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EEVblog 1601 - How VFD (Vacuum Fluorescent) Displays Work

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How VFD (Vacuum Fluorescent) Displays Work.

Extracted from a hacking video #717:

I had a moment rejuvenating a 34401a VFD, connected power to it and it didn't light up. Applied filament power and +30V on the segments, grid floating.
I expected segments to light (normally on unless the grid biased negative) but it stayed dark.
Turns out the "grid" works like a screen grid, not a control grid.

I do the usual filament bake off up to 2x Vfil absolute max, and then also a grid bake off was needed. There is some buildup on it as well.

Useful VFD links:
Futaba's VFD Characteristics & Operation guide AN-E-1103A
Noritake's A Guide to Fundamental VFD Operation

I had a Sony MHC-DX7 shelf stereo/mini system that bought in 2000 or 2001, was the display a VFD or just an LCD one?

VFD's are superiour for readability in sunlight and low temp (below -30°C) I used them a lot in industrial panels that are located outdoors. Instead of low temp fluid and heaters in LCD's.
Noritake iTron/Futaba were kings making the best VFD's but LCD's took over and had the lower power consumption, you don't need a few watts for the filaments.

Interesting the Korg Nutube 6P1 (by Noritake) is just a VFD as a low voltage twin triode. They're just exploiting the non-linearities I think THD 1-20% very fuzzy and perhaps corny.

Sony MHC-DX7 uses a VFD


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