We found this circuit in an 80's manual. The same configuration can be adapted to make use of modern operational amplifiers. The power supply is symmetrical.
We found this audio amplifier stage with 500 ohms of input impedance in an old American...
In this circuit the 555 is configured as an adjustable timer for long intervals. The capacitor C1 can be...
This simple circuit published in the November 1962 Radio Electronics magazine beeps when the light...