This circuit is from 1999 documentation. The integrated circuit used is not very common today. Both transistors are used if the motor current is greater than 500 mA.
Yes, tunnel diodes can also be used in voltage regulators, as shown in this circuit from a Radio...
The gain of this circuit at 1 kHz [and 40 dB falling rapidly when the frequency deviates from this...
A frequency of up to a few kilohertz can be obtained with this oscillator. The frequency is given...