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Old 3rd Jul 2017, 12:23 pm   #1
ThePillenwerfer
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Question Induction Coil Winding Details.

As some Members may know, I recently did-up an ATM T3903 telephone and had to change it's induction coil.

I'm now wondering about the possibility of rewinding the original as a GPO No 27. The DC resistances and number of turns are given on N Diagrams but not the gauge of the wire used or the order in which they are wound onto the former. Does anybody have this information? Am I mad to even be thinking about it?

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Joe
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Old 3rd Jul 2017, 2:25 pm   #2
russell_w_b
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Default Re: Induction Coil Winding Details.

Quote:
Originally Posted by ThePillenwerfer View Post
Am I mad to even be thinking about it?
Does it have the 30 Ohm non-inductive resistor winding on it?

Go for it! I successfully rewound a multi-tap autotransformer from a Beethoven shot-firing exploder and it works fine. You'll need a micrometer to gauge the wire diameter, translate it to SWG (if you don't already know it) and source something the same, or similar, and a winding machine with turns counter would be more than a 'nice-to-have'.

I have a Cam-Metric Wheatstone Bridge and I salvaged as long a length of intact wire as I could from the damaged transformer and found the Ohms / metre, using this figure as a check against physical diameter when finding out the SWG.

There're plenty companies out ther who will sell you the correct size wire.
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Old 3rd Jul 2017, 4:55 pm   #3
TrevorG3VLF
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Default Re: Induction Coil Winding Details.

You can estimate the wire diameter from the number of turns and the area and a guess at the packing density.
I do not know what your component does but I doubt if it is critical

I have an old AVO coil winder here with the traverse not working. You are welcome to use it. I am not too far from Sheffield and one chap comes here from Sheffield to test valves, he travels by bus to Matlock or Buxton, then on the Transpeak bus to Whatstandwell.
I have wound a solenoid with 30,000 turns for a slave clock. It is handy to have a turns counter if you do not wish to go to sleep.
The AVO is made of cast iron and is far too heavy to transport.

Edit: Look up Ludens transformer for good advice. wire diameters and packing density.

Last edited by TrevorG3VLF; 3rd Jul 2017 at 5:00 pm.
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Old 3rd Jul 2017, 5:20 pm   #4
ThePillenwerfer
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Default Re: Induction Coil Winding Details.

Thanks for reading this, Trevor. I've got micrometers, both a metric and a proper one, but don't have a coil I'm willing to wreck to measure its wire and examine its construction. I was hoping that somebody may have this information as other Members have larger collections of literature and experience than do I. As for the non-inductive resistances I was assuming, maybe erroneously, that these could be formed from normal fixed resistors; I doubt that the difference between the specified 30Ω and the nearest preferred value of 33Ω would make any odds.

Thanks for the offer, Trevor. I think it would be possible to wind by hand though. Besides that buying a coil would cost less than the travelling expenses; of course the cost of new wire may also scupper the whole idea in any case.

I attach a details from an N Diagram.
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Old 3rd Jul 2017, 11:36 pm   #5
AC/HL
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Default Re: Induction Coil Winding Details.

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Old 3rd Jul 2017, 11:37 pm   #6
PJL
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Default Re: Induction Coil Winding Details.

It would be possible to calculate the wire gauge by estimating the average length in a turn but the gauge may not be consistent as 2600T=35 but 1800T=75. This might be due to the 1800T being wound over the 2600T but we also don't know the size or location of the resistors. You must also consider the core which will affect the inductance but also the risk of saturation from the DC current. It would end up being an R&D project.
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