Review on 🎛️ TOPINCN 6J1 Vacuum Electron Tube Valve Preamp Amplifier Board Headphone Amp Parts Preamplifier Musical Fidelity Kit AC12V 0.8A" - "TOPINCN 6J1 Vacuum Electron Tube Valve Preamp Amplifier Board Headphone Amp Parts Preamplifier Kit, Musical Fidelity, AC12V 0.8A by Greg Stevenson

First a word: I'm by no means an audio enthusiast. I just bought this kit because it was a cheap circuit with working vacuum tubes. The kit arrived in perfect condition with all the parts needed. The tubes were well lined with a layer of bubble wrap. The building process was pretty easy. All parts are clearly marked on the circuit board with their component values and polarity. Assembly requires no special equipment - just a standard chisel-tipped soldering iron and a couple of wire cutters. I skipped installing the blue LEDs because they look gaudy - I prefer the warm glow of the bulbs themselves. One thing I noticed is that the filament smoothing capacitor (C9) is a bit too high. Everything still fits together, although the condenser slightly touches the glass jacket of the tube. It appears that the PCB lists a physically smaller capacitor than the one listed, although this has no electrical significance. I fixed this by pulling the bulb out of its socket about a millimeter to clean the condenser. Since this is a stereo amplifier, there are two balanced amplifier circuits on the board, each with its own 6J1 tube. There is also a voltage doubler circuit to create a plate voltage. That being said, the schematic should be easy to understand by looking at the circuit board traces and comparing them to various online schematics. I can confirm that the tubes do indeed work - I checked the output with an oscilloscope and could only see the signal when the cathode was hot, although checking the connections with a multimeter can also verify this. The beauty of this amp is that the voltages are fairly low for a tube circuit, around +/- 30V. While you still don't want to accidentally touch elements on the board when it's on, it's a lot lower than hundreds of volts in other amplifiers. The sound quality seems pretty good, I tested it with random music on my phone in a few minutes. Again, I'm not a sound expert, so I'm not sure what to hear. The sound is a little quieter, although online sources seem to suggest this is just a "buffer" amp that doesn't really offer much gain. This would make sense for use with a high impedance input such as a B. a phonograph pen. When testing with the function generator, I noticed that it tends to "soften" the edges of the square wave, which could potentially affect the sound. Again I could imagine things. I bought this mainly to experiment with tubes so the sound quality doesn't bother me. All in all it was quite a fun kit to put together and play with. I definitely recommend looking at schematics if you're interested in how it works. Search for "amplifier circuit 6j1" and you will get many results. This greatly increased my interest in vacuum tube electronics, that's for sure!