This interesting circuit was found on the Internet and is based on the 555. The circuit uses power MOSFETs that determine its output. No information about the transformer was provided.
This circuit was found in a 90s Hands-on Electronics. The transistor can be a BC548. What it does...
This circuit separates the bass from the treble in an audio signal. The circuit is from a Hands On...
The frequency of the signal produced by this circuit depends on the temperature of the diode used...