Using JFETs, this circuit from a 90’s American documentation can generate signals of 0.15 Hz. The JFET can be of any general-purpose type like the BF245 or MPF102.
This circuit is from an April 2000 Poptronics. The magazine no longer exists, but the circuit can...
This broadband amplifier was found in an Elektor from the 90's. The gain is 10 dB with a noise...
We found this load control circuit on the power grid using a SCR and PUT in a thyristor manual...