I build this small magic eye level meter module for my vacuum tube car amplifier project. I knew that the tube amp that I build for my brother must be something that he can show off, ( Ah! youngsters!) and he don't like the classic tube amp's look. He request for a vacuum tube car amp that looks like a car amp but with special things to amaze his friends.
I have several magic eyes in hand, and I like EM87, and Chinese version 6E2. The EM87 looks like bar graph display but it glows wide open and closed when max. signal input into it. The data sheet says it's supply is 250V, my power is 365V so I add in a 68K 2W to drop the voltage to 250V. The sensitivity is quite high ,that's why the input from 2 channel need to be divided by 2 resistors. The signal rectified and feed into grid. I use schottky diode, its Vf is low, I can display the smallest signal on the magic eye. The grid is grounded by 1M resistor with a 0.047uF, it provide a bit of delay for display, and looks smoother.
The layout looks simple, I immersed it with chemical to coat a thin layer of tin. I'm looking for magic eye that can display as same as bar graph display but I forgot what's the tube number. I can build another one for my tube amp too.
The schematic is as shown below and it can be build in just an evening! simple eh?