Leak Detector (CB22456E)

We found this circuit in a Popular Electronics from 1992. The transistor is general purpose, assuming equivalent.

Electromechanical Counter (CB21682E)
This photoelectric circuit from a 1960 publication uses a 6.3 V electromechanical counter, common at...
Universal VFO (CB21145E)
We found this circuit in a magazine 73 from the 90's. It is a circuit indicated for radio-amateur...
Alarm Siren (CB15086E
) This circuit uses two 4046 CMOS PLLs to produce a modulated signal of good intensity. The MOSFET can...