Since last year, I have been focused on building my own tube amplifier, especially using 300B tube in the single-ended configuration. I got more enjoyable moment when listening music through the tube amplifier instead of solid-state amplifier, especially with the 300B tube amplifier. The sound is more musical, more engagement to the music, and human voice alike compare with the solid-state amplifier. Previously, I also had experience using others tube such as 2A3, KT88, 6L6 and EL34, but I still believe the 300B is a holy grail of all tubes, so I stick to this choice. 300B tube is direct-heated tube (DHT) , meaning this tube heater also act as the cathode. In the single-ended amplifier, using DHT tube will potentially contribute the hum to the speaker. This is because the power supply voltage along with the noise feed into the heater tube and direct impact to the cathode itself. Annoying hum needs to take care. I took so many lesson when building several 300B amplifier before...