6DJ8, 12AX7, 6922, E88CC, 7316, 5814, ECC81, 5751, 12AU7, E188CC, 12AT7, ECC802S, 12AY7, 6072. Better surfaces, more surface area (more space) and colors could help dissipate heat. Made from durable steel, anodized black, twist-on, spring loaded, J-Slot type with.