[Milsurplus] N-1 Carbon Mic Element and T-17s

[C.Whitaker]

de WB2CPN
Way back in the '50's there were articles in the
ham radio magazines about the problem with
the carbon in T-17's, and similar mics.
The carbon units I have examined while in the
employment of AT&T usually could be helped
by shaking up the carbon by whacking the edge
against a table top.   The current through the
carbon, if it is too high over time, will cause the
granules to stick together.  When carbon mics,
very large ones, were used in broadcasting, the
polarity of the battery was reversed regularly
to prevent clustering.
Another hint:  The audio quality and over all
performance of  most of these carbon mics can
be improved if the cover of the mic is gently
removed, and one or more of the little paper (?)
shims around the outside edge are removed.
This lowers the pressure of the carbon in its
little cup.
73  Clete
++++++++++++++++++++++++++++++++++++

On 1/31/2013 8:17 PM, Clare Owens wrote:
> Hi Dave,
>
> I was just able to win a "pile" of old Bell System headsets (4 of them)
> from Will Donzelli and all 4 mic elements, apparently N-1s seem to work.
> So I decided to see if I can salvage one of my T-17s.  The one I opened up
> has basically no audio.  In your posting of last October 12 you mentioned
> just hot melt gluing the N-1 into place - I guess without boring out the
> hole where the original capsule was located???  Looks like there'd be room
> in there for me to do that but I just wanted to check with you.  One other
> guy talked about boring out the hole but I have no way to do that...
>
> I have 7 or 8 T-17s and three RS-38s and only two of the T-17s had any real
> audio when I just tested them with a 9V battery and a Bell speaker that
> came in the "pile" and with this primitive setup I couldn't tell if the
> audio would be usable.  Once I "convert" the T-17 I'm working on I'll wire
> up the possibly good mics with a battery and an input transformer to the
> line input of my little 60W amp one of these days and see about the
> fidelity.
>
>
> On Sun, Oct 21, 2012 at 2:40 PM, David Stinson <arc5 at ix.netcom.com> wrote:
>
>> Re: Using T-17 mics.
>> I've found exactly one T-17 that would deliver usable
>> audio to a BC-456.  No amount of bashing or baking
>> (or cussing) did any good with the others.
>> So I temporarily hung a telephone element in the case,
>> which does not fit inside but works, waiting for a better idea.
>>
>> Came across a few small carbon mic elements
>> in round cardboard containers labeled:
>> "ONE N-1 TRANS. UNIT"
>> IIRC, these are used used in some 50s-60s handsets.
>> I gave them a "table bump",removed the thick rubber
>> moisture barrier and replaced it with light fabric,
>> then hot-glued the elements in place of a couple
>> of stone-dead and unrecoverable T-17 carts,
>> with some "stuffing" behind to fill the chamber.
>> To my surprise, through the small-diameter holes
>>   in the T-17 face, these  elements delivered ample audio
>> to a BC-456 modulator.  In fact, I can over-modulate.
>>
>> Are these elements available and at reasonable prices?
>>
>> TNX ES 73 DE Dave AB5S
>>
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