The vintage telephone speaker I used for my Bluetooth Handset project has a mysterious component wired across it’s terminals, as shown above (it’s the black cylinder with two leads on the upper left).  The component measures as an open circuit on my DMM, but obviously it has some hidden function.

So far my guesses are:

• A lightning arrestor/spark gap or back to back diodes that protect the person using the phone from strikes or other high voltage on the line
• Some sort of lowpass filter to keep you from hearing otherwise audible tones used for signaling
• A device that keeps the high voltage ring signal from damaging the speaker

I found a schematic at the Bell System Memorial that shows a symbol for the device, but I don’t recognize it.

Does anyone know what this thing is and what it’s for?

We’re also having a discussion about it on flickr.

Last weekend at the Electronics Flea Market I picked up some very strange items, including this one, pictured above.  It’s a tin can that looks very similar to an ordinary soup can, except that it has the following markings on it:

R16-C-28604-15
COIL
QTY.1

NSC.OAKLAND JULY 1953
PRES METH. 2D

Thus far the only information I have learned from the markings are that NSC.OAKLAND stands for the former Oakland Naval Supply Center, closed a decade ago in 1998.  According to Wikipedia, NSC supplied components to the fleet in the Pacific during WWII.  Beyond this I have not been able to find any information.  Presumably this is a replacement part for some piece of obsolete military hardware.  A “coil” is another name for an inductor, a clue that this may be part of a radio system or other high frequency equipment.

After staring at this mysterious object for almost forever (a week) I decided to open it.  Realizing that the can could be full of cold war era hazardous chemicals, munitions, objects under high compression, or nasty sharp edges, I did this very carefully and documented the entire process of discovering the contents.

First, the obvious – opening the can.  Pretty straightforward.

What’s inside?

Weird.  Lots of oiled green paper.  Whatever is inside is packed very well, when the can is shaken nothing moves around.

This is the clump of stuff to come out.

Packing material?  The precursor to styrofoam peanuts?

Below the packing material…

What’s this?  Vintage dessicant!!!

The last object left in the can looks interesting.  It’s wrapped in oiled green paper and sealed with tape.

Inside the paper we find this:

Not a huge surprise – it’s a coil (inductor).  It has a knob or grabby thing on the top and a funny connector on the bottom.  It looks brand new.

Here are a few more pictures.

The markings are “ARC” and “7270 239 KC”.  ARC might be American Radio Corporation?  239 might be 239 kHz (kilocycles)?  Hard to say, google didn’t turn up anythign interesting.

An impressive amount of stuff was packed into that can!

This solves the mystery of what’s in the can, but what is it for?  Does anyone know?  I’d love to find out – leave a comment or contact me directly.

More photos are on flickr here.