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Old 18th April 2007, 12:51 AM   #1
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Default Lamination Size

I want to buy laminations for winding transformers. Since there is a 100 pound minimum for each size i can only get one or two sizes of EI. I want to wind a transformer for a 304tl set, some chokes for the supply's, HV power transformers and maby some smaller stuff.

Silicon steel M6, 29 gauge (.014")?

How much should i expect to per per pound?

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Old 18th April 2007, 08:55 PM   #2
BudP is offline BudP  United States
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For a medium size of E/I of 1 1/4 inch 29 M6 you can expect to pay a raw material price of $3.25 per pound. This from Temple Steel in Chicago. Then, there are freight and duties into Canada.

Why do you not just get hold of Hammond and speak to them about custom designs, from their current product line? Unless you have intimate knowledge of transformer design and construction, any price they charge you will be cheaper than what you will end up paying in time, labor, freight and materials costs.

If you absolutely must have custom work, and they have nothing they can easily modify, email me and I will let you know what first quality custom transformers will cost you.

Please note, the devices you are thinking about are lethal. An error you did not know you could make, of no more than 0.010 inch could kill you because you touched a knob or face plate. Transformers are only simple mathematically and then only for the most rudimentary of calculations.

You can obtain copies, on line, of two required texts that pertain to transformer design of the sort you are contemplating. There are no texts that cover safe, commercial, reasonably cost effective manufacturing procedures, though there are some web sites that proclaim themselves able to teach you. All that I have looked at are fatally flawed in procedures and comprehension of safety protection from both fire and shock hazards.

If you really want to learn enough to build your own transformers, ones that are not lethal and work to the highest levels of performance, again, get hold of Hammond and talk to them about your desire. There are so few analog designers left on planet that a new person willing to learn this subtle art will be welcomed. But you will have to start at the beginning.

Bud
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Old 18th April 2007, 09:23 PM   #3
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I have got the idea from a few quotes that for a pair of 100watt SE transformers that is rated at 3kv rms are quite a bit more expensive than some laminations and wire. I have got plenty of time to spend on making a transformer right. Do you have any tips for me?

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Old 18th April 2007, 09:36 PM   #4
Tweeker is offline Tweeker  United States
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You have a long road ahead of you if you want a big SE transformer with wide bandwidth. Theres a reason that quote is high. Biamping is one way to deal with this. The challenge is to get leakage inductance down without ending up with too high an interwinding capacitance instead all while supporting an airgap to maintain inductance for SE.

I suggest starting with Chapter 5 of the Radiotron Designer's Handbook.
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Old 18th April 2007, 10:29 PM   #5
BudP is offline BudP  United States
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The power alone is a 1.5 kva, 2600 vac power transformer. You must know very specific high voltage design procedures that allow for long life at these very stressful conditions. You must be able to vacuum impregnate with silicone gel potting compound at 30 inches of mercury and then be able to bake this out at 350 deg C minimum for 12 hours. Anything less than these two criteria will kill you at some point because the transformer will loose all dielectric strength and all safety within about 60 hours of turn on. This thing will also weigh about 60 pounds and fit inside of a 10 inch cube.

The output is no less severe in it's needs and the likely hood of you designing an output that will live at these levels and provide a frequency response greater than 50 Hz to 9 kHz is exactly zero. Does not matter how smart you are nor how "simple" it seems from the perspective of a pile of laminations and some wire all you will do is kill yourself and probably someone else too.

And then we get into containment of corona at these voltages within the amplifier chassis and then the specialized solder techniques absolutely required to keep arcing from being your only power transfer process.

My hint is to just forget about this "ultimate" sexy dream machine and build something you have a shot at getting to work, using transformers designed by professionals. Meanwhile, begin to read both the Radiotron Designers Handbook and Reuben Lee's book "Electronic Transformers and Circuits". Both of these are available at
http://www.pmillett.com/technical_books_online.htm

You have a very long and quite difficult learning curve in front of you and by the time you get to the top there will be very few designers that are your peers, as most of us will be dead, since we are almost all in our 60's by now.

Bud
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Old 18th April 2007, 10:37 PM   #6
billr is online now billr  New Zealand
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also

in the back articles of Valve at www.bottlehead.com there are a series of articles on how a chap built a SE transformer for a 211 project of his.

I extracted them from the PDF files that i bought from bottlehead.

worth a look

bill
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Old 18th April 2007, 10:43 PM   #7
Tweeker is offline Tweeker  United States
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Id probably operate a 304TL in SE at higher current and less voltage. Something more like 1,200V and 250ma each. No more than 1,500V. Its easier to build for a lower load impedance. You may be looking at A2 for good power, but that is an easier to solve problem in my opinion. The PSU is also way cheaper this way.

Think of it as more like 4 75TLs in parallel than a 304TL.

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Old 18th April 2007, 10:55 PM   #8
Tweeker is offline Tweeker  United States
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Hammond claims 20-20khz +/- 1dB for its 1642SE, which can support a 304TL. Max DC is listed at 300ma, impedance is 5k ohms. Hipot is 3,500RMS.

Many Hammonds dont actually meet this spec, and roll off at more like 13khz, but its still wider than 50-9khz.
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Old 18th April 2007, 10:58 PM   #9
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I have some pages originally provided by the National Lamination Company (since acquired by Tempel Steel) that lists the dimensions of a large range of EI laminations, including (of interest to you) the number of cores that you can expect to get per pound. At 49 pages it's a hefty 3.7MB.

NLC_Lam_Dims.pdf

As Bud said, designing and winding transformers that operate at these voltages is serious business. But, it can be done provided you are serious, conscientious and clear headed about it.

One comment: the cost can add up quickly, especially since you will need to buy a LOT more material than you need for this project. (You should buy plenty of wire and count on scrapping your first few winds... ) So, if your only motivation is to save money, then I suggest you add everything up before you place any orders. OTOH, if you want to do it just because you can, then I won't try to stop you.

-- Dave
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Old 18th April 2007, 11:22 PM   #10
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I'd suggest a consult with Dave Slagle of Intact Audio. I have heard a 304TL amp built with his Iron. Nice stuff. Not exactly what I'd want laying around the house, unless my wife acquired a cat.
cheers,
Douglas
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