So I was just messing around with my kit and noticed something odd.

I recently acquired 2 used f9800k tubes. I posted earlier this week about their performance vs Omni vii. Anyway, I just put one of the tubes into my mum housing and went outside to look around. Got things focused and adjusted, Image looks great, awesome. I turned on the ir illuminator for a second and looked at the exterior wall of my house then back out in the yard. I then noticed what I would describe as a light dot near the center of my image. I don't think it was there before I looked at the wall but it's kind of inconspicuous so I'm not sure if it was already there. It almost looks like a real faint IR dot from a low power laser. It's definitely within the image as it's location doesn't move when I look around. Is it possible I damaged this tube? Never heard this described around the forum so curious for input from those who might know.

Could be a bright spot - though these tend to be large.
Could be an emission point with a very low output.
Could be related to charge effect.

Many possibilities - Are you able to photograph it? Generally, if you can't get an image of it, it's not a problem.

Regards
David.

In a darkened area, cup your hand over the objective lens to block out all light. If you can see rhe dot of light at all when all light is blocked from entering the tube, tgennit is an emission point. Also emission points will be visible after removing power so if the bright dot remains in the image for a short time after the tube is powered off it is an emission point. If its small enough and hasent caused burn yet, then sometimes the emission point can be taken out by tearing the tube down to its individual parts and cleaning the module well to get rid of any contaminants on the surfaces of the ceramic wafer disks and then rebuilt and reootted. this works sometimes if the EPis small enough and the tube hasnt been run long enough for the EP to cause any damage or burns. Also emission points can form on the aluminized conductive layer of the phosphor screen. These emmision points cause the aluminized layer to be damaged which shows up on the output screen as a bright point when tubes is powered on and also as dark spot in the location of the phosphor screen EP will be visible even when the tube isnt being powered. These are permanent

I'll see if I can get a picture of it.

Not always permanent.

Frickin laser beams

I have a PVS-7 with two bright spots: they stay on after I power the tube off and slowly fade away, show up even if NO light is entering the unit, etc. So I guess these are emission points?
Last night I was out and the smaller of the two (I would describe it as being one or two "pixels" in size) was flickering almost out at times.
Do they burn out over time? Do they get worse?

This tech was originally feveloped by someone who worked at ITT and it was used to get rid of Eps that formed after final potting of tubes. The zap takes the EP out of the image and in its place it leaves behind a black burn spot. Your basically trading  a damaging defect( an EP that if left alone will contiue to cause damage to the tube)  for an image defect that wont cause continued damage. Deffinitly a trade id want to mak! I understand the laser zapping process to an extent as i am actuqlly working with a very smart dude who is developing his own such method and has been helping me learn about it. ive been sending him surplus tubes that i get that have EP's. So far ge has done a gen 2 10130 and a gen 3+ omni VII mx-11769/uv. They were both zapped. The gen 2 10130 had MCP EP and the gen 3+ 11769 had a phosphor screen EP. He took the Ep's out of a gen 2 and gen 3 having phosphor screen and MCP. So two different generations and two differebt tyoes of EP's. He deffinily knows his stuff abd understands how the process is supposd to work when everything has been fully developed. He is just noe needing to focus on getting the beam to a slightly more collimated point as far as i can tell. Which he will deffinitly be able to do.i just hace to find a few more modules with good size EP's to send him so he cam continue the R&D phase. He sent me back the tubes and also before and after pictures. There is a comany that offers such lazer zapping and i know afellow tube builder who has the module that was thos copanies firat attempt at a laser EP zap, and when i compare it to the first gen 3 attemt of the guy im helping supply EP tubes for his R&D, its quite apparent to me that the this guy im working with is at a higer level of understanding what has to haappen for this to work correctly is a at a higher level than the other offerring this service's understanding of the whole process on their first gen 3 attempt. Although t fixed the EP, The burn that they put in that module made about half of image's area from the center outward unusable as it was now a huge solid non-transparent black circle with a green ring around it. My guy zapped the EP, took it out, and the burn left was only about a 1/4 or less of the area of th image. Theres no comparison between each ones first attempt. The guy im working with's first gen 3 EP zap is clearly the more succesful attempt. However the company offering this service started a wgile ago and their first attempt i have a picture of wasa while ago so obviously they ahave refined there process and have way finer of an end result noe and were just now starting out so dont take what i just said to mean we have a bettter result than they do at this point in time. That is in no way what i mean. I simply mean that tge guy im working with has better understanding, it would seem, on out first attempt than the other guy had at thr time of his first attempt. So please dont twist that up and go around saying things like i was saying we have a better result than they do at this exact point in time. thats not what is being said in this post at all. We are no where near being able to offer this as a service at this point in time.  Still need alot morw R&D to refine  the  end result.

Yes those ar Emission Points for sure. Those are two of the ways to positively ID true emission points that arent juwt bright spots. if they remain in image for a bit aftter power has been removed abd also are there when no light can enter the tube.

Emission points can flicker or remain a constant brigtness so thats what your observing. 

A true EP will continue to damage the tube module some slowly and some can destroy a tube tather quickly. If the have been left alone and the tube run long enough tgen they will eventually cause a burn and they will be a bright point at lower lrcels and as the light levels rise the EP will gradually change from a bright point to a black spot and vice versa, de to the changes in the elecrostatic field that occur whrn light levels increase or decrease. 

Sometims if the EP or EP's arr very tiny they can be removed by tearing down tye tube completetly and cleaning the module very well to remove contaminants on the surface of the ceramic wafer disk stack and then repotting. I have done this multiple times.  however some EP's are at a point where they are simply just too big to be fixed unless the laser EP zapping process that was mentioned is used to fix it.

Did you look at the before and after pics? The emission point is gone and there is no burn whatsoever.
Attached File

Attached File

That EP is super tiny and as i said their process has been refined. A larger Ep wouls as i explained in the last post cause a burn spot of its own which would be in tge image permanently even if the EP is fixed and the laser used is at the perfect wavelenth that the photocatode is blind too and collimated just right. As i said they have had much much more development of the process than we do. We are basically just staring out. They hace already perfected their method. 

Also i should add that i hace fixed EP's thar size that is shown in this pictures many times when they started forming in factory tubes for whatever reason.  Simply tearing the tube down to its individual parts and cleaning the modules ceramic surfaces very well to get rid of contaminants on the surface thenakimg sure that the solder points connecting the OSU wire leads tonthe module arw very smooth and rounded and repotting the tube with the good stuff, Dow Corning Sylgard 170. This will most of the time remove EP's that are of similar size to the obes in the pictures you posted.

Thanks for all the info.

So, who can laser tubes for EPs right now, or who can tear a tube down, scrub, and then repot?
It's a nice tube; thin filmed and auto-gated. I don't want it to get worse.

Honestly ? I would not worry about it. Have tubes with emission points for years on end and they have not got worse. Repotting is just resetting the module and not completely tearing apart a tube. This is a expensive process either way and not cost effective. Enjoy your tube and don't worry about it. I know the snobs will disagree with me but I have tubes with emission points for over 10 years and they have not got worse. Tubes have defects but I can always get a new tube if a catastrophic event happens which it rarely does. Personally , I would not worry. Enjoy your scope and worry about more important things.

Like, when FLIR is releasing Bosun?

EP'S are more or less damaging depending on where they have formed in the image and on which of the screens they have formed on within the tube. MCP EP'S seem to be, from my experience, the least damaging type of EP. However it would be the easier of the two to get rid of and keep the resale value on your tube if the Ep wasnt able to cause a burn that can be seen in the image when powered on. an MCP EP that has been able to cause a burn wiill be bright when light is not allowed tonenter the tubes input and as the electrostatic field changes as light levels rise the bright point will gradually turn into a dark spot which is the nurn caused by the EP. These, as i said, tend to be more of a concern vecause of the burn spots they put in the image, but can continue to cause new EP's to form around it. It may take a while but evebtually any EP will likely be the cause of tube failure.

The other type of EP forms on the phosphor screebs aluminized conductive layer. Now when one consider the voltage required bythe screen its quite obvious why thewe are the worst case EP's . Beside leaving burns and damage on the aluminized layer of the phosphor screen, which usually show up very soon after EP forms and un most cases instantly, that can be seen on the output screen when the tube is powered off and one just looks at the FO output screen. These EP's will destroy the phospjor screen at a very rapid pace usually. So if you have a tube that you are partial yo it would ve a good idea to get to get either type of EP removed, especially phosphor screen type. Ive seen an EP on the phosphor screen make almost half of the screens viewable area completely useless in less than 15 minutesin one of the experiment i did when o was trying to figure out how where and why EP's form and the damaging effects they have.

If you really want to see something that is pretty rediculous, and i would assume startling if one is not expecting it when it happens,  simply allow a corona to arc from the high voltage SCREEN solder tab to the MCP IN solder tab. This can be accomplishe by leaving pointed protrusions from the solder points on the Screen and MCP in tabs where the wire leads from the power supply connect to the clean tube module. Make sure the solder points at the photocathode and MCP OUT solder points have nice and rounded solder joints. Basically you want the path of least resistance to be between the Screen and MCP in tabs. Then apply power.  The result will be one of yhe loudest sounds one will ever hear come from a tube from the sonic crack it plroduces and also causes some of the brightest, largest abd most distracting MCP emission points ive eve seen. Bad for tube. Good for learning haha

The first part of this is true in the difference between rebuilding and repotting except that repotting does involve teqring the tube down completeley into its idividual parts due to the fact that the module must be cleaned before the repot. A repot is neccesary when a tube is suffering from something such as a flickering image caused by the breakdown/degredation of the potting material and contaminants may have been allowed to get to the modules ceramic surfaces. Rebuild/repair means to completely tear down the tube to its individual parts and clean module and replace a bad power supply and repot into a tube assembly. i dont know what the few others who are able to even offer this service charge for it, but even my most expensive price for both parts and labor to rebuild a tube, which is rebuilding an mx-11769 with an autogated power supply, is still less than one could buy a similar used tube with a clean image for on ebay. And thats if im rebuilding the tube and adding a new power supply from my inventory. A repot will be much less as the cost of the power supply from my stock wouldnt be applied as the original power supply is good and would he reused. I think the notion of not being cost effective would apply if for some reason, which i dont seee to ever having an economically logical reason to have done, someone wanted to replace a bad module with a good module and having it mated to their good power supply and having it repotted into a tube assembly. At that point you would most deffinitly be reaching used tube prices found on Ebay for sure.