Looking for an analog electronics guru for help

[Tedyp]

analog electronic guru

We use at work headsets for comunnicate from point to point, i.e. let's say we are about 5 miles apart, 2 wires between us, 2 headsets. The headsets have a Carbon microphone and a dynamic headphone, connected in series. now we attach a 6V battery in series and we can talk point to point. I cannot find this kind of microphones - about an inch in diameter - anywhere, and decided to construct a device that may replace them...I have no idea how to do that yet, as the charcoal mike change its resistance in function of speech (air pressure)...
The point is that I can find here only headsets with ELECTRET mikes...
I'll be very thankful if anyone could give me an idea or a place where I could find an idea...It's VERY important for me, my top priority project ....
Please HELP !!!

 

[Roscoe]

replacing carbon mic with electret schematic

Hi,

i think the construction of your headset is similar the old "bell telefon" style.

In the past, 30 years and more ago, the carbon microphon was a part of all the telefon sets. I think you must search for old schematic and parts for old phones.

roscoe

 

[Tedyp]

Right, I have those plans, but my problem is I have to change from carbon to electret type mikes, as i need to connect 3 persons to speak over 2 wires...I'm working at the telecom company, and workers have to use those devices for testing.

___battery____I|________
| |
>II earpiece II<
| |
IO Carbon Mike OI
| |
| |
|_____________________|

this is the simple circuit. I MUST replace the carbon cartridge to an electret one. Changing to dynamic one is no problem, but I need an ELECTRET replacement....
Well, I see my drawing is not exactly piece of art....
Thanx

 

[btbass]

Hi mate, I work for a telecomms company that makes a lot of mics. We used to make those carbon mics, I remember those old knockerboxes to tap the carbon down, those were the days!

pm me, we can sort it out.