From: SFPhysics <SFPhysics@aol.com>
Date: Wed, 6 May 1998 00:47:12 EDT
To: pinhole@exploratorium.edu
Subject: Re: RS Communication Project Answer
Hi Tom -
The shortwave receiver on pg. 37 of the Radio Shack Communications Projects
booklet uses the 741C for an audio amplifier. The 741C is a frequency
compensated operational amplifier (two input voltage differential amp). The
Amplitude Modulated signal from the tank circuit of L1 and C1 is rectified by
the "detector diode" D1 for the audio signal. That audio is greatly amplified
by the 741 which feeds the volume control, potentiometer R3. The 386 chip is
the power audio amplifier that has enough current to drive the 8ohm speaker.
The 741 gives the high audio signal gain then the 386 gives the current gain.
Hope that helps and that I'm not in my usual "clear-as-mud" state.
I would recommend these Radio Shack booklets for all Physics and "Integrated
Science" teachers. The Science Projects booklet has a really simple yet very
effective seismograph (you supply the strip chart recorder).
Al Sefl
SFPhysics@aol.com
p.s. Only 23 more working days until vacation in SFUSD! :-)