Opening a DeArmond = Courting Disaster?

[rjb]

Years ago, I acquired a DeArmond pickup in a cross between a gift exchange and a horse trade. It looks like this pic from the Harmony Guitars Database- except the control box and jack have been cut off, leaving a 2-inch stub of lead wire: http://harmony.demont.net/pickups/images/0002.jpg

I now have a potential use for the pickup and- rather than make an ugly splice- would like to replace the lead. Well, actually, I want to detach the coil from the baseplate and install a twisted shielded pair. And- to make the situation more interesting- before deciding to replace the lead, I potted the pickup in wax.

Having heard that DeArmond coils are wrapped with spider thread, on bobbins made from the eggshells of DDT-laden eagles, I have some trepidation about opening the case.

I have little experience with pickup surgery, and don't know the configuration of this particular pickup.

If it as sturdy as this one, I'm pretty confident I can do the job:
http://harmony.demont.net/pickups/images/0034.jpg

If (as I fear) it looks like this, I'm afraid the coil will adhere to the cover and self-destruct:
http://harmony.demont.net/pickups/images/0014.jpg

Can someone advise on how to proceed without killing the patient?

I plan to drill the backs off the rivets. Once the pickup is safely disassembled, I'm pretty sure how to install the new lead. Then I would solder the case closed and glue the rivets to the cover, just for show. I could use some help with the in-between steps.

Thanks,
-rb

[salvarsan]

Clamp the bobbin before you lift the cover.

[rjb]

Clamp the bobbin before you lift the cover.

I bet this is something that's obvious after you've done it once or twice- but I'm not following. How do I clamp the bobbin? I don't see how I could get anything inside the pickup before removing the cover.

Say I've successfully removed the 2 rivets. From the back, I see the 2 rivet holes, the lead access hole in one corner, and a small "L" notch in another corner. From the front, I see 2 rivet holes plus 4 toaster slots backed with black plastic. Should I push on the plastic while lifting the cover?

Thanks,
-rb

[Spence]

A wise man with a garage full of broken things used to tell me that if some idiot put it together, some idiot can take it apart.
My advise is to advance with caution. If you break it, you will be able to fix it but it may not ever look quite right under the hood.
As for the rivets, try using a sharp implement to lift the curled over rivet ends. You will be able to reset them after and therefore save them.

[jonson]

As Spence said try and lift the rivet curls on the back and slide rivets out to reuse. That will do no damage as the rivets go through the mags ad won't touch the coil. The small notch is where the start of the coil solders to the baseplate and the top is a bit tougher and stiffer then you think and will push down to remove the bobbin. Most of these pickups were similar construction just different mags'wire and covers but go careful and you will be ok. This is what it should look like if it is a good clean one.

[salvarsan]

The bobbin top shows through the black toaster slots.

Put uniformly high standoffs on the toaster slots so that
the pickup can be clamped from top to bottom.
The standoffs must be smaller width than the
toaster slots so that the cover can slide off.

Next: take an antidepressant drug.
You'll need it when you realize that the pickup has
an inner winding around the top four poles
plus an outer winding around all six poles.

To rewind it, you must remove the bottom two poles for the inner coil,
then replace them for the outer coil.

-drh

[rjb]

The bobbin top shows through the black toaster slots. Put uniformly high standoffs on the toaster slots...

D'oh. Thank you very much for that patient, detailed explanation.

To rewind it, you must remove the bottom two poles for the inner coil, then replace them for the outer coil.

I hope not to have to rewind the coil- just replace the lead cable.
The coil reads ~11.25K. Does that sound about right?

I knew (from browsing this forum) that Rhythm Chiefs are configured that way, but didn't think all DeArmonds were. I'm not sure of the pickup's childhood background, but it's not a monkey-on-a-stick; it has a metal mounting strip riveted to the back, as shown in the first pic of my first post.

Of course, I'll know for sure once I use your advice to open the thing!

Thanks again,
-rb

[salvarsan]

D'oh. Thank you very much for that patient, detailed explanation.

Yer welcome. That's what should happen when this forum is working right.

Good luck with your DeArmond.

The good news is that you can actually pull them apart and fix them, unlike some more recent designs.
-drh

[rjb]

...Most of these pickups were similar construction just different mags'wire and covers....

That yellow & grey insulated coax does look awfully familiar... and so does everything else, except the cover cutouts. Thanks for the advise, and especially for the photos- they clearly show everything I need to know.

-rb

[nhall]

Jonson's Pictures

In fact jonson's pictures are so clear they are also illustrating his recent attempts at a new crackle finish, as can be evidenced on his finger tips!

[Spence]

In fact jonson's pictures are so clear they are also illustrating his recent attempts at a new crackle finish, as can be evidenced on his finger tips!

I'll have to correct you there Nigel. Those aren't Jonson's fingers. He had to hire someone for the hand modelling assignment as he didn't want people to see his talons and red skin. Apart from that, he does have beige cord carpet hairpiece.

[jonson]

I'll have to correct you there Nigel. Those aren't Jonson's fingers. He had to hire someone for the hand modelling assignment as he didn't want people to see his talons and red skin. Apart from that, he does have beige cord carpet hairpiece.

That's it you two. Next time we meet it's the silent treatment and no choc buscuits.
That's all i'm saying as I'm off to the beauty parlour now to get me nails clipped.

[Sweetfinger]

the pickup has
an inner winding around the top four poles
plus an outer winding around all six poles.

To rewind it, you must remove the bottom two poles for the inner coil,
then replace them for the outer coil.

-drh

The "toaster" version is constructed like the "hershey bar" version with just a single coil, no secondary coil like the soundhole pickups. There's just one solid magnet in the center. Still, I try to avoid opening Dearmonds until ABSOLUTELY necessary. I'd just splice new lead- that coil wire is REALLY thin.

[Spence]

That's it you two. Next time we meet it's the silent treatment and no Bonio buscuits.
That's all i'm saying as I'm off to the poodle parlour now to get me nails clipped.

EDIT

[rjb]

I never meant to take up pickup winding... but I've got a knack for breaking things.

Reporting back, a year later:

Good News

• Although I lacked the skill and cleverness to un-pry the rivets, I did manage to open the pickup without mishap.
• The paraffin-beeswax potting actually may have made the job easier, by stabilizing the somewhat fragile assembly. It also seemed to have floated 40 years worth of crud out to the surface of the coil.
• Upon examining the coil's "start" connection, I quickly abandoned the notion of converting the pickup to "2-conductor plus shield"- I wasn't sure I could even see the start connection.
• Connecting the lead wire was easier than I had imagined. The DeArmond scheme of soldering the coil finish and the lead wire to opposite ends of a strip of heat-dissipating copper tape made the operation relatively stress-free.
• Although the Canare GS-4 I used is significantly fatter than the original coax, I was able to finagle the cover back- with a bit of strategic filing.
• Cover soldered to the baseplate without a hitch.
• Potting in pure beeswax (melting temp 180 F) may have been somewhat foolhardy- but nothing fell apart, and the coil DCR read about the same as before I opened the pickup (11K and change).
• Attaching the mounting bracket and “for show” rivets with high-temp hot glue may not meet “professional” standards- but is good enough for my purpose. DCR still ~11K.

Not-So-Good News

In “playing around” with different bread-boarded circuit configurations, I managed to hook up a signal generator directly across the pickup- with no current-limiting resistor. The DCR now reads infinity.

New Question

Would this pickup, rewound with 42AWG I have on hand, sound “OK”- or “weak, thin, and strident”?
Since I’ve yet to hear it on a guitar, I wouldn’t know what I was missing....

My intended application is this:

• Mounted to the suspended pickguard of a Harmony Patrician archtop, at the “24^th fret” position.
• Electronics similar to DeArmond Rhythm Chief control box (volume, tone, and “rhythm switch” = series bass-block capacitor) but shielded differently (components mounted directly to plastic pickguard) and capacitor values determined by pickup’s impedance and personal taste.
• For playing early Country, rudimentary Western Swing, 50s era Cajun, and maybe a Charlie Christian riff or two.

Thanks,
-rb

PS

For what it’s worth, I’ve found out this pickup is called a Model 40.
Folks interested in DeArmond pickups might want to check out this site: DeArmond numbered items