The operational amplifier of this circuit can be the 741. The circuit has very low consumption and can be powered by two 9-B batteries. Low voltage amplifiers can be used.
This very simple 1-transistor oscillator is from Raytheon's transistor manual of the 60s. The...
This circuit is from a 1957 Raytheon transistor manual. The diode can be of general-purpose...
We have in the figure an ultra-simple alarm found in a 1981 publication. As the author indicates, it is...