The Eyes Have It With This Solid State Magic Eye

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].

Readers will be forgiven if this seems a tad familiar, since the current work is based strongly on [Gord]’s previous Magic Eye work. But the 6T5 was a unique tube, with a display that looked more like a dilating pupil than the sweeping circle of the more common 6E5 and 6U5 tubes. Luckily, most of the basic circuitry of the previous tubes, which was based on the classic LM391x LED bar graph display chips, could be leveraged for the 6T5 substitute. [Gord] did need to come up with a new display board, which holds 160 green surface-mount LEDs in six concentric rings. He also added a single orange LED to the very center of the display board, to simulate the cheery glow of the original tube’s heater filament.

As seen in the video below, the solid-state circuit lives in the exact same base and glass envelope that the original tube used. The animation is pretty smooth, and the look is quite convincing. The color isn’t quite right, though, but that’s limited by the color of the LEDs. We wonder if a similar circuit using addressable RGB LEDs could get a closer match to the original 6T5 phosphor. Or perhaps just replacing the green LEDs with white ones and tweaking the tint of the diffuser would be an easier approach.

Not that we’re complaining, mind you; the solid-state substitutes came out great!

Thanks to [hackbyte] for the tip.

7 thoughts on “The Eyes Have It With This Solid State Magic Eye

  1. Very nice! That orange LED in the center is a nice touch.

    Did it really need 160 diodes to get each of the rings? I wonder if rectangular LEDs (say 5x2mm) could be used save some parts and make it simple to assemble?

  2. It would be nice to be able to program the fill effect to more closely match what the path of the plasma in the original vacuum tube. There have been a few of these posted on HaD over the years. Nothing beats the original. I wonder, a carefully crafted voltage divider, perhaps a little zenner for regulation, perhaps we might have a drop in replacement at some point. Unless one of these tube startups decides to have a go at recreating them.

    1. Being able to program different types of eye tubes would be an interesting option. Perhaps several types selectable with a dip switch.
      Imagine trying to study that board after soldering to make sure all the LEDs were seated and in the correct orientation, without a pick and place.
      I wonder about adding vacuum tweezers to a 3d printer head. You could build several at once.
      If the bed could get hot enough or you could use low temperature solder, it could apply paste and flow it too. Maybe add a pencil hot air gun. Hmm.

  3. This is clever (and appealing) but the thought of populating the board with those SMD LEDs is terrifying to me – I’m wondering if a round full-color OLED display would do as well since they both run through a diffuser anyway.

    1. Wonder how much it would cost to get an LED board(s) from PCBWay or any of the other online custom PCB places? It would cost more but you’d get it done right I suppose.

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