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 many record players with crystal phono pickups. The output power is 800...
This mixer or audio mixer uses common FETs that can be the BF245 or MPF102 and an operational...
This circuit was found in July 1986 Radio Electronics magazine. The maximum current is 1.5 A. The...