Check out these scanning electron micrographs of the interior of a 572B triode. Please note that the filament was broken and can be seen skewed inside the grid loops. It’s interesting to see the crimp entrapment of the grid as it winds a coil up the center of the tube. Note that each fgrid strand is in parallel electrically, they would have been physically close to parallel had I not damaged them removing the plate!
On the micrographs, I’ve had a scanning electron microscope for many years- mostly for pleasure but for hire on occasion. The data on the bottom is, far left voltage in kilovolts, the magnification when viewed as a 4″ x 5″ image- the size of the original Polaroid prints. When viewed on your monitor multiply by perhaps a factor of 4. Next to the right is the micron bar- it’s identical to a map key- use this bar to determine the size of objects in the image. Finally, the number to the far right is a resettable counter that indexes the image in a series.
My SEM is an ISI DS-130 and was the Cadillac in it’s day – back in the early ’80s. It still takes great images and can resolve to about 3 nanometers.