[ARC5] Carbon Microphone Inquiry

[Jim Haynes]

Even when new T-17 mics are quite insensitive, and carbon mikes don't
improve with age.  It's my unsubstantiated theory that they were
intentionally so insensitive so they aren't too sensitive to airplane
noise.  Thus the user has to yell into the mike and will be heard
over the airplane noise.  We were discussing recently about a replacement
for the T-17 carbon element.  The opening is just slightly too small
to take a modern T-1 carbon element such as used in 500-type telephone
handsets.  One could probably turn it out on a lathe and have an
authentic-looking T-17 that would be of normal sensitivity.

There is also an electret replacement for the T-1 carbon element in
telephone handsets.  I got some from Mike Sandman near Chicago.  They
are made to fit into handsets using modular cords, but with some
carving they will fit into a handset with fixed cord.  And I took one
apart - if I could find it now I could see if it might fit into a
T-17 without modification.  They are cheap, less than $5 so you don't
mind cutting one up.  Consists of the electret element plus a bridge
rectifier to make it not polarity sensitive and a transistor amplifier.

I can send you a schematic of the electret element, but probably can't
post it to the whole list.

jhhaynes at earthlink dot net