[Milsurplus] SIMPLE Carbon Microphone Substitute.

[hwhall at compuserve.com]

That's interesting about the T-17 series resistance, because when I was doing some research into carbon button alternatives, I couldn't find any data on T-17 buttons other than "low impedence." 

Some of the telephone-type carbon buttons I found available ranged from 40 to 60 ohms resistance according to maker's data. I thought that T-17 buttons would also have to be fairly low resistance since (from the little I understand of them) the carbon buttons controlled current flow (essentially a variable resistor). ARRL Handbooks indicated "the usual" button currents were 50 - 100 mA. Getting 50mA thru 20Kohms would require a whopping lot more than the 4 - 6 volts the old Handbooks showed for running carbon mikes.

What am I missing??

Wayne
WB4OGM


-----Original Message-----
From: David Stinson <arc5 at ix.netcom.com>
To: COURYHOUSE <COURYHOUSE at aol.com>; kgordon2006 <kgordon2006 at frontier.com>
Cc: milsurplus <milsurplus at mailman.qth.net>
Sent: Sat, May 28, 2016 11:48 am
Subject: Re: [Milsurplus] SIMPLE Carbon Microphone Substitute.


----- Original Message ----- 
From: <COURYHOUSE at aol.com>
Subject: Re: [Milsurplus] SIMPLE Carbon Microphone Substitute.


> ah... what about a carbon microphone element  from an  old 
> telephone
> handset?

Too lo-Z for the BC-669.  I've looked at lots of Carbon mike
elements and they come in various impedances.
The series resistance of the best T-17 I have is over
20K Ohms.  Telephone mics are usually around 500 ohms.
Some are as low as 200.   That works OK with some rigs,
like the "ARC-5" sets,. but not well with the 669 or TCS.

73 Dave S.

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