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 a National Semiconductor manual that is now a Texas group company. The...
We found this 5-digit circuit in a 1990 publication. The displays are of a common cathode and the...
This experimental radio was obtained in an old Argentine publication. Germanium transistors are...