Crystal Radio
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Inside a Sound Powered Element
Balanced Armature

Simplified Balanced Armature Element

Each element is different in construction, but the basic idea is the same.

Inside the RCA Sound Powered Element (handset)
Handset MI-2040-A
These are very similar to the old style "Big Can" headsets also

In the view below you can see the armature balanced between the two magnets.
It is a thin flat sheet trapped (in this case) between two adjustment nuts.

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 armature.
It is part of  the "perm magnet unit".

That armature should be centered evenly between the two magnets units.
If it is not, the element will loose performance.

Below is the diaphragm (large yellow object). It is connected to the drive rod,
which is connected to the armature.


The RCA "mic" Element Dissassymbled

Inside the Western Electric Sound Powered Element
D-173012(mic), D173014(ear) the same.

Note that unlike the above RCA unit, the Western Electric unit does not have
nuts for adjustment. The mass of the drive rod is much smaller also.

The following is a "Tip" from John Hz on centering the armature on Western Electric
elements for better performance. John just finished up a headset using these elements.

There are two screws inside. The diaphragm is connected via a rod to the armature. The
armature was all the way down, touching the lower magnet pole, so I loosened the two screws
and shimmed the flap off the magnet poles with paper, then tightened the screws.

Thanks John!

1)    Extreme caution must be taken when working with any balanced
       armature element. They are very vulnerable to dirt and metal particles
       that might enter in while working on them. They are very delicate also,
       and will not take very much abuse
2)    "Tinkering" with the spacing till it is centered yields more sensitivity

Inside the United States Instruments (USI)
Sound Powered Element (ear)

Looks very close to the Western Electric element.
Biggest difference is the USI elements have adjustment nuts where the WE's do not.
Also the diaphragm is much different.
There are a couple different version, but they are all very close.

The USI "mic" Element Dissassymbled

If you've gone this far, you've gone too far!!!

Inside the DLR  No 5  S

The DLR5's are a British military headphone. They are very hard to "center" the armature on,
almost the same as the Automatic Electric. The magnets and interior are a little cruder made than most,
but are real performers.

Inside the Canadian
RCA Sound Powered Element (handset)
MI-22151-E & MI-22151-A

The Canadian RCA element is almost exactly the same as the Stromberg Carlson
handset element. As a matter of fact the magnets are interchangable. The Canadian
version has more in common with the Stromberg Carlson than they do with the American
RCA's. Even the housing that holds the elements are almost exactly the same as the
Stromberg Carlsons. RCA must have at some time acquired the rights of Stromberg Carlson.

Inside the RCA Electric Sound Powered Element
This is from a headset of the newer type MI-2454-B.
Much smaller in size than the "Big Can" type headsets


Inside the Automatic Electric Sound Powered Element
From a set of "decktalker" type headset.
element model GD-51002-B

This element is built very massive in the "frame", but the drive rod
and armature are very delicate. Much more delicate than the RCA elements and much
closer to the Western Electric elements.

Inside the Stromberg Carlson Sound Powered Element
UA1611-1, UA1611-1
also very simular to Telephonic 14070-2 and Dynalec UA1611-1, UA1611-2

There are small differences between the Stromberg Carlson elements and the
Telephonic or Dynalec elements. The Stromberg Carlson seem to be made with a little
more quality then the other two. Mainly in the coil and magnets. The Diaphragm is much
more flat that most other balanced armature elements.
Very easy to adjust because the adjusting nuts are out in the open.

Inside the Shure Element (ear)



The RCA Balanced Armature 100B Loud Speaker Unit


Stand about 4" tall !!!

This is a RCA 100B Loud Speaker (I wouldn't call it loud by todays standards)
It is an early 1900's speaker. Some of the early units were Balanced Armature units.
Not Sound Powered, but I thought you might like to see it.
Very Large (compared to the Sound Powered elements).

Inside the British Telephone Sound Powered Element

I believe this element came from a British telephone unit.
It is a balanced armature unit.

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