[Sparks]

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).