so it is properly balanced to line common mode noise you shouldn't need an interwinding screen. Tried it ? Wind every alternate winding on the primary the opposite direction with the core the other way round......you know what I mean but it's alot of work. I did a tube amp tranny rewind for a friend who was having alot of problems on stage as so much lighting control uses phase controlled junk. The problem disappeared.
If you fit an interwindg cu/Al screen on audio parafeeds, it will cause ringing and overshoot.
I agree with you on large cross EI section core....but there are advantages with toroids......far lower winding resistance and Z for the same VA with an EI and the regulation factor is nearly halved. What many don't realise .....most toroids are pile wound and have a temp rise limitation whereas a well wound EI can gracefully stew.

rich
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