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Old 17th Sep 2021, 4:45 pm   #1
vinrads
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Default Sterling Primax loudspeaker

I am rewinding the coils on this speaker , looking for some info regarding turns, I have done one half up to 3.45k ohms not sure what the resistance was ,it's (26) fig 842 in Radio/Radio Thanks Mick.




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Old 18th Sep 2021, 7:33 am   #2
crackle
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Default Re: Sterling Primax loudspeaker

The best you can do is to unwind the turns and count as you go. Be prepared for lots of breaks where greenspot has corroded through the wire.
If they are in distinct layers then note down the turns in each layer. If you can count the layers then you can work out the total number of turns.
This is how I rebuilt an energising coil for a loudspeaker.
If it is a solid lump of pitch and wire and you cant unwind it. An alternative maybe measure the diameter of the wire and work out how many turns per layer. Then work out how many layers in the height of the coil.
I worked out the average diameter of the coil and used that to gain an estimation of the average length per turn. i then had a very rough idea of how much wire to order and the approximate resistance.
There is probably a better mathematical way of working out the average length of a turn.
Mike
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Old 18th Sep 2021, 8:58 am   #3
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Default Re: Sterling Primax loudspeaker

Some wire gauge tables gave the number of turns which could be fitted into a given cross-sectional area of winding. If done as a layered winding with paper between the layers, the number would be somewhat less.

In the past I've re-wound solenoids from this data, just picking the appropriate gauge and filling the bobbin did the trick.

David

Note that for fill calculations, the varnish thickness gets in on the act, especially for very fine wires. Fill is set by the overall outside diameter, while wire gauges are rated by the copper diameter.
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