This circuit was found in the July 1969 Radio Electronics magazine. The circuit controls resistive loads and universal motors with power according to the SCR used.
This transmitter for the 80-meter band (3.5 MHz) was found in an old documentation for radio...
This interesting bandpass filter using an operational amplifier 741 has its cutoff frequency...
Found in 1966 General Electric documentation, this circuit uses solicon unilateral switches (SUS)...