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right to the point, I'm study physics and I want to do some experiments like q/m, oscilloscope, etc and I needed an electron gun. I had an old crt TV and I took out it's electron gun and vacuum tube out.

but the gun has a 9 pin head with names on it: F1, F2, AQUA, G1, SCREEN, R, G, B. and I have no idea what to connect to what.

I guess F1 and F2 are filament but again i don't know it's working current or voltage. I just need it to shoot electrons and make bright dots on the screen to measure. I'm a bit weak on practical electronics so... need real help.

Thanks in advance. :)

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closed as unclear what you're asking by ThreePhaseEel, Dmitry Grigoryev, laptop2d, Dave Tweed Dec 20 '16 at 1:43

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ Google crt oscilloscope \$\endgroup\$ – Passerby Dec 17 '16 at 17:11
  • \$\begingroup\$ r-type.org/articles/art-004f.htm \$\endgroup\$ – JIm Dearden Dec 17 '16 at 17:12
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    \$\begingroup\$ Schools used to have simple cathode-ray tubes to demonstrate the deflection of electrons by magnetic and electric fields. There might be one where you are studying - ask a lab technician. \$\endgroup\$ – Andrew Morton Dec 17 '16 at 17:13
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    \$\begingroup\$ Keep in mind Colour TV's used very high voltage but had poor Bandwidth compared to CRT monitors , like 4MHz vs 250MHz for high end types. AS ALWAYS, define your precise experiments then consider what you need if it will work. \$\endgroup\$ – Sunnyskyguy EE75 Dec 17 '16 at 18:08
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    \$\begingroup\$ @AndrewMorton Crookes tube. Traditionally they have a Maltese cross anode \$\endgroup\$ – Spehro Pefhany Dec 17 '16 at 22:11
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It is NOT CLEAR from your question whether you have an INTACT cathode-ray tube, because you say "I took out it's electron gun and vacuum tube out." If the tube is still intact (and retains original vacuum, etc.) then simply take the picture tube number (how to read) and Google for the circuit diagram which shows the various pins and what signals and voltages it needs. For example...

example CRT circuit

NOTE CAREFULLY: In addition to all the vey legitimat warnings about high voltages, dangerous glass shattering, etc. etc. those tubes (ESPECIALLY THE COLOR VERSION) require EXTENSIVE external circuitry to operate properly, and you seem to have said that you discarded all the required external bits.

It is ESPECiALLY difficult to do this with a COLOR CRT because of the three separate electron guns and special "fiddling" that is done inside. You would be MUCH better off with a MONOCHROME CRT with a single, simple electron gun.

I would recommend finding an old camcorder with a tiny CRT viewfinder. Those will be much easier to experiment with, typically having the accelleration (high voltage) and deflection (magnetic or electrostatic) circuits, yokes, etc still intact.

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Don't. This is not a piece of hardware you can safely experiment with.

Driving a CRT requires extremely high voltages -- often up to 30 kV. Working with these voltages is inherently very dangerous. Additionally, driving a CRT improperly may cause it to emit X-ray radiation, which may cause injury to you or to any bystanders.

Since you no longer have any of the parts that were associated with the CRT, you don't even have an easy way to generate those voltages, nor to guess what voltages are even appropriate for your CRT. It's junk now -- throw it away. (Carefully; the glass will break violently if mistreated.)

If you need an oscilloscope, buy one.

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  • \$\begingroup\$ thanks for sharing your experience and knowledge. will keep that in mind. \$\endgroup\$ – Alireza Dec 18 '16 at 5:09
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I fiddled with CRTs and am still here (with minor scars) so it is possible. However a bare electron gun is pretty much useless except maybe as a cool sculpture component.

In order to work it needs a rather high 2nd anode voltage, of the order of a few kV. Old TVs (monochrome) tended to use about 15kV if memory serves, and more for color TVs (up to about 30kV). Electrons don't just shoot out of the end at high velocity like a 9x19mm round from the barrel of a Glock, they are accelerated by the high voltage toward the screen. Further, if you power up the filament in air it will last only minutes or seconds before oxidizing and failing.

The high voltage is by far the easy part. To get it to work it has to be in quite a good vacuum, which would require something like a two-stage mechanical roughing pump and a diffusion pump (or a very expensive turbomolecular pump that will die if mistreated). High vacuum systems require a certain set of skills that has to be acquired. Once the system is pumped down, a 'getter' (something like a barium material heated by an external induction heater) is used to gobble up some of the remaining gas. That's what the shiny spot was on the neck of the tube. None of this is impossible but it takes a lot of care and commitment and a certain amount of cash even if stuff is scrounged or bought on eBay.

If you really want to fiddle with CRTs try to get ahold of an electrostatic-deflection oscilloscope or radar display tube from mid-last century- maybe 3" or 5" round with green P1 phosphor. You need to take care about the potentially lethal high voltage on the second anode, anode and focus electrodes. Implosion injury if the glass breaks is also possible. Deflection voltages are often pretty modest (the smaller the screen size and the longer the tube, the less voltage it takes to deflect the beam a certain distance), and a dual op-amp can drive them directly in some cases. Pick one that you can get a datasheet for, in a language that you are fluent in (or that has a translation- there are some ex-Soviet tubes out there). Lower anode voltages will reduce the required deflection voltage too, but there are limits (brightness and perhaps optimum focus will suffer). TV set CRTs used electromagnetic deflection which is much more limiting (but it can result in higher deflection angles and thus shorter tubes).

enter image description here

Edit: FYI, the below (from this site) is what an electron gun (triple type for color) looks like:

enter image description here

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  • \$\begingroup\$ Thanks. I do have the cathode ray emitter and it's vacuum set ready. just need to identify the pins. \$\endgroup\$ – Alireza Dec 18 '16 at 5:16
  • \$\begingroup\$ Sounds like you are actually talking about the PCB attached to the CRT base. Totally different matter. \$\endgroup\$ – Spehro Pefhany Dec 18 '16 at 5:24
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As already pointed out, you're going to need some HV signalling to drive that CRT. If you are not comfortable with low voltage electronics, I wouldn't suggest you diving into HV.

We used to work in HV lab and trust me, mistakes are costly. At best, your eqipment is burnt. At worst, well you could completely injure a part/whole of your body.

With that said,

If you really need to do this project, work closely with someone who has done a similar project and go step by step. Work from low voltage electronics and see how things go from the beginning.

Here is an example that you can find on the net:

How to drive a CRT

High Voltage power supply

As you can see, the task you asked is not easy to accomplish.

If I were you, I would work with an experienced team mate majoring in electronics/power engineering and take my time. Give your project 6-12 months to finalize and don't push things.

High voltage punishes hasty people!

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  • \$\begingroup\$ Thanks for the guidance and the links! I may be able to ask someone with major in electronics and maybe a professor to help. \$\endgroup\$ – Alireza Dec 18 '16 at 5:11
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For use as a TV, high voltages are required. But you can still create an electron beam using lower voltages. You must drive the heater filaments (F1 & F2) at its rated voltage & current to get decent beam current, but accelerating voltages need not be kilovolts. For some tubes, filament voltage is in the 20v (rms) ballpark. Can be DC or AC (50 Hz or 60 Hz).
If you have broken the tube to free the electron gun, you have exposed the filament to air. It has oxidized, and also the getter will have oxidized too. These will both require pumping-out when you re-vacuum the gun.
If you intend to use the vacuum tube as is, looking for bright spots on the CRT face, this is a still dangerous, because you'll still have to use fairly high voltages. And the tube itself, unenclosed is a considerable danger because of its large volume of high-vacuum. I've done this demo for students, under very tightly controlled conditions - don't trivialize the dangers involved, and become very familiar will all aspects of its physical & electrical properties.

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  • \$\begingroup\$ The vacuum tube is safe and unbroken. and the CRT face has nothing on it. Thanks \$\endgroup\$ – Alireza Dec 18 '16 at 5:17
  • \$\begingroup\$ A shadow-mask COLOR CRT requires special circuits, static magnets, and dynamic electro-magnets to cause each of the Red, Green and Blue electron beams to strike the phosphor inside the face of the tube. That is one of the reasons it is MUCH more difficult to do your experiments with a COLOR instead of a monochrome CRT. \$\endgroup\$ – Richard Crowley Dec 18 '16 at 6:29
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First of all, don't do this. A CRT can kill you in at least three ways (high-voltage electrocution, implosion, and X-rays).

But to answer your question: F1, F2 are the filament. AQUA is "Aquadag",a graphite coating on the inside of the tube; this is connected to the high voltage. (But I wouldn't expect it connected to one of the pins, so maybe this is the Aquadag on the outside of the tube, which gets grounded.) G1 is the control grid, which controls brightness. SCREEN is the screen (cutoff) grid. R, G, B will be the cathodes for the three colors. I'd expect a focus grid too, unless F1 and F2 are focus grids, but then where's the filament?

You'll just get a spot in the center of the screen unless you use the deflection coils, which you haven't mentioned.

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  • \$\begingroup\$ Thanks. this was helpful. I'm going to connect the coils to a signal generator to move the dot around. I'd have the voltage on the coils and can measure how much the light spot on the screen has moved so i can determine mass of an electron for my experiment. \$\endgroup\$ – Alireza Dec 18 '16 at 5:20
  • \$\begingroup\$ Can you help me which pins do I need to use just to make a light dot on the screen? I suppose I don't need a few of them right? \$\endgroup\$ – Alireza Dec 18 '16 at 5:21

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