Ultrasonic repellent 4011 (CB9385E)

This circuit was found in Radio Electronics from the 90s. The transducer is a tweeter and the power transistor must have a heatsink.

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2400 Hz Neon Oscillator (CB21457E)
Found in an old documentation about neon lamps, this circuit has the frequency basically...
Standing Wave Ratio Meter (CB4121E)
This simple standing waveform (ROE or SWR) meter is used to adjust antenna matching with...
High Pass Filter with Operational (CB19677E)
This is the traditional configuration of a high-pass filter with an operational amplifier, such as...