This is a work in progress. It was horrible when I first got it though. I'm not sure it would have lasted an hour! It was running the tube at double voltage. I used a Traco power supply to run 6.3 volts to the tube, which I replaced with a Thomson 6021. That removed most of the distortion at high volumes and also caused it to run at a more reasonable temperature. I also added trimmer resistors to the cathodes of the tube for channel balancing. I need to add some input capacitors to reduce the DC offset and also change the volume pot. I am currently designing a new PCB and my hope is to include a USB DAC that will work with the output on my phone.