The elusive Mosrite pickup...

[epizootics]

Hey guys,

My bandmate asked me to wind him a couple of Mosrite single coils to fit onto the Frankenstein strat I built for him. I told him, "yeah, sure, they can't be that complicated to make", then realized there was very little technical data on the internet. I dug into the depth of this board but didn't find anything either.

I know there are a few types of Mosrite pickups out there, but from what I gathered, he wants the classic single-coils that are wound to around 10-11K with Phillips-style pole screws. Here's what I know so far:

-they use a thick wooden bobbin core, much bigger than the bobbin spacer found on p90s
-AWG 43 wire
-there seems to be a layer of insulating foil between the bobbin and the magnets for shielding
-the screws are fitted onto nuts that act as the magnet spacers (does this mean the bobbin core itself is not tapped?)
-the bottom of the pickup is covered with foam, on top of which lays the height adjustment metal mounting bar, both of which are drowned in epoxy, which seals the pickup inside its cover forever and keeps things from moving around too much.

Does any of you guys have anything more accurate than my Mr. Obvious observations? The bobbin does look like a P90 bobbin from afar but I can't be sure, having never seen one of those in the flesh.

[MWaldorf]

Construction definitely follows the P90 format overall. I don't think the insulating foil is part of the original Mosrite design. Here's some info on bobbin dimensions from mosriteforum.com. Given that the original style magnets with snap-to-length corregation are pretty much impossible to find, you're never going to have it "exact", but there are a few builders making Mosrite style pickups with modern parts that sound great.

Good luck! Mel

66 Ventures bass bobbin:
height: 11.5mm
width: 10.5mm
length: 55mm
This may differ a little as the bobbin is crudely handmade. 10,000 turns of AWG43 will result in around 10kOhms – so I'd put 11,000–12,000 turns on the bridge PU and a little less on the neck PU.

[MWaldorf]

Another note - Mosrite pickup construction varied. Tym Guitars has a good example of a Mosrite pickup from the early 70s where the coil was wound separately from the maple core, and the parts were just glued into the cover.

https://tymguitars.com.au/blogs/blog...2-mosrite-mk-i

[epizootics]

Oh my, this is amazing! Thanks a lot Mel (I assume you're the same Mr. Waldorf from the SurfGuitar101 board? I used to hang there although I never posted much). Tym Guitar's pictures are great, this one has to be the crudest bobbin I have ever seen!

They do make a point though. The one big difference in design between P90s and Mosrites is that the coil seems to be further away from the core in the latter, be it because of the large maple spacer or that incredible sausage coil in the pictures. Wouldn't moving the coil away from the core decrease the impact of the metal pole pieces on the pickup's response? I always found the 'Mosrite sound' pretty bright for pickups wound this hot...

[MWaldorf]

Epizootics, yes, the same guy. Also the webadmin for MosriteForum.com so I guess you could say I like Mosrites.

You're probably right about the coil shape, but given the wide range of manufacturing techniques used by Mosrite, there's not a specific coil diameter that makes the sound.

Interestingly, I've found Mosrite pickups to be relatively mid heavy compared to hot pickups like Dynasonics where the poles are magnets. This mid heavy character is what I like about Mosrite pickups - you can turn up the treble and presence on the amp to get bright attack on the low strings without ice-pick brightness on the high strings.

Not sure if you've seen my demo of M3's Mosrite style pickups from five years ago on youtube. Talking first, actual playing begins around 1:45
https://www.youtube.com/watch?v=Nmoo...ature=youtu.be

The M3 pickups are tapped for roughly 7K/12K output, and you can hear how much brighter the low power setting is. Gives a good sense of how much the amount of winds affects the tone.

[SonnyW]

Hey guys,

My bandmate asked me to wind him a couple of Mosrite single coils to fit onto the Frankenstein strat I built for him. I told him, "yeah, sure, they can't be that complicated to make", then realized there was very little technical data on the internet. I dug into the depth of this board but didn't find anything either.

I know there are a few types of Mosrite pickups out there, but from what I gathered, he wants the classic single-coils that are wound to around 10-11K with Phillips-style pole screws. Here's what I know so far:

-they use a thick wooden bobbin core, much bigger than the bobbin spacer found on p90s
-AWG 43 wire
-there seems to be a layer of insulating foil between the bobbin and the magnets for shielding
-the screws are fitted onto nuts that act as the magnet spacers (does this mean the bobbin core itself is not tapped?)
-the bottom of the pickup is covered with foam, on top of which lays the height adjustment metal mounting bar, both of which are drowned in epoxy, which seals the pickup inside its cover forever and keeps things from moving around too much.

Does any of you guys have anything more accurate than my Mr. Obvious observations? The bobbin does look like a P90 bobbin from afar but I can't be sure, having never seen one of those in the flesh.

Well, as luck might have it, I just finished rewinding one of these and repairing it's mate. Since they are still in my shop I took some photos. It's not like seeing in the flesh, but it's as close as we can come digitally. Here's the pics, then I will try to answer your questions. First here's a top and bottom view of the pair, after repairs.

Note: these are both the same size, camera angle makes one look smaller.

Here's the neck, which I had to rewind, but the bottom part was able to be saved.



Here's the bridge, which I was able to repair but I had to fabricate a new foam part for the bottom, which just crumbled to pieces.



OK so here goes on the questions.
- on these, the bobbin core was machined out of nylon or some similar plastic. it was black and I'll give the core dimensions later in this post. The top and bottom of the bobbin was made of clear plastic - kind of like the plastic used for the rear windows in convertible tops. I've used the heavy vacuum formed packages off of things like batteries or ink cartridges, (the kind you have to use scissors to get into) as a suitable substitute.
- the wire has been Awg #44 SPN on all the examples I have seen. This one the wire measured .0023, .0022, and .0023 inch diameter.
- the foil shielding is there you can see it in the pics, and it is brass. I think copper tape would be fine for the same job.
- the screws are different lengths for the neck and bridge, longer for the bridge. I didn't see nuts on this one, there was a machined keeper, it's threaded.
- you can see the foam and the mounting bar in the pics.

I'm going to continue this in the next post before I time out on this one.

[SonnyW]

OK so here is the info I wanted to add to the last post. (btw, I already wrote this once, but it timed out on me, logged me out, and I lost it. Hate it when that happens. Hope I can remember what I wrote)

The bobbin is fabricated. The core is machined out of nylon or something similar. I haven't seen any made of wood, but I don't see why it wouldn't work. I have seen one with no bobbin at all, just a taped coil. It might have been a prior rewind though. Here are the core dimensions: Length: 2.16", Width: 0.36", Height: 0.28", Flange: 1.15". The top and bottom of the bobbin are made of clear plastic like would be used for the back window in a convertible top. It's glued together with contact cement, which is why it has that brown discoloration. The core is not tapped it has clearance holes.

Both the pickups from this set were wound Clockwise as viewed from the top, North poles up. (Not a humbucking set). This is also true of another pair that I rewound in the past. I used about 9400 - 9450 turns of #44SPN wire on all the ones that I rewound. This neck was 11.27 K ohms DCR. The bridge, which I only repaired and did not rewind measured 12.93K, The others were 11.05K, and 11.22K. I also repaired a bass unit once and it was wound with #42 SPN to 8.21K ohms.

I used a tooling jig to hold the bobbin on my winder. It consisted of a piece of wood that was screwed to the faceplate with other screws countersunk the other direction to hold screws and nuts. Then there were two thin brass plates that formed a sandwich to keep the bobbin from flaring. Heres a couple of pics without any bobbin in place.



I didn't see nuts for a keeper bar, all the ones I have seen had a machined keeper that was tapped, the best I could tell. It's hard to see inside that assembly because it is all glued up with epoxy. The magnets looked like alnico, and were made so they could be broken off to length. The configuration was like a P-90. I guess you could use nuts to make a keeper though if you could figure out how to hold everything in place for the gluing and then get the screws back out again. The magnet gauss measured somewhere between 200-300 gauss at the polescrews. The averages of the four I have measured are 197, 243, 228, 285.

The dimensions of the mounting bar are 3.57" long, x .25" wide, x .050 thick, aluminum with tapped holes for the ring, at 3.33" center to center. It is glued on to the foam by epoxy. When I had to replace them I have used epoxy thickened with Cabosil (fumed Silica) to glue it in place, using the mounting ring as a jig. It's kind of a tricky deal to get it right. I glued the foam in place with Duco cement.

That's about all I have, hope this helps.

[epizootics]

A bit of a late reply...Thank you so much Sonny! This is a lot more than I hoped for and a nice reminder of how the internet can be a nice place sometimes.

I'm realizing that the screws also seem quite a bit bigger than the usual #4/#5 found in P90s. From the picture I'd say they are coarse threaded #8's, is that a fair assumption?

Screws are an absolute pain to source here in Europe. I've been using metric screws until now but I'm seriously thinking of ordering a set of US taps, since the only thing we have here resembling fillister screws is what the British call cheese head (the old Din 84, which is not quite close to a fillister). The main issue is that most European machine screws have a head diameter that is too big to fit through pickup cover holes, and also get in the way of height adjustment screws on P90s. Sorry for my little rant here

[SonnyW]

The screws in this pair that I have in my shop are #6-32 x 3/4 Fillister head for the bridge pickup, and the same screw but cut down by hand to 1/2 inch length for the neck pickup. Both have phillips sockets in the Fillister head. I measured one and it was about 3.45mm diameter. I would guess that regular humbucker / P-90 polescrews (either the US #5-40 or the 3mm ones) would probably be sufficient unless your friend really has to have the phillips socket in them.

Also just an afterthought, upon looking at one of the links provided in one of the other posts, the "incredible sausage coil" does look a whole lot like the one I remember in one of the ones that I previously rewound. It was a while back, but if I remember correctly that one was a 1970's version and it said "Mosrite of California" on it. My notes aren't the best on that one. But it had a very similar taped up coil inside. Also if I remember, I was not able to reproduce a loose coil like it exactly, I think I ended up fabricating a bobbin.

[Jason Rodgers]

Cool stuff! So, is the keeper AND mounting bracket made of aluminum, or could you only confirm the metal of the bracket?

[rjb]

Denotation Police

So, is the keeper AND mounting bracket made of aluminum,...

If it's made of aluminum, then it isn't really a keeper. Right?

-rb

[SonnyW]

The bracket is definitely made of aluminum. The keeper is some kind of steel I assume, but it is enclosed in the epoxy so I can't tell exactly what it even looks like. It could also possibly be made of individual nuts that are held in place by the epoxy. The epoxy or whatever compound it is binds both magnets and the keeper (or keeper construction) to the brass foil. Here's a photo from yet another one that came in for a rewind that shows a keeper/magnet assembly a little better. Just from the way the threads are formed on this one indicates to me that it could possibly be made from hex nuts, but it is still very hard to tell without having an x-ray image. Others that I have seen looked more like a one piece keeper. The epoxy on this one is cream colored, where it was black on most of the others I have seen.

[mb1685]

Fantastic thread! I know it's a few years old but still the most educational one I've come across after doing a lot of searching.

Did you happen to measure the inductance or resonant frequency? I'm looking to eventually get my hands on a Mosrite bridge pickup if the right deal comes along and in the meantime I'm looking to plan out some potential wiring setup ideas with LTspice by creating a circuit simulation.

[SonnyW]

I have rewound quite a few of them considering their scarcity, but only three of them had intact original coils to measure. The construction methods varied a lot Here is the data on the three with intact coils.

Mosrite Pickups
Example Measured, Construction Notes		Inductance	DCR @68F	FRES
Originals Coils Good
Repair of Original '60's bridge, fabricated bobbin		8.683 H	12.93K	7.14 KHz
Repair of Mosrite of Calif. (neck) plexiglas threaded core		6.655 H	11.17K	6.52 KHz
Repair of Mosrite Bass '60's, magnets epoxied in		6.642 H	8.21K	6.77 KHz

I would say most of the rewinds I have done ended up with about 9400-9500 turns of #44 SPN, for about 11 to 11.4 K ohms DCR, and about 7 Henrys inductance. They measured around 7KHz resonant frequency. Some examples had fabricated plexiglas bobbins, others had just a taped up donut coil with no bobbin. Except for the molded covers, they mostly look almost homemade and somewhat amateurish internally. Pretty much all that was consistent was the magnets, which are like the ones in the photos, with notches where they can be broken to size.

hope this helps,
I don't have much other info on them.

[mb1685]

You are my hero! Thank you so much for sharing this detailed information.