This simple timer with unijunction transistor was found in an old American technical documentation. We can use 2N2646 for the unijunction and BC548 for the transistor.
This circuit generates sinusoidal signals between 300 and 3000 Hz. We find a 303 Circuits from the 90's....
This amplifier for audio transmission lines was found in a 1961 American publication. The critical...
Old phones with dials can be used in a simple home intercom system, as this circuit from Popular...