[Boatanchors] Carbon Mic Rejuvination

[Richard Knoppow]

----- Original Message ----- 
From: "rbethman" <rbethman at comcast.net>
To: <boatanchors at mailman.qth.net>
Sent: Saturday, March 16, 2013 3:52 PM
Subject: Re: [Boatanchors] Carbon Mic Rejuvination


> Today's telephone elements are NOT built anywhere near the 
> quality of the phones of old.
>
> The insides are solid state, and the microphone and 
> earpiece are not very tolerant of that solid WHACK!
>
> You would most likely need to replace the phone.
>
> That would be *unless* you happen to have an old Western 
> Electric rotary phone.  (I do have one downstairs.)
>
> In that event go ahead.   Just try and replace it!  LOL!
>
> Bob - N0DGN
>
> On 3/16/2013 6:41 PM, Ken wrote:
>> Why not?

     There is another reason:  Modern telephones use 
electret microphones. The old carbon mics were subject to 
"packing" where the carbon granules would clump together. 
The result was a severe loss of sensitivity.  By striking or 
shaking the case the granules were knocked apart and 
re-distributed.  The cure does not last long because packing 
really has to do with the condition of  the granules. 
Sometimes removing the carbon and baking it would effect a 
longer cure but the problem really stems from the shape of 
the granules, something not fixable except by replacing them 
with fresh ones.  It was common in the old days to put too 
much current through the carbon which would burn the sharp 
edges that were supposed to make the contact. Where current 
is low and limited, as in a telephone set, the life of the 
microphone can be very long.
     There is a fair amount of voodoo in the manufacture of 
the granules but I do not have citations to any literature 
describing it.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com