This circuit was found in a 1967 General Electric documentation. Tunnel diodes can oscillate at very high frequencies. These are not currently easy to obtain components.
This experimental amplifier was found in the 1960 Mullard transistor reference manual. The...
This circuit from Motorola is from 1968, appearing elsewhere on this site. The transistors admit...
This circuit triggers the LED when the monitored battery voltage drops below 9 V for 12 V...