1955 P90 muddy - defect insulation?

[rjb]

Micro cracks causing eddy currents? Stupidest thing I have ever heard.

Come on, Mike. Surely you've heard things much dumber than that!

[Fluoroscope 5000]

Before you slice the wire off the bobbin weigh it without screws, unwind to determine the turn per layer and also read the outer diameter of the wire with a micrometer, then take 10 feet of the wire by wrapping around a one foot ruler 5 times and take an ohms reading and divide by 10 to get an ohms per foot. If you want to keep the tone as true to original as possible use the above info for the rewind.

That's an interesting method for determining total wind, etc, and could well prove useful. First, there are experts who measure the C of pickups, but it involves sensitive equipment and the proper technique. I don't know how to do it, myself.

Before you do a rewind, keep in mind that the thickness of the insulation will affect the size of the coil, hence the tone. Gibson probably used Heavy Formvar wire back then, which may be thicker than PE, or poly wire. Not sure what happens with Formvar, but Poly insulation stretches around the corners, increasing capacitance. PE doesn't stretch, but requires a heat treatment process after winding to patch cracks on the edges. You may actually get the best results with PE wire, if you follow proper post wind heating method. There's also the matter of annealing, which makes the wire both more brittle and more consistent. Check into that.

No matter what you do, you wouldn't likely get the same results as the original wind. No two pickups are quite the same, anyway. Now you have a P90 chassis. You're free to experiment. You might want to wind lower for more highs, or use thicker wire for more of a "woody" mid emphasis, or use thinner wire for better clarity and smoother highs. I think 42awg is the standard, but go for whatever whatever appeals to you.

[David Schwab]

I never heard of Gibson using heavy Formvar. Fender sure liked it though.

[Fluoroscope 5000]

The skin depth of copper at 10 KHz is a bit under a mm. #42 wire is something like .05 mm in dia. I do not think skin effect is an issue, period.

How is he going to measure the capacitance? Not going to get an accurate reading with a normal meter.

Micro cracks causing eddy currents? Stupidest thing I have ever heard.

You are offering advice on things you know nothing about. Your advice is best ignored.

You're right about the skin affect not likely being an issue, but if the copper near the surface is much higher resistance than the rest of the wire, there could be significant phase differences in signals traveling closer to the surface, wrong?

Yeah, he won't get an accurate C measurement with a normal meter, but it can be done with the right equipment and technique.

Eddy current shorts from micro-cracks on PE wire insulation are indeed a possible cause of the problem. I am not an engineer, but have done a fair amount of research on the subject over many years. I have also had the privilege of having many discussions with legendary pickup designer Bill Lawrence (a.k.a.Willi Lorenz Stich). He was the one who explained about eddy-currents from micro-cracks. He has a method to pinpoint and measure them, and even taught Abigal Ybarro about the correct wire treatment process to avoid them.

There may be more going on in pickup tech than meets the eye. Please refrain from personal verbal attacks in future, sir.

[JGundry]

No matter what you do, you wouldn't likely get the same results as the original wind. No two pickups are quite the same, anyway. Now you have a P90 chassis. You're free to experiment. You might want to wind lower for more highs, or use thicker wire for more of a "woody" mid emphasis, or use thinner wire for better clarity and smoother highs. I think 42awg is the standard, but go for whatever whatever appeals to you.

It is possible. I have done it but I'm using the same machine and tensioning as Gibson did in the 50's. With the coil the big variables the wire specs, turn per layer count, tension and tension points and wire guide distance from bobbin. I have a good selection of wire to choose from so I can do it. But if you don't have all of these variables worked out you can't really nail it the same way. There is one wild card with a P-90 coil. Gibson used to wrap the pigtail wire around the core of the bobbin and did not tape it to the inside of the bobbin coil former. Gibson only taped the solder joint and sometimes didn't even do that leading to shorted turns that wore on the solder joint. The result with winding is even if the joint was taped there is a large pigtail lead creating quite a bit of randomness to how the wire goes down on the inner 1/3rd or so of the coil.

[copperheadroads]

Be Careful if your going to rewind it yourself ,Those old 50's styrene bobbins are prone to self destruct when rewound ......Keep the superglue handy

[Fluoroscope 5000]

I don't know a lot of the history of this stuff, just speculating. If they used PE, that would more likely indicate a problem, since proper post winding heating technique may have not been used. Isn't it likely that the lacquer used in PE might break down over 50 years? I'd think so.

[JGundry]

I don't know a lot of the history of this stuff, just speculating. If they used PE, that would more likely indicate a problem, since proper post winding heating technique may have not been used. Isn't it likely that the lacquer used in PE might break down over 50 years? I'd think so.

In a P-90 bobbin the wire is pretty well encapsulated and unless the bobbin is cracked, which often happens, the wire will look new.

What would be the proper post winding heating technique for PE?

[Fluoroscope 5000]

The lacquer might look relatively new, but I'd wonder what kinds of chemical changes take place that might affect it's insulating properties, or even cause corrosive interaction with the copper? I honestly don't know, but it bears some research.

Proper PE wire post-wind treatment involves heating to 256 F within a few hours of winding. It must be at least that temp, but not too high to melt the lacquer. It was apparently in the original instructions with the wire and was a commonly employed practice by Fender that may well have been compromised as a cost cutting measure during the CBS era. Enamel is actually an incorrect term to use. Enamel is very brittle and can't be used as wire insulation. PE is a lacquer.

[Steve Conner]

I think the most likely explanation is just plain shorted turns. Never heard of "micro-cracks" either.

Nor did I ever hear of baking plain enamel wire at "256" (256 what?) Maybe it was done in old transformers and motors, but I thought that was to speed up drying of the varnish they were commonly dipped in, and drive any remaining moisture out of the kraft paper used as inter-layer insulation. I think the heat might be too much for plastic pickup bobbins.

[Mike Sulzer]

You're right about the skin affect not likely being an issue, but if the copper near the surface is much higher resistance than the rest of the wire, there could be significant phase differences in signals traveling closer to the surface, wrong?

Different phases across the cross section of the wire imply fields to support them. Show me that these fields can exist.

Yeah, he won't get an accurate C measurement with a normal meter, but it can be done with the right equipment and technique.

Of course it is possible to measure the capacitance of a pickup, but most people cannot.

Eddy current shorts from micro-cracks on PE wire insulation are indeed a possible cause of the problem...

How does the law of magnetic induction (the cause of eddy currents) interact with micro cracks in insulation? If you cannot explain that, then you have nothing to discuss.

There may be more going on in pickup tech than meets the eye. Please refrain from personal verbal attacks in future, sir.

I have not made a personal attack on you. I am stating the facts, and drawing the conclusion that your advice should be ignored. Did we have a verbal conversation? In your imagination, perhaps.

[Fluoroscope 5000]

I don't know why I originally referred to them as micro-cracks. It's just cracks in the insulation at the bobbin ends. It's one possible cause of frequency loss. That's why I mentioned it, and to encourage proper procedure for PE wire. I meant to write 256 F/125 C. Bill Lawrence told me about the issue and the heating process. He knew Leo Fender back in the 60's, and was chief engineer at Gibson in the 70's. Abigal Ybarro told him that Fender changed/discarded the process when they started using plastic bobbins. It is too hot for the plastic. Don't know when they started using poly wire, but it's not required for that.

[Fluoroscope 5000]

Obviously, we didn't have a verbal exchange. Not sure why I added that word. I think I may have been flustered by the hostile nature of your remarks, and I posted in haste. No, I'm not a delusional paranoid...nor a vindictive dick. Fair enough? Making a blanket statement that someone doesn't know what they are talking about, and that their comments should be ignored appears as a thinly-vialed attack on someone's character. I don't really give a hoot what you think of me, but I do wish you would refrain from making such comments in future...like the last insinuation you made. It's just unnecessarily inflammatory, and disconcerting to see when I'm trying to offer real world possible explanations for a problem.

Moving on -- maybe surface corrosion has no effect on phase. I don't know. If you want to find out more about that, and how insulation cracks can cause eddy currents, call Bill Lawrence and ask for an explanation. I don't know enough to prove it one way, or another. He has tested many vintage pickups and found the evidence. He even has a proprietary method for pinpointing them.

[David Schwab]

Maybe it was done in old transformers and motors, but I thought that was to speed up drying of the varnish they were commonly dipped in, and drive any remaining moisture out of the kraft paper used as inter-layer insulation. I think the heat might be too much for plastic pickup bobbins.

Yes, and yes. Bobbins start to deform at fairly low temperatures.

[David Schwab]

call Bill Lawrence and ask for an explanation. I don't know enough to prove it one way, or another. He has tested many vintage pickups and found the evidence. He even has a proprietary method for pinpointing them.

Yes, Bill has a method for finding shorts in the coil. And that's what we are talking about here. Cracks in the insulation can lead to shorts, since the wire is exposed at those spots, and most likely where the wire stretches at the ends of the bobbin.

But that has nothing to do with phase cancellation or eddy currents. A closed loop around the coil will cause issues due to eddy currents though. Maybe that's what you are thinking of?