Hi there!
I've seen a few videos of people using vacuum florescent displays as triodes. I thought you needed a high temperature cathode in order to have thermionic emissions, but these don't seem to be heated at all? The voltage is quite low as well on these so I really don't understand. I thought I'd the voltage was higher you could maybe develop some kind of static or something hahaha I really have no idea. This is also how the "nutube" works.
Could someone please shed some light on this for me?
Thank you!
Here's a link to one of the videos
YouTube
I've seen a few videos of people using vacuum florescent displays as triodes. I thought you needed a high temperature cathode in order to have thermionic emissions, but these don't seem to be heated at all? The voltage is quite low as well on these so I really don't understand. I thought I'd the voltage was higher you could maybe develop some kind of static or something hahaha I really have no idea. This is also how the "nutube" works.
Could someone please shed some light on this for me?
Thank you!
Here's a link to one of the videos
YouTube
Thank you! Do you know where I could get more information? I'm curious about what the coating is, advantages and disadvantages vs heated filament etc.
From my naive position, they look allot better from a manufacturing position so I wonder why they aren't a thing for triode use? Higher density, better cooling, smaller size etc
From my naive position, they look allot better from a manufacturing position so I wonder why they aren't a thing for triode use? Higher density, better cooling, smaller size etc
The filament of a VFD IS heated. Sometimes you can see a faint glow in a dark room, especially if all the display segments are dark, sometimes you can't.
The Korg Nutube is a redesigned VFD made by Noritake who also makes VFD's.
Ordinary VFD's do work as triode vacuum tubes. They are designed to be off or on, so linearity was never a design criteria.
There are also special purpose vacuum tubes that operate from 12 volts or less, some with thin filaments that run on 1.2 volts at 10 ma. You can't see the glow in these either. Look up the 6418 tube, also the 6088 and 5678.
The Korg Nutube is a redesigned VFD made by Noritake who also makes VFD's.
Ordinary VFD's do work as triode vacuum tubes. They are designed to be off or on, so linearity was never a design criteria.
There are also special purpose vacuum tubes that operate from 12 volts or less, some with thin filaments that run on 1.2 volts at 10 ma. You can't see the glow in these either. Look up the 6418 tube, also the 6088 and 5678.
So… in other words - as fascinating as they are, one might as well just get a "real tube" that has the same operation characteristics like the 6418, 6088 and 5678 (as well as another few dozen others).
https://frank.pocnet.net/sheets/127/6/6418.pdf output pentode. For headphones.
https://frank.pocnet.net/sheets/127/6/6088.pdf equally picayune "power" amp pentode
https://frank.pocnet.net/sheets/030/5/5678.pdf yet another pentode. 50 ma.
There you go, for your dining pleasure. linkies
GoatGuy
https://frank.pocnet.net/sheets/127/6/6418.pdf output pentode. For headphones.
https://frank.pocnet.net/sheets/127/6/6088.pdf equally picayune "power" amp pentode
https://frank.pocnet.net/sheets/030/5/5678.pdf yet another pentode. 50 ma.
There you go, for your dining pleasure. linkies
GoatGuy
Barium oxide is a very typical coating material from what I know, no clue about what other options there are. Filaments run at fairly low temperature (600...800ºC) so they barely glow. I'm not sure what the wear cathode wear is like on indirectly heated things, but the filaments will gradually lose emission and display will get darker and darker, also there's a sputtering effect happening where particles of the filament end up on other surfaces. You can see this effect here :
It does take a while for that to happen, that particular tube had been in use nonstop for at least 3 decades (in a clock used in a public place).
Another problem is that with long filaments there is going to be a big voltage gradient across it when DC is used, making one side brighter than other. Normally AC is used so that only the middle is slightly dimmer than the rest.
I cannot comment on use of VFDs as triodes, I have only ever used them as display devices. I cannot image they'll make a very good triode, those filaments are not exactly secure and vibrate for a long time (tens of seconds even) when you strike the tube, I can imagine they'll be very microphonic.
They have vacuum inside so no convection, only radiative effects matter and tiny amount that gets into the glass via filament electrodes. Tube which filament is driven very hard will get pretty warm though, but you only do that to get extra life out of already worn tubes.
The wear isn't related to heat generation per se, the coating just wears off after a long while, boosting voltage to get more heat helps to some extent. Tungsten that's under the coating will not emit any substantial amount of electrons and once the oxide coating is gone it is time to say goodbye.
The wear isn't related to heat generation per se, the coating just wears off after a long while, boosting voltage to get more heat helps to some extent. Tungsten that's under the coating will not emit any substantial amount of electrons and once the oxide coating is gone it is time to say goodbye.
Thank you so much for explaining all that to me. I really appreciate it. I'm fascinated by a flat form factor valve. I guess the current valves are so common, work so well, and so easy to swap out that a brand new form factor like the nutube really isn't necessary. Most, (but obviously not all) uses for valves do not really need tiny form factors and the added cost may not be worth it. Like, portable valve headphone amps are a bit of a novelty IMO and car audio spent seem like the best environment for them either, which are the only needs in audio that I can think of, of the top of my head that could benefit from a small form factor.
Anyway, cheers again for all the info!
Anyway, cheers again for all the info!
People, including Nelson Pass, seem to be getting good results from the VFD "NuTubes". The Vox AD50 guitar amp also used these VFDs and sounds quite fabulous.
These VFD-based triodes are just a way of keeping a production line going. I don't think anyone seriously thinks they are an improvement on traditional valve structures. There was a similar attempt a few years ago to produce triodes based on CRT electron gun structures (again to keep a factory going). They were only on the market for a few years.
This is worth looking at it may be another diferent triode. If you look at the circuite it looks like no "heater " curent is used. B1 with Korg Triode
Attachments
17 mA per section per Korg datasheet. Single unit sample price is about $50 each. I got small quantities of the tubes I mentioned for less than $1 each. I got a pair of surplus clock VFD units for $1.50 each and ripped the VFD off them. They do amplify, but that's about it. I would rather use a real tube. The tiny tubes and the VFD's all exhibit microphonics which may limit their usefulness in car audio or other portable applications.
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