aluminum bobbins

[Joe Gwinn]

We all know 7 means 7K don't we?

No, we don't, not in a coil that is most likely shorted. A bad enough short could achieve seven ohms. Safest policy is to give the actual resistance.

I must assume that this is the DC resistance. If so, eddy currents cannot be the cause.

Wound several Alum. bobbins : result is the same for all.

Then went and wound a couple dozen plastic bobbins with no such malady occurring.......same as last 10 years............

Exactly how are these aluminum bobbins made? The pressure on the internal turns is very large, and even very slight imperfections in the surface upon which the wire presses (like machining marks) will be forced through the wire insulation, causing a short.

What is the pressure at the bottom? Assume 10,000 turns of #42 wire, wound with a tension of 20 grams. There are 20,000 wires trying to pull the ends of the bobbin together, each wire exerting a force of 20 grams, so the total is (20)(20000)= 400 kilograms, or 880 pounds. This is exerted in an area of 3/16" by 1/4" or so, or 0.0469 square inches, so the pressure is 18,800 pounds per square inch at the bobbin surface. It's easy to generate large pressures when winding thousands of turns.

The other problem with a metallic bobbin is that it will act as a shorted turn, killing the tone. Measurements of DC resistance cannot detect shorted turns, but AC resistance will show a large increase.

If you must use a metallic bobbin, make a radial saw cut (thus opening the shorted turn), so the bobbin makes a large letter C with tips almost touching. Fill the saw kerf with epoxy wetted paper and allow to cure, so the pressure of winding won't be able to force the tips together. Then carefully smooth the inside of the bobbin, put a layer of tape at the bottom, and wind on top of the tape.

If the wire at the bottom comes through a drilled hole, sleeve the wire with thin teflon spaghetthi tubing so the wire won't be cut by the sharp edges of the hole.

[dazzlindino]

If you must use a metallic bobbin, make a radial saw cut (thus opening the shorted turn), so the bobbin makes a large letter C with tips almost touching. Fill the saw kerf with epoxy wetted paper and allow to cure, so the pressure of winding won't be able to force the tips together. Then carefully smooth the inside of the bobbin, put a layer of tape at the bottom, and wind on top of the tape.

If the wire at the bottom comes through a drilled hole, sleeve the wire with thin teflon spaghetthi tubing so the wire won't be cut by the sharp edges of the hole.

These are humbucker bobbins, wire channel is very smooth machined finnish.
So if it notched through at some point that will eliminate eddy currents?
would not the pole pieces in effect make the loop complete even with a notch?
and what if Eddie is my hero?
Thanks, and may the noise engulf you.....

[Joe Gwinn]

These are humbucker bobbins, wire channel is very smooth machined finish.

Smooth is a relative term. Try wet-sanding all the surfaces that the wire will touch.

So if it notched through at some point that will eliminate eddy currents?

Yes, so long as all the circles are broken.

Would not the pole pieces in effect make the loop complete even with a notch?

Yes, if you allow it. That radial cut must break all the webs between the magnets.

It may be better to cut the bobbin in half along the long dimension, cutting all webs in the process, and glue things back together with epoxy-wetted paper separating the halves from one another and from the magnets as well.

and what if Eddie is my hero?

Then you must use gold, not base metals like aluminum.

Thanks, and may the noise engulf you.....

Welcome, but wouldn't music engulfment be preferred?

[Possum]

...

You need to tape wrap the core, metal is alot harder than plastic and you are cramming wire in there under alot of pressure, where it usually shorts out is where the top and bottom flanges meet the vertical core you're winding on, there is a right angle there and its getting crunched in there and shorting out. Winding on bare metal is not a good idea. the reason you can do it on strat bobbins for instance is because of the lacquer dip which leaves (hopefully) a fillet of hard lacquer in those spots that round it off a bit and leave extra insulation there. Tape wrap the core and overlap so the tape also protects a bit of the flange area. Guitar JOnes sells excellent bobbin wrapping tape for this kind of thing. You can use scotch tape but quarter inch width is alot easier to deal with. I've tried all kinds of liquid insulation products on strats and none of them work, wire has always cut through everyone of them except super glue which is a hassle to deal with so I use tape only, it just works, try it....

[dazzlindino]

Smooth is a relative term. Try wet-sanding all the surfaces that the wire will touch.

Yes, so long as all the circles are broken.

Yes, if you allow it. That radial cut must break all the webs between the magnets.

It may be better to cut the bobbin in half along the long dimension, cutting all webs in the process, and glue things back together with epoxy-wetted paper separating the halves from one another and from the magnets as well.

Then you must use gold, not base metals like aluminum.

Welcome, but wouldn't music engulfment be preferred?

One mans music is another mans noise............

[David Schwab]

One mans music is another mans noise............

I can say for certain that hum is not music.... But I do hum along when I don't know the words. So hum is also not language. And I bet it's not dance or architecture either.

And that my friends is the hum-dinger.

[dazzlindino]

I can say for certain that hum is not music.... But I do hum along when I don't know the words. So hum is also not language. And I bet it's not dance or architecture either.

And that my friends is the hum-dinger.

I also spekem da jibberish