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Old 21st May 2020, 12:06 pm   #1
Sparks
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Default GPT Reliance E Link 101 telephone

I dismantled the handset on this old phone yesterday and was struck by the amount of circuitry built into the microphone compartment. Underneath it all is a simple 2 wire elecret microphone, using surprisingly bulky wires to connect it to the circuit board. Does anyone know what this circuit board actually does ? It it an amplifier to bring the mic output to carbon level or something else ? I've never seen a telephone handset quite like this. I did consider that in other telephones this sort of circuit might normally be found within the telephone body rather than the handset. There is 7 volts going from the main phone circuit board via the handset cord to said circuit.

Thankyou. It's quite a curiosity (to me anyway).
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Old 21st May 2020, 1:14 pm   #2
OscarFoxtrot
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Default Re: GPT Reliance E Link 101 telephone

I can't trace the IC number.

The wires on an electret mic capsule must be kept very short to avoid interference, so it's normal for there to be a preamplifier very close. In GPO/BT phones with an electret transmitter the mic and the preamp are formed together in the transmitter.
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Old 21st May 2020, 3:23 pm   #3
Sparks
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Default Re: GPT Reliance E Link 101 telephone

The IC number is ST LS656B 98921. Thanks, OF.
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Old 21st May 2020, 3:42 pm   #4
Sparks
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Default Re: GPT Reliance E Link 101 telephone

A slightly better picture. The white, red, green and black wires on the left are from the handset cord. At the top, the yellow wires are for a mic muting button, red and black for the mic itself and grey for the earphone.
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Old 24th May 2020, 1:30 pm   #5
Sparks
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Default Re: GPT Reliance E Link 101 telephone

I've found out a little about the IC, if nothing else. It has something to do with Texas Instruments and is for telephony purposes. Lots of diagrams available to download which are beyond my understanding! That's all.
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Old 24th May 2020, 1:32 pm   #6
dazzlevision
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Default Re: GPT Reliance E Link 101 telephone

Quote:
Originally Posted by Sparks View Post
I've found out a little about the IC, if nothing else. It has something to do with Texas Instruments and is for telephony purposes. Lots of diagrams available to download which are beyond my understanding! That's all.
The IC is branded "ST" = SGS-Thomson, a French-Italian company, now known as ST Microelectronics.
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Old 24th May 2020, 1:38 pm   #7
dazzlevision
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Default Re: GPT Reliance E Link 101 telephone

Here is the opening description in the SGS data:
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Old 24th May 2020, 1:59 pm   #8
Sparks
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Default Re: GPT Reliance E Link 101 telephone

Thankyou dazzle.
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