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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 27th May 2014, 2:35 am   #1
audion_1908
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Join Date: Nov 2009
Location: Chertsey, Surrey, UK.
Posts: 246
Default Need info on Igranic midget 3:1 transformer

I have a small audio transformer thanks Bryan M, its a Igranic midget 3 to 1 transformer in parts, that needs rewinding, dose any one have any technical details on the transformer, or advice on rewinding transformer as this will be my first, I do have an untested coil winder!
any one have a precision micrometer that would be happy to measure the wire for me, it very thin! I can post a sample, I am in surrey UK

I plan to use the transformer in my junk box radio

my junk box radio project so far
http://www.vintage-radio.net/forum/s...d.php?t=105235
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Old 27th May 2014, 10:16 am   #2
TrevorG3VLF
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Location: Matlock, Derbyshire, UK.
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Default Re: Need info on Igranic midget 3:1 transformer

I have a micrometer and could measure the wire but you can probably get away without one.
Wind say ten turns around a rod, close spaced, and measure the length of the coil, then using high level mathematics divide by ten.
This should be easy to do with a coil winder.

I am thinking of getting an antique coil winder going so would be pleased to know all the trials and tribulations that you manage to solve.
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Old 27th May 2014, 5:40 pm   #3
Ed_Dinning
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Location: Newcastle upon Tyne, Tyne & Wear, UK.
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Default Re: Need info on Igranic midget 3:1 transformer

Hi, most of these transformers used 48SWG or finer wire. This is difficult to wind and quite expensive. It is possible to cheat and simply fill the smallest bobbin with wire. The largest bobbin should then have 3 times the number of turns (assuming it is a 3:1 ratio transformer. It is not necessary to use tissue paper between layers of wire and it can be random wound, especially if you are using grade2 double enamelled wire. No extra insulation is required between pri and sec if it has separate bobbins. If wound "on top", 2 layers of polyester type 52 tape should be OK at the voltages involved here.

Ed
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Old 27th May 2014, 11:06 pm   #4
John_BS
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Join Date: Dec 2008
Location: Wincanton, Somerset, UK.
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Default Re: Need info on Igranic midget 3:1 transformer

If Ed's right, you'll only have to look at some 48swg wire and it will break!

The problem with measuring very thin wire (especially older stuff) is that
1. the insulation thickness is a substantial fraction of the actual copper diameter, and
2. the insulation thickness is not known to any reasonable tolerance.

If you can extract a meter or so of the wire and carefully measure its resistance, you can determine the diameter from first principles.
(e.g. swg and resistance per meter):

44 3.32
45 4.34
46 5.9
47 8.5
48 13.2
49 23.6
50 34.0

You can see that the change in R is a better measure of fine wire gauge than a mechanical method.

John
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