Hi Intricate,
The background hiss is just one of the intrinsic traits of tube gear, which has inherently more thermal noise than well-designed solid-state equipment. As you noted, most good solid-state gear is dead-quiet, unless you have an extra gain stage like a moving-coil transistor phono preamp. There is so much gain in the latter that it makes thermal transistor noise audible.
Late1960s and early 1970s transistor stuff often had audible residual hiss, but designs have greatly improved over the decades since.
Regards,
