[ARC5] Carbon Mic Replacements

[Chris Bowne]

You might consider feeding it with audio from a external audio chain through a suitable isolation transformer and a series decoupling cap to block the DC carbon mike excitation from feeding back into the coupling transformer winding.  I have been doing this with my command set and TCS systems in the shack for years.  I use a small mono utility amp fed by a small Rat Shack octave octave band EQ, into a 600 ohm line to voice coil transformer hooked up in reverse.  In my setup I feed the external audio into an old RM-12 remote control unit that was designed for and used with the BC-191 in the field to couple a field telephone circuit into the carbon mic input of that set.  I just connect the external audio chain to one of the two parallel telephone circuit input terminals on the RM-12. The RM-12 is a great little accessory to use for this purpose.  It has a level setting pot and a VU meter along with a TX/RX toggle switch along with jacks in which you can plug in a local T-17 type or any similar military carbon miles and a key jack as well.  Can be used with any mil transmitter of the era that takes T-17 or similar carbon mic.  I you can't find one you can easily do
the audio transformer and series cap
arrangement.  You will be a amazed
how good the audio from the class A 1625 in the BC-456 sounds fed this way!

Sent from my iPhone

> On Mar 24, 2016, at 21:14, Mark K3MSB <mark.k3msb at gmail.com> wrote:
> 
> Hi All
> 
> I want to start using my SCR-274N on AM and have been looking for ways to use non Carbon Mic with the BC-456 modulator.
> 
> There was a potentially interesting solution about this on an old QRZ.com post:
> 
> http://forums.qrz.com/index.php?threads/carbon-mic-replacement-for-mily-transmitters.443437/
> 
> with the schematic (no documentation) listed here:
> 
> http://forums.qrz.com/index.php?attachments/img312-jpg.190336/
> 
> I went to the ER Web site and there doesn't seem to be relevant article in the August 1990 issue.  Does anyone have this issue to verify?
> 
> I was also looking at back issues of ER and the only two related articles I found were:
> 
> January/1992  Microphone Replacement, TCS Carbon by (Mike?) Murphy.
> 
> March/2008  Regular Mic preamp for Carbon-Mic-Only Transmittters by Heidelman.
> 
> I don't have any of these back issue in my collection, and I'd be interested in know if any of those articles provide a suitable solution to using a non carbon mic.
> 
> 73 Mark K3MSB
> 
> 
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20160325/455646fc/attachment.html>