This circuit was found in a General Electric documentation from 1970. Equivalent transistors can be used. The maximum signal frequency for the indicated components is 250 kHz.
This conventional astable multivibrator circuit with operational amplifier can be found elsewhere on...
The LDO series (Low Dropout) TPS80 from Texas Instruments (www.ti.com) can provide output voltages...
This circuit was found in a Hands On Electronics from the 80's. The circuit emits an audible alert...