I wanted to share my results with the EM84 magic eye indicator tube. I made a VU Meter with it to show the signal strength of my Vacuum tube amplifier. By the way if someone has an interest in these things, and has a few tubes in the junkbox i designed a pretty reasonable class A vacuum tube amplifier with very common tubes, and I'm willing to share the circuit. It uses EL82 (6п18п), which can be easily replaced with ЕL84 (6п14п) and a simple preamp with ECC88 (6н23п) or any other of the ECC8x series. That's the amplifier playing in the video, it has very deep basses and very sharp highs. The preamp revolves around the double triode ECC88 with one half bootstrapped to increase the linearity and the other working as an autobiased common cathode amplifier. The power amp is a normal single ended topology. Sometimes the power amp needs the cathode resistor readjusted to rebias it correctly because in the schematic I've shown you the tube's heat dissipation is at almost its maximum (12W), and it shouldn't exceed it. The power stage ia perfectly calculated. Keep it as it is. The only change you can do is switch the operating mode from pentode to triode by connecting the second grid to the anode plate via a 150ohm resistor. If you have the right transformer you can play with the ultralinear mode but i don't have such a transformer and i couldn't verify how it works.
Here's the link for the Magic eye indicator video - https://youtu.be/k3axWpAJOIY
Here's the circuit for the Class A power Amplifier - http://s10.postimg.org/ws6gautft/DSC_0444.jpg
