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|RCA "Big Can
Servicing and Repair Page
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of elements from headsets and "Cans"
the element up
Magnetizing the element
of armature ("Centering")
|Before we start, Never open a balanced armature
you have a real problem. It is ill advised to do so "just for a look
If it is not broken it might be by the time you are finished looking
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
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
totally worthless without advice and help.
Close up of "can" mounted in lower headband
Although this is a "Mic" element, it
same as a headset element
of elements from headsets
RCA MI-2045-E "Big Cans"
Remove the "Cans" from the lower head band. Pry apart
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
Keep as equal pressure all the way around the cap while
A small strap wrench works well if available.
You will see the "face" or "diaphragm" side of the
the "can" (on right of photo above,yellowish item).
You can "shuck" or pry the element out of the rear
a sharp knife.
Be very careful and go slow.
Check out all
and figures below and read the
|I'm assuming you're
about RCA "Big
After unscrewing the ear
the element will
be just sitting there in the can. Take a sharp knife and pry on the
by twisting the knife (see photo below). Work it gently all the way
the element, between the element and the housing, twisting the knife
as you go. There is a rubber gasket between the housing and the
That is what is sticking the two together.
It's sort of like
and very easy is the key here.
Check out the photos
sharp knife placed
at a tilt and slowly twist the knife. All of a sudden it will pop
caps just won't unscrew
off by hand, heat them lightly with a hair dryer then give it another
Just take your time and
won't have too
The "section of knife" shown below is a "cross
section" of the knife.
We are not using the "tip" or "end" of the knife,
See photos below this one.
Once the element is removed from
you can solder new wires on to the "cans" contact arms fairly easy.
Opening The Element Up
The three main units of the "can"
Cap (left), element Unit (middle), rear housing (right).
Remove the screw in the center and carefully remove the
off of the element.
There is a rubber seal that sometimes sticks, so go
and do not force it.
Tip: If it is sticky, heat
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
Now the rubber gasket is removed also.
Sorry for the bad photo!
Now what you have is the "workings" of the element.
The magnets used to recharge the magnets on the
Also known as neodymium or rare earth magnets.
As Gil Stacey says "They are so powerful that Steve
the roof of his
mobile magnet laboratory, which also serves as a pick-up
The round metal piece with a smaller pedestal is a pole
from a wrecked speaker which
concentrates the magnetism into the center of the
Polarity is established with a compass and opposites are
A “controlled slam” is necessary to fully impart the
to prevent breakage of the magnets and bakelite housing. The
slam” is nothing more than one hand holding the element to prevent the
element from striking the charging magnet’s pole director with
Want to see a video of Steve Bringhurst charging an
Filmed by that famous cinematographer, Gil Stacy
307 KB rm file (Real Movie)
Get Real Player Free at
2638 KB AVI file
Real Player, Quick Time (Apple)
1.443KB WMV file
Windows Media Player
Cut! and Print!!
I'm hoping this works out as it is my first time
of armature ("Centering")
Note: The label "perm. magnet unit" is not pointing to
itself, but instead
to the laminated plates that bring the magnetic field into play with
balanced armature leaf.
It is part of the "perm magnet unit".
One cannot determine the proper alignment of the
viewing its relationship in the gap in which it sits. In other
if the armature appears properly centered, that does not by itself
that the element is in best alignment. Note in the attached photo
that the element is connected to the crystal set. It is tuned to
a station. While cupping the element in his hand to assist
so that the signal can be heard, Steve gently pushes the armature up
down to find peak volume. The sound is heard without the element
being placed to the ear; holding in the hand while working is
to hear the sound, provided the hand is cupped. Manipulation of the
is accomplished with a toothpick resting on the respective armature
or lower armature nuts, alternately pushing up and down. The
of best volume is noted and only then does he adjust the nuts in the
of best volume.
Written by Gil Stacy
Technical skill by Steve
With hemostats adjust the nuts in the direction
After retightening the nuts, the armature is
if the sound change is the same in both directions, it is properly
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
A good set of
pair of them is the only thing needed for adjustment. If you can get
wrenches that would be nice. Below is a spanner wrench that can
made for taking off the face of the element. I would not recommend
this unless you have a major problem. The other reason for removal is
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
that you remove the face to do this. A nice description is below to
you make this spanner wrench.
The spanner wrench was constructed from a
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
are 1 and 7/16" apart. The pins are 3/32" in diameter.
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
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
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
used to watch the diaphragm while removing the covers with the big
Special thanks to Gordon McCall for the photo of
and directions to build it.
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