Jim Haynes wrote:
On 2009-02-08, terryS wrote:
On Feb 2, 6:48Â*pm, "Richard Knoppow" wrote:
"K3HVG" wrote in message

...
Jim, Â*I'm surprised you didn't need an amplifier with that
electret element? Â*That's what the carbon-compatible mics
use in 2-way and avionic installations to get the required

The electret elements from Radio Shack include an amplifier, which
is why you have to power them; but I don't know if it brings the output
level up to that of a carbon mike. The electret T-1 replacement I got
from Mike Sandman obviously has enough amplification built into it
somewhere, since it directly replaces the T-1. But I didn't tear it up
to see what is inside.

All those electret elements have a FET-IC in them, which is a J-FET with
controlled leakage so that they don't need a grid leak resistor inside them.
Apply voltage across them through a resistor, pick the modulated signal
off through a capacitor. With a little tinkering with series and shunt
resistances you can make one fit right in place of a carbon element.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."