View Full Version : Ions and ion traps


dtvmcdonald
07-04-2013, 08:32 PM
I was just thinking about ion traps.

Does anybody know exactly what ions? What's off is that if they hit the screen,
they have to be NEGATIVE ions!

The only common negative ions that could be in a CRT are H-. O-, and
OH-, of which is first is by far the easiest to make.

Does anybody know?

Doug McDonald

electroking
07-04-2013, 09:20 PM
There is some air (O_2 and N_2) in the CRT. If an air molecule captures an electron,
it does become a negative ion. The trick with ion traps was to install the electron
gun slanted and straighten the path of the electrons with the magnet. The same
magnetic field acting on the heavier and slower negative ion shas a negligible effect,
and the ion just hits the first anode and is neutralized.

old_coot88
07-05-2013, 11:47 AM
The trick with ion traps was to install the electron
gun slanted and straighten the path of the electrons with the magnet. The same
magnetic field acting on the heavier and slower negative ion shas a negligible effect,
and the ion just hits the first anode and is neutralized.
Just like winnowing grain in the wind.
:D:D

Electronic M
07-05-2013, 01:50 PM
The reason for ion traps is that before aluminized screens(a coating of vaporized aluminum over the phosphor which reflects light towards the viewer and shields the phosphor from ions) the unprotected phosphor screen was vulnerable to damage from being hit by ions. This effect known as ion burn is common in pre-ion trap era CRTs and manifests itself as a browning of phosphors in the center region of the screen(this brown region also does not get as bright as the surrounding area).

bandersen
07-05-2013, 02:03 PM
Some early post war sets also didn't have ion traps. Here's an example of ion burn in a Stromberg Carlson TV-12.
http://farm9.staticflickr.com/8495/8372389936_52c6dac067_z.jpg (http://www.flickr.com/photos/70039806@N00/8372389936/)

compucat
07-05-2013, 08:12 PM
I read the instruction manual for one of the early pre-war RCA TVs. It was the console model with the 5 inch screen and shortwave radio. I forget the model number. It was one of the TRK sets. The manual said that the screen would naturally discolor as the kinescope ages. This obviously referred to ion burn which was unable to be prevented at the time. Aluminized tubes were a real improvement in CRT performance.

compucat
07-05-2013, 08:22 PM
I have never seen an ion burn in an electrostatic set yet they do not use an ion trap. Anyone know why a 7JP4 doesn't need an ion trap? Is it because the high voltage is relatively low or are the ions absorbed by the deflection plates?

bandersen
07-05-2013, 08:45 PM
I've read that electrostatic fields deflect the ions along with the electrons. So the ions are spread evenly over the screen rather than bombarding a circle in the middle. Eventually the screens do get dimmer but it takes a while.

compucat
07-05-2013, 09:38 PM
I've read that electrostatic fields deflect the ions along with the electrons. So the ions are spread evenly over the screen rather than bombarding a circle in the middle. Eventually the screens do get dimmer but it takes a while.

Maybe that explains why older electrostatic tubes are not as bright as ones that are new old stock. I have a NOS 8BP4 for my Motorola 9VT1 that I have never tested as I am saving it until I really need it. I wonder how much brighter it would be compared to the one in my daily use set that was installed in 1954. Apparently the original CRT only lasted five years.

old_coot88
07-06-2013, 12:00 PM
I've read that electrostatic fields deflect the ions along with the electrons. So the ions are spread evenly over the screen rather than bombarding a circle in the middle. Eventually the screens do get dimmer but it takes a while.
Ions being vastly heavier than electrons would make them (ions) harder to deflect, causing them to hit nearer center of the screen. Seems like, anyhow.

The principle of the ion trap itself is the easier deflectability of electrons vs. ions ("winnowing").

bandersen
07-06-2013, 03:41 PM
It's my understanding that ions are more easily deflected by an electric field vs a magnetic field used in ion traps.

jr_tech
07-06-2013, 04:08 PM
IIRC, the force on a charged particle in an electrostatic field depends upon the amount of charge and the strength of the field. In a magnetic field the force depends on the amount of charge, the magnetic field strength as well as the *velocity* of the charged particle.

jr

egrand
07-06-2013, 07:08 PM
Here's a couple of links about it and different ion traps:

http://books.google.com/books?id=PnoRTG84d5cC&lpg=PA17&ots=DSRp9WjXeC&dq=ion%20burn%20electrostatic%20tube&pg=PA17#v=onepage&q=ion%20burn%20electrostatic%20tube&f=false

http://www.r-type.org/articles/art-004e.htm

old_tv_nut
07-06-2013, 08:38 PM
It just struck me that the magnet gizmo we call the ion trap is really the electron un-trapper.

old_coot88
07-07-2013, 11:52 AM
It just struck me that the magnet gizmo we call the ion trap is really the electron un-trapper.
Eggzackly.:yes: It's the electron beam re-directer.
Sorta like the definition of a shock absorber is really the rebound damper.. while the spring is what does the shock absorbing.

:nerd:

Phil Nelson
07-07-2013, 12:04 PM
It's the electron beam re-directer.Some old manuals actually call it the "beam bender," a more descriptive term than "trap." The ions aren't trapped; they're allowed to escape in a harmless direction.

Phil Nelson

Tom Albrecht
07-07-2013, 10:20 PM
I have a 7JP4 with obvious browning, even though the brightness is still pretty decent. The browning is darker near the center, but covers about half the screen or more.

It's correct that electrostatic deflection should deflect both electrons and ions equally, while magnetic deflection deflects the much lighter (and therefore much faster moving) electrons much more than ions. That being said, I'm not sure why the browning is more severe near the center of my 7JP4. Maybe there is a little more to the story.

Tubejunke
07-09-2013, 09:39 PM
What amazes me about electronics in general is how the further we progress in "technology" it seems the further we seem to be dumbed down from the heart of the whole matter. By that I mean basic atomic theory concerning the control of electrons, ions, or what have you through resistance, capacitance, inductance, or other forms of impedance.

What I'm getting at is that we now can obtain college degrees in electronics with only a few classes based in these things, and Ohm's Law, Kirchoffs Law, and other "Laws" based on trigonometric explanations of how all these things work and can be proven to work. I make no claim to being an expert. I got a degree after many years of looking at school books from the 1930s-1960s and was frankly appalled at what we now understand or are required to understand as compared to what to me seems to have been FAR more in depth. Yet it is now written off as being archaic and/or obsolete information. I say it is the farthest thing from the truth.

Now I am not an engineer from M.I.T., so perhaps there are curriculums still that go further into these things. Perhaps they spend more than a semester working with oscilloscopes and surface component troubleshooting. Sorry, this may sound like a rant, but I felt these things as I went through my discipline worrying more about how to understand Boolean Algebra and digital logic which we were pushed through so fast working with single chips or programming robots with P-Basic computer programming that many students retained almost nothing. Especially the ones that were placed in Digital Logic courses before basic electricity.

Even what I took in high school 25 years ago started off based in math or trig AND we only had Simpson analog meters, so we could actually read scales. I blew peoples minds a few years back bringing in hard wired, tube driven chassis and analog meters and working in labs. The "hot dog" students minds were blown completely. An adjunct instructor had to have me help a student who showed up with an old Simpson V.O.M. The resistance mode would not fully deflect for "zeroing" which he found on a Google search. Some new C cells tool care of that! And this was a TRAINER of future techs.

WOW!! Anyway, neat thread on "beam bending" and it's one reason why I love this site. I think you could get more useful knowledge here than in many colleges. I know I do....

electroking
07-09-2013, 10:36 PM
You have to understand that the emphasis is more on semiconductor physics and less
on free electrons in a vacuum, but rest assured that there is still a lot of fundamental
physics in EE curricula.

On the other hand, there is a lot of misconceptions in the mind of a recent EE graduate, but wasn't it always that way?

egrand
07-09-2013, 10:41 PM
The same thing is true for cars today. It's amazing how little people who work in the industry know about the basics of mechanics. I talk to a lot of car guys and we all laugh about how easy it is to confuse the kid at the counter at Auto Zone. Even those who are supposed to be SAE trained mechanics have no idea today what a carburetor is. Mostly what they know to do is plug in a diagnostic port and let the computer tell them what is wrong. People have lost the skill of diagnosing a problem themselves.

I bet hardly any mechanic today knows the first thing about hydraulics or Pascal's law. They just know that if you cut open a brake line you have to bleed the air out, but I bet they can't tell you why.

When I was in high school chemistry class we had a chapter on four stroke engines. We had to learn each of the four strokes and what they did. I remember some in the class thought it was stupid. Our teacher explained that the internal combustion engine was one of the most important inventions in history and that it was one of the most common machines on the face of the planet and that we needed know the basics of it so that we wouldn't be taken advantage of by others when we got a car fixed. I bet few schools bother to teach that now. All students learn is that engines are bad and must be eliminated as quickly as possible.

ChrisW6ATV
07-09-2013, 11:09 PM
I don't think today's students have dumbed-down knowledge at all. Case in point: Explain MPEG-4. All of it. Can you do it in the same space as explaining NTSC? :)

Boobtubeman
07-09-2013, 11:25 PM
Ones digital... one isnt???? hehehe :D

Hey i have one of those old simpson meteres with the tubes that make the digits... Accidently fried one of the parts shutting it off without disconecting the leads and poofed a part somewhere...

SR

dtvmcdonald
07-10-2013, 09:47 AM
The thread has drifted! But still, I will say this! I teach,
sometimes (I'm retired, but come back to help) a lab course
in Chemistry for Juniors/Seniors. I've now done this for
40 years. This is Physical Chemistry Lab.

Experiments have changed, a bit, in those 40 years. There is much
more optics and much less mixing chemicals. We no longer, for example,
have them measure thermochemistry with wet methods or battery voltages
(i.e. "electrochemical potentials" ... an experiment in which, I should add,
the good students could get 4 significant figures right, and I could get 5,
with equipment made in the 1920s.) But they still do unwatered down
experiments, and learn as much fundamental stuff. And learn MORE about
setting up experiments. For example, they have to put together all the
lenses and the laser for a Raman experiment. This is not easy if you've
never done it. I can do it in five minutes. The students are lucky if they
can get it all done in three hours, the first time around.

But the toughest thing they have to learn is how to use an oscilloscope!
We have several experiments where they need to do this. One uses a simple
low frequency analog scope, one uses a low-end Tektronix 60 MHz digital
scope, and one uses the very fanciest of the fancy 1GHz high end Tektronix
digital ones (and needs all that GHz using the cutest little TO-5 can
photomultiplier you've ever seen ... a photomultiplier in a transistor can!)
The TA's have trouble learning to use scopes! I have trouble using
the fancy one and I've used these since they first came out ... you folks
probably have never had the "pleasure" of one of these in a totally unknown
state ... that's what "factory reset" is for.

But they learn a LOT. The old stuff, the new stuff. I really feel that
all this talk about students learning more in the old days is bunk. For
example ... they still use one analog scope.

And in fact thinking about one experiment was why I started this topic ...
we have a mass spec in the lab that does negative ions, and
except for F- and Cl-, which won't be in the gas in a CRT, they
are hard mostly quite hard to make. O- and OH- exist but generally
come from water, which also won't survive the getter in a tube.
The most likely molecules in a tube are H2 and CO, both of which
ooze out of iron and steel forever, and don't getter well on
the usual Barium getter (they do on Ti, but tubes don't use that.)
So the most likely negative ion in a CRT is H-. At least that's
my first guess. I wonder what it does to the phosphors to ruin them?

Doug McDonald

Tubejunke
07-13-2013, 11:50 AM
I sort of started this comparison of the way that electronics was once seen and taught as more of a science than what I believe it to be and remember it being in two different decades. I never meant to say that the students have dumbed it down. I guess simply the progress of technology has slowly over time eliminated the need to dig quite as deep into the various ways of movement and control of electrons; especially under a vacuum (thermionic emission).

The students can't help it that they have the ease of reading voltage, current, and resistance measurements on a digital display having to have little knowledge of component level troubleshooting with signal generators and scopes, or even just a meter. Again, this happened over a number of decades. For us TV nuts it started with the late 60s hybrid sets with remove and replace (modular) section pc boards. What section is causing the problem? Find the board and replace it. That didn't last too long before solid state took over and the TV repairman was becoming the next dinosaur.

As far as "MPEG" and "NTSC" go; I think that those are computer file system terms which would be off topic. Either way, I know am somewhat familiar with the terms, but don't have much reason to be able to write term papers on them.

Folks look up vacuum tube full wave bridge rectifier on YouTube. There is a wonderful training video posted there that to me gives an idea of this difference of how we took on the study of electronics. And it, along with the textbooks of that era that I have gave me, or reaffirmed the thoughts that I conveyed earlier in this thread.



I don't think today's students have dumbed-down knowledge at all. Case in point: Explain MPEG-4. All of it. Can you do it in the same space as explaining NTSC? :)