This 80's circuit uses a germanium transistor like the AC121. The circuit has an output transformer of the type found on many transistor radios of the time.
Figure bellow shows how the 4510, a divide-by-1U, up/down counter with three-state outputs is...
This simple light meter or photometer circuit uses an analog indicator of 0-1 mA. Power is...
The frequency of this oscillator depends on the inductor and capacitors in parallel with it. In...