Potting

[Paulkstadden]

Epoxy

David, what type of epoxy do you use? Mouser has 44 different types of epoxy!

[David Schwab]

David, what type of epoxy do you use? Mouser has 44 different types of epoxy!

It sure takes forever to locate parts in their catalog!

590-832B-375ML
MG Chemicals Epoxy C
Epoxy Compound

It's black. I didn't see that many epoxys. I think I was specifically looking for potting compound.

I found a bunch of things at Mouser that sure make my life easier.

[David Schwab]

Hehehe....Bruce Springsteen's old Esquire has a hole near the bottom of the body, so that Bruce's sweat can drain right on out.

Wasn't there an XLR jack there? I remember seeing it in an old photo.

[Paulkstadden]

That's excellent! I've been wanting to make an accurate copy of John Birch's Magnum, and now I can use an appropriate epoxy.

[David Schwab]

I'd love to see what the magnet structure is for that pickup. Gibson filed for a patent on the Iommi model, which is based on the Birch Magnum.

A lot of bass pickups are potted in epoxy, such as Bartolini, Q-Tuner, and Lane Poor. I think all three are cast in resin, and don't even use a shell the way EMG does.

I make no claims as to any sonic differences, but I just started potting some, and I have some that are un-potted, so I'll see how they compare.

My motivation is feedback suppression, and to make it real difficult to see inside the pickups! Makes everything nice and solid.

[Joe Gwinn]

The guitar was from Finland. Clint couldn't figure out what was causing the green corrosion all inside the pickup, and it even went past the paper tape and corroded the solder joints. When he melted out the wax it looked like this (see attached photo): [lots of green stuff]. The pickups were sealed and filled with wax.

I've never been in Finland, but I did live for a year in Stockholm, Sweden, across the water from Finland. It is more likely to be very dry than very wet - the climate reminded me of Maine. But I would guess that this pickup has to have been stored in very high humidity.

This [that there are millions of pickups potted with beeswax that nonetheless work] is true.

There are acids, and there are acids. Rosin, used as a flux for soldering electronics (and pickup coils) also contains organic acids, and yet it is safe to leave the rosin on the soldered joint, even with #45 wire. It is the organic acids in rosin that allow it to work as a flux, removing the oxides from copper and tinned surfaces, allowing the solder to wet the now-clean metal surfaces.

That said, perhaps beeswax comes in grades, although I have never heard of such a thing.

There's also many pickups (and other circuits) out there potted in epoxy. I have a Hi-A pickup from 1972 which still works. I use epoxy specially made for encapsulating and potting ... not sure if it's different from "normal" epoxy. I get it from Mouser.

Potting epoxies are thin enough to penetrate the winding, have solvents that won't destroy the wire enamel or bobbin, and don't change size enough to cause undue stresses upon hardening.

The last set of pickups I made I coated the coils with polyurethane after I wound them. I happened to have had a can and thought I'd give it a try.

By "polyurethane", do you mean varnish, as for coating wood? This should work.

[David Schwab]

Potting epoxies are thin enough to penetrate the winding, have solvents that won't destroy the wire enamel or bobbin, and don't change size enough to cause undue stresses upon hardening.

Oh good... It was expensive enough!

By "polyurethane", do you mean varnish, as for coating wood? This should work.

Yes. I had a small can I was using on some wood, and figured I'd give it a try.
Seems to have worked fine.

Regarding the beeswax, the poster on the other forum assumed it was acidic, so I looked it up. But who knows what caused the corrosion. It was off that it went al the way through the wax to the coil. You would think the wax would prevent that kind of thing.

[Paulkstadden]

There's not much info available on the Birch Magnum. I've really tried hard to find out about it, too! John Carling says it uses a Cobalt Steel magnet (only described as "huge"), black epoxy potting, stainless steel covers, and the old ads say it has a 20k ohm resistance and a frequency response of 3,000-8,000 khz. The Gibson Iommi is based on the "Jaydee Special" which is in the bridge position of Iommi's Jaydee SG. Unfortunately, I've heard that John Diggins doesn't remember how he made it! J.T. Riboloff yanked the pickup from the guitar and took every measurement he could in preparation for production of the Gibson Iommi. I used to have a couple of them, really loved the sound they got. Great for hard rock! They, as far as I could tell, were epoxy potted, too. As soon as John Diggins gets the time and the tooling, I will order a P-90 size Magnum. Can't wait to get that into an SG!

As a matter of fact, that's the pickup that made me want to try my hand at winding. I'm still buying every tool I can get that will help me get closer to that goal. Also, since I'm just a newbie, I'm still trying to get as much info as I can before I start winding. Made some electronic stuff before without research first and ended up with hissing, popping, dry jointed garbage. Not doing that again! Thanks for everyone's info and advice, it's been excellent!

Oh, one more thing. If I epoxy pot a pickup, is there any way to take the pickup apart if I'd need to? I've heard that an epoxy potted pickup would be destroyed if it were taken apart.

[Sweetfinger]

It may be a purity issue. No wax is acidic. Or an environment issue: where did this failed pickup live? maybe the problem was ingress of beer.

In any event, there must be millions of pickups potted with beeswax, and very few have failed.

Whenever I see serious corrosion on a pickup, it is usually due to a celluloid pickguard that has deteriorated and outgassed corrosive fumes. Maybe those Malmstrom pups used celluloid bobbins- I couldn't find the thread referred to- but if celluloid went south inside the cover, I'd be surprised if there was anything metal LEFT inside!

[Spence]

Go Green

You should be aware that the RoHS directives may exclude you from selling pickups potted with some compounds.
At my company we've gone green and have developed a high tech replacement for wax and epoxy compounds :

[David Schwab]

Whenever I see serious corrosion on a pickup, it is usually due to a celluloid pickguard that has deteriorated and outgassed corrosive fumes. Maybe those Malmstrom pups used celluloid bobbins- I couldn't find the thread referred to- but if celluloid went south inside the cover, I'd be surprised if there was anything metal LEFT inside!

I don't see how celluloid would cause corrosion on a plated brass cover and wires... celluloid is not much different from nitrocellulose lacquer. You'll notice only the metal parts have been affected.

Here's the bobbins. I don't know what they are made from, but they look intact. Of course I'm just going by the photos. I haven't seen the pickup in person. I'll ask Clint what he thinks the bobbins were made of.

[David Schwab]

The Gibson Iommi is based on the "Jaydee Special" which is in the bridge position of Iommi's Jaydee SG.

Oh that's right... I forgot about the Jaydee. I see the Jaydee has a Birch Magnum copy Diggins made at the neck. The bridge pickups looks quite interesting with dual rails. Those humbuckers are P-90 size!

Oh, one more thing. If I epoxy pot a pickup, is there any way to take the pickup apart if I'd need to?

Nope. Do all your experimenting and testing prior to potting. I don't think epoxy potting the pickup will effect the tone as wax does. I'll let you know.. I'm potting a couple today.

I have disassembled an old broken Lawrence pickup potted in polyester resin. I ended up with a usable magnet and bobbins, but forget about the magnet wire!

Here's a photo of an EMG 81 taken apart.. same outcome.

[David Schwab]

You should be aware that the RoHS directives may exclude you from selling pickups potted with some compounds.
At my company we've gone green and have developed a high tech replacement for wax and epoxy compounds :
:

The epoxy I got from Mouser is RoHS compliant.

http://www.mouser.com/search/refine....590-832B-375ML

However my solder is not! I'll have to cross that bridge when I get there.

What is that in the photo?

[Spence]

The epoxy I got from Mouser is RoHS compliant.

http://www.mouser.com/search/refine....590-832B-375ML

However my solder is not! I'll have to cross that bridge when I get there.

What is that in the photo?

composte, good for potting. It was a joke Dave.

[David Schwab]

composte, good for potting. It was a joke Dave.

Ah! I couldn't tell from the photo... Potting... ha!