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Power transformer (advise needed)
Power transformer (advise needed)
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Old 3rd December 2017, 05:04 PM   #11
audiowize is offline audiowize  United States
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Quote:
Originally Posted by Schmitz77 View Post
Those trannies without shielding are not first choice for any tube amp.
First choice is C-core or double C-core or toroid trannies.
It's funny, every time I've built a tube amp with a toroidal power transformer, I've ended up removing it and going back to EI type transformers. The transformer posted in that link has a flux band, and unlike toroidal transformers, it will have predictable nulls.


I actually believe that toroidal transformers are the cheap choice, and that they are to be avoided at all costs. After all, how much does it cost to "stack" a toroidal transformer? How much does the bobbin cost on a toroidal transformer? How much does the varnish vacuum impregnation cost on a toroidal transformer?
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Old 3rd December 2017, 05:57 PM   #12
Eli Duttman is offline Eli Duttman  United States
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There are things which are necessary to obtain good performance from a toroid power trafo. The high bandwidth of toroids is a negative in this role. Ferrite beads that suppress the inevitable trash riding on the mains are very much in order. Toroids behave poorly in the presence of "standing" DC. If a substantial amount of DC pollution is present in the power mains, definitely install "Da Blok".

The low stray magnetic fields of toroids is a definite plus.

BTW, some toroids have a copper flux band around the perimeter. Surprise (NOT), they cost more.
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Old 3rd December 2017, 06:20 PM   #13
audiowize is offline audiowize  United States
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I have an EI isolation transformer with a bunch of taps so I can apply 120V with no DC to my system with some isolation from the hash.
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Old 3rd December 2017, 07:12 PM   #14
FullRangeMan is offline FullRangeMan  Brazil
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Quote:
Originally Posted by Tom1973 View Post
Hi,

I’m planning to build a stereo 2A3 SE amp (JE Labs) and I’m currently gathering parts. One of the things I still need is a power transformer. In The Netherlands there are several companies that will wind a transformer to customer specifications, but none of them list what you actually have to specify.
but none of them list what you actually have to specify.
PM member E55L2 here: Login
He is from Holand, Martin will guide you, he have huge experience and can made everything you need.

[*]EI-coreor C-core?
It is said EI OPTs have the old fashioned warming tube sound and C core a more neutral sound, for power trafos perphaps it be less relevant, but in the Yamamoto A08 45 amp all transformers are C core;
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Last edited by FullRangeMan; 3rd December 2017 at 07:18 PM.
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Old 3rd December 2017, 10:03 PM   #15
Schmitz77 is offline Schmitz77  Germany
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Quote:
Originally Posted by audiowize View Post
It's funny, every time I've built a tube amp with a toroidal power transformer, I've ended up removing it and going back to EI type transformers. The transformer posted in that link has a flux band, and unlike toroidal transformers, it will have predictable nulls.


I actually believe that toroidal transformers are the cheap choice, and that they are to be avoided at all costs. After all, how much does it cost to "stack" a toroidal transformer? How much does the bobbin cost on a toroidal transformer? How much does the varnish vacuum impregnation cost on a toroidal transformer?
Its not about the cost of all the materials, its about the price for the labour and complex winding machinery of a toroid what makes them more expensive than the cheap conventionals.
If they are to be avoided at all costs, why so many good amps today use them? Why they havent been used extensively in the past is a clear thing: they were much more expensive.
Yes, this trannie has a flux band. But a good toroid is shielded all around and that shielding is much more efficient than a single flux band.
Toroidals are more expensive to produce, but an excellent EI core can be expensive, too because of the cost of the lams. But most of them have cheap lams.
My own experience is: toroids generate much lower hum (almost non existing, if its a completely shielded type), they have significantly lower winding resistance which results in more dynamic and lively sounding (thats pure physics, too). Their sound signature is much more neutral and dynamic, whereas an EI have more of a flavour (depends on the lams used).
Most reputated companies use toroids nowadays and thats for the reasons written above.
So if you dont like or cant use toroids, use at least C-cores. They outperform EI or other conventional ones with ease.

Last edited by Schmitz77; 3rd December 2017 at 10:21 PM.
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Old 3rd December 2017, 10:24 PM   #16
Schmitz77 is offline Schmitz77  Germany
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Quote:
Originally Posted by audiowize View Post
It's funny, every time I've built a tube amp with a toroidal power transformer, I've ended up removing it and going back to EI type transformers.
For what reasons? Did you miss the 60 Hz humm? Or the stray fields?
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Old 3rd December 2017, 10:31 PM   #17
TonyTecson is offline TonyTecson  Philippines
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Power transformer (advise needed)
different strokes for different folks....that is all...
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Old 3rd December 2017, 11:28 PM   #18
pieter t is offline pieter t  Netherlands
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Quote:
Originally Posted by Tom1973 View Post
I’m planning to build a stereo 2A3 SE amp (JE Labs) and I’m currently gathering parts. One of the things I still need is a power transformer. In The Netherlands there are several companies that will wind a transformer to customer specifications, but none of them list what you actually have to specify. <snip>
You might check transformers offered by Thomas Mayer.
He has a range of power supply transformers; one of those would likely suit your wishes nicely.
These transformers are high quality (well impregnated; double screening; outer flux band; quiet operation).
Reasonably priced.
VinylSavor: transformers
Scroll down.

Last edited by pieter t; 3rd December 2017 at 11:56 PM.
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Old 4th December 2017, 01:43 AM   #19
audiowize is offline audiowize  United States
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Quote:
Originally Posted by Schmitz77 View Post
For what reasons? Did you miss the 60 Hz humm? Or the stray fields?
Stray fields... everywhere!
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Old 4th December 2017, 02:37 AM   #20
TonyTecson is offline TonyTecson  Philippines
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Power transformer (advise needed)
and some fields are stronger than others...
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