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RCA "Big Can
Servicing and Repair Page



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Breakdown of parts

Removal of elements from headsets and "Cans"

Opening the element up

Re- Magnetizing the element

Adjustment of armature ("Centering")

Tools

Before we start, Never open a balanced armature element up unless you have a real problem. It is ill advised to do so "just for a look inside". If it is not broken it might be by the time you are finished looking around. It is very important that if you have to open it up, it is done in an area that is as clean as you can get. Small pieces of dirt will find it's way in if you are not careful. Another good piece of advice is get help.  Sometimes a picture is worth a thousand words", but it is also totally worthless without advice and help.


Breakdown of parts

 
 


Close up of "can" mounted in lower headband
 

Although this is a "Mic" element, it is virtually the same as a headset element


 
 
 

Removal of elements from headsets


RCA    MI-2045-E   "Big Cans"

Remove the "Cans" from the lower head band. Pry apart the the lower headband (with short pins) that hold the "Cans" in place. Take care not to scratch the bakelite "Cans" with the pins, as they are being removed.
 


Removed "Can" from headset frame
 
 

Unscrew the "cap" from "can". "Cap" is on left side in photo above
Keep as equal pressure all the way around the cap while trying to unscrew it.
A small strap wrench works well if available.

You will see the "face" or "diaphragm" side of the element, inside the "can" (on right of photo above,yellowish item).
 

"Shuck" the element out.
You can "shuck" or pry the element out of the rear housing with a sharp knife.
 Be very careful and go slow.
 
 

Check out all the photos and figures below and read the
following section prior to trying this.

I'm assuming you're talking about RCA "Big Cans" here. 

After unscrewing the ear cup, the element will be just sitting there in the can. Take a sharp knife and pry on the element by twisting the knife (see photo below). Work it gently all the way around the element, between the element and the housing, twisting the knife slightly as you go. There is a rubber gasket between the housing and the element. That is what is sticking the two together. 

It's sort of like shucking an oyster. Slow and very easy is the key here. 

Check out the photos below. A sharp knife placed at a tilt and slowly twist the knife. All of a sudden it will pop out. 

Tip: If the caps just won't unscrew off by hand, heat them lightly with a hair dryer then give it another go.

Just take your time and you won't have too much problems.
 
 

The "section of knife" shown below is a "cross section" of the knife.
We are not using the "tip" or "end" of the knife, but the "cutting edge".
See photos below this one.

 
 


Note:  Not my hands!!!
 
 


 
 
 
 


Once the element is removed from the can, you can solder new wires on to the "cans" contact arms fairly easy.
 
 
 


Element removed.





 


 
 
 
 
 

Opening The Element Up


The three main units of  the "can"
Cap (left), element Unit (middle), rear housing (right).
 


Another view.
 
 


Remove the screw in the center and carefully remove the rear cover off of the element.
There is a rubber seal that sometimes sticks, so go slow and do not force it.
Tip:  If it is sticky, heat it slightly with a hair dryer. This soften the rubber gasket.
 
 


Now you can see the internal working of the element.
Remember, cleanliness is next to godliness at this point.
Any metal on your work place can find a way into the element.
 
 
 


Now the rubber gasket is removed also.
 
 
 


Sorry for the bad photo!
Now what you have is the "workings" of the element.

 


 
 
 
 


Re-magnetizing Element
The magnets used to recharge the magnets on the elements are NdFeB.
Also known as neodymium or rare earth magnets.

As Gil Stacey says "They are so powerful that Steve stores them on the roof of his 
mobile magnet laboratory, which also serves as a pick-up truck"(photos below). 

The round metal piece with a smaller pedestal is a pole director from a wrecked speaker which
concentrates the magnetism into the center of the element’s back.


Polarity is established with a compass and opposites are placed together.
 

A “controlled slam” is necessary to fully impart the charge and also to prevent breakage of the magnets and bakelite housing.  The “controlled slam” is nothing more than one hand holding the element to prevent the element from striking the charging magnet’s pole director with unrestrained force. 
 
 

Want to see a video of Steve Bringhurst charging an RCA element?
Filmed by that famous cinematographer, Gil Stacy
 

307 KB rm file  (Real Movie)
Real Player
Click Here

Get Real Player Free at

 
 

2638 KB AVI file 
Real Player, Quick Time (Apple)
Click Here
 


1.443KB WMV file
Windows Media Player
Click Here


Cut! and Print!!
I'm hoping this works out as it is my first time offering videos


 
 
 
 
 

Adjustment of armature ("Centering")


 


Note: The label "perm. magnet unit" is not pointing to the magnet itself, but instead
                     to the laminated plates that bring the magnetic field into play with the balanced armature leaf.
It is part of  the "perm magnet unit".

Adjustments
Written by Gil Stacy
Technical skill by Steve Bringhurst
One cannot determine the proper alignment of the armature by simply viewing its relationship in the gap in which it sits.  In other words, if the armature appears properly centered, that does not by itself insure that the element is in best alignment. Note in the attached photo (below) that the element is connected to the crystal set.  It is tuned to a station.  While cupping the element in his hand to assist amplification so that the signal can be heard, Steve gently pushes the armature up and down to find peak volume.  The sound is heard without the element being placed to the ear; holding in the hand while working is sufficient to hear the sound, provided the hand is cupped. Manipulation of the armature is accomplished with a toothpick resting on the respective armature upper or lower armature nuts, alternately pushing up and down.  The direction of best volume is noted and only then does he adjust the nuts in the direction of best volume. 


 


With hemostats adjust the nuts in the direction determined to give greater sound.



After retightening the nuts, the armature is manipulated again, and if the sound change is the same in both directions, it is properly aligned. After alignment is completed, often the armature is perfectly centered, sometimes it is not. This alignment technique while listening to sound is as important, maybe more important, than re-charging the elements. 

   

Tools

A good set of hemostats or maybe a pair of them is the only thing needed for adjustment. If you can get jewelers wrenches that would be nice.  Below is a spanner wrench that can be made for taking off the face of the element. I would not recommend doing this unless you have a major problem. The other reason for removal is if you are using the "mic" elements of a RCA handset and wanted to open up the small holes in the center to 1/2" like the "ear" elements. It is recommended that you remove the face to do this. A nice description is below to help you make this spanner wrench.
 Spanner Wrench Construction

 The spanner wrench was constructed from a 1/4" by 1" by 8" piece of steel. It could be any size stock you may have on hand, but it needs to be rigid enough so that it does not flex. The holes for the pins are 1 and 7/16" apart.  The pins are 3/32" in diameter.  After being pressed into the holes, they should be 1/8" long. If they are too long they will hit the diaphragm, so it is best to keep them at 1/8".  Also, if the pins fit tight in the cover, file them where needed until they fit good.  A loose fit is better to avoid cracking the fragile bakelite. It's ok to use some light penetrating oil on the threads. The hole in the center of the wrench is not required, I had a mark there to find the center and just drilled a hole there when I was done. It can be used to watch the diaphragm while removing the covers with the big (1/2") opening.

Special thanks to Gordon McCall for the photo of the spanner wrench and directions to build it.





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