Mystery WWII Navy Gear With Magic Eye

January 28, 2022 by Chris Lott 34 Comments

There’s an unknown piece of military electronic gear being investigated over on [Usagi Electric]’s YouTube channel (see video below the break). The few markings and labels on the box aren’t terribly helpful, but along with the construction and parts, seem to identify it as relating to the US Navy from the WWII era. Its central feature is a seeing-eye tube and an adjustment knob. [David] does a bit of reverse engineering on the circuit, and is able to fire it up and get it working, magic eye squinting and all.

But there’s still the unanswered question, what was this thing supposed to do? Besides power, it only has one input signal. There are no outputs, except the “data” presented visually by the magic eye tube. Commenters have suggested it was used with sonar equipment, calibration tool, RTTY tuning aid, light exposure meter, etc. But if you dust off your copy of Navships 900,017 “Radar Systems Fundamentals” from 1944 and turn to page 249, there’s a section entitled Tuning Indicator that describes this circuit, almost.

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A circuit sculpture based on an indicator tube

“Buggy” Circuit Sculpture Based On A Tuning Indicator Tube

December 31, 2021 by Robin Kearey 4 Comments

If you’ve ever used an old tube radio, you might be familiar with that mysterious little green display that helps you to tune exactly to a station. That display is called a tuning indicator, or magic eye tube; in essence it’s a minimalistic cathode ray tube that can sweep its electron beam along only one axis. It thereby outputs a kind of bar graph that varies with the input voltage.

With few modern uses other than being pretty, it only makes sense that these tubes find their way into works of art: [Patrice] used one to make an insect-like piece of circuit sculpture. The tube he used is an EM34, which is one of the most common indicator tubes around and has a circular, iris-like display area. This becomes a large eye, peering forward from the bug’s body. The legs are made from 1.5 mm thick brass wire, while a DC/DC converter generates the 210 Volts DC needed to operate the tube.

An interesting “touch” is the addition of two antennae that are hooked up in such a way that the tube’s image changes when you push them; this interactivity makes the bug come alive a little bit. Speaking of touch, we think it would be prudent to put some insulation around the 210 V wires; even though the bug is battery-powered, touching the high voltage and ground wires simultaneously would deliver a nasty shock.

Nevertheless, the bare-wire retro design looks beautiful and would make a great ornament for any electronics-lover’s office. We’ve seen magic eye tubes being used for various purposes: you can turn them into a spectrum analyzer, measure capacitors with them, or simply use them as a bar-graph display. Continue reading ““Buggy” Circuit Sculpture Based On A Tuning Indicator Tube” →

Eye Tube Tests Capacitors

July 26, 2017 by Al Williams 13 Comments

Most component testers require removal of a component to test it. [Mr Carlson] recently restored an old Paco C-25 in-circuit capacitor tester. He does a very complete video tearing it down and showing how it works and why.

The tester uses an eye tube (sometimes called a magic eye tube) as an indicator. A 40 MHz oscillator produces a signal that finds open and shorted capacitors. You can also measure resistance, although you have to wonder how accurate it would be in circuit. If you want to read the original manual, there are a few copies online.

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Magic Eye Spectrum Analyzer

January 14, 2013 by Brian Benchoff 13 Comments

its goddamned magic

If Nixies aren’t cool enough, maybe it’s time to step it up to magic eye tubes.

Magic eye tubes are, like Nixies and Dekatrons, display tubes. Unlike the alphanumeric characters of Nixies or rotating points of light in a Dekatron, Magic eye tubes are either bar graph or ‘Pac-Man’ displays that were used to show the signal strength of a radio station on very expensive radio sets.

After doing a few experiments with tubes, [sylvain] thought it would be cool to do something with magic eye tubes. He sourced eight vertical ‘bar graph’ magic eye tubes and built an audio spectrum analyzer.

One of the more difficult things to do was to compute the power levels for each frequency band. There are a few graphic equalizer ICs available, but [sylvian] decided to go the old-school, harder way by putting an FFT algorithm on an ATMega624.

An impressive piece of work that would look amazing next to a nice tube stereo system.