AC Tachometer (CB9353E)

This circuit was found in a 1969 EEE. It detects when there is a phase failure in a circuit using an inductive sensor.

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Electronic Flute (CB4570E)
I found this circuit in an English magazine from July 1982. The circuit is still viable by using...
High Input Impedance AC Follower (CB14137E)
The circuit shown was found in the 1994 National Semiconductor's Linear Application Handbook. The...
Door buzzer or alarm (CB20492E)
This solar powered circuit was found in a 1991 documentation. The transistor is a general purpose...