Hello night chenanigan enthusiast. Thank you for sticking around for more esoteric night vision content. Today we will take a look at PVS-31A Lego. Where I mix and match parts using PVS-31A components. I learned some interesting things doing this and wanted to share with you.
PVS-31A Lego Pods
I recently acquired three PVS-31A pods while on a trip and needed to test them. While I have an L3Harris PVS-31A, I was not prepared to remove the factory installed pod just to test these other pods. Luckily I had my NAVSEA Crane Survival Night Vision Scope with me for testing tubes. I unbolted the power supply housing from the monocular and touched the brass spring prongs to the outer contact points of the PVS-31 Lego pods. They turned on. The two middle contact points are for manual gain through the PVS-31A bridge.
Since the PVS-31A pods worked it got my brain fired up about what to do with them. I reached out to my friend Frank of AeonTac and he met up with me and brought some ARGUS 1431 bridges for me to try. ARGUS 1431 bridges fit the L3 PVS-31A Lego pods. The thread pitch is different though. L3 PVS-31A pods use 2-56x3/8 screws. You might be able to get away with 2-56x1/4 screws but they seemed a little too short and rather use longer screws.
ARGUS makes a PVS-31A clone that has manual gain. Internally it is a little different from their 1431 MKII.
Below is the board inside the knuckle of the ARGUS 31A bridge. You can see the two small contact points for manual gain in between the outer pins for delivering power to the image intensifier.
We tested the L3 PVS-31A Lego pods on the ARGUS 31A bridge. While manual gain technically worked, there is something different about the resistance of the ARGUS system. The L3 PVS-31A Lego pods would only go up to about 50% of full gain. We could dim the pods lower but we could not increase gain beyond 50%.
Frank also brought me a tan molded 1431 MKII housing. We removed the 1431 pods and bolted the PVS-31A Lego pods. It worked!
Not only did the PVS-31A Lego pods work, they were at full gain. Since the 1431 MKII doesnt have the two extra pins, there is no manual gain control. I could solder something but I think it will be the same as the ARGUS 31A clone and I would only get 50% gain. I rarely use manual gain so I did not mind losing this feature to have a working back up PVS-31A.
To my surprise, this new hybrid PVS-31A is still rather light weight. Just over 1 lbs with battery.
The molded tan bridge blends pretty well with the Galvion IHS helmet cover.
PVS-31A Lego Pod Manual Gain Discovery
I ended up taking one for the team and removed a pod from my factory built L3Harris PVS-31A. Here you can see what the board looks like under the knuckle. ARGUS is very similar.
Since I removed one pod. I attached one of the three newly acquired PVS-31A Lego pods to the L3Harris bridge and tested the manual gain. It works! I turned the PVS-31A bridge off and removed the pod then reinstalled the original pod. I put that Lego pod back onto the 1431 tan bridge. Later I tried using the hybrid PVS-31A and noticed the one monocular. that I used to test manual gain, looked dimmer than the other pod. At first I thought something happened to the tube. Maybe it was dying? But then I remembered the manual gain test. I did not turn the gain back up before removing this pod. Somehow the image intensfier power supply remembers the level of gain you last left it at.
So I removed this pod and reattached it t the L3Harris PVS-31A bridge and turned the gain back up to full gain. Reinstalled that pod back to the 1431 bridge and now the two pods look the same. Normal 11769 tubes have manual gain but as soon as you remove the resistance from the goggle housing. they go back to full gain. Not the case with PVS-31A.
MNVD PVS-31A Lego Monocular
Since the 1431 bridge fits the PVS-31A Lego pods I had and idea. I acquired three PVS-31A Lego pods, two of which were already used to make a bino . I planned to convert the third pod into a monocular using the NeoWang 714 battery housing which cvonverts a 1431 pod into a monocular.
Without a battery or diopter, the PVS-31A Lego monocular is one of the lightest 18mm night vision monoculars I have seen.
With battery, diopter and Noise Fighters X-14 arm, the whole PVS-31A Lego monocular weighs just 8 ounces.
One downside to this setup is the orientation of the 716 battery housing and the Noise Fighters X-14 arm when using a COTI.
In order to orient the ECOTI vertically, the buckle of the QD mount hits the protrusion on the PVS-31A Lego pod. It causes the mounting ring to tilt a ittle bit. If I rotate the mounting ring to clear the battery housing, then it sits better on the pod but now the ECOTI will be in some awkward angle.
PVS-31A Objective Lenses
On top of the PVS-31A Lego pods I also acquired PVS-31A objective lenses. I was curious of they could work with the ARGUS PNVG.
Here is the L3 PVS-31A objective lens assembly. On the left is what I call the "top hat". The donut ring next to it slides over the top had and screws into the PVS-31A pod and acts as a tube retainer. The top hat is epoxied to the image intensifier once they establish collimation. Then the objecte lens screws into the top hat. There is actually a fourth piece not in the photo below. It is a split ring that clamps around the second step of the objective lens. This split ring is the infinite/close focus stop for the lens.
Well to my surprise the tube retaining ring screws perfectly into the ARGUS PNVG pod. You can see the infinite focus stop split ring between the lens and tube retaining ring. There are blobs of epoxy that set the stop to the objective lens.
This setup would not work though if I use the L3 top hat. Since I would have to glue the top hat to the image intensifier. However I tried screwing the L3 PVS-31A objective lens into the ARGUS PNVG top hat. While it is not a perfect fit, it is a smidge too loose, the lens does engage the threads of the top hat. It is jsut barely touching them. If I pull on the lens, it will slide out of the top hat.
When I tested the ARGUS PVS-31A clone, my friend Frank had put filmless L3 WP tubes in it and we compared it to a real L3Harris PVS-31A. We noticed the contrast was lower with the ARGUS optics. I was hoping to see that with the L3Harris PVS-31A lenses and the ARGUS PNVG lenses. I tested this setup with one L3Harris lens over my right eye and an ARGUS lens over my left eye. The ARGUS lenses have lens flaring when strong lights are just outside the FOV of the lens. I did not see this with the L3 lens. Other than that, I did not notice any significant difference in image quality.
Final Thoughts On PVS-31A
I had a lot of fun experimenting with the PVS-31A Lego pods. I ordered another 1431 conversion battery housing. This one will be injection molded and it runs on a CR123 so the run time. I want to bridge two PVS-31A MNVD on a pano bridge to see how well PVS-31A pods can work if flared out for a pano setup. Once I test it I will add it to this article.
Thank you for reading and see you next time.
Comments