Tuesday, March 20, 2012

Changing the Microphone in a Bakelite Telephone

Old British Bakelite Telephones such as the 200 series and 300 series telephones used the same handset. This Bakelite handset was known as a model no 164 handset, and was used for over 30 years. It was the standard telephone handset in 1929 and was manufactured all the way through to the early 1960's.

Compared to today’s modern telephone handsets it has a very good ear piece (or receiver). Its only weakness is that the microphone (or transmitter) in the mouthpiece does not live up to today’s expectations of sound quality. This lack of sound quality is only noticeable to the people at the other end of the telephone call. When you are using one of these antique telephones the person at the far end will think you are calling them from the bottom of a well :-) This can be rectified by swapping the old carbon granule microphone out with a modern electronic (electret) microphone. Several makes of replacement electret microphones are available however they must be designed for use in old telephones.

The instructions below show you how this microphone change can be performed.

1) First remove the Bakelite mouthpiece from the handset. If you are unsure how to remove it safely, please see the details on our web page removal of a bakelite mouthpiece.

2) The old Carbon Granule Microphone should just lift out (it is not hard wired).

3) Use a small flat bladed screwdriver to remove the old microphones spring clips (see photographs below).

4 ) Attach two wires to the new electronic microphone ideally red and white wire should be used to make life easier when you fit it (see photograph below). Thankfully new electret microphones used in these vintage telephones are not polarity sensitive, so it does not matter which way round you connect the wires.

5) Connect the new red wire from the microphone to the old red wire inside the mouthpiece, and the new white wire to the old white wire inside the telephone mouthpiece.

6) Modern electronic microphones are smaller than the old carbon granule ones, so you will usually need to cut a small piece of foam to fill the gap to stop the new microphone from rattling around inside the old telephone handset.

7) Finally refit the Bakelite mouthpiece on your handset and test the Bakelite telephone.

Providing the rest of your antique telephone is in good order, the sound quality and usability of your old Bakelite Telephone should be significantly improved.

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