DC-DC 12V-1kV

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I don't know, this thing is so unstable. The only thing it doesn't react to is me blinking the eyes, everything else is instantly displayed and in the most unpredictable manner. The deflection amps are not yet done. Is this normal that there's no way to get a focused dot in the centre of the screen? I either get it blurred, or rather far away from the middle.

The Dark Boxes are coming.

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Svo,

Are you really using 1N4148 diodes? I thought that they had a PIV rating of 100 volts.

Cheers,

Ross

Ross McKenzie ValuSoft Melbourne Australia

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@Ross, I'm using SM4937, they are rated to 600V and have 200nS recovery time. The caps are 0.1µF/1kV. Here's a closeup, sorry for the excess of flux :)

The Dark Boxes are coming.

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Hi Svo,
bringing up the 6.3 volts of the heater is a real pain.
inmy scope-clock it takes I think more than 30 seconds
to heat up. Sometime its good to limit the supply
current. Getting a sharp dot can also need some
experimentation as I remember. I remember it was
important to have the deflection grids at the right
potential with respect to cathode and anodes. Then
having too much AC on the voltages modulates the
focus and may blurr the picture. If you have a
magnetic field near to the tube, that will also blurr.

Good luck, in the end you will win !

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Heater resistance will change with temperature and eventually the current will drop.

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Here you can see a short video of my scope-clock

http://www.youtube.com/watch?v=h...

The clk gets its time from DCF77 time signal
transmitter. Below the center you see a "rolling"
display of the incoming pulses.

Current consumption at 12V is 300mA. During heatup
it needs more than 600mA.

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@ossi what a lovely sight! It's really hard to believe that mine is going to be like that one day.

Do you have some sort of feedback in your power converter, or do you just let it pump happily? I have noticed that with time the voltages tend to climb up a bit. OTOH, I have also noticed that my tube is happy enough with much lower voltages too, so I'm feeding the circuit with 7.5V, just barely enough for a 7805 to work. It appears that some +/- 100V don't really make a lot of difference for such a tiny tube.

The Dark Boxes are coming.

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I have no regulation/feedback. The load seems fairly
constant so I simply let it pump. Do you have the data
of your tube ? Old scope schematics are also interesting
to get ideas how to built up th supply/defelection
and what voltages to apply to which electrodes.

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Enjoy with me a perfect wireframe of just one of the dark boxes which are about to come:

Those darker green patches are not highlights or reflections on the glass, they're some nasty electrons flying sideways.

Now with the deflection amps working, the transistors in the pushpull are getting rather hot. Uh oh, no me gusta.

The Dark Boxes are coming.

Last Edited: Mon. Apr 9, 2012 - 09:07 PM
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Congrats,
the shadow-lights probably will disappeear
by reducing the beam intensity. What is the supply
voltage of your deflection amp and what is the
collector-resistor ?

In my deflection amp I use 220k collector resistor,
so the amp draws only a few mA.

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The deflection amp has about 200V. The collector resistor is 2M2, which I'm afraid is too huge for driving a capacitive load. My biggest problem is now to achieve symmetry in the long-tail amps. It's always pulling much harder to the common-emitter side (the active drive side), and this results in a huuuuuge nonlinearity on screen, I guess of inverse square nature. I guess I need to reduce the bridge potentiometer (it's 50K now).

I don't know, when I'm fiddling with the Gate potentiometer, I get all kind of special effects, like zooming, sliding sideways, but nothing that I would classify "brightness reduction". I can remove the beam from the screen alright.

The Dark Boxes are coming.

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I've made a scope clock using the 3LO1 tube, a few years ago now. Here's a picture and the schematic. I used the ferrite transformer out of a small switching PSU, the core is about 18mm across, with the turns as marked on the schematic and mylar spacers across the legs of the E to achieve the right inductance. That's a roll of mumetal around the tube, by the way, as it's sensitive to magnetic fields from the power supply and external transformers.

I found, however, that these tubes don't live very long. After about six weeks the phosphor fades in the places the beam hits, until it can only be seen in a dark room. I can see this clearly by adjusting the X and Y so it scans different areas, that the burned out areas are nowhere near as bright as the new areas, though there's nothing visible, no burning, on the face. I replaced the tube and it was perfectly bright again for a month, then the same thing happened. I have a couple more spare tubes and now I only get it out and turn it on when I want to impress someone :) Otherwise it sits dark to save the tube.

Attachment(s): 

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I have seen that some scope clocks always move the
picture slowly a small amount in order
to avoid the wear out of the phosphor.

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@peret: in fact I used your schematic as a reference (and your clock for inspiration). Thanks for making it public! If only I could make a circle round...

Indeed, even the documentation from these tubes says that the projected time is about 800 hours, which is about one month of non-stop work. The datasheet (etiketka) also says that you're kindly asked to return the sheet to the manufacturer after the device has completed its lifecycle, specifying the time it was used, the operating parameters and the cause of going out of service. Given that the majority of them they were made in the 60s-70s, I doubt that this kind of information is still expected.

Here are the scans:
http://istok2.com/data/250/

That's rather sad. By making the image float around, you can extend the time to a few months but that's about it. Do other tubes also tend to have life this short, or do they last slightly longer?

The Dark Boxes are coming.

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My tube DG 7-74A is from this equipment:

http://shortwaveradio.ch/radio-m...

This equipment was certainly meant for continous operation over some years. The base-line is heavily
burned in.

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svofski wrote:
@peret: in fact I used your schematic as a reference (and your clock for inspiration). Thanks for making it public! If only I could make a circle round...

Oh good! Thanks for the credit, it's good to know I occasionally do something inspirational :D I didn't have many problems with the HV supply for this, but the long tail pairs gave me many headaches. It's a difficult compromise to do it with a single pair of transistors. I think if I did it again I'd use a cascode circuit, with low voltage high gain transistors at the bottom and low gain high voltage transistors up top. The reason I didn't do that here is the lack of an intermediate voltage around 40V.

The phosphor coating on these tubes is extremely thin, almost transparent. It's much thicker on other tubes. Perhaps with it being so thin, it gets sputtered away by the impact of the electron beam. I have a 6LO1 tube also, the 50mm rectangular version. Its phosphor is also very thin. Unfortunately I've never been able to get even a green dot out of it, otherwise I might have used it for something similar.

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Here's the datasheed of 6ЛО1И:
http://istok2.com/data/533/
It's very similar to 3ЛО1И, but it needs slightly larger voltages in general:
A1: 45..135V
A2: 600..1200V
It also states worktime 1500 hrs. A curious thing about this tube is the gate, look at the picture. It has pin 3 called modulator and pins 12 and 6 called something that I can't really translate: landing modulator, mounting modulator, fitting modulator, planting modulator... I'm not sure what does it mean. Could it be that it's because of this second modulator you did not see anything?

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Are pin 6 and 12 connected inside the tube ?
Are there given voltages in the datasheet ?

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It only says that modulator voltage is -125..0 relative to cathode. From the diagram I guess that they are 6 and 12 are connected inside, while 3 is separate.

Meanwhile, a set of ideal concentric circles :mrgreen:

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The bright circles are coming :lol:

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ossi wrote:
The bright circles are coming :lol:

HAHAhAHA

here's today's result:
http://www.youtube.com/watch?v=I...

The Dark Boxes are coming.

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svofski wrote:
pins 12 and 6 called something that I can't really translate: landing modulator, mounting modulator, fitting modulator, planting modulator... I'm not sure what does it mean.

"Grounding Modulator" perhaps? It's the screen grid. It's taken to a moderately high, steady positive voltage and the effect is to be a barrier (screen) to isolate the control grid, or modulator, electrically from the anode. The capacitive coupling of voltage fluctuations at the anode to the control grid is greatly reduced. I'm not sure that's of much importance in a CRT, where the anode voltage is effectively constant, so perhaps here it acts as an accelerator to boost the electron beam speed.

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Grounding modulator sounds plausible, yes.

It's not really clearly visible from you picture, but am I seeing some focusing imprefection in your clock? I'm asking because I seem to be unable to converge the beam well. Part of this probably has to do with the ripple, when zooming/panning around I can see some running texture in the lines, but there is definitely some intrinsic problem with the focusing too -- if I get it almost okay on one side, it blurs more on the other side.

The Dark Boxes are coming.

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My clock is in the same focus all over the screen. The minute ticks and the second hand are one pixel wide and that is meant to be a double tick at the top, with one pixel in between. So while the beam may not be all that narrow, it is thinner than 2 pixels. The deflection sensitivity is 256 pixels from side to side, by the way. The voltage on your deflection plates will affect the focus - you should aim to have them rest close to A2 voltage when the beam is centered, and swing above and below it. That isn't always possible I know, but the close the voltage the better it will look. Also the deflection sensitivity is not exactly the same for the X and Y plates, because one set is closer to A2 than the other and the electrons are moving faster, but if you have a variable resistor in the tail you can adjust the gains to make the sensitivity equal.

The tube is really quite sensitive to magnetic fields, and if you have any kind of mains transformer within a couple of meters it will pick it up. If you don't have mumetal you can probably make a shield out of thin steel from a tin can - it must be magnetic - it won't be perfect but better than nothing.

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Just an update:

And here playing with shapes and transforms:
http://www.youtube.com/watch?v=_...

The focus has become much better after I gave it back +12VDC, thus increasing A2 voltage significantly. I can see how it reacts to a metallic screwdriver when I trim the pots, but it doesn't seem to care at all about sitting on top of the transformer, I guess it helps that the transformer is toroidal and it's rather far away from the deflection plates. There is also some nonlinearity across the screen, visible on the grid, but at this point I do not really care: it looks great.

Haven't yet tried to power the heater from the same supply. One of the things that bothers me currently is that the voltages of my converter tend to drift a little bit, especially immediately after the power-up and every time I have to either adjust the image to be centered, or wait 10-30 minutes until it stabilizes itself. For a clock that runs 24/7 it's not a problem, but I'm not sure if I really want to burn it out in just 1 month.

The Dark Boxes are coming.

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That looks really good! Congratulations.
My scope-clock is also very sensitive to voltage
fluctuations. I think the deflection amps are
sensitive. But when I run the clock I do it for
longer times, so it's not a real problem for me.

Do you etch PCBs for your setups ? Your setup
looks really clean and well built, while my
perf-boards always look ugly.

What about some kyrillic letters
(not that I could read them...)

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And scary music under the Youtube-movie. Fantastic result, Svo !

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Very nice! Brings to mind the idea that the medium is the message.

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Thanks! Sorry for not replying in time, I was away from the computers and soldering irons and close to grills and wineries.

The cyrillic letters I really would want to display, perhaps later. This font I borrowed from somewhere for my plotter and of course it did not have cyrillic characters so I would have to do them myself first.

I etch the boards at home, for me it's one of the most fascinating parts of every project, the magic does not fade with years. With cheap laminators and laser printers these days making pretty and rather complex double-sided boards has become ridiculously easy. BTW, I had to be rather creative with this one because it's longer than the free version of Eagle allows. I started it in Eagle and finished in gEDA/PCB. Had to write a data converter for that. For the curious the brave it's here (it's not a direct converter, it reads Specctra dsn/ses pair):
http://code.google.com/p/svofski...

Speaking of free PCB tools, the impression that I've formed while doing this project is that KiCad == EMACS, PCB == vi (but unfortunately not vim). Both appear to have stuck in the seventies usability wise. With PCB one can at least have some predictable results while doing some simple routing and refinement tasks, in the worst case you always have the text file to edit in a real vi. I don't want to say anything bad about KiCad but I couldn't do anything with it. Unlike EMACS, exiting it is very easy: it just crashes at will (disclaimer: unofficial OSX build) and the board files, although plain text, are streams of uncomprehensible gibberish.

The Dark Boxes are coming.

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I'm puzzled by something weird. I'm using a TLV5625 DAC from TI. It's a single-supply 8-bit internal reference, voltage output blah blah DAC. Programmed via SPI. So when the programmer is plugged (it's a reprogrammed pickit2) everything works. When I unplug it, nothing works.

Scoping the signals revealed that pickit2 kind of trims down the signals to 3.3V. But the DAC datasheet says that it's good for 2.7-5.5V operation, and it's powered by 5V. What gives? My SPI lines are connected directly, without pullups or inline resistors. I tried adding pullups, they do nothing. Inline.. I guess they could help but I would like to hear some educated opinions first since they would require doing some controlled damage to the board. Any ideas?

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The PICkit2 has pulldowns, not pullups.

Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

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I am confused: Does the TLV5625 really have an internal
Vref ? The headlines in the datasheet say so, but I
only find a description for a VREF input in the
following sections. :shock:

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Yes, it has internal VREF.

I "solved" the issue by adding 220Ω/50pF network on SCK line. I can't believe I added a RC filter to a clock line, but with TI all bets are off.

I also solved my double-supply problem. Adding 0.5Ω in line with the heater worked a charm: it takes maybe a little bit longer to warm up than with a separate supply, but that's unimportant. There's still Z-modulation to do, but I'm so lazy about this now — looking at a dekatron tube and some egg-shaped cores I happen to have around ;)

The Dark Boxes are coming.

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Quote:
I "solved" the issue by adding 220Ω/50pF network on SCK line. I can't believe I added a RC filter to a clock line, but with TI all bets are off.
Transmission line theory. My first contribution to AVRfreaks: the PPPPD. Same issue. It still resides in my signature.

Even digital is kind of analog ;)

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia, Tessa and Tina, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Yeah well.. But in PPPPPPPGJXJJ the lines are long. Here they are like 2cm long and have a groundplane. And it's the first SPI device in my practice that's so sensitive to transients.

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I have a Anita Sumlock (dismanteled) here, contains
also a Dekatron, many thyratrons, and a lot of nixies,
and in fact, there is one transistor in it !

http://www.vintagecalculators.co...

Seems we share the love for high voltages and glowing
tubes...

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We definitely do. That Anita is sexy with that argon-filled Dekatron!

I liked that silkscreen marking of the transistor. "That expensive thingy in a top hat goes here".

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