Anyone recognize this VFD?

[Spitfirejoe]

Looks kinda like the one that was on an old AKAI receiver I had a while back. It had a touch sensitive pad for a volume control that I found a real pain in the butt to adjust.

 

[biscuithead]

Display unmounted - display switched on.

Dang! This wasn't "Finding Nemo"... This was "Nemo Found" ! Good work sir!

 

[biscuithead]

I really should not be surprised at people's ignorance of these devices. And I do not mean that as an insult, it means the lack of knowledge of...- whatever it is.

The device is a Vacuum Flourescent Display and I got and a co-worker got into and argument about who knew better how they worked and we were both ASC grads.

It is actually a tube, somewhat like a CRT in that it uses phosphors. however, unlike a CRT it does not use a deflection yoke or plates, instead, there is an array of grids, cathodes and anodes. The thing is actually a triode ! Just happens to have a hundred grids or whatever.

Typically, the cathode is embedded into the front glass in the form of skinny little wires which form the cathode. Generally they were fed by a floating source at like a few volts, it wasn't very much but the whole thing was usually at negative 30 volts.

All the multiple pins were anodes and grids. Remember the cathode is in the front. It scanned the display, and persistence of vision made it look fine. Just like television. when the high speed shutter video cameras came out you could see them scan. (and a few other things)

The chip that drove the display would put out 12 volts to the anodes selectively, and it was all a matter of timing.

The VFD tube typically had a getter as well as the typical evacuation port, sealed of course. The getter was positioned to be out of the field of view, but you can see it usually when the eschucheon(sp) is removed. It should look like metal, like in a tube, and if it is white and flakey, the VFD is aired, just like a tube.

I went on Usenet with those %&%*# engineers and asked why they did not go with VFD technology for flat screen TVs rather than plasma, which is embarrasingly inefficient and they explained that it would actually be worse. I still disagree. A plasma TV makes an arc, and the duration of the arc versus your persistence of vision determines your perceived brightness level of any given cell. This is ridiculous.

So they could not access that many pixels with about 40 volts but they can with about 400.

OK.

Anyway, that is a tube, literally, and the cathode is right on front. If you look close you can see the filaments. When screwing with them, keep in mind they only get a couple of volts on the filament. I had a power supply fault in a VCR and I saw them light up yellow, like a tube ! Like OH ****, UNPLUG THIS NOW. Unlike the filament in regular tubes, these filaments do not put out visible light. that is a function of the fact that the cathode is so close to the plate(s). The thing is flat so therefore it needs less voltage and actually less thermionic emission.

Even though I do not remember all of it, it was explained why too many things were too hard to deal with and why this expensive as hell plasma TV technology prevailed. Having linearity in the brightness and all that. These things were more suited to display the setting of your stereo. You either turn on an element or off.

And that's their job, and that is probably twenty times as much as you wanted. So I stop now.

Like a flat Nixie... Thanks for the tutorial! I'll try to retain 10%,

 

[Prime Mover]

Like a flat Nixie... Thanks for the tutorial! I'll try to retain 10%,

Not like a Nixie at all. A nixie is a cold cathode device (with a low pressure gas fill) and has no grid or heater/filament. It's the gas around the cathodes that glow on a nixie and the phosphor coating on the anodes that glow on a VFD. There are flat nixies. Panaplex displays and neon gas plasma displays are examples.

I terms of making flat panel TV's out of VFDs, I would expect the main issue to be the size of the directly heated cathode required and the amount power required to run it. It would likely make the whole set run quite hot. Then you would have to drive groups or lines of pixels selected by separate grids. The grids would have to be below the cathodes and hence could not be attached to directly to the glass. I'm not sure how you could support the grids over a large span. I do have quite a large (maybe 8" diagonal active area) graphical (monochrome green, 256x128 pixels) VFD and it's got quite a wide aspect ratio. This appears to be so that the grids can be strung from the top to the bottom without being too long to support themselves. The issue doesn't exist with cold cathodes (just a whole bunch of other issues). I've seen very wide VFDs but very never wide and tall VFDs.

 

[biscuithead]

Not like a Nixie at all. A nixie is a cold cathode device (with a low pressure gas fill) and has no grid or heater/filament. It's the gas around the cathodes that glow on a nixie and the phosphor coating on the anodes that glow on a VFD. There are flat nixies. Panaplex displays and neon gas plasma displays are examples.

I terms of making flat panel TV's out of VFDs, I would expect the main issue to be the size of the directly heated cathode required and the amount power required to run it. It would likely make the whole set run quite hot. Then you would have to drive groups or lines of pixels selected by separate grids. The grids would have to be below the cathodes and hence could not be attached to directly to the glass. I'm not sure how you could support the grids over a large span. I do have quite a large (maybe 8" diagonal active area) graphical (monochrome green, 256x128 pixels) VFD and it's got quite a wide aspect ratio. This appears to be so that the grids can be strung from the top to the bottom without being too long to support themselves. The issue doesn't exist with cold cathodes (just a whole bunch of other issues). I've seen very wide VFDs but very never wide and tall VFDs.

Dang... and I thought I had a pinching grasp on this... I will pour over this thread again to seek more understanding...