This QST circuit generates 4 frequency signals according to the crystals used. Transistors admit equivalents although the indicated types can still be found with some ease.
This basic configuration of voltage regulator using operational amplifier and zener was found in a...
This 75 W power supply was found in American documentation from the 1980s. Transistors can be...
This circuit was found in a 1987 magazine. It measures the pulse rate produced by a cardiac...