A tickler coil is a small inductor placed in the anode or plate circuit of a vacuum tube and magnetically coupled back to the grid coil. This arrangement creates positive feedback, which dramatically increases the gain and selectivity of the circuit. It was the defining feature of early regenerative radio receivers, allowing a single tube to pull in weak distant stations.
Adjust the coupling on the tickler coil just until the receiver starts to oscillate, then back it off a hair.
Related terms
Coil
A passive electrical component made of wire wound into a spiral or cylinder to create a magnetic field.
Vacuum tube
An evacuated glass or metal envelope containing electrodes used to control electron flow.
Feedback
A portion of an output signal routed back to the input to alter a circuit's behavior.