We found this circuit in a Japanese publication in 1967. The circuit consists of a 15 W audio amplifier with germanium transistors including a voltage indicator power supply.
This simple circuit, which requires a low current (50mA) relay for 5 to 12V power supplies, was...
We found this circuit in a publication from the 1970s, but it can still be assembled today by...
Found in a Motorola documentation from the 70s, this circuit makes use of transistors of the time....