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Old 23rd May 2013, 07:26 AM   #1
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Default Transformer specs?

Hi, i am considering building a gainclone of some sort and i found this old transformer from a Bang and Olufson amplifier. The wireing confuses me a bit, so a thought you could help me. I know the red wire is one of the primary, and the other four others is for 4 different input settings. It is mostly the secondary wiring i am wondering about. There are two blue wires with fuses. One black in the middle and two greys. Could anyone help me explain the wires? Thanks
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Old 23rd May 2013, 07:35 AM   #2
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Let's assume, possibly incorrectly, that the black is the centre tap of the seconday. Try measuring the resistance between black and the four other secondary wires. If you post the results we might be able to draw some conclusions.
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Old 23rd May 2013, 09:20 AM   #3
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I think the right side of transformer the primary side.

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Old 23rd May 2013, 09:37 AM   #4
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I took it out myself, and the red wire on the left was directly attached to the power line. The four other lines are for 220, 130, 240 and 110 input.
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Old 23rd May 2013, 09:54 AM   #5
AndrewT is offline AndrewT  Scotland
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You can check the primaries by measuring the resistances of the tappings.
You can check the secondaries by measuring the resistances of the tappings.
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Old 23rd May 2013, 10:01 AM   #6
AJT is offline AJT  Philippines
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your primary windings will have the highest resistance of all the windings...
you can get a small 6.3 volt filament transformer and feed voltages on windings and then monitor voltages on the other windings...
this will give you an idea...
how does it weigh in kgs?...
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Old 23rd May 2013, 02:28 PM   #7
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I now done some meassurements. Just too clear, all the wires was attached to a switch that switched between 220,130,240,110. Now i dont know witch wires too use for 240 volts (EU). How can i figure that out?

Meassurements.

Secondary side:

There is a resistance of 02.0 (200) ohm, between the two grey wires. They seem too connect with nothing else.

Black-Blue: 00.3

Blue-Blue: 00.6

Primary side:

There is resistance between yellow-black and brown.

Black-Brown: 05.2

Black-Yellow: 06.4

Brown-Yellow: 01.0

There is resistance between red and blue.

Red-Blue: 05.2

(The red wire was directly attachted too one of the input wires)
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Old 23rd May 2013, 03:08 PM   #8
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OK so we have the windings. GREY - GREY is one winding. BLUE - BLACK - BLUE is another winding that looks like it's centre tapped. The Left Hand side looks like a multi-voltage primary. As Red - Blue is the same as Black - Brown I would assume that these are 2 x 110V primaries, one of the primaries has extra turns for possibly 240V.

Now we need to sort out the phasing of the windings. Best thing for that is a small transformer outputting a few volts AC.

Let's assume that the Primaries are Black - Yellow and Red - Blue. If you connect Yellow and Red together and connect a small AC voltage across Black and Blue, you should see a small voltage across Grey - Grey. If you get nothing then the primaries are probably in anti-phase. Try connecting Black and Red and the AC voltage across Yellow and Blue, the higher of the two voltages across Grey - Grey will reveal the phase of the primaries.
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Old 23rd May 2013, 03:17 PM   #9
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If you get ridiculously low voltages that don't seem to make any sense, try connecting say 5V AC across Grey to Grey and then measure the voltages across Blue - Blue, Red - Blue and Black Brown.

I'm assuming here that not many transformers these days output less than 5V.

There will then be several known factors.

Vp1, Vp2, Vs1 and Vs2. The ratio between them will NEVER change, that is transformer theory.

If you have put 5V across S1 (Grey - Grey) and measure 50V across P1, we know that Np1/Ns1 = 10.

We can use these figures to determine the voltages that the transformer can provide, this is not exact but it's a safe starting point.
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Old 23rd May 2013, 03:17 PM   #10
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Quote:
Originally Posted by KatieandDad View Post
OK so we have the windings. GREY - GREY is one winding. BLUE - BLACK - BLUE is another winding that looks like it's centre tapped. The Left Hand side looks like a multi-voltage primary. As Red - Blue is the same as Black - Brown I would assume that these are 2 x 110V primaries, one of the primaries has extra turns for possibly 240V.

Now we need to sort out the phasing of the windings. Best thing for that is a small transformer outputting a few volts AC.

Let's assume that the Primaries are Black - Yellow and Red - Blue. If you connect Yellow and Red together and connect a small AC voltage across Black and Blue, you should see a small voltage across Grey - Grey. If you get nothing then the primaries are probably in anti-phase. Try connecting Black and Red and the AC voltage across Yellow and Blue, the higher of the two voltages across Grey - Grey will reveal the phase of the primaries.
Where can you find these kinds of few volts AC transformers. Is there any easy way to test these things?
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