This 1969 circuit uses a 117 V filament tube powered directly by the power grid. The original circuit makes use of a charcoal microphone, a common component at the time.
This circuit is one of many that we have in our section. It was taken from the Electronics...
This is a bridge for the measurement of low value resistances and high values too. The circuit...
This circuit for the two-meter band of radio amateurs was found in 1980s documentation....