Continuity tester (CB7386E)

This circuit was found in a Hands-On Electronics from the 90's. The FET can be any general purpose.

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Snitcher (CB21964E)
With this name, we find in a documentation by Hugo Gernsback from 1960 this small transmitter for...
Bi-Quad Voltage Controlled Filter (CB19072E)
This circuit uses operational amplifiers that must be powered by a symmetrical source to implement a...
Symmetric power source using a single secondary transformer (CB5459E)
In the figure we have a way to obtain a 15 V symmetrical source with a 30 V single winding...