This low frequency divider uses unijunction transistors. The bipolar transistor can be a BC548 and the zener diode Z4XL can be a 12 V zener. The circuit was found in a 1967 publication.
This circuit was found in Radio Electronics magazine from the 90's. The circuit is for small NiCad...
This transistor tester was found in a publication by Gernsback from 1960. The circuit can be used...
This logic probe or logic level indicator is suitable for use in CMOS circuits. The power comes...