Found in an Elektor from the 90s, this circuit can be powered directly by the power grid. The circuit uses a rectifying bridge that can be replaced by 4 common diodes.
The circuit shown is a documentation on 80's tunnel diodes. The frequency depends on the delay line...
This circuit generates excellent sinusoidal signals and has the frequency adjusted by VR1 which is...
This circuit was adapted from an Italian publication that no longer exists. This is “Onda Quadra”...