This amplifier with old germanium transistors is from a 1957 documentation. The power is a few hundred milliwatts and the transformers are common types of driver and output of the time.
This 1987 circuit has a very interesting concept. It powers a second set of rhythmic lights from...
This circuit with reed sensors is very simple, feeding a 12 V siren when triggered. The circuit has a...
The signal from this transmitter is injected into a cable that you want to follow along a...