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Night Vision The PVS-4: All about them...

GBMaryland

Herr Oberst
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Full Member
Minuteman
  • Feb 24, 2008
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    3,877
    Maryland, US
    Good info about the AN/PVS-4 and it's big len brother, the AN/TVS-5 can be found here:

    Wikipeida AN/PVS-4 / NVS-700 / SU-87 Page (yeah, it's known as all of those to the US)

    I've spent the last year playing picking up parts and playing with various PVS4/TVS5 systems. Installing new parts, upgrading to Gen III, comparing reticle patterns, and learning about the devices and how they work.
    The first thing to know about the PVS-4 (and all of my statements will always include the TVS-5 unless otherwise noted), and that it's super tough.

    The PVS-4 was clearly designed to be stomped on or mistreated within reason. The parts don't break easily, but they can have their issues.

    The PVS-4 is made of the following main components:

    The <span style="font-weight: bold">Objective Lens</span> (95mm for a PVS-4, 155mm for a TVS-5)

    The object lens contains three primary use components:

    - The windage and elevation knobs (1/4 MOA)
    - The reticle adjustment assembly / holder
    - The reticle cover screw cap
    - The reticle LED
    - The reticle cell

    One of the neatest features about the PVS-4 is that you can swap out the reticle cell for one that supports the mission at hand. I’ve run across: (M16/M203/M79) (M14/M60) (M2) (M72A1) (M67) (Forward Observer) (Bradley Stadia) (Israeli C4 7.62/5.56/RPG7) so far.

    Interestingly, all the reticle cells are simply small pieces of material with lithographed patterns on them, embedded in a small metal tube.

    The <span style="font-weight: bold">Battery Housing</span>, which comes in at least 3 flavors:

    - Original: contains two proprietary BA-5367/U lithium battery housings, also, some of them have iridium “glow in the dark” paint to enable the operator to see the brightness control and reticle control.

    - Variant 1: contains a single BA-5367/U battery slot for use with a single battery or a AA Battery Adapter (on top)

    - Variant 2: contains an integrated AA battery assembly (in the right side)

    Inside the battery housing are:

    - The on/off/gain switch/varistor (potentiometer), which is used to turn the PVS-4 on or off, but also to turn up the power to the IIT (Image Intensifier Tube) which is another way to saying “turns up the gain.”
    - The reticle brightness control varistor (potentiometer), which varies the amount of power supplied to a LED in the center of the objective lens, which in turn shines through the currently installed reticle cell.
    - A 4 pin IIT connector that slides back and forth slightly because the IIT moves back and forth as part of the scope’s course focus adjustment
    - Two resistors
    - Several wires to connect the components together and attach to the battery assembly
    - Mount point for weapon mounting hardware
    - Rubber o-ring to seal the objective lense
    - Power connector for objective lens reticle assembly
    - Two metal backed rubber grommets for the varistors

    <span style="font-weight: bold">The Eye Piece Assembly:</span>

    The eye piece assembly on a PVS-4 is where the IIT (MX-9644UV or MX-11620) screw into. It also contains the course focus and a diopter adjustment. Most importantly, it also SHOULD contain TWO slip rings that hold the IIT in place to resist shock. This makes properly installing the IIT a pain in the ass.

    If you are looking for compressive information on IIT’s, then you may want to go to this site:

    Aussie site with complete OMNI tube breakdowns including MX-9644UV vs MX-11620 tubes

    This is where I get a chuckle: when someone indicates that a Gen II and Gen III PVS don’t perform differently. Gen III PVS-4s have better S/N ratio, higher resolution, small halo, and hugely increased sensitivity. Now, some people will argue the fact, but “seeing is believing,” and I’ve been able to see a person at ~1500 meters with a Gen III TVS-5 under starlight… [LRFs are great…]

    Eye piece assembly parts:

    - MX-9644UV (Gen II) or MX-11620 (Gen III) IIT
    - Metal base housing
    - Course adjustment screw on ring WITH a gasket
    - Rubber o-ring at base of the eye assembly between the diopter and main base
    - (2) TWO split rings, used to hold the IIT in place during fire
    - Eye piece optical assembly (multiple lenses and a diopter adjustment)
    - TVS-5: 3 inch forward observer eye piece assembly ( an option, but something to behold as it truly makes a huge difference.)

    The last part is attached to the PVS-4 (or TVS-5 when used as a weapon sight) eye piece and is called the <span style="font-weight: bold">Eye Guard</span>.

    The eye guard prevents you from:
    - Getting you eye too close to the [very hard] glass of the eye piece
    - Has a shutter that opens when you put the optic to you face, which prevents spilling light as well as acting as a cushion

    Some important things I’ve noticed about PVS-4 systems:

    1) PVS-4s have seen a lot of use. Some are in great shape and some are not. They do tend to show up with dirt inside the lenses, and sometimes even inside the objective lenses. (Which are supposed to be sealed with some sort of toxic gas that prevents moisture from messing with the components.) The eye piece assemblies can suffer from similar issues when dirt gets into them, but they aren’t sealed units.

    2) Keep up with the “dirt inside the lenses” concept: Sometimes it’s possible to have a PVS-4 with dirty lenses and think that you’ve got dead spots on/in the IIT. An internally clean PVS-4 is your friend… and it’s not always easy to achieve.

    3) The “varistors” [the proper electronic name for it is a potentiometer, and varistor is short for “variable resistor”] in the PVS-4 are impossible to find once they break. Basically, at this point, it doesn’t appear you can find them. The good news is that they really don’t go bad all too often. The reason they are difficult to replace is that no really makes military grade sealed on/off/potentiometers anymore. ...and if they do, they don’t make them for the PVS-4 and publically available.

    4) One of the biggest difficulties with the PVS-4 is installing the IIT tube properly. You MUST have both split rings around the tube while you screw it in, and it’s difficult to do. Companies that refurbish these units or build them from parts frequently don’t install them. So you want to watch out for that. Varo/Litton/Northrup Grumman/L3 didn’t put these in because they wanted to… (that’s at least the partial succession of owners of the original producer of the PVS-4 system).

    I’ve got to move on to other things today, but I’ll correct this or add to it as people chime in or I remember other things.
     
    Re: The PVS-4: All about them...


    An excellent breakdown - one of the best I've seen -
    smile.gif


    Just something to add to your detail though.

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: GBMaryland</div><div class="ubbcode-body">
    This is where I get a chuckle: when someone indicates that a Gen II and Gen III PVS don’t perform differently. Gen III PVS-4s have better S/N ratio, higher resolution, smaller halo, and hugely increased sensitivity. Now, some people will argue the fact, but “seeing is believing,” and I’ve been able to see a person at ~1500 meters with a Gen III TVS-5 under starlight… [LRFs are great…]</div></div>

    One small thing to be aware of - the Gen3 has a halo, but the Gen2 tubes have no halo. Gen2 PVS-4's are one of the few night vision devices that do not suffer from any halo whatsoever. You may be a little overdriving of the phosphor around the light and the MCP will saturate, but halo is completely eliminated by the anode cone inside the tube. This makes the Gen2 tube more suited for high light environments such as urban areas.

    Anyway, your other comments are correct but the only thing to keep in mind is that the performance increase from Gen2 to Gen3 isn't as huge as it is going from something like a PVS-5 to a PVS-14. Mainly due to the problems of laying down a GaAs crystal onto a FO plate as happens with the MX11620. As such, it's difficult to know when it's worth the upgrade, especially with the cost of a MX11620 and especially as some have the same effective photocathode sensitivity as Gen2 models when measured at the MCP.

    The question then is whether it is better to upgrade or whether it is better to pay the extra and go for a modern high-resolution MX10160 based tube in a more modern scope?

    If you really love the PVS-4 though and want to see a little further and with better detail on dark nights however, it offers an improvement and you can often find the tubes secondhand on Ebay. Also the PVS-4 is a good choice is you're planning on using 7.62 or other larger calibers.

    Something to be aware of though - some of the observation models ( eg, TVS-5 ) will allow the fitment of a different kind of tube - known as a Gen3+1.

    These models are a kind of "Supertube" and are a cascade between a Gen3 tube and a Gen1 tube, with the Gen1 tube stage offering high levels of additional gain with very low noise. As a result, these tubes can be up to three times the gain levels of conventional modern Gen3 tubes and can have S/N ratios as high as 50:1. These tubes are powerful enough to make individual photons visible.

    However... Due to the thickness of the glass ( about 5mm ) that holds the GaAs substrate, many of these will not focus in a normal PVS-4 night scope and so cannot be used to upgrade the PVS-4 itself. It will assemble OK but the problem manifests itself as an inability to focus the scope to infinity. A lot of us have shed tears at this discovery, because the 3+1 supertubes really do perform on a whole different level to other Gen3 tubes. Though I have heard that some people are working on overcoming this limitation presently.

    Thank you for the write up - those of us who use and love the PVS-4 really enjoy seeing others use it too.

    Regards
    David
     
    Re: The PVS-4: All about them...

    Interestingly, I think you are correct... I was tracking an air craft with the Stano provided 9644uv, and had to pump up the gain.

    What I suspect is that what I considered halo could have been a combination of improper focus and over brightness.

    I will say, with out doubt, that a TVS-5 with a 3 inch eyepiece is a wonder.

    It's SO completely nicer than a normal weapon sight eyepiece, that it's hard to believe its the same unit.

    The GEN III does seem to see man sized targets at about 1500m, which is not a surprise....

    What is neat is that you can slap different reticles, and if you need to, start shooting with military surplus ammo quite effectively.
     
    Re: The PVS-4: All about them...

    David,

    I've got a question for you... you ever see an Isreali tube marked "9744" as opposed to 9644UV?

    When I picked that TVS-5 unit, it came with that. Of course, I'm moving on to other neat things and selling the upgrade Gen III unit... but that's always been a curious point to me.

    I was pretty sure the US sold Israel all of their tubes... at least initally.
     
    This was a beast of an optic to mount for on any weapon system... Awkward and heavy. Trying to conduct a react to contact drill with this optic mounted was a "B"!!!!!!!!!

    However, non the less a Fantastic optic for its time. The capability it delivered was impressive to say the least.
     
    This was a beast of an optic to mount for on any weapon system... Awkward and heavy. Trying to conduct a react to contact drill with this optic mounted was a "B"!!!!!!!!!

    However, non the less a Fantastic optic for its time. The capability it delivered was impressive to say the least.
    Still a fantastic optic with that crazy fast Cat lens with a Gen 3 tube!
     
    I went to power up my PVS-4 for the second time after a couple of years and a hazy green splotch is all I could see, at the bottom of the tube. My friend thinks the split rings weren’t installed properly. Odds that’s the problem?
     
    i've always wanted one just because it's neat. good revival.