HOWTO make a 4,000-volt infrared "snooperscope"

From the August 1951 ish of Mechanix Illustrated, a modest HOWTO describing a "Snooperscope" that requires a 4,000 to 6,000-volt power-supply to fire infrared light at and through the materials around you.

Construction of the snooperscope: The image converter tube is mounted in a plastic drinking cup 3-1/2 in. high by 2-1/2 in. in diameter. The optical system required depends upon your intended use. We used a small tripod type magnifier lens of 10 power (1 in. focal length) for the front lens and objects from three inches to one and a half feet can be focused. There is no reason why a greater range cannot be had with this lens by moving it closer or farther away from the tube.

After selecting the lens system mount it in a hole cut into the bottom of the cup. A jeweler’s saw or coping saw is ideal for cutting the hole. Paint the inside of the cup with black paint. Black airplane dope works fine. No light other than that from the lens must be permitted to hit the tube. Place an infrared filter between tube and lens to reduce effects of stray white light.

The image converter tube is inserted with the graphite side toward the front lens and the metal ring toward the mouth of the cup. A thin flexible lead from the metal ring connects to the positive side of the power supply. Some tubes were manufactured without this lead, in which case a piece of spring metal pressed against the metal ring will work just as well. The front end of the tube has a graphite ring around it. This is the end where the infrared image is to be focused. The graphite coating is the cathode or negative lead. Connect this lead to the B minus side of the power supply. A piece of spring brass or even the flat sheet metal carefully removed from a tin can should be formed with the fingers so it fits snugly around the cathode terminal.

make this SNOOPERSCOPE and see in total darkness (Aug, 1951)


  1. Those were the days. Pop out to the shed and blow the dust of your 4000V transformer, and look around for your old can of black airplane dope. Got yourself an infrared snooperscope, right there.

    You’d be positively thrilled with the rising number of home invasions!

  2. For the time, money and effort invested in this, she probably could have installed a trapdoor and an alligator pit.

    1. Or just buy a cheap lamp for the nightstand.  Unless she sleeps with this, her visitor will probably hear her fumbling for it anyway.

  3. Actually the design is a converter tube which translates Near IR light to visible. The 4-6kV tube does not emit Near IR light, a filtered incandescent  lamp does that.

    Now $40 of plastic, CCD, and LED’s do the same thing:
    And incredibly well

    1. After the WWII there were lots of these IR scopes around. They didn’t need illumination. You could see people at night as fuzzy green images just from their body heat. Mine was completely sealed watertight so the high tension battery could not be changed. After a couple of years the image faded away to nothing.

  4. Relax, Cory.  4000V is not particularly sensational.  A flyback transformer from a CRT assembly might put out in excess of 20kV.

    1.  Actually, getting 4,000 volts out of three D cells is pretty interesting.  Mind you, small electronic camera flashes have been doing this for a long time; disposable cameras’ flashes manage to get high voltages out of just one AA battery.

      And, like the flyback transformer, you treat these circuits, when live, with lots of respect.  And with one hand in your pocket.

    2. The battery supply had a cap to story energy so was still hazardous despite being powered by batteries. BUT… the neon sign transformer is lethal and overkill. Would I power the tube with a neon sign transformer centimetres from my face and eyes….. not likely!!!!!!

    3. Yeah, every video camera with a CRT viewfinder has a multiple-kilovolt supply inches from your face. No headlines yet.

      1. No,  but the internal impedance of the CRT supplies is considerably higher than the neon sign transformer. Meaning, the CRT supplies can only supply limited current, a neon sign transformer, depending on size can usually deliver 50 mA or more which is easily fatal.

  5. If there’s a person in your bedroom and you don’t already know, if it’s a friend or foe, I don’t think such a device is going to help you much.

  6. That sounds like a neat little gadget.  Use it to detect burglars and  then divert the 4,000 volts and ZAP them.

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