I saw similar on the smaller ILC-1/8, so I applied rectified AC on the grid and the problem went away. In my case, only the vertical filaments caused dark bands, not the mesh.
I concluded there are some electrostatic patterns that are, well, static when the grid is pure DC. With the grid varying from the rectified AC, the field changes and the phosphor averages it out. The other departure from normal vacuum-tube behavior is that the grid current can be surprisingly high, over 100mA compared to microamps for a vacuum tube, because the grid is biased positively. If you look at aging VFD's, you can clearly darker bands closer to the filament (phosphor degradation) which I concluded were caused by electron bombardment. On Sunday, November 23, 2025 at 6:35:38 AM UTC-8 Tom Katt wrote: > Almost looks like the fluorescent material was unevenly applied or > delaminating somehow.. Like thick / thin spots or similar thickness or > distance issue. > > Does the anomaly align with the cathode heater wires? > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion, visit https://groups.google.com/d/msgid/neonixie-l/77dd03f2-b01b-4ba0-8836-1bd905b77028n%40googlegroups.com.
