The classic “Magic Eye” tuning indicator was a fantastic piece of vacuum tube technology that graced all kinds of electronic gear for a fair fraction of the 20th century. But despite its prevalence, finding a new-old-stock Magic Eye tube is a tall order these days, especially for the rare versions like the 6T5. No worries, though, since direct plug-in solid-state replacements for the 6T5 are now a thing, thanks to [Gord Rabjohn]. Continue reading “The Eyes Have It With This Solid State Magic Eye”
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Magic Eye Tubes Go Solid State With This Plug-In Replacement
Perhaps nothing added quite so much to the charm of vacuum tube circuits from back in the heyday of the vacuum tube as did the “Magic Eye” indicating tube. With the ghostly green glow of its circular face, magic eyes stood in for more expensive moving-coil meters for things like tuning indicators and VU meters. And while they may be getting hard to come by today, fear not — this solid-state replacement for the magic eye tube is ready to stand in for your restoration projects.
To pull off this clever build, [Gord Rabjohn] started with original 6E5 and 6U5 magic eye tubes, presumably ones that either no longer worked or had become too weak to see. The glass envelopes of the cathode-ray tubes were carefully cut from the sockets, and the guts of the tubes were discarded to make room for the replacement circuit, which lives on two PCBs. A rectangular control board holds an LM3915 bar graph LED driver chip, while a round display PCB holds 120 surface-mount green LEDs. The circular display board is mounted at the top of the control board and perpendicular to it, with a diffuser mounted above the LEDs. Everything is stuffed back into the original glass envelope and socket, making this a plug-in replacement for the tube.
The effect is quite convincing, as shown in the video below. True, you can see some evidence of the individual LEDs even with the diffuser, but honestly this just makes the display look more like the iris of an eye. We really like the look of this and we appreciate the work [Gord] put into it, especially the documentation. For a little more on how the tubes worked, check out [Al Williams]’ article.
Continue reading “Magic Eye Tubes Go Solid State With This Plug-In Replacement”
1938 Radio Has Awesome Dial
[Mr. Carlson] is truly an old radio surgeon. The evidence? He recently restored an 83-year-old DeForest radio by transplanting an identical chassis from another similar radio. The restoration is fun to watch, but the 7D832 radio dial looks amazing. The dial is very colorful and the wooden knobs and preset selector are beautiful. To seal the deal, the center of the dial has a magic eye tube, giving the radio a retro high tech look.
The donor chassis needed some work before the surgery. In addition, [Carlson] makes some improvements along the way. The radio showed signs of previous service work, which is not surprising after 83 years.
Meet The Magic Eye Vacuum Tube
Vacuum tubes ruled electronics for several decades and while you might think of them as simple devices analogous to a transistor or FET, there were many special types. We’re all familiar with nixie tubes that act as numeric displays, and there are other specialty tubes that work as a photomultiplier, to detect radiation, or even generate microwaves. But one of the most peculiar and distinctive specialty tubes has an intriguing name: a magic eye tube. When viewed from the top, you see a visual indication that rotates around a central point, the out ring glowing while the inner is dark, like an iris and pupil.
![](https://hackaday.com/wp-content/uploads/2021/01/eye.gif?w=299)
These tubes date back to the RCA 6E5 in 1935. At the time, test equipment that used needles was expensive to make, so there was always a push to replace them with something cheaper. They were something like a stunted cathode ray tube. In fact, the inventor, Allen DuMont, was well known for innovations in television. An anode held a coating that would glow when hit with electrons — usually green, but sometimes other colors. Later tubes would show a stripe going up and down the tube instead of a circle, but you still call them magic eyes.
The indicator part of this virtual meter took the form of a shadow. Based on the applied signal, the shadow would be larger or smaller. Many tubes also contained a triode which would drive the tube from a signal.
There’s a great web site full of information on these venerable tubes and it has examples of these tubes appearing in plenty of things. They frequently appeared in service equipment, radios, and tape recorders. They even appeared in pro audio equipment like the Binson Echorec echo-delay unit.
Hackaday Links: September 7, 2014
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Magic Eye Spectrum Analyzer
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.
ATtiny Controlled Magic Eye Tube
In the early days of broadcast radio, the most expensive radio sets were extremely impressive pieces of furniture. With beautifully crafted wooden cases polished to a high shine, these wireless receivers were the focal point of any family room. Some of the most expensive radio sets even included a visual indicator signaling the strength of the reception, something [Marcus] decided to re-engineer using an ATtiny85.
The display tube in question is an EM800 magic eye tube, used in radio sets, stereos, and electronic test equipment as a rudimentary display indicator. By applying a control voltage (from 0 to -10V), the illuminated display can be controlled like a bar graph display.
[Marcus]’ tube display is built around an ATtiny85 microcontroller, using a homemade PCB. It’s a fairly simple build, once the issue of supplying 250 Volts to the EM800’s anode is taken care of.
In the video after the break, you can see the bar display of [Marcus]’s magic eye tube slowly growing and receding, perfect for either displaying the current CPU load on your computer or anything else a dynamic bar graph display would be used.