A Hartley Oscillator

Author: J.B. Hoag

Fig. 14 B. A Hartley oscillator

As in the circuit just discussed, so also in the Hartley circuit (Fig. 14 B), the amplified energy of the plate circuit is fed back to the grid circuit by means of fluctuating magnetic fields. They are both of the so-called magnetic feedback type.

The Hartley circuit uses only one coil, part of which is in the plate circuit and part in the grid circuit. The amount of magnetic coupling between the two parts of the coil is adjusted by moving the tap. This tap is indicated by the arrowhead in Fig. 14 B. The circuit shown is of the so-called parallel-feed type. In other words, the plate circuit is divided into two parallel branches, one of which carries the direct current and the other the alternating current. A choke coil (r.f.c.) keeps the alternating current out of the d.c. path, and a blocking condenser C_b keeps the d.c. out of the a.c. circuit. The grid condenser C_g and the grid-leak resistor R_g serve the same purpose as in the tickler circuit.