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Story time. A very long time ago I was gazing in the shop windows of a large Glasgow department store called Lewis's. They had some unusual illuminated tubes in the window that had a plug-in power supply and a coiled cable leading to a very narrow plastic tube with a neon tube inside it.
I asked a shop assistant if she knew where they got them from and she contacted the window dressing team who took me up to their workshop.
They said they had been a bit unreliable and gave me a faulty one, warning me to be careful as one of their crew had received an electric shock from the wires while it was unplugged.
Inside the plug was a circuit board potted in deep resin to hide the components. It had two spade terminals at either side - mains in and high voltage out. The label indicated which terminals were which and also gave a footage range for the neon (actually argon/mercury) tube.
These units may have been made by Masonlite - a big player in neon sign components.
I reverse engineered the circuit, carefully digging away at the resin to reveal the hidden components. Once I'd worked out the circuitry I started experimenting with DIY versions, and got some custom tubes made by a Glasgow based company called The Neon Workshop.
It was always a pleasure visiting the Neon Workshop, as Donald the manager was a veteran of Glasgow's sign industry when it had competed with Las Vegas for big animated skyline signs made by a company called Franko Signs. It was interesting hearing about the older technology used in them.
Running tubes on a DC multiplier does have some disadvantages. It restricts the length that can be run, only seems to work properly with mercury based tubes and has a side effect of causing mercury migration where the mercury vapour in the tube gradually moves to the negative end and either needs the polarity reversed, or the bead of mercury shaken back to the other end.
The upside is that it is a very simple and cheap circuit that can be made with ordinary components. I've seen these used in some of the neon radios that were popular for a while. The clear case had the multiplier circuitry in full view.
The use of multipliers also allows very simple circuitry to be used to animate short sections of tubes. I made a prototype module with four multipliers and opto-triacs that could connect to my fairground lighting control system.
Note that the circuit I show in the video is a very basic 240V circuit suited to about 2' (600mm) of 12mm diameter tube. Using a longer tube may result in striking/flickering issues and a shorter one will put extra strain on the current limiting resistors.
For 120V use or longer tubes it will be necessary to increase the number of multiplier stages with beefier capacitors for the first few stages and then a decent number of the 10nF capacitors to get the strike voltage.
Treat the output as high voltage referenced to the mains supply. To quote a dutch friend (Dirk Boonstra) touching the output of these power supplies will blow all the hair out of your head.
I used to use double insulated meter lead wire to connect to tubes with crocodile/alligator clips (while the power was on!), so it's a miracle I didn't get zapped.
This circuit is presented for personal experimental use only. It's not really suited to commercial use, especially with the common availability of electronic neon power supplies.
The DC mercury migration effect is what I was aiming for in the "M" tube. It has a deliberate dip in the middle to hold a droplet of mercury in an attempt to do a colour split when the mercury migrates through the neon carrier gas. Where just the neon is present the tube glows orange, but when the mercury vapour is present it glows blue. It works, but takes a VERY long time for the migration to occur.
Although using the same science as a germicidal UVC tube, no significant amount of UV escapes from this tube due to the natural blocking characteristic of soda/lead glass.
Compared to modern high frequency electronic power supplies, the simple DC multiplier produces much less electrical and RF noise. Possibly part of the reason they were used in the ornamental neon radios.
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This is a very unusual tube. It's what i call the m tube and it's made of clear glass and it's got a fill that is composed of neon gas, but with mercury in it as well. Now, normally neon tubes are either just purely the name gas, which makes a clear tube light, bright red or it's uh, either neon and mercury or argon and mercury, or a mixture of both, but with mercury. The mercury vapor is important, but and the mercury vapor gives off a lot of ultraviolet light and it gives off some visible light, not much visible light, which is why this tube isn't very bright.

However, what they normally do is they coat the inside of the tube with phosphor the mercury vapor inside the ultraviolet wavelength stimulate phosphorus, and it makes for bright neon tubes and fluorescent tubes in this case, neon. What's unusual about this, one is that i'm running on dc and it's i got a neon gas fill with a droplet america. You can see little beads american a little bit of staining as well, but it's also got this little dip here. The dip is why i call it the m tube.

It's got that little sort of m bit at the top, and that is designed to trap the mercury, because when you run a tube in dc, the mercury gradually migrates from the positive electrode over to the negative electrode. It's very slow i'd like to have shown you this much further up the orange tongue here, but i can't because uh it takes a while eve when you've had it off for a while. The mercury vapor settles back down and it happens an absolutely microscopic level that just gradually migrates up. I also have to be careful not to bump it there's tiny little beads of mercury here.

If one of those finds its way down, the red will disappear and it will just go into a completely blue tube. But when, when it's been up for a while, it does go completely red at this side and then transitions with this little tongue into blue. At the other side - and that is because it's basically separating the mercury out in the tube with dc, i suppose in a way migration of the mercury. Now i could give you a big long story about this: how it came about making one of these in the first place, but i'm going to put that down in the description, because you guys want to see the circuitry and that's exactly what we're going to do.

So i'm going to carefully tilt this back because it does operate at 240 volts, which is bumped up rapidly to a much higher voltage, and i'm going to show you what's going on in here, um i may have to focus down onto here. I shall focus down onto here. What we have in here is a voltage multiplier and that converts the 240 volts coming on here into a fairly beefy supply, based on a couple of electrolytic capacitors at the bottom. But then it's got the blue capacitors behind that are for uh, multiplying that up to actually ignite the tube with high voltage and the tube is simply in this case the circuit board slots into this case and uh the tube the electrodes just fold over and tack Onto some connections at back, so i shall show you the schematic and i'll put this out the way before i stick my fingers in the back of it.

So here is the schematic which is going to be horribly out of focus, but that's okay. We can fix that. I could also take the exposure off i'm not going to take the exposure off because that will just make it go very dull, very quickly. I'm going to put this down carefully, i'm going to leave it on, though precarious.

Oh, oh, just balance. This high voltage thing off camera right. What should we zoom down a bit? Let's zoom down just a little bit. This is probably swamping out horribly, but that's okay.

I could tame it down, but it would it. I just know: what's going to happen, it's going to go extreme tame down. Then it's going to look a bit odd right. I don't have a pen here.

I shall use a screwdriver uh. I could have done with a pen i'm going to go and grab a pen. Just give me a second i'm gon na grab that pen bear with me. I have a wireless mic phone on.

You can follow me as i run around the house. Looking for pens, i have found the pen return back to the workshop yeah. That makes a change having a microphone that can go with me asunder, so the circuitry is based on a dual voltage multiplier. The reason it's using a dual multiplier is because it's more efficient that way - and it's got one one microfarad electrolytic capacitor at the bottom - and then a series of 10 nano farad capacitors just to boost the voltage up to strike the tube and effectively the use of Two electrolytic plasters, the fact i've got a positive side and a negative side means that this capacitor is charged up to a peak of say about 300 or so volts, and this one's negative, 300 or so volt.

So it gives about 600 volts, which is enough to sustain a short length of tubing, typically about 2 feet or twelve millimeter tubing and the way the multiplier works. If this end goes positive - and this end goes negative, current will flow through this diode and charge. This capacitor up, then this n goes negative and this end was positive, because this is in the ac of the mains and because that was already charged about say, 350 volts on the uk mains. This rises up to another 350 volts and it pushes the current through this diode and charges this capacitor up, because this end is negative and that end is receptive to the voltage being pushed up.

So that ends up with double the voltage across it and it keeps doing that it pushes up adding that doubled voltage each time. So you end up with quite a high strike voltage that can break down the uh, the electrode to gas barrier, the electrode. What's the best way to describe that cold cathode barrier, not really sure the best way to describe that i'm just spotted i've got the flash on the camera, it doesn't really matter, but it breaks down the uh, electrode drop and uh strikes the tube and the tube Will then be sustained? There are two 4.7 000 ohm resistors in series, quite high power ones. They don't get too hot and the reason for those.

If, without them, it would just instantly try and dump all that current through the tube and just make like popping noises and flash this limits, the current but uh in doing so, it drops a small amount of the voltage and dissipates a bit of heat. This little resistor here is 33 ohms. I just added that because it felt like you should um and basically that's it now. This is designed to operate on roughly 240 volts.

If you swap this capacitor here out for uh, say a one microfarad capacitor or two microfarad capacitor, but not polarized, then you can go you can it will multiply it up and the original power supply this is based on, did actually have the one microfarad and then It had a film capacitor there and it drove much much longer lengths of tube because once you've broken over, this voltage drop across the electrode. The actual drop through the gas isn't too bad and i think it drove five or six feet i'll say feet because, instead of meters, because i even though i've said it's a 12 millimeter trip just because they tend to measure neon tubes in feet, because it's an Old technology, but that is it it's a very simple circuit um, when you initially power a tube up a new tube with this circuit, the tube may not quite strike easily at first, it seems to take a while to get conditioned and that if you touch the Tube, it will help it strike just by capacitive coupling to ground, but it will flicker initially, but then it will gradually stabilize and then it will work and the power consumption is very low. Things worthy of note. The positive end stays called the negative end.

The cathode gets hot, it's doing all the work um and also the mercury migrates in that direction. It goes from the positive to the negative, so if you're actually making these tubes up and they're likely, you know if they're going to be in long-term use. If you mounted the tube vertically, for instance, it would make sense to have the bottom positive and the top negative, because, as the mercury migrates up, it will just drop back down to the other end. Naturally, um other versions of this been made for picture frame lights.

Uh, where there was actually name tubing, pictures that used this multiplier a circuit and they actually had a switch. A voltage selector switch that actually swapped the polarity, but they were kind of pushing these components for the the rated design voltage in this. But that is it. How to use a capacitive multiplier to drive a short length of neon tube? I think i've featured this in the past, but it's worth featuring again and the unusual effects you can get uh when you actually apply it to a tube with neon with the mercury in it where the actual migration of the mercury can be seen as a the Red neon, if this was an argan mercury tube, it would just be going pretty dark.

At this end, it would go a deep properly colour uh, but the mercury would then dominate later on but interesting stuff. It's a very neat circuit. I've had a lot of pleasure. Making a lot of variations in this, i'm just trying to think i've got another one knocking about here somewhere that i could show you where i could show you, but i've just propped the knee in on it.

Just give me a second, this version a smaller case, i'll just unwrap the cable. I actually spread the circuitry across either side of the tube, instead of just being up the middle and also added an extra stage just to encourage it to strike easier, but read the description down below, because the story of the way i discovered this circuit is actually Quite interesting um and it's led on to many variants since, but that is it uh how to drive a neon, tube or well an argan tube, not pure neem. It doesn't work with pure knee. It tends to flash or work initially and then just not work it.

It needs the mercury but how to drive it from just basic circuitry on a circuit board with no transformers.

14 thoughts on “The m tube neon-mercury dc migration effect with schematic”
  1. Avataaar/Circle Created with python_avatars Pp Ss says:

    Perhaps a good terminology for the breakdown of the electron barrier would be the flash point???

  2. Avataaar/Circle Created with python_avatars Scodiddly says:

    Very cool! But when you say "a long time", do you mean hours, weeks, or years?

  3. Avataaar/Circle Created with python_avatars Peter A1466 says:

    I seem to recall that tube made an appearance on the channel before? Is the tube below atmospheric pressure? And what is the power factor of a circuit like this?

  4. Avataaar/Circle Created with python_avatars Paul Mew says:

    Ah, thanks Clive. This reminds me of the "Quad" as in quadrupler in my CRT projector. It's one of the last before the digital age and was "state of the art" at the time….. (turn of the century). Pushing out 35kV or so, the quad is probably the single biggest point of failure for these devices. Replacements are getting hard to find. The components are potted in a rubber like substance, and amateur attempts at making replacements don't last long at all. This has just made me smile at the number of hours of my life spent trying to converge these machines, and then sitting there wondering/waiting/expecting the quad to go "pop"!

  5. Avataaar/Circle Created with python_avatars Some Guy says:

    Wireless microphone… its only a matter of time before a pooping clive cursing the heavens during a "break" in a livestream… or a BigClives Pooping Onlyfans site starts. Maybe both.

  6. Avataaar/Circle Created with python_avatars Ni5ei says:

    More like this please!!!!
    We love LED but some of us love gas discharge lighting even better!

  7. Avataaar/Circle Created with python_avatars Prolific Invention says:

    Another idea: what would a gold/mercury amalgam look like (or the effect, if anything) if used inside a neon tube?

  8. Avataaar/Circle Created with python_avatars Gazr Gazr says:

    Transformer-less supplies are pretty good for low power high voltage requirements.๐Ÿ‘

  9. Avataaar/Circle Created with python_avatars mikeselectricstuff says:

    In addition to current limiting, series resistors in the output are usually necessary as most gas discharges have a negative resistance characteristic, so without external resistance they can oscillate or become unstable.

  10. Avataaar/Circle Created with python_avatars Prolific Invention says:

    I wonder if there's an alternative use for a neon tube control box/circuitry? I have one but the tube is broken, any ideas?

  11. Avataaar/Circle Created with python_avatars Stephen Eyles says:

    That's a very interesting story, and I bet you never thought you'd be able to make such good use of the tube (i.e. share it with so many people!) when you first obtained it! Makes me want to hoard more interesting stuff but the shed is already full!! :-))

  12. Avataaar/Circle Created with python_avatars zh84 says:

    The Cockcroft-Walton multiplier is a splendidly clever circuit, pumping electrons up like water out of a mine. Cockcroft and Walton won the Nobel prize for the research they did with it, and they deserved it.

  13. Avataaar/Circle Created with python_avatars ESC crasci says:

    I really love the look of the simple enclosure and circuit style. I have always liked looking at neon lamps which might explain why I purchase neon LED strips. Finding Neon Tubes is faar too difficult and I'm worried that I'll shock the hell out of me with it. Great Video as always.

  14. Avataaar/Circle Created with python_avatars paul martin says:

    First a concern about the UV from the un-phosphor covered lamp, but I see you address this in "Story time"
    Similarly therein you cover the HV output dangers from such a circuit. Dirk Boonstra (presumably not the one on wikipedia who was a member of the Dutch resistance) provides appropriately deterrent symptoms for someone as hirsute as you.
    Finally, whilst you are still in Glasgow maybe a video about old Neon tube companies would be worth a thought. A quick search revealed litle apart from a Science Museum link to Franco (note spelling) of Oxford Street and Neon Workshop of Wakefield. Maybe Donald has some stories.

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