Well, I'm thinking of that image you posted above, the ring with the dial on top of it. That would be conspicuous.
Have you thought of a creating a movable wider, thinner ring, over the original banded ring? A part that you could turn around the voltage, to acquire a sort of 'rate'. It would have that same circular nature, but be even more compact. If your having trouble visualizing, think washer and screw. Although this time, the screw is the original ring with the coil and such, while the washer is the dial so to speak. But your turn the washer, not the screw.
Tough to make an analogy for it.
I'm trying to think outside the box, but I generally use a sigil that operates as the perfect rate(with great success), so I haven't really hit this problem. This is what I meant by foregoing the initial issue. I was introduced to this solution by a friend of mine.
Physically, I'm trying to hold my tongue on all this cathode, amplification, and voltage talk. I am completely ignorant of this subject, and have little experience and not expertise to speak of. If you have some sort of newbie guide or resource, that could explain all these uses to me, I'd appreciate it.
Radionics was one of the first fields I hit, but I was lucky enough to be introduced, and have success with, symbolic radionics, before getting mired in the physical goods, specifically those concerned with frequency and such.