[Milsurplus] SIMPLE Carbon Microphone Substitute.

[Mike Feher]

Yep, I agree Pete. It is just hat an electret is such a high impedance
device. I would think a FET might be more appropriate.  I'll have to look up
the specs on that BJT. - Mike 

Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 


-----Original Message-----
From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf Of
Peter Gottlieb
Sent: Saturday, May 28, 2016 11:58 AM
To: milsurplus at mailman.qth.net
Subject: Re: [Milsurplus] SIMPLE Carbon Microphone Substitute.

The current source of the electret must be right in the correct range for
that kind of transistor.

On 5/28/2016 10:57 AM, Mike Feher wrote:
> Dave -
>
> I am actually surprised that circuit works with nothing but the base 
> of the BJT going to one side of the electret I would at least expected 
> to see a resistor, audio bypassed, in the emitter, and, a high value 
> resistor from the base to ground. But, it is hard to argue with "it 
> works" HI. 73 - Mike
>
> Mike B. Feher, N4FS
> 89 Arnold Blvd.
> Howell, NJ, 07731
> 732-886-5960
>
> -----Original Message-----
> From: Milsurplus [mailto:milsurplus-bounces at mailman.qth.net] On Behalf 
> Of David Stinson
> Sent: Saturday, May 28, 2016 10:25 AM
> To: milsurplus at mailman.qth.net; boatanchors at mailman.qth.net
> Subject: [Milsurplus] SIMPLE Carbon Microphone Substitute.
>
> Been working on a simple substitute for the Carbon microphone used 
> with the BC-669.  I've seen some multi-IC, 3-dozen-part designs which 
> hugely violate The Law of Pernicious Parts Count:
>       "Every part in a project beyond about eight
>       reduces the number of people who will build it
>       by 50%."
> So no one builds them.  I hope this one will get tried and improved:
>
> https://goo.gl/photos/26HUmzVuqhZKWrNZ7
>
> Cobbled it together and it works well with the BC-669.
> I picked that transistor because it was the first one I grabbed from 
> the "NPN Small Signal" drawer and my Android phone called it "General
Purpose."
> Other common NPNs will likely work as well.
> The electret element isn't mark +/-.  I soldered it in one way and it 
> didn't work.  Turned it around and it did.
> Will try it on other rigs as the weekend goes on.
>
> 73 DE Dave AB5S
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