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 Inside Classic Western Electric Speakerphone
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 Return to top of page · Post #: 1 · Written at 10:20:00 AM on 7 March 2015.
NewVista's avatar
 Location: MilwWI, US
 Member since 10 May 2013
 Member #: 1340
 Postcount: 606

Bell Labs scientists worked on solving the challenges of a hands-free speakerphone since the 1950's. By the 1970's they had a product that worked as good - or better - than many of today's desk phone products.

Here I peek inside some units from the mid 1970's and early 1980's - just before the demise of Western Electric [WE] in 1984.

Speakerphone
Speakerphone
Speakerphone


These are interfaced to a conventional desk or wall phone network terminals with many connections to provide continued service in event of a power failure as hands-free mode requires an 18v.ac wall transformer. Everything is connected with an outboard modified Centronics (printer) plug and sockets.

There are two modules, the speaker unit and the separated microphone/control unit. Separating the mic is one reason they work so well. Opening the speaker unit reveals a gutsy 3" speaker with larger voice coil, magnet and doped surround. Its circuit boards fold out to reveal eight WE-502 IC's, a relay and discrete transistors, all made by WE. Not much difference between the 1970's and the 1980's versions (shown side by side) except for those mysterious 3 big red "CAP-PAK" units.

The "futuristic" Mic/Control unit has momentary rocker switch that latches electronically and lights red LED indicator. It is difficult to dismantle (must tap out small diameter rocker pin) but when open reveals its secret microphone tech: A rectangular WE EL-2 electret mic with 3 terminals implying an inbuilt FET. This mic's small 2mm port faces downwards through a 4 x 10mm rubber tunnel (shown removed) to receive reflected sound from the desk/conference table. There are more transistors and 1970's Tantalum Caps as well as a miniature volume control made by "CRL"(Centralab), so all components are domestic and even union-made by the look of it.


 
 Return to top of page · Post #: 2 · Written at 6:24:07 AM on 29 April 2015.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 725

Even though they look well built, they still sound like the phone line, not hi-fi for sure. Not that the phone company intended them to be hi-fi.


 
 Return to top of page · Post #: 3 · Written at 11:24:31 PM on 5 May 2015.
NewVista's avatar
 Location: MilwWI, US
 Member since 10 May 2013
 Member #: 1340
 Postcount: 606

Low audio frequencies would have been carefully tapered off below 300 Hz. This, along with using a "surface boundary" microphone to avoid reflections, avoids the "you sound like you're talking in a tunnel" syndrome of loudspeaking telephones.

One wonders if Edward Long's PZM microphone patent of the early 1980s impinges on some of Bell Labs' earlier research/patents?


 
 Return to top of page · Post #: 4 · Written at 12:14:07 AM on 10 September 2015.
Art's Gravatar
 Art
 Location: Somewhere, USA
 Member since 22 October 2013
 Member #: 1437
 Postcount: 895

Are those clear cases relays? Certainly don’t make them like they used to!
I love those early “don’t quite know if it’s through hole, point to point, or wire wrap” product.
I lot of it continued in domestic product into the 80’s with wire wrap PCB interconnect.
Those were the days.


 
 Return to top of page · Post #: 5 · Written at 10:14:01 PM on 10 September 2015.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5263

Are those clear cases relays? Certainly don’t make them like they used to!

Omron, for one, still makes them:

http://www.omron.com.au/products/category/relays/general-purpose-relays/for-control-panel/index.html


 
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