We found this circuit in a 1976 publication. The transistors can be BC547 or 2N2222. Crystals up to a few tens of Megahertz can be tested. The LED can be of any type. The capacitors must all be ceramic.
This circuit was found in an American telecommunications documentation from the 1980s. The circuit...
This circuit is from a 1970 publication. The time constant is given by 1.3R x C where R is the...
This 18 V x 300 mA power supply was found in a 1969 documentation. The integrated circuit is...