[Boatanchors] Motorola carbon-mike-replacement schematic

[Al Klase]

Thanks, Dave.

I like this circuit.  I was considering designing something similar, but 
here it is.  I'd prefer to be working whit an electret mic. They're 
small.  They're cheap.  They're everywhere in modern electronics.  I 
also maintain that a single transistor is not going to have enough gain 
for a dynamic mic.

The 12-volt zener will protect it from over voltage and reverse connection.

Al

On 3/17/2013 9:52 AM, Dave Maples wrote:
> All: Here is a link to a Motorola mike that "looks" like an old carbon mike.
> I can't say that it's an equivalent, for example, to a T-17; however, it's a
> starting point.
>
> This particular mike uses an electret element rather than a dynamic element.
> For a dynamic element there would have to be some isolating capacitor
> between the mike element and the rest of the circuit.
>
> Does anyone have the normal operating points (i.e. bias voltage and load
> resistance) for a typical WWII carbon mike?  Having that info should allow
> someone to design a transistor circuit to replace the carbon mike with an
> equivalent.
>
> Here's the link:
>
> http://www.repeater-builder.com/motorola/pix/hmn1052a.jpg
>
> Thanks,
> Dave WB4FUR
>
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/