This circuit was found in a 1971s English magazine. We can still assemble it using BC548 transistor. The other components are common. The supply voltage of 6 or 12 V depends only on the relay.
This circuit was found in a 1980s US publication. There may be some difficulty in obtaining the...
The circuit shown is from the Motorola Linear Databook of 1990. In the example, the components are for the...
Ideal for benchtop use, this dual-band circuit was obtained from the 1995 Electronics Now...