• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Success or problems with ferrite beads / rings as stoppers?

Smaller beads can give the same impedance - the ratio of length to diameter is what matters. The 43 material (850 perm) is essentially non-conductive, higher permeability materials are lower resistivity (and less effective at VHF). But shunt capacitance will change if it moves, hence securing is a good idea.

A bead about twice as long as OD will be about 200 Ohms at VHF, nearly pure resistance.
 
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