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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Second Order High Pass Filter (CB12573E)
The configuration shown in the figure is a second order filter (12 dB per octave) with an...
FM AC Transmitter (CB20347E)
This transmitter, indicated for espionage applications, is permanently powered by the power grid....
SCR Incandescent Indicator (CB14902E)
This circuit was obtained in an old French publication from the 80s. The maximum power of the lamp...