Perhaps in the heyday of the vacuum tube, nothing could add more charm to the vacuum tube circuit than the “magic eye” indicator tube. With its ghostly green light on its round face, the magic eye replaces the more expensive moving coil instrument for tuning indicators and Vu instruments. Although they may be hard to find today, don’t worry – this solid-state alternative is ready to replace your repair project.
In order to achieve this ingenious construction, [GORD rabjohn] started with the original 6E5 and 6u5 magic eye tubes, which may have become ineffective or too weak to be seen. The glass shell of the cathode ray tube was carefully cut off from the socket, and the inside of the tube was discarded to make room for the replacement circuit, which relies on two PCBs. The rectangular control board accommodates lm3915 bar graph LED driver chips, while the circular display PCB accommodates 120 surface mounted green LEDs. The circular display panel is installed on the top of the control panel and perpendicular to the control panel. A diffuser is installed above the LED. Everything is plugged back into the original glass housing and socket, making it a plug-in replacement for the tube.
The effect is very convincing, as shown in the following video. Admittedly, even with the diffuser, you can see some evidence of individual LEDs, but to be honest, this will only make the display look more like the iris of the eye. We really like its appearance, and we appreciate the work [GORD] has put into it, especially the documentation. For more information on how tubes work, see [al Williams] article.