T&T: Old Electronics Question

[Ken Bloomfield]

Rich,
The comment that was made about carbon mikes being nearly indestructible is 
very true.  Just to give you an idea of where/how to look, the following is 
a brief description of how it works.

There is a supply source of voltage from the Loud Hailer to the mike element 
on one wire.  The carbon element is essentially a variable resistor, who's 
resistance varies with the alternating sound pressure.  This effect rapidly 
varies the current passing through the element producing a current variation 
that is at the frequency of the sound impinging on the diaphrgm.  In turn, 
this current passed flows on the return wire to the Loud Hailer.  Inside the 
loud hailer, this current is made to pass through a fixed resistor, and 
following VOLTAGE = CURENT x RESISTANCE creates a varying voltage drop 
across the fixed resistor at the audio frequency.  This is normally stripped 
off the DC level (i.e. decoupled) by a capacitor and fed to the amplifier 
input.  This is the same amplifier input that you mentioned works fine with 
audio from other sources.

Therefore:
1.  The greatest likelihood is the broken wire theory.
2.  You can verify this with an ohmeter.
3.  If you measure across the terminals, there should be some voltage across 
the carbon element.
4.  If no voltage across the carbone element, and no wires are broken, then 
there is a fault in the loud hailer.

Hope this is of some help.

Ken Bloomfield
MTOA# 2062
AGLCA# 3529
M/V Tellico Lady, 50' Marine Trader-Walkaround
Maryville, TN