This sophisticated circuit with two LF411 operational amplifiers appeared in the November 1984 issue of Radio Electronics magazine. The circuit uses a Mallory buzzer as an indicator.
This VCO or Voltage Controlled Oscillator uses common components. TR1 can be a BF245 and TR2 a...
The transformer for this project found in a 1986 documentation is an output type, found on old...
We found this circuit in a 1978 documentation. The SCR conducts when the regulator's output...