Doping (protecting) coil tails

[Sheldon Dingwall]

Looking at Bruce's excellent pickup process sparked another area that's not talked about a lot. On pickup styles where there is a fixed solder point - eyelets, solder pads, buss wire etc. one of the weak links is the exposed magnet wire between the coil and the solder point. Bruce is using PVA glue to coat and protect them which I'd never thought of. We've tested and used latex contact cement, nail polish, CA glue. I think potting with epoxy makes protecting these wires even more critical due to thermal tension caused by the epoxy. We've recently switched to a polyurethane specifically formulated for potting.

I'd like to hear from anyone who's found a bullet proof method of protecting these wires from either the elements or epoxy.

[David Schwab]

First, you need to use epoxy made for potting. I use MG Chemicals potting epoxy, and it's nylon filled. Because of that it doesn't shrink. It also takes 24 hours to set, unless you heat it up. That further helps because it doesn't get very hot.

If you are using fast set polyurethane, I would worry more about that! I had some very bad experiences with that stuff.

On the couple of pickups I make that use eyelets and get epoxy encapsulated, I don't do anything special to the wires leading to the eyelets. Haven't had any failures yet.

But probably not a bad idea to cover the wires with something. 5 minute epoxy maybe?

[Bruce Johnson]

Yep, my engineer brain says that's the most critical potential failure point inside a pickup: that little junction where the end of the magnet wire is soldered to a hard point. The soldering makes the wire a little more brittle at that point, and any small movement between the main bulk of the coil and the hard point could snap the wire.

So, I've done several things to minimize the problem.

The first is my technique of building terminals into my bobbins. My terminals are made from short lengths of buss wire (uninsulated tinned coppper) fitted into holes in the bobbin's casting. They are mechanically solid to the bobbin, and are made in a U-shape. The magnet wire solders to one end of the U, and the leadout wire solders to the other end of the U. That's so that the two are physically isolated. If someone yanks on the lead wire, the deflection won't get transmitted to the other end of the U. So, hopefully, the magnet wire solder joint is protected from breakage. I haven't tried it, but I think that you could yank on the lead wire hard enough to break it, without breaking the terminal or breaking the magnet wire.

That's why I've never liked the little eyelets that are crimped into the bobbin flange. If you solder the magnet wire to the eyelet, and then solder the lead wire to the eyelet, you are linking the two wires together, and depending on the mechanical joint between the eyelet and the bobbin material. But how good is that? How tight is the eyelet in hole? How tight is the crimp of the flanges against the material? If you pull on the lead wire, and the eyelet deflects at all within the flange, then you are pulling directly on the magnet wire. Worse yet, if you pull sideways on the lead wire or rotate it in any way, and the eyelet turns a tiny bit within its hole, then you are also pulling directly on the magnet wire. There's not much keeping the eyelet from turning.

That brings up the second precaution that I take: I always leave a small amount of slack in the magnet wire as it attaches to the terminal. I never want the magnet wire to be tight between the point where it comes out of a hole in the side of the bobbin, to where it winds around the terminal. I make sure that it has a small C or S bend. The way I do it is to hand wrap the end of the magnet wire 5-10 turns around the terminal, but starting the wrapping up maybe 1/16" above the surface of the bobbin flange. Then I use a fingernail to push the wraps down against the flange, which takes the tension out of the short length of exposed magnet wire, and leaves it laying on the surface in an S-bend.

If you are using eyelets, I recommend that you do something like this. Leave a small amount of slack between the point where the wire leaves your potting, and where it goes on to the eyelet. Don't stretch the wire tight. That's asking for a failure, if anything moves.

The third thing I do to protect that exposed bit of magnet wire is to encapsulate it in some soft, rubbery glue. After it's soldered and tested, I put a blob of glue over the area, covering the terminal (the short end only), the exposed bit of magnet wire, and the hole in the bobbin that the wire comes out of. The purpose of doing this is to encapsulate the whole area in a material that has some cushion and give. I don't want to surround that delicate area with the hard West Systems epoxy that I use for encapsulating my pickups. (Note: this is not the same epoxy that I use for potting the coils. The West Systems is for the final outer shell) I want the delicate area to be surrounded by the soft material, which is within the hard outer shell. For the soft stuff, I've tried a few different glues including Titebond, the LMI glue, and plastic cement. These days I'm using Liquid Insulation that I bought at Home Depot. It's a black, rubbery PVA-based stuff that you paint on electrical connections to insulate them. All of these things seem to work okay. I haven't yet had a pickup fail after it's been encapsulated and finished.

So, is all this extra thought and care worthwhile, or merely a sign of creeping insanity? You be the judge. I don't want my pickups to ever fail in 50 or 100 years. My basses are designed specifically for these pickups and vice versa. So, if the pickup fails 50 years from now, there will be nothing that can easily replace it. I don't want my bass to get trashed because of some little magnet wire breaking down deep in the epoxy.

This is exactly what's happening now with the Ampeg AMB-1 Scroll Basses, made in 1967-68. The pickups are failing on many of them, due to internal breakage of the magnet wire terminations, deep down inside a pickup that's permanently encapsulated in epoxy. And it's a special design/shape pickup. So, many of these instruments are getting trashed or badly modified. I don't want that to happen to my basses.

So, I'm not completely, totally crazy. Only partly.

Edit:

Per David's comment above, I want to make sure that readers aren't getting confused. There are two different types of "potting", although they are both technically called Potting. One is the saturation of the wound coil, which most of you do in wax. I happen to do that potting in a special water-thin epoxy called CPES, which I've talked about on other threads.

The other "potting", which David talks about above (and I'm calling Encapsulation) is where you dunk the finished (and previously potted) coil in a harder material to make a permanent shell around it. For that, I'm using West Systems epoxy, and he's recommending some other similar types of materials. I like the West Systems, because I'm familiar with it, and I use it throughout my instruments for all kinds of things. I use the 105 resin with the 206 Slow Hardener. In that mix, it takes about 12 hours to cure, and doesn't seem to generate any heat. I can't feel any warming in the mold or the pickup. I also haven't seen any measurable shrinkage with the Slow mix. The 205 Fast Hardener mix will heat up and shrink. Don't use that for any casting process.

Neither of us are recommending using these hard epoxies in place of the wax (or CPES) potting of the coils! That won't work.

[David King]

I guess I'd always rather see something reversible like rubber cement or hot glue to tack the wires down.

[David Schwab]

I guess I'd always rather see something reversible like rubber cement or hot glue to tack the wires down.

Hot glue is good. I use that for lots of stuff. I even found black glue sticks.

It doesn't matter if the pickup is going to be encapsulated.

[big_teee]

Hot glue is good. I use that for lots of stuff. I even found black glue sticks.

It doesn't matter if the pickup is going to be encapsulated.

I don't have any problems with how most are made, If I am the one that installs them.
Some of these so called Yayhoo guitar pickup installers, can tear up a Cannon Ball with a Feather.
I have rewound several strat, and tele coils that were strictly Installation, "Oooops" !

[Chris Turner]

Lately I've been using hot glue to cover the wire from the coil to the eyelet on the little single string coils I'm fooling around with.

[David Schwab]

I don't have any problems with how most are made, If I am the one that installs them.
Some of these so called Yayhoo guitar pickup installers, can tear up a Cannon Ball with a Feather.
I have rewound several strat, and tele coils that were strictly Installation, "Oooops" !

Well now you see one benefit of a closed cover and epoxy encapsulated pickup. It's fairly bullet proof.

[big_teee]

Well now you see one benefit of a closed cover and epoxy encapsulated pickup. It's fairly bullet proof.

Yes, but we don't get to make any money rewinding your pickups, if they can't be tore up!
Where's the fun in that. lol

[Bruce Johnson]

That's one of those tradeoffs that you have to consider in any product that you design and manufacture: Should you concentrate on making your product bulletproof, so it never fails? Or do you assume that it will fail and concentrate on making it easy to repair? Or make it so cheap that it's a throw away when it fails? It all depends on what part of the market you are selling your product in (high end or cheapo) and how long you expect your product to be used by the original buyer.

For me, I do a lot of things all over my basses to make them easy to repair over the long years. But with the pickups, I take the approach of making them bulletproof and unrepairable. They should never fail unless you beat them with a large hammer or put a torch to them.

Seeing all of the pickup failures happening on instruments from the '60's and '70's, is an indication that manufacturers in those days didn't put much effort into the design of their instruments, to make them last a long time. They honestly expected their guitars to last 20 years at most. And here we are, still messing around with them 45 years later. And a small industry has grown up just to repair their poorly-made pickups! Not to mention paint....And poorly selected wood....And cheap plating.....and crummy hardware. Some of the cheapest instruments built today are higher quality than the expensive ones of the '60's. And they'll probably last longer.

[David Schwab]

Yes, but we don't get to make any money rewinding your pickups, if they can't be tore up!
Where's the fun in that. lol

I make money making the pickups. I don't have to rewind them. I still make money rewinding other pickups though.

[ScottA]

Well now you see one benefit of a closed cover and epoxy encapsulated pickup. It's fairly bullet proof.

I recently had a shipment of pickups returned that looked like they were (literally) run over by a truck.

Everyone of them still worked.

[RedHouse]

Seems a bit of "over-thinking" going on (wouldn't be the first time right?) .

Pickups with eyelets in the flatwork are easy, just don't pull the wire tight before soldering them into the eylets, leave a little slack, then pot them briefly, the wax will hold the wire still, the slack will not allow flatwork flexing to cause breakage, easy peasy, no epoxy necessary.
(who would epoxy pot a Fender style pickup anyway?... cough, cough, Lindy, cough cough, Bill...)

YMMV

[Bruce Johnson]

Am I over-thinking? Look at how many Fender pickups, more than 25 years old, are failing these days. Enough to support a small industry of rewinders. I wonder what the numbers are: of all the Fender pickups made, what percentage of them are still working after 25 years? How many 25 year old Fender guitars still have the original pickups in them? Any repair guy will tell you that a big part of their business is old guitars with dead pickups.

They used Forbon, eyelets, and wax. And a lot of their pickups are failing. So, ask yourself: Are you doing anything better than what Fender did in the '60's? Is your design/process higher quality than theirs? Will your pickups last longer than the original Fenders? Do you care? I'm not trying to start an argument, but I think that these are real things to consider.

Are you willing to stake your legacy on 25 year old dried wax? That just sounds gross....

[RedHouse]

Am I over-thinking? Look at how many Fender pickups, more than 25 years old, are failing these days. Enough to support a small industry of rewinders. I wonder what the numbers are: of all the Fender pickups made, what percentage of them are still working after 25 years? How many 25 year old Fender guitars still have the original pickups in them? Any repair guy will tell you that a big part of their business is old guitars with dead pickups.

They used Forbon, eyelets, and wax. And a lot of their pickups are failing. So, ask yourself: Are you doing anything better than what Fender did in the '60's? Is your design/process higher quality than theirs? Will your pickups last longer than the original Fenders? Do you care? I'm not trying to start an argument, but I think that these are real things to consider.

Are you willing to stake your legacy on 25 year old dried wax? That just sounds gross....

Well theres no doubt you have a great thinker on your shoulders Bruce, but what I meant to say (or should have said) was IMHO hard-potting isn't always "the best solution".

Most Fender coils that need repair are not due to the lead wire interface failing, but 99% of the time it's the magnet-vs-wire corrosion/interaction causing shorts or breaks. If one cuts the wire off a dead Fender coil one still has leads connected to the eyelets and I've tested that connection so many times and (so far) have always found it sound.

The other most common thing is the start wire tends to break (because it has no slack as I described) but not at the eyelet.

I totally agree about improving assembly techniques on my own stuff though. I'm guilty of this myself, case in point is my Rick pickups, I just hate the crappy way they do the lead-wire hookup and had to change that in my pickups:

RIC -vs- Classic Amplification

When it comes to Fender type coils and buckers for that matter, most "guitar players" want legacy things and don't embrace new/better things so much or as readily as bass players.

I have no legacy, I'm just a small-fry in the big picture.

BTW, I'll be PM'ing you soon asking you to look at a couple parts I need fab'd on your mill/lathe setup if you're not too busy.