It's fun to wave a magnet around a VFD. I bet you could make a fairly
sensitive magnetic-field detector from one.

John


The best way I could think of doing that is feeding an AC signal through the
filaments so that they distort in some way when in the presence of a
magnetic field, then monitor the electrode current in some way to determine
the amount of filament displacement that is happening. That would give you
an indication of magnetic polarity, and intensity.

Second idea. Just have one grid positively biased, and monitor the current
of just two anodes behind it. When the electrons move through the magnetic
field, they will be shifted to one side or the other. electrode current will
also shift. That would also allow you to determine polarity and intensity.

Hmm... The second idea would also work with standard vacuum tubes that have
more than one anode. Or even two or more electrodes of any type that is
separated from each other by a small amout, that can be used as anodes. The
magnetic field would shift the electron flow from one electrode to the
other. I'll have to do some experiments on that subject.