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When is a coil not a coil?

At frequencies where these tubes might oscillate, these ferrite beads look like small resistors more than like inductors, paradoxically. That's due to intentional losses in the core. If they were purely inductive, they could contribute to the problem. At frequencies in the audio band and somewhat above, these beads are hoped to disappear. There is a bandwidth advantage compared to using a resistor, since there is less series resistance to interact with grid capacitance. But then there is the neurosis about the non-linear B/H characteristic of ferrite creating distortion. To me, the jury is still out on that one. As always, it probably depends on implementation details.

I have to agree with Triode Kingdom’s comment below: the easiest, most effective approach is to just use a simple resistor as a stopper.

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