One factor that makes me like tube is its glow. Well, it’s hard to explain, but some tubes have a beautiful color, especially in dark room. Here is some of them.
Below is the 0A3/VR75 tube. It has red/fire color. Very bright and aggresive.
Below is 0C3 (VR105). It has purple color, tends to have “softer” light. The higher voltage variant, the 0D3 (VR150) also shares similar color.
Below is one of the most “dangerous” tube. It’s tube #83 Mercury Vapor Rectifier. It has Mercury inside and will glow blue when the plates conduct the high voltage. Very-very beautiful tube – despite the danger of the Mercury. It has 2 plates, and will show blue color when glowing. Since I use my Knight 600 tube tester, I can’t activate both plates together. That’s why you only see blue light glowing from left plate.
Photo below shows the right plate is conducting the high voltage, so only the right plate is glowing blue.
I switch the tube tester to activate the left plate, so you can see the blue glowing comes from left side.
On the real world, both plates will conduct the high voltage, so you will see a “complete” blue glowing from both plates.
Many more beautiful tubes in the world, like the white light from Thoriated Tungsten. Hope I can have enough life, courage, and money to enjoy those tubes someday 😉