[Milsurplus] FW: Postmortem on DEF headphone elements

[Hubert Miller]

Looks like my first shot was rejected by milsurplus. Maybe it was 3 bytes over the line, or it doesn't like more than one photo ?
So I removed on. Photo shows coil and its thin wire and fatter lead-out connection wire.
-H

Sent: To: milsurplus at mailman.qth.net; tetrode at googlegroups.com
Subject: Postmortem on DEF headphone elements

So I found in my storage this box of headphone elements which I had bought back around 1985. It occurred to me I should do something with these, one way or another,
so I brought them home. I recalled Jim Barrows, W7BCT ( SK ), telling me these had a high defective rate.
I had thought because of the stock number on the boxes, that these were replacement part for the BC-611 handie-talkie. They are WWII dated.
No such luck. Robert Downs had the real info, as usual, and identified them. Unfortunately at moment I don't recall what exactly he named these as.
So anyway I thought I should ohm them. Of 8 I had, 7 were defective ! In some I tried randomly many years ago, I seem to recall a much better success rate, like the opposite
ratio. I wonder if they're failing more as time goes on ?

I wanted to do a postmortem on this failure. The elements are sealed, no way to unscrew anything to reveal the innards. I even tried sticking a screwdriver in the audio hole
in the diaphragm side to try to pop off the diaphragm cover, no go. Finally, near giving up, I rapped the diaphragm cover with a heavy wrench, and what do you know, the whole
front popped off. I reckon the front had been glued to the heavy metal back, and the shock cracked the glue bond.
There were two coils inside. I scratched some MFP off the soldered posts but no continuity. So I cut the leads to the coils, pulled out the coils, and scraped the lead ends.
Still no continuity ! These leads from the coils to the screw terminals at the headphone back, were something like 32 or 30 gauge stranded. So I decided I would unwind the
coils to see if I could locate the open. I carefully removed the tape covering the coils and lo and behold, about the same time I did this, I found the coil's lead wire came loose,
made no contact with the coil wire itself, which looked about No. 44 gauge, very thin wire. I have no idea how the lead wire was connected to the thin coil wire. I didn't see
any sign there was any soldering. Could they have been just twisted together? Seems unlikely. Or maybe there was a tiny solder joint I didn't see ?

Stromberg - Carlson, this is not good. You risk losing your big " E " for War Effort.
-Hue

    [cid:image003.jpg at 01D54E8D.E6A22940]







-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/milsurplus/attachments/20190809/739b9ec3/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image003.jpg
Type: image/jpeg
Size: 8342 bytes
Desc: image003.jpg
URL: <http://mailman.qth.net/pipermail/milsurplus/attachments/20190809/739b9ec3/attachment-0001.jpg>