Trouble with tele bridge pickup

[Jeff Callahan]

Can anyone explain what I may be doing wrong...

I wound two tele bridge pickups with 9200 turns 42 PE, the first came in at 7.5K, the second at 5.5K. I checked to see if the magnets had a short, but found none, I tape them before winding. I rewound the second pup and it came in at 3.5K! Can't figure it out! I used the same tension, and bobbin construction, and wound them 15 minutes apart from each other. What could cause this?

Thanks,
Jeff

[Jeff Callahan]

I move the pickup from my garage (pretty cold) to my house and now reads 7.48K. Go figure, temp alone shouldn't cause this, but something is going on I can't figure out.

Jeff

[copperheadroads]

DC resistance will not vary that much from temperature change
A pickup can short out & still work & it don't always short on the magnet
Too much tension & kinks in the wire can cause shorts

[jason lollar]

heres an article on temp and resistance Lollar Pickups Blog » Blog Archive » Temperature and Guitar Pickup DC Resistance

it shouldnt vary as much as you say you are experiencing but I do get people saying- hey its listed as 6.2 but its 6.6- of course they live in los angeles for example compared to seattle
you are having shorts some how which is not uncommon- at least you know enough to recognise it!

[Joe Gwinn]

The temperature coefficient of resistance of pure copper is 0.00393 per degree centigrade. Room temperature is about +20 C, so let's compare 10 Kohms at 20 C (room temperature) to 0 C (32 F) and to +40 C (104 F).

In both cases, the change is 20 C (36 F), up or down:

(0.00393)(20)(10000)= 786 ohms, so the 10 K will read 10-0.786= 9.214 Kohms at 0C and 10+0.786= 10.786 Kohms at 40 C.

[Jeff Callahan]

Thanks once again for the input, it must be shorting out within the coil (not the magnets), I think it is due to poorly set traverse stops, but I measured them, and they are well within the total height of the coil. Does anyone have a general rule for setting the guides? I usually just set them in a "hair" from the insides of the flatwork (about .030"), and don't get any snags/kinks or for that matter, "pregnant" coils. I also use a tensioner described in Jason's book using felt and a knob from a guitar.

Jeff

[David Schwab]

Maybe it's the magnet wire? Try a different roll and see if it still happens.

[Magnut]

Just a thought. Is it possible your guides could be rubbing a bit of the insulation off the wire?

[Jeff Callahan]

Thanks David, I was hinting at that, but I don't want to beleive it, stuff is expensive! It is a year old spool, can the insulation go bad from humidity or temperature fluctuations (THE ideal guitar building environment!)

Jeff

[Joe Gwinn]

Thanks David, I was hinting at that, but I don't want to believe it, stuff is expensive! It is a year old spool, can the insulation go bad from humidity or temperature fluctuations (THE ideal guitar building environment!)

If the temperature and humidity variations don't kill you, the magnet wire is safe.

If well made - Possum got some cheap wire from some Korean source, and the enamel flaked off during winding.

I'd bet on a winding problem. One way to diagnose the problem is to hand unwind the worst offender, inspecting as you go. Do not cut the wire off the bobbin, unwind it layer by layer.

[David Schwab]

Thanks David, I was hinting at that, but I don't want to beleive it, stuff is expensive! It is a year old spool, can the insulation go bad from humidity or temperature fluctuations (THE ideal guitar building environment!)

I was thinking about Possum's bad roll of wire. I'd try winding one with some poly or formvar without changing your setup and see what happens.

Have you checked the resistance between each magnet and one coil end? Even with tape the wire sometimes gets up between the tape and the flatwork. That used to happen to me.

[jason lollar]

you know what else happens once in a while other than an occasional bad spool of wire or the wire getting piched between the flatwork and magnet is if youve rewound that sucker three or four times and it keeps coming out wierd- if you have the magnets charged before you wind sometimes a little piece of steel will get stuck to one of the magnets- a tiny piece you can hardly see and it keeps cutting the insulation. It can even be under the tape if you tape off your magnets.
Seen it happen a couple times a year so its pretty rare if you keep your shop fairly clean but almost everytime I had to rewind something more than once - that was the problem.

[Jeff Callahan]

Interesting thought Jason, Thanks. You know these pups are the first I've wound with precharged magnets. I've never had this kind of short happen before and I've been winding pretty consistently for almost 2 years. After potting, the pup actually functions, so I'll use it to see how it holds up, just for experiment sake.

Oh yeah, Joe, coastal Northern Califorinia sucks this time of year, rain, rain, rain. I have a "dry closet" to keep the important stuff dry, but space is limited.

Thanks for all the help everyone,
Jeff

[EtLa]

To avoid shorts I wind one layer and then I put nail varnish on the magnet wire that is between the eyelet and the first magnet that wire is touching. Sometime shorts cease after wax potting but I wouldn't sale that pickup.

[big_teee]

Some Rod magnets are rougher than others.
I had some trouble with shorting to the magnets on first layers.
Now I assemble the single coil, sand all the edges of flatwork.
I spray the entire pickup with Krylon Clear Lacquer.
It dries really fast.
I then put one layer of 1/2 inch Scotch brand tape over the magnets.
I haven't had a single issue, since I started this process.
The Krylon Lacquer sure helps to keep the magnets well seated in the flatwork.
Good Luck,
Terry