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Old 3rd November 2004, 12:28 PM   #1
hacknet is offline hacknet  Singapore
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Default winding a simple PP output transformer

i am trying to wind a PP output trans for a tube power amp.
the the transformer needs to be around 1.7k p-p and around 15H to support the bass till ~25hz at 90ma bias.

i`ve done some simple calculations that were based for SE trans and have come up with this. please help me check my work.

i need a turns ratio of 14.5:1 for a 8 ohm tap.

To support the tube`s 90ma bias, i need to use ~0.25mm of copper enamel wire on the primary and ~ 0.75mm copper enamel wire on the secondary to support my tubes output of around 6w.

I intend to use Z11 cores but my transformer material supplier only as 66mm laminations and a standard sized bobbin a 35mm stack. it works out i can only get 4 watts single ended but since this is a push pull transformer and i only need a maxium of 8 watts. i was thinking i could get away with it. what are your opinions?

would H14 cores be better compared to limiting myself to 66mm Z11 laminates?

how many rounds do i require for my primary to achieve the 20H?

thank you for reading through!
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Old 3rd November 2004, 03:06 PM   #2
EC8010 is offline EC8010  United Kingdom
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You need to decide the maximum flux density that you can tolerate in the core. For that, you need the B/H curves for the magentic material and you need to know the cross-sectional area of the core. The primary inductance will be dominated by the air gap. In theory, when you interleave E I laminations, you don't have an air gap. In practice, you do because they can never butt together perfectly.

Output transformer design has many variables (that's why it's hard). Try a search for output transformer design on this site. I seem to remember a post that had a great number of excellent references for transformer design.
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Old 3rd November 2004, 03:09 PM   #3
hacknet is offline hacknet  Singapore
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i did do a search before posting and came up with a lot of single ended designs.

i`m more interested in push pull designs. anyway, where do i find the BH curves for the core material, all i seem to find is a bunch of numbers telling me the number of watts lost at 1.7T @50hz and the 800A/m is 1.8T. what does this mean?
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Old 3rd November 2004, 03:21 PM   #4
EC8010 is offline EC8010  United Kingdom
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I'm not suggesting that you didn't do a search before posting, but I know that there was a thread/post on output transformer design, so you just need to find it.

Tesla (T) is the unit of flux density (the B bit of the B/H curves). H is the magnetising force, and this is usually measured in Amperes/turn. When you apply an alternating magnetic field to a magnetic material, you are alternately flipping magnetic dipoles within that material from NS magnetisation to SN. This takes energy, and the more times you do it, the more energy you require. The amount of energy used in a second is power, and this is measured in Watts, so core losses are given in Watts at a specified frequency, such as 50Hz. You can expect that core loss to rise with frequency because you are flipping the magnetic dipoles more times per second, but the relationship is not necessarily linear because as frequency rises the dipoles tend to become decoupled.
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Old 3rd November 2004, 03:36 PM   #5
hacknet is offline hacknet  Singapore
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this is getting terribly interesting but i can`t seem to find the BH curves of any of the materials. not even the common ones like H14 or M6. is it possible for you to do a rough guess on what the figures are like?
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Old 3rd November 2004, 03:47 PM   #6
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I'm afraid not. If you can't find anything on the Internet you will have to resort to going to a library and looking through real books.
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Old 3rd November 2004, 09:48 PM   #7
Yvesm is offline Yvesm  France
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Hi !

I've no data about Z11 cores, but assuming they accept to be run at 1 Tesla, here is a posible solution with the lamination size you have:

Primary: 1160 turns, 0.25mm wire, split in four sections.
Secondary: 5 sections each 79 turns, 0.315mm wire, tied in paralell (beware than they have EXACT the same turns number)

Doing so, the induction will be 1.1 tesla for 8W at 30Hz, and less than 1 at 6W.
The inductance will be 15 Hy if the permeability of your core is at least 2200, wich is quite common (M6X may reach 15000 in that configuration).

Start with a secondary section, then put 0.3mm spacer, then a primary section, and so on.
Each secondary section should fit in 1 layer, and primary in 3.

Such interleaving promises a leakage induction lower than 1mH.

The four primary sections must be tied in serie, and since the inner one has less resistance than the outer, it is good to use the inner one in serie with the outer for an anode, and the two remaining for the other to balance the resistance.

My 2 pence !

Yves.
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Old 4th November 2004, 02:52 AM   #8
hacknet is offline hacknet  Singapore
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oh.. thanks... thats very enlightening.

35Z155

does this make any sense or help us in anyway?
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Old 4th November 2004, 11:41 AM   #9
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Yves, I'd say your two pence was worth a few Euros! Could I ask how/where you derived your information, particularly the prediction of leakage inductance?
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Old 5th November 2004, 03:41 AM   #10
jlsem is offline jlsem  United States
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Quote:
this is getting terribly interesting but i can`t seem to find the BH curves of any of the materials. not even the common ones like H14 or M6. is it possible for you to do a rough guess on what the figures are like?
For 12 mil (.3mm) M-6, the initial permeability for DC is about 350, although for practical purposes in an output transformer with some DC inductance and an intrinsic gap, initial permeability is closer to 6600 at 100 guasses and .015 oerstads. The knee in the magnetization curve occurs at about the same place for all audio frequencies, i.e. 6000 guasses and .15 oerstads. DC permeability there is about 40,000 and decreasing to about 15,000 at 2khz and 3000 at 20khz. The figures for permeability for AC were extrapolated from magnetization curves for much thinner material and may not be accurate. You can operate in the region between 100 and 8000 guasses (.015 and .15 oerstads) without too much distortion.

Quote:
The inductance will be 15 Hy if the permeability of your core is at least 2200, which is quite common (M6X may reach 15000 in that configuration).
At 30hz it is easily over 15000 at 1.1 tesla.

John
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