Audio amplifier 741 (CB20478E)

This low power audio amplifier was found at 1992s Popular Electronics. Transistors are general purpose common types.

Regulator with tunnel diode (CB23584E)
Yes, tunnel diodes can also be used in voltage regulators, as shown in this circuit from a Radio...
1 kHz Tuned Filter 741 (CB19118E)
The gain of this circuit at 1 kHz [and 40 dB falling rapidly when the frequency deviates from this...
Relaxation oscillator with operational (CB25191E)
A frequency of up to a few kilohertz can be obtained with this oscillator. The frequency is given...