Restoration of the US / C-3 infrared signaling telescope
In Greek mythology, the prophet Tiresias was blinded by the gods as a punishment for revealing their secrets. He begged the goddess Athena to restore his sight, but she could not. Instead, she gave him the gift of foresight, and Tiresias spent the rest of his days prophesying.
Tiresias had seen too much and had paid the price. Such may also be the case with a damaged US / C-3 infrared signaling telescope which has been placed in the care of this writer for restoration.
Before you can even begin to broach the question of how to fix something, you first need to know exactly what you have and how it’s supposed to work. Fortunately, there were enough clues to find the answers to all of these questions in a fairly short period of time.
The US / C-3 was developed during World War II in response to the need for secure nighttime signage. In collaboration with RCA and its laboratories, the Navy developed what was then a practically (or at least it was believed) unbreakable method: the use of infrared light. Aldis lamps, spotlights and beacons could be filtered through glass to emit only infrared light. Such tools could be used by covert operations to help guide ships to landing sites, or to transmit signals covertly. Not being in the visible light range, detection could be minimized. Germany and Japan had experimented with the use of infrared light and had developed detectors, and had even deployed them in an operational manner.
But the key to good signage is detection. A signal sent but not received is practically useless. Such was the need for the US / C-3 telescope. Key to the whole operation was the RCA 1P25 image vacuum tube, developed in secret and patented after the war. Tubes were high-tech then, and although largely superseded by solid-state electronics, their continued use in the future of electronic warfare is attracting renewed interest in some circles.
At one end of the 1P25 tube, a thin layer of metal oxides sensitive to infrared light would emit electrons. This energy flow would then be focused with adjustable high voltage electric fields on a phosphorescent screen at the other end, producing a bright green image seen through an eyepiece.
The image on the cathode itself was focused through a traditional telescope, manufactured by the Polaroid Corporation. The focal length has been set short enough to better scan the signals. The whole unit has been built very sturdily to combat corrosion and sea water, with rubber gaskets around each attachment, a sturdy metal casing and several mounting options including handles and a plate for sliding into an edge holder.
The telescope technology is the same as that used in the much more famous “Sniperscopes” and “Snooperscopes” night vision goggles of the day, the main difference being that these goggles featured a large infrared filter projector that illuminated targets in the eye. darkness. .
But its robustness belies the rather fragile nature of its components. The weather is often hostile to old electronic parts, and the challenge in restoring any of these parts is figuring out how to fix parts that haven’t been made in decades.
Like Tiresias, this telescope had seen a lot but had been “blinded”, in a sense, by the awe-inspiring power of time. It was in a bad state.
The telescope was powered by two D-cell batteries, which powered electric vibrators to power the high-voltage rectifier circuits of the picture tube. The alkali (not the acid, it’s popular belief) in batteries can leak and corrode the metal, which has happened here. The judicious use of a plumbing wrench was successful in lifting the battery cover and exposing the extent of corrosion. It was in poor condition, but not impossible to restore. The only real damage was to the cover itself, which had been eaten away in places was rebuilt with metallic epoxy. All the rest of the damage from leaking batteries was easily cleaned up. A new ball chain and rivet were however needed to replace the original, which had almost dissolved in places.
Another problem was with the internal vacuum tubes. The picture tube had shattered, scattering glass and pieces of tube in the telescope mount. Not exactly a desirable situation by any account. Replacement tubes are hard to find, having not been made for almost 60 years, but an unused tube was found and it worked.
The other problem was one of the dirty little secrets of old electronics: Components break down over time. We like to think of the systems we design as static things, at least in terms of hardware. But it is far from being the case. Over time, the capacitors, at the time of the manufacture of this device, enclosed in paper and wax, begin to leak; drift of resistance; and the wire insulation hardens and cracks. The life is long, however, so most of the time maintenance is not a problem, until it becomes. In such cases, the foresight given to maintenance in the design of an equipment becomes evident.
A critical part to replace was a series of four 100 megohm resistors that ran between two pins of the tube and were crammed between the socket and the eyepiece. As part of the electrical focusing mechanism, these vital resistors had drifted into unusable condition. The circuit should be as close to 400 megohms as possible. The new resistors wouldn’t hold in place, but a single 400 megohms resistor could just be inserted without too much trouble.
The tubes were put in place, the wires welded, the connections checked and rechecked, the screws tightened, the lenses cleaned. Then came the moment of truth: the batteries were charged and the device was turned on. A hum as the high voltage vibrating circuit came to life, followed by an increasing green glow in the eyepiece. It worked! The damage of time is apparent when looking through the tube. Just as we appreciate a patina on an old painting, we must also respect the evidence of time by looking through the eyepiece of a small device as robust.
Today, the tiny telescope graces the desk of its proud owner, a testament to wartime ingenuity and design principles that can stand the test of time.