I was told in a post a couple of years ago that gen 2 are less susceptible to damage due to light exposure than gen 3. I'm curious as to why that is and to what degree. I've also been told that they have a higher shock rating as well and also wonder why that is.

The gen2 photocathode has a lower quantum efficiency compared to gen3, which means less electrons in other parts of the system, plus less chance of photocathode depletion.  You can still damage either one with high light levels.

Shock damage is relatef to the fact that the spacing between the photocathode and the MCP is greater on older tubes not neccisarily generation specific . Reducing the spacing was done to reduce halos around point light sources, but made tubes less durable as if the gap is small the MCP can slam into the PC as they are a bit flexy.

I see. The gen 2s seem to have a pretty low halo. Maybe even lower than my gen 3 which has a halo of .91.

True, and probably the gap size isn't the largest factor in their recoil handling capability, though I couldn't know for sure. Photonis tubes tend to have (or had, I don't know about the newest from L3. Some L3 tubes seem to show the honeycomb even in low light so that suggests the MTF is pretty good at MCP - PS gap) better MTF values that suggest either some pretty clever trickery inside or very small gaps between the PC and MCP, and MCP and PS. Or both which I guess is closer to the truth, but that'd mean their MCP does not flex as much as those used by other companies.

This is probably where the truth lies. Even PHOTONIS tubes have two grades of recoil resistance that I know of - 500G's (standard) and 700G's, which tend to have larger halo's so their MCP's must flex internally still - but I suspect they are doing something that makes them tougher than their US counterparts. I've asked them about this a few times and I get roundabout answers, so I imagine that it's something they don't want to talk about, but they are quite happy to talk about how all of their tubes are tough enough to handle recoil.

Here's another factor - no one ever had problems with Omni IV era ITT tubes... And it wasn't that they weren't advanced enough- they were VERY advanced. By all considerations, they were probably a lot tougher than current technology and I'm guessing that if you stuck an omni IV MCP into a modern tube, it would probably be pretty strong still.

But something no one considers is that the US has LOST a lot of technology since 2000 - It's forgotten how to make some of the better image tube technology it had. ITT had the best scientists in the world around 2000 - seriously, no one could touch them. Filmless is pretty common now, but back then there were too many unresolved problems. And ITT developed Thin Film in just a year - and it was bulletproof!  That's some serious capabilities. Then the corporate side of ITT decided to deliberately break the law and send US technology into China to be manufactured so they could save a few bucks and take the work away from Americans JUST FOR PROFITS... And the 20 million dollar fine... Which really shouldn't have hurt them at all, but ITT's decline began. Tube demand slowed and more people were laid off. And the corporates who run these companies forget that much of their IP isn't on paper - it's locked up inside the heads of the scientists that work for them. And as these scientists are laid off, that knowledge is lost forever to them... ITT --> Excelis --> Harris... Now it's barely a shade of it's former self, all because a bunch of greedy wealthy executives figured they could make a quick buck by selling out US technology and figured no one would catch them in the act. ( When they did see the end coming, they went about trying to cover their tracks, but not once did they ever consider just making the secret stuff in the US and paying for it even with a reduced profit margin ).

So the US probably lost something in MCP manufacture somewhere around 2002... Who knows what it was... The newer tubes are pretty tough though, so perhaps they found it again?

David

+1 on US tube manufacturers losing technology since 2000. A perfect example of a manufacturer losing technology can be found when looking back at the process that ITT used for some time to fix emission points that formed in tubes during the potting procedure. Developed by an ITT scientist, therefore the procedure was only known to be used by ITT on ITT tubes, the procedure invilved precisely zapping the emission point with a very tightly collimated and accurately positioned laser beam that would ultimately cause the EP to be removed. Most usually leaving a dark spot in the location where the EP was before it was zapped. The scientist and ITT had some soert of falling out that reaulted in the scientist leaving ITT and taking the knowledge of how to perform the procedure out the door with him and ITT instantly and completely lost the ability to fixs EP's and sell the tubes as factory spot tubes at a reduced cost as opposed to not being able to sell them at all and losing money on every tube that formed an EP during Potting. Which is what ended up being the case. The EP zap has been slowly been rediscovered, but not by tube manufacturers.. there is a company in Texas that has figured out how to fix PC side EPs which can be zapped through the glass input and usually wont leave any black spot, if the EP hasnt already burned a spot. PC side EP's dont usually burn dark spots into the image from what ive seen in my experience. then a buddy of mine is developing currently the other part of the procedure for zapping the more common and far more damaging screen side EP's as well as EP's that form on the aluminuminized conductive layer of the screen itself(which are the most damaging form of EP's that occur). This procedure will always leave a black spot where the EP was due to the fact that the beam enter at the rear of the tube, which makes things alot more comllicated thatn shotting a beam through glass, and it passes through the phosphor screen which will cause a dark burn spot in the phosphor everytime, but at the same time will save a tube from a certain doomed fate as a black spot in the image is much better than a sxreen EP destroying the tube in a very quick timeframe.

As for the spacing between the PC and the MCP, yes it is very important but isnt the only factor in a tubes resistance to recoil. Another factor that is very important is the type of power supply used. A DC Power supply, like the ones used to make omni 4 tube assemblies, will always help a tube to have more recoil resistance. The addition of autogated power supplies to tubes can deffinitly be atttibuted to tubes losing alot of their recoil resistance and overall toughness. Autogated power supplies cyvle the tube on and off constantly at a very rapid rate not perceivable by the human eye. This rapid cycling of the tube on then off causes constant Changes in the electrostatic field between the PC and the MCP causing the center of the semi rigid MCP to be be attracted and repelled towards and away from the MCP all the time while power is being applied tonthe tube. This constant flexion of the center of the MCP is what causes that humming/whining sound that everyone knows to listen for to determine if a tube is autogated or not. The problem for recoil resistance posed by this flexion of the MCP's centeris that if the rearward motion caused by the force of recoil as the gasses trapped behind a round escape from the rifle barrel as the bullet exits, happens to coincide with the forward flexion of the MCP at its center then you will likely end up with the MCP striking the photocathode causing a violent end to a tube or at the very least make the tube image almost unusable. the patent states autogated power supplies were developed so that a tube could retain as much resolution as possible u high light environments/conditions. This is accomplished by keeping the Photocathodes operating voltage constant and at its optimal voltage no matter how high the light levels go. The automatic cycling the tube on and off rapidly and cotinuously is how the regulation of the PC voltage to keep it at its optimal voltage is achieved. Nowhere does it say that a function of autogating is a measure of damage protection from over exposure to light. That was an unexpected side effect although autogated tubes are not immune to over exposure to light indeffinitly. So basically the resistance to recoil that tubes with DC power supplies had was traded in for the ability to allow the tube a higher resolution in light polluted environmets or other high lighting condiitions encountered by the tube. So thats what happened there.

One thing that is most deffinitely not a super important aspect in the tubes ability to resist forces applied to it from recoil or shock is the film thickness or lack of film as most people seem to think. it can affect the damage that is seen from an MCP strike, but has little to no impact on whether a strike will occur or not. An ion barrier film, thick or thin, has a measured width that is so minute that it makes absolutely no difference whether it is there or not. Having a film can actually cause the image to be even more nasty looking after an MCP strike because besides the honey comeb shaped burn left on the PC by the center of the MCP  from a strike, the film also smears all over the PC making the image look very ugly and unusable if the tube isnt destroyed by the collision. a filmless tube will not have any smearing from an MCP strike to tthe PC due to the lack of a film. Also in filmed tubes, the film can still smear all over the PC if shock thatbis heavy enough is applied to the tube while it is powered off. There wont be a honeycomb burn to the PC like would occur during an MCP strike while the tube is powered on, but it will render the tubes image basically unusable anyways in most cases. So when people are telling others that thick film tubes have the mostbrecoil resistance it is not because they have a thick film, rather it is because olderr thick filmed tubes usually had higher halo values than what is seen in tubes today.

Filmed tube MCP strike damage as seen in tube image



Filmed tube MCP strike damage while tube was powered off as seen in tube image



Filmless tube MCP strike damage as seen in tube image

Excellent break down of the technology there dts-blackout25,

Thanks for sharing the pics too - though if I might ask, there seems to be a story behind the one that is marked in red - is that something that can be shared at all?

I remember about 10 years ago when there were quite a few thin-film strikes and there was a belief that it was the thin film that was responsible for causing the impacts and it took quite a bit for people to realize at the time just how thin it was - If the MCP was scaled up to the size of a car, the thin film would just be a thin layer of powder coat. Thin films were also not that different in thickness to thick films - they were just thinned out enough to gain the added benefits without losing too much of the structural integrity.

Because the technology of tubes is so secretive, it really hinders the pace at which the technology evolved. US manufacturers are now struggling with the emerging out-of-band gaps at the top at bottom of the Gen3 spectrum and how to detect them in a world that is rapidly evolving. But behind every new issue, there's usually a scientist they lost... Was the one back around 2000 Scorba? I don't know if he's still around, but his son is on Quora and often talks about his dad's research.

Anyway, I'm getting too off topic there. I will mention that the semiconductor photocathode is FAR thicker than the metal photocathode ( Gen2 tubes are literally a piece of metal for a photocathode ) - so the mechanics of damage are related to the material properties more than the thickness of the material. Although since we've been talking about MCP related impact damage I should clarify that the thickness of the photocathode is not a factor in MCP strikes.

David.

Thanks. I figured I would try to clear up some common misconceptions that still linger around the NV community. Also, i wanted to give those who are interested some insight into what makes a tube resistant to forces/shock that it may likely encounter during it's serviceable life. I also figured I should explain how these processes work so that people can get a better understanding of a few, out of many, of the different processes that occuri within a tube.

By asking about a "story" are you asking if I know what happened that caused the damage which is what im thinking you mean, the last part of the question kind of throws me off a bit. I can share what I was told  had happened to cause the damage if that is what you meant and want to know.

Thats what I had gathered from my research. I wasnt around for much of any of that as I only discovered NV about 5 years ago. Coincidentally, the very first device I ever owned was also my first NV project build, was the p8079hp triple cascade gen 1 diy NV spotter/scope build. From there it just turned into a 24/7 hunt for knowledge and to learn as much as possible. this led to a ton of experience and great opportunities as well as getting to know some of the most knowledgable experts around. Which led to even more knowledge imparted on me by them and Ed noticing my potential, I guess you could say, and taking it upon himself to mentor me further and taught me the basics of rebuilding tubes. I then went about developing my own potting technique, including a method of final potting that does not require a vacuum degas after tube is filled with potting material. Ed is the only one to whom i have disclosed the details of the method. His response was thati should pursue a patent for the method. Also, my method allows me to use the fast curing Sylgard 170 which soft sets in lile 3-5 minutes and full cures in around 30-45 mins at which time the tube is 100% done and ready to use. Its how I pot all the tubes I do. So, although I havent been around for very long at all, I do have a lot of experience and am aware of alot of things that happened in the past before I got into NV, such as the thin film MCP strike misconception and others. The whole scaling up tge MCP yontge size of a car and the film being a layer of powder coat is a good way to put it.  if that layer of poweder coat was to thin it would not be able to keeps its structure and would start to separate from the surface of the car. the poweder coat has a minimum thickness that it must meet or exeed when it is applied to the surface of the car.

I agree with all that about the secrecy being what is holding back developement of the tech as well as a manufacturer losing scientists being the reason behind many of the issues that pop up. Makes me think about the 9916 tubes and early 10160 and 10130 tubes as there were quite a few manufacturers back then. Like Ni-tech, Varian, Intevac, Varo(Litton) and a myriad of others. I have heard that many of these manufacturers couldnt keep up with the evolving technology and  quality suffered greatly because they lost the scientists that  had the knowledge and the skilled experience that kept tube operations going smoothly and the tube quality high. That is why you dont see tubes made by such manufacturers today, and some still exist . As for the scientistvwho left ITT in 2000 I am actually not sure who it was. I just heard the story and did further research to find out what I could, however the name of the scientist never came about while I was looking into it. I didnt know that about his son and him talking about his fathers research. interesting.

Those are good points. Im glad you included them. I also should add that when I was explaining how the film can smear onto the PC from an mcp strike while the tube is powered down, I should have included that filmless tubes can hace their MCP strike the PC with the tube powered off as well. there wont be any film smearing and there may not be any sort of visible damage within the image, but a strike still occurred and that isnt a good thing to have happen in any case.  I have a ton of tube damage pics and I have some that I theorize may be the direct result of a filmless MCP striking the PC while tube is powered off. Ill have to go through all the pictures to find the ones with this type of damage and get some opinions. Will post the pics as soon as I have time to go through the pictures and find them. there are alot of wierd, interesting and perplexing types of tube damage thats for sure.

I was able to find one of the pictures of the type of damage I was explaining as to my theory of what may result from a really heavy force causing a filmless tubes MCP to strike the PC in a hard collision when the tube is not powered. This is just a theory I have at the moment and could be totaly wrong, but it may be something similar to what I think occured and it may actually be what im theorizing it to be. At this point I just dont know for sure. What do you think?



Here are a couple of examples of what reults when the center of the MCP travels too  far in the other direction.





Heres an example of a tube that started out with only one EP that had formed on the aluminized conductive layer of the phosphor screen and after a relatively short time in use this is what the single screen EP turned into.



This line up of modules shows a comparison between modules built by each of the three manufacturers  ITT/Exelis/Harris in that same order from left to right. On the very right is an OMNI VIII L-3 tube module for referrence. You can actually see the quality drop from left to right for the ITT/Exelis/Harris tubes. Mainly in the areas where the indium seals are made. They get sloppier and sloppier each time the tube operations were taken over by another manufacturer. I will say that May 31st 2015 was the worst day ever for ITT tubes. Well actually maybe the next day, June 1st 2015, was the worst day ever for ITT tubes. If you know what I mean. Ive seen more ITT tubes that were made after those  dates that have gone to air than almost any other tubes from any other era. Besides possibly the very first ANVIS contract tubes made by Intevac back in day that experienced very high numbers of premature tube failures due to the tubes going to air. Well i didnt actually see the first ANVIS contract debacle first hand but learned of it from Ed.

Or the day that the manufacturer of a specific line of tube technology didn't get a contract they needed, and let some of their remaining scientists go... It was a long way to fall, but somehow, that wasn't the end of it's plummet.

But if they can solve that, there's one crazy idea that Harris has that might actually pay off in the long run as it could turn out more important than all of the tube quality they lost. Time will tell.

I pour the Sylgard170 post-degassing as well, since I don't have a vacuum chamber, so I wonder if we use similar methods. Yours is probably slightly more accurate than my method as I don't have a vacuum pump so I use a mechanical distortion method to create the same effect and the degassing is initially quite violent due to the very sudden pressure changes it causes, but once it settles, it settles very quickly. It's not common for me to repot tubes, but I make my own boots so it's not too bad - and I'm hoping to try out the new system I've been building which should produce lens-clear boots ( or opaque grey ) to within 40 micron resolution for 10160 and 11769/10130. Anyway, if you impressed Ed, then whatever method you came up with must have been really impressive. Ed's still the old man of night vision... And I have a copy of all of his original posts squirrelled away somewhere. Let me know if you want access to read through them sometime... Lost of old knowledge hidden away in the nooks and crannies of that archive which I made before the site crashed and disappeared.

David

Yes thats true. I guess it would be more accurate for me to say that May 31/June 1 2015 were the latest of a few bad days for those tubes in terms of losing quality in their construction.

I wonder what that idea may be. I will have to do some digging now. My interest has been sparked.

Nice. Do you use the regular cure time 170 or the fast cure? the reason I started to play with different ideas that eventually led to the development of the method I came up with was basically due to my need for a different way of final potting than the standard method used by everyone else. This is because when I first started potting I used the vacuum degass method and was using regular sylgard that had been given to me by a friend who had access to the stuff. When I finally ran out ofthe sylgard he had given me, I went looking to buy more. While looking around to see where I could get some, I had never actually bought the stuff before so I was kind of floundering around trying to figure out where I could get it and what a good price to pay was, I came across a guy who was selling two 50# buckets of 170 part A and Part B for a price that I could tell right away was almost certainly much less than I would pay anyone else for the same thing. It was well within the expiration date and so I bought both 50# part A and the 50# part B and when I went to use it for the first time it was quite a surprise. I had 5 tubes all mated and seated in their boots and was ready to place them into the potting jig and fill with 170 and place the jig into the vac chamber for a degass and then let them set for 8-12 hours to cure. So I started filling the tubes with the 170 I had just mixed up, filling one and then moving on to the next one and so forth. Well after I filled the fifth tube I picked up the jig to place it in the vac chamber and I touched some of the 170 overflow near the area where the first tube was secured in the jig and noticed that it wasnt wet and flowing like it usually was, but was semi solid and no longer a flowing viscous liquid as it should have been. I realozed sometging was not roght and so I opened ip the jig and found that all 5 pots had basically soft set in the couple of minutes it took me to fill all five tubes. They had set up to the point where putting them in the degassing chamber was pointless due to the fact that you cant pull up air bubbles that are in a semi solid mass of material. I was perplexed by what had just happened as well as dissapoi ted by the fact that I now jad to depot all five tubes and start again. When I started tryi g to figure out why this happened, I looked on the label on the buckets and i saw it, plain as day, it read Sylgard 170 Fast Cure. Dont know how I missed it whenni bought the stuff. I was stuck with it as I didnt even bother to contact the guy as it was my fault for not seeing the "Fast Cure" part, not his. So that started my quest to vome up with a way that I could use the fast cure stuff to pot tubes reliably and allow the tube to be stable and unaffected by outside variables that would cause possible malfuntion of the tube as well as modes of failure. The method I developed resulted from about 1200 R&D pots, probably could have called the method fully developed after 600 of them, but I wanted to be 100% sure it was good to go and I didnt miss anything. I took annexisting apparatus that is used in other types of manufacturing of totally unrelated products and modified it a good deal to be able to use it for potting tubes with my method. So I cant claim that I invnted the apparatus, but I can say that I invented the method that uses the modified apparatus to pot tubes without any chance of air bubbles being able to enter the potting compound from the time it is mixed to the time it has filled the tube. Ed was deffinitely impressed callin the method "the first innovation to the standatd potting process in 30 years!" Or something very close to that. Dont recall the quote verbatim but it was very similar. Ed isnt the type to give out compliments when he doesnt feel they are deserved so any compliments or criticisms  or advice he gives I hold in the highest regard. thats basically the story behind my developement of the method, an invention born out of necessity, like most are.

As to your offer of access to Ed's old posts, that would be great. of course I would like to see them. let me know how you want to go about it. Thanks

Paul

So would i be correct in assuming that the system your buliding is a 3d printer? I figure ithat is what you mean due to your saying that it should produce boots with a 40 microns resolution. thats impressive. I have 3 3d printers that I use every so often, although none are able to come close to anywhere near 40 microns. When I first started out I had no sources for boots so Ed gave me a .stl file for a 10160/11769 boot that he had. Problem was that it based on the design of the old ,pre Pinnacle one piece power supply/body, ITT silver bullet metal cans that only have one tube contact and use the metal can body as the negative contact. So I tried it out and printed a few and measured and marked out the second contact and cut it out. It worked but it was too much of a hastle to have to do that for every boot, considering the number of tubes I pot regularly.

Paul