Unfortunately due to how the helmet is assembled, replacing the mic
would require quite a hack job, so I'm trying to avoid that. I'm
pretty sure the mic element is electret rather than dynamic. Although
it will probably be more costly than building the amplifier circuit,
would the amp be contained in a david clark electret mic assembly
(i.e. part #22 in this:
http://www.davidclark.com/PDFfiles/19515p39.pdf)?
Bruce

(John) wrote in message ...
The easiest way is to replace the mic with a David Clark or Telex
aviation mic.
If you can not do this then you can strip the amp out of an old Telex
100TRA slim line mic if you have a dynamic mic element in your helmet.
Put this amp in a box and plug in the 9 pin D connector into it and
run the aviation style plugs from the box so you have a lumpy
interface cable. Nine times out of ten the old telex mic died due to a
bad switch which you don't need anyhow. Most intercoms will drive the
32 ohm speaker. If it will not drive it to the level you need get a
low cost speaker amp of a watt or two. See the National semiconductor
data book for circuits if you want to make your own.
John