This 100 MHz bridge circuit was found in an American 1970s documentation. The supply voltages are not indicated, nor are the tubes.
This brightness control for incandescent lamps or engine speed has been found in a 1970 English...
This circuit adjusts the drained current to values up to 20 A, allowing the testing of power...
This PWM control circuit was found in an old documentation, but appears elsewhere on this site...