PAS-6 Varo Metascope Model 9902E

© Brooke Clarke 2008

PAS-6 targer end
PAS-6 Canvas Bag
PAS-6 Eye end
ITT 6929 68 05 date codePAS-6 6929 IR Image Tube

PAS-6 IL-1-12
                  12 KV Power Supply
ITT IL-1-12
12 kV Power Supply

12 KV output at top

1.3 V input at bottom


During or just after W.W. II there were Sinper-Scopes M1 and M3 that were the near IR type and used a large IR filtered light source and IR image converter tube.  Typically mounted on the .30  carbine.  Probably the carbine because the range was 70 yards for the M1.  They used vibrator power supples and the tube ran at about 4 kV.


This is a near IR (not heat type IR) viewer and source.

The source, MX-7987/PAS-6, is a two "D" cell flashlight with a reflector and 1.6" diameter IR filter.  The center off switch is momentary when pressed aginst the source and stary on when moved away from the source (ON)-OFF-ON.  When you look directly into the filter with the light on you can barley see any light.  The beam width of the source is very narrow when compared to the field of view of the SU-43.  The range is greater than 150 feet, maybe more like 100 yards (to be determined).

The IR viewer, SU-43/PAS-6, is made in a side by side tube arrangement.  One tube holds the BA-1312/U Mercury battery (equivalent Radio Shack 23-901), High Voltage Power Supply and  ON-OFF switch and the other tube holds in target side optics, IR converter tube and eye side optics.  Both the target and eye side optics can be focused.

The ITT 6929 IR conversion tube has metal ring contacts at each end to make contact to the 12 kV supply.  Inside the SU-43 housing there are metal fingers that contact both rings.  The input end of the tube is mirror like and dome shaped, not flat so the objective optics need to correct for that.  The output is a flat screen.

I'm guessing the 12 kV power supply is a simple blocking oscillator driving a Cockcroft-Walton high voltage generator (Wiki).

The back of the carry bag is fitted with a couple of ALICE clips.

PAS-6 Working The viewer has a groove that accepts the two pins on the source so they can be assembled into a single unit.  Although there are two ways to combine them only the way where both target ends point the same way makes sense.

When indoors in the daytime the switch can be turned on and then off and it works for a number of minutes, but when outside on a sunny day the screen goes black after a few seconds after turning off the switch.  You can hear a faint whine when the switch is on and the SU-43 is next to your ear.

Focus Adjustments


The knurled ring closest to the eyepiece (not the larger ring that opens the body) allows focusing your eye (diopter correction) on the back of the imaging tube.


The knurled ring closest to the objective lens allows focusing on distant or near subjects.

Metascope Battery Installation

PAS-6 SU-43 Metascope
        Battery InstallationThe Alkaline Radio Shack battery has the base and cylinder as the Positive terminal, like most othe Alkaline cells.  The button contact is the negative terminal.
Install the battery into the switch assembly with the button contact up.  I.e. the button contact (negative) touches the center contact on the power supply module.

You may need to clean the top surface of the spring if it's rusty or coroded.

What Goes Wrong

PAS-6 SU-43 Switch
        DisassembledAfter receiving the Radio Shack 23-9011 battery it was not clear from the -10 manual which way to put it in.  Trying both ways resulted in no joy.
Removing the power supply and using a lab power supply (HP E3617A) it was clear that the center contact on the power supply should be the negative terminal.
After seeing current (about 15 ma) drawn from the power supply it was placed into the SU-43 and the switch installed without the battery.  The scope worked fine for a number of minutes on the charge in the power supply.

Used a 3/8" nut driver to remove the boot-switch nut.

Testing the switch assembly with the battery installed showed no voltage.  Checking just the switch with an Ohm meter (Fluke 87) showed no continuity.

The switch is marked:

Spraying some Radio Shack Contact/Control Cleaner & Lubricant (64-4315) into space between the toggle and the switch body and working the switch a number of times caused the feel of the switch to free up and the contacts and the SU-43 are working.


TM 11-5855-239-10 Operator's Manual for Metascope AN/PAS-6 (5855-790-9197), 17 April 1973


1936514 Discharge Tube, T.C. Lengnick, Nov 21 1933, 250/332 ; 102/418; 250/214LA; 250/214.1; 250/333; 313/329; 313/524; 348/164; 367/7 - oldest patent in 250/333
2131185 Electro Optical Device, M. Knoll (Telefunken), Sep 27 1938, 250/214VT ; 313/524; 315/10; 348/164; 348/832- IR amplification
2189321 Electro Optical Device, G.A. Morton , RCA, Feb 6 1940, 313/529 ; 250/333; 315/213 - visible light amplifier only?
2490740 Image Tube, F.H. Nicoll (RCA), Dec 6 1949 (filed Sep 6 1946), 313/526 ; 250/333; 250/368; 313/146; 313/249; 313/286; 348/164; 348/335; 445/14 -
Near IR Schmidt Optical System (Wiki: Corrector, Schmidt–Cassegrain)
2506018 Image Tube, L.E. Flory, John E Ruedy, George A Morton, (RCA), May 2 1950 (filed Oct 5 1946), - visible light only? See 1P25A
2692341 Electron-Optical Image Converter, P. Schagen (Hartforn National Bank), Oct 19 1954, 250/214VT ; 313/541
Single accelerating voltage, not multiple anodes, hemispherical input -
2739244 Infrared Sensitive Tube, E.E. Sheldon, Mar 20 1956, 250/214VT ; 250/330; 252/301.6R; 313/380 -
Instead of using an input optical system like the prior art tubes this one has about 1,000 times gain inside the tube.
2903596 Image Transducers, W.O. Reed, Sep 8 1959, 250/214VT ; 250/333 - longer than 1.2 micron IR
2994798 High Voltage Image Tube, G.L. Krieger, George A Morton, (Army), Aug 1 1961 (filed Dec 26 1946), 313/529 ; 250/214VT; 252/301.6S -
Four accelerating anodes at up to 16 kV, maybe  M3 Sinper-Scope, very limilar to the 1P25.
3280356 Image tube with truncated conical anode and a plurality of coaxial shield electrodes, Richard G Stoudenheimer, Joseph C Moor, RCA, Oct 18 1966 (filed: Jul 17, 1958), 313/529 ; 250/214VT; 313/107; 313/530 -
Hemispherical input at ground, one other potential of 16 k, flat output window. very much like the 6929 tube in the PAS-6
2535708 X-Ray Generator
2666864 Image Intensifier Tube, R.L. Longini (Westinghouse), Jan 1954, 313/527 ; 250/214VT; 313/107; 427/107; 427/109; 427/122; 427/124; 427/64; 427/74; 445/11; 445/12 -
Hemispherical input, but output is a much smaller flat screen
2555545 Image Intensifier, Hunter (Westinghouse),  Jun 1951 - designed for X-Rays
2686885 Insulated Coated Grid for Electron Discharge Devices, Bailin (Sylvania) - tetrode power tube
2752519 Method and Apparatus for use in Chemical Evaporation Process, Ruedy (Navy), -
method of making image converter tube like the 2506018
2774002 Image Tube, D.R. Carlo (International Telephone and Telegraph, aka ITT), Dec 11 1956, -
Hemispherical input, flat smaller output, 2.3 kV& 16 kV to tube
2834889 Electronic Camera, Fries, May 13 1958, - image amplification then to film
2839601Visualize Electric & Magnetic Fields
2851625 Image Tube, Ruedy (RCA), Sep 9 1958 - hemispherical input, multiple anodes, 1,000 times gain
2857589 Adapter Device for Image Tubes, S.G. Fong (International Telephone and Telegraph, aka ITT),  Oct 21, 1958, -
Fits on front of tube and contains voltage divider to provide 2.3 kV from 16 kV  Sniper-Scope type tube.
2928969 Image Device, Schneeberger (Westinghouse),  - maybe for TV use
3376421 Quantum Counters, E. Snitzer (American Optical Co), Apr 2 1968, 250/333 ; 385/115 - fiber optic bundle
3415990 Invisible Light Sensor Tube and Faceplate Material R.T. Watson, (ITT), R. Dec 10 1968, 250/338.1 ; 250/214VT; 250/330; 250/363.01; 250/367; 250/484.4; 313/103R -
uses UV light to be more sensitive to IR
4037132 Image Tube Power Supply, A.W. Hoover, ITT, Jul 19, 1977, - for microchannel plate Image Intensifiers
4041343 Electron Multiplier Mosaic Structrue, R.K. Orthuber (ITT), Aug 9 1977, fiber optic micro channel plate - visible
4131818 Night Vision System, M. Wilder (Varian), Dec 26 1978, 250/214VT ; 250/333; 313/528; 313/534- micro channel plate
4173727 Electron Image Device, J. Vine (Westinghouse), Nov 6, 1979 (filed Jun 23, 1966), 313/529 ; 250/214VT; 313/537 -


Night Vision Techniques and the use of the Metascope and Starlight Scope, 9:52, - this is only a short clip from the full film.

The discussion showed a camera iris and the eye's iris, but only later points out that night adaption takes time because of the rods becoming active, not the iris dilating.
Night Vision Techiques And The Use Of The Metascope And Starlight Scope, 9:44 - looks like a different clip from the above film.
Off Center Vision is called Averted Vision (Wiki) in astronomy.
6:07 Metascope

Related Equipment

See my Optics web page


 “Fight at Night!” U.S. Army Night Vision, 1945-1980 - various Sniper-Scope versions and rifles as well as starlight scopes
FAS - Carbine, Cal. .30, M1/M2/M3 -
Sarco - M3 Carbine Sniper Scope Parts -

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