Buffer for VFO (CB7282E)

This circuit was obtained in a Popular Electronics from the 90's. The gain depends on R4 and R3. Transistors are general purpose types.

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560 kHz to 1 MHz VCO (CB21499E)
This circuit was obtained from an Electronic Design from 1964. Transistors admit modern...
Audible pulse analyzer (CB7139E)
Found in an English documentation from the 90's, this circuit makes slow logical pulses audible,...
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Using a 4-layer diode, an unusual component today, this circuit was found in an American...