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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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17th Sep 2021, 4:45 pm | #1 |
Dekatron
Join Date: Feb 2009
Location: Chesterfield, Derbyshire, UK.
Posts: 3,738
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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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18th Sep 2021, 7:33 am | #2 |
Rest in Peace
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
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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 |
18th Sep 2021, 8:58 am | #3 |
Moderator
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,803
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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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