SkaerE:
All of the PVS-7 series goggles are available in GenII or GenIII. The differences are in the housings, whereas the -7A and the -7C are essentially the same, and the -7B and -7D are essentially the same also.
Some of the differences: the PVS-7C, built by Litton, uses a facemask that allows the goggles to flip-up, and is submersible to 66 feet. The -7A does not "flip-up", and is only rated at 3 feet for about 30 minutes.
The -7D differs from the -7B in that it uses an improved circuit board for better flash response, and uses the top of the line GenIII 64 lp/mm MINIMUM resolution image intensifier, with an enhanced signal to noise ratio, etc.
You'll know if its a shitty tube the second you look through it at night, and see:
- A lot of "crackling" or scintillation, which may mean the tube is running hot, or has had the gain turned up to appear brighter
-Blemishes, including dark areas and larger than normal black spots directly in the field of view (the center of the viewed image, vs. the edges)
-Fading or darkening of any edges, or a "shadow" that creeps across one side of the viewed scene
-Tube burn, caused by using the unit / tube in conditions that were too bright, looking at a bright light source / laser / reticle for an extended time (also called reticle burn in scope intensifiers)
-And any other thing that just looks abnormal
If there is any trace of superglue, JB weld, pro-poxy, duct or electrical tape, etc, you probably don't want it. Any screws missing, won't lock into the head harness, "takes a minute to light up", lenses won't focus, etc, the same thing goes...
Here are some pics to help:
AN/PVS-7A and -7C (from Litton):
[img]www.littoneos.com/products/images/ANPVS-7C_square.jpg[/img]
AN/PVS-7B and -7D (from Litton, ITT, NVEC):
[img]www.littoneos.com/products/images/ANPVS-7D.jpg[/img]
Hope this helps,
havoc