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 Brian Benford

Fun little project, but the fact that it uses AC power and has its own bridge rectifier confuses me. I might be missing something, but it seems to me that it would be a bit cheaper to design the circuit with only DC input. I also had to buy a 12V AC transformer because I didn't have one (unlike the half-dozen old 12V DC adapters I had in stock). And it basically doubled the price to just over $30, so the value proposition is a bit misleading. You may have a 12V power supply lying around. I saw another review that said there was an English PCB version, maybe I should have looked at that instead. If you settle for this version, if you're looking straight ahead with the volume knob aimed at you, the input is on the right and the output is on the left. Edit: I was able to find the schematic online. My kit had 50V capacitors, not 35V ones, but other than that they basically look the same. The 50V capacitors are good as 35V is pretty close, technically within spec, but it's nice to have some breathing room. I used to complain about the adapter, but you can see from the schematic that they needed AC power to run the voltage doubler. I also found the spec for the tubes and unfortunately this model runs the tubes at about 50% of the intended voltage. Maybe it would sound better if they had a voltage pentapler instead of a doubler, but it's also possible that the resulting low current from the multiplier won't be enough. I might make some modifications to my model and see if I can get noticeable performance improvements by changing a few components and will mention it here if I ever do. You can also find acrylic cases for these chinese tube amps, I ordered one with prime for $15 but you can find them with regular shipping for about $5.