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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Filter with the LM102 (CB12559E)
In the figure we have a circuit suggested by National Semiconductor, using an operational...
High Voltage Inverter (CB25669E)
For experiments with ionization chambers and Geiger valves this circuit generates high voltage from...
Continuity Test 555 (CB14933E)
We found this circuit in a 1979 documentation, but it can be changed to use more modern...