This circuit is from a 1966 publication. The frequency depends on the capacitors and on R1 which can have values between 47k and 2.2 M typically. The supply voltage can be between 200 and 300 V.
This circuit has a full scale of 1 kW, being indicated for the 110 V power grid. Adaptations can...
This crystal filter is normally used in receivers and the frequency depends on the crystal used...
This simple 2004 circuit uses a common sensor used in television and other equipment. It checks...