the hartley oscillator is distinguished by a tank circuit consisting of two series-connected coils (or, often, a tapped coil) in parallel with a capacitor, with an amplifier between the relatively high impedance across the entire lc tank and the relatively low voltage/high current point between the coils. the original 1915 version used a triode as the amplifying device in common plate (cathode follower) configuration, with three batteries, and separate adjustable coils. the simplified circuit shown to the right uses a jfet (in common-drain configuration), an lc tank circuit (here the single winding is tapped) and a single battery. the circuit illustrates the hartley oscillator operation: