Search Results for: audio amplifier

Output frequency or tone of the project temperature controlled oscillator circuit varies with the temperature at which the input germanium diode is held. Reverse resistance of D1 varies from 500-Ω to 10 KΩ, when temperature varies between 200C and 800C. (At higher temperature germanium devices show very low resistance.) This variation of resistance changes the tone of the output sound of the oscillator which is built around the AF amplifier IC (IC1). Instead of germanium diode, base-emitter junction of an ordinary medium-power transistor such as AC128, AC188, 2N360 or 2N610…

The telephone spy circuit published here is used to hear telephone conversations remotely or to amplify the telephone conversations and also transmits the speech signals in the MW range so that one can listen to a telephonic conversation on a radio set. The device picks up telephone conversations remotely if the telephone set is in the range of a few meters to some tens of meters, the device then amplifies the received signal and plays it through the speaker, and also transmits the signal as a Medium Wave signal. The…