Using a vacuum to pot your coils?

[voodoochild]

Polyurethane would be ideal I guess but you would be creating a big mess. I can't imagine how difficult it would be to clean and not to mention the fumes. Wow!!!. I'll stick with the old wax myself. Especially if I ever need to rewind one for whatever reason.

[jonson]

not polyurethane foam but polyurethane glue. Same stuff but liquid pourable form and still sets like foam. Issue here maybe is it sets very quick and uses moisture in the air to help speed the cure so could cause more problems again.

[dpm]

Myself, I'm after a thorough potting of the coil, preferably without murdering the sound of it in the process. My guitars are often used in high gain applications and nothing bugs me (or my customers) more than squealing pickups.

So maybe shellac isn't the answer, but I'm certainly interested in whatever options are available. Wouldn't anyhthing that expands, such as polyurethane, have potential to damage the coil?

The dialectric constant of a Die-Thane, a specific polyurethane potting compound, ranges from 7.58-9.25 at 75 degrees F.

[David Schwab]

I would stay away from using anything that draws moisture. Your coil would surely break down over time. Why do you think most vintage Fender pickups need rewinding? They used lacquer, which by the way is much more effective than shellac and they all had moister related issues. Just wondering thats all.

Two things here... I always assumed Fender used lacquer, but I just read recently that they stopped using lacquer altogether in the 60's. That includes as a guitar finish also. They switched to some type of poly finish, and I recently read they used something other than lacquer on the pickups. I have no idea if that's correct though.

The old Tele pickups were potted with wax mixed with lampblack (which contains carbon!).

Rickenbacker also use something like lacquer on the bridge pickup of the 4001 bass. It might have been conversion varnish, which is what they use for their finish. I have two of those from 1973 and they didn't stop working because of the lacquer.

The real reason Fender pickups often die is from the inner windings corroding from contact with the magnets. I say tape off the magnets first. This doesn't happen to Gibson pickups, or the newer molded Fender bobbins because the wire doesn't touch the magnets.

I don't see where lacquer would have a problem with moisture absorption. If it did, your guitar's finish would get soft and cloudy. Lacquer doesn't draw moisture.

I don't use wax for any other reason than I don't use wax. So I have no direct knowledge as to the effect it has on the tone, other than reading reports by people who say it does. Than others say it doesn't.

So since I hadn't had a wax potting setup already, I didn't bother to put one together. I don't pot the Gibson style humbuckers I've made, because originally they weren't potted. I can see where this would be a problem in high volume situations.

The pickups in my personal basses aren't potted ether, but I do use epoxy on the ones I've sold. I'd use it on my basses, but I'm often taking the pickups apart. I have been brushing polyurethane on my coils lately because I had a can laying around.

I've seen pictures of the insides of an EMG 85, and they used both wax and epoxy!

So.. I guess the answer is give it a try and see what you get. We have a vacuum chamber used for casting with rubber molds. I'm going to be casting my pickups in epoxy in the vacuum chamber, so that will also pot them at the same time.

[David Schwab]

So what would you recommend other than wax Dave? If feedback is an issue then something is needed to pot the coil. Anyone tried expanding polyurathane foam?

I got those numbers from this list Dielectric Constants Chart

I've been using an epoxy potting compound, but that's not an easy thing to do with pickups not sealed in a cover.

The old Bill Lawrence pickups were potted in clear polyester resin. (POLYESTER RESIN (RIDGID CAST ) 2.8 - 4.1). I always wondered why he used that instead of epoxy, but maybe he thought it sounded better?

And maybe it doesn't matter. As I said, I haven't even used wax, so I have no experience with it. I have been using clear Minwax fast drying polyurethane finish to solidify my coils before potting them in epoxy.

Neither has changed the tone from when I tested them unpotted... or at least I didn't hear an undesirable change. But my pickups aren't a good guide here.

[dpm]

I'd be concerned about the thinners in lacquer dissolving the insulation of the windings. Drying it would likely take a lot longer than shellac.

Anyways, personally I've decided to stick with wax for the urgent stuff and experiment a little with shellac some time down the line. Maybe wind a heavy coil, let it dry a while, then cut it in half to see just how dry it is in there.

[David Schwab]

I'd be concerned about the thinners in lacquer dissolving the insulation of the windings. Drying it would likely take a lot longer than shellac.

There are solvents in lacquer, but unless you add thinner, you wont have any. I suppose it's the same as the solvents (mixture of naphtha, xylene, toluene, and ketones, including acetone), but I'm not sure. The insulation on the wire is not lacquer, so it shouldn't dissolve it. For example, PE is a backed on long oil varnish, and that dissolves in alcohol, but not lacquer thinner.

Lacquer dries very quickly unless you have a thick coat. And even then, it's dry, but not very hard.

I wouldn't use lacquer for potting.

I opened a broken Lawrence pickup that was potted with polyester resin. The resin was still tacky in a few places. The pickup was about 25 years old, and until I cracked the case off, the resin didn't fully cure!

Didn't harm the tone of the pickup though. The pickup was broken because the pickup lead had developed a break in it, and since it was potted, it wasn't fixable. The older EMG pickup are made that way too.

[dpm]

I wouldn't use lacquer for potting.

Agreed.

I've dealt with nitrocellulose quite a bit and the initial cure if fairly quick but it takes weeks to harden properly even when used as a surface coating. I can't see it penetrating a coil without being thinned somewhat.

I think what we've established is that anything that cures by solvent release probably isn't great for potting, though shellac might be OK because it's so quick. That leaves temperature cure (wax), or chemical reaction (epoxy), or 'other'. What are the possibilities for 'other'?

David what's the viscosity of the epoxy you use?

[Satamax]

Huh, guys, chemicaly Epoxy is a wax I was thinking, what do they use on motor windings? I know that they bake the motors. Looks like something in the phenolic family i think.

[Joe Gwinn]

Myself, I'm after a thorough potting of the coil, preferably without murdering the sound of it in the process. My guitars are often used in high gain applications and nothing bugs me (or my customers) more than squealing pickups.

So maybe shellac isn't the answer, but I'm certainly interested in whatever options are available. Wouldn't anything that expands, such as polyurethane, have potential to damage the coil?

The dielectric constant of a Die-Thane, a specific polyurethane potting compound, ranges from 7.58-9.25 at 75 degrees F.

For potting a fine-wire coil, two-component urethane varnish may be better. These varnishes are usually used for conformal coating of circuit boards, but they make dandy wood finishes too. They are very thin, and so with some vacuum should be able to fully penetrate the winding. Being two-part, the cure is catalytic, and does not depend on solvent evaporation, which will take weeks for the core to fully dry.

[Zhangliqun]

The real reason Fender pickups often die is from the inner windings corroding from contact with the magnets. I say tape off the magnets first. This doesn't happen to Gibson pickups, or the newer molded Fender bobbins because the wire doesn't touch the magnets.

I tape them off because I suspect you're right about that.

I don't use wax for any other reason than I don't use wax. So I have no direct knowledge as to the effect it has on the tone, other than reading reports by people who say it does. Than others say it doesn't.

In my experience, it really depends on how thick and how long. Keep it under 10 minutes and keep the parafin to beeswax ratio down to 3:1 or even a bit lower and the effect on tone is zero to negligible -- certainly FAR FAR less than the effect of the average Tele or humbucker cover. (The first time I potted a pickup it was a killer Tele bridge but I left it in the pot for a half-hour and the tone was like 10 blankets over the amp.)

So I think I'll stick with wax over lacquer.

[David Schwab]

Huh, guys, chemicaly Epoxy is a wax

How so? Epoxy (polyepoxide) resins are produced from a reaction between epichlorohydrin and bisphenol-A.

(From Wikipedia):

Epichlorohydrin is manufactured from propylene through the intermediacy of allyl chloride.

Bisphenol A is a chemical compound containing two phenol functional groups. It belongs to the phenol class of aromatic organic compounds. It is prepared by the reaction of two equivalents of phenol with one equivalent of acetone.

On the other hand, paraffin wax is made of long-chain alkane hydrocarbons, and the main components of beeswax are palmitate, palmitoleate, hydroxypalmitate[1] and oleate esters of long-chain (30-32 carbons) aliphatic alcohols, with the ratio of triacontanylpalmitate CH3(CH2)29O-CO-(CH2)14CH3 to cerotic acid[2] CH3(CH2)24COOH, the two principal components, being 6:1.

So epoxy is not a wax, and in fact will not stick to paraffin wax. But they are all derived from organic compounds.

I was thinking, what do they use on motor windings? I know that they bake the motors. Looks like something in the phenolic family i think.

Probably some kind of enamel or varnish. It's magnet wire after all.... just a heavy gauge.

[David Schwab]

David what's the viscosity of the epoxy you use?

It's epoxy specifically made for potting. It's MG Chemicals 832B Black Epoxy Encapsulating and Potting Compound.

It's a bit like thick syrup. Not stiff like the stuff in the two part tubes. Maybe like warm honey.

[dpm]

So a mixed viscosity of 3300cps = thick syrup/warm honey. Interesting.

I was looking at some epoxies online, the ones intended for potting LEDs go as thin as 250cps. Trying to get a mental picture of what the values flow like in real life.

http://www.epoxies.com/potting.htm

[David Schwab]

Now that I have access to a vacuum chamber, I'm going to start potting them under vacuum to get the bubbles out. The stuff took 24 hours to set, and another 24 to not be tacky, so I think it had to have seeped in by then.