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Bought some old speakers from ebay - here's what I found inside

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andy_cristea:
Hello everyone!
So I bought these vintage speakers from e-bay some time ago and decided to give them a listen today since I had some time and the right mood. Since they were listed as perfectly working last time used, the tweeters are blown on both, of course :palm:. No problem since I have another pair that I've blown the bass drivers on so I have a perfect match. I opened them up to replace the tweeters and found this beige box inside:

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Needless to say that this box is not present in any other speakers from this series (I have all of them). The box is not electrically attached to the speaker's wiring and it is mounted using double sided tape (the spongy type). I could tell that the tape was very old but it still held up pretty good so I pried the box off using a screwdriver. This is what was inside:

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The PCB was held with hot snot that did not stand the test of time as good as the double sided tape - I just pulled the board out and the hot snot came off very easy, almost in one piece:

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The (dead) CR2032 cell is isolated from the PCB with the same double sided tape. I removed it:

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Closeup of the IC (best i could do with my phone):

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It is labeled F  4013BPC and with a date code of 810A (it looks like 8101 in the photo but with my bare eyes I think the last digit looks like an A). So a CD4013BP dual flip-flop from 1981. Makes sense since the speakers have been manufactured since 1979 until sometime in the early eighties.

What is this thing? It looks like an oscillator to me but what is it's purpose? Please tell me it's some audiophile tomfoolery and not some spy tracking stuff.

Oh, and the second speaker has a similar box inside.

Thanks!

Red Squirrel:
You should be getting a call from the NSA agent that is assigned to you.   Follow all directions, and nobody gets hurt.    :-DD


Wonder if it's a vintage anti theft device?  Like from back in the day when it was being sold in stores. 

james_s:
My first thought is maybe some kind of anti-theft tracking device? Hifi speakers and other gear used to be a very commonly stolen item. Put a new battery on it and see what it does. 

Refrigerator:
Probably the old-fashion theft protection before magnetostrictive tags were invented.  :-//

ucanel:
This reminded to me 74ls13 fm transmitter,

https://fmuser.org/news/fm-transmitter/Micro-FM-transmitter.html

But it would be notch filter, 50 Hz or 60Hz line filter.

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